LEGACY UNIVERSITY, THE GAMBIA Knowledge and Research for Integrity ANA 212 LECTURES WEEK FOUR SUMMER SEMESTER

Aims&Objectives Of The Lectures On The Embryology&Histology Of The Central Nervous System. 1.To Comprehend early neural development. 2.To Comprehend the formation of spinal cord. 3.To Comprehend the formation of the brain; grey and white matter from the neural tube. 4.To Comprehend the role of migration of neurons during neural development. 5.To understand the main derivatives of the brain vesicles and their walls. 6.To understand how the nervous system is modelled, cell death etc. 7.To understand the contribution of the neural crest to central and peripheral neurogenesis. 8.Understand the developmental basis of certain congenital anomalies of the nervous system, including hydrocephalus, spina bifida, anencephaly and encephalocele.

Embryology&Histology Of The Central Nervous System Neural development is one of the earliest systems to begin and the last to be completed after birth. This development generates the most complex structure within the embryo and the long time period of development means in utero insult during pregnancy may have consequences to development of the nervous system. The early central nervous system begins as a simple neural plate that folds to form a neural groove and then neural tube. This early neural is initially open initially at each end forming the neuropores. Failure of these opening to close contributes a major class of neural abnormalities (neural tube defects).

Embryology& Histology Of The Central Nervous System

Within the neural tube stem cells generate the 2 major classes of cells that make the majority of the nervous system : neurons and glia. these classes of cells differentiate into many different types generated with highly specialized functions and shapes. This Lecture covers the establishment of neural populations, the inductive influences of surrounding tissues and the sequential generation of neurons establishing the layered structure seen in the brain and spinal cord.

Legend For The Neural groove closing to neural tube, early week 4- Carnegie Stage(Stage 10)

Early Neural Timeline -Carnegie Stage& Events Early Neural Timeline -Carnegie Stage Event Carnegie Stage 8 (About 18 postovulatory days) neural groove and folds are first seen Carnegie Stage 9 Three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open. Carnegie Stage 10 (Two days later) neural folds begin to fuse near the junction between brain and spinal cord, when neural crest cells are arising mainly from the neural ectoderm Carnegie Stage 11 (About 24 days) the rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in several areas simultaneously. The two lips, however, behave differently. Carnegie Stage 12 (About 26 days) The caudal neuropore takes a day to close. The level of final closure is approximately at future somitic pair 31 (corresponds to the level of sacral vertebra 2). Secondary neurulation begins, is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate.

Relative Brain Size Embryonic (Week 4, 5, 6, & 8) & Late Fetal (Third Trimester)

LEGENDS Embryonic Central Nervous System- Week 4 to 8(Carnigies Stages 13 To 23 -Legend Below Is For Week 4 Carnigies Stage 13

LEGENDS Embryonic Central Nervous System- Week 4 to 8(Carnigies Stages 13 To 23-Legend Below Is For Week 5 Carnigies Stage 14.

LEGENDS Embryonic Central Nervous System- Week 4 to 8(Carnigies Stages 13 To 23-Legend Below Is For Week 6 Carnigies Stage 16.

LEGENDS Embryonic Central Nervous System- Week 4 to 8(Carnigies Stages 13 To 23-Legend Below Is For Week 8 Carnigies Stage

Gestational Ages In Weeks&Its Carniegies Equivalence

Development Overview of The Nervous System Development Overview Neuralation begins at the trilaminar embryo with formation of the notochord and somites, both of which underly the ectoderm and do not contribute to the nervous system, but are involved with patterning its initial formation. The central portion of the ectoderm then forms the neural plate that folds to form the neural tube, that will eventually form the entire central nervous system. Early Developmental Sequence: Epiblast - Ectoderm - Neural Plate - Neural groove and Neural Crest - Neural Tube and Neural Crest.

Events At Neurogenesis-Neural Tube Development.

Notochord Does not contribute to the final nervous system, but is critical to patterning the development. Forms initially as the Axial Process, a hollow tube which extends from the primitive pit, cranially to the oral membrane The axial process then allow transient communication between the amnion and the yolk sac through the neuroenteric canal. The axial process then merges with the Endodermal layer to form the Notochordal Plate. The notochordal plate then rises back into the Mesodermal layer as a solid column of cells which is the Notochord. Notochord Ectoderm Two main parts with different morphology Columnar - midline neural plate forming neural tube and neural crest Cuboidal - lateral surface ectoderm forming epidermis and sensory placodes Epidermis of skin, hair, glands, anterior pituitary, teeth enamel Sensory placodes

Neural Plate The neural plate forms above the notochord and paraxial mesoderm and extends from the buccopharyngeal membrane to primitive node. The cells are described as neuroectodermal and form initially two regions along the head to tail axis: a cranial broad plate region (brain plate) and caudally a narrower plate region (spinal cord). Neural Determination Neuronal populations are thought to be specified before the plate folds by signals from underlying notochord and mesoderm, as well as signals spread laterally through the plate. Secrete Noggin, Chordin, Follistatin All factors bind BMP-4 an inhibitor of Neuralation Bone Morphogenic Protein acts through Membrane Receptor Lateral Inhibition Generates at spinal cord level 3 strips of cells Expression of delta inhibits nearby cells, which express notch receptor, from becoming Neurons Delta-Notch- generates Neural Strips.

Lateral Inhibition.

Neural Plate- Neural Bending. Neural Plate. Neural Bending. There are two bending processes occurring in the formation of the neural groove and neural tube. [1.]-Occurring in the midline due to cells in this region having a basal nuclear localisation. This initial bending leads to formation of the neural groove. [2.]-Occurring at the dorsolateral hinge points by different mechanism involving buckling. This later bending leads to formation of the neural tube.

Neural Tube Bending Model

Neural Groove& The Neural Tube Neural Groove In the human embryo the neural groove forms in the midline of the neural plate (day 18-19). Either side of which are the neural folds continues to deepen until about week four(4) Neural folds begins to fuse At 4th somite level Neural Tube Fusion of neural groove extends rostrally and caudally Begins at level of 4th somite, zips up neural groove Leaves 2 openings at either end- Neuropores Forms the brain and spinal cord Secondary Neuralation - caudal end of neural tube formed by secondary neuralation, develops from primitive streak region, solid cord canalized by extension of neural canal. mesodermal caudal eminence

Neural Groove Human Embryo (Carnegie Stage 10, Week 4)

Neuropores Cranial (Anterior) neuropore closes before caudal (posterior) Failure neuropores to close causes Neural Tube Defects (NTD), The severity of the Neural Tube Defects (NTD), Is dependent upon the level, anencephaly results from failure of the Cranial (Anterior) neuropore to close and spina bifida results from failure of the Caudal (Posterior) neuropore close. Previous studies Found that supplementation of maternal diet with folate reduces incidence of NTDs A randomised controlled trial conducted by the Medical Research Council of the United Kingdom demonstrated a 72% reduction in risk of recurrence by periconceptional (ie before and after conception) folic acid supplementation (4mg daily). Women who have one infant with a neural tube defect have a significantly increased risk of recurrence (40-50 per thousand compared with 2 per thousand for all births) Lamina Terminalis Note the site of the embryonic cranial neuropore can later be identified within the central nervous system as the lamina terminalis. Human Fetus (week 10) brain showing lamina terminalis region

Cranial Neuropore(Stage 11)

Caudal Neuropore(Stage 12)

Neural Crest& Neural Crest Derivatives. Neural Crest The Neural Crest is a population of cells at the edge of the neural plate that lie dorsally when the neural tube fuses Dorsal to the neural tube, as a pair of streaks. Cells migrate throughout the embryo. Studied by quail-chick chimeras - transplanted quail cells have obvious nucleoli compared with chicken. Neural Crest Derivatives The Neural Crest is pluripotential, forms many different types of cells: dorsal root ganglia (neurons, sheath cells, glia), autonomic ganglia, adrenal medulla, Pia-arachnoid sheath, skin melanocytes, connective tissue of cardiac outflow, thyroid parafollicular cells, craniofacial skeleton and teeth odontoblasts.

