Motor and Brain Function Pathophysiology

Vocabulary practice flashcards covering motor function pathways, movement disorders, traumatic brain injuries, intracranial pressure dynamics, stroke pathophysiology, and meningeal signs.

Upper Motor Neuron (UMN)

A motor neuron with its cell body in the motor cortex of the brain; it originates signals and transmits them down the spinal cord to initiate voluntary movement.

Lower Motor Neuron (LMN)

A motor neuron with its cell body in the spinal cord; its axon exits the spinal cord and travels through a peripheral nerve to innervate target muscle tissue.

Reflex Arc

A direct neural pathway where a stimulus activates a sensory receptor, sending a signal along a sensory neuron into the spinal cord to synapse directly onto a motor neuron, producing an automatic response without brain involvement.

Pyramidal Tract

A direct, single-relay motor pathway running straight from the motor cortex to the spinal cord or brainstem that controls voluntary, skilled, and precise movements, crossing over at the medullary pyramids.

Extrapyramidal System

Indirect, multi-relay pathways running through the basal ganglia, cerebellum, and brainstem nuclei that modulate and refine movement, regulating muscle tone, posture, coordination, and automatic movements.

Presynaptic Terminal

The axon terminal structure that stores neurotransmitters in synaptic vesicles and releases them into the synaptic cleft upon an influx of $Ca^{2+}$.

Synaptic Cleft

The microscopic extracellular space separating the presynaptic terminal from the postsynaptic membrane across which neurotransmitters diffuse.

Postsynaptic Membrane

The specialized membrane on a receiving neuron or effector cell containing specific receptors that bind released neurotransmitters.

Acetylcholine (ACh)

An excitatory neurotransmitter active at every neuromuscular junction and within CNS circuits responsible for memory and arousal.

Dopamine

A mostly excitatory neurotransmitter produced in the substantia nigra that coordinates smooth, purposeful movement and plays key roles in motivation and reward.

GABA

The primary inhibitory neurotransmitter in the central nervous system that acts as the brain's main brake to dampen neuronal excitability.

Glutamate

The primary excitatory neurotransmitter in the central nervous system that functions as the brain's main gas pedal.

Norepinephrine

An excitatory neurotransmitter involved in mood regulation that drives alertness, arousal, and the fight-or-flight response.

Serotonin

A mostly inhibitory neurotransmitter that regulates mood, sleep-wake cycles, and appetite.

Cerebrospinal Fluid (CSF)

A fluid continuously produced inside the brain ventricles that circulates around the brain and spinal cord to provide physical cushioning and maintain a stable chemical environment.

Blood-Brain Barrier (BBB)

A selective barrier formed by tightly joined capillary endothelial cells that strictly controls which substances can move from the blood into brain tissue.

Myelin Sheath

An insulating layer wrapped around axons—formed by Schwann cells in the PNS and oligodendrocytes in the CNS—that accelerates electrical signal transmission.

Saltatory Conduction

The process by which nerve action potentials jump from node to node along a myelinated axon, significantly increasing signal speed.

Multiple Sclerosis (MS)

An autoimmune CNS disorder characterized by immune-mediated demyelination of axons, leading to impaired signal conduction and a classic relapsing-remitting course.

Guillain-Barré Syndrome (GBS)

An autoimmune demyelinating disorder of the peripheral nervous system, often triggered by infections like Campylobacter jejuni, causing symmetric ascending flaccid weakness and areflexia.

Myasthenia Gravis

An autoimmune disorder where autoantibodies attack acetylcholine receptors at the neuromuscular junction, leading to muscle weakness that worsens with activity and improves with rest.

Parkinson Disease

A progressive movement disorder caused by the loss of dopamine-producing neurons in the substantia nigra, resulting in resting tremor, rigidity, bradykinesia, and postural instability.

Alpha-Synuclein

A neuronal protein that misfolds and aggregates in Parkinson disease to form toxic intracellular deposits known as Lewy bodies.

Lewy Bodies

Damaging intracellular protein deposits composed of misfolded alpha-synuclein that build up inside dopamine-producing neurons.

