PERIPHERAL NERVOUS SYSTEM
PERIPHERAL NERVOUS SYSTEM
• It includes nerves arising from brain and spinal cord innervating different parts of the body respectively
called as, cranial and spinal nerves.
Comprises of all nerves which connect the central nervous system with receptors and effectors.
Nerves connecting the receptor organs to the CNS are called sensory or afferent nerves; they contain
sensory fibres only.
Nerves connecting the effector organs (muscles and glands) to CNS are motor or efferent nerves; they
contain motor fibres only.
A third type of nerve, the mixed nerves have both sensory and motor nerve fibres.
Nerves connected to brain are called cranial nerves while those connected to spinal cord are spinal nerves.
On the basis of presence and absence of myelin sheath around the axons the nerve fibres are myelinated or
nonmylinated, respectively.
• Each nerve is composed of many nerve fibers enclosed within a connective tissue sheath. A nerve fiber is a
long axon or dendrite of a neuron, which could be either sensory or motor or both.
CRANIAL NERVES
• These are 12 pairs in humans.
• The name, origin and nature of these nerves are as follows:
• Trigeminal and abducens nerves emerge through Gasserian ganglion located within the cranium.
• Motor component of vagus nerve controls sound production;
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1. Trigeminal nerve (V) is the largest.
2. Vagus (X) nerve regulates the functions of organs in thoracic and abdominal cavities.
SPINAL NERVES
• These nerves originate from the spinal cord and innervate the nearby parts of the body.
• The numbers generally relate to the number of vertebrae
• All spinal nerves are essentially of mixed nature and are generally medullated named as per their site of
emergence these are classified in mammals as
(i) Cervical nerves (neck part) = 8 pai