Chapter 8Chapter 8The Neurological Control of Movement

Levels of Control of Levels of Control of MovementMovementMovements can range from simple to

complex:

• The simplest movements are reflexive• Other movements are more complex than

reflexes, but less complex than other skills• More complex movements can be learned

Stimulation and Control of Stimulation and Control of MovementMovementStimulated by the motor neurons of the

CNS.Neural control of a particular movement

operates on several different levels:• Most basic level of control is the spinal cord• Next level involves brain stem structures• Highest level of control involves the cerebral

cortex structures such as the dorsolateral prefrontal cortex, the primary and secondary motor cortex, and the somatosensory cortex.

Basal ganglia – Smoothes and refines movementCerebellum - Plays a central role in translating

uncoordinated movements into a skilled action

Mechanics of Movement Mechanics of Movement ControlControl

Three types of muscle tissue in the body: Smooth muscles - Control the movement of internal

organs Cardiac muscles - These heart muscles actively work to

pump blood through the circulatory system. Skeletal muscles - Enable us to perform the movements

necessary to exercise and engage in other activities. Contracting an extensor muscle produces limb extension Contracting a flexor muscle causes flexion Muscles that work in opposition to each other are called

antagonistic muscles Muscles whose contraction results in the same movement are

called synergistic muscles.

The Motor UnitThe Motor UnitEach branch of an axon synapses with a

single muscle fiber.Collectively, a motor neuron and the

muscle fibers it controls form a motor unitWhen the axon of a motor neuron has few

branches and controls only a few muscle fibers, fine motor control is possible.

When the axon has many branches and controls many muscle fibers, gross motor movement is possible.

Neural Neural Control of Control of

Muscle Muscle ContractionContraction

Motor impulseMuscle action

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Muscle AdaptationMuscle AdaptationDifferent types of muscles facilitate

diverse abilities:

• Slow-twitch muscle - A muscle fiber that contracts and fatigues slowly; produces slower contractions that can be maintained for long periods of time.

• Fast-twitch muscle - A muscle fiber that contracts and fatigues quickly; produces rapid contractions.

• Intermediate-twitch muscle - produces contractions of moderate speed and duration.

Golgi Tendon OrgansGolgi Tendon Organs

Renshaw CellsRenshaw CellsInhibitory interneurons excited

by an motor neuron that causes it to stop firing, preventing excessive muscle contraction.

Combats muscle damage that can result from fatigue, which results from muscles contracting often in a short period of time.

The Gamma Motor SystemThe Gamma Motor SystemContraction does not always lead to

movement.

Gamma motor neuron - synapses with intrafusal muscle fibers to produce continuous muscle tension – muscle tone

This muscle tone is maintained at all times, except during REM sleep.

The gamma motor system also gives us the ability to anticipate certain movements and react quickly.

Cortical Cortical Control of Control of MovemenMovementt

Tracts Tracts OriginatinOriginating in the g in the Primary Primary Motor Motor CortexCortex

Tracts Tracts Originating Originating in the in the SubcortexSubcortex

The CerebellumThe CerebellumThe brain area responsible for

developing rapid, coordinated responses or habits.

Ballistic movement - A habitual, rapid, well-practiced movement that does not depend on sensory feedback; controlled by the cerebellum.

The CerebellumThe CerebellumInput/output for the cerebellum is conveyed

by large bundles of axons called peduncles.Integrates information about motor activity,

balance, head and limb position, and extent of muscle contraction then determines whether ongoing movements are deviating from their intended course.

If movements begin to deviate, the cerebellum correcst them by sending signals to other structures, such as the deep cerebellar nuclei.

Consequences of Cerebellar Consequences of Cerebellar DamageDamageDifficulty maintaining a stable posture, making

movements such as walking unsteady, slurred speech, and uncoordinated eye movements.

Research suggests that the cerebellum plays a significant role in cognitive behaviors in addition to its role in fine-tuning motor movements and in motor learning.

Neurons in the cerebellum are sensitive to alcohol

Alcohol intoxication can lead to signs of cerebellar malfunction.

The Basal GangliaThe Basal GangliaGroup of structures that integrates

movement and controls postural adjustments and muscle tone.• Consists of three subcortical nuclei:

Caudate nucleus Putamen Globus pallidus

• Corpus striatum - Part of the basal ganglia consisting of the caudate nucleus and putamen.

The Basal GangliaThe Basal Ganglia

The Basal GangliaThe Basal GangliaIntegrates movement via connections

with the primary motor cortex, the cerebellum, substantia nigra, red nucleus, and other motor centers in the brain.

Damage to the basal ganglia results in impairments in muscle tone, postural instability, poorly integrated movements, and difficulty performing voluntary movements.

Damage to the Motor Damage to the Motor SystemSystemParkinson’s diseaseMuscular DystrophyPolioHuntington’sALSMultiple SclerosisCerbral Palsy

Other Movement Other Movement DisordersDisordersApraxia - characterized by missing or inappropriate

actions not caused by paralysis or any other motor impairment.

Constructional apraxia - characterized by difficulty drawing pictures or assembling objects.

Limb apraxia - impairment in the voluntary use of a limb caused by damage to the left parietal lobe or the corpus callosum.

Apraxia of speech - characterized by difficulty speaking clearly, caused by damage limited to Broca’s area.

Strabismus – eye muscles do not work together