Basal Ganglia and Vestibular System

Vocabulary practice flashcards covering basal ganglia anatomy, motor loop direct and indirect pathways, vestibular organ mechanics, descending motor tracts, and clinical balance assessments.

Basal Ganglia (BG)

A group of five distinct nuclei located in the cerebrum and midbrain that sends information to and receives information from the primary motor cortex.

Caudate Nucleus

A basal ganglia nucleus situated above the thalamus that regulates the speed and accuracy of movement and participates in executive function (decision-making).

Putamen

A basal ganglia nucleus responsible for the regulation and storage of movement.

Globus Pallidus

A component of the basal ganglia divided into internal (GPi) and external (GPe) segments, functioning within motor loops and postural tone regulation.

Subthalamic Nuclei

Nuclei within the basal ganglia responsible for movement suppression.

Substantia Nigra

A midbrain structure of the basal ganglia that produces dopamine and acts as part of the output system.

Input Nuclei (Striatum)

The portion of the basal ganglia consisting of the caudate and putamen that receives input messages directly from the cerebral cortex.

Output Nuclei (Paleostriatum)

The basal ganglia nuclei consisting of the Globus Pallidus internus (GPi) and Substantia Nigra (SNr) that selectively inhibit the thalamus before signals project to the cortex.

BG Postural Tone Circuit

A motor circuit connecting the Globus Pallidus to the midbrain and descending via the reticulospinal and vestibular tracts; interruptions lead to excessive contraction of postural muscles.

Four Loops of the Basal Ganglia

The functional circuits of the basal ganglia: Motor Loop (learned movements), Learning Loop (learning a movement), Limbic Loop (emotional aspects of movement), and Oculomotor Loop (gaze and eye movement).

Direct Pathway

A motor loop pathway whose primary aim is to excite the thalamus and motor cortex to initiate or facilitate movement.

Indirect Pathway

A motor loop pathway routing via the GPe and subthalamic nucleus whose net effect is to inhibit the thalamus, thereby suppressing cortical activation and movement.

Glutamate

The excitatory neurotransmitter used by projections from the motor cortex and subthalamic nucleus in basal ganglia circuitry.

GABA (Gamma-Aminobutyric Acid)

The inhibitory neurotransmitter utilized by striatal neurons, the globus pallidus, and the substantia nigra to modulate thalamic activity.

Hypokinetic Conditions

Disorders characterized by excessive basal ganglia inhibition on the thalamus, leading to too little movement.

Hyperkinetic Conditions

Disorders characterized by insufficient basal ganglia inhibition on the thalamus, leading to uncontrolled, excessive movement.

Semicircular Canals

Three fluid-filled loops (lateral, medial, posterior) in the inner ear that detect angular motion and rotation of the head.

Ampulla

A dilated structure located at the base of each semicircular canal housing the crista ampullaris and sensory hair cells.

Cupula

A gelatinous structure within the ampulla that is deflected by endolymph fluid movement during head rotation, bending hair cells and generating action potentials.

Utricle and Saccule

Otolithic organs of the vestibule containing maculae that detect linear acceleration, deceleration, and head tilt relative to gravity.

Otolithic Membrane

A gelatinous layer embedded with calcium carbonate crystals (otoliths) that shifts under gravitational pull or linear acceleration to displace stereocilia and kinocilia.

Vestibular Hair Cell

A separate mechanoreceptor cell providing proprioceptive sensory modality by transducing mechanical deflection into action potentials.

Vestibulo-Ocular Reflex (VOR)

A reflex that stabilizes vision by driving eye movement in the opposite direction at the exact same velocity as head movement.

Lateral Vestibulospinal Tract (LVST)

A descending motor pathway originating in the vestibular nuclei that innervates motor neurons controlling the limb muscles.

Medial Vestibulospinal Tract (MVST)

A descending motor pathway terminating in the cervical spine responsible for reflex control of neck musculature.

Righting Reflex

A postural corrective reflex in which leaning triggers sensory inputs that rapidly cause contraction of the contralateral scalene muscles to restore head orientation perpendicular to gravity.

Static Postural Control

The maintenance of stability by keeping the center of mass (COM) over the base of support (BOS) while the body remains at rest.

Dynamic Postural Control

The maintenance of stability by keeping the center of mass (COM) over the base of support (BOS) while body segments are in motion.

Anticipatory Postural Control

Postural adjustments executed prior to performing a voluntary movement (such as bracing during weightlifting).

Adaptive Postural Control

The modification and tuning of balance strategies in response to varying tasks and environmental demands.

Postural Sway

The natural, continuous oscillation of the trunk over the ankle joint, managed by ongoing muscular corrections to preserve equilibrium.

Romberg's Test

A clinical balance assessment where a patient stands with feet together and closes their eyes to evaluate proprioceptive and vestibular integrity in the absence of visual feedback.