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KIN365 Functional Aspects of Sensory Motor System

by: Jess Snider

KIN365 Functional Aspects of Sensory Motor System KIN 365

Marketplace > University of Alabama - Tuscaloosa > KIN 365 > KIN365 Functional Aspects of Sensory Motor System
Jess Snider

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Class notes on functional aspects of sensory motor system lecture
Applied Biomechanics
Colleen Geary
Class Notes
KIN365, sensory motor system
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This 11 page Class Notes was uploaded by Jess Snider on Tuesday February 16, 2016. The Class Notes belongs to KIN 365 at University of Alabama - Tuscaloosa taught by Colleen Geary in Spring2015. Since its upload, it has received 34 views.


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Date Created: 02/16/16
Functional Aspects of Sensory Motor System January 26, 2016  Fiber Composition of Motor Units  Motor Units  A motor nerve & all that it innervates or communicates with  Signals the contraction of muscle fibers if stimulus is adequate for each of the fibers  Action potential  To produce more force, the main method is to recruit more fibers to contract, i.e. Recruitment  Recruitment: increase the number of fibers innervated  The main muscular response used to produce greater muscle tension  The number of motor units responding (& number of muscle fibers contracting) within the muscle may vary significantly from relatively few to virtually all  Depends on  The number of muscle fibers within each activated motor unit  The number of motor units activated  All or none Principle:  Regardless of number, individual muscle fibers within a given motor unit will either fire & contract maximally or not at all  Fiber Composition of Muscles  ALL muscle fibers w/in one motor unit are the same type of muscle fiber  The Motor Nerve dictates what type of fiber (SO, FG, FOG) the particular motor unit is  The recruitment of fiber types usually occurs in a preferential manner according to the size of the motor never supplying the fibers  The smallest fibers are recruited first  The largest muscle fibers are recruited last  Fiber Composition of Motor Units  Can have motor units with a lot or with a few fibers  Very Precise:  Small motor unit  A small # of fibers controlled by one motor unit  Ex.: motor units that control eye movement  Less Precise:  Large motor unit  A large # of fibers controlled by one motor unit  Ex.: quad muscles can have some 500 fibers in motor unit  Players during Muscle Action/ Contraction: Muscle fibers  All muscle contractions/ actions are caused by muscle fibers  Two types of muscle fibers have been identified  Slow twitch  Fast twitch  Muscle Fibers: Types  Two types of muscle fibers  Slow twitch  Build & decrease tension slowly  Only one type of slow twitch muscle  Slow Oxidative (SO)  Fast Twitch  Build & decrease tension quickly  Two types of fast twitch  Fast Glycolytic (FG)  Fast Oxidative & Glycolytic (FOG)  Slow Oxidative (SO)  Fuel source: Oxidative Phosphorylation  Oxidative phosphorylation creates ATP through the electron transport chain  Requires Oxygen to create energy  Characteristics  Low strength of contraction  Low anaerobic capacity  Small in size  High capillary density  Highly resistant to fatigue  Use:  Activities that are done over a longer period of time but that don’t require a great deal of strength  EXs: running a marathon, hiking, walking, swimming long distances  Fast Oxidative & Glycolytic (FOG)  Energy source: Hybrid  Can use energy made fast without oxygen (anaerobic pathway)  Can use energy mad slowly with oxygen (aerobic pathway)  Characteristics:  High speed & strength of contraction  Can use energy made aerobically & anaerobically  Intermediate sized fibers  High capillary density  Fatigability varies  More fatigable than SO  Not as fatigable as FG  Uses:  Depends on energy source  Fast Glycolytic (FG)  Fuel source: Glycolysis  Glycolysis: energy pathway with 12 steps that gives off a lot of ATP quickly but also runs out quickly  No oxygen required to create energy  Characteristics:  High speed & strength of contraction  High anaerobic capacity  Largest of the three types of muscle fibers  Low capillary density  Low aerobic capacity  Most easily fatigable  Uses:  Activities that are forceful & quick  Ex.: sprints, grabbing kid from in front of bus  Fiber Composition & Training  Cannot change fiber composition  Fast twitch fibers to slow twitch fibers  Slow twitch fibers to fast twitch fibers  Can change fiber composition of  Fast glycolytic fibers into fast oxidative & glycolytic fibers  Fast oxidative & glycolytic fibers into fast glycolytic fibers  Possible because all with in the fast twitch category  The aerobic capacity & glycogen content of the muscle can be improved with training  Done through specific training  Ex. with distance training  Produce shift from FG to FOG fibers  Ex. with weight training  Produce shift from FOG