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magnetic resonance imaging (MRI)
A noninvasive, non-x-ray diagnostic procedure based on magnetic fields of hydrogen atoms within the body. A magnet linked to a computer is used to create images of the body’s internal tissues and organs.
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malignant
Refers to cells or tumors growing progressively and in an uncontrolled fashion. Such growths may spread to and disrupt nearby normal tissue or reach distant sites via the bloodstream.
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malignant peripheral nerve sheath tumor (MPNST)
A type of soft tissue sarcoma that develops in the cells that form a protective sheath (covering) around peripheral nerves, which are the nerves that are outside of the central nervous system.
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mandibular paralysis
See trigeminal neuritis.
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medial
Toward the midline of the body or structure.
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medulloblastoma
A cerebellar tumor composed of neuroepithelial cells.
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megaesophagus
Interruption of the reflexes that cause contraction and relaxation of the esophageal muscles resulting in dilation and loss of tone of the espophagus.
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megalencephaly
Abnormally large, heavy, and usually malfunctioning brain; thought to be related to a disturbance in the regulation of cell reproduction or proliferation.
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melanoma
A cancer arising from the pigment cells of the skin.
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meningitis
Inflammation of the meninges.
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meningoencephalitis
Inlammation of the brain and meninges.
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mesencephalic aqueduct
See cerebral aqueduct.
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metabolic
Relating to metabolism, the sum of the chemical processes in a cell or in the body that are necessary to sustain life; includes creating energy by breaking down substances (e.g. oxygen, food) and using energy to synthesize substances (e.g. proteins, fats, sugars), called catabolism and anabolism, repectively.
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metastasis
The transfer of disease from one part of the body to another part that is not directly related to it; characteristic of many malignant tumors.
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metronidazole toxicity
Idiosyncratic reaction to this common antibiotic that can result in neurological signs, particularly those associated to the vestibular system.
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microorganism
Minute living organisms such as bacteria, rickettsiae, viruses, fungi, yeasts, and protozoa.
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middle ear
Portion of the ear that transfers sound from the eardrum to the inner ear.
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miosis
Abnormally small pupil.
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monoparesis
Paresis of one limb.
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monoplegia
Paralysis of one limb.
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motoneuron
See motor neuron.
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motor nerve
A nerve originating from motor neurons supplying muscle or other target organs.
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motor neuron
A nerve cell that conducts action potentials away from the central nervous system and innervates effector organs (muscle and glands); it forms the ventral roots of the spinal nerves; also called an efferent neuron or motoneuron.
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motor unit
Composed of the motor neuron → axon → muscle fibers.
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muscular dystrophy
A group of congenital muscle diseases in which muscle fibers are unusually susceptible to damage and become progressively weaker. The most common types of muscular dystrophies are due to a genetic deficiency of the muscle protein dystrophin.
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myasthenia gravis
An autoimmune disease that affects the neuromuscular junction, interrupting the communication between nerve and muscle, thereby causing muscle weakness.
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myelin
The lipid substance coating the axons of certain neurons; formed by neuroglial cells: oligodendrocytes and Schwann cells; enables action potentials to travel faster while using less energy.
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myelitis
Inflammation of the spinal cord.
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myelography
Diagnostic procedure in which contrast material is injected into the spinal subarachnoid space allowing visualization of the spinal cord and nerve roots.
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myelopathy
Any disease affecting the spinal cord.
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myoclonus
A brief, involuntary twitching (contracting) of a muscle or group of muscles.
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myoneural junction
See neuromuscular junction.
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myopathy
Non-specific term for any disease affecting muscle (usually skeletal muscle) which causes muscles to become weak or wasted.
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myositis
Inflammation of a muscle, especially a voluntary muscle (i.e. skeletal muscle), characterized by pain, weakness and sometimes spasm in the affected area.
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myotonia
Decreased ability to relax muscles after contraction which can be a specific form of myopathy.
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