KIN365 Functional Aspects of Sensory Motor System
KIN365 Functional Aspects of Sensory Motor System KIN 365
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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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