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Chapter 8. The Neurological Control of Movement. Levels of Control of Movement. Movements 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.
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Chapter 8 The Neurological Control of Movement
Levels of Control of Movement • Movements 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 Movement • Stimulated 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 movement • Cerebellum - Plays a central role in translating uncoordinated movements into a skilled action
Mechanics of Movement Control • 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 Unit • Each branch of an axon synapses with a single muscle fiber. • Collectively, a motor neuron and the muscle fibers it controls form a motor unit • When 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 Control of Muscle ContractionMotor impulseMuscle actionpearson 1
Muscle Adaptation • Different 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.
Renshaw Cells • Inhibitory 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 System • Contraction 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.
The Cerebellum • The 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 Cerebellum • Input/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 Damage • Difficulty 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 Ganglia • Group 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 Ganglia • Integrates 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 System • Parkinson’s disease • Muscular Dystrophy • Polio • Huntington’s • ALS • Multiple Sclerosis • Cerbral Palsy
Other Movement Disorders • Apraxia - 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