KIN 461 Exam 1 Study Guide
KIN 461 Exam 1 Study Guide KIN 461-401
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This 10 page Study Guide was uploaded by Tanski Notetaker on Saturday February 20, 2016. The Study Guide belongs to KIN 461-401 at University of Wisconsin - Milwaukee taught by Dr. Peterson in Spring 2016. Since its upload, it has received 103 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
Exam 1 Study Guide 1 Exam 1 Study Guide Introduction to Movement sensory systems: transform physical energy into neural signals motor systems: translate neural signals into contractile force in muscles to produce movement The Psychophysics of Movement o Motor processing begins with an internal representation/ an image of the desired result of movement Constructs behaviors or major acts by assembling and coordinating elementary motor components o Motor equivalence: the same result can be accomplished in different ways by the motor system Example: writing a sentence with left hand, right hand, or feet will still produce the same sentence, even if it looks different o 4 attributes of a stimulus Quality (or modality) Intensity: signaled by the firing rate and the recruitment of motor neurons Location Duration Motor system generate 3 types of movement o Reflex Responses (e.g. knee jerk or swallowing) simplest motor behaviors rapid, stereotyped involuntary responses controlled by the eliciting stimulus o Rhythmic Motor Patterns (e.g. walking, running, chewing) Combine features of voluntary and reflex acts Only initiation and termination are voluntary Once initiated, relatively stereotyped and repetitive CPGs (central pattern generators: networks of motor neurons) in locomotion o Voluntary Movements (e.g. driving a car or play the piano) Most complex Purposeful (goal directed) Learned – less conscious with practice Motor system has 4 tasks o Controlling contraction of individual muscles o Convey commands to many muscle groups o Take into account the distribution of body mass and plan postural adjustments o Take into account the motor plant; mechanical properties of muscles, bones and joints Exam 1 Study Guide 2 Adjust commands to compensate for inertia of limbs and the mechanical arrangement of the muscles, bones and joint prior to the movement Motor systems organized into 3 control levels: o Spinal cord Contains neural circuits that mediate variety of automatic and stereotyped motor patterns and reflexes Final common pathway: control signals ultimately converge on motor neurons that innervate skeletal muscles Final path to muscles Sir Charles Sherrington Contains the cell bodies of motor neurons in the ventral horns Motor neuron pools: clusters of individual motor neurons that innervate individual muscles Proximaldistal rule: motor neurons innervating the most proximal muscles are located most medially Flexorextensor rule: motor neurons innervating extensor muscles lie ventral to those innervating flexor muscles o Brain stem Has its own motor neurons axons project to and regulate networks of spinal cord interneurons and motor neurons necessary for behavioral acts important for controlling posture and balance o Motor areas of the cerebral cortex Consists of 3 areas: Sensory cortex Primary motor cortex Secondary motor area Corticospinal tract: can even control neurons in the limbs Right hand is controlled by left side of cerebral cortex Somatotopically organized: different areas control different parts of the body (hands and mouth area have the greatest area) Muscles and Muscle Receptors Controlled contraction of muscles allows us to: o Move our limbs o Maintain posture o Perform tasks with great precision Force produced in contraction results in change of length of muscle o Dependent on 3 factors: The initial length Velocity of length change External loads acting to oppose movement Exam 1 Study Guide 3 Proprioceptive information: information about length of muscles and the forces they generate o Monitored by 2 types of receptors: Muscle spindles Golgi tendon organs o Information from these sensory receptors reaches all levels of nervous system Cerebral cortex uses it for perception of limb position and controlling voluntary movement Lower levels use it to control reflexes Motor Unit: consists of a single motor neuron and the muscle fibers it innervates o All or nonresponse: all fibers innervated contract in response to an action potential in the neuron the smallest functional unit within motor systems Innervation ratio: # of muscle fibers innervated by one motor neuron o Varies among muscles o About proportion to size of muscle o Small innervation ratio=finer grading of the muscle’s total force by the nervous system o In hand muscles ratio is ~100 o In larger gastrocnemius ratio is ~2,000 Nervous system grades force of muscle contraction by: o Recruitment: vary # of motor units activated Increase # of motor units activated = increase in force whole muscle will produce o Rate modulation: vary rate of action potentials in a motor neuron Forcefrequency relationship: increase firing rate in neuron = increase in force motor unit will produce Allows forces of successive twitches to summate Forces produced by each twitch add until a plateau of force, tetanus, is reached Unfused tetanus: individual twitches can be detected o Produces ripple in contractile force of isolated muscle Fused tetanus: individual twitches can no longer be detected o Rate of AP increases and force produced by muscle increases to steady max value 3 types of motor units o Fast fatigable Muscle fibers contract and relax rapidly Fatigue rapidly when stimulated repeatedly Generate greatest force during a twitch or tetanic contraction Motor neurons have largest cell bodies out of the three types o Slow fatigueresistant Exam 1 Study Guide 4 Fibers have much longer contraction time High resistance to fatigue Generate only 110% of force of fastfatigable Motor neurons have smallest cell bodies out of the three o Fast fatigueresistant Contraction time slightly slower than fast fatigable Almost as resistant to fatigue as slow fatigueresistant fibers Able to produce twice as much force as slow fatigueresistant Size principle: when motor neuron pool is activated synaptically, the initial weak inputs activate the cells with the lowest threshold for synaptic activation (those with smallest cell bodies o As synaptic input increases in strength, motor neurons with larger cell bodies are recruited according to size or strength o Has 2 important functional advantages: Simplifies task of regulating muscle force Slow motor units most heavily used Energy efficient Sensory Receptors Muscle spindles o Sensitive to stretch o Innervated by 2 types of myelinated afferent fibers: Group Ia Group II o Intrafusal muscle fibers of the spindle: Smaller than skeletal (extrafusal) muscle fibers Don’t contribute significant force to muscle contraction Changes in their lengths sensed by the sensory terminals in the intrafusal fibers 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 Exam 1 Study Guide 5 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, so entire muscle spindle does not slacken This increases firing rate of sensory endings Makes afferent ending more sensitive to stretch in muscle spindles 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 (associated with slow fatigueresistant motor unit) Type IIa (associated with fast fatigue resistant motor unit) Type IIx (associated with fast fatigable motor unit) Exam 1 Study Guide 6 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 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. Exam 1 Study Guide 7 You can calculate EMG amplitude by drawing an outline around the rectified EMG o Called a filtered EMG o Image below 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 Exam 1 Study Guide 8 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 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 Exam 1 Study Guide 9 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 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 Exam 1 Study Guide 10 Demonstrates how strength of stimulus determines amplitude of response 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 o Movement direction is encoded by population of cortical neurons 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 Basal ganglia proce information needed for triggering selfinitiated movement
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