Muscle tissue pt 2 Flashcards
Muscle mechanics
- contraction produces muscle tension
- contraction may/may not shorten muscle
- isometric contraction: no shortening; muscle tension increases but does not exceed load
- isotonic contraction: muscle shortens because muscle tension exceeds load
Motor unit
- each muscle served by at least 1 motor nerve
- motor nerve: contains axons of up to hundreds of motor neurons
- motor unit = motor neuron and all muscle fibers it supplied (smaller number = fine control)
- motor unit in muscle usually contract asynchronously; helps prevent fatigue
Muscle Twitch
- motor units response to single action potential of its motor neuron
- 3 phases of muscle twitch
1. Latend period: events of excitation-contraction coupling, no muscle tension
2. Period of contraction: cross bridge formation, tension increases
3. Period of relaxation: Ca2+ reentry into SR; tension declines to zero
Graded Muscle responses
- graded muscle responses: varying strength of contraction for different demands
- required for proper control of skeletal movement
- increased force graded by (changing frequency of stimulation and changing strength of stimulation)
Recruitment
- smooth increase in muscular tension produced by the increase in number of active motor units
- contraction starts w/ activation of smallest motor units in a stimulated muscle
- as movement continues, larger motor units are activated + tension production rises steeply
Response to change in stimulus strength
recruitment works on size principle
- motor units w/ smallest muscle fibers recruit first
- motor units with larger + larger fibers recruit as stimulus intensity increases
- largest motor units activated only for most powerful contractions
Isotonic contractions
- muscle changes in length + moves load
- isotonic contractions either concentric/eccentric
- concentric contractions: muscle shortens + does work
- eccentric contractions: muscle generates force as it lengthens
isometric contractions
- load greater than tension muscle can develop
- tension increases to muscle’s capacity, but muscle neither shortens nor lengthens
- cross bridges generate force but do not move actin filaments
3 muscle contraction requiring ATP
- Direct phosphorylation: coupled reaction of creatine phosphate CP and ADP (CP)
- Anaerobic pathway: glycolysis + lactic acid formation (glucose)
- glycolysis does not require oxygen and a small amt of ATP produced
- 70% max contractile activity
- bulging muscles compress blood vessels; oxygen delivery impaired
- lactic acid is produced which changes pH results in MM fatigue - Aerobic pathway: aerobic cellular respiration
- requires oxygen
- produces 95% ATP during rest and light to moderate exercise
Excess post exercise oxygen consumption
to return muscle to resting state
- oxygen reserves replenished
- lactic acid converted to pyruvic acid
- glycogen stores replaced
- atp and creatine phosphate reserves replenished
- all require extra oxygen; occur post exercise
- paying back the oxygen debt
Force of muscle contraction
force of contraction depends on number of cross bridges attached which is affected by
- number of muscle fibers stimulated (recruitment)
- relative size of fibers - hypertrophy of cells increases strength
- frequency of stimulation
- degree of muscle stretch: length-tension relationship (muscle fibers at 80-120% normal resting length –> more force)
Velocity + duration of contraction
influenced by
- muscle fiber type: slow + fast fiber type
- load: greater load, slower contraction
- recruitment: more motor units contracting, faster and more prolonged contraction
