Motor Systems and Oculomotor Control

Comprehensive vocabulary flashcards covering oculomotor control, muscle contraction, spinal reflexes, motor systems, cortex areas, basal ganglia disorders, and the cerebellum.

Fixation

Maintaining eye gaze on a single location.

Abduction

Movement away from midline.

Adduction

Movement toward the midline.

Elevation

Upward eye movement.

Depression

Downward eye movement.

Intorsion

Rotation of top of the eye towards the nose.

Extorsion

Rotation of top of eye away from nose.

Primary Position

Position of eye when no rotation around a major axis has occurred.

Vergence

Movements of both eyes on visual axes in opposite directions.

Convergence

Movement of both eyes towards each other.

Divergence

Movement of both eyes away from each other.

Electro-oculography (EOG)

Method used to measure eye movements via electrical potential differences in eye.

Light Lever

Method used to detect very small eye movements using a light reflection off of a small mirror on a contact lens.

Scleral Search Coil

Method used to detect very small eye movements using magnetic fields.

Conjugate eye movement

Displacement of both eyes along the visual axes in the same direction.

Smooth Pursuit

Process by which the eyes track a moving target in a smooth, conjugate deviation.

Vestibulo-Ocular Reflex (VOR)

A reflex that allows one to maintain a steady gaze despite head motion.

Optokinetic Reflex (OKR)

A reflex that allows for image stabilization that occurs when the entire visual scene is moving.

Nystagmus

The jerking movement of the eyes composed of a slow phase and a quick phase.

Physiological Nystagmus

The continuous tremor of the eye even presence during intense voluntary fixation.

Neural Integrator

A circuit that actually performs a calculus integration of signals.

Isometric

Constant length.

Isotonic

Constant force.

Hooke’s Law

$f = kx$, where $f$ = force, $k$ = spring constant, and $x$ = distance.

Motor Unit

One alpha motor neurons and all the muscle fibers it innervates.

Tetanus

High frequency neural activity.

Size Principle

Small motor neurons are activated before large motor neurons.

Sarcomere

Smallest functional unit of a muscle. Contains actin (thin filament) and myosin (thick filament).

Golgi Tendon Organ (GTOs)

Small encapsulated structures near the junction of tendon and muscle that act as a muscle proprioceptor signaling tension within the muscle.

Muscle Spindle

Intramuscular proprioceptor that transduces several aspects of muscle length.

Ib fibers

Sensory nerve fibers that innervates GTOs and convey information about muscle force.

Ia fibers

Sensory nerve fibers that contact spindles and convey information related to muscle length.

Reciprocal innervation

When one muscle or set of muscles receive a signal to contract, the opposing muscle receives a signal to inhibit it contraction.

Reciprocal inhibition

Stretch of extensor muscles inhibits the activity of flexor motor neurons, and vice versa.

Stretch reflex or myotatic reflex

“If one pulls on a muscle, it pulls back”, muscle contraction in response to a muscle stretch.

Extrafusal fiber

Large, power/force generating muscle fibers that form the main mass of the muscle, innervated by alpha motor neurons.

Intrafusal fiber

Small, thin muscle fibers enclosed in fibrous capsule found within muscle spindles, contract in a graded fashion dictated by synaptic depolarizations produced by fusimotor neurons.

Gamma motor neurons

Innervates intrafusal muscle fibers.

Interneuron pool

Groups of interneurons organized in the spinal cord and brain directly modulate motor neurons, provide ready made circuits for a range of coordinated movement patterns.

Spasticity

Combination of hypertonia and hyperreflexia.

Hyperreflexia

Increased reflex excitability of the stretch reflex.

Hypertonia

Increased resting muscle tone/tension.

Flaccid Paralysis

Muscle paralysis characterized by a loss of muscle tone and strength in affected muscles.

Spastic Paralysis

Muscle paralysis characterized by increased muscle tone, muscle stiffness, and muscle spasms.

Servo Mechanism

Low power device (spindle) is used to control a high power device (muscle) through a feedback loop.

Withdrawal Reflex

Excitation of flexors and inhibition of extensors so that the limb is withdrawn from the offending stimulus.

