Muscle Action, Muscle Action, Recruitment, and Recruitment, and Energy SourcesEnergy Sources

Muscle ActivationMuscle Activation

► Caused by message Caused by message from brainfrom brain

►Message sent along Message sent along motor neuron motor neuron (nerve cell attached (nerve cell attached to muscle)to muscle)

►M.n. ends in M.n. ends in synaptic cleftsynaptic cleft

Synapse Synapse ► Synaptic cleft Synaptic cleft

terminates in terminates in sarcolemma (outside of sarcolemma (outside of muscle cell)muscle cell)

► Releases acetylcholine, Releases acetylcholine, which causes which causes sarcolemma to release sarcolemma to release CaCa++ ions into muscle cell ions into muscle cell

► Begins muscle Begins muscle contractioncontraction

Action PotentialAction Potential

► Influx of CaInflux of Ca++ ions ions causes an electrical causes an electrical current called action current called action potentialpotential

►Once sarcolemma is Once sarcolemma is activated, begins activated, begins chain reaction along chain reaction along entire muscle cellentire muscle cell

RememberRemember

►Each muscle is composed of hundreds of Each muscle is composed of hundreds of muscle cells stacked into a bundlemuscle cells stacked into a bundle

►So far we have only activated ONE So far we have only activated ONE muscle fibermuscle fiber

►When a single muscle fiber is activated, When a single muscle fiber is activated, it is an “all-or-nothing” responseit is an “all-or-nothing” response

Muscle recruitmentMuscle recruitment

► If more force is If more force is needed, nerve will needed, nerve will activate more activate more muscle fibers in the muscle fibers in the fascicle (muscle fascicle (muscle recruitment)recruitment)

Another way to provide more Another way to provide more forceforce

►Nerve can also Nerve can also increase rate of increase rate of stimulation, stimulation, causing muscle to causing muscle to contract fastercontract faster

► Can reach complete Can reach complete tetanus (full tetanus (full contraction with no contraction with no relaxation)relaxation)

Other forms of contractionOther forms of contraction

► Twitch- short, weak Twitch- short, weak signal causes brief signal causes brief contractioncontraction

► Summation- Summation- contraction rate contraction rate increases (no complete increases (no complete relaxation)relaxation)

► Incomplete tetanus – Incomplete tetanus – faster rate; faster rate; contractions closer contractions closer togethertogether

Complete TetanusComplete Tetanus

► Continuous contraction Continuous contraction with no relaxationwith no relaxation

► Evident in isometric Evident in isometric exerciseexercise

► Also happens as a Also happens as a result of some diseases result of some diseases and infectionsand infections RabiesRabies C. tetaniC. tetani

In reviewIn review

►Two ways to increase forceTwo ways to increase force Recruit more musclesRecruit more muscles Increase rate of contractionIncrease rate of contraction

Energy for ContractionEnergy for Contraction

► 3 possibilities3 possibilities

1) Aerobic respiration1) Aerobic respiration

2)Lactic acid 2)Lactic acid fermentationfermentation

3)Direct 3)Direct phosphorylation phosphorylation (fastest, but only lasts (fastest, but only lasts about 20 seconds)about 20 seconds)

Direct PhosphorylationDirect Phosphorylation

► ADP encounters ADP encounters Creatine Phosphate Creatine Phosphate (CP)(CP)

► Takes phosphate Takes phosphate molecule to form molecule to form ATP, leaves ATP, leaves creatinecreatine

► CP only present in CP only present in muscle cellsmuscle cells