ABSTRACT
The nervous system is one of the two regulatory systems in the human body that influences the activity of all the other organ systems. It consists of literally billions of neurons interconnected in a highly organized manner to form circuits. The number of neurons and the manner in which they are interconnected in a given circuit distinguishes one region of the brain from another and the brain of one individual from that of another. In addition,
plasticity
, the ability to alter circuit connections and function in response to
sensory input and experiences adds further complexity and distinctiveness to neurological responses and behavior. The nervous system is divided into two anatomically distinct regions:
• Central nervous system • Peripheral nervous system
The
central nervous system
(
CNS
) consists of the brain and spinal cord. The
peripheral nervous system
(
PNS
) consists of 12 pairs of cranial nerves that arise from the brainstem and 31 pairs of spinal nerves arising from the spinal cord. These peripheral nerves carry information between the CNS and the tissues of the body. The PNS consists of two divisions:
• Afferent division • Efferent division
The
afferent division
carries sensory information toward the CNS and the
efferent division
carries motor information away from the CNS toward the effector tissues (muscles and glands). The efferent division is further divided into two components: (1) the somatic nervous system, which consists of motor neurons that innervate skeletal muscle; and (2) the autonomic nervous system that innervates cardiac muscle, smooth muscle, and glands.
