A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron). An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the non-axon glial cells that ensheath the axons in myelin. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information Glial cells, commonly called neuroglia or simply glia (Greek for "glue" are non- Neuronal cells that provide support and nutrition Myelin is an electrically-insulating Dielectric Phospholipid layer that surrounds only the Axons of many Neurons It is an outgrowth

Contents 1 Anatomy 2 Clinical importance 3 See also 4 Additional images

Anatomy

Nerves are part of the peripheral nervous system. The peripheral nervous system ( PNS) resides or extends outside the Central nervous system (CNS which consists of the Brain and Spinal cord. Afferent nerves convey sensory signals to the central nervous system, for example from skin or organs, while efferent nerves conduct stimulatory signals from the central nervous system to the muscles and glands. In the Nervous system, afferent neurons --otherwise known as sensory or receptor Neurons -carry nerve impulses from receptors or sense Senses are the physiological methods of Perception. The senses and their operation classification and theory are overlapping topics studied by a variety of fields In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. In the Nervous system, efferent nerves – otherwise known as motor or effector Neurons – carry nerve impulses away from the Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the A gland is an organ in an animal's body that synthesizes a substance for release such as Hormones or Breast milk, often into the Bloodstream Afferent and efferent axons are often arranged together, forming mixed nerves. For example, the median nerve controls motor and sensory function in the hand.

Billions of long nerve cells, called neurons, make up the body's nervous system. Neurons receive and transmit chemical-electrical messages to and from the brain. Each neuron is long and thin. One end receives messages and the other transmits the message to the next neuron. The messages "jump" across a gap from neuron cell to another.

Each peripheral nerve is covered externally by a dense sheath of connective tissue, the epineurium. The epineurium is the outermost layer of Connective tissue surrounding a peripheral Nerve. Underlying this is a layer of flat cells forming a complete sleeve, the perineurium. In the Spinal cord, nerve fibers are each wrapped in a protective sheath known as the Endoneurium. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurial sheath. The Nerve fibers are held together and supported within the Funiculus by delicate connective tissue called the endoneurium. This forms an unbroken tube which extends from the surface of the spinal cord to the level at which the axon synapses with its muscle fibres or ends in sensory receptors. In a Sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an Organism. The endoneurial sheath consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres. Glycocalyx is a general term referring to extracellular Polymeric material produced by some Bacteria, Epithelia and other cells Peripheral nerves are richly supplied with blood.

Most nerves connect to the central nervous system through the spinal cord. In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. The spinal cord is a long thin tubular bundle of Nerves that is an extension of the Central nervous system from the brain and is enclosed in and protected The twelve cranial nerves, however connect directly to parts of the brain. Cranial nerves are Nerves that emerge directly from the Brain stem in contrast to Spinal nerves which emerge from segments of the Spinal cord. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain Spinal nerves are given letter-number combinations according to the vertebra through which they connect to the spinal column. The term spinal nerve generally refers to the mixed spinal Nerve, which is formed from the dorsal and ventral roots that come out of the Spinal cord. A vertebra (plural vertebrae) is an individual Irregular bone in the spinal or Vertebral column ( aka ischis a flexuous and flexible column Cranial nerves are assigned numbers, usually expressed as Roman numerals from I to XII. Roman numerals are a Numeral system originating in ancient Rome, adapted from Etruscan numerals. In addition, most major nerves have descriptive names. Inside the central nervous system, distinguishable bundles of axons are termed tracts rather than nerves.

The signals that nerves carry, sometimes called nerve impulses, are also known as action potentials. In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal These are rapidly (up to 120 m/s) traveling electrical waves, which typically begin in the cell body of a neuron and propagate down the axon to its tip or "terminus. " The signals cross over from the terminus of the axon to the adjacent neurotransmitter receptor through a gap called the synapse. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands Motor neurons innervate or activate muscles groups. In Vertebrates the term motor neuron (or motoneuron) classically applies to Neurons located in the Central nervous system (or CNS that project

Clinical importance

Damage to nerves can be caused by physical injury, swelling (e. g. carpal tunnel syndrome), autoimmune diseases (e. Carpal tunnel syndrome (CTS or median neuropathy at the wrist is a medical condition in which the Median nerve is compressed at the Wrist, leading g. Guillain-Barré syndrome), infection (neuritis), diabetes or failure of the blood vessels surrounding the nerve. Guillain-Barré syndrome ( GBS) (in French ɡilɛ̃ baˈʁe in English ˈɡiːlæn ˈbɑreɪ /ɡiːˈæn bəˈreɪ/ etc See also Neuropathy, Neuralgia Neuritis is the general Inflammation of the Peripheral nervous system. Diabetes mellitus (ˌdaɪəˈbiːtiːz or /ˌdaɪəˈbiːtəs/ /məˈlaɪtəs/ or /ˈmɛlətəs/ often referred to simply as diabetes ( Ancient Greek: grc A pinched nerve occurs when pressure is placed on a nerve, usually from swelling due to an injury or pregnancy. Nerve damage or pinched nerves are usually accompanied by pain, numbness, weakness, or paralysis. Pain, in the sense of physical pain, is a typical sensory experience that may be described as the unpleasant awareness of a noxious stimulus or bodily harm Paralysed redirects here For other uses see xx Paralysed (disambiguation Paralysis is the complete loss of Muscle function Patients may feel these symptoms in areas far from the actual site of damage, a phenomenon called referred pain. Referred pain is a term used to describe the phenomenon of pain perceived at a site adjacent to or at a distance from the site of an injury's origin Referred pain occurs because when a nerve is damaged, signalling is defective from all parts of the area from which the nerve receives input, not just the site of the damage. Neurologists usually diagnose disorders of the nerves by a physical examination, including the testing of reflexes, walking and other directed movements, muscle weakness, proprioception, and the sense of touch. Physical examination or clinical examination is the process by which a Health care provider investigates the body of a Patient for signs A reflex action, also known as a reflex, is an involuntary and almost instant movement in response to stimulus. Walking (also called ambulation) is the main form of Animal Locomotion on land, distinguished from Running and crawling Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the Proprioception (ˌproʊpriːəˈsɛpʃən PRO -pree-o-SEP-shun from Latin proprius, meaning "one's own" and perception is the Sense This initial exam can be followed with tests such as nerve conduction study and electromyography (EMG). A nerve conduction study (NCS is a test commonly used to evaluate the function especially the ability of Electrical conduction, of the motor and Sensory nerves Electromyography (EMG is a technique for evaluating and recording the activation signal of muscles

See also

• Nervous system
• Dermatome (Anatomy)
• Nerve injury

Additional images

Peripheral nerve, cross section

The nervous system is a Network of specialized cells that communicate information about an animal's surroundings and itself A Dermatome is an area of Skin associated with a pair of Dorsal roots from the spine There is no single classification system that can describe all the many variations of nerve injury.

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