M

Malignant tumour

A tumour that invades and destroys the tissue where it originates and which can spread to other sites in the body.

Median nerve

A large nerve running down the arm and into the hand which controls the movement of some muscles and carries sensation from the thumb, index and middle fingers and part of the ring finger back to the brain.

Membrane

A thin layer of tissue surrounding an organ, lining a cavity or separating adjacent structures or cavities.

Ménière’s disease

A condition in which repetitive attacks of vertigo are accompanied by pressure in the ears, tinnitus and deafness.

Meninges

The three connective tissue membranes that line the skull and vertebral canal and enclose the brain and spinal cord.

Meningitis

An inflammation of the membranes covering the brain (the meninges) due to infection by a virus or bacterium.

Menopause

The time when a woman’s menstrual periods stop, usually during her forties or fifties.

Metastases

The spread of disease, especially a malignant tumour, remote from its
site of origin.

Microdiscectomy

An operation to remove part of an intervertebral disc, usually in order to release a trapped nerve, but with minimal disruption of the spinal muscles and other tissues.

Micrographia

Small handwriting.

Migraine

A disabling headache which is frequently limited to one side of the head and is often linked with nausea or vomiting. In a few people the attacks are preceded by aura symptoms.

Motor evoked potentials

Electrical responses in limb muscles seen following stimulation of the brain or spinal cord which can give information about whether the nervous system is functioning as it should.

Motor nerve

A nerve which runs down to a muscle and controls its movement.

Motor neurone disease (MND)

A condition in which there is degeneration of nerve pathways controlling muscle activity. This leads to progressive weakness and wasting of muscles.

MPTP

A toxic substance with the chemical formula 1-methyl-4-phenyl- 1, 2, 6-tetrahydropyridine.

MRI scan

Magnetic Resonance Imaging is a technique that gives very clear pictures of an area of the body (e.g. the ear) in any plane. The pictures obtained are of very high quality and use magnetism rather than x-rays. The scan process is painless but somewhat claustrophobic, and can be noisy.

MRI/CT contrast

A dye injected into the veins to improve MRI and CT scan pictures.

Multiple sclerosis (MS)

A disease affecting the nervous system usually with a relapsing and remitting pattern (at times the symptoms are severe, while at other times they seem to disappear). Movement, vision, speech and memory may be
affected.

Muscular dystrophy

A group of muscle diseases characterised by weakness and wasting of selected muscles.

Mutation (genetic)

The inherited instructions which determine how all living things, including humans, develop and function are carried in a biological code contained in structures called genes. Errors in this code are called mutations and they may result in diseases in those who inherit them, as in familial CJD.

Myalgia

A term referring to pain generated in muscles.

Myelin

The fatty protein coat around nerve fibres. Myelin sheaths increase the speed at which electrical impulses or messages travel.

Myelogram

An x-ray test in which dye is introduced into the fluid circulating around the spine to allow pictures to be taken of the spinal cord.

Myoclonus

These are brief, "jumping", jerking movements. Some myoclonus is
normal (during or just before sleep, for example). However it can be a feature of certain diseases, especially, but not only, CJD.

Myodil

The name given to a contrast medium which was for many years the sole agent available for myelography. It has not been used for many years, being replaced by more modern substances.

Myotome

A group of muscles supplied by a single nerve root.