Peripheral Nervous System:
The nervous system outside the brain and
spinal cord.The PNS consists of the nerves
and ganglia outside the brain and spinal cord.
CNS and PNS communicate with each other to
make sure our body parts, such as our fingers,
can send signals to the central nervous system
for processing in our brains.
The peripheral nervous system includes all
the nerves that go from the skin, muscle, and
organs to the spinal cord and eventually the
brain. However, the central nervous system is
composed of the brain and spinal cord.
The peripheral nervous system consists of 12
pairs of cranial nerves and 31 pairs of spinal
nerves.
I. Cranial nerves:
12 pairs – 10 pairs originate from brain stem.
There are 3 types of CN sensory nerves
(sensory fibres), mixed nerves (has both) and
motornerves (motor fibres).
II. Spinal Nerves:
All the spinal nerves are mixed nerves.
Each spinal nerve has two roots, a dorsal
sensory and a ventral motor root.
At the middle of each dorsal root, is a swelling
called dorsal root ganglion, which contains
sensory neurons.
The motor neurons for the ventral root are
present in the grey matter of spinal cord.
These nerves are:
Cervical = 8 pair in neck
Thoracic = 12 pair in thorax
Lumbar = 5 pair in upper abdomen
Sacral = 5 pair in lower abdomen
Coccygeal = 1 pair in tail region
Total spinal fibers = 31 pairs
So the spinal formula is C 8 Th 12 L 5 S 5 Co 1