Neural Crest Development Neural Crest A population of cells at the edge of the neural plate that lie dorsally when the neural tube fuses. Dorsal to the neural tube, as a pair of streaks Cells migrate throughout the embryo. Studied by quail-chick chimeras - transplanted quail cells have obvious nucleoli compared with chicken Neural Crest Derivitives Pluripotential, forms many different types of cells: Dorsal Root Ganglia (Neurons, Sheath Cells, Glia), Autonomic Ganglia, Adrenal Medulla, Pia-Arachnoid Sheath, Skin Melanocytes, Connective Tissue of Cardiac Outflow, Thyroid Parafollicular Cells, Craniofacial Skeleton and Teeth Odontoblasts.

Early Brain Structure- Primary Vesicles Early Brain Structure. Primary Vesicles. Rostral Neural Tube Forms Three(3) Primary Brain Vesicles (Week Four(4) Three(3) Primary Vesicles: Prosencephalon (ForeBrain), Mesencephalon (midbrain), Rhombencephalon (HindBrain) Secondary Vesicles From the Three(3) Primary Vesicles developing to form Five(5) Secondary Vesicles (Week Five (5) Prosencephalon- Telencephalon (End-Brain), Forms cerebral hemispheres), diencephalon (Between-Brain), forms Optic Outgrowth),The Thalamus,The Epithalamus,the Hypothalamus. Etc, Mesencephalon Forms the MidBrain Rhombencephalon- Metencephalon (Behind Brain), Myelencephalon (Medulla Brain)

Neurogenesis Of Secondary Vesicles At Carnegie Stage 14 (Week 5)

Lateral View of the central nervous system of embryo at Carnegie stage 14 (Scale bar is 1 mm).Depicting The Sites Of Neurogenesis Of The Cranial Nerves(CN)

Lateral View Of The Central Nervous System Of Embryo At Carnegie Stage 14 (Scale Bar is 1 mm).

Week 8 - Stage 23 For Mation Of The CNS Ventricles CNS ventricles The cavity within tube will form the contiguious space of the ventricles of the brain and central canal of spinal cord This space is filled initially with amniotic fluid, later with CerebroSpinal Fluid (CSF) CSF is secreted by a modified vascular structure, the chorioid plexus, lying within the ventricles Neural - Ventricular System Development) Brain Flexures Rapid Growth Folds the Neural Tube forming Three(3) Brain Flexures (Cranial To Caudal) Cephalic flexure - (Mesencephalic) pushes The Mesencephalon upwards. Pontine flexure - (Metencephalon) generates The Fourth(4 th ) Ventricle Cervical Flexure - (Myelencephalon) between Brain Stem and Spinal Cord.

Legend For The Central Nervous System(CNS)Ventricles

Neural Layers Neural stem cells lie in the layer closest to the ventricular space, the ventricular layer This layer generates both neuroblasts and glioblasts Neuroblasts - neurons arise first as neuroblasts and migrate along radial gial, their migration stops at cortical plate. Glioblasts - glia arise later as glioblasts Both neurons and glia undergo a complex process of growth, differentiation and interaction over a long developmental time period. Spinal Cord Axes Experimental manipulation of interactions. Initial experiments looked at how isolated tissues may influence the development of the spinal cord such as: The Repositioning of Specific Tissues Both In Vivo & In Vitro The specific markers of or alteration of differentiation. Notochord Induction Notochord Induction occurs through: Ventral- Sonic Hedgehog. Notochord secretes sonic hedgehog. Gene expression studies (ISH) showed shh gene expression occurred in a subset of inducing tissues. Has a patterning role elsewhere (limb, sclerotome, lung). Two(2) signaling activities acting (locally and at a distance) Ventral- Sonic Hedgehog. Binds to cell surface receptor patched. Without shh, patched (Ptc) binds smoothened (Smo). With shh shh-Ptc releases Smo activating G protein pathway.

Human Embryo (Week 8, Stage 22) Developing Head Section

Stage 22 Developing Cortex.

Neuron & Supporting Glial Cells

Early Development & Neural Derivatives Early Development & Neural Derivatives. Bilaminar Embryo- Epiblast&Hypoblast. Trilaminar Embryo Then Ectoderm Layer, Neural Plate, Neural Groove, Neural Tube & Neural Crest. Cranial Expansion Of Neural Tube- Forms The Central Nervous System. Caudal Remainder Of Neural Tube-Forms The Spinal Cord. The Neural Crest Forms The Following Structures: Dorsal Root Ganglia. ParaSympathetic / Sympathetic Ganglia. Ectodermal Placodes- Components Of The Special Senses: Otic Placode (Otocyst), Nasal Placode, Lens Placode.

Neural Tube & Genes Time for Radical Changes in Brain Stem Nomenclature-Applying the Lessons From Developmental Gene Patterns. The traditional subdivision of the brain stem into midbrain, pons, and medulla oblongata is based purely on the external appearance of the human brain stem. There is an urgent need to update the names of brain stem structures to be consistent with the discovery of rhomobomeric segmentation based on gene expression. The most important mistakes are the belief that the pons occupies the upper half of the hindbrain, the failure to recognize the isthmus as the first segment of the hindbrain, and the mistaken inclusion of diencephalic structures in the midbrain. The new nomenclature will apply to all mammals. This essay recommends a new brain stem nomenclature based on developmental gene expression, progeny analysis, and fate mapping." Molecular Patterning Molecules segmented along its length - Hox/Lim gene expression ventral identity - sonic hedgehog, BMP7/chordin interaction dorsal identity - dorsalin

Neural Tube Patterning -Neural Tube and Genes: Neural Specification- Notch/Delta, Patched Receptor. Border- Fibroblast Growth Factor (fgf), BMP (BMP4, msx1) Rostral Border- Dlx5

Fetal Development Human Fetus (CRL 240mm) Brain Three-dimensional magnetic resonance imaging and image- processing algorithms have been used to quantitate between weeks volumes of: total brain, cerebral gray matter, unmyelinated white matter, myelinated, and cerebrospinal fluid (grey matter- mainly neuronal cell bodies; white matter- mainly neural processes and glia). A study of 78 premature and mature newborns showed that total brain tissue volume increased linearly over this period at a rate of 22 ml/week. Total grey matter also showed a linear increase in relative intracranial volume of approximately 1.4% or 15 ml/week. The rapid increase in total grey matter is mainly due to a fourfold increase in cortical grey matter. Quantification of extracerebral and intraventricular CSF was found to change only minimally.

Legend For Human Fetus Brain (CRL 240mm) Brain (left dorsolateral view)

Legend For The Events Of Neurogenesis AT Fetal - Second Trimester

Gliogenesis & Myelination Glial cells have many different types and roles in central and peripheral neural development, though historically described as supportive. These central glia develop from the same neural stem cells as neurons, while peripheral glia (Schwann cells) are derived from neural crest. Early in neural development a special type of developmental glia, radial glia, provide pathway for developing neuron (neuroblasts) migration out from the proliferating ventricular layer and are involved in the subsequent lamination and columnar organization of the central nervous system. Types of glia: radial glia, astroglia, oligodendroglia, microglia and Schwann cells.

