Peripheral nervous system 25096 225187874 2008-07-12T10:29:25Z 117.198.146.114 /* By direction */ The '''peripheral nervous system''' ('''PNS''') resides or extends outside the [[central nervous system]] (CNS), which consists of the [[brain]] and [[spinal cord]], to serve the limbs and organs. Unlike the central nervous system, however, the PNS is not protected by [[bone]], leaving it exposed to [[toxin]]s and mechanical injuries. The peripheral nervous system is divided into the [[somatic nervous system]] and the [[autonomic nervous system]]. <ref>{{cite book | last = Maton | first = Anthea | authorlink = | coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright | title = Human Biology and Health | publisher = Prentice Hall | date = 1993 | location = Englewood Cliffs, New Jersey, USA | pages = 132-144 | url = | doi = | id = | isbn = 0-13-981176-1}}</ref> ==General classification== The peripheral nervous system can be classified either by direction of [[neurons]] or by function. ===By direction=== There are three types of directions of the [[neuron]]s: *[[Sensory system]] by [[sensory neurons]], between the sensory and motor neurones. However, there are relay neurons in the CNS as well . ===By function=== By function, the peripheral nervous system is divided into the [[somatic nervous system]], [[autonomic nervous system]] and the [[enteric nervous system]]. The [[somatic nervous system]] is responsible for coordinating the body movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control. The [[autonomic nervous system]] is then split into the [[sympathetic nervous system|sympathetic division]], [[parasympathetic nervous system|parasympathetic division]], and [[enteric nervous system|enteric division]]. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and [[genitourinary]] systems. The role of the enteric nervous system is to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon. == Naming of specific nerves == [[Image:Nervous system diagram.png|thumb|290px|The Human Nervous System. Blue is PNS while red is CNS.]] Ten out of the twelve [[cranial nerves]] originate from the [[brainstem]], and mainly control the functions of the anatomic structures of the head with some exceptions. The nuclei of cranial nerves I and II lie in the forebrain and thalamus, respectively, and are thus not considered to be true cranial nerves. CN X (10) receives visceral sensory information from the thorax and abdomen, and CN XI (11) is responsible for innervating the [[sternocleidomastoid muscle|sternocleidomastoid]] and [[trapezius muscle]]s, neither of which is exclusively in the head. [[Spinal nerve]]s take their origins from the [[spinal cord]]. They control the functions of the rest of the body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. The naming convention for spinal nerves is to name it after the [[vertebra]] immediately above it. Thus the fourth thoracic nerve originates just below the fourth thoracic vertebra. This convention breaks down in the cervical spine. The first spinal nerve originates above the first cervical vertebra and is called C1. This continues down to the last cervical spinal nerve, C8. There are only 7 cervical vertebrae and 8 cervical spinal nerves. ==Cervical spinal nerves (C1-C4)== {{Further|[[Cervical plexus]]}} The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of nerves that subserve the neck and back of head. Spinal nerve C1 is called the [[suboccipital nerve]] which provides motor innervation to muscles at the base of the [[skull]]. C2 and C3 form many of the nerves of the neck, providing both sensory and motor control. These include the [[greater occipital nerve]] which provides sensation to the back of the [[head (anatomy)|head]], the [[lesser occipital nerve]] which provides sensation to the area behind the [[ear]]s, the [[greater auricular nerve]] and the [[lesser auricular nerve]]. See [[occipital neuralgia]]. The [[phrenic nerve]] arises from nerve roots C3, C4 and C5. It innervates the [[diaphragm (anatomy)|diaphragm]], enabling breathing. If the spinal cord is transected above C3, then spontaneous breathing is not possible. See [[myelopathy]] == Brachial plexus (C5-T1)== {{Further|[[Brachial plexus]]}} The last four cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve, T1,combine to form the [[brachial plexus]], or plexus brachialis, a tangled array of nerves, splitting, combining and recombining, to form the nerves that subserve the arm and upper back. Although the brachial plexus may appear tangled, it is highly organized and predictable, with little variation between people. See [[brachial plexus injuries]] ===Before forming three cords=== The first nerve off the brachial plexus, or plexus brachialis, is the [[dorsal scapular nerve]], arising from C5 nerve root, and innervating the [[rhomboid]]s and the [[levator scapulae]] muscles. The [[long thoracic nerve]] arises from C5, C6 