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.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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