The reason for this difference is due to the naming and location of the spinal root between C7 and T1 vertebrae (C8 spinal nerve root). In the thoracic to the coccygeal region, the spinal nerve root originates below the corresponding vertebrae. In the cervical region, the nerve root exits above the corresponding vertebrae (the nerve root between the skull and C1 vertebrae is the C1 spinal nerve). Their names match the adjacent spinal vertebra from which they exit. The 31 pairs of spinal nerves include 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. The spinal nerves help to control the function and movement for the rest of the body. The formation of nerve plexuses rather than a direct continuation of the nerve roots to peripheral nerves serves as an essential safety measure so that injury at one site or body region may not affect the vital functions of our body.
They arise from the spinal cord as nerve roots and merge to form a web (plexus) of interconnected nerve roots and once again branch to form nerve fibers. Spinal nerves carry somatosensory information into and motor instructions out of the spinal cord. Of note, the accessory nerve innervates the sternocleidomastoid and trapezius muscles, neither of which control muscles used exclusively in the head. The others originating from the brainstem include oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, spinal accessory, and hypoglossal. The nucleus of the olfactory and optic nerve are located in the forebrain and thalamus, respectively, and are not considered true cranial nerves. Ten of the cranial nerves originate from the brain stem and mainly control the voluntary movement and structures of the head with some exceptions. Besides these, there are thousands of other association nerves in the body.Ĭranial nerves are responsible for carrying information in and out of the brain.
It is also responsible for the reflex arc, which involves the use of interneurons to perform reflexive actions. The somatic nervous system consists of both afferent (sensory) and efferent (motor) nerves.
A substantial portion of the peripheral nervous system is the 43 different segments of nerves- 12 pairs of cranial and 31 pairs of spinal nerves, which help us perform daily functions. It is responsible for all the functions we are aware of and can consciously influence, including the movement of our arms legs and other parts of our body. The somatic nervous system is a component of the peripheral nervous system associated with the voluntary control of the body movements via the use of skeletal muscles.
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