Human Thyroid System &Neural Development Timeline Of Human Thyroid System& Brain Development From Conception To Birth. Estimation Of Neurogenesis Adapted From Bayer et al.

Third Trimester- Brain & Ventricular System Development

Third Trimester- Brain Fissure Development

Gene Diseases - Sonic Hedgehog. Gene Diseases - Sonic Hedgehog SHH Human mutation- Holoprosencephaly 3 Characteristic facies of the severe form of HPE which included a single fused eye (cyclopia) and a nose-like structure (proboscis) above the eye Downstream targets of Sonic hedgehog signalling: transcription factors like Gli3 (responsible for Greigs polycephalosyndactyly in humans), d Hoxd13 (responsible for polysyndactyly)

The Histology & Microscopic Anatomy Of The Central Nervous System THE NERVOUS TISSUES. The Structural and functional unit of the central nervous system is the neuron. It has a body with a nucleus surrounded by a cytoplasm replete with Nissls granules and peripherally extending dendrites processes, the dendrites. The body of the neuron continues as an elongated axonal processes ensheated with Oligodendrocytes derived myelin in the cerebrum, but in the myelin in the peripheral nerves are Swann cells deived,whereas the myelin in the ganglia are satellite cells derived. In between the myelin sheaths are regions of interruptions referred to as the Nodes of Ranvier, the axons continue until it ends at the terminal plate.

The Histology & Microscopic Anatomy Of The Central Nervous System Development. The central nervous system is of ectodermal origin and appears as the neural plate at the middle of the third week. After the edges of the plate become folded, these neural folds approach each other in the midline and fuse into the neural tubes. The cranial end is in continuation with the amniotic cavity and is referred to as the superior neuropore or the anterior neuropore, which usually closes at about day 25, whereas the caudal end which is also continuous with the amniotic cavity and is referred to as the posterior neuropore or the inferior neuropore which closes at about the 27 th day. The CNS then forms a tubular structure with a broad cephalic portion, the brain and a long caudal portion, the spinal cord. The spinal cord forms the caudal end of the CNS and is characterized by the basal plate containing the motor neurons; the alar plate for the sensory neurons, and a floor and a roof plate as connecting plates between the two sides. These basic features could be recognized throughout most of the brain vesicles. The brain forms the cranial part of the CNS and consists originally of three brain vesicles [I]-The Rhombencephalon [II]- The mesencephalon and [III]-The Prosencephalon or the forebrain.

The Histology & Microscopic Anatomy Of The Central Nervous System Development. The Rhombencephalon is divided into: [I]-The Myelencephalon which gives rise to the medulla oblongata.This region has a basal plate for somatic and visceral efferent neurons, and an alar plate for somatic and visceral afferent neurons, AND [II]-The Metaencephalon with its typical basal (efferent) and alar ( afferent) plates. This brain vesicle, the Metaencephalon is in addition, characterized by the formation of the cerebellum, a coordination centre for posture and movement and the pons, the pathway for nerve fibres between the spinal cord and the cerebral and cerebellar cortices.

The Mesencepahlon (OR) Midbrain The mesencepahlon or midbrain is the most primitive brain vesicle and most resembles the spinal cord with its basal efferent and alar afferent plates.Its alar plate forms the anterior (superior) colliculi and the posterior (inferior) colliculi as relay stations for the visual and auditory reflex centres respectively. The aqueduct of Sylvius is the cerebrospinal fluid conducting pathway from the third ventricle to the fourth ventricle.

The Diencephalon The diencephalon, the posterior portion of the forebrain, consists of a thin roof plate and a thick alar plate in which the thalamus and hypothalamus develop. The third ventricle is the cavity of the diaencephalon. It participates in the formation of the pituitary gland, which also develops from the Rathkes pouch. The diaencephalon forms the posterior lobe of the pituitary or pars nervosa, which contains neuroglial cells and receives nerve fibers from the hypothalamus. Where as Rathkes pouch forms the adenohypophysis, the intermediate lobe, and the pars tuberalis.

The Telencephalon The telencephalon, the most rostral aspect of the brain vesicles, consists of two lateral outpocketings, the cerebral hemispheres, and a median portion, the lamina terminals, The two lateral ventricles are the ventricular cavities of the telencephalon. The lamina terminalis is mainly used by the commisures as a connection pathway for fiber bundles between the right and left hemispheres. The cerebral hemispheres, originally two small outpocketings expand gradually and cover the lateral aspects of the diencephalon, mesencephalon, and metaencephalon. Eventually, nuclear regions of the telencephalon come in close contact with those of the diencephalon.

The Embryology Of The Ventricular System The ventricular system, containing the cerebrospinal fluid (CSF), extends from the lumen in the spinal cord to the fourth ventricle in the Rhombencephalon, the narrow aqueduct of Sylvius in the mesencephalon, and subsequently to the third ventricle in the diencephalon. By way of the Foramina of Monro, the ventricular system extends into the lateral ventricles of the hemispheres. The cerebrospinal fluid is produced in the choroid plexus of the fourth, third, and lateral ventricles. The cerebrospinal fluid flows from the two lateral ventricles (the cavities of the telenencephalon) into the interventricular foramen of Monro from where it flows into the third ventricle (the cavity of the diaencephalon) then from here through the acqueduct of sylvius (the cavity of the mesencephalon) into the fourth ventricle (the cavity of the rhombencephalon) from where the CSF flows through the median aperture (the foramen of Magendie) from where the CSF escapes into the cerebellomedullary cistern.

The Embryology Of The Ventricular System The cavity of the fourth ventricle is prolonged laterally as a narrow, tubular lateral recess which gets modified into a patent extremity referred to as the Foramen of Luschka which opens anteriorly, just behind the eight nerve into the pontine cistern. Through these three apertures (one median and two laterals) the cerebrospinal fluid escapes from the ventricular system into the subarachnoid space for absorption by the arachnoid villi. These are the only exits from the system; if blocked, e.g following meningitis, the result is hydrocephalus

The comparative Morphological and Histological Features of the Cerebellum: The cerebellum is presumed to be a modified brain stem nucleus which, in the course of vertebrate evolution has become so massive that it has grown increasingly bigger and bigger. The cerebellum is believed to have three distinct morphological parts which evolved sequentially with each component having a divergent function. The Archaeocerebellum has vestibular connexions only. It is represented in the mammals by the lingual, the uvula and the flocculonodular lobe. Lesions of this part produce vestibular symptoms: disturbances of equilibrium and no alteration to spinal reflexes. This condition is known as Truncal ataxia because the affected subject walks with as if drunk.

The comparative Morphological and Histological Features of the Cerebellum: The palaeocerebellum, which evolved between the lingual at the front and flocculonodular lobe at the back, so splitting the archaeocerebellum, has spinal connexions (spinocerebellar tracts) and it is concerned with postural and righting reflexes.It is represented in mammals by the anterior lobe, the pyramid and the paraflocculus and the uvula. Lesions of this site cause major disturbances of postural mechanisms with increased muscle reflexes. The neocerebellum spanning over the palaeocerebellum evolved between the anterior lobe and the pyramid, so splitting the Palaeocerebellum.The neocerebellum is most highly evolved and developed in man and has cerebro-pontine connection between the pontine nuclei via the middle peduncle. The neocerebellum is concerned with feed back circuits with the basal nuclei and the cerebral cortex. It functions in the control of the synergic background of muscle tone in the performance of accurate voluntary movements. Lesions of the neocerebellum lead to such clinical features as hypotonia, diminished or pendulum muscle jerks, intention tremors, dysdiadochokinesia and nystagmus.

