Jittipan Chavadej,Ph.D.

Dept. of Anatomy,Fac. of Science, Mahidol University September,2000

Diagrams showing formation of the neural groove, neural tube and neural crest

Neural tube-neural crest

Neural tube-brain & spinal cord Neural crest-most components of PNS -non-neural component in the body and head.

Fundamental processes in Nervous system formation

•Induction-Proliferation •Migration-Differentiation •Pattern formation •Intercellular communication •Stabilization or Elimination •Development of integrated pattern

Changes in Gross Structure of NS

•Closure of neural tube 24 th -day -cranial neuropore 26 th -day -caudal neuropore •Cephalic end-primary brain vesicles -procencephalon -mesencephalon -rhombencephalon •Spinal cord

3-wk.

Embryo :

- C shape - cephalic flexure (mesencephalon) - cervical flexure (hind brain&spinal cord) 5-wk.

Embryo :

- procencephalon-Telen., Dien.

-mesencephalon -rhombencephalon-Meten., Myelen.

A lateral view of the brain vesicles and part of spinal cord . B diagram showing the cavities of the three brain vesicles and spinal cord

Diencephalon - optic vesicles Mesencephalon - sharply bend by cephalic flexure Rhombencephalon - Pontine flexure thin roof

Basic anatomy of the five-part human brain

Histogenesis within Nervous System •2 major cell lineages - Neuronal progenitor cell neurons - Glial progenitor cell astrocyte, oligodrendrocyte, ependyma (neural tube) * Microglia-enter CNS from outside

Cell lineages in the developing central nervous system

Neuron large cell body -long processe axon carry signals to targets dendrites receive input Neurons need to “

and touch

forming

synapses

reach out

“ each other by to

survive

.

Development of nervous system components

Formation of Zones 1. Ventricular zone-ependymal cells become epithelial lining of central canal 2. Mantle zone-neuroblast cells become gray matter of the CNS 3. Marginal zone-neuronal processes become white matter of the CNS

Formation of zones & fundamental organization of the developing neural tube Note: -ependymal zone -mantle zone -marginal zone

Fundamental Organization of Neural tube

Dorsal portion/Alar plate/sensory <---Sulcus limitans Ventral portion/Basal plate/motor Roof plate - Floor plate

A-development of regional specialization across the neural tube. B-formation of the spinal cord

Spinal cord formation

** Basic plan of neural tube is preserved in spinal cord ** •Mantle zone = H-shape of gray matter with central canal •Marginal zone = White matter -->>myelinated nerve fibers

Spinal cord - PNS

Ventral aspect

•Neuroblasts of basal plate ->> outgrowth of axons -->ventral nerve root

Dorsal aspect

•Thin processes of neuroblast of spinal ganglion-->dorsal nerve root

Development of a peripheral nerve A-showing motor axon, growing fiber of nerve cell in DRG. B-showing ventral motor and dorsal sensory root joining to form the trunk of spinal nerve

Myelination - in CNS -->> oligodendroglia - in PNS -->> Schwann cell

Gross change of spinal cord

•6-wk.-->full length of vertebral column •8-wk.-->end ~Co4 •14-wk.-->end ~S1 •23-wk.-->end ~L4 •Birth-->end ~L3 •Adult--> end~L2-3-filum terminale &cauda equina

Functional components

Dorsal alar horn = Afferent neurons •2 functional categories: -GSA (soma,body) & GVA (viscera) Ventral basal horn =Efferent neurons •2 functional categories: GSE & GVE

Dorsal alar plate-sensory horn of spinal cord Ventral basal plate-motor horn of spinal cord

Brain Formation

•The original organization of neural tube is altered in the formation of many regions of the brain.

•Nerve cells form concentrated collections called nuclei in the brain

•Dilatations of the central lumen form ventricles in the brain -lateral ventricle-> Telen.

-third ventricle-> Dien.

-cerebral aqueduct-> Midbrain -fourth ventricle-> Hindbrain * CSF - choroid plexus

A

Development of the ventricular system of the brain A-early embryo B-during expansion of cerebral hemisphere C-postnatal morphology of ventricular system

Formation of specific brain regions

Rhombencephalon - Metencephalon - Myelencephalon Medulla oblongata-transitional zone *-major alteration --> 4 th ventricle

Expansion of roof plate- 4 th ventricle Basal plate&Alar plate in brainstem Basal plate-->close to midline <---Sulcus limitans Alar plate--> lateral

Alar and basal plates in myelencephalon showing the position of nuclear groups at different stages of development

Basal plate contains three motor nuclei medial somatic efferent gr.=SE intermediate special visceral efferent gr.=SVE lateral gr.=GVE general visceral efferent

Alar plate contains sensory nuclei *-most lateral special somatic afferent gr.=SSA general somatic afferent gr.=GSA *-intermediate special visceral afferent gr.=SVA *-medial general visceral afferent gr.=GVA

Special functional categories of cranial nuclei in the brainstem

Brain Formation

Hindbrain-meten.-->pons&cerebellum

Pons contains

- fiber tracts - cranial nerve nuclei - pontine nuclei

Cranial end

cerebellum.

