Question

Place muscle contraction steps in order. ACh (acetylcholine); NMJ (neuromuscular junction) A) ACh (excitatory neurotransmitter for skeletal muscle) that is stored in the synaptic vesicle of the

synaptic end bulb is released and diffused across the synaptic cleft
B) Depolarizing graded potential called end plate potential (EPP) is generated
C) Now that the binding sites are free, ATP is hydrolyzed into ADP and a phosphate. This energizes the myosin head which then assumes the "cocked" position
D) Action potential occurs in the somatic motor neuron
E) At the onset of muscle fiber contraction, the sarcoplasmic reticulum releases calcium ions into the sarcoplasm
F) ACh binds to nicotinic ACh receptors on the motor end plate
G) Another molecule of ATP binds to the ATP binding site on myosin allowing for myosin to detach from actin
H) The energized myosin head then attaches to the myosin binding site on actin and a phosphate is released. This is referred to as the "crossbridge"
1) Adjacent regions of the sarcolemma are then depolarized, resulting in the generation of a muscle action potential. This action potential propagates through the muscle fiber membrane in both directions away from the NMJ towards the end of the fiber
J) The calcium ions then bind to troponin, which moves tropomyosin away from myosin binding
sites on actin
K) The myosin head pivots changing its position from 90 degrees to 45, pulling the thin filament past the thick filament towards the center of the sarcomere. This is referred to as the power stroke

Answer 1

Muscle contraction begins with the release of acetylcholine at the neuromuscular junction, leading to the formation of crossbridges between myosin and actin and the sliding of thin filaments past thick filaments.

Step-by-step explanation:

Muscle contraction begins with the release of the neurotransmitter acetylcholine (ACh) at the neuromuscular junction (NMJ). This triggers a depolarizing graded potential called the end plate potential (EPP). As a result of the EPP, calcium ions are released from the sarcoplasmic reticulum into the sarcoplasm. The calcium ions then bind to troponin, causing tropomyosin to move away from myosin binding sites on actin. This allows for the crossbridge formation between myosin and actin, leading to the power stroke and sliding of the thin filaments past the thick filaments.