The comparative Morphological and Histological Features of the Cerebellum: The essential function of the cerebellum can thus be briefly summarized as the co- ordination movement. Cerebellar lesions do not cause paralysis, but disturbances of movement and balance such as ataxia, intention tremor ( which are absent rest but seen mostly towards the completion of the finger-nose test),nystagmus and speech defects. Like the cerebrum, the cerebellum is surfaced with a cortex of grey matter, with the white matter internal. Each hemisphere contains subcortical nuclei of grey matter near the roof of the fourth ventricle. The dentate nucleus is the largest and the most important. It forms a large crenated crescent, resembling the inferior olivary nucleus of the medulla. Its main connexions are from the neocerebellum and its efferent fibres leave the hilum and pass to the contralateral red nucleus and thalamus. Three small masses lie medial to the hilum of the dentate nucleus, the emboliform, the globose and the fastigial nuclei. Given their intimate proximity to the fourth ventricle, these nuclei are given the name the roof nuclei of the cerebellum. The fastigial nucleus belongs to the archaeocerebellum, the other two to the palaeocerebellum.

The comparative Morphological and Histological Features of the Cerebellum: The cerebellar cortex is very characteristic and is usually uniformly identical in all areas. Two equally thick cortical layers sandwich a single layer of Purkinje cells between them The molecular layer of the cerebellar cortex lies on the surface, it consists almost entirely of fibres, with a few cells scattered amongst them. These are called the basket cells because their axons arborize in almost in a basket shape around the Purkinje cell bodies. The granular layer lies deep to the molecular layer and consists overwhelmingly of small round granular cells tightly packed together (in low power appearance somewhat resembling the lymphocytes in lymphoid tissue) the layer of Purkinje cells lies between the two and consists of very large flask-shaped cells lying separately at intervals. The essential microscopic connections are as follows. Incoming (afferent) fibres are of only two kinds.Both activate the Purkinje cells, one (the climbing fibres) directly, the other (the mossy fibres) through the intermediary of granular and basket cells. The Purkinje axons usually synapse in the dentate and other nuclei. The Purkinje dendrites form an elaborate branching pattern in the molecular layer. All the branches lie in one plane. The climbing fibres (the terminals of the pontine and vestibular fibres) pass from the white matter through the granular layer and weave around the purkinje dendrites in the molecular layer. The mossy fibres (the terminals of spinocerebellar and olivocerebellar) fibres arborize as a tuft around a granular cell. The axon of a granular cell passes out into the molecular layer and bifurcates in T-shaped manner Some of these fibres arborize around the few basket cells, the majority arborize directly with the purkinje dendrites. The axon of the basket cell divides and arborizes around the cell bodies of some 500 Purkinje cells.

The Internal Structure of The Cerebrum: The Internal Structure of the Cerebrum: The white matter of the central hemisphere is made up of fibres belonging to three main groups. [I]The Commissural Fibres: [II]-The Associational Fibres and Arcuate Fibres and [III] - The Projection Fibres: [IV]-The Mixed Fibres. [I]-The Commissural Fibres: The Corpus Callosum as an Example of a Commissural Fibre: The commissural fibres join the cortices of the two hemispheres. Most of them are gathered together in the corpus callosum. They radiate widely and symmetrically through the white matter of the hemispheres. The Structure and Function of the Corpus Callosum: The corpus callosum consists of a mass of over one hundred million commissural fibres, each of which extends from the cortex to cortex between symmetrical parts of the two hemispheres. It commences at the anterior commissure, at the upper end of the lamina terminalis of the diaencephalon and, traced from this point to its termination, it becomes increasingly thicker. It is described as having four parts, [i] - the rostrum, [ii]-the genu, [iii]-the body and [iv]-the splenium. The fibres of the corpus callosum extend to all parts of the cerebral cortex.In a horizontal section the fibres of the genu could be seen arching forwards on each side to the frontal cortex; this appearance gives them the name forceps minor. Also, in the same way, the fibres of the massive splenium bend posteriorly symmetrically to the occipital cortex, forming the forceps major. In between the forceps major and the forceps minor the fibres of the corpus callosum spread out to the cortex on the lateral surface of the hemisphere. They pass across the anterior horn and body of the lateral ventricle, for each of which they form the roof. As they turn down into the temporal lobe they form the lateral wall of the inferior and posterior horns of the lateral ventricle, where they are known as the tapetum.

[II]-The Associational Fibres: The associational fibres are confined to their own hemisphere, in which they connect different parts of the cortex. The cortical areas as examples of Associational Fibres which are also Mixed: The four main motor and sensory areas of the cortex outlined below have many interconnexions, both within their own and with the opposite hemisphere. Although certain areas of the cerebral cortex have long been identified with specific functions, which are still practically relevant, modern investigations are modifying the traditional concepts and principles as far as an explicit categorization of the cerebral cortex into strict motor and sensory functional units.

Broadmans classical study of cerebral cortical Histology) and Investigations Directed Modifications: Given that it has been recognized that many motor fibres for example have their origin outside the traditional motor cortex and some arise from what were previously recognized as absolutely sensory areas. A novel definition has ensued, and it is now conventional to refer to a unified sensorimotor cortex dissected into four areas designated by the UPPERCASE and lower case letters Ms and Sm – the uppercase letter M or S indicating whether the association is predominantly with motor or sensory functions. Thus the area MsI (first or primary motor sensory area) includes the old motor and premotor regions of the precentral and proximate gyri of the frontal lobe corresponding to areas 4 and 6 of Broadman in his classical study of cerebral cortical Histology) The area MsII (the supplementary motor area) is on part of the medial surface of the frontal lobe (parts of areas 6 and 8).Similarly SmI (The first sensorimotor area) includes most of the postcentral gyrus (areas 3, 1 and 2) and its extension on to the medial surface of the parietal lobe, and SmII is the most dependent and lowest part of the postcentral gyrus (areas 40 and 43)

Broadmans classical study of cerebral cortical Histology) and Investigations Directed Modifications: The area MsI is where movements of the various parts of the body are induced and impulsated for initiation and it receives its main inputs from the cerebellum and the thalamus. Some of the cortical cells send their axons down as the corticonuclear and corticospinal (pyramidal) tracts. MsII receives many fibres from the basal nuclei and is concerned with postural mechanisms, but this area is still a subject several challenging investigations to elucidate completely its exact role. In the precentral gyrus of MsI the body is represented upside down along this cortex, although the face itself is represented the right superiorly. The face lies most inferior and dependent, then the hand (represented by a very large area given its most frequent use in daily activities), then the arm, trunk and leg. The leg and the perineum areas overlap the superior border and extend down on the medial surface of the hemisphere into the paracentral lobule.

The Motor (Anterior) Speech Area of Brocas Areas 44 and 45) The Motor (Anterior) Speech Area of Brocas areas 44 and 45) The Motor (Anterior) Speech Area of Brocas areas 44 and 45) is most often situated in the inferior frontal gyrus on the left side (in right-handed and in most left-handed people. Below and in front of the face area and centred on the pars triangularis between the anterior and ascending rami of the lateral fissure, Lesions to this area results in motor aphasia –that is difficulty in finding the right words,but not paralysis of the laryngeal musculature.

The Motor (Posterior) Speech Area of Wernicke&Auditory Areas 41 and 42) &The olfactory area: The Posterior Speech Area of (Wernicke): The Posterior Speech Area of (Wernicke) is in the posterior parts of the superior and middle temporal gyri, and extends into the lower part of the parietal lobe. Its integrity is necessary for the comprehension of speech. The Auditory Area (areas 41 and 42) The auditory area (areas 41 and 42) is mostly inconspicuously localized in the lateral sulcus,in the anterior transverse temporal grace.It extends into the superior temporal gyrus beneath the sulcus,and it is at this point surrounded by the auditory association area(area 22) These regions receive fibres from the medial geniculate body of the thalamus through the auditory radiation. The cochleas are bilaterally represented as lesion in one cochlea does not cause deafness. The olfactory area: The olfactory area is in the uncus in the front of the parahippocampal gyrus and adjacent parts of the cortex.

