Page 12 - LN-NEURAL CONTROL & COORDINATION

1. Somatic Neural System

The somatic neural system contains nerves which relay impulses from CNS to
skeletal muscles. These can be further categorised into cranial (from brain) and
spinal nerves on the basis of their origin.
i.Cranial Nerves
These nerves emerge specifically from the forebrain and brain stem.
Note:
* Trochlear is smallest and thinnest nerve and possess difficulty in surgical
operations.

* Trigeminal is also called dentist nerve. It is the largest cranial nerve. At its
origin it is associated with ‘Gasserian Ganglion’.
* Facial nerve is associated with geniculate ganglion at its origin.
Their functions in comparative manner in a nut shell are given below
ii. Spinal Nerves
All spinal nerves are mixed, having sensory and motor fibres in approximately
equal numbers. In humans, 31 pairs of spinal nerves are present as Cervical (8

pairs), Thoracic (12 pairs), Lumber (5 pairs), Sacral (5 pairs), Coccygeal (1 pair).
Note:
There are 10 pairs of cranial nerves in fishes and amphibians and 12 pairs in
rest of the higher chordates.
There are 10 pairs of spinal nerves found in fishes and amphibians and 31 pairs
in humans.
Based on their functions, the nerve fibres of PNS are divided into two groups,
i.e., afferent fibres and efferent fibres.

The afferent nerve fibres transmit sensory impulses from tissues/organs to the
CNS and form the sensory or afferent pathway. The efferent nerve fibres
transmit motor impulses from CNS to the concerned tissues/organs and form
the motor or efferent pathways.
2. The Autonomic Neural System (ANS)
The autonomic neural system consists of the sympathetic and parasympathetic

nervous system. The former is called thoraco-lumber outflow and the latter is