Select from the terms in the \'word bank list\' to create a map of skeletal musc

Question

Select from the terms in the 'word bank list' to create a map of skeletal muscle excitation, contraction, and relaxation.  Some additional terms have been added to guide you in your choices.

Events start at the ____ extending to the ____ junction, where the ______ reaches the ____, causing the ____ to open.  The local increase in _____ concentration at the presynaptic membrane triggers ______.   ______ diffuses into the synaptic cleft and binds to the ______ on the ________.  There, the influx of ______ causes the _____.  The resultant action potential is conducted by the sarcolemma to the ______ where the ______ open calcium channels in the underlying _____, releasing _______ to the sarcoplasm.  Based on the law of mass action, this calcium diffuses, reaches, and binds to _____.  Then _____ shifts position, exposing the ______ binding site on the D-actin.  If sufficient ____ is present to bind to the myosin, the ____ binding site on the myosin head reaches a higher affinity.  Contraction proceeds.

WORD BANK

Axon terminal

Ca2+

Tropomyosin
T-tubules

Somatic motor neuron

Myosin

Troponin

Voltage-gated Ca2+ channels

Actin

End-plate Potential

ACh receptor

Sarcoplasmic reticulum

Action potential

Na+

Motor end plate

Acetylcholine

Neuromuscular

Exocytosis

DHP receptors

ATP

Explanation / Answer

Events start at the somatic motor neuron extending to the neuromuscular junction, where the axon terminal reaches the motor end plate, causing the voltage gated Ca2+ channel to open.  The local increase in Ach concentration at the presynaptic membrane triggers end plate potential.   Ach diffuses into the synaptic cleft and binds to the Ach receptor on the motor end plate.  There, the influx of Na+ causes the action potential.  The resultant action potential is conducted by the sarcolemma to the T-tubule where the action potential open calcium channels in the underlying sarcoplasmic reticulum, releasing Ca2+ to the sarcoplasm.  Based on the law of mass action, this calcium diffuses, reaches, and binds to troponin.  Then tropomyosin shifts position, exposing the myosin binding site on the D-actin.  If sufficient ATP is present to bind to the myosin, the actin binding site on the myosin head reaches a higher affinity.  Contraction proceeds.

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