For Med Students

Organization of the Nervous System

This topic will discuss about the Organization of the Nervous System – this will help some student to understand the nervous system organization.

ANATOMICAL DIVISION

1.     CNS

• Brain
• Spinal cord

2.     PNS

• Cranial nerves, except CN I
• Spinal nerves – origin: spinal cord
• Associated ganglia

ª       Collection of nerve cell bodies:

• CNS: nuclei/nucleus
• Outside the CNS: ganglion / ganglia

3.     ANS – constituent part of the CNS and PNS

a.     Parasympathetic

• Origin: Cranio-sacral
• Cranial – CN 3, 7, 9 & 10
• Sacral – sacral cord levels and sacral spinal nerves 2, 3 & 4

b.    Sympathetic

• Origin:Thoraco-lumbar
• Arises from the spinal cord – T1-L2 or L3
• Forms the sympathetic trunk with its ganglia

Read more in Conditions and Diseases

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FUNCTIONAL DIVISION

1.     Sensory / Afferent

• Receives and transmits impulses to the CNS

2.     Motor/ Efferent

• Impulses originate from the CNS

ª       Gray matter / cerebellar cortex / cerebral cortex – collection of nerve cell bodies

ª       White matter – collection of myelinated axons (tracts,fasciculus,peduncle, columns)

** note: in spinal cord – gray matter is found at the center while white matter is at the periphery

TYPES OF FIBERS

1.     Commissural

• Helps communicate one hemisphere to another
• i.e. corpus callosum

2.     Association

• Communicates within the same hemisphere

a.     Long

b.    Short

3.     Projection

• Need to communicate (in the gray matter) involving several fibers in different locations
• i.e. corona vadiata

TRACTS – fibers with common origin and destination

1.     Ascending

• Spinothalamic tract
• Sensory

2.     Descending

• Corticobulbar tract
• Corticospinal tract
• Motor tract

ª       White matter of the spinal cord

• Fasciculus – cervical part of the cord

§       Ganglia – upper

§       Cunneatus – lower

• Funniculus – anterior, lateral, dorsal

>> Additional Info (from Dr. Elma) – in order to identify which side of the spinal cord is dorsal or ventral

àseen cross sectionally the spinal cord has:

• Ventral median fissure – deeper
• Dorsal median sulcus – shallow (Posterior)

Glial cells / Neuroglia

• Astrocytes
• Oligodendrocytes
• Microglia – macrophage system
• Macroglia – collective term for astrocytes and oligodendrocytes
• Ependymal cells – lining the central canal of spinal cord

Homunculus

• Motor – bigger hands (left)
• Sensory – bigger lips and arms (right)

This post was written by: Franklin Manuel

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