KIN 461 Week 4
KIN 461 Week 4 KIN 461-401
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This 5 page Class Notes was uploaded by Tanski Notetaker on Saturday February 20, 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 17 views. For similar materials see Principles of Motor Learning in Kinesiology at University of Wisconsin - Milwaukee.
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Date Created: 02/20/16
Week 4 Tanski 1 Motor Units and EMG (cont.) Some terminology Recruitment threshold: force at which a motor unit becomes active Orderly recruitment: recruiting motor units according to size o Advantage: simplifies the task o Disadvantages: can’t immediately generate great amount of force Derecruitment: motor unit that is active stops being active Rate coding: modulating firing rate (or discharge rate) Interspike interval: time between two spikes o The larger it is, the lower the discharge rate Double discharges: motor neuron firing twice in 10 milliseconds o Ramp up force quickly Motor unit synchronization: idea that there is shared activity across motor units o Piano players have low motor unit synchronization because need small, precise movements o Olympic weight lifters have high motor unit synchronization Common drive: waves of period excitation in motor unit pool o Increase in common drive can cause tremors EMG One of the few techniques available to examine the neuromuscular system in humans performing voluntary contractions Also able to monitor the response of the neuromuscular system to electrical stimulation The image below is of electrical stimulation. You can calculate EMG amplitude by drawing an outline around the rectified EMG o Called a filtered EMG o Image below Week 4 Tanski 2 EMG issues o Varies from muscle to muscle o Extracellular, not intracellular recordings o Influenced by many different factors o Amplitude cancellation: when positive and negative signals cancel each other out o Location on muscle (e.g. innervation zone) o Filtering (e.g. movement noise, 60 hz. Noise) o Cross talk EMG during electricallyevoked contractions o Test the integrity of the motor system o EMG is more reliable measure of muscle activity during isometric contraction Spinal Reflexes Every movement requires coordinated action of many muscles Motor coordination: process of linking the contractions of independent muscles so that they act together Reflex is the most elementary form of motor coordination o Relatively stereotyped response to a specific sensory stimulus o 2 important features of a stimulus Locus of the stimulus Determines which muscls will contract to produce reflex response Strength Determines amplitude of response o Increased strength = greater amplitude Reflexes are graded in intensity Week 4 Tanski 3 Neural circuitry responsible for a reflex is located within spinal cord Spinal reflexes have essential role in all voluntary movement Importance clinically o Absent or weak reflex: Muscle spindle, Ia afferent axon, motor neuron, motor efferent axon, or muscle o Hyperactive (e.g., spasticity, rigidity) Central lesions Most spinal reflexes are polysynaptic one or more interneurons are interposed between sensory and motor neurons Stretch Reflex Stretch reflex is monosynaptic it’s produced by a twoneuron circuit consisting of a single set of synaptic connections o KNOW HOW TO DRAW MONOSYNAPTIC STRETCH REFLEX Reciprocal innervation: causes excitation of the motor neurons to the stretch muscles (synergist muscles) and inhibition of motor neurons to the antagonist muscles o Role of Ia inhibitory interneurons Synergist muscles control the same joint and have a similar mechanic action Negative feedback: circuitry of stretch reflex acts as a loop to resist changes in muscle length Stretch reflexes regulate muscle tone o Muscle tone: the fore with which a muscle resists being lengthened Serves important functions Assists in maintaining posture Allows muscles to store energy, like springs, and release it later Springlike qualities of muscles help to smooth movements Spinal Reflexes in General Week 4 Tanski 4 Spinal reflexes are governed by 3 main levels of control o Control of individual muscles o Coordination of muscle action around a single joint o Coordination of muscle at several joints Muscle action around a joint is coordination by inhibitory interneurons o Prevents muscles from acting independently of each other o Group Ia inhibitory interneurons inhibit antagonist muscles. Mediate reciprocal inhibition through excitatory inputs from the muscle spindle afferents This way high motor centers do not need to send separate commands to opposing muscles Limits cocontraction, which is contraction of both prime mover and antagonist muscles simultaneously o Group Ib inhibitory interneuron inhibits homonymous motor neurons Receives input from Golgi tendon organs Provides negative feedback mechanism for regulating muscle tension Signaled by an increase in in Golgi tendon organs Inhibits the homonymous motor neurons = decreases muscle tension Protective mechanism Crossed extension reflex: flexion of stimulated limb produced opposite effect in contralateral limb o Enhances postural support o What happens when you step on something sharp Nociceptor: pain receptor Excite flexors while inhibiting extensor in leg you are trying to pick up Crossed extension reflex excites the extensors in the opposite leg to maintain posture Certain reflexes consist of rhythmic movements o Ex: scratch reflex which is not seen in humans Main features of walking movements are controlled by the spinal cord o Central Pattern Generators (CPGS) Local spinal circuits that coordinate the contraction of the several muscle groups needed to generate rhythmic stepping Simplifies the control of locomotion Voluntary Movement Voluntary Movement o Primary motor cortex o Premotor cortical areas o Cerebellum o Basal Ganglia Neurons in the primary motor cortex encode force an direction Movement direction is encoded by population of cortical neurons Week 4 Tanski 5 Neurons in premotor cortical areas prepare the motor system for movement o Activity of neurons in supplemental motor area is linked to planning of movements Neurons in the cerebellum regulate movement indirectly and participate in motor learning o Coordination and motor adaptation Premotor cortical areas prepare Basal ganglia processes information needed for triggering selfinitiated movement
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