Medullated nerve fibre Health Dictionary

See VESTIBULOCOCHLEAR NERVE.... auditory nerve

The seventh cranial nerve (arising from the BRAIN), supplying the muscles of expression in the face, being purely a motor nerve. It enters the face immediately below the ear after splitting up into several branches. (See BELL’S PALSY.)... facial nerve

The 12th cranial nerve, which supplies the muscles of the tongue, together with some others lying near it. This nerve is responsible for movements required for swallowing and talking. (See also NERVOUS SYSTEM.)... hypoglossal nerve

A nerve is a bundle of conductory ?bres called axons (see AXON) that emanate from neurones (see NEURON(E)) – the basic anatomical and functional units of the NERVOUS SYSTEM. Nerves make up the central nervous system (BRAIN and SPINAL CORD) and connect that system to all parts of the body, transmitting information from sensory organs via the peripheral nerves to the centre and returning instructions for action to the relevant muscles and glands.

Nerves vary in size from the large pencil-sized sciatic nerve in the back of the thigh muscles to the single, hair-sized ?bres distributed to the skin. A nerve, such as the sciatic, possesses a strong, outer ?brous sheath, called the epineurium, within which lie bundles of nerve-?bres, divided from one another by partitions of ?brous tissue, in which run blood vessels that nourish the nerve. Each of these bundles is surrounded by its own sheath, known as the perineurium, and within the bundle ?ne partitions of ?brous tissue, known as endoneurium, divide up the bundle into groups of ?bres. The ?nest subdivisions of the nerves are the ?bres, and these are of two kinds: medullated and non-medullated ?bres. (See NEURON(E) and NERVOUS SYSTEM for more details on structure and functions of neurons and nerves.)... nerve

See ANAESTHESIA – Local anaesthetics.... nerve block

See EYE.... optic nerve

This NERVE arises from the BRACHIAL plexus in the axilla. At ?rst descending posteriorly and then anteriorly, it ends just above the elbow by dividing into the super?cial radial and interosseous nerves. It supplies motor function to the muscles which extend the arm, wrist, and some ?ngers, and supplies sensation to parts of the posterior and lateral aspects of the arm, forearm and hand.... radial nerve

The ?fth cranial nerve (arising from the BRAIN). It consists of three divisions: (1) the ophthalmic nerve, which is purely sensory in function, being distributed mainly over the forehead and front part of the scalp; (2) the maxillary nerve, which is also sensory and distributed to the skin of the cheek, the mucous membrane of the mouth and throat, and the upper teeth; and (3) the mandibular nerve, which is the nerve of sensation to the lower part of the face, the tongue and the lower teeth, as well as being the motor nerve to the muscles concerned in chewing. The trigeminal nerve is of special interest, owing to its liability to NEURALGIA – TRIGEMINAL NEURALGIA, or tic douloureux as it is also known, being the most painful form known.... trigeminal nerve

The fourth cranial nerve (arising from the BRAIN), which acts upon the superior oblique muscle of the EYE.... trochlear nerve

A major NERVE in the arm, it runs from the brachial plexus to the hand. The nerve controls the muscles that move the ?ngers and thumb and conveys sensation from the ?fth and part of the fourth and from the adjacent palm. Muscle weakness and numbness in the areas supplied by the nerve is usually caused by pressure from an abnormal outgrowth from the epicondyle at the bottom of the humerus (upper-arm bone).... ulnar nerve

Also called the pneumogastric nerve, this is the tenth cranial nerve, with many fibers leading to parasympathetic ganglia in internal organs, and can be considered the presynapse starter for the upper parts of the parasympathetic functions.... vagus nerve

The eighth cranial nerve. It consists of two sets of ?bres, which constitute two separate nerves. One is known as the vestibular nerve, which connects the semicircular canals and inner ear to the BRAIN and conveys information on posture and movement of the body; it is the nerve of equilibration or balance. The other is known as the cochlear nerve, which links the COCHLEA (organ that responds to sounds) with the brain and is the nerve of hearing. Disturbance of the former causes giddiness (VERTIGO), whilst disturbance of the latter causes DEAFNESS.... vestibulocochlear nerve

