Nervous System Organization

• Formation of 3 germ layers
• 1. Ectoderm (epidermis / neural tissue)

2. Mesoderm (muscle / CT)

3. Endoderm (epithelium of GI & resp. tracts)

• Beginning of 3rd week
• notochord induces overlying ectoderm to form neural plate

• End of 3rd week
• lateral edges of neural plate form neural folds
• (depressed mid-region = neural groove)

Neural tube formation by fusion of neural folds (rostro-caudal direction)

Rostral neuropore (cranial opening) & caudal neuropore are open to amniotic fluid

Coincides with establishment of blood supply to the neural tube

neural tube (caudal to 4^th pair of somites)

• Dorsal horn of spinal cord
• Sensory (afferent)

• Ventral horn of spinal cord
• Motor (efferent)

Ventricular zone: cell proliferation into neurons / macroglia

• Intermediate zone: neurons differentiate / form axons and dendrites
• (a.k.a mantle layer)

Marginal zone: edge of cord where longitudinal axon fasicles grow

neural tube (rostral to 4th pair of somites)

• Forebrain - Prosencephalon
• - Telencephalon
• - Diencephalon

• Midbrain - Mesencephalon
• - Mesencephalon

• Hindbrain - Rhombencephalon
• - Metencephalon
• - Myelencephalon

Causes folding / bending of developing brain

• 3 main flexures (folds):
• - midbrain flexure
• - pontine flexure
• - cervical flexure

• Neuron cell bodies in nuclei
• Astrocytes
• Microglia
• Some oligodendroglia

• Myelinated axons
• (myelin formed by oligodendroglia)

Neural crest

Myelinated axons (covered by endoneurium)

Fascicles (covered by perineurium)

Nerves (covered by epineurium)

Neural crest

Visceral innervation

• 3 Components
• - sympathetic
• - parasympathetic
• - enteric

• Preganglionic neuron
• - gray matter of CNS

• Postganglionic neuron
• - sympathetic = autonomic ganglia
• - parasympathetic = visceral wall / ganglia close to organ

• CN III, VII, IX, X
• Spinal nerves C1 - S2/S4

Spinal nerves T1 - L2

Neurons in the spinal cord lateral horn from T1-L2 or 3

• Some synapse in paravertebral ganglia
• Others travel via splanchnic nerves to prevertebral ganglia

cholinergic

Neurons in paravertebral (sympathetic chain) or some prevertebral (collateral) ganglia

adrenergic (except to eccrine sweat glands = cholinergic)

Neurons in brainstem nuclei or sacral spinal cord

Cholinergic

Neurons in wall of viscera

Cholinergic