Broadmans classical study of cerebral cortical Histology) and Investigations Directed Modifications: The areas SmI and SmII The areas SmI and SmII receive large thalamic input. SmI is for the appreciation of touch, kinaesthetic and vibration sense, and the parts of the body are approximately represented in the same way as in MsI. SmII appears to be associated with pain and temperature sensations. Although the conscious appreciation of pain may occur at the thalamic level, the role of the cortex is imperative for its exact localization. The Gustatory Area: The Gustatory Area for the conscious appreciation of taste lies in the inferior part of the postcentral gyrus (the frontoparietal operculum), near the tongue areas of SmI. The Frontal Eyelid Field Area (Parts of Areas 6, 8 and 9) The Frontal Eyelid Field Area (Parts of Areas 6, 8 and 9) are areas are involved in the impulsations of the voluntary eye movements and the accommodative pathway it is localized in the centre of the middle frontal gyrus. The Olfactory area: The Olfactory area is in the uncus at the front of parahippocampal gyrus and adjacent parts of the cortex.

Broadmans classical study of cerebral cortical Histology) and Investigations Directed Modifications: The Visual Area (Area 17) The visual area (area 17) is principally on the medial surface of the occipital lobe in the depths of the Calcarine Sulcus, more precisely, it lies along the lower lip of the anterior part of the sulcus and along both upper and lower lip of the posterior part, and it extends for about a distance of one centimetre or so on to the lateral surface of the occipital lobe or as far as the Lunate Sulcus. Histologically, the true visual cortex is characterized by a white line corresponding to the Stria of the visual area of the cerebral cortex (referred to as the striae of Gennari) which bisects the grey matter of the cortex, in cortical sections it appears glaringly striking and it is often given the name the striate cortex. The cortex adjacent to the striate part of the medial and lateral surfaces of the hemisphere (and which does not have the Stria) forms the visual association area (areas 18 and 19) Each visual area receives from its own half each retina, i.e.it registers the opposite visual field. In each cortex the upper half receives from the upper half of each half-retina, the lower half from the lower half of each half-retina.i.e the upper and lower visual fields are crossed. The macula registers at the posterior end of the visual area and more peripheral parts of the retina progressively more anterior. When contemplating about visual anatomy, it will be expedient not to misrepresent parts of the visual fields with parts of the retina. The temporal (lateral) half of the visual field of one eye conveys its impressions to the nasal (medial) half of the retina of that eye, similarly the temporal half of the retina receives its impressions from the nasal half of the visual field.

Morphology Of The Cerebral Cortex: Certain aspects of the cortex, notably the insula and piriform area, can be regarded as remnants of the primitive brain (archaeopallium) The Anterior and Posterior commisures unite the two halves. The anterior pole of the thalamus and the globus pallidus provide the subcortical nuclei. The archaeopallium was predominantly an olfactory brain. Its contemporary cerebellum was principally vestibular in its connexions (archaeocerebellum). The massive growth of hemispheres which buries the insula is the neopallium.Its commissure is the corpus callosum and it is associated with the appearance of the putamen and caudate nucleus and the lateral nuclei of the thalamus. Contemperoneously along with neopallium appeared also the neocerebellum, in addition to the red and the olivary nuclei. So in essence with regards to the principles of comparative anatomy, the olfactory era in the more dependent aspects of the organismal phylum has been upgraded to an advanced and novel visual, auditory and tactile existence, in this way precise and regulated motion is now achievable.

The Limbic System and the Olfactory Pathways: Encircling the corpus callosum and the diaencephalon are a number of features that have come to be known collectively as the limbic system. Because the olfactory tracts and its associated structures were originally included in this descriptive concept, much of the function of the limbic system was thought to be concerned with olfaction. However, this view is no longer very popular and it is now recognised that the limbic system participates in such intricate and complexity ingrained functions such as behaviour, mood and selective retention of short term recent memory much more than remote memory. The Limbic System: The components of the limbic system will include but not limited to: [1]-The septal and piriform areas of the cerebral cortex, near the lamina terminalis (the anterior boundary of the third ventricle) [II]-The amygdaloid body. [III]-The hippocampus, fimbria, fornix and mammilary body. [IV]-The uncus, the insula, and the cingulate and parahippocampal gyri. In addition to the hypothalamus and the anterior part of the thalamus in view of their functional connexions with the limbic structures.

The Olfactory Apparatus, Receptors & Pathways. The olfactory tract like the optic nerve is a modified elongation and extension of the white matter of the brain. It is contained in the olfactory sulcus beside the rectus gyrus on the inferior surface of the frontal lobe. Its anterior end is magnified as the olfactory bulb which contains the mitral cells with which the olfactory nerve filaments synapse after passing through the cribriform plate of the ethmoid. The axons of the mitral cells course back in the tract to the anterior perforated substance, through which some of the fibres reach the region of the uncus( at the front of the parahippocampal gyrus, and adjacent parts of the cortex. Other fibres make complex connexions with parts of the limbic system. Note that from the olfactory receptors in the nasal mucosa to the cortex there are two groups of neurons, and that the second neuron has arrived to the cortex without relay in the thalamus which is a unique occurrence. Further synapses connect the olfactory bulb with the hypothalamus and brainstem, as is the case with the other sensory pathways such as (visual, auditory, gustatory and tactile) for both the visceral and somatic effects, distinct from conscious appreciation.

The Histological Fine Structure of the Cerebral Cortex: The cerebral cortex is composed of layers of cells which vary in their characteristics in different regions. Overall, on the average, the motor cortex has several huge pyramidal cells, where as the sensory cortex has smaller round granular cells.All these groups of cells are intermixed with blood capillaries, the neuroglial cells and their processes namely [i]-the microglia (modified macrophage like cells and are scavengers that migrated from the blood vessels), The [ii]-Oligodendrocytes which gives the white substance to axons by providing myelin an insulating substance. The Schwann cells and the satellite cells will take over the functions of the oligodendrogliocytes in the peripheral nerves and ganglia respectively in addition to The Astrocytes.There are basically two types of astrocytes encountered in the brain. [I]-The fibrous astrocytes, which contain several intermediate filaments, and are found primarily in the white matter.And the [II]-The protoplasmic astrocytes which are found in the grey matter and is endowed with granular cytoplasm.Both types of astrocytes send processes that envelope synapses and the surface of nerve cells. They have a membrane potential that varies with the external potassium ion concentration but they do not generate propagated potentials. the astrocytes are neurotrophic by providing nutritive substances, maintaining the internal milieu and ionic acid- base haemostasis, assisting the modulation of the uptake neurotransmitters especially the glutamate and gamma Y- aminobutyric acid in addition to its sustentecular function in assisting the provision of the blood-brain barrier by closing the gap junctions or fenestrations in the endothelium of the cerebral blood vessels).

The Histological Fine Structure of the Cerebral Cortex: In most parts of the cerebral cortex, six layers of nerve cells could be distinguished, and these are conventionally numbered from the surface inwards employing the Roman numerals. These layers are roughly named from the density and shapes of their cells. [I]-Layer I - The Plexiform Layer The Plexiform Layer has an abundance of fibres of relatively few cells and as such it is referred to as the Plexiform layer. [II]-The external Granular Layer The external Granular Layer. [III]- The Pyramidal layer. The Pyramidal layer. [IV]-The Internal Granular Layer. The internal granular layer. [V]- The Ganglionic Layer The Ganglionic Layer. [VI]- The multiform Layer. The multiform Layer The External and The internal bands of Baillarger. In layers IV and V there are often prominent strands of horizontal fibres, the external and internal bands of Baillarger.

