Peripheral Nervous System And Rami


Peripheral Nervous System And Rami  

The peripheral nervous system includes cranial and spinal nerves that connect the central nervous system with receptors and effectors of the body. Based on the nature of the impulse passing through the nerve fibers, the neurons and the nerve fibers may be classified into sensory neurons and nerve fibers, motor neurons and nerve fibers, and intermediate neurons or association aneurons.

The sensory neurons conduct sensory impulses from receptors and evoke sensations like pain, hat, taste, smell and so on. They are afferent in nature i.e. they conduct motor impulses from the central nervous system to the neurons. Motor neurons conduct motor impulses to the effectors like muscles and glands. Intermediate neurons connect sensory and motor neurons with each other and with other nerve cells in CNS.

As far as cranial nerves are concerned, there are twelve pairs of cranial nerves that arise from the brain in mammals. The spinal nerves are thirty one pairs which arise from the spinal cord. They consist of 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and 1 pair of coccygeal nerves.  Each spinal nerve is a mixed nerve. It arises from the spinal cord by two roots -- the dorsal root and the ventral root. The dorsal root is formed of only sensory or afferent nerve fibers. The ventral root is formed of motor nerve fibers. The cytons of motor neurons are located in the ventro-lateral horn of gray matter. 

Each spinal nerve divides into three branches, namely dorsal ramus, ventral ramus and ramus communicans. These are collectively referred to as rami.

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