Ch. 3 Study Guide PDF

3.1 Neurophysiology Movement occurs through biomechanical responses to neurological inputs -this is why there must be an integration of systems w/in any movements that occurs Afferent neurons are sensory neurons Efferent neurons are motor neurons Resting membrane potential -cell membrane has an exce...

3.1 Neurophysiology Movement occurs through biomechanical responses to neurological inputs -this is why there must be an integration of systems w/in any movements that occurs Afferent neurons are sensory neurons Efferent neurons are motor neurons Resting membrane potential -cell membrane has an excess of potassium ions inside of the cell—designated as K+ -an excess of sodium ions outside of the cell—designated by NA+ At rest leaky channels allow for passive diffusion of NA+ and K+ into and out of the cell -most channels are more permeable to K+, so it is more prevalently diffused across the membrane -permeability of K+ at rest is 100x more than NA+ -in order to keep resting membrane potential at ~-70 millivolts, a sodium potassium pump has to transport 3 NA+ molecules out and 2 K+ molecules back into the cell -if too much potassium leaves the cell, then the inside will become too negative since K+ is positively charged Action Potential -to propagate an action potential, dendrites of a neuron pickup signals from adjacent cells — this is the postsynaptic neuron ↓ -soma or cell body of neuron then collects the information from the action potential and sends it down the axon, if the stimulus is strong enough A fiber- if nerve cell is myelinated, which is an efferent fiber or motor neuron B fiber- afferent fiber or sensory neuron C fibers- unmyelinated fibers C fibers are the “wait for it” fibers ex: when you hit your arm and it doesn’t hurt right away but then hurts bad after a couple seconds -bc they’re unmylinated it takes longer to reach destination Node of Ronvier -action potential gets refueled ↓ Voltage gate Na channels open and Na flows into the cell- down it’s concentration gradient ↓ Once a specific threshold is reached, cells become depolarized -meaning that if there is sufficient amount of stimulus to reach the threshold, the action potential will proceed Note: if it does not reach threshold, then it stops Repolarization will happen once cell is depolarized and the nerves potential of Na or plateau occur, then the Na channel close quickly while the K channels open • since K channels close slower, there ends up being a moment of hyperpolarization, where another action potential is not generated —this is called refractory period -once k channels close fully and the cell nears resting membrane then threshold, another action potential is then generated and the process continues to the next node -stimulus then travels from one node of ranvier to the next and so on —this is saltatory conduction -once it has reached the end of the axons, the axons terminals stimulate the release to neurotransmitters -neurotransmitters then relay the same message to another nerve cell and continue the action potentials -they relay from one neuron to the next- called a synapse WHITE MATTER upper motor neurons, are housed w/in the white matter of the cerebral cortex and SC -white matter synapse onto the lower motor neuronsSummary: -saltatory conduction is propagated by myelin surrounding the axon of the neuron -action potentials occur when a stimulus reaches threshold -at this time, Na rapidly floods the cell until it is saturated w/in the cell according the Nernst equation -THEN at this point, slow K channels open and K slowly diffuses out to regain the negative charge inside the cell -hyperpolarization or a refractory period then occurs due to slowly closing K channels -action potential then propagates over and over again and reaches a new neuron to send the signal down the chain 3.2 Muscle Physiology skeletal muscle develops tension based off • chemical stim • electrical stim • mechanical stim muscle components myofilament -> myofibril -> muscle fiber -> muscle fasciculus -> muscle main contractile • unit of muscle • contains • sarcomere • Z lines (2) • H zone • I bands • A bands muscle contraction what is the absolute first step of muscle contraction? • nerve impulse creating an AP what two structures causes contraction • actin: thin • myosin: thicker sliding filament theory At rest: cross bridges are perpendicular b/w actin & myosin (most potential for cross bridges!) no contact yet coupling: action potential caused, crossbridges link actin & myosin contraction: actin filament pulled along myosin myofilament (power stroke) recharge: linkage of cross bridge broken only continues if ATP available or calcium available (bc of troponin) muscle fibers type 1: slow twitch, low force, fatigue resistant ex: LD running, postural muscles type 2: high force production, large