When activated by ACh, which ions does the nicotinic receptor become permeable t
ID: 3482034 • Letter: W
Question
When activated by ACh, which ions does the nicotinic receptor become permeable to? In which direction does each of these ions move? Why is flux dominated by one of these ions?
Generally, what is unique about the NMJ relative to other synapses?
esting Membrane Potential for a cell as defined below 0 mV Ion ECE (out) ICF (in) Nernst E (mV)Permeability Movement ECG (mV) Na 150 mM 15 mM +61 5 mM 150 mM -90 26 CI 98 mM 7 mM -70 45 2.4 mM 0001 mM +134 51. Calculate the movement (In or Out: if channels for each suddenly opened) for each ion. Would each of these cause depolarization or h yperpolarization? 52. If Cl permeability suddenly increases to 1000 (a lot of chloride channels open), does that alter the resting membrane potential? Why or why not? 53. Which of the ions above has the largest electrochemical potential? Which has the lowest? 54. Speculate on the relative permeability of the plasmalemma to Ca". Why? 55. If a large and equal number of sodium, potassium, and chloride channels suddenly opened (equal increase in Permeability for each), which ion would have the highest rate of flux into or out of the cell? Why? 56. Why is the equilibrium potential for calcium typically more positive than sodium? (two good reasons, another way of saying this is "why does calcium want to go in more than sodium?") 57. What is the typical resting membrane potential of a neuron? Skeletal Muscle Fiber? Cardiac Myocyte?Explanation / Answer
Answer;
A nerve impulse reaches the neuromuscular junction releasing acetylcholine, which binds the receptors on muscle cell membrane. Acetylcholine causes opening of Na+ channels (Na+ ions enter the muscle cells) causing depolarization of muscle cells. Depolarization results in the release of Ca2+ from the sarcoplasmic reticulum. The concentration of sodium ions is considerably higher in the extracellular fluid than in the intracellular fluid. Hence the influx is dominated by one of these ions. NMJ are unique since they are always excitatory, whereas other synapses can be inhibitory or excitatory. Also, NMJ always uses ACh, whereas other synapses can use adrenaline and noradrenaline and other neurotransmitters.
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