The Histological Fine Structure of the Cerebral Cortex: The External Band and the Striae of Gennari. In the visual cortex the external band is named the Stria of Gennari. Modifications and alterations in the differential distribution of these layers which are most pronounced in the recognised motor or sensory areas on the basis of the original concepts of the Broadmans classical histology of the cerebral cortex and its scientific modifications. For instance the notable and established sensory areas of the postcentral gyrus for tactile sensation, the superior temporal gyrus for auditory sensation, the calcarine sulcus in the occipital lobe and striae of Gennari for visual sensation are endowed with cortical structures have an amplified magnitude of granular cells. Amongst the cells of layer V of the precentral gyrus a predominantly motor area of the cerebral cortex, there is an abundance of numerous giant pyramidal cells (of Betz),which are structurally very similar to the large anterior horn cells of the spinal cord, these cells contribute to about one in fifty of the corticospinal fibres. The white matter is composed of myelinated nerve fibres which are bound tightly together by the fibres of the neuroglia; Myelin within the central nervous system is derived from the Oligodendrogliocytes (in contrast to the peripheral nervous system where it comes from the Schwann cells. In depth neurohischemical examinations infers that there are appreciable subcortical masses of grey matter which invariably contains neuronal cell bodies with localization dependent differentially specialized characteristics.

[III]-The Projection Fibres: The Internal capsule as a very important example of a projection fibre. [III]-The Projection Fibres: The Internal capsule as a very important example of a projection fibre. The Projection Fibres are those which execute the synaptic connexion between axons of the cell bodies in the grey matter of the hemisphere with cell bodies of the subcortical nuclei in the hemispheres and with nuclei in the brainstem and the spinal cord. In the base of the hemisphere, a major collection of projection fibres lie lateral to the thalamus and the head of the caudate nucleus, forming the internal capsule. The lentiform nucleus lies lateral to the internal capsule and the tail of the caudate nucleus curls around, also laterally. From the internal capsule, the fibres radiate upwards and outwards in the shape of a curved fan to reach the cortex and similarly pass from the cortex down to the capsule, this fan-shaped arrangement is the corona radiata.Fibres of the corpus callosum intersect.

The structure and function of the Internal capsule A typical horizontal section through the hemisphere at the level through the interventricular foramen and the pineal body depicts the internal capsule as a band of white matter that is not a straight line but bent into a lateral concavity by the convex medial border of the lentiform nucleus (i.e. the globus pallidus) Given this approximately L-shaped structure of the internal capsule, it is described as having an anterior limb, genu, posterior limb, and there are also two other portions posteriorly,the sublentiform and the retrolentiform parts. Amongst all these parts of the internal capsule, the posterior limb which lies between the thalamus medially and the lentiform nucleus laterally is the most critical and sensitive region, because right behind the corticonuclear fibres in the genu part of the internal capsule, lies the corticospinal fibres.From the cell bodies in the cortex these corticospinal fibres pass down through this part of the capsule, then through the brain stem to the lower medulla where most of them decussate to form the lateral corticospinal tract and eventually arborize with the anterior horn cells that innervate the skeletal muscle. Thus passing through a small part of the internal capsule – (thus the genu and the anterior two-thirds of the posterior limb – are the motor fibres that control all the skeletal muscles in the body. The head (corticonuclear) fibres lie most anteriorly and immediately behind them are corticospinal fibres for the arm, hand, trunk, leg and perineum in that order from front to back. (In the cerebral peduncle of the midbrain the head fibres lie medially and the fibres for the perineum laterally, in the same order)It is in this part of the internal capsule that haemorrhage or thrombosis of a striate artery commonly occurs. The muscles of the opposite side of the body are thus paralysed; they become spastic with increased stretch reflexes, the signs of an upper motor neuron lesion.Fibres from the speech (Brocas) area are interrupted in lesions of the left internal capsule; thus loss of speech accompanies hemiplegia of the right side of the body. In the posterior limb of the internal capsule are also the thalamocortical fibres passing from the cell bodies in the thalamus to the cerebral cortex. These contain sensory fibres conveying impulses derived from the contralateral side of the body which projects superiorly through the corona radiata to the sensory cortex. There are also large numbers of corticopontine fibres.

The structure and function of the Internal capsule In the retrolentiform part of the internal capsule, at the posterior end of the lentiform nucleus are several projection fibres running superiorly from the pontine region to cerebral cortex (the corticopontine fibres), specifically to the parietal, temporal and occipital regions. These will occupy the lateral third of the base of the cerebral peduncle. However, much of much more importance for the retrolentiform part of the internal capsule is that it contains the visual fibres which are passing from the lateral geniculate body in the thalamus projects as the optic radiation to the visual area of the cortex at the calcarine fissure in the occipital lobe of the cerebral cortex. Furthermore another group of fibres runs from the medial geniculate body below the posterior end of the lentiform nucleus, so forming the sublentiform part of the capsule. These are the fibres of the auditory radiation which reach the auditory area of the cortex in the superior temporal gyrus. Although, the corticopontine fibres which are at least a score of millions form the largest group of internal capsule components, the corticonuclear, corticospinal and thalamocortical fibres and those of the optic radiation are of greater practical importance, although they are much smaller in number.

Basal nuclei equally referred to as the basal ganglia. The interior of the cerebrum is characterized by the presence within the white matter of large masses of another grey matter due to its numerous containing nuclei, in addition to cavities which contain cerebrospinal fluid. The greatest number of cells in each hemisphere is encountered in the thalamus, which belongs to the diaencephalon, the central part of the forebrain. The other groups of cells belong to the lateral part of the forebrain and some of them constitute the basal nuclei equally referred to as the basal ganglia. The basal ganglia are usually classified as containing the caudate nucleus, the lentifom nucleus (which has an outer part the putamen and an inner part the globus pallidium.) in addition to the amygdaloid body and the claustrum.Also the substantia nigra and the sub- thalamic nuclei are closely associated with this system.The putamen part of the lentiform nucleus and the caudate nucleus are intimately linked by several interconnecting fibres to form what is collectively known as the corpus striatum. The corpus striatum is the input side of the basal ganglia by receiving fibres mainly from the cerebral cortex, thalamus and the substantia nigra. Whereas, the globus pallidium is the output side by sending fibres to the thalamus, and also to the subthalamic nucleus, substantia nigra and the reticular formation. Functionally, the basal ganglia exert a supraspinal control over the skeletal motions by influencing their rate, range and co-ordination. There are several pathways conveying projection fibres across these nuclei and ganglia. Different pathways involve different transmitters which include acetyl choline, dopamine, glutamate, serotonin and GABA. The most common pathology of the basal nuclei is parkinsonism, characterized by tremor, rigidity and akinesia due to a decrease in the nigrostriatal pathway.

The Mixed Fibres. As demonstrated by the above examples, most motor fibres could not be neatly classified into any of the categories above and as such are mainly of the mixed form, although they may assume predominantly one of the above prototypes.