This is the sixth nerve rising from the brain and controls the external rectus muscle of the EYE, which turns the eye outwards. It is particularly liable to be paralysed in diseases of the nervous system, thus leading to an inward squint.... abducent nerve

See ROUGHAGE.... fibre, dietary

A branch of the ophthalmic nerve supplying the lacrimal gland and conjunctiva of the EYE.... lacrimal nerve

See NEURON(E).... nerve cell

The NERVE which chie?y supplies the DIAPHRAGM. A phrenic nerve arises on each side of the SPINAL CORD from the third, fourth and ?fth cervical spinal nerves; both follow a long course down the neck, and through the chest to the diaphragm. They play a key part in RESPIRATION through control of the diaphragm. Injury to one nerve paralyses one half of the diaphragm. Occasionally the phrenic nerve may be surgically crushed as part of the treatment to repair a HIATUS HERNIA or, rarely, to stop intractable hiccups.... phrenic nerve

The nerve that operates the lowest muscles of the ?oor of the PELVIS and also the anal SPHINCTER muscle. It may be damaged in childbirth, resulting in INCONTINENCE.... pudendal nerve

It has been discovered that various cultures round the world, e.g. the Hunza Colony near Pakistan, the 7th-Day Adventists and others who eat high fibre foods have fewer cases of diabetes, heart disease, arthritis and other degenerative diseases. Natives of Hunza may live to great ages and have few dental problems, emotional illness and never require a laxative. Today, foods may be over-processed.

Other diseases recognised to be characteristic of modern western civilisation and claimed to be causally related to diet are: appendicitis, coronary heart disease, hiatus hernia, diverticulosis, piles and other anal disorders, obesity, gall stones, hypertension, deep vein thrombosis and varicose veins.

Low fibre intake results in slow transit of food and exposes potential carcinogens a longer period of time in contact with the alimentary canal. A high fibre diet tends to absorb a variety of environmental pollutants and eliminate them from the body.

Foods rich in fibre: wholemeal bread, grains, cereals, brown rice, beans, peas, boiled cabbage, sweetcorn, banana, prunes (stewed), dried apricots. One of the highest is All Bran, which has the highest proportion of dietary fibre among breakfast cereals with no preserves, artificial colouring or flavouring. Contains one-third fewer calories than most breakfast cereals and because of its glycaemic effect is useful in diabetic diet. ... fibre

The 11th cranial nerve. Unlike the other cranial nerves, most of the accessory nerve originates from the spinal cord. The small part of the nerve that originates from the brain supplies many muscles of the palate, pharynx (throat), and larynx (voice box). Damage to this part of the nerve may cause difficulty in speaking and swallowing. The spinal part of the nerve supplies large muscles of the neck and back, notably the sternomastoid and trapezius. Damage to the spinal fibres of the nerve paralyses these muscles.... accessory nerve

The part of the vestibulocochlear nerve (the 8th cranial nerve) that is concerned with hearing. It is also known as the auditory nerve.... acoustic nerve

One of the main nerves of the leg. The nerve fibres making up the femoral nerve emerge from the lower spine and run down into the thigh, where they branch to supply the skin and quadriceps muscles.

Damage to the femoral nerve (which impairs the ability to straighten the knee) is usually caused by a slipped disc in the lumbar region of the spine (see disc prolapse). Damage may also result from a backward dislocation of the hip or a neuropathy.... femoral nerve

The transmission of images through bundles of thin, flexible glass or plastic threads which propagate light by total internal reflection. This means that all the light from a powerful external source travels the length of the fibre without losing its intensity. Fibre-optics have led to the development of endoscopes, which enable structures deep within the body to be viewed directly.... fibre-optics

The ninth cranial nerve.

This nerve performs both sensory and motor functions.

