The peripheral nervous system (PNS) is made up of two divisions: the somatic nervous system and the autonomic system. Each part of this system plays a vital role in how information is communicated throughout the body. This article discusses what the peripheral nervous system is, how it works, and the influence that it has on how the body functions, including what happens when there is a problem affecting the PNS.
What Is the Peripheral Nervous System?
The nervous system is divided into two parts: the central nervous system and the peripheral nervous system. The central nervous system (CNS) includes the brain and spinal cord, while the peripheral nervous system includes all of the nerves that branch out from the brain and spinal cord and extend to other parts of the body, including muscles and organs. The primary role of the PNS is to connect the CNS to the organs, limbs, and skin. The nerves of the PNS extend from the central nervous system to the outermost areas of the body. The peripheral system allows the brain and spinal cord to receive and send information to other areas of the body, which allows us to react to stimuli in our environment. The four primary functions of the PNS are to:
Control autonomic body functionsControl motor movementsDigestionRelay sensory information to the central nervous system
Examples of processes controlled by the peripheral nervous system include dilating or constricting the pupils in response to light, stimulating digestion, activating the sweat response, controlling blood flow, and regulating heart rate.
Structures of the Peripheral Nervous System
The peripheral nervous system itself is divided into two parts: the somatic nervous system and the autonomic nervous system. Each of these components plays a critical role in how the peripheral nervous system operates.
The Somatic Nervous System
The somatic system is the part of the peripheral nervous system responsible for carrying sensory and motor information to and from the central nervous system. The somatic nervous system derives its name from the Greek word soma, which means “body.” The somatic system is responsible for transmitting sensory information as well as for controlling voluntary movement. This system contains two major types of neurons:
Motor neurons: Also called efferent neurons, motor neurons carry information from the brain and spinal cord to muscle fibers throughout the body. These motor neurons allow us to take physical action in response to stimuli in the environment. Sensory neurons: Also called afferent neurons, sensory neurons carry information from the nerves to the central nervous system. The sensory neurons allow us to take in sensory information and send it to the brain and spinal cord.
The Autonomic Nervous System
The autonomic system is the part of the peripheral nervous system that’s responsible for regulating involuntary body functions, such as blood flow, heartbeat, digestion, and breathing. In other words, it is the autonomic system that controls aspects of the body that are usually not under voluntary control. This system allows these functions to take place without needing to consciously think about them happening. The autonomic system is further divided into two branches:
Sympathetic system: By regulating the flight-or-fight response, the sympathetic system prepares the body to expend energy to respond to environmental threats. When action is needed, the sympathetic system triggers a response by accelerating heart rate, increasing breathing rate, boosting blood flow to muscles, activating sweat secretion, and dilating the pupils. Parasympathetic system: This helps maintain normal body functions and conserve physical resources. Once a threat has passed, this system will slow the heart rate, slow breathing, reduce blood flow to muscles, and constrict the pupils. This allows the body to return to a normal resting state.
Nerves in the Peripheral Nervous System
The PNS is composed of nerves that are responsible for carrying signals between the central nervous system and the parts of the body that lie outside the CNS. This includes information from the senses, organs, and muscles. The axons of these nerve cells are bundled together and can be found throughout the body. Information is received by the dendrites of these cells, the information travels down the axon to the cell body. The message can then be communicated to other cells. The nerves that make up the peripheral nervous system connect with either the spinal cord or brain in order to transmit information to the CNS.
Spinal Nerves
Spinal nerves are responsible for transmitting information from the muscles, organs, and glands to the spinal cord. There are 31 spinal nerves that branch out to different areas of the body from the spinal cord.
Brachial plexusFemoral nerveLateral femoral cutaneous nervePeroneal nerveSciatic nerveSpinal accessory nerveTibial nerve
Cranial Nerves
The cranial nerves are responsible for the receptors found in the head and neck area. Instead of connecting with the spinal cord, these nerves travel directly to the brain. There are 12 pairs of cranial nerves that transmit motor and sensory information from areas including the face, mouth, eyes, nose, and ears.
Diseases of the Peripheral Nervous System
There are a number of diseases and disorders that can affect the peripheral nervous system. Problems with the sensory and motor neurons in the PNS can result in changes in sensation, muscle weakness, or muscle paralysis. Some of the conditions that can affect the PNS include:
Amyotrophic lateral sclerosis (ALS)Carpal tunnel syndromeDiabetesEpstein-Barr virusGuillain-Barre syndromeLupusPeripheral neuropathyPeripheral nerve injuriesRheumatoid arthritisThoracic outlet syndromeTumorsVitamin deficiency
Symptoms of PNS diseases and disorders can include numbness, pain, tingling, burning, sensitivity to touch, and muscle weakness.
Treatment for PNS Conditions
Treatment for peripheral nerve problems depends on the cause and focuses on treating the underlying disorder and offering supportive care. For example, some PNS conditions may be caused by injury while others may be related to underlying health conditions, viruses, toxins, or genetic disorders. In addition to treating conditions that may be causing dysfunction or damage to PNS nerves, treatment may also involve surgery, physical therapy, occupational therapy, speech/language therapy, and respiratory support.
A Word From Verywell
The peripheral nervous system plays a critical role in motor and sensory function. If you are experiencing symptoms such as muscle weakness, numbness, loss of sensation, or sensitivity, talk to a healthcare provider for further evaluation. Some research suggests that traumatic brain injury may be associated with an increased risk for disorders that can affect the peripheral nervous system, such as ALS.