to FG fibers  Selective Recruitment of Fiber Types  Neurons tend to recruit smaller fiber types then larger fiber types  Remember:  Smallest output of force  Slow oxidative (smallest)  Fast Oxidative & Glycolytic (slightly larger)  Fast Glycolytic (largest)  Largest output of force  Factors Affecting Muscle Tension Development  If summation/ tetanus is reached, the force of the muscle contraction of fiber will increase accordingly, because of increased calcium available & a muscle contraction will occur  Two types of muscle contraction  Isometric: no movement (i.e. like doing a plank)  Isotonic: movement  Type of Muscles Actions  Contractions: when tension is developed in a muscle as a result of a stimulus  Muscle “contraction” term may be confusing, because in some contractions the muscle does not shorten in length  As a result, it has become increasingly common to refer to the various types of muscle contractions as muscle actions/ joint actions instead  Type of Contractions, aka: Muscle Actions  Muscle contractions/actions can be used to cause, control, or prevent joint movement or  To initiate or accelerate movement of a body segment  To slow down or decelerate movement of a body segment  To prevent movement of a body segment by external forces  All muscle contractions/actions are either isometric or isotonic  Types of Muscle Actions  Isometric contraction/action  Active tension is developed within muscle but joint angles remain constant  Static contractions that prevent motion  Significant amount of tension may be developed in muscle to maintain joint angle in relatively static or stable position  May be used to prevent a body segment from being moved by external forces  Isotonic contractions/actions  Involve muscle developing active tension to either cause or control joint movement  Dynamic contractions  The varying degrees of tension in muscles result in joint angles changing  Isotonic contractions are either concentric or eccentric on basis of whether shortening or lengthening occurs  Players during Muscle Action/Contraction: Proprioceptors  Proprioceptors  Are mechanism by which the body is able to regulate body position & movement by responding to stimuli subconsciously & sending that information back to brain  These internal receptors are located:  In the skin  In the inner ear  In & around the joint, muscles, & tendons  Proprioceptors  Respond to changes in position & acceleration of body segments  Provide feedback relative to the:  The position of the body & limbs  Movement of joint  Multiple types of proprioceptors  Two stimulated during muscle actions/contraction called: musculotendinous receptors  Musculotendinous Receptors  Musculotendinous Receptors  Used in muscular control & coordination  Provide feedback relative to the movements of the joint, specifically:  Tension within muscles  Length of muscles  Rate-of-change in length of muscles  Contraction state of muscles  Two types of musculotendinous receptors:  Golgi Tendon Organs(GTO)  Muscle Spindal  Musculotendinous Receptors: Golgi Tendon Organs  Located in the tendons  Sensitive to tension development in tendons  Due primarily to:  Muscle contraction  Passive stretch of tendon  Golgi Tendon keeps muscle from excessively contracting by  Inhibiting the motor nerve (protective effect)  Tension in tendons & GTO increases as muscle contractions, activating GTO  GTO stretch threshold is reached  Impulse sent to CNS  CNS sends signal to muscle to relax  Facilitates activation of antagonist as a protective mechanism  Signals  Afferent signals sent up spinal cord in response to excessive contraction or passive stretch of tendons  Responding efferent signal has two purposes:  Inhibition (relaxation) of the contraction of the associate muscle (agonist)  Excitation (contraction) of the opposing muscle, the associated muscles’ antagonist  I.e. when the Golgi Tendon signals fire, the result is  Inhibition/relaxation of the agonist (working muscle)  Excitation/contraction of the antagonist(associated muscle)  Example:  A weight lifter attempting an extremely heavy resistance in biceps curl  Lifter reaches a point of extreme overload  GTO activated  Biceps suddenly relaxes/triceps suddenly contract  Appears as if lifter throwing weight down  Really GTO has caused inhibition of biceps & contraction of triceps  Musculotendinous Receptors: Muscle Spindal  Located in muscles between the fibers  Sensitive to  Degree if muscle strength  Rate of muscle stretch  As you stretch a muscle  Stretch of muscle spindals  Causes excites sensory nerves to sends signal up spinal cord  CNS sends motor signal to cause a reflexive contraction of the associated muscle(agonist contracts) occurs  Called: Myotatic or Stretch Reflex  Signals  Afferent signal sent up spinal cord in response to excessive stretch or rapid stretch  Efferent sent in response to “stretch” has two purposes  Excitation & contraction of the associated muscle(agonist)  Inhibition & relaxation of the associated muscles’ antagonist  Antagonist prevented from contracting  I.e. when muscle spindal signals fire, the result is  Contraction of the agonist (working muscle)  Inhibition/relaxation of the antagonist(opposing muscle)  Examples:  Patellar tendon reflex  Sudden tap on patellar tendon causes quick stretch of musculotendinous units of quads  Quick quad stretch activates muscle spindal  Info sent to CNS to quickly contract quads  Cause knee jerk  Musculotendinous Receptors: Reciprocal Inhibition  Two things can happen when muscle contracts:  Sensory nerve excites agonist & inhibits antagonist  Caused by: Muscle Spindal  Sensory nerves excites antagonist & inhibit agonist  Caused by: Golgi Tendon organs  Either one occurring is called: Reciprocal Inhibition  Players during Muscle Action/ Contraction: Fiber Length  Another factor that affects the contraction of the muscle is the length of the muscle fiber before it is stimulated  This length before stimulation & subsequent tetanic tension development is called the length-tension relationship  For each muscle, an optimal length exists for developing tetanic tension (maximal tension development during the contraction)  This is optimal length corresponding with maximum overlap of thick myosin filament & thin actin filament  I.e. development of tension optimized when maximal number of active actin sites are available for attachment of myosin cross bridges  If a sarcomere is stretched beyond its optimal length, force output steadily declines  Decline occurs because thin filaments pulled away from thick filaments preventing myosin heads from binding to active sites  If a sarcomere is not stretched to its optimal length, force output is virtually zero  Lack of force production is due to actin sites being blocked by previously attached myosin heads physically preventing new myosin cross-bridge from binding  Therefore, the theoretical optimal length of an intact muscle corresponds to muscle’s resting length  HOWEVER….  The elastic force contributed by elastic components changes this optimal length for optimal force production  Elastic Components  Optimal resting length without series of components but because of passive tension developed during motion, elastic components allow for greater tension as the muscle lengthens or passively stretches  Elastic structures  Non-contractile components of muscle  Lay parallel to or in series with the contractile elements w/in muscles & tendons  These non-contractile muscle tissues stretched passively  Rather than by muscle contraction  Note:  These muscle tissues are NOT stretched by muscle contraction; rather, they are stretched passively  Tension between them prevents muscles damage that could occur from external stretching forces  Two types of elastic structures found w/in musclotendon unit  Parallel elastic component  Series elastic component  Series Elastic Component  Passive elasticity derived from: tendons  The elastic component that lies ins series (in line) with the tendons and the contractile structures (actin & myosin and their cross-bridges)  Provides resistive tension when muscles is passively stretched  If stretched, will spring (recoil) back  Example: Box Jumping in Plyometric Training  This is an example of an eccentric contraction followed immediately by a concentric contraction  Players during Muscle Action/Contraction: Length –Tension Relationship of Muscle Summary  Maximal ability of a muscle to develop tension & exert force varies depending upon:  The length of the muscle during contraction  The relationship between muscle length & muscle tension, at time muscle is stimulated to contract is as follows:  Shorter muscle=less tension  Longer muscle= more tension  But if muscle is too long  If don’t stretch beyond 70%-80% of resting length  =ability to develop contractile tension and exert force is essentially reduced to zero  If stretched beyond 120% -130% of resting length  =significant decrease in the amount of tension a muscle can develop & amount of force a muscle can exert  Generate greatest amount of tension can be developed when a muscle is stretched between 70%-80% and 120%-130% of its resting level  Without elastic component/connective tissue  Get most tension out of muscle @ resting length  … in real life  With elastic component/ connective tissue  Generate greatest amount of tension can be developed when a muscle is stretched between 120%-130% of its resting level  Players during muscle action/contraction: muscle articulation-biauriculate disadvantage  Active & passive insufficiencies  Cannot contract (active) the same amount of muscle tension or stretch (passive) with the same amount of flexibility across two joints at the same time  NOTE: active & passive insufficiencies ONLY applies to 2 joint muscles  NO insufficient with one joint muscle  Two types: active insufficiency  Passive insufficiency  Active insufficiency  Point reached when muscle becomes shortened to point it can no longer generate/maintain active tension  Ex: