Malcolm Rivera
The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, the other being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain and spinal cord. The PNS can be divided into two subsystems: the autonomic and somatic nervous systems. The autonomic nervous system is further divided into sympathetic and parasympathetic components, which often have opposing effects on organs to maintain homeostasis. The somatic nervous system includes the sensory nervous system and consists of sensory nerves and somatic nerves, and many nerves that hold both functions.
| Characteristics | Values |
|---|---|
| Main Function | Connects the CNS to the limbs and organs |
| Location | Outside the brain and spinal cord |
| Number of Cranial Nerves | 12 pairs |
| Number of Spinal Nerves | 31 pairs |
| Number of Nerve Cells | 100 billion |
| Number of Subsystems | 2 |
| First Subsystem | Somatic |
| Second Subsystem | Autonomic |
| Somatic Subsystem Function | Voluntary movements |
| Autonomic Subsystem Function | Involuntary movements |
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What You'll Learn
Somatic and autonomic subsystems
The peripheral nervous system (PNS) is divided into two subsystems: the somatic nervous system and the autonomic nervous system. The somatic nervous system is responsible for voluntary actions such as scratching an itch, and the transmission of signals from outside the body between the central nervous system and certain organs/muscles. It is also known as the voluntary nervous system. The somatic nervous system consists of efferent nerves responsible for stimulating muscle contraction, including all the non-sensory neurons connected with skeletal muscles and skin. The somatic nervous system controls all voluntary muscular systems within the body, and also mediates involuntary reflex arcs.
The autonomic nervous system, on the other hand, is responsible for most involuntary movements in the body, such as digestion. It is concerned with visceral functions that occur below the level of consciousness. The autonomic nervous system has two parts: the sympathetic division and the parasympathetic division. The sympathetic nervous system controls the fight or flight response in animals, while the parasympathetic nervous system controls processes like rest and digestion. The autonomic nervous system also has an enteric component that helps with digestion and the filtering of toxins.
The somatic nervous system has connections in all 31 spinal nerves. The spinal nerves branch out further and become the nerves that spread out through the body. Some of the nerves in this system are sensory, conducting information from the senses to the brain. Others are motor nerves, conducting information from the brain to the muscles. The somatic nervous system also includes cranial nerves, which are nerve fibres that carry information into and out of the brain stem.
The autonomic nervous system, meanwhile, is a visceral efferent system, which means it sends motor impulses to the visceral organs. It functions automatically and continuously, without conscious effort, to innervate smooth muscle, cardiac muscle, and glands. It is concerned with heart rate, breathing rate, blood pressure, body temperature, and other visceral activities that work together to maintain homeostasis.
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Cranial nerves
The peripheral nervous system (PNS) is made up of nerves that travel from the spinal cord and brain to supply the face and the rest of the body with information from the outside world. The cranial nerves are a set of 12 paired nerves that arise directly from the brain. The first two nerves (olfactory and optic) emerge from the cerebrum, while the remaining ten emerge from the brainstem.
The olfactory nerve (I) is essential for detecting smells. It transmits signals between scent receptors and the brain. The optic nerve (II) emerges from the lateral colliculus, which are swellings on either side of the temporal lobes of the brain. The oculomotor nerve (III) emerges from the midbrain, while the trochlear nerve (IV) comes from the posterior side of the midbrain. The trigeminal nerve (V) is the largest cranial nerve and has both motor and sensory functions. Its motor functions help a person to chew and clench their teeth. The trigeminal nerve also gives sensation to the muscles in the tympanic membrane of the ear.
The abducens nerve (VI), facial nerve (VII), and vestibulocochlear nerve (VIII) emerge from the pontine-medulla junction. The facial nerve (VII) supplies the muscles of the face. The remaining four cranial nerves emerge from posterior to the olive: the glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI), and hypoglossal nerve (XII). The vagus nerve is the longest cranial nerve and carries out mechanisms of taste, movement, and swallowing in the brain. The hypoglossal nerve (XII) is located anterior to the olive.
