VPB 121: Veterinary Physiology - II (2+1)

SOMATIC COMPONENTS

• The spinal nerves emerge as a pair of nerves from each spinal segment through the inter-vertebral foramina, which lies between the two adjoining vertebrae.
• Thus, the number of pairs of thoracic, lumbar and sacral nerves is similar to the respective vertebrae.
• Although the cranial portion has seven cervical vertebrae, eight pairs of cranial nerves emerges, while the caudal vertebrae have fewer pairs of coccygeal nerves.
• The terminal portion of the spinal cord, the meninges and the nerves are collectively referred to as cauda equinae.

• The dorsal spinal root is the afferent neuron and it propagate sensory impulses from the periphery towards spinal cord and the cell bodies of these neurons are located in the dorsal root ganglion. 
• The somatic motor nerves or the efferent nerves emerge from the cell bodies of ventral roots, located in the ventral horn of the spinal cord.  Both the dorsal and ventral roots unite to form the spinal nerves that emerge through the inter-vertebral foramen.
• Thus, the spinal nerves are mixed nerves, containing both sensory and motor fibres.  However, outside the vertebral canal it divides into dorsal and ventral branches.
• The  nerves from the last three cervical and the  first one  or  two thoracic nerves form a net work, the  left  and  the right  brachial  plexus‚ supply to the respective  fore limbs.
• The ventral branches of the last 3 to 5 lumbar and first 2 to 3 sacral nerves unite to form the right and left lumbo-sacral plexus, supplying to the respective hind limbs.