The Neuromuscular Junction

Question 1

What receptors are present on the postsynpatic membrane?

Answer 1

nicotinic ACh receptors

Question 2

What is the Ca2+ sensor called?

Answer 2

synaptotagmin

Question 3

What is the role of ACh at the motor end plate?

What is the receptor channel permeable to?

Answer 3

ACh binds to nicotinic receptor
Channel open - permeable to Na+ and K+
Na+ influx > K+ efflux 
Em muscle cell = -90mV
EPP = -20mV

Question 4

EPP initiates an AP in muscle if it exceeds the threshold

What happens to both of these as the distance from the NMJ increases?

Answer 4

AP travels through muscle cell

EPP decays as it moves away from end-plate because nACHRs absent away from synapse

Question 5

What is the DHP receptor and what role does it have at NMJ’s?

Answer 5

Connects SR to t-tubules?

Question 6

What is the cause of myesthenia gravis?
What are the signs and symptoms?
What is the treatment?

Answer 6

muscle weakness during sustained activity
autoimmune disease of nAChR (reduced number at NMJ)
eye drooping, difficulty moving eye
treatment = AChE inhibitor, to prolong signal