Motor Systems Part 2

Vocabulary practice flashcards covering the components, pathways, disorders, and clinical manifestations of the motor systems lecture.

Sensorimotor Cortex

All areas of the cerebral cortex involved in muscle movement; plays a critical role in planning and ongoing control of normal voluntary movements, operating at both the highest and middle levels of the motor control hierarchy.

Motor Control Hierarchy: Highest Level

Composed of 'command' neurons, including areas of the sensorimotor cortex as well as brain regions involved with memory, emotions, and motivation that initiate general motor intentions.

Motor Control Hierarchy: Middle Level

Structures that specify the individual postures and movements needed to carry out an intended action, including the sensorimotor cortex, basal nuclei, thalamus, cerebellum, and brainstem.

Motor Control Hierarchy: Local Level

Composed of brainstem and spinal cord interneurons, afferent neurons, motor neurons (the final common pathway), and muscle fibers.

Primary Motor Cortex

A middle-level motor hierarchy structure organized somatotopically that contributes directly to contralateral movements involving individual muscles.

Motor Homunculus

A topographic mapping of the body on the primary motor cortex where the size of the cortical area devoted to a body part is proportional to the fineness of movement that part performs.

Premotor Cortex

A sensorimotor cortex region that participates in the preparation for movement, concerns itself with posture, and gives rise to a medial descending pathway controlling trunk and head muscles.

Supplementary Motor Cortex

A cortical motor area important for complex movements, planning sequences of movement, and coordinating both voluntary movements and the two sides of the body (such as bi-manual coordination).

Parietal Association Cortex

A brain area that integrates and provides processed multisensory information to other regions of the sensorimotor cortex.

Readiness Potential

A wave of electrical activity in the supplementary motor cortex that represents the earliest indication that a voluntary movement is about to occur (preparation for movement).

Motor Potential

A wave of electrical activity occurring in the primary motor cortex after the readiness potential and immediately before voluntary movement begins.

Basal Ganglia (Basal Nuclei)

A group of subcortical nuclei including the putamen, globus pallidus, and caudate nuclei that select motor plan components, suppress unwanted behaviors, and function at the middle level of the motor hierarchy.

Parkinson Disease

A basal ganglia disorder caused by the loss of dopaminergic neurons in the substantia nigra, leading to an increase in inhibitory GABAergic output to the thalamus and motor cortex and generalized motor suppression.

Signs of Parkinson Disease

Reduced amount and slowness of movement, muscular rigidity, mask-like unemotional facial expression, resting tremor ('pill-rolling'), and difficulty starting new behavior or stopping ongoing activity.

Deep-Brain Stimulation (DBS)

A surgical procedure involving the implantation of an electrode, lead wire, and neurostimulator to stimulate or modulate structures like the subthalamic nucleus to treat Parkinson disease.

Huntington's Disease

An inherited basal ganglia disorder characterized by the loss of GABAergic and cholinergic neurons and cortical degeneration, presenting with dementia, facial grimacing, and rapid flicking movements of the extremities and facial muscles.

Cerebellum

A brain motor center that acts as a comparator between intended and actual movement, fine-tuning motor activity and contributing to coordination, precision, and accurate timing without initiating movement.

Intention Tremor

An oscillatory to-and-fro tremor characteristic of cerebellar damage that worsens as a voluntary movement reaches its completion and may continue for a few moments afterward.

Lateral Corticospinal Tract

The descending motor tract formed by the $80\%$ of corticospinal axons that cross over to the contralateral side of the central nervous system within the medulla.

Ventral Corticospinal Tract

The descending motor tract formed by the uncrossed $20\%$ of corticospinal axons that remain on the ipsilateral side as they descend through the medulla into the spinal cord.

Corticobulbar Pathway

A descending motor pathway originating in the motor cortex and terminating in the brainstem to control muscles of the eye, face, tongue, throat, and voluntary movements of the head and neck.

Brainstem Pathways

Phylogenetically older descending motor pathways (including the vestibulospinal and reticulospinal tracts) originating in the brainstem that are essential for upright posture, balance, and walking.

Spinal Shock

The early phase following severe spinal cord injury marked by areflexia (absent reflexes), flaccid paralysis (low muscle tone), and complete loss of sensation below the level of the lesion.

Hyperreflexia (Post-SCI)

The hyperactive return of stretch reflexes along with increased muscle tone (hypertonia), rigidity, and pathological reflexes appearing $3\text{--}4\text{ weeks}$ after a spinal cord injury.