of hindbrain (meten.) expands outwards to form Cerebellum - specialization of alar plates --> Rhombic lips Two cerebellar hemispheres+Vermis

Motor and sensory nuclear groups in the basal and alar plates of caudal part of metencephalon

The development of the cerebellum.- Dorsal view Note: 3 apertures - Foramen of Magendie(1-median) -Foramen of Luschka(2-lateral)

Formation of the cerebellum or cerebrum involves formation of multiple neuronal layers in the cortex There is a second wave of proliferation fron the inner ventricular layer-->Germinal layer and give rise to cerebellar cortex

A-D=development of cerebellum A&B=development of cerebellar cortex

Glia play an important role in migration of cortical neurons Radial glia-->for guidance neurons to their destination The external cortical neurons-layers * The cerebellar hemispheres undergo extensive folding =

Folia

Radial glial cells and their association with peripherally migrating neurons during development of the brain

DEVELOPMENT of Nervous System

(cont.) Dr. Jittipan Chavadej Anatomy Department yr ,

2000

Mesencephalon

The alar region forms 4 swellings called

corpora quadrigemina

The ventral region forms -gray matter in tegmentum -white matter in cerebral peduncles

Dorsal view of the midbrain & hindbrain

Colliculi =relay nuclei for auditory & visual systems Tegmentum -cranial motor nuclei -2 prominent relay nuclei=red nucleus & substantia nigra Cerebral peduncle=fiber tracts from cerebrum > cerebellum > spinal cord

Cross section-early&later developing mesencephalon (blue-sensory, red-motor)

Forebrain-->dien. & telencephalon Dien. forms midline brainstem regions from its alar plate-contain relay nuclei.

Dorsal -thalamus & epithalamus Ventral -hypothalamus

Medial surface & X-section of prosencephalon. Note: corpus striatum bulge from the floor of lateral ventricle

A medial surface of telencephalon & diencephalon B X-section Note : thalamus,hypothalamus & corpus striatum

Midline -epiphysis Pituitary gl.-downgrowth of hypotha. + upgrowth of pharyngeal ectoderm *Craniopharyngioma-remnant of Rathke’s pouch

Functions

Thalamus-relay center for cerebral cortex Epithalamus -olfactory input Pineal gl.-extension of epithalamus *-neurosecretory cell-->melatonin

Hypothalamus-receiving input from many CNS areas.

-regulates autonomic visceral fn. including sleep,body temp.,digestion -regulates endocrine secretions of pituitary gland

Telencephalon forms the cerebral hemispheres by bilateral expansion Cerebral cortex-waves of migration to form cerebral cortex=neocortex -intermediate zone-->white matter *Forming multiple synaptic connections is important to the development of the brain*

*The cerebral hemispheres fold into lobes and gyri->begin 14 weeks Fetal period-frontal,parietal, temporal and occipital lobes Sulcus/sulci separate some lobes Convolutions - gyrus/gyri -begin betw.6&8months

Showing the development of gyri and sulci on the lateral surface of the cerebral hemisphere A=7 months B=9 months

Corpus striatum formation

•At the base of telencephalic vesicle •Dorsal to the thalamus C -shaped corpus striatum -caudate nucleus -lentiform nucleus

A medial surface of telencephalon & diencephalon B X-section Note : corpus striatum caudate&lentiform nucleus -internal capsule

Commissures

**Lamina terminalis**

•1 st - ant r commissure •2 nd - hippocampal commissure •3 rd - corpus callosum-biggest -post r & habenular commissures (pineal gland) -optic chiasm

Medial surface showing various commissures

Meninges form a protective coating around the entire CNS Meninges -3 layers of CNT 1. Tough outer coat = Dura mater 2. Middle layer = Arachnoid mater 3. Inner layer = Pia mater

Subarachnoid space is filled with CSF, forming a protective cushion for the brain.

CSF Lat. ventricle 3 rd ventricle Cerebral aqueduct 4 th ventricle Foramen of Magendie Foramen of Luschka

Development of the ventricular system of the brain B showing the lateral and medial apertures in the roof of the 4 th ventricle

Meninges from 2 sources Outer dura - mesoderm surrounding neural tube Arachnoid & Pia cranial caudal neural crest cells mesoderm

Congenital defects of the CNS

•Mental retardation-no detectable brain abnormality •Gross morphological defects -spina bifida/occulta/cystica -meningocele/meningomyelocele /meningoencephalocele -rachischisis

Congenital malformations of the NS

Rachischisis -spinal cord is exposed.

Herniation in the cranial region Occipital meningocele Frontal encephalocele

PNS development

PNS consists of the neural tissue outside CNS •ganglion/ganglia-neurons •peripheral nerve-nerve cell process Neural crest forms most of the PNS

Organization of ANS at thoracic level

Neural crest

Neural crest forms most of the PNS Two types of ganglia  sensory ganglia  autonomic motor ganglia

Major neural crest migratory P’W