To MBBS 2nd year

Dr Laxman Khanal

Assistant Professor, Department of Anatomy

BPKIHS, Dharan, Nepal

12-02-2017

Development of nervous system

Cranial nerves1. Motor parts2. Sensory parts3. Autonomic parts

Parasympathetic

Spinal nerves1. Motor parts2. Sensory parts3. Autonomic parts

A. Sympathetic (thoracic and lumbar segment)

B. Parasympathetic (sacral segment)

Parts of nervous system1. CNS- brain and spinal cord2. PNS- cranial and spinal nerve3. ANS- contributed by both CNS and PNSANS -cardiac muscle, smooth muscle and glands.

Notochord acts as aninducer for developmentof nervous system.

BMP

• Ectoderm • Neuroectoderm• Neural plate• Neural fold• Neural groove• Neural tube

Neuroectoderm Neural tubeEdge of Neuroectoderm and embryonic ectoderm Neural crest cellsEmbryonic ectoderm Ectodermal derivatives

Development of neural crest cells

Epithelial Mesenchymal E- Cadherin

Pharyngeal arch derivatives• Skeletal component• Nerves and ganglia of each arch• Dermis overlying each arch• Blood vessels of face.

Migration of neural crest cells

Cranial neuroporeClosure at 25th day

Caudal neuroporeClosure at 27th day

Brain

SC

Alpha feto protein (AFP) increasesin maternal AF if neuropores fail toclose (neural tube defects).

Anencephaly Craniorachischisis

Neural tube defects of cranial part of neural tube

Neural tube defects of caudal part of neural tube

Rachischisis

Myelomeningocele

Spina bifida occulta

Prevented by maternal use of folic acid prior to and during pregnancy.

Spina bifida occulta Meningocele Myelomeningocele

Rachischisis

Anterior portion of neural tube forms three primary brain vesicles.

1. Prosencephalon: Telencephalon + Diencephalon2. Mesencephalon:3. Rhombencephalon: Metencephalon + Mylencephalon

I & II CN

III & IV CN

V- XII CN

Development of ventricular system

4th

Development of spinal cord

L

TS neural tube

Neuroepithelial cellsL

Neuroblast cell

L

Mantle cell layer

Marginal cell layer

L

A

B

A

B

R

F

Anterior horn

Posterior horn

intermediate horn

Sensory

Motor

Autonomic

Neuroblast Glioblast

Microglial cells

Ependymal cells

Origin of various types of cells

Brain stemArrangement of alar andbasal plate is intact butthe arrangement isdifferent.

Higher centerBasal plate regress andalar plate accentuate.

A

B

GSE

SVE

GVE

Development of functional columns in brain stem

Basal plate – motor componentsSkeletal muscle1. Somatic muscles - GSE2. Pharyngeal arch muscles- SVESmooth muscle- GVE (autonomic)

CN supplying somatic skeletal muscles

Motor nerve of pharyngeal archCN with parasympathetic actions

GSE

SVE

GVE

GSA

SVA

GVA

SSA

Development of functional columns in brain stem

Alar plate- sensory columnSenses• General senses • Special sense- taste• Senses from viscera• Special sense-hearing & Eqb

Pain, touch, temperature, pressure

Taste Sense of distension of viscera

Hearing & equilibrium

Mesencephalic flexure

Cervical flexure

Pontine flexureRhombic lip• Postero-lateral extension of alar plate

of metencephalon.• Give rise to cerebellum.

Rhombic lip

TS of caudal part of Pons

Rhombic lip Cerebellar plate

TS Mesencephalon

Alar plate

Basal plate

Alar plateSup colliculusInf colliculus

Basal plateNuclei of 3rd CNNucleus of 4th CN

Development of Prosencephalon

Diencephalon3rd ventricle

Telencephalon2 lateral ventricles

1. Thalamus2. Hypothalamus3. Epithalamus4. Subthalamus 5. Metathalamus6. Neurohypophysis

Summary

• The CNS develops from a dorsal thickening of ectoderm-the neuralplate, which appears around the middle of the third week.

• The neural plate is induced by the underlying notochord and paraxialmesoderm to form neural tube.

• The cranial end of the neural tube forms the brain and the remainderforms the spinal cord.

• The neural canal, the lumen of the neural tube, becomes theventricles of the brain and the central canal of the spinal cord.

• Defects in the closure of the neural tube (NTDs) account for mostsevere anomalies of nervous system.