Neurology Glossary

A rapid, transient reversal of the electrical potential across a neuron's membrane, propagated along the axon to transmit signals. It is generated by sequential opening of voltage-gated sodium and potassium channels.

Carrying signals toward the central nervous system. Afferent (sensory) neurons transmit information from peripheral receptors to the brain and spinal cord.

An acquired language disorder resulting from damage to language-dominant (usually left) hemisphere brain regions, affecting the ability to produce or comprehend spoken and written language.

A lack of voluntary coordination of muscle movements, typically caused by dysfunction of the cerebellum, its afferent or efferent pathways, or the sensory (proprioceptive) system.

The division of the peripheral nervous system that regulates involuntary body functions including heart rate, blood pressure, digestion, and thermoregulation, comprising sympathetic and parasympathetic branches.

The long, slender projection of a neuron that conducts action potentials away from the cell body to synaptic terminals, where neurotransmitters are released.

The outer layer of gray matter of the cerebral hemispheres, composed of six neuronal layers, responsible for higher cognitive functions including perception, voluntary movement, language, and executive function.

A clear, colorless fluid produced by the choroid plexus that fills the ventricles and subarachnoid space, providing buoyancy, protection, and a medium for nutrient transport and waste removal for the brain and spinal cord.

Involuntary rhythmic muscular contractions and relaxations elicited by sudden, sustained stretching of a muscle, indicative of an upper motor neuron lesion.

Twelve pairs of nerves emerging directly from the brain and brainstem (olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal) that innervate structures of the head, neck, and viscera.

Branching projections of a neuron that receive synaptic inputs from other neurons and conduct graded electrical signals toward the cell body.

A motor speech disorder caused by weakness, spasticity, or incoordination of the muscles used in speech production, resulting in slurred or indistinct articulation while language comprehension and formulation remain intact.

Abnormal accumulation of fluid in the brain parenchyma. Vasogenic edema results from blood-brain barrier disruption; cytotoxic edema results from cellular swelling due to energy failure, as in ischemic stroke.

Carrying signals away from the central nervous system. Efferent (motor) neurons transmit commands from the brain and spinal cord to muscles and glands.

A diagnostic technique that records electrical activity of the brain through electrodes placed on the scalp, used primarily for evaluating epilepsy, encephalopathy, and sleep disorders.

Spontaneous, involuntary contractions of a motor unit visible as brief muscle twitches under the skin, often associated with lower motor neuron disease, nerve irritation, or benign causes.

The proliferation and hypertrophy of glial cells (primarily astrocytes) in response to CNS injury, forming a glial scar that can inhibit axonal regeneration.

Weakness affecting one side of the body, typically resulting from a lesion in the contralateral motor cortex, internal capsule, or brainstem corticospinal tract.

The pressure within the cranial vault, normally 5-15 mmHg in adults. Elevated ICP can result from mass lesions, hydrocephalus, or cerebral edema and may cause herniation if untreated.

A diagnostic procedure in which a needle is inserted into the subarachnoid space of the lumbar spine (typically L3-L4 or L4-L5) to collect cerebrospinal fluid for analysis or to measure opening pressure.

The lipid-rich insulating sheath formed by oligodendrocytes in the CNS and Schwann cells in the PNS that wraps around axons, enabling rapid saltatory conduction of action potentials.

Involuntary, repetitive, rhythmic eye movements consisting of a slow phase and a corrective fast phase. It can indicate vestibular, cerebellar, or brainstem pathology depending on its pattern and direction.

The sense of body position and movement in space, mediated by mechanoreceptors in joints, tendons, and muscles. Proprioceptive information travels via the dorsal columns of the spinal cord to the somatosensory cortex.

The specialized junction between two neurons (or a neuron and an effector cell) across which neurotransmitters are released from the presynaptic terminal and bind to receptors on the postsynaptic membrane.

The progressive degeneration of the distal segment of a severed axon and its myelin sheath, occurring after nerve injury. It is a prerequisite for potential axonal regeneration in the peripheral nervous system.