In other words, it carries sensations from the body (pain, touch, temperature, proprioception) and innervates skeletal muscles that are under conscious, or voluntary control. In addition, the somatic nervous system is involved in spinal reflexes, an example being the withdrawal reflex. The somatic, voluntary, nervous system is responsible for providing sensory and motor innervation to skin, muscles and sensory organs. If you want more detail about spinal nerves take a look below: Note that grey rami communicantes exist at all levels of the spinal cord, whilst white rami are only found at T1-L2 levels. 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. Immediately after the division of the spinal nerve into the two rami, smaller communicating fibers branch out.
#Example of somatic nervous system skin#
The anterior rami supply the skin and muscles of the limbs and anterior trunk. The posterior rami travel backward and divide into branches that supply post-vertebral structures. Each spinal nerve then divides into two branches called posterior/dorsal and anterior/ventral rami. Both rami carry mixed fibers. Spinal nerves leave the vertebral column through the intervertebral foramina located between two successive, adjacent vertebrae. The anterior and posterior roots subsequently join to form the spinal nerve proper that carries mixed (sensory, motor, autonomic) fibers.
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 posterior root transports sensory fibers from neurons which have their cell bodies in the dorsal root ganglion. The anterior root carries motor fibers from neurons whose cell bodies are located in the anterior horn of the spinal cord. 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. 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. Cranial nerves emerge from the cranium ( brain/ brainstem) whilst spinal nerves leave the CNS via the spinal cord. Nerves can also be classified as ‘cranial’ or ‘spinal’ according to where they exit the CNS. They are responsible for initiating voluntary and involuntary motor functions, such as muscle contraction and gland secretion. In contrast, efferent neurons bring general nervous information towards effector organs, like skeletal muscles, visceral organs and glands. Some also transmit more special, sensorial information like the special senses of smell, vision, hearing and balance. They carry general sensations like touch, pain, temperature and position in space (proprioception). 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. Somatic nervous system (SNS) - voluntary part in control of skeletal muscles and processing of somatic sensation. It consists of sympathetic and parasympathetic divisions. Peripheral nerves (spinal nerves, cranial nerves, autonomic nerves)Īutonomic nervous system (ANS) - involuntary part in control of cardiac, smooth and glandular cells. 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. Let’s take a closer look at all of the above terms in order to better understand the divisions of the nervous system. It might sound complicated, but it’s not. Both of these can be further subdivided the former into sympathetic and parasympathetic arms and the latter into sensory and motor divisions. Functionally, the PNS can be divided into the autonomicand somatic nervous systems. There are two main types spinal nerves and cranial nerves.
The PNS is built almost entirely from nerves. These allow electrical impulses to travel to and from the furthest regions, or periphery, of the human body. If you imagine the CNS as the main highway, then the PNS forms all the connecting secondary roads. The peripheral nervous system (PNS) consists of all the nerves branching out of the brain and spinal cord ( the central nervous system, CNS). In this article, we’ll discuss the peripheral nervous system and its divisions, as well as the peripheral nerves.
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