Structure: CNS

The spinal cord extends from the base of the skull to L2 vertebral level. The spinal cord is composed of white matter (axons with myelin sheath) and grey matter (neuronal cell bodies and ganglion). Inferior to L2, the spinal nerevs are known as the cauda equina. The level at which the nerves exit the spinal cord is classed as the root value of the nerve, named according the vertebral level.

 

Structure: PNS 

The PNS is further sectioned into the sensory division and motor division.

• Sensory division: also known as the afferent division, directs nerve impulses from the sensory receptors to the CNS through sensory neurons

• Motor division: also know as the efferent division, conducts action potentials from CNS to periphery such as organs and muscles through motor neurons. The motor division is further subdivided into the somatic nervous system (transmits impulses from CNS to skeletal muscle) and autonomic nervous system (transmits impulses from CNS to smooth muscle, cardiac muscle and glands)

Organisation of the sensory and motor neurons is illustrated in the diagram below.

 

Structure: Spinal Cord Cross Section