Nerve Impulse & Membrane Potential — NEET Biology MCQs with Solutions
Free NEET Biology Nerve Impulse & Membrane Potential MCQs with step-by-step solutions (43 questions). Part of Neural Control and Coordination. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Nerve Impulse & Membrane Potential · easy · theory
At rest, the inside of a neuron's membrane is ______ relative to the outside:
A. Positively charged
B. Negatively charged ✓ Correct
C. Neutral
D. Highly positive
Solution: The resting membrane potential (~ −70 mV) keeps the axon interior negative relative to the outside.
Q2 — Nerve Impulse & Membrane Potential · easy · theory
During the generation of an action potential, the membrane suddenly becomes permeable to ______ ions:
A. Sodium (Na⁺) ✓ Correct
B. Magnesium (Mg²⁺)
C. Chloride (Cl⁻)
D. Calcium (Ca²⁺)
Solution: Depolarisation occurs when Na⁺ channels open and Na⁺ rushes in, reversing the membrane polarity.
Q3 — Nerve Impulse & Membrane Potential · medium · theory
The resting potential is maintained mainly by the ______, which pumps 3 Na⁺ out and 2 K⁺ in:
A. Sodium-potassium pump (Na⁺/K⁺ ATPase) ✓ Correct
B. Calcium pump
C. Chloride channel
D. Proton pump
Solution: The Na⁺/K⁺ ATPase keeps high K⁺ inside and high Na⁺ outside, maintaining the polarised resting state.
Q4 — Nerve Impulse & Membrane Potential · medium · theory
The restoration of the resting potential after an action potential (repolarisation) is caused by the outflow of:
A. Proteins
B. Potassium (K⁺) ions ✓ Correct
C. Sodium ions
D. Calcium ions
Solution: Repolarisation occurs as K⁺ channels open and K⁺ flows out, restoring the negative interior.
Q5 — Nerve