When a muscle fiber is activated by the neuromuscular junction, tension does not

Question

When a muscle fiber is activated by the neuromuscular junction, tension does not begin to rise until about 1 msec after initiation of the action potential in the muscle fiber. While several things occur during this delay, the biggest time consuming step is diffusion of ACh across the neuromuscular junction, The following equation allows calculation of the time required or this diffusion to take place:

X2= 2 D t   

Where X is the distance travelled by the molecule (the width of the cleft), about 200 nm and D is the diffusion coefficient of Ach, assume 1 x 10-5 cm2/sec. How long does it take to diffuse across the neuromuscular junction?

Explanation / Answer

Equation for time taken for diffusion across neuro muscular junction is:

t =X2/2d

where t is the time taken

X is the distance travelled by the molecule

d is the diffusion coeffcient

substituting the given values in the question,

t = 200 x 200 /2 x .oooo5

=.00002 sec

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