Peripheral Nervous System
Published: Jul 17, 2023
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Updated: Jul 31, 2023
Written by Oseh Mathias
Founder, SpeechFit
The peripheral nervous system (PNS) is one of the two main divisions of the nervous system, the other being the central nervous system (CNS). It consists of all the nerves and ganglia (clusters of nerve cells) located outside the brain and spinal cord, which comprise the CNS[1].
The boundary between the CNS and the PNS is generally referred to as the the Redlich-Obersteiner's zone, which is where the myelin coating of nerve fibres changes from the CNS-type (made by oligodendrocytes) to the PNS-type (made by Schwann cells). This zone is typically seen in the region of the spinal cord where the dorsal root ganglia, clusters of nerve cell bodies, become the sensory nerves of the peripheral nervous system[3].
The PNS is divided into the somatic nervous system (SoNS) and the autonomic nervous system (ANS)[6].
Somatic Nervous System: The SoNS is responsible for voluntary body movements, and for receiving external stimuli. It is associated with activities that the organism consciously controls. This system consists of afferent nerves or sensory nerves, and efferent nerves or motor nerves. Afferent nerves are responsible for relaying sensation from the body to the CNS, while efferent nerves are responsible for sending out commands from the CNS to the body, triggering muscle contraction or gland secretion[7].
Autonomic Nervous System: The ANS is responsible for involuntary control of the body, generally for the regulation of internal organs. It is further divided into the sympathetic, parasympathetic, and enteric systems[8].
Sympathetic Nervous System: The sympathetic nervous system is often associated with the fight-or-flight response, as it prepares the body for intense physical activity[9].
Parasympathetic Nervous System: The parasympathetic nervous system is often associated with resting and digesting, or feed and breed activities. It slows heart rate, increases intestinal and gland activity, and relaxes sphincter muscles[10].
Enteric Nervous System: The enteric nervous system (ENS) controls the gastrointestinal system. It is capable of operating independently of the brain and the spinal cord, but usually works in conjunction with them.The PNS also includes the Enteric Nervous System (ENS) which controls the gastrointestinal system. It can operate independently of the CNS, but typically works in conjunction with the parasympathetic and sympathetic systems[11].
The primary function of the peripheral nervous system is to connect the central nervous system to the rest of the body, including the limbs and organs. This enables a multitude of essential functions, such as conveying sensory information from the body to the CNS, and carrying motor commands from the CNS to the muscles and other tissues[12].
The sensory (afferent) component of the PNS is responsible for transmitting sensory information to the CNS from the rest of the body. This includes a range of sensory modalities such as touch, temperature, pain, and proprioceptive information about the position and movement of the body. It also includes special senses like vision, hearing, taste, and smell[6].
The motor (efferent) component of the PNS is responsible for transmitting commands from the CNS out to the rest of the body. This can be further divided into the somatic and autonomic systems. The somatic system controls voluntary movements of skeletal muscles. The autonomic system, on the other hand, regulates involuntary functions like heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal[6].
Through these complex and diverse functions, the PNS plays a crucial role in maintaining the body's homeostasis and enabling its interaction with the external environment.
Oseh is a software engineer, entrepreneur and founder of SpeechFit. Oseh is passionate about improving health and wellbeing outcomes for neurodiverse people and healthcare providers alike.
References
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