Back to Blog
Releases ACh at its axon terminal with a skeletal muscle fiber. Thisĭiffers again from the ANS, which uses a two-neuron chain to reach its These myelinated group A fibers conduct nerve impulses very quickly. Somatic motor fibers are usually thick and heavy. The CNS, with their axons extending in spinal or cranial nerves, to reach In the SNS, motor neuron cell bodies lie in Other differences are based on the physiology of In this article, we’ll discuss the peripheral nervous system and its divisions, as well as the peripheral nerves.That it stimulates skeletal muscles, whereas the ANS innervates glands as wellĪs cardiac and smooth muscle. The peripheral nervous system (PNS) consists of all the nerves branching out of the brain and spinal cord ( the central nervous system, CNS). If you imagine the CNS as the main highway, then the PNS forms all the connecting secondary roads. These allow electrical impulses to travel to and from the furthest regions, or periphery, of the human body. The PNS is built almost entirely from nerves. There are two main types spinal nerves and cranial nerves. Functionally, the PNS can be divided into the autonomicand somatic nervous systems. Both of these can be further subdivided the former into sympathetic and parasympathetic arms and the latter into sensory and motor divisions. It might sound complicated, but it’s not. Let’s take a closer look at all of the above terms in order to better understand the divisions of the nervous system. Key facts about the peripheral nervous system DefinitionĪ nervous system division composed of all the neural tissue found outside the cranial vault and vertebral canal. Peripheral nerves (spinal nerves, cranial nerves, autonomic nerves)Īutonomic nervous system (ANS) - involuntary part in control of cardiac, smooth and glandular cells. It consists of sympathetic and parasympathetic divisions. Somatic nervous system (SNS) - voluntary part in control of skeletal muscles and processing of somatic sensation. Transmits motor and sensory information between the central nervous system and peripheral body tissues.Īfferent neurons transmit a variety of impulses from sensory receptors/sense organs. They carry general sensations like touch, pain, temperature and position in space (proprioception). Some also transmit more special, sensorial information like the special senses of smell, vision, hearing and balance. In contrast, efferent neurons bring general nervous information towards effector organs, like skeletal muscles, visceral organs and glands. They are responsible for initiating voluntary and involuntary motor functions, such as muscle contraction and gland secretion. Nerves can also be classified as ‘cranial’ or ‘spinal’ according to where they exit the CNS. Cranial nerves emerge from the cranium ( brain/ brainstem) whilst spinal nerves leave the CNS via the spinal cord. There are 12 pairs of cranial nerves and 31 spinal nerve pairs, giving a total of 43 paired nerves forming the basis of the peripheral nervous system. To learn more about the structure of peripheral nerves and clarify the ‘afferent vs efferent’ difference, take a look at the following:Įach spinal nerve starts as several rootlets that unite to form two main roots. The anterior root carries motor fibers from neurons whose cell bodies are located in the anterior horn of the spinal cord. The posterior root transports sensory fibers from neurons which have their cell bodies in the dorsal root ganglion. In the thoracic and upper lumbar region, the anterior root also carries autonomic fibers from preganglionic sympathetic neurons whose cell bodies are located in the spinal cord’s lateral horn. The anterior and posterior roots subsequently join to form the spinal nerve proper that carries mixed (sensory, motor, autonomic) fibers. Spinal nerves leave the vertebral column through the intervertebral foramina located between two successive, adjacent vertebrae. Each spinal nerve then divides into two branches called posterior/dorsal and anterior/ventral rami. Both rami carry mixed fibers. The posterior rami travel backward and divide into branches that supply post-vertebral structures. The anterior rami supply the skin and muscles of the limbs and anterior trunk. Immediately after the division of the spinal nerve into the two rami, smaller communicating fibers branch out. These white and grey rami communicantes establish a connection between spinal nerves and the two sympathetic trunks of the autonomic nervous system that run along the length of the vertebral column.
0 Comments
Read More
Leave a Reply. |