Histology Of The Central Nervous System CONSTITUENTS OF THE CENTRAL NERVOUS SYSTEM Neurons are traditionally recognized in Nissl stained sections by their generally large size,large pale nucleus, prominent cytoplasmic Nissl substance and single large nucleolus (First Legend Figure on the Second Row From the Left in The Slides Below ). However, small neurons are easily missed using this stain and it could be more reliable to use an antibody to neuron-specific nuclear protein (NeuN) which stains the nucleus and cytoplasm of neurons but not other cells (Second Legend Figure on the Second Row From The Left in The Slides Below ). Other neuronal proteins that occupy a particular cell compartment can also be demonstrated with antibodiesfor example, microtubule-associated protein II antibodies which are used to demonstrate dendrites (Third Legend Figure on the Second Row From The Left in The Slides Below ) and neurofilament antibodies that are used to demonstrate axons (Fourth Legend Figure on the Second Row From The Left in The Slides Below), Expression of the cytokine IL-17 in astrocytes in multiple sclerosis. (First Legend Figure on the First Row From the Left in The Slides Below ) Red staining of astrocytes with the specific marker glial fibrillary acidic protein. (Second Legend Figure on the First Row From the Left in The Slides Below) Green immunostaining of the same section for IL-17. (Third Legend Figure on the First Row From the Left in The Slides Below )The images merged with superimposed green and red staining in double-labelled astrocytes showing as yellow.

Legends Demonstrating Astrocytes,Axons.Neurons& Dendrites

TERMINOLOGIES Terms Adeno hypophyseal Placode - Specialised cranial surface ectoderm placode region that will form the endocrine anterior pituitary (adenohypophysis). Adenohypophysis - (anterior pituitary, pars anterior) The anterior part of the pituitary, which develops in the early embryo from the surface ectoderm adenohypophyseal placode. This placode will fold inward on the roof of the pharynx forming a transient structure Rathke's pouch, that looses its connection with the surface. Anterior pituitary - (adenohypophysis, pars anterior, pars distalis) Neurohypophysis - (posterior pituitary) pars tuberalis - (pars tuberalis of the hypophysis) anatomically is the region of anterior pituitary (adenohypophysis) extending along the anterior and lateral surfaces of the hypophyseal stalk. Tuberalis principal cells are low columnar, with cytoplasm containing lipid droplets, glycogen granules, and some colloid droplets. Posterior Pituitary - (neurohypophysis) Rathke's Pouch - An ectodermal fold in roof of pharynx forming anterior pituitary (adenohypophysis) and pars intermedia. Named after German embryologist and anatomist Martin Heinrich Rathke ( ).

The Embryology&Histology Of The Pitutary Gland The pituitary organizer is a domain within the ventral diencephalon that expresses Bmp4, Fgf8, and Fgf10, which induce the formation of the pituitary precursor, Rathke's pouch, from the oral ectoderm. The WNT signaling pathway regulates this pituitary organizer such that loss of Wnt5a leads to an expansion of the pituitary organizer and an enlargement of Rathke's pouch. WNT signaling is classified into canonical signaling, which is mediated by β- CATENIN, and noncanonical signaling, which operates independently of β- CATENIN....This result suggests that canonical WNT signaling promotes pituitary organizer function, instead of inhibiting it. See Legend Figure Below

Rabbit Pituitary Development

Legend demonstrating The Dual Ectoderm Origins of The Pitutary Gland Dual Ectoderm Origins Ectoderm - Ectoderm Roof of Stomodeum, Rathke's pouch, Adenohypophysis Neuroectoderm - Prosenecephalon, neurohypophysis Adenohypophysis Anterior wall proliferates - pars distalis Posterior wall little growth – pars intermedia Rostral growth around infundibular stem – pars tuberalis Neurohypophysis Infundibulum – median eminence, infundibulum, pars nervosa

Red - Surface Ectoderm Blue - Neural Tube Ectoderm

Pituitary Timeline Mouse Pituitary Development Embryonic development of pituitary stalk during week 7 and 8 based upon Streeter. Carnegie stage 19 - Thick stalk with remnant of lumen (Rathkes pouch); angiogenesis beginning. Capillaries appearing in mesodcrm at rostral surface of anterior lobe. Carnegie stage 20 - Long, slender stalk. Carnegie stage 21 - Thread-like stalk; beginning absorption. Carnegie stage 22 - Remnant of incomplete stalk at either end. Carnegie stage 23 - Practically no trace of stalk remains. Oriented epithelial follicles. Abundant angioblasts and capillaries in vascular component of anterior lobe. See Legend Figure Below

Pituitary Development In A Rodent Model

Time Line Of Pitutary Development Week 4 - hypophysial pouch, Rathkes pouch, diverticulum from roof Week 5 - elongation, contacts infundibulum, diverticulum of prosencephalon Week 6 - connecting stalk between pouch and oral cavity degenerates Week 10 - growth hormone and ACTH detectable Week 16 - adenohypophysis fully differentiated Week 20 to 24 - growth hormone levels peak, then decline. See Legend Figures Below.

Legend Figure Demonstrating Human Pitutary Developmnent

Legend Figure Demonstrating Carnegie Stage 22 Developing Pituitary - Human embryo (Carnegie stage 22, week 8)

Carnegie Stage 22 Developing Pituitary - Human embryo (Carnegie stage 22, week 8)

Legend Figure Depicting Carnegie Stage 23 Of Pitutary Development

Legend For The Fetal Pituitary The epithelium of the anterior lobe has become partly subdivided into lobule which project into the mesodermal component of the gland. The abundant vascular elements are well demonstrated.

Human Fetal Head AT (Week 12) – THE Pituitary Gland Is Indicated By An Arrow

A study in rats has identified the role of a known regulator of blood vessel development (Vascular Endothelial Growth Factor, VEGF) in the development of the pituitary portal vascular system. "The primary capillaries extended along the developing pars tuberalis, whereas the portal vessels penetrated into the pars distalis at E15.5 (rat) and subsequently expanded into the lobe to connect with the secondary capillary plexus, emerging in the pars distalis.....study suggests that VEGF-A (Vascular Endothelial Growth Factor A) is involved in the development of the primary capillaries and in the vascularization of the pars distalis, but not in the portal vessels since the formation of portal vessels begins at E13.5 (rat), before the appearance of VEGF-A in the rostral region of the pars distalis." The pars distalis is vascularized by hypophysial portal vessels that arise from the capillary beds in the median eminence of the hypothalamus, and this hypophyseal portal system provides an important link for carrying hormonal information from the central nervous system to the pituitary. The capillaries of the pituitary gland are characterized by richly fenestrated endothelia.

Hypothalamus - Pituitary – Adrenal

Hypothalamus - Pituitary - Gonad (Male)

Hypothalamus Endocrine Axes Hypothalamus The hypothalamus is a small region located within the brain that controls many bodily functions, including eating and drinking, sexual functions and behaviors, blood pressure and heart rate, body temperature maintenance, the sleep-wake cycle, and emotional states (e.g., fear, pain, anger, and pleasure). Hypothalamic hormones play pivotal roles in the regulation of many of those functions. Because the hypothalamus is part of the central nervous system, the hypothalamic hormones actually are produced by nerve cells (i.e., neurons). Hypothalamus Pituitary The anterior pituitary produces several important hormones that either stimulate target glands (e.g., the adrenal glands, gonads, or thyroid gland) to produce target gland hormones or directly affect target organs. The pituitary hormones include adreno-corticotropic hormone (ACTH); gonadotropins; thyroid-stimulating hormone (TSH), also called thyrotropin; growth hormone (GH); and prolactin. The first three of those hormones (ACTH, gonadotropins, and TSH) act on other glands. ACTH stimulates the adrenal cortex to produce corticosteroid hormones (primarily cortisol) as well as small amounts of female and male sex hormones. Gonadotropins comprise two molecules, luteinizing hormone (LH) and follicle- stimulating hormone (FSH). These two hormones regulate the production of female and male sex hormones in the ovaries and testes as well as the production of the germ cells (oocyte and spermatozoa). TSH stimulates the thyroid gland to produce and release thyroid hormone. The remaining two pituitary hormones, GH and prolactin, directly affect their target organs.

