excitation contraction coupling + Steps

where does excitation contraction coupling 

occurs at the NMJ between motor neurons and skeletal muscle cells 

True or False

Skeletal Muscle Cells can have AP’s

true

RMP of skeletal muscle cells

-70mv to -95mv

goal of excitation contraction coupling 

to release Ca+ from the sarcoplasmic reticulum

AP reaches axon terminal of motor nueron 

VG-Ca+ channels open causing the release of ACh into the NMJ

ACh @ the NMJ

binds to nicotinic ACh receptors on sarcolemma (post synaptic membrane) 

nicotinic ACH receptor

ionotropic receptor that allows for Na+ entry into the skeletal muscle when 2 ACh molecules bind 

Na+ diffuses into skeletal muscle cell from ACh binding 

initial depolarization of muscle cell from EPP

EPP 

end plate potential 

analogous to EPSP 

EPP’s summate to -65mV

thresehold of AP is reached

at thresehold 

VG-Na+ channels open 

-rapid depolarization 

-start of skeletal muscle AP 

skeletal muscle AP

travels along sarcolemma into T tubules

AP @ T tubules

activates DHP receptors (VG Ca+ CH) along the T tubules

activated DHP receptors

VG Ca+ channels open

Ryanodine receptors are coupled with DHP receptors

are activated when DHP receptors are activated 

activated ryanodine receptors

Ca+ release channels on the sarcoplasmic reticulum that releases more Ca+ into the intracellular enviorment 

initial ca++ rise

creates a positive feedback by triggering more ryanodine receptors to open

high intracellular Ca++

binds to troponin and initiates contraction