It conveys sensations, especially taste, from the back of the tongue, regulates secretion of saliva by the parotid gland, and controls movement of the throat muscles.... glossopharyngeal nerve

The 3rd cranial nerve, controlling most of the muscles that move the eye. The oculomotor nerve also supplies the muscle that constricts the pupil, that which raises the upper eyelid, and the ciliary muscle, which focuses the eye. The nerve may be damaged due to a fracture to the base of the skull or a tumour. Symptoms include ptosis, squint, dilation of the pupil, inability to focus the eye, double vision, and slight protrusion of the eyeball. (See also trochlear nerve; abducent nerve.)... oculomotor nerve

The first cranial nerve, which conveys sensations of smell as nerve impulses from the nose to the brain. Each of the 2 olfactory nerves has receptors in the mucous membrane lining the nasal cavity. These receptors detect smells and send signals along nerve fibres, which pass through tiny holes in the roof of the nasal cavity and combine to form the olfactory bulbs. From here, nerve fibres come together to form the olfactory nerve, leading to the olfactory centre in the brain. Sense of smell may be lost or impaired due to damage to the olfactory nerves, usually as a result of head injury.... olfactory nerve

The main nerve in each leg and the largest nerve in the body.The sciatic nerves are formed from nerve roots in the spinal cord.... sciatic nerve

See TENS.... transcutaneous electrical nerve stimulation

A visualising technique enabling the operator to examine the internal organs with the minimum of disturbance or damage to the tissues. The procedure has transformed the management of, for example, gastrointestinal disease. In chest disease, ?breoptic bronchoscopy has now replaced the rigid wide-bore metal tube which was previously used for examination of the tracheo-bronchial tree.

The principle of ?breoptics in medicine is that a light from a cold light source passes down a bundle of quartz ?bres in the endoscope to illuminate the lumen of the gastrointestinal tract or the bronchi. The re?ected light is returned to the observer’s eye via the image bundle which may contain up to 20,000 ?bres. The tip of the instrument can be angulated in both directions, and ?ngertip controls are provided for suction, air insu?ation and for water injection to clear the lens or the mucosa. The oesophagus, stomach and duodenum can be visualised; furthermore, visualisation of the pancreatic duct and direct endoscopic cannulation is now possible, as is visualisation of the bile duct. Fibreoptic colonoscopy can visualise the entire length of the colon and it is now possible to biopsy polyps or suspected carcinomas and to perform polypectomy.

The ?exible smaller ?breoptic bronchoscope has many advantages over the rigid tube, extending the range of view to all segmental bronchi and enabling biopsy of pulmonary parenchyma. Biopsy forceps can be directed well beyond the tip of the bronchoscope itself, and the more ?exible ?breoptic instrument causes less discomfort to the patient.

Fibreoptic laparoscopy is a valuable technique that allows the direct vizualisation of the abdominal contents: for example, the female pelvic organs, in order to detect the presence of suspected lesions (and, in certain cases, e?ect their subsequent removal); check on the development and position of the fetus; and test the patency of the Fallopian tubes.

(See also ENDOSCOPE; BRONCHOSCOPE; LARYNGOSCOPE; LAPAROSCOPE; COLONOSCOPE.)... fibreoptic endoscopy

See BELL’S PALSY.... idiopathic facial nerve palsy

A branch of the vagus NERVE which leaves the latter low down in its course, and – hooking around the right subclavian artery on the right side and round the arch of the aorta on the left

– runs up again into the neck, where it enters the larynx and supplies branches to the muscles which control the vocal cords.... recurrent laryngeal nerve

A method of electrical stimulation that is being used for the relief of PAIN, including that of MIGRAINE, NEURALGIA and phantom limbs (see AMPUTATION). Known as TENS, its mode of action appears to have some resemblance to that of ACUPUNCTURE. Several controlled trials suggest that it provides at least a modicum of relief of pain after operations, thereby reducing the amount of ANALGESICS that may be called for.... transcutaneous electrical nerve stimulation (tens)

A diet high in rich carbohydrate foods with sufficient protein to promote efficient elimination and supply vital trace elements in the form of minerals. Such foods produce moist bulky stools easy to pass and reduce blood cholesterol. It reduces LDLs and increases HDLs.

