Neuromuscular Junction

Question 1

1 motor neuron plus all of the muscle fibers innervated by that motor neuron

Answer 1

motor unit

Question 2

T or F

each motor neuron can innervate multiple muscle fibers

Answer 2

True

but…

each fiber only receives innervation from 1 motor neuron

Question 3

What is the first step in triggering an action potential in a muscle fiber

Answer 3

1. release of ACh

• ap arrives from motor neuron, travels down to each terminal button

Question 4

What is the second step in triggering an action potential in a muscle fiber

Answer 4

2. depolarizing at terminal button opens voltage gated calcium channels, increased intracellular concentration of calcium

Question 5

What is the third step in triggering an action potential in a muscle fiber

Answer 5

increased intracellular Calcium triggers fusion of ACh vesicles with membrane, increasing concentration of ACh in neuromuscular cleft.

ACh out of the axon terminal (a lot!)

Question 6

What is the fourth step in triggering an action potential in a muscle fiber

Answer 6

ACh crosses synaptic cleft and binds nicotinic receptors on motor end plate.

tremendous SA. flooded with nicotinic receptors

Question 7

What is the fifth step in triggering an action potential in a muscle fiber

Answer 7

nicotinic receptors open, permeable to both NA and K driving force favors NA, creates end plate potential (EPP, EPSP graded potential)

sodium moving inside the cell. Excitatory post synaptic potential ( end plate potential)

Question 8

What is the 6th step in triggering an action potential in a muscle fiber

Answer 8

local current flow spreads out from motor end plate and opens voltage gated sodium channels on sarcolemma

Question 9

What is the 7th and 8th step in triggering an action potential in a muscle fiber

Answer 9

action potentials propagate down sarcolemma via contiguous conduction

Question 10

What is the 9th step in triggering an action potential in a muscle fiber

Answer 10

ACh is quickly broken down via acetylocholinesterase in synaptic cleft; graded potential dissipates