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KIN 461 Week 3 Notes

by: Tanski Notetaker

KIN 461 Week 3 Notes KIN 461-401

Tanski Notetaker
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Hi everyone! Here are the week 3 notes for Motor Learning. I hope they help!
Principles of Motor Learning
Dr. Peterson
Class Notes
Kinesiology KIN 461 Motor Learning
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This 2 page Class Notes was uploaded by Tanski Notetaker on Sunday February 14, 2016. The Class Notes belongs to KIN 461-401 at University of Wisconsin - Milwaukee taught by Dr. Peterson in Spring 2016. Since its upload, it has received 27 views. For similar materials see Principles of Motor Learning in Kinesiology at University of Wisconsin - Milwaukee.

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Date Created: 02/14/16
Week 3 1 Introduction to Movement (continued) Sensory Receptors  Muscle Spindles (cont.) o Response to stretch  Myelinated sensory axons enter muscle spindle capsule in its central   Sensory axons terminate on central portion and spiral around intrafusal  fibers  When intrafusal fibers stretch (called loading the spindle), sensory endings increase their firing rate due to elongation of afferent endings  Unloading: stretch is released   Intrafusal fibers slacken  Decrease firing rate of afferent endings  Golgi Tendon Organs o Sensitive to changes in tension o Located at junction between muscle fibers and tendon   Myelinated   Have slightly smaller diameter than group Ia fibers o Slender, encapsulated structures o Collagen bundles within capsule divide into fine fascicles that form braided  structure o Stretching of tendon organ straightens the collagen bundles  This compresses and elongates nerve endings, causing them to fire  Because nerve endings intertwine with collagen fiber bundles, firing rate  of tendon organs is very sensitive to changes in tension of the muscle  Central Nervous systems controls sensitivity of the muscle spindles through the Gamma  motor neurons o This ensures that information on changes in muscle length is transmitted during  contraction o Intrafusal fibers innervated by small gamma motor neurons o Extrafusal fibers innervated by larger alpha motor neurons o Alpha­gamma coactivation: electrical stimulus of motor cortex and other higher  centers leads to simultaneous activation of alpha and gamma motor neurons o Gamma motor neurons regulate activity of muscle spindle afferents  Gamma neurons innervate ends of intrafusal fibers where contractile  elements are located  Activation of gamma neuron causes contraction and shortening of fiber  ends  This increases firing rate of sensory endings  Makes afferent ending more sensitive to stretch in muscle spindles Side Notes: Week 3 2  Afferent carry sensory information from muscles to spinal cord  Efferent carry motor information from spinal cord to muscles  Advantage of decreasing 1a firing rate after an increase in velocity of joint movement o It makes movement steadier  Exam Question: What would happen if an object was lighter than expected? Motor Units and EMG  Force exerted by muscle is controlled by a population of alpha motor neurons whose cell  bodies cluster in the ventral horn of the spinal cord  Alpha motor neurons have extensive dendritic trees o Receive ~100,000 synaptic connection from descending pathways, spinal  interneurons and afferent fibers  95% of the surface area of a motor neuron is located in the dendrites o The thousands of inputs that a motor neuron receives occur primary on dendrites  Average muscle unit innervation number is 340 o However, they are not evenly distributed  Contractile properties o Twitch: the basic contractile property of a motor unit o Tetanus  Muscle fiber types o Three types of muscle fibers based on myosin ATPase activity  Type I (slow twitch)  Type IIa (fast twitch)  Type IIx (fast twitch) o Beneficial for soleus, a lower limb muscle, to have 80% type I fibers  We use it all of the time.  Do not want it to fatigue quickly o Beneficial for orbicularis oculi (a muscle in the eye) to have 15% type I fibers?  We need it to act quickly, for only a short period of time.  Motor units and muscle force o Activation of the motor unit pool is proportional to the synaptic input it receives  Synaptic input: chemical released that will either increase excitation or  decrease excitation (increase inhibition) o The change in muscle force that occurs during a voluntary contraction is  accomplished by the concurrent recruitment of motor units and variation of  discharge rate


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