Fibre-deficient foods lead to poor elimination of body wastes and constipation, disposing the colon to a toxic state. This induces depression, a coated tongue and tiredness during the day. Such foods bring about a change in the balance of bowel bacterial flora, and form gas which may cause pouches of diverticulitis to develop. One of its less obvious effects is to enhance the risk of tooth and gum disease. Soon calcium is expelled by the urine and the intake of magnesium reduced, thus favouring the development of stone.

All plant material; leaves, stalks, seeds etc contain fibre. High-fibre foods include: whole grains, wholemeal bread, wholemeal flour (100 per cent extraction rate), crispbreads, biscuits (digestive, bran, oatmeal or coconut), raw green salad materials, potatoes boiled in their jackets, breakfast cereals (porridge, muesli, All-Bran, Shredded Wheat), brown rice, bran (2 teaspoons thrice daily; increase if necessary), fresh or dried fruit once or twice daily. ... diet - high fibre

See: SEDATIVE. ... nerve relaxant

All degenerative changes in the nervous system arise from breakdown of cell integrity through causes including stress, disease or faulty nutrition. J.M. Thurston classifies the restorative effect of herbs as:

Stomach and intestines: Wild Cherry bark, Black Haw.

Heart: Lily of the Valley, Cactus. Liver: Wild Yam.

Eye: Blue Cohosh, Poke root.

Brain: Oats, Black Cohosh.

Spine: Damiana, Oats, Kola, Unicorn root (Aletris). Hops. Womb: False Unicorn root (Helonias).

General Restoratives: St John’s Wort, Vervain. ... nerve restoratives

Often necessary to bring added vitality to the body or one of its parts. Often combined with circulatory stimulants to help support the nervous system in the presence of nerve weakness and paralysis.

Ephedra, Ginseng, Siberian Ginseng, Oats, Damiana, Kola, Gotu Kola, Thuja, Vervain. ... nerve stimulants

To invigorate and restore. Regarded as nutrients for strengthening nerve fibres and their protective sheaths. Help resolve effects of stress and replace mineral deficiencies in nerve tissue. They bring a new vigour in place of enervation and debility.

Betony, Damiana, Oats, St John’s Wort, Skullcap, Vervain.

Combination. Tea: Equal parts, Skullcap, Betony, Vervain. 1 heaped teaspoon to each cup boiling water; infuse 15 minutes. Half-1 cup freely. ... nerve tonics

Nervous excitability, irritability, prone to over-reaction by anger or other destructive emotion.

Teas. Cowslip flowers, St John’s Wort flowers, Passion flower, Valerian, Hops, Lime flowers, Balm, Motherwort, Woodruff, Skullcap, Oats.

Formula, tea: equal parts, Balm, Motherwort, Passion flower. 1 heaped teaspoon to each cup boiling water; infuse 5-10 minutes. 1 cup thrice daily.

Tablets. Valerian. Pulsatilla. Natracalm. (English Grains) 500mg Passion flower tablets: 1 tablet thrice daily.

See: SEDATIVES. ... nerve tension

One of a pair of nerves that carry instructions from the brain to the larynx and send sensations from the larynx to the brain.... laryngeal nerve

One of the main nerves of the arm. It is a branch of the brachial plexus and runs down the arm from the shoulder into the hand. The median nerve controls the muscles that carry out bending movements of the wrist, fingers, and thumb, and that rotate the forearm palm-inwards. The nerve also conveys sensations from the thumb and first 3 fingers, and from the region of the palm at their base.

Damage to the nerve may result from injury to the shoulder, a Colles’ fracture just above the wrist, or pressure on the nerve where it passes through the wrist (carpal tunnel syndrome).

Symptoms of damage include numbness and weakness in areas controlled by the nerve.... median nerve

See nerve, trapped.... trapped nerve

the sixth *cranial nerve (VI), which supplies the lateral rectus muscle of each eyeball, responsible for turning the eye outwards.... abducens nerve

a mixed sensory and motor nerve of the upper arm. It arises from the fifth and sixth cervical segments of the spinal cord and is distributed to the deltoid muscle of the shoulder and the overlying skin.... circumflex nerve

Tests carried out to assess the extent of nerve damage caused by disorders of the peripheral nervous system (see neuropathy). In the test, an electrical stimulus is applied to a nerve, and the speed at which the nerve responds to the stimulus and transmits a signal is recorded.

nerve injury Damage or severance of conducting fibres within a nerve as a result of trauma, causing loss of skin sensation and muscle power. (See neuropathy for nerve damage from cause.

other than injury.)