amt of force, fatigue quickly ex: sprints, quick initial burst type 2A: more moderate, oxidative (400m/800m sprints) type 2B: super short distances & high intensities, glycolytic ex: short sprints note: adaptations occur w/ changing demands @ birth: type 11 fibers ex: quick movements of baby 2 y/o: type 1 greater ex: sitting up right/posture on a continum 3.3 physiology to Fxnal Movement Motor unit a motor neuron and all the fibers that it innervates amount of control that a muscle needs depends on the # of motor units, & the # of muscle fibers • associated w those motor units Ex: intricate muscles of fibers or face may have less muscle fibers to nerve fiber ratios devoted to them in order for the movements to be precise -the quads and hamstrings however do not need to have as much control as the movements are not needed to be as precise -in order to grade certain muscle contractions, a subconscious neurophysiological order or sequence is adapted Henneman’s size principle there the smallest motor units are activated first -tend to innervate type 1 slow twitch fibers, which are fatigue resistance -also produce less force, as they are known for integrating the smaller vessels -each time a motor unit is stimulated, it creates a single twitch of the muscle fiber In order to create increased muscle, multiple twitches must build on each other to create a tetanic contraction (tentany) 2 other ways motor unit recruitment can grade a muscle contraction 1. When multiple motor units are activating simultaneously -when each of the motor units produce an action potentional, the summation of those action potentials created a stronger stimulus to the motor end plates, therefore increasing tension 2. Rate coding in motor unit recruitment if a single motor unit increases the frequency of the stimulation Note: Golgi tendon organs are located in series within the tendon of an adjacent muscle -they act to modulate muscle force or tension of agonist muscle Muscle fibers - Intrafusal muscle fibers: if muscle fibers are wound inside coil considered nuclear chain or bag fibers - Extrafusal: surrounding muscle fibers parallel to muscle fibers, lack nerve coils Nuclear chain: (chain fibers) have the cell nuclei in a line, forming a chain Bag fibers: contain nuclei that come together centrally Muscle spindles also have 2 kinds of sensory nerve endings 1. Type 1A 2. Type 2 Type 1A- coiled around the center of each of the intrafusal fibers provide both phasic and tonic information Type 2: found at the end of each spindle provide tonic signals Both detect changes in length -constant modification of muscle tension made by muscle spindles contribute to the way in which we move functionally Proprioceptors contribute postural tone -is the appropriate development of muscle tension to hold the body against gravity Ex: baby holding head up for the first time or holding ourselves erect for ambulation Hypotonic individuals who have a lower tone then is necessary to hold body against gravity Hypertonic individuals who have high muscle tone -might see after a neurological injury -proprioceptors also contribute to other characteristics, the ability to detect dynamic joint motion or kinesthesia and the ability to detect one’s static position in space (proprioception) Kinesthetic system responses of the GTO and muscle spindles -provide our body w a sense of normal muscle tone and dynamic and static position sense Vestibular + visual system work together to maintain equilibrium and balance -if one system goes out the other two care over Summary -Motor recruitment is graded through 3 mechanics 1. The henneman’s size principle firing smaller motor units 2. Larger, two sychronicity of motor unit firing, where multiple motor units fire on the muscle fiber to increase tension -w/in the muscle itself and the tendon, there are 2 different organs that help to grade muscle tension -GTO responds to muscle tension and supplies an inhibitory effect on the agonist -while muscle spindle responds to muscle length changes or stretch, and supplies an excitatory effect on the agonist muscle -both of these organs contribute to proprioception and kinesthesia, which fxn as the kinesthetic system -vestibular and visual system then work w the kinesthetic system to maintain the body’s equilibrium and balance 3.4 Muscle Activation Tools to measure muscle activation Electromyography (EMG): fine needle inserted into muscle (smaller muscles) or electrode adhered to muscle measures neurophysiological processes involved in muscle tension • info on motor unit activation/ muscle activation • asses muscle activation changes/ diagnostic • does NOT measure force production types of contraction isometric contraction: no change in jt angle (balance b/w external & internal torque produced) • allow static or non moving contraction • control type