Amyotrophic Lateral Sclerosis (ALS)

A progressive neurodegenerative disease characterized by simultaneous degeneration and death of upper and lower motor neurons, leaving sensory and cognitive functions intact.

Poikilothermia

The loss of independent thermoregulation caused by high spinal cord injuries, resulting in body temperature drifting toward ambient room temperature.

Autonomic Dysreflexia

A life-threatening medical emergency in spinal cord injuries at or above $T6$, where a noxious stimulus below the injury triggers an uninhibited sympathetic response causing severe hypertension, pounding headache, and bradycardia.

Concussion

A traumatic brain injury marked by temporary disruption of brain function following a jolt or blow, typically without visible structural damage on neuroimaging.

Contusion

A traumatic brain injury involving actual structural bruising of brain tissue at the impact site or on the opposite side (contrecoup).

Diffuse Axonal Injury

A severe traumatic brain injury resulting from rapid acceleration-deceleration forces that cause widespread shearing and stretching of axons.

Glasgow Coma Scale (GCS)

A standardized scoring system that assesses eye opening ($1$–$4$), verbal response ($1$–$5$), and motor response ($1$–$6$), with total scores ranging from $3$ to $15$.

Monro-Kellie Doctrine

The principle stating that inside the rigid skull, the total volume of brain tissue, blood, and CSF is fixed, so an increase in one component requires a decrease in another to prevent ICP elevation.

Cushing's Triad

A late, ominous sign of brainstem compression and impending herniation consisting of hypertension with a widening pulse pressure, bradycardia, and irregular respirations.

Uncal Herniation

A form of transtentorial herniation where the temporal lobe's uncus shifts over the tentorial notch, compressing CN III and the midbrain to cause an ipsilateral blown pupil and declining LOC.

Central Herniation

A transtentorial herniation where the diencephalon and middle brain structures are pushed downward through the tentorium, causing progressive rostral-to-caudal deterioration.

Cerebellar Tonsillar Herniation

A life-threatening herniation where cerebellar tonsils push down through the foramen magnum, compressing the medulla and threatening respiratory arrest.

Rostral-to-Caudal Deterioration

The predictable top-down sequence of neurological decline as elevated ICP progresses from the cerebral cortex down through the midbrain and brainstem.

Cerebral Perfusion Pressure (CPP)

The net pressure gradient driving blood flow to the brain, calculated as Mean Arterial Pressure minus Intracranial Pressure ($CPP = MAP - ICP$).

Ischemic Stroke

A type of stroke accounting for approximately $85\%$ of cases, caused by a blood clot obstructing cerebral blood flow.

Hemorrhagic Stroke

A type of stroke accounting for approximately $15\%$ of cases, caused by a ruptured blood vessel bleeding into or around brain tissue.

Core Infarct

The central zone of an ischemic stroke experiencing near-total loss of blood flow, where severe ATP depletion causes rapid cell swelling and irreversible death within minutes.

Ischemic Penumbra

The ischemic brain tissue surrounding a core infarct that receives reduced collateral blood flow; its cells are functionally silent but metabolically viable and salvable with timely reperfusion.

Expressive Aphasia (Broca's)

A language disorder resulting from damage to the left frontal lobe where language comprehension remains intact, but speech production is impaired.

Receptive Aphasia (Wernicke's)

A language disorder resulting from damage to the left temporal lobe where speech output is fluent but incomprehensible, and language comprehension is severely impaired.

Dysarthria

A motor speech impairment caused by weakness or altered control of the muscles used for speech production, while language formulation and comprehension remain intact.

Dysphagia

Difficulty swallowing following neurological injury that creates a high risk of aspiration, requiring a formal screening prior to oral intake.

Status Epilepticus

A neurological emergency defined as a continuous seizure lasting more than $5\,\text{minutes}$ or recurrent seizures occurring without a return to baseline consciousness between episodes.

Kernig's Sign

A clinical indicator of meningeal irritation where extension of the knee with the hip flexed to $90^\circ$ elicits hamstring pain and resistance.

Brudzinski's Sign

A clinical indicator of meningeal irritation where passive neck flexion induces involuntary flexion of both hips and knees.

Epidural Hematoma

An accumulation of blood secondary to trauma that forms in the space between the inner skull bone and the dura mater.