Session 6 Flashcards
Which of the following is the main channel contributing to the resting membrane potential?
A: Sodium channels B: Chloride channels C: Calcium channels D: Cation channels E: Potassium channels
E - Potassium channels
Open potassium channels allow positive K ions to leave the cell down its concentration gradient, therefore setting up a negative resting membrane potential.
Why is the resting membrane potential not the same as the equilibrium potential for potassium?
Cell is not purely permeable to potassium, movement of other ions occurs, therefore cell is slightly less negative than Ek. (Increasing membrane permeability to a particular ion moves the membrane potential towards the Equilibrium Potential for that ion.)
How does the Na-K-ATPase contribute to the resting membrane potential?
Indirectly, the active transport of ions is responsible for the entire membrane potential, because it sets up and maintains the ionic gradients that generate the resting membrane potential
When does the depolarisation, repolarisation and hyperpolarisation stage of a changing membrane potential occur?
Depolarisation - upstroke
Repolarisation - downstroke
Hyperpolarisation - undershoot
When the nerve cell becomes highly permeable to sodium, the potential across the plasma membrane changes to ______ and this is called ______.
A: -55mV; repolarisation B: +55mV; repolarisation C: +55mV; depolarisation D: -55mV; depolarisation E: -95mV; hyperpolarisation
C: +55mV; depolarisation
The influx of sodium ions into cells moves the membrane potential closer to the ENa, which is a high positive value. In the initial phase, a small movement towards -55mV occurs (this is the start of depolarisation), and once fast sodium channels open, the potential across the membrane goes to zero and then overshoots becomes more positive. Hyperpolarisation occurs when excess chloride or potassium ions flood into a cell.
Complete the sequence of events at the neuromuscular junction that gives rise to a change in membrane potential:
Motor neurones release (A) –>
(A) binds to the (B) receptor on the muscle membrane –>
The receptor has an intrinsic (C) channel –>
This allows movement of (D) and (E) –>
This moves the membrane potential towards 0mV
A: Ach B: nACh C: Ion D: Na E: K
Events that occur at the NMJ which give rise to a change in membrane potential is an example of which type of gating?
A: Voltage-gated B: Mechanical-gated C: Ligand-gated D: Gating via an intracellular messenger E: Direct G-protein gated
C: Ligand-gated
Ach is the ligand, which binds to the receptor, to allow movement of ions across a membrane. G proteins are not involved (E), there is no signalling cascade (D), and no stretch involved (B). The change in membrane potential will then subsequently activate voltage-gated channels (A)
Examine the gaps in the following sentence to determine the correct answers about the movement of signals from neuron to neuron.
When depolarisation occurs ______; this allows the release of ______ into the ______.
A: Calcium channels open; dopamine; cell body
B: Calcium channels open; neurotransmitters; synaptic cleft
C: Potassium channels open; neurotransmitters; cell body
D: Sodium channels open; serotonin; cell body
E: Sodium channels open; neurotransmitters, synaptic cleft
B: Calcium channels open; neurotransmitters; synaptic cleft
In stimulus-secretion coupling, the influx of calcium allows the fusion of vesicles with the plasma membrane and the release of the contents into the extracellular space. If this occurs in a neuron that is in contact with another neuron, then the space is a synaptic cleft. The substance released is normally a neurotransmitter. If this is an endocrine cell, then the substance released is normally a hormone.
For each of the stages below, indicate the channel responsible and whether it is open or closed causing the shape of the cardiac myocyte action potential:
Stage 0 (upstroke) Stage 1 (rapid downstroke) Stage 2 (plateau) Stage 3 (downstroke)
Stage 0 - Na channels, open
Stage 1 - K channels, open
Stage 2 - Calcium channels, open
Stage 3 - Calcium channels, closed
When acetylcholine binds to the nicotinic acetylcholine receptor (nAchR), which ions travel through its central channel pore?
A: Fluoride, sodium, chloride B: Sodium, lithium, iodine C: Iodide, bromide, chloride D: Fluoride, calcium, lead E: Sodium, calcium, potassium
E: Sodium, calcium, potassium
The nicotinic Ach receptor is a promiscuous cation ion channel and so will allow many cations to flow across membranes, but is refractory to anions, which are prevented from entering the core. All answers except for E contain anions in the list and so are incorrect.
