Muscle Physiology 2 PDF

SKELETAL MUSCLE FIBRE TYPES 1. Slow-oxidative (tupe 1) Slow-twitch fibres 3. 2 fast -oxidative (type 119) fast-twitch fibres. 3 fast-glycolytic (type 1IX)...

SKELETAL MUSCLE FIBRE TYPES 1. Slow-oxidative (tupe 1) Slow-twitch fibres 3. 2 fast -oxidative (type 119) fast-twitch fibres. 3 fast-glycolytic (type 1IX) * most skeletal muscles contain all 3 types of muscle fibres ; just diff. proportions CHARACTERISTICS OF SKELETAL MUSCLE FIBRES type I d type 11a : rely on O. P caerobic. pathways for ATP generation contains large" amts of mitochondria capillaries , & high myoglobin content cred) ↓ stores Or & releases it during muscle contraction type IIX : high amts of enzymes for anaerobic - glycolysis  COMPARING MUSCLE FIBRES 1. Slow vs fast fibres - higher myosin-Aipase activity > faster hydrolysis of ATP ; energy for cross bridge cucling available faster. Oxidative vs glycolytic fibres 2 oxidative fibres more resistant to fatigue than glycolytic fibres ~ able to produce more ATp for longer duration. Genetic endowment 3 % of each type of muscle fibre largely determined by genes & partly by activity muscle is engaged in MUSCLE ADAPTATIONS muscle fibres adapt in response to demands · tin oxidative capacity /aerobic endurance exercise muscle hypertrophy coverall muscle ; ↑in muscle fibre size canaerobic size ↑) >↑ cross-sectional area high intensity training & exercise training influence of testosterone ; promotes synthesis & assembly of active myosin muscle Growth  highintentiare interconversion btw fibre types ; type llas process of muscle proper exercise - hypertrophy CONTRACTION OF WHOLE MUSCLES tough , collagenous t issues 5 whole muscles bundles of muscle fibres attached to bones by tendons V allows small degree of passive elasticity ; able to withstand stress when stretched tension first produced internally within sarcomeres (pulling of actin filament by myosin) V as tension ↑ , tension transmitted to bone as tendon tightens V movement of bone LEVER SYSTEM moves level along fulcrum e point lever ; can move load at distance bones = levers ↳ where lever Pivots/turn joints = fulcrums force= provided by skeletal muscles * muscle contractions only PULL bones to create movement - amplification of velocity & distance (X7) Il ↑ agility insertion of muscle close to joint ; more force required to lift load (eg. 35 kg of force to lift 5 kg load) BUT velocityofloadfanterthan (munceycontracta m  PRIMARY TYPES OF CONTRACTION in normal human movement * used mostly 1. isotonic constant tension ; load remains constant as muscle length changes. isometric 2 constant length ; muscle length remains constant as tension + (crossbridges still form but filaments don't slide enough to shorten muscle) 3. isokinetic constant motion ; velocity remains constant as muscle fibres shorten ( not typical during normal human movement) other types of contraction : ! some skeletal muscles do not have insertion but can still produce movement leg tongue muscles). V concentrate ~ eccentric contraction 11 1 muscle cload lengthens muscle shortens muscle under load lengthens butmoin stilgeneratis under load EXERCISE-INDUCED MUSCLE DAMAGE eccentric exercises more likely to damage muscles leg. running downhill) tension exerted when muscle lengthens >ultrastructural damage Il sarcomere disruption, loss of 2 lines, thick & thin filaments become further apart fast-twitch fibres more susceptible dueto smaller sarcomeric proteins  LOAD-VELOCITY RIS opp for eccentric ; more challenging to lower load slowly e greater load> lower velocity fibre shortens at which muscle * lifting light vs heavy weight analogy muscles; 25 % external 75 % heat energy used by , work O load cannot be overcome by max tension , GRADED CONTRACTIONS Muscle contractions of varying strength due to : 1. no · of muscle fibres contracting 2. amt. of tension generated by each contracting fibre V 1 MOTOR UNIT RECRUITMENT motor neuron 1 motor unit : 1 motor neuron + all muscle fibres it innervates * more motor units (more muscle fibres) recruited = stronger contraction sequence of recruitment : during sustained · smallest to largest motor units muscle contraction : · least to most fatigable alt activation of motor. neurons ; allow Aip recovery V mostly mostin type I type 11  2 FACTORS INFLUENCING MUSCLE TENSION a) frequency of stimulation b) length of fibre at onset of contraction c) extent of fatigue d) thickness of fibre 29. FREQUENCY OF STIMULATION NO summation : if allow muscle fibre to completely relax , 2nd twitch will have same magnitude an 1 st twitch Twitch summation : fibre not completely relaxed before and Ap > 2nd twitch added onto 1st twitch higher tension level Tetanus rapid stimulation (multiple AP) < maximal sustained contraction of muscles (maximal tension level) M dueto : · sustained elevation in cytosolic Cart; drives continuous cross bridge cycling · more time to transmit tension ; allows build-up of tension  2b. LENGTH OF FIBRE AT ONSET OF CONTRACTION optimal muscle length (10) : max. no. of myosin cross bridge & & actin accessible for binding pulling D (too short) : undesirable overlapping, non-ideal mechanics for shortening In tension produced *C Bctoolong) unused cross bridges & : notension no overlapping ; generated actin In tension produced 2 c EXTENT OF FATIGUE. inability to maintain muscle tension at given level may be peripheral central fatigue : · exercising muscle no longer responds to stimulation w/ same degree of contractile CtPi of cast , ↓ activity , leakage glycogen) interfere V w/ power lesser energy Stroke available · inadequate activation of motor neurons > reduced central drive by CNS (may be caused by change in serotonin * defence mechanism ; protects body against muscle failure 2d. THICKNESS OF FIBRE muscle fibres ↓ size of myofibres ; ↑ sunthesis of activa myosin chypotrophy Istrength/resistance training) ↑ no of muscle fibres ; achieved · by differentiation of satellite cells (both Stestosterone , steroids , vigorous weight training V ↑ overall size of Muscle But X contribute to thickness of muscle fibre CONTROL OF MOTOR ACTIVITY movements : 1 voluntary triggers cyclical 2. reflexes (automatic) rements sequenceof. 3 rythmic (central pattern generators drive ruthmic patterned outputs) leg. walking ; does not require conscious effort) AFFERENT INPUTS proprioception : understanding relative position & movement of body 1. muscle spindles, convey muscle length 2 muscle tension. golgi tendon organs > conven 1. MUSCLE SPINDLES cordinary - extrafusal fibres : contracts, helps more arm (muscle spindles) intrafusal fibres : sends info. about muscle length bicaps through sensory neuron alpha motor neuron cause contraction & : of extrafusal fibres efferent gamma motor neuron : cause contraction of intrafusal fibres afferent neuron : sends signal to CN3 when detect stretch  alpha gamma coactivation ↓ ↓ no firing of tension afferent V maintained in neuron loose Muscle muscle spindle ; spindle ; cannot communicate muscle length can in be communicated change length 2 GOLGI TENDON ORGAN. > bundle of connective +issues found within tendon detects tension generated by muscle contraction ; sends signals toCNS via afferent fibers allows precise control of muscle strength STRETCH REFLEX sensory neuron synapses w/ - motor neuron monosynaptic stretch reflex & force exerted patellar on * to sense & resist tendon pulls quads femoris (extensor knee muscles) > - changes stretch ; detected by in muscle muscle spindles ; length ; stabilise signal transmitted along afferent neuron balance V directly synapse onto contractionare [ motor neuron innervating extensor muscle (leg extends involuntarily (  WITHDRAWAL REFLEX * must occur at the (biceps) agonistic 3 muscles contract to create movement same time to allow (triceps) relax to allow movement withdrawal of hand antagonistic muscles CROSSED EXTENSOR REFLEX > - 'opposite signal sent to uninjured > bears weight limb > reflex movement of 2 limbs ( withdrawal reflex ; 1 limb)