If a peripheral nerve (a nerve outside the brain or spinal cord) is only partially severed, the cut fibres may be able to regenerate. Provided the severed ends are still aligned, new fibres can grow across the cut to rejoin the connection, restoring function. If a nerve is totally severed, the individual fibres cannot regenerate successfully and there is no recovery of function. Nerve tracts within the brain and spinal cord are structurally different from the peripheral nerves, and severed fibres in these tracts do not regenerate. For example, vision cannot be restored if the optic nerves are cut.Microsurgery can sometimes be used to stitch a severed peripheral nerve into place, but recovery is rarely complete.... nerve conduction studies

Compression or stretching of a nerve, causing numbness, tingling, weakness, and, sometimes, pain. Common examples of a trapped nerve include carpal tunnel syndrome, in which pressure on the median nerve as it passes through the wrist causes symptoms in the thumb, index, and middle fingers; a disc prolapse, in which pressure on the nerve root leading from the spinal cord produces symptoms in the back and legs; and crutch palsy, in which the radial nerve presses against the humerus (upper-arm bone), producing symptoms in the wrist and hand.

A damaged nerve may take some time to heal. In severe cases, surgical decompression to relieve pressure on the nerve may be necessary.... nerve, trapped

(acoustic nerve, auditory nerve) the nerve connecting the cochlea to the brain and therefore responsible for transmitting the nerve impulses relating to hearing. It forms part of the *vestibulocochlear nerve (cranial nerve VIII).... cochlear nerve

either of two nerves that supply the teeth; they are branches of the trigeminal nerve. The inferior dental nerve supplies the lower teeth and for most of its length exists as a single large bundle; thus anaesthesia of it has a widespread effect (see inferior dental block). The superior dental nerve, which supplies the upper teeth, breaks into separate branches at some distance from the teeth and it is possible to anaesthetize these individually with less widespread effect for the patient.... dental nerve

(roughage) nonstarch polysaccharides (NSP), which cannot be digested and absorbed to produce energy; specifically, sources of NSP that do not contain lignin or resistant starch. Fibre is divided into two types: insoluble (cellulose and hemicelluloses) and soluble (pectins). Highly refined foods, such as sucrose, do not contain dietary fibre. Foods with a high fibre content include wholemeal cereals, vegetables, nuts, and fruit. A diet high in insoluble fibre (e.g. wheat bran, wholegrain and wholemeal bread and cereals) may help prevent bowel diseases, such as constipation, diverticulitis, and colon cancer. Soluble fibre (e.g. oats, barley, beans, pulses, fruit, and vegetables) slows the reabsorption of *bile salts and so helps to lower cholesterol as well as dampening the glycaemic response to glucose (see glycaemic index). A high-fibre diet used to be the first-line advice for irritable bowel syndrome; however, a low *FODMAP diet can be more effective.... dietary fibre

n. an *endoscope that uses *fibre optics for the transmission of images from the interior of the body. Fibrescopes have a great advantage over the older endoscopes as they are flexible and can be introduced into relatively inaccessible cavities of the body.... fibrescope

