PHSL-P 225, Excitation-contraction coupling

neuron

1. action potential travels to axon terminal

2. voltage-gated calcium channels open

3. calcium influx

4. exocytosis

5. acetylcholine is released and binds to nicotinic cholinergic receptors on muscle cell

excitation-contraction coupling

= process where a nerve signal triggers an action potential in a muscle cell

- leading to calcium release from the sarcoplasmic reticulum

- which enables muscle contraction

action potential

- electrical signal that travels along cell membrane as a wave

- travel quickly over long distances

= change in membrane potential due to opening and closing of voltage-gated ion channels

what is found in neuron

- axon

- axon terminal

- voltage-gated calcium channel

- vesicles

what is found on muscle cell

- ligand-gated sodium channel

exocytosis

- vesicles contain neurotransmitters

= movement of vesicles from inside of cell to membrane, where they release their contents (acetylcholine)

1st step of muscle cell

- sodium enters mc via ligand-gated sodium channels

--> causes graded potential that makes membrane potential less negative (depolarizing)

2nd step of muscle cell

- graded potential activates voltage-gated sodium channels

--> more sodium enters muscle, which depolarizes cell even more and causes threshold to be reached

3rd step of muscle cell

- action potential occurs

4th step of muscle cell

- action potential travels down t-tubule

--> activates DHP receptor (voltage-gated calcium channel) on sarcolemma in t-tubule

5th step of muscle cell

- activation of DHP leads to

- calcium influx

- opens ryanodine receptor on sarcoplasm reticulum (SR)

sarcoplasm reticulum

- storage site for calcium in the cell

ryanodine receptor

- unique because activated by

- calcium binding (ligand-gated)

- opening of DHP (mechanical-gated)

6th step of muscle cell

- activation of DHP leads to more calcium influx from SR

tropomyosin

- prevents myosin from attaching to actin

troponin binds to

- actin

- calcium

- tropomyosin