movements isotonic: constant shortening of muscle through limb excursion in detached muscle concentric: muscle shortening • internal torque outweighs external force • origin & insertion move closer ex: bringing arm to scratch face • biceps/brachioradialis concentric contraction eccentric: lengthening • external forces of hand/gravity winning • origin & insertion move further apart bc gravity doing the work • greater force output than in concentric or isometric ex: stroke patient trying to maintain arm flexión as it slowly falls down isokinetic contraction: contract at constant rate or speed same amt of external resistance applied through entire ROM • ex: need machine to determine note: how to produce greater force • combination of average force per cross bridge linkage or rapid reattachment phase with cross bridge • passive tension produced by visceoelastic properties case study: pt 2 days post TK replacement what contractions at this point? • know in inflammatory stage • rubor • dolor • calor don’t want to have max force output concentric or isometric bc want to limit movements due to inflammation case study: 3 months post ACL reconstruction, chronic stage of healing, return to sport, previously active bc return to sport increased force production eccentric & mix other two depending on goals EMG Reading motor recruitment/muscle activation ex: bicep curl concentric contractions: need more motor units wave form amplitude: burst & high • eccentric contractions: less motor units • ex: lowering bicep curl wave form amplitude: smaller note: cannot directly compare force production w/ motor unit activation why EMG • accurately compare across muscle groups & people math: % of Maximal Voluntary Isometric Contraction %MVIC = Value from test contraction (volts) Value obtained from MVIC (Volts) ex: %MVIC = 0.005 V 0.1 V x 100% X100% = 5% summary • EMG measures muscle activation • Isometric, concentric & eccentric contractions occur in body • Isokinetic contractions require outside resistance 3.5 Functional Activity of Muscles -Most often the antagonist passively moves the opposite direction to the agonist Synergist refers to muscles that are not the prime mover, but act in the same manner to assist in performing the activity act as helpers and stabilizers EMG measure muscle activity, not force -a neurological injury can create an imbalance to the harmony of agonist, antagonist and synergistic contractions, leafing to paradoxical contractions, such that the stretch reflex thresholds w/in agonist and antagonist muscles are impaired Summary: Agonists are muscles that the prime movers of the motion they can be working concentrically, eccentrically or isometrically depending on the task Antagonist- Passively lengthen in the opposite direction to the agonist to allow the motion to occur Synergist- work alongside the agonist in order to help produce the motion, whether it is actively participating, interfering with other competing movements or stabilizing 3.6 Muscle Characteristics creep: deformation of tissues over Muscles are meant to handle stress • adapt to forces • if can’t adapt injury occurs time when subjected to constant suddenly applied load • ex: everyday stress on neck extensors, looking at phone force constant, length changes ex: looking down, creep extensors viscoelasticity: resistance to external forces that cause permanent deformation • inhibits muscle from reacting too quickly ex: lifting a heavy load this slows the contraction elasticity/extensibility: succumb elongating force & return to normal length when released ex: rubber band strain: amount of deformation structure can sustain before succumb to distress ex: stretch a rubber band so far it doesn’t go back/ spaghetti stretching? stress strain relationship 1. graph of ligament tension or tension stretch to point of failure rubber band still returns 2. toe region: small stress w/crinkle 3. linear region: stiffness 4. elastic region micro damage to tissue 5. plastic region normal amt of strain warm up vs gain ROM elastic range b/c muscle return to OG length dynamic warm up to prevent injury plastic range passive stretching or static stretching w/ lil deformation 3.7 Muscle Anatomy Review Muscle force depends on size, fibers, passive components, length-tension relationships, moment arms, speed of contraction, active tension, age and gender For this lecture were only covering 4. 