4. Muscle movement

How do opposing muscles cause joints to flex and extend.

• Antagonistic muscles

Sarcomere

• muscle cells outer wall

• sends its own electric message to contract muscle (release Ca)

• then shortens

Sarcomere (Steps)

• Motor neurons in the spinal cord send action potentials to muscle fibers.

• Each motor neuron sends axon branches to different muscle fibers.

• The action potential in the motor neuron triggers an AP in the sarcolemma, which spreads across the muscle cell and initiates contraction.

• This occurs at the motor end-plate.

Sliding filament theroy

• The sarcomere shortens when myosin heads pull actin fibers toward the M-line.

• purple and green

How calcium enter the muscle cell

• Motor neuron send an action potential down its axon to the muscle (ACh) acetycholine

• Signal reaches the sarcolemma and spreads across it

• The electrical signal goes down the T-tubules to get deep in the muscle cell

• T-tubes signal to release calcium from the sarcoplasmic reticulum

• Calcium comes out of the sarcoplasmic reticulum

How does Calcium in the muscle cell cause a power stroke (Rigor mortis)

• Calcium goes to troponin protein

• Triponin holds onto long rope tripomyosin which covers the actin binding sites

• Calcium makes Tropin move the tipomyosin away reveling the binding spot

• Now myosin heads grab the actin

• Myosin use ATP to bend the actin and make the sarcomere shorter

  • muscle contraction (ADP)

• ATP makes the hand let go

3 roles of ATP in muscle contraction

• Fuel the power stroke (compress the molecular spring in myosis head)

• Free the mysin from the actin during rigor mortis

• Fuels calcium re uptake in the sarcoplasmic reticulum after a conrtactile

• Also fuels Na/K pump for T-Tubels

How skeletal muscle genrates graded force

Tetanus

• A the rate of AP increases so does the strength of contractions

• Graded

Motor unit recruitment

• bran increases force by recruiting more motor units

• more unit = more fiber = more force

Motor unit

• Motor neuron + all muscle cells it innervates

How to increase graded contractions

• Tetanus (increase AP frequency)

• Motor unit recruitment (recruit more units)