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6.2 Electrical Signals — Test 1
Q1. The resting membrane potential of a typical neuron is about:✓ −70 mV (inside negative)
Q2. The resting membrane potential is maintained largely by the:✓ Na⁺/K⁺-ATPase pump and potassium leak channels
Q3. During the rising (depolarising) phase of an action potential, the membrane becomes permeable mainly to:✓ Sodium ions (Na⁺ influx)
Q4. Repolarisation of the neuron during an action potential is due mainly to:✓ Potassium efflux (K⁺ leaving the cell)
Q5. The brief period after an action potential when no new impulse can be generated regardless of stimulus strength is the:✓ Absolute refractory period
Q6. The action potential obeys the all-or-none law, which means:✓ A stimulus at or above threshold gives a full-sized impulse
Q7. A graded potential differs from an action potential in that a graded potential:✓ Varies in size with stimulus strength and fades with distance
Q8. The threshold for triggering an action potential is the membrane potential at which:✓ Enough sodium channels open to make depolarisation self-sustaining
Q9. The Na⁺/K⁺-ATPase pump moves:✓ 3 Na⁺ out and 2 K⁺ in per ATP
Q10. After-hyperpolarisation following an action potential occurs because:✓ Potassium channels stay open slightly too long
Q11. The equilibrium potential of an ion (e.g. potassium) is described by the:✓ Nernst equation
Q12. At the peak of the action potential, the membrane potential is close to the equilibrium potential for:✓ Sodium
Q13. A stimulus below the threshold strength will:✓ Fail to trigger an action potential
Q14. The ion that is at higher concentration inside the resting neuron than outside is:✓ Potassium
6.2 Electrical Signals — Test 2
Q15. The conduction of a nerve impulse along an axon is best described as:✓ A self-propagating wave of depolarisation
Q16. Local anaesthetics such as procaine block nerve impulses by:✓ Blocking voltage-gated sodium channels
Q17. The minimum stimulus strength needed to excite a neuron is called the:✓ Threshold (rheobase) stimulus
Q18. During the relative refractory period, an action potential can be triggered only by:✓ A stronger-than-normal stimulus
Q19. The rapid reversal of membrane potential during an action potential is called:✓ Depolarisation
Q20. The ionic basis of the resting potential is best explained by the fact that the resting membrane is most permeable to:✓ Potassium
Q21. The speed of impulse conduction along an axon increases with:✓ Larger axon diameter and myelination
Q22. In a myelinated axon, the action potential 'jumps' between the:✓ Nodes of Ranvier
Q23. Inactivation of sodium channels during an action potential is important because it:✓ Helps cause repolarisation and ensures one-way conduction
Q24. The Goldman–Hodgkin–Katz equation improves on the Nernst equation by accounting for:✓ The permeabilities of several ions at once
Q25. The trigger zone where an action potential is usually first generated in a neuron is the:✓ Axon hillock (initial segment)
Q26. Tetrodotoxin (TTX), a potent nerve poison, acts by:✓ Blocking voltage-gated sodium channels
Q27. The magnitude of the resting potential would become less negative (depolarise) if the extracellular potassium concentration were:✓ Increased
Q28. The refractory period of a neuron ensures that:✓ Impulses travel in one direction and at a limited frequency
6.2 Electrical Signals — Test 3
Q29. The energy used to maintain the ionic gradients underlying the resting potential comes ultimately from:✓ ATP (used by the Na⁺/K⁺ pump)
Q30. A neuron is said to be 'polarised' at rest because:✓ There is a voltage difference across its membrane (inside negative)
Q31. Saltatory conduction (in myelinated fibres) is more energy-efficient than continuous conduction because:✓ Ion exchange occurs only at the nodes, not along the whole axon
Q32. Secondary active transport across a mammalian cell membrane is powered by:✓ An electrochemical ion gradient (e.g. the Na⁺ gradient)
Q33. The sodium–potassium pump in a neuron transports:✓ Na⁺ out of and K⁺ into the cell
Q34. Which cells/tissues are likely to have the highest level of Na⁺/K⁺-ATPase activity?✓ Tissues with high transport activity, such as nerve and kidney
Q35. In testis and sperm cells, fructose is taken up by the transporter:✓ GLUT5
Q36. The patch-clamp technique is used mainly to:✓ Measure ion currents through single ion channels
Q37. The action potential is best described as a signal that:✓ Serves as a long-distance, all-or-none signal
Q38. A nerve fibre cannot be re-stimulated during the absolute refractory period because:✓ The voltage-gated sodium channels are inactivated
Q39. The conduction velocity of an action potential in a myelinated fibre is greater than in an unmyelinated one mainly because:✓ Saltatory conduction lets the impulse jump between nodes
Q40. If the equilibrium potential for Na⁺ is +55 mV and [Na⁺] inside is 20 mM, then by the Nernst relation the outside [Na⁺] is about:✓ 145 mM
Q41. Increasing the membrane's permeability to K⁺ in a resting neuron would:✓ Hyperpolarise the membrane (make it more negative)
Q42. Local anaesthetic drugs (e.g. lignocaine) act by:✓ Blocking voltage-gated sodium channels in nerve fibres
6.2 Electrical Signals — Test 4
Q43. Conduction of a nerve impulse is fundamentally an ____ process:✓ Electro-chemical
Q44. During an action potential, the membrane potential changes in the sequence:✓ Negative → positive → negative
Q45. When a threshold stimulus is given and then a second stimulus follows almost immediately, the second often fails because of the:✓ Refractory period of the first impulse
Q46. When sodium channels open and Na⁺ rushes into a cell, the membrane becomes:✓ Depolarised
Q47. The dark current in retinal rod cells (in darkness) is due to:✓ Open cation channels keeping the cell partly depolarised
Q48. Thin, flat glial cells that contribute to the blood–brain barrier are the:✓ Astrocytes
Q49. The resting membrane potential is most strongly determined by the:✓ Potassium (K⁺) concentration gradient
Q50. At rest, the axonal membrane of a neuron is:✓ More permeable to K⁺ and nearly impermeable to Na⁺
Q51. Which neurotransmitter opens a single kind of cation channel almost equally permeable to Na⁺ and K⁺ (at the neuromuscular junction)?✓ Acetylcholine (at the nicotinic receptor)
Q52. The Na⁺/K⁺-ATPase is described as electrogenic because it:✓ Moves unequal numbers of charges (3 Na⁺ out, 2 K⁺ in)
Q53. Which of the following is NOT a property of the action potential?✓ It is a graded, decremental signal
Q54. Myelination increases conduction speed partly by:✓ Raising membrane resistance and reducing current leakage between nodes
Q55. Calcium ions are NOT directly required for which one of the following?✓ Generation of the nerve action potential
Q56. The compound action potential recorded from a whole mixed nerve has several peaks because:✓ Different fibre types conduct at different speeds