(House–Brackmann score, House–Brackmann scale, House–Brackmann facial weakness scale) a six-point grading system for patients with *Bell’s palsy or other forms of facial nerve palsy. Grade I is normal function; grade VI is a total palsy. [J. W. House and D. E. Brackmann (21st century), US otorhinolarygologists]... house–brackmann facial nerve grading system

one of the nerves that carry impulses outwards from the central nervous system to bring about activity in a muscle or gland. Compare sensory nerve.... motor nerve

a nerve of the *brachial plexus that supplies some muscles of the arm and the skin of the lateral part of the forearm.... musculocutaneous nerve

a test done to assess the peripheral nervous system. It involves activating the nerves electronically with electrical pulses and measuring the responses obtained.... nerve conduction study

the final part (terminal) of one of the branches of a nerve fibre, where a *neuron makes contact either with another neuron at a synapse or with a muscle or gland cell at a neuromuscular or neuroglandular junction.... nerve ending

any syndrome resulting from pressure on a nerve from surrounding structures. Examples include the *carpal tunnel syndrome and *meralgia paraesthetica.... nerve entrapment syndrome

the long fine process that extends from the cell body of a *neuron and carries nerve impulses. Bundles of nerve fibres running together form a *nerve. Each fibre has a sheath, which in medullated nerve fibres is a relatively thick layer containing the fatty insulating material *myelin.... nerve fibre

any gas that disrupts the normal functioning of nerves and thus of the muscles they supply. There are two groups, the G agents and the V agents. The latter are more than 300 times as deadly as mustard gas: one inhalation can kill by paralysing the respiratory muscles. V agents also act through the skin, therefore gas masks are ineffective protection against them.... nerve gas

(NGF) a protein (see growth factor), consisting of two polypeptide chains, that is required for the development and longevity of some neurons, including those in the sympathetic nervous system and some central nervous system and sensory neurons. Nerve growth factor is necessary for axon growth and also for initiating new neuronal connections with other cells. The role of NGFs in preventing the degeneration of brain cells is being explored in research into Alzheimer’s disease.... nerve growth factor

the electrical activity in the membrane of a *neuron that – by its rapid spread from one region to the next – is the means by which information is transmitted within the nervous system along the axons of the neurons. The membrane of a resting nerve is charged (polarized) because of the different concentrations of ions inside and outside the cell. When a nerve impulse is triggered, a wave of *depolarization spreads, and ions flow across the membrane (see action potential). Until the nerve has undergone *repolarization no further nerve impulses can pass.... nerve impulse

the growth of new nerve tissue, which occurs at a very slow rate (1–2 mm per day) after a nerve has been severed and is often partially or totally incomplete. *Microsurgery has improved the results by facilitating primary repair in the immediate aftermath of injury. See also axonotmesis; neurotmesis.... nerve regeneration

the smallest of the three branches of the *trigeminal nerve. It supplies sensory fibres to the eyeball, conjunctiva, and lacrimal gland, to a small region of the nasal mucous membrane, and to the skin of the nose, brows, and scalp.... ophthalmic nerve

see atrioventricular bundle.... purkinje fibres

microscopic, almost nonelastic, branching fibres of *connective tissue that join together to form a delicate supportive meshwork around blood vessels, muscle fibres, glands, nerves, etc. They are composed of a collagen-like protein (reticulin) and are particularly common in lymph nodes, the spleen, liver, kidneys, and muscles.... reticular fibres

a large branch of the *femoral nerve that arises in the upper thigh, travels down on the inside of the leg, and supplies the skin from the knee to below the ankle with sensory nerves.... saphenous nerve

a nerve that carries information inwards, from an outlying part of the body towards the central nervous system. Different sensory nerves convey information about temperature, pain, touch, taste, etc., to the brain. Compare motor nerve.... sensory nerve

a small subdivision of the *vestibular nerve that carries information from the posterior *semicircular canal to the brain. Singular neurectomy is a surgical procedure to divide the singular nerve, occasionally used in the treatment of *benign paroxysmal positional vertigo.... singular nerve

see accessory nerve.... spinal accessory nerve

any nerve, usually belonging to the autonomic nervous system, that controls the circulation of blood through blood vessels by its action on the muscle fibres within their walls or its action on the heartbeat. The *vagus nerve slows the heart and reduces its output, but sympathetic nerves increase the rate and output of the heart and increase blood pressure by causing the constriction of small blood vessels at the same time.... vasomotor nerve

the division of the *vestibulocochlear nerve that carries impulses from the semicircular canals, utricle, and saccule of the inner ear to the brain, conveying information about the body’s posture and movements in space and allowing coordination and balance.... vestibular nerve