and C7 to innervate the [[serratus anterior]]. The brachial plexus first forms three trunks, the superior trunk, composed of the C5 and C6 nerve roots, the middle trunk, made of the C7 nerve root, and the inferior trunk, made of the C8 and T1 nerve roots. The [[suprascapular nerve]] is an early branch of the superior trunk. It innervates the suprascapular and infrascapular muscles, part of the [[rotator cuff]]. The trunks reshuffle as they traverse towards the [[arm]] into cords. There are three of them. The lateral cord is made up of fibers from the superior and middle trunk. The posterior cord is made up of fibers from all three trunks. The medial cord is composed of fibers solely from the medial trunk. ===Lateral cord=== The lateral cord gives rise to the following nerves: *The [[lateral pectoral nerve]], C5, C6 and C7 to the [[pectoralis major]] muscle, or musculus pectoralis major. *The [[musculocutaneous nerve]] which innervates the [[biceps brachii|biceps]] muscle *The [[median nerve]], partly. The other part comes from the medial cord. See below for details. ===Posterior cord=== The posterior cord gives rise to the following nerves: *The [[upper subscapular nerve]], C7 and C8, to the [[subscapularis]] muscle, or musculus supca of the [[rotator cuff]]. *The [[lower subscapular nerve]], C5 and C6, to the [[teres major]] muscle, or the musculus teres major. *The [[thoracodorsal nerve]], C6, C7 and C8, to the [[latissimus dorsi]] muscle, or musculus latissimus dorsi. *The [[axillary nerve]], which supplies sensation to the shoulder and motor to the [[deltoid]] muscle or musculus deltoideus, and the [[teres minor]] muscle, or musculus teres minor, also of the rotator cuff. *The [[radial nerve]], or nervus radialis, which innervates the [[triceps brachii]] muscle, the [[brachioradialis]] muscle, or musculus brachioradialis,, the extensor muscles of the fingers and wrist ([[extensor carpi radialis]] muscle), and the extensor and abductor muscles of the thumb. See [[radial nerve injuries]]. ===Medial cord=== The medial cord gives rise to the following nerves: *The [[median pectoral nerve]], C8 and T1, to the pectoralis muscle *The [[medial brachial cutaneous nerve]], T1 *The [[medial antebrachial cutaneous nerve]], C8 and T1 *The [[median nerve]], partly. The other part comes from the lateral cord. C7, C8 and T1 nerve roots. The first branch of the median nerve is to the [[pronator teres]] muscle, then the [[flexor carpi radialis]], the [[palmaris longus]] and the [[flexor digitorum superficialis]]. The median nerve provides sensation to the anterior palm, the anterior [[thumb]], [[index finger]] and [[middle finger]]. It is the nerve compressed in [[carpal tunnel syndrome]]. *The [[ulnar nerve]] originates in nerve roots C7, C8 and T1. It provides sensation to the ring and pinky fingers. It innervates the [[flexor carpi ulnaris]] muscle, the [[flexor digitorum profundus]] muscle to the ring and pinky fingers, and the intrinsic muscles of the hand (the [[interosseous muscle]], the [[lumbrical muscle]]s and the [[flexor pollicus brevis]] muscle). This nerve traverses a groove on the elbow called the [[cubital tunnel]], also known as the funny bone. Striking the nerve at this point produces an unpleasant sensation in the ring and little finger. ==Neurotransmitters== The main [[neurotransmitters]] of the peripheral nervous system are [[acetylcholine]] and [[noradrenaline]]. However, there are several other neurotransmitters as well, jointly labeled [[Non-noradrenergic, non-cholinergic transmitter|Non-noradrenergic, non-cholinergic]] (NANC) transmitters. Examples of such transmitters include non-[[peptides]]: [[adenosine triphosphate|ATP]], [[gamma aminobutyric acid|GABA]], [[dopamine]], [[nitric oxide|NO]], and peptides: [[neuropeptide Y]], [[vasoactive intestinal peptide|VIP]], [[gonadotropin releasing hormone|GnRH]], [[Substance P]] and [[calcitonin gene related peptide|CGRP]]. <ref name=Rang>Pharmacology, (Rang, Dale, Ritter & Moore, ISBN 0443071454, 5:th ed., Churchill Livingstone 2003). Page 132. </ref> ==References== <references/> {{Refimprove|date=November 2007}} {{nervous system}} [[Category:Peripheral nervous system]] [[Category:Neuroanatomy]] [[bs:Periferni nervni sistem]] [[ca:Sistema nerviós perifèric]] [[de:Peripheres Nervensystem]] [[dv:ޕެރިފެރަލް ނާރވަސް ސިސްޓަމް]] [[es:Sistema nervioso periférico]] [[fr:Système nerveux périphérique]] [[id:Sistem saraf tepi]] [[is:Úttaugakerfið]] [[it:Sistema nervoso periferico]] [[he:מערכת העצבים ההיקפית]] [[lt:Periferinė nervų sistema]] [[mk:Периферен нервен систем]] [[nl:Perifeer zenuwstelsel]] [[ja:末梢神経系]] [[no:Det perifere nervesystemet]] [[pl:Obwodowy układ nerwowy]] [[pt:Sistema nervoso periférico]] [[simple:Peripheral nervous system]] [[sl:Obkrajno živčevje]] [[sr:Периферни нервни систем]] [[fi:Ääreishermosto]] [[sv:Perifera nervsystemet]] [[ur:ملحقہ عصبی نظام]] [[zh:周围神经系统]]