The nerves is an enclosed, cable-like bundle of nerve fibers called axons, in the peripheral nervous system. A nerve transmits electrical impulses and is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system. Each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as some Schwann cells that coat the axons in myelin.
Types of a Nerve
- Structure of the nervous system
- Development of the nervous system
- The spinal cord or medulla spinalis
- The brain or encephalon
- The hindbrain or rhombencephalon
- The midbrain or mesencephalon
- The forebrain or prosencephalon
- Composition and central connections of the spinal nerves
- Pathways from the brain to the spinal cord
- The meninges of the brain and medulla spinalis
- The cerebrospinal fluid
- The cranial nerves
- The olfactory nerves
- The optic nerve
- The oculomotor nerve
- The trochlear nerve
- The trigeminal nerve
- The abducens nerve
- The facial nerve
- The vestibulocochlear nerve
- The glossopharyngeal nerve
- The vagus nerve
- The accessory nerve
- The hypoglossal nerve
- The spinal nerves
- The posterior divisions
- The anterior divisions
- The thoracic nerves
- The lumbosacral plexus
- The sacral and coccygeal nerves
- The sympathetic nerves
- The cephalic portion of the sympathetic system
- The cervical portion of the sympathetic system
- The thoracic portion of the sympathetic system
- The abdominal portion of the sympathetic system
- The pelvic portion of the sympathetic system
- The great plexuses of the sympathetic system
Alphabetical list
- Abdominal aortic plexus
- Abducens nerves
- Accessory nerve
- Accessory obturator nerve
- Alderman’s nerve
- Anococcygeal nerve
- Ansa cervicalis
- Anterior interosseous nerve
- Anterior superior alveolar nerve
- Auerbach’s plexus
- Auriculotemporal nerve
- Axillary nerve
- Brachial plexus
- Buccal branch of the facial nerve
- Buccal nerve
- Cardiac plexus
- Cavernous nerves
- Cavernous plexus
- Celiac ganglia
- Cervical branch of the facial nerve
- Cervical plexus
- Chorda tympani
- Ciliary ganglion
- Coccygeal nerve
- Cochlear nerve
- Common fibular nerve
- Common palmar digital nerves of median nerve
- Deep branch of the radial nerve
- Deep fibular nerve
- Deep petrosal nerve
- Deep temporal nerves
- Diagonal band of Broca
- Digastric branch of facial nerve
- Dorsal branch of ulnar nerve
- Dorsal nerve of clitoris
- Dorsal nerve of the penis
- Dorsal scapular nerve
- Esophageal plexus
- Ethmoidal nerves
- External laryngeal nerve
- External nasal nerve
- Facial nerve
- Femoral nerve
- Frontal nerve
- Gastric plexuses
- Geniculate ganglion
- Genital branch of genitofemoral nerve
- Genitofemoral nerve
- Glossopharyngeal nerve
- Greater auricular nerve
- Greater occipital nerve
- Greater petrosal nerve
- Hepatic plexus
- Hypoglossal nerve
- Iliohypogastric nerve
- Ilioinguinal nerve
- Inferior alveolar nerve
- Inferior anal nerves
- Inferior cardiac nerve
- Inferior cervical ganglion
- Inferior gluteal nerve
- Inferior hypogastric plexus
- Inferior mesenteric plexus
- Inferior palpebral nerve
- Infraorbital nerve
- Infraorbital plexus
- Infratrochlear nerve
- Intercostal nerves
- Intercostobrachial nerve
- Intermediate cutaneous nerve
- Internal carotid plexus
- Internal laryngeal nerve
- Interneuron
- Jugular ganglion
- Lacrimal nerve
- Lateral cord
- Lateral cutaneous nerve of forearm
- Lateral cutaneous nerve of thigh
- Lateral pectoral nerve
- Lateral plantar nerve
- Lateral pterygoid nerve
- Lesser occipital nerve
- Lingual nerve
- Long ciliary nerves
- Long root of the ciliary ganglion
- Long thoracic nerve
- Lower subscapular nerve
- Lumbar nerves
- Lumbar plexus
- Lumbar splanchnic nerves
- Lumboinguinal nerve
- Lumbosacral plexus
- Lumbosacral trunk
- Mandibular nerve
- Marginal mandibular branch of facial nerve
- Masseteric nerve
- Maxillary nerve
- Medial cord
- Medial cutaneous nerve of arm
- Medial cutaneous nerve of forearm
- Medial cutaneous nerve
- Medial pectoral nerve
- Medial plantar nerve
- Medial pterygoid nerve
- Median nerve
- Meissner’s plexus
- Mental nerve
- Middle cardiac nerve
- Middle cervical ganglion
- Middle meningeal nerve
- Motor nerve
- Muscular branches of the radial nerve
- Musculocutaneous nerve
- Mylohyoid nerve
- Nasociliary nerve
- Nasopalatine nerve
- Nerve of pterygoid canal
- Nerve to obturator internus
- Nerve to quadratus femoris
- Nerve to the Piriformis
- Nerve to the stapedius
- Nerve to the subclavius
