BIO 335 Lab 9 - NEUROANATOMY SESSION 2. FOCUS ON MOTOR...

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NEUROANATOMY SESSION 2. FOCUS ON MOTOR SYSTEMS Although the final common pathway is synapse of motor neurons on muscle, activating motor neurons and getting them to fire and cause muscle contraction is only a small part of the functional system(s) that produce purposeful movement. FOUR COMPONENTS OF MOTION : 1. BASAL GANGLIA: Initiation of movement 2. MOTOR CORTEX & DESCENDING TRACTS: Issuing the motor command 3. CEREBELLUM: Improving on the command 4. LOCAL SPINAL REFLEXES: In case of emergency- guards against muscles being too contracted or stretched . IN PREPARATION FOR LAB SESSION 2 1. Review the atlas you created in preparation for Session I. Refresh your familiarity with the appearance of major features of the brain's exterior and interior. 2. Review the materials and write-up associated with the laboratory session on the stretch reflex . 3. Read the following background materials (the following 8 pages), and view the linked videos showing particular types of movements and movement disorders.
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Look up the following terms and connect each to its component of motion above . o Tremor at rest/ Intention tremor o Paralysis/parethesis/weakness o Upper motor neuron disorder/ lower motor neuron disorder o Decorticate rigidity/decerebrate rigidity o Hyperkinetic/hypokinetic disorders o ALS
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Descending pathways bring commands from the primary motor cortex to motor neurons – specialized neurons with axons that terminate on the muscles themselves and through action potential and release of neurotransmitter (acetylcholine) cause the muscle to contract. Nearly every skeletal muscle in the body can be voluntarily controlled by primary motor cortex commands. However, it would be highly inefficient for the cerebral cortex to control each and every movement that is made, particularly those that are responses to changes in posture or highly stereotyped- like swinging the arms and legs while walking. Thus, for some muscles such as those that support the trunk (postural muscles) the input from primary motor cortex is secondary; these workhorse muscles are most often driven by sensory inputs on a more automatic level to perform their simple but essential function: if you are tilted, they respond by contracting to straighten you up. But the cerebral cortex can override them - for example when you want to bend in a particular way.
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The motor cortex commands to motor neurons are not terribly accurate; if you are reaching for something, the motor cortex only gets your arm moving in pretty much the right direction. It is the sensory feedback created by moving the arm that is used by the CEREBELLUM to make corrections to the activity of motor cortex and refine the reaching movement. This system is very FAST and UNCONSCIOUS- it happens automatically and on the fly- the end result is a smooth and precise
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BIO 335 Lab 9 - NEUROANATOMY SESSION 2. FOCUS ON MOTOR...

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