The sensory endings in the skin initiate an electrical signal that travels along the sensory axon within a nerve into the spinal cord, where it synapses with a neuron in the gray matter of the spinal cord. Sensation starts with the activation of a sensory ending, such as the thermoreceptor in the skin sensing the temperature of the water. In the PNS, satellite cells are supporting cells for the neurons, and Schwann cells insulate peripheral axons. Ependymal cells are responsible for filtering the blood to produce cerebrospinal fluid, which is a circulatory fluid that performs some of the functions of blood in the brain and spinal cord because of the BBB. Microglia act as phagocytes and play a role in immune surveillance. Oligodendrocytes are the myelinating glia in the CNS. Astrocytes are important for maintaining the chemical environment around the neuron and are crucial for regulating the blood-brain barrier. In the CNS, astrocytes, oligodendrocytes, microglia, and ependymal cells are found. Several types of glial cells are found in the nervous system, and they can be categorized by the anatomical division in which they are found. Specific types of glial cells provide this insulation. Many axons are insulated by a lipid-rich substance called myelin. Signals are received at the dendrites, are passed along the cell body, and propagate along the axon towards the target, which may be another neuron, muscle tissue, or a gland. Neurons are polarized cells, based on the flow of electrical signals along their membrane. Glial cells are supporting cells, maintaining the environment around the neurons. Neurons are the cells responsible for communication through electrical signals. Nervous tissue contains two major cell types, neurons and glial cells. The enteric nervous system is exclusively found in the periphery because it is the nervous tissue in the organs of the digestive system. Parts of the autonomic nervous system overlap with the enteric nervous system. Somatic and autonomic integrative functions may overlap as well.Ī special division of the nervous system is the enteric nervous system, which is responsible for controlling the digestive organs. The sensations that lead to autonomic functions can be the same sensations that are part of initiating somatic responses. Autonomic functions are distributed between central and peripheral regions of the nervous system. The autonomic nervous system (ANS) is responsible for functions that affect cardiac or smooth muscle tissue, or that cause glands to produce their secretions. Any sensory or integrative functions that result in the movement of skeletal muscle would be considered somatic. The somatic nervous system (SNS) is responsible for functions that result in moving skeletal muscles. The nervous system can also be divided on the basis of how it controls the body. In the PNS, ganglia are basically gray matter and nerves are white matter. Gray matter is where nuclei are found and white matter is where tracts are found. These descriptions are more often used in the CNS. Nervous tissue can also be described as gray matter and white matter on the basis of its appearance in unstained tissue. The name for that specific structure depends on its location. A single axon can be part of a nerve and a tract. Whereas nuclei and ganglia are specifically in the central or peripheral divisions, axons can cross the boundary between the two. A bundle of axons is referred to as a tract in the CNS and as a nerve in the PNS. A localized collection of neuron cell bodies is referred to as a nucleus in the CNS and as a ganglion in the PNS. All of these functional areas are found in both the central and peripheral anatomy.Ĭonsidering the anatomical regions of the nervous system, there are specific names for the structures within each division.
Functionally, the nervous system can be divided into those regions that are responsible for sensation, those that are responsible for integration, and those that are responsible for generating responses. The anatomical divisions are the central and peripheral nervous systems. The nervous system can be separated into divisions on the basis of anatomy and physiology. 12.1 Basic Structure and Function of the Nervous System
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