Transcript Chapter 8
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 Contraction Motor impulse Muscle action pearson 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. Golgi Tendon Organs 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. Cortical Control of Movement Tracts Originating in the Primary Motor Cortex Tracts Originating in the Subcortex The Cerebellum The brain area responsible for developing rapid, coordinated responses or habits. Ballistic movement - A habitual, rapid, wellpracticed 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 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