Different Types of Nerves and What They Do
The human body basically has two types of nerves: the sensory nerves and the motor nerves. The sensory, or afferent nerves take impulses toward the brain from receptors in the skin and other sense organs. The motor, or efferent nerves, take impulses from the brain to the glands and the muscles. Internuncial nerves carry signals between different areas in the brain and the spinal cord.
The Central Nervous System
The sensory and motor nerves belong to larger systems of nerves. The nerves of the central nervous system radiate from the spinal cord. Some nerves send messages to the brain, so the person can take conscious action. Other types of nerves operate outside of conscious control. These include the nerves that control the heartbeat and the complex actions that allow the digestion of food such as secretion of enzymes and the contraction of the intestines.
The Peripheral Nervous System
The nerves in the peripheral nervous system carry messages to and from the central nervous system. The cranial nerves leave the brain directly and control the sensory organs, while the spinal nerves come from the spinal cord and control the muscles. The autonomic nerves control the internal organs and operate independently of the central nervous system.
The autonomic system itself is separated into two parts, which are the sympathetic and parasympathetic systems. These nerves have opposite actions from each other. For example, if a nerve from one system makes the heart beat faster, a nerve from the other system slows it down.
Nerve Cell Structure
Like other cells in the body, nerve cells are made of a nucleus enveloped by cytoplasm. In the case of the nerve cell, the cytoplasm elongates into a long thread called an axon and branched threads called dendrites, named because they resemble the branches of trees. Dendrites bring information into the body of the neuron, while axons take information away.
Nerve cells can have a great variety of shapes depending on what they do. Some brain cells are shaped like triangles, while other cells, called Purkinje’s cells, are shaped like cones. The axons of some nerve cells are very short, while others have axons are several feet long.