Skeletal Muscle Contraction

Whats must happen in order for muscle to contract?

neuromuscular stimulation; signal from nerve

Things need to be place in order for neuromuscular stimulation to occor like what?

Sodium Potassium Pump where more positive ions are pumped out toegther with negative ions, producing a polarized membrane

Resting membrane potential; (- interior) (+ exterior) to maintain cells excitability

Resting Membrane Potential

• What’s the primary ion responsible for establishing the RMP?

• What role does the sodium-potassium pump play in resting potential?

• What is the membrane potential generated by ion diffusion alone (excluding the Na+/K+ pump)?

• What is the typical resting membrane potential (RMP) of a neuron?

• Potassium (K+) ions diffusing down their concentration gradient

• It helps maintain the ion gradient and contributes about -3 mV to the resting membrane potential.

• -67 mV.

• -70 mV

Why does potassium leave the cell during resting potential?

What is the role of sodium (Na+) in the resting potential?

Because its concentration is higher inside the cell than outside, so it diffuses out via leak channels.

leaks into cell slowly, but has a high concentration on the outside

Action Potential:

Motor neurons:

Neuromuscular Junction:

• Synapse:

Acetylcholine (ACh):

• what does it allow to enter cell?

• nerve impulses/ electrical current

• in the brain and axons travel into the muscle cells they activate

• junction between the terminal of motor neuron and muscle fiber

  • space between motor neuron and muscle fiber

• neurotransmitter contained in synaptic vesicles released via exocytosis

  • Na+, causing deoplorization

MEMBRANE POTENTIAL

Polarized:

• example

Depolarized:

• example

Repolarized:

• voltage (potential) difference across membrane/ polar opposites rdy to be excited

  • inside negative versus the outer membrane

• Na+ enters; less of a potential difference where membrane has already been excited

  • interior of sacrolemma becomes slightly less negative

• K+ leaves; restores the membrane to initial polarized state

Motor end plate:

Absolute refractory period:

Relative refractory period:

bulb at end of axon

when muscle cant be stimulated again because it is depolarized

when membrane is hyperpolarized and requires a greater than normal stimulus in order to depolarize (much harder time reaching threshold)

When the action potential passes along the sacrolemma what do the T-tubules do?

allow AP to continue to cells interior and attach to the sacroplasmic reticulum, and when AP moves along tubules it causes the sacroplasmic reticulum to release Ca+

STRIATIONS OF MYOFIBRILS

A Band:

I Band:

H Band:

M Line:

Z-Disc:

Sacromere:

• DARK, partially overlap w thin filament

• LIGHT, thin filaments only

• lighter region in middle of A bands ( thick filaments only)

• dark line that bisects the H band

• in middle of I band; thin filaments and elastic are anchored at each end of sacromere

• distance from one Z disc to another

Contraction:

Relaxation:

What happens to the striations once a muscle contracts?

• why?

activation of myosin crossbridge

contraction ends when crossbridges become inactive

The I bands disappear, the A bands move closer together, Z lines pull together, and the sarcomere shortens

• due to the sliding of actin and myosin myofilaments against one another

List steps of muscle contraction from excitation to Muscle Contraction

1. Impulse arrives at motor end plate → Ca2+ enter axon

2. Ca2+ binds to ACh vescicles → release ACh into synapse via exocytosis

3. ACh binds to receptors on sarcolemma opening gated ion channels causing Na+ to enter cell (depolarization)

4. K+ leaves cell as Na+ channels close (repolarization)

5. Na+ (Action Potential) spreads along sarcolemma and travels down T-tubules

6. T tubules signal sarcoplasmic reticulum to release Ca2+

7. Ca2+ binds to troponin, Tropomyosin removes it block from actin, myosin heads bind to active sites (actin)

8. Myosin heads swivel (working stroke) = Z-lines are closer, sarcomeres shorter, Products of ATP hydrolysis released (ADP & Pi)

9. ATP is grabbed by myosin heads and crossbridges detach

10. ATP is hydrolyzed and energy → myosin heads ( cock and reset for next stimulus)