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Spinal nerves
The peripheral nervous system (PNS) is made up of nerves that travel from the spinal cord and brain to supply the face and the rest of the body. The spinal nerves are a key part of this system.
Each spinal nerve is connected to the spinal cord by a dorsal root and a ventral root. The dorsal root is composed of afferent sensory axons that transmit visceral and somatic sensory information from peripheral receptors back to the CNS. The sensory cell bodies of these pseudounipolar neurons are in the dorsal root ganglion, an oval enlargement just outside the cord. The motor neuron cell bodies, on the other hand, are in the gray matter. The two roots join to form the spinal nerve just before it leaves the vertebral column.
The spinal plexuses include the cervical plexus, brachial plexus, lumbar plexus, sacral plexus, and coccygeal plexus. The cervical nerves innervate muscles such as the sternohyoid, sternothyroid, and omohyoid. The dorsal rami of spinal nerves innervate paraspinous muscles and regions of skin related to the ramus' vertebral level. The ventral rami, meanwhile, are more robust and provide the spinal contributions to all major neural plexuses, thus playing a key role in the body's sensorimotor innervation.
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Sensory nerves
The peripheral nervous system (PNS) is how your brain receives information about the outside world. It is made up of nerves that travel from the spinal cord and brain to supply the face and the rest of the body. The PNS is divided into two main subsystems: autonomic and somatic. The somatic system includes sensory and motor pathways.
Cranial nerves are special nerves that connect directly to the brain. They carry signals from the nose, ears, and mouth, as well as many other organs. They also give us a sense of touch in the skin on our face, head, and neck.
Sensory neurons have an axon that extends to the periphery and another axon that extends into the central nervous system (CNS) via the posterior root. The cell body of this neuron is located in the posterior root ganglion or one of the sensory ganglia of the sensory cranial nerves. Both the peripheral and the central axon attach to the neuron at the same point, and these sensory neurons are called "pseudounipolar" neurons. Before a sensory signal can be relayed to the nervous system, it must be transduced into an electrical signal in a nerve fiber. This involves a process of opening ion channels in the membrane in response to mechanical deformation, temperature, or, in the case of nociceptive fibers, signals released from damaged tissue.
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Motor nerves
The peripheral nervous system (PNS) is made up of two main subsystems: autonomic and somatic. The somatic system includes sensory and motor pathways, while the autonomic system controls involuntary functions. The autonomic nervous system (ANS) is further divided into the sympathetic and parasympathetic nervous systems.
The motor nerves are an integral part of the body's ability to initiate and control movements. They transmit electrical signals, known as action potentials, from the brain and spinal cord to the muscles. These signals travel along the motor nerves and result in muscle contractions, allowing for voluntary movements such as walking, running, or reaching for an object. Damage to these nerves can lead to muscle cramps, spasms, tremors, or even loss of control in the affected area.
The peripheral nervous system includes cranial nerves, spinal nerves, and their roots and branches. The cranial nerves are a vital component of the motor system, with twelve pairs emerging from the inferior surface of the brain. These nerves innervate structures in the head, neck, and facial regions, contributing to functions such as eye movement, facial expression, and chewing.
Additionally, the spinal nerves play a significant role in the motor functions of the PNS. Each spinal nerve is connected to the spinal cord by a dorsal root and a ventral root. The motor neuron cell bodies are located in the grey matter, and they send signals to the muscles, enabling movement and coordination. The spinal nerves also provide sensory information back to the brain, creating a feedback loop that allows for precise control and adjustments during movement.
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Frequently asked questions
The peripheral nervous system (PNS) is made up of the somatic nervous system and the autonomic nervous system. The somatic nervous system includes the sensory nervous system and consists of sensory nerves and somatic nerves. The autonomic nervous system, on the other hand, controls involuntary functions and has sympathetic and parasympathetic components.
The somatic nervous system guides voluntary movements and transmits signals from the brain to end organs such as muscles. It also includes the cranial nerves, which carry somatosensory data.
The autonomic nervous system (ANS) is responsible for the innervation of involuntary structures such as the heart, smooth muscle, and glands within the body. It influences the function of organs outside voluntary control, such as heart rate and the functions of the digestive system.