1. Size 2. Fibers 3. Passive components 4. Length tension-relationship Length of muscle longer muscles might provide more mobility, while shorter muscles provide more stability Hypertrophy increase in muscle size Atrophy decrease in muscle size -might see with a lack of exercise or inactivity Muscle size -use MRI is most accurate for cross section -muscle biopsy -circumferential measurements with the tape measure Muscle fibers comes in different architecture such as: Fusiform -a strap like muscle -fascicles are parallel and long -provides a greater shorter distance (meaning when the muscle short ends it is over a greater area) -produce less force Pennate -more feather like -attaches obliquely to the central tendon -short than the fusiform and produce great force Unipennate Bipennate one or more groups of parallel fibers Multipennate most common always has more than two pennate groups attaching to central tendon ex: deltoid Passive components Fascia surrounds the muscles and tendons—called a passive elastic component complies with muscle as it changes in length but is all passive Series Elastic Component if muscles surrounded by fascia and connective tissue, consider the tendon that is connected to the bone -allows the contracting muscle to produce movement Summary: Muscle size determines the amount of force it can produce Muscle architecture also provides either mobility or stability -there are passive components that provide stiffness to a muscle during stretch and allow the tenant to also produce force and movement 3.8 Length Tension resting length of a muscle: position in which there’s no tension within muscle • maximal # of actin & myosin cross bridge available • max force can be generated muscle lengthened • less cross bridges available -> less forces a: shortened muscle -> lowest tension -> no more crossbridges available b: can produce more tension bc some unoccupied crossbridges c: all crossbridges available (myosin attach to actin) d: no longer any overlap b/w actin & myosin = no potential for crossbridges, lowest tension take these with a grain of salt!! • no true in vivo study • jt prevent extreme ranges • passive structures provide tension beyond resting length 3.9 Speed and Velocity Speed defined as the rate of motion and is unrelated to direction -considered a scalar quantity -“basically how fast an object is going” Velocity is a vector where direction is a factor -changes in speed cause different contractile forces and vice versa depending on the type of contraction that is performed -for isometric contractions, no movement occurs, yielding a zero velocity contraction -concentric and eccentric contractions however, vary with contractile speed Concentric contractions produce less force output than eccentric contraction -force output though changes with respect to speed -reduced capacity of the muscle to generate force at higher velocities is due primarily to the limited ability for attachment and reattachment of cross-bridges linkages at higher speeds if velocity is fine, the myosin and actin are able to form the cross bridge linkage without a problem as velocity increases, the workers have trouble keeping up and therefore you don’t get quite as many myosin and actin cross bridge formation Power= f x v defined as the rate of work and is expressed by force output of the muscle multiplied by velocity -if we wanted to manipulate power of an intervention, we could either change the resistance of the external load applied to the muscle, which would then require an increase in force production or we could increase or decrease the contractile velocity If we want to make activities harder, we could add resistance or weight and maintain the same velocity, or we can maintain the same resistance and then just have the patient increase velocity of the contraction Note: positive work if the muscle is performing a concentric contraction or negative work if the muscle is performing an eccentric contraction C=+ E=Concentric contractions have inverse relationship, so as contraction velocity increases, muscle force production decreases and vice versa Eccentric contractions have a direct relationship, where increases in velocity create increases in contractile force 3.10 Work, Passive, Active Insufficiency work: object moves @ constant velocity over certain distance • force must be applied • object must move • move in same direction W = F x D positive & negative work positive work: max concentric contraction • shortening of the muscle negative work: maximum force production during an eccentric contraction • lengthening of the muscle active insufficiency: muscle at shortest length, ability to produce force is minimal A: weak grip bc of wrist flexion, finger flexors shortened B: good grip w/ slight wrist extension allowing finger flexors to contract passive insufficiency: muscle becomes elongated over 2 or more jts simultaneously • can’t achieve full ROM of each jt it crosses ex: hamstrings crossing both hip & knee, stretch may be limited when it comes to ROM • bend the knee to remove tension both: occur over multiple jts (but one at shortest one longest) Tenodesis: muscles that cross 2 joints or may produce passive movements of these jts ex: flex wrist fingers extend, extend wrist finger flex helpful for those who can’t