Topic Resources The peripheral nervous system refers to the parts of the nervous system that are outside the central nervous system, that is, those outside the brain and spinal cord. Thus, the peripheral nervous system includes The nerves that connect the spinal cord to the rest of the body, including the 31 pairs of spinal nerves More than 100 billion nerve cells that run throughout the body Using the Brain to Move a Muscle
Dysfunction of peripheral nerves may result from damage to any part of the nerve:
Typical Structure of a Nerve CellA nerve cell (neuron) consists of a large cell body and nerve fibers—one elongated extension (axon) for sending impulses and usually many branches (dendrites) for receiving impulses. The impulses from the axon cross a synapse (the junction between two nerve cells) to the dendrite of another cell. Each large axon is surrounded by oligodendrocytes in the brain and spinal cord and by Schwann cells in the peripheral nervous system. The membranes of these cells consist of a fat (lipoprotein) called myelin. The membranes are wrapped tightly around the axon, forming a multilayered sheath. This myelin sheath resembles insulation, such as that around an electrical wire. Nerve impulses travel much faster in nerves with a myelin sheath than in those without one. Insulating a Nerve FiberMost nerve fibers inside and outside the brain are wrapped with many layers of tissue composed of a fat (lipoprotein) called myelin. These layers form the myelin sheath. Much like the insulation around an electrical wire, the myelin sheath enables nerve signals (electrical impulses) to be conducted along the nerve fiber with speed and accuracy. When the myelin sheath is damaged (called demyelination), nerves do not conduct electrical impulses normally. Peripheral nerve disorders can affect If motor nerves (which control muscle movement) are damaged, muscles may weaken or become paralyzed. If sensory nerves (which carry sensory information—about such things as pain, temperature, and vibration) are damaged, abnormal sensations may be felt or sensation may be lost. Peripheral nerve disorders can be hereditary or acquired (caused by exposure to toxins, injury, infections, or metabolic or inflammatory disorders). Certain disorders cause progressive deterioration of the nerve cells in the spinal cord and brain that control muscle movement (motor neuron diseases Amyotrophic Lateral Sclerosis (ALS) and Other Motor Neuron Diseases (MNDs) Motor neuron diseases are characterized by progressive deterioration of the nerve cells that initiate muscle movement. As a result, the muscles stimulated by these nerves deteriorate, become... read more ) as well as in the peripheral nerves. Motor neuron diseases can resemble peripheral nerve disorders, which affect nerve cells outside the brain and spinal cord rather than those in the spinal cord or brain. Motor neuron diseases may be caused by viruses (such as the polio Polio Polio is a highly contagious, sometimes fatal enterovirus infection that affects nerves and can cause permanent muscle weakness, paralysis, and other symptoms. Polio is caused by a virus and... read more virus), be inherited, or have no clear known cause (such as amyotrophic lateral sclerosis Amyotrophic Lateral Sclerosis (ALS) and Other Motor Neuron Diseases (MNDs) Motor neuron diseases are characterized by progressive deterioration of the nerve cells that initiate muscle movement. As a result, the muscles stimulated by these nerves deteriorate, become... read more ). Novichok was developed in Russia and has been used in assassination attempts. Curare has been used to help relax muscles during surgery and to paralyze and kill when placed on the tip of poison darts. Disorders that affect muscle rather than nerves (as peripheral nerve disorders do) also cause muscle weakness. Muscle disorders may be categorized as
Doctors do tests to determine whether the cause of weakness is a muscle, a neuromuscular junction, or a nerve disorder.
To diagnose a peripheral nerve disorder, doctors ask people to describe their symptoms, including
Doctors also ask about possible causes, such as whether people have had any infections or other disorders, whether they may have been exposed to toxins, and whether any family members have had similar symptoms. This information gives doctors clues about the cause of symptoms. What doctors find during the examination may suggest possible causes and the tests that need to be done. Tests may include the following:
If a disorder is causing symptoms, it is treated if possible. Otherwise, doctors focus on relieving symptoms. Care provided by a team of several types of health care practitioners (a multidisciplinary team) can help people cope with progressive disability. The team may include
CLICK HERE FOR THE PROFESSIONAL VERSION Copyright © 2022 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved. What makes up the peripheral nervous system?The peripheral nervous system is divided into two main parts: Autonomic nervous system (ANS): Controls involuntary bodily functions and regulates glands. Somatic nervous system (SNS): Controls muscle movement and relays information from ears, eyes and skin to the central nervous system.
What are the 3 parts of the peripheral nervous system?Parts of the PNS. The PNS can be divided into two components: the somatic nervous system and the autonomic nervous system. The somatic nervous system (SNS) and the autonomic nervous system (ANS) are both part of the peripheral nervous system.
What cells is the peripheral nervous system made of?As with the central nervous system, the basic cell units of the peripheral central nervous system are neurons. Each neuron has a long process, known as the axon, which transmits the electrochemical signals through which neurons communicate.
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