Anatomy & Physiology

Anatomy & Physiology Study Guide

Chapter 13: Neural Tissue The nervous system contains all the neural tissue located within the body. The basic functional units of the nervous system are individual cells called neurons . Supporting cells, or neuroglia , separate and protect the neurons and provide a supportive framework for neural tissue. Neuroglia, also called glial cells, far outnumber neurons. Neural tissue shapes the organs of the nervous system: the brain; the spinal cord; the receptors in complex sense organs; and the nerves that link the nervous system with other systems. There are two major anatomical divisions of the nervous system: the central nervous system and the peripheral nervous system. 13.1 Divisions of the Nervous System Structural The nervous system has two divisions: the central nervous system and the peripheral nervous system. The central nervous system (CNS) consists of the brain and the spinal cord. The CNS integrates, processes, and coordinates sensory data and motor commands. Sensory data convey information about conditions inside or outside the body. Motor commands control or adjust the activities of peripheral organs. The CNS houses the structures that provide the higher functions, such as memory, emotion, learning, and intelligence. The peripheral nervous system (PNS) includes all the neural tissue outside the CNS. The PNS sends sensory information to the CNS and carries motor commands to the peripheral tissues, organs, and systems that carry out the orders. Bundles of axons, or nerve fibers, carry sensory information and motor commands in the PNS. These bundles of axons with their associated blood vessels and connective tissues are called peripheral nerves. Cranial nerves connect to the brain; those nerves attached to the spinal cord are called spinal nerves . Functional The PNS further divides into afferent and efferent divisions. Sensory communication that is passed to the CNS from receptors located in the peripheral tissues is transported by the afferent division . The efferent division of the PNS transports motor commands from the CNS to muscles, glands, and adipose tissue. These focus organs that respond to the demand with an action are called effectors . The efferent division has both somatic and autonomic components. The somatic nervous system (SNS) controls skeletal muscle contractions. Skeletal muscles under conscious control contract voluntarily. Involuntary contractions are contained at the subconscious level and may be simple, automatic responses or complex movements. This type of automatic response is called a reflex. The autonomic nervous system (ANS), or visceral motor system, provides automatic regulation of cardiac and smooth muscle and glands at the subconscious level. The ANS includes a sympathetic division and a parasympathetic division . They perform opposing activities and work to offset the actions of each other. For example, when the body senses danger, the sympathetic division accelerates the heart rate, whereas, when the sense of danger subsides, the parasympathetic activity slows the heart rate.

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