Electromyogram (EMG)

Recording technique to record the electrical activity of muscles.

Fibrillation

Asynchronous contraction of the muscle fibers.

Fasciculation

Sporadic series of twitches caused by diseased motor neurons.

Proximal

Located closer to the center of the body or point of attachment.

Distal

Located farther to the center of the body or point of attachment.

Decussation

The crossing of a nerve across the midline.

Axial Muscles

Muscles of the trunk.

Distal Muscles

Muscles farther from center of body, including in lower arms and legs, hands and feet.

Upper Motor Neuron

A neuron with an axon in the long motor tracts that do not directly cause movement, sends signals to lower motor neuron.

Lower Motor Neuron

Alpha motor neuron that directly innervates a muscle, receives signals from upper motor neuron.

Paretic(-paresis)

Muscle weakness (not paralysis).

Hemiparesis

Muscle weakness on one side (e.g. right arm and leg).

Paraparesis

Muscle weakness only in lower body/legs.

Quadriparesis

Muscle weakness in all four limbs.

-plegia

Complete paralysis.

Hemiplegia

Paralysis on one side of the body.

Paraplegia

Paralysis only in lower body/legs.

Quadriplegia

Paralysis in all four limbs.

Sign of Babinski

Upon specific simulation of foot, toes extend/fan (normal plantar reflex) instead of flex; positive sign occurs in infants, or in adults results in lesions to the pyramidal tract.

Clonus

Abnormal reflex response, involuntary and rhythmic muscle contractions.

Supraspinal

Neurons originate from above the spinal cord, influencing motor output at the spinal level.

Wallerian degeneration

Degeneration of the neuron distal to a cut, interrupts normal anterograde axonal transport mechanisms.

Anterograde transport

Movement along axons from soma to terminals.

Retrograde transport

Movement along axons from terminals to soma.

Horseradish peroxidase

Tracer that is transported both anterogradely and retrogradely; used for tract tracing.

Orthodromic

Direction of normal action potential conduction (soma to terminal).

Antidromic

Opposite direction of normal action potential conduction (terminal to soma).

Area 4

M1, primary motor cortex.

Area 6

Anterior to Area 4/M1, brain region plays a role in sensorimotor control, contains PMA and SMA.

Premotor Area (PMA)

Anterior to Area 4/M1 and contained in Area 6; important for motor planning.

Supplementary Motor Area (SMA)

Contained in Area 6, involved in planning voluntary movements and execution of goal directed actions.

peri-Rolandic cortex

Another name for sensory motor cortex, plays a role in sensorimotor integration.

Striatum

The caudate and the putamen.

Dystonia

Neurological motor disorder characterized by a disturbance in muscle tone.

Dyskinesia

Neurological motor disorder characterized by abnormalities of movement.

Ballism or ballismus

A condition/dyskinesia as the result of a lesion to the subthalamic nucleus that results in more movement than intended when trying to make a voluntary movement.

Athetosis

A movement disorder characterized by slow and writhing movements.

Chorea

A movement disorder caused by neurodegeneration characterized by quick, dance-like movements.

Bradykinesia

A marked slowing of movement.

Hypokinesia

A marked reduction in movement.

Akinesia

The absence of movement.

Lead-pipe Rigidity

A symptom of Parkinson’s disease, which is the resistance to passive movement of the limbs, causing stiffness and rigidity.

Cogwheel Rigidity

Symptom of Parkinson’s disease, where muscle rigidity is interrupted by small, repeated, ratchet-like jerks of the limbs.

Dysmetria

Improperly scaled movements, leading to results such as overshooting or past-pointing.

Dysdiadokokinesis

Inability to perform rapid alternating movements.

Mossy Fibers

The majority of input axons to cerebellum.

Granule cells

Most numerous cell in cerebellum, sends a single axonal connection that rises to cortical surface and splits into a parallel fiber.

Purkinje cells

Cerebellar neurons with elaborate, flattened dendritic trees; provide the only out axons of the cerebellar cortex and use the neurotransmitter GABA.