Hamstring Muscle  If shorten/contract across one joint, ex: Hip  Cannot keep shortening (contracting) across other joint: Knee  I.e. muscle can only shorten/contract so much  Passive Insufficiency  State reached with a muscle becomes stretched to point where it can no longer lengthen & allow movement  Ex: Hamstring Muscle  If lengthen across one joint, ex: Hip  Cannot keep lengthening (stretching) across another joint: Knee  I.e. muscle can only lengthen/stretch so far  Players during Muscle Action/ Contraction: Force-Velocity Relationship  Final player affecting force production during muscle action is: velocity of the contraction  Called the Force-Velocity Relationship: the greater the load against which a muscle must contract, the lower the velocity of that contraction will be  Players during Muscle Action/ Contraction: Force-Velocity Relationship: Angle of Pull  @ 90 degrees= 100% of muscle force contributes to movement of the bones  Muscle is strongest at 90 degree  Muscle is weaker @ either end of 90 degree  But most actions do not require you to hold muscle at 90 degree, so what happens to force production during different types of muscle contractions  Players during Muscle Action/ Contraction: Muscle Tension  One of two situations occurs when tension is produced in a muscle:  A segment moves  A segment does not move  Two types of tension  Dynamic tension(isotonic contraction)  Static tension (isometric contraction)  Dynamic tension (isotonic contraction)  When the segment moves in the direction or opposite to the direction of applied muscular tension  Two types  Concentric tension  Contraction of a muscle during which the muscle shortens & causes movement towards the midline of the body  Ex: up movement of push-u[ for triceps  Ex: down movement of push-ups for biceps  Eccentric tension  Contraction of a muscle during which the muscle lengthens & causes movement away from the midline of the body  Ex: down the movement of push-ups for triceps  Ex: up movement of push-up for biceps  Static tension(isometric contraction)  When a muscle produces tension or force against an opposing force or resistance & the segment of muscle does not move  Only one type of static tension  Isometric tension  Muscular contraction during which no discernible segmental movement is taking place  I.e. muscles develop tension with no visible change in muscle length  Ex: plank; wall squats  Ex: arm wrestling someone with exactly equal strength  Players during Muscle Action/ Contraction: Force-Velocity Relationship  A muscle can adjust the force of its contraction to match the resistance that it experiences during a contraction, at the cost of the speed of the contraction  The greater the load against which a muscle must contract, the lower the velocity of that contraction (fig. 11.20 pg. 323 in hardback)  The amount of force exerted then depends on the length of time the muscle has to contract= force-velocity relationship  Concentric (isotonic) contractions  Slower speed (velocity) of concentric contraction- more force  Faster speed (velocity) of concentric contraction- least force  Probably due to:  High metabolic cost  Faster the contraction= fewer cross-bridge interactions (inability of some myosin cross-bridges to bind with actin sites)= the loss of force production  Static (isometric) contraction  Because static contraction occurs without muscle movement- velocity is not an issue  Static contraction= more force than nay concentric contraction  I.e. static contraction can develop more force than even the slowest concentric contraction  Probably due to:  Maximal cross-bridge interaction= maximum force output  Myosin cross-bridges, without time constraints, attach freely to active actin sites  Eccentric (isotonic) contraction  Slower eccentric contraction-not as much force…  Faster eccentric contraction- more force (*up to a certain point where maximal force production reached)  Note: eccentric contractions, no matter the velocity, can develop more force than ANY velocity concentric contractions & even more than static contractions  Possibly due to:  Low metabolic cost  Elastic (series/parallels) component assistance  Some cross-bridges remaining bound, increasing total # of active cross-bridges  Summary:  Amount of force generates listed from least to greatest:  Faster Concentric Contraction  Slower Concentric Contraction  Static/Isometric Contraction  Slower Eccentric Contraction  Faster Eccentric Contraction  *up to a point at which force production levels off  Players during Muscle Action/Contraction: Force-Velocity Relationship: Muscle Power  Due to force-velocity relationship, get maximum amount of force generation @ approx. 30% of maximal contraction velocity  Beyond -30% of maximal velocity, force production decrease with increasing velocity  =slow down amount of time spent on contraction (velocity of shortening) with any amount of force in order to produce greatest amount of power


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