- Nervus intermedius
- Nervus spinosus
- Nodose ganglion
- Obturator nerve
- Oculomotor nerve
- Olfactory nerve
- Ophthalmic nerve
- Optic nerve
- Otic ganglion
- Ovarian plexus
- Palatine nerves
- Palmar branch of the median nerve
- Palmar branch of ulnar nerve
- Pancreatic plexus
- Patellar plexus
- Pelvic splanchnic nerves
- Perforating cutaneous nerve
- Perineal branches of posterior femoral cutaneous nerve
- Perineal nerve
- Petrous ganglion
- Pharyngeal branch of vagus nerve
- Pharyngeal branches of glossopharyngeal nerve
- Pharyngeal nerve
- Pharyngeal plexus
- Phrenic nerve
- Phrenic plexus
- Posterior auricular nerve
- Posterior branch of spinal nerve
- Posterior cord
- Posterior cutaneous nerve of arm
- Posterior cutaneous nerve of forearm
- Posterior cutaneous nerve of thigh
- Posterior scrotal nerves
- Posterior superior alveolar nerve
- Proper palmar digital nerves of median nerve
- Prostatic plexus (nervous)
- Pterygopalatine ganglion
- Pudendal nerve
- Pudendal plexus
- Pulmonary branches of vagus nerve
- Radial nerve
- Recurrent laryngeal nerve
- Renal plexus
- Sacral plexus
- Sacral splanchnic nerves
- Saphenous nerve
- Sciatic nerve
- Semilunar ganglion
- Sensory nerve
- Short ciliary nerves
- Sphenopalatine nerves
- Splenic plexus
- Stylohyoid branch of facial nerve
- Subcostal nerve
- Submandibular ganglion
- Suboccipital nerve
- Superficial branch of the radial nerve
- Superficial fibular nerve
- Superior cardiac nerve
- Superior cervical ganglion
- Superior ganglion of glossopharyngeal nerve
- Superior ganglion of vagus nerve
- Superior gluteal nerve
- Superior hypogastric plexus
- Superior labial nerve
- Superior laryngeal nerve
- Superior lateral cutaneous nerve of arm
- Superior mesenteric plexus
- Superior rectal plexus
- Supraclavicular nerves
- Supraorbital nerve
- Suprarenal plexus
- Suprascapular nerve
- Supratrochlear nerve
- Sural nerve
- Sympathetic trunk
- Temporal branches of the facial nerve
- Third occipital nerve
- Thoracic aortic plexus
- Thoracic splanchnic nerves
- Thoraco-abdominal nerves
- Thoracodorsal nerve
- Tibial nerve
- Transverse cervical nerve
- Trigeminal nerve
- Trochlear nerve
- Tympanic nerve
- Ulnar nerve
- Upper subscapular nerve
- Uterovaginal plexus
- Vagus nerve
- Ventral ramus
- Vesical nervous plexus
- Vestibular nerve
- Vestibulocochlear nerve
- Zygomatic branches of the facial nerve
- Zygomatic nerve
- Zygomaticofacial nerve
- Zygomaticotemporal nerve
Structure
Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibers. Surrounding each such fiber is the endoneurium. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibers, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres.[2] Nerves are bundled and often travel along with blood vessels, since the neurons of a nerve have fairly high energy requirements.
Within the endoneurium, the individual nerve fibers are surrounded by a low-protein liquid called endoneurial fluid. This acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier.[3] Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation (or injury), the amount of endoneurial fluid may increase at the site of irritation. This increase in the fluid can be visualized using magnetic resonance neurography, and thus MR neurography can identify nerve irritation and/or injury.
Categories
Nerves are categorized into three groups based on the direction that signals are conducted:
- Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from the mechanoreceptors in the skin.
- Efferent nerves conduct signals from the central nervous system along motor neurons to their target muscles and glands.
- Mixed nerves contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. All spinal nerves are mixed nerves, and some of the cranial nerves are also mixed nerves.
Nerves can be categorized into two groups based on where they connect to the central nervous system:
- Spinal nerves innervate (distribute to/stimulate) much of the body, and connect through the vertebral column to the spinal cord and thus to the central nervous system. They are given letter-number designations according to the vertebra through which they connect to the spinal column.
- Cranial nerves innervate parts of the head and connect directly to the brain (especially to the brainstem). They are typically assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included. In addition, cranial nerves have descriptive names.