Hypothalamus - Pituitary - Thyroid

Hypothalamus - Pituitary - Gonad (female)

Pituitary Hormones- Follicle Stimulating Hormone Follicle Stimulating Hormone FSH regulation of AMH transcriptional activation[7] Follicle-stimulating hormone (FSH, gonadotropin) is produced in the anterior pituitary (adenohypophysis) by basophil cell gonadotropes. This glycoprotein hormone postnatally during puberty acts on the gonads (testis and ovary) to regulate fertility. FSH at the cellular level binds the membrane follicle-stimulating hormone receptor (FSH receptor, FSHR), a G protein-coupled receptor (GPCR)/seven-transmembrane domain receptor. Testis - Sertoli Cell Ovary - Granulosa Cell In females - FSH acts on the ovary to stimulate follicle development. Negative feedback by inhibin from the developing follicle decreases FSH secretion. In males - FSH acts on the testis Sertoli cells to increase androgen-binding protein (ABP) that binds androgens and has a role in spermatogenesis. FSH-defficiency in females results in infertile (block in folliculogenesis prior to antral follicle formation) and in males does not affect fertility (have small testes but are fertile). FSH protein has a molecular weight 30 kDa and a 3-4 hour half-life in circulation. Gonadotrophins have been used clinically in humans for the treatment of infertility. Other glycoprotein hormones include luteinizing hormone (LH), thyroid stimulating hormone (TSH), and chorionic gonadotropin (hCG).

Luteinizing Hormone (lutropin, lutrophin, LH) produced in the anterior pituitary (adenohypophysis) by basophil cell gonadotropes. LH at the cellular level binds the membrane luteinizing hormone receptor (LH receptor, LHR), a G protein-coupled receptor (GPCR)/seven-transmembrane domain receptor. Testis - Leydig cell Ovary - Theca cell Postnatal Postnatal thyrotropin (TSH) Neonatal_Development &Puberty Development Sexual Dimorphism Quantitation of the human pituitary by magnetic resonance imaging (MRI) from childhood through puberty has identified volmetric differences between male and female pituitary sizes between 14 to 17 years of age. Females had larger pituitary glands than males in the age 14 to 17 year old groups. Young (19 years and under) and old (20 years and older) females demonstrated a correlation between pituitary volume and age. Males did not show this relationship.

Postnatal thyrotropin (TSH) Trends

Adult Histology Adenohypophysis Acidophils - cytoplasm that stains red or orange polypeptide hormones: Somatotropes, produce growth hormone; Lactotropes produce prolactin) Basophils - cytoplasm that stains a bluish colour glycoprotein hormones: Thyrotropes produce thyroid stimulating hormone; Gonadotropes produce luteinizing hormone or follicle-stimulating hormone; Corticotropes produce adrenocorticotrophic hormone) Chromophobes - cytoplasm that stains very poorly acidophils or basophils that are degranulated and depleted of hormone Neurohypophysis Infundibular process - usually referred to as posterior pituitary (unmyelinated axons from hypothalamic neurosecretory neurons, supraoptic and paraventricular hypothalamic nuclei) 2 other parts: median eminence and infundibular stalk

Pituitary - Neurohypophysis (Large Histology Image)

Pituitary - neurohypophysis (large histology image) Molecular Pituitary development: regulatory codes in mammalian organogenesis. "During mammalian pituitary gland development, distinct cell types emerge from a common primordium. Appearance of specific cell types occurs in response to opposing signaling gradients that emanate from distinct organizing centers. These signals induce expression of interacting transcriptional regulators, including DNA binding-dependent activators and DNA binding-independent transrepressors, in temporally and spatially overlapping patterns. Together they synergistically regulate precursor proliferation and induction of distinct cell types. Terminal cell type differentiation requires selective gene activation strategies and long-term active repression, mediated by cell type-specific and promoter-specific recruitment of coregulatory complexes. These mechanisms imply the potential for flexibility in the ultimate identity of differentiated cell types." Pax6 is essential for establishing ventral-dorsal cell boundaries in pituitary gland development. "The transcription factor Pax6 (paired homeodomain) has been shown to be expressed transiently in the dorsal portion of the developing pituitary before the ventral/dorsal appearance of specific cell types. Transient dorsal expression of Pax6 could establish the boundary between dorsal and ventral cell types, based on the inhibition of Shh ventral signals."

Pituitary - Neurohypophysis (Large Histology Image)

Genes Pit1 (pituitary-specific transcription factor) is a transcription factor important for pituitary development and muations in this gene can lead to abnormalities in pituitary development and hormone production. PIT1 Pituitary-Specific Transcription Factor 1 - transcription factor responsible for pituitary development and hormone expression in mammals. OMIM | Gene Map Locus: 3p11 | is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals and is a member of the POU family of transcription factors that regulate mammalian development. PitX1 Paired-Like Homeodomain Transcription Factor 1 - transcription factor expressed in pituitary primordium. Member of bicoid-related vertebrate homeobox genes. OMIM | Gene Map Locus: 5q31 PitX2 Paired-Like Homeodomain Transcription Factor 2 - transcription factor expressed in pituitary primordium and other anterior structures, including the eye Member of bicoid-related vertebrate homeobox genes. OMIM | Gene Map Locus: 4q25-q26 TPIT T-box transcription factor Pituitary OMIM | Gene Map Locus: 1q23-q24 VEGF Vascular Endothelial Growth Factor - mitogen growth factor for vascular endothelial cells. Role in pituitary vascular development. OMIM | Gene Map Locus: 1q23-q24

FSH regulation of AMH transcriptional activation

Neurohypophysis

Abnormalities Anatomical abnormalities asssociated with the Rathke's pouch include a craniopharyngeal canal, from the anterior part of the fossa hypophyseos of the sphenoid bone to the under surface of the skull. The stomodeal end may also be present at the junction of the septum of the nose with the palate. Abnormal functional development of the pituitary can lead to a wide range of other organ diseases due to the effect of hormones released from the pituitary on many other endocrine and non-endocrine organs (For example: dwarfism, hypothyroidism) Pituitary Duplication Occurring as either a complete or partial duplication, this is an extremely rare abnormality with poor neonatal survival due to associated abnormalities. Recently a heterozygous deletion of chromosome 14, including the thyroid transcription factor-1 gene, has been identified with duplication of the pituitary stalk. Pituitary Adenoma Classification There are several abnormalities associated with abnormal levels of the hormonal output of the pituitary due to the development of pituitary tumours (adenomas). Growth hormone (GH) adenoma Growth hormone (GH) adenomas, which are benign pituitary tumors lead to chronic high GH output levels, that may lead to acromegaly in adults and gigantism in children. Acromegaly (Greek, acro = "extremities"; megaly = "enlargement") is a clinical term for a hormonal disorder that results from excess growth hormone (GH) in the body. The pituitary produces excessive amounts of growth hormone, usually due to benign, or noncancerous, pituitary tumours (adenomas). Childhood adenomas lead to gigantism rather than acromegaly, due to continued and excess growth in the still unfused growth plates in the long bones of the legs. acromegaly Adrenocorticotropic (ACTH) adenoma Cushing's disease caused either by a pituitary adenoma produces excess adrenocorticotropic hormone (ACTH, corticotropin) or due to ectopic tumors secreting ACTH or corticotropin-releasing hormone (CRH). Classification can be applied using specific criteria (clinical presentation, biochemical data, histology of growth pattern, tinctorial characteristics, proliferative activity, immunohistology marker expression, ultrastructure and molecular biology). The current classification used is the World Health Organization classification of 2000 recently updated in 2004.