1.If a substance is moving from inside a cell to outside via simple diffusion th
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Question
1.If a substance is moving from inside a cell to outside via simple diffusion then which ONE of the following is CORRECT?
Select one:
a.Its transport rate is directly proportional to the substance’s lipid solubility (partition co-efficient).
b.Its transport is likely to be mediated by exocytosis of a vesicle containing the solute.
c.If the substance is uncharged, then its extracellular concentration must be greater than its intracellular concentration.
d.Its transport across the membrane requires coupling to the transport of a second substance down it’s pre-existing electrochemical gradient.
e.Its transport rate will quickly saturate because the binding sites on the membrane transporter involved becomes fully occupied.
2.
A sensory nerve cell in the skin of the finger is quiescent (not firing action potentials) with a steady resting membrane potential of -70 mV. This nerve cell detects when the finger touches something, responding to touch by firing a burst of action potentials. This signal is then transmitted to the somatosensory cortex in the brain where the sense of touch is perceived. In regard to this sensory nerve cell, which ONE of the following options is most likely to be CORRECT?
Select one:
a.When the finger touches the object, an IPSP (inhibitory postsynaptic potential) occurs in the sensory nerve cell.
b.The touch causes the membrane potential of this sensory nerve cell to cross the threshold for activation of voltage-dependent Na+ and K+ channels.
c.The sensory nerve cell becomes hyperpolarized in response to the touch stimulus.
d.At all times (i.e. both before and during touch), the membrane of the sensory nerve cell is likely to be more permeable to K+ as compared to Na+.
e.The response of the sensory nerve cell is transmitted to the brain via passive or electrotonic propagation of action potentials via the sensory nerve and spinal cord.
3.Choose the MOST CORRECT option. With regard to the ion channels underlying the action potential in a typical nerve axon:
Select one:
a.The voltage-dependent Na+ channels are inactivated when the action potential threshold is reached.
b.Voltage-dependent K+ channels are open during the repolarization phase.
c.Voltage-dependent K+ channels are closed during the afterhyperpolarization phase.
d.Background or “leak” K+ channels are closed during the depolarization phase.
e.Voltage-dependent K+ channels activate before the voltage-dependent Na+ channels.
4.Which ONE of the following statements regarding electrical signals in excitable cells is CORRECT?
Select one:
a.The lipids that comprise the plasma membrane have a high conductance, or low resistance, to current flow.
b.The intracellular solution of a nerve cell always has the same electrical potential as the extracellular solution.
c.The plasma membrane can be represented electrically as a resistor and capacitor in parallel.
d.Electrical signals occur as the influx of a cation across the membrane occurs simultaneously with the influx of an anion.
e.Movement of electrons in the lipid bilayer results in electrical signals passing from one cell to another.
5.
At the neuromuscular junction, the motor nerve communicates with the skeletal muscle by releasing a chemical neurotransmitter. In regard to this neuromuscular transmission which ONE of the following typically occurs?
Select one:
a.Acteylcholinesterase helps to terminate the response by metabolising the neurotransmitter.
b.Binding of the neurotransmitter to the muscle receptor generates an inhibitory postsynaptic receptor potential (IPSP).
c.The neurotransmitter released by the nerve terminal is adrenaline.
d.A metabotropic receptor mediates a slow postsynaptic response to the neurotransmitter
e.The neurotransmitter acts on gap junctions to cause a synchronized contraction.
Explanation / Answer
1-d Its transport across the membrane requires coupling to the transport of a second substance down it’s pre-existing electrochemical gradient.
2-c, The sensory nerve cell becomes hyperpolarized in response to the touch stimulus.
3-c, .Voltage-dependent K+ channels are closed during the afterhyperpolarization phase.
4-d, Electrical signals occur as the influx of a cation across the membrane occurs simultaneously with the influx of an anion.
5-b, Binding of the neurotransmitter to the muscle receptor generates an inhibitory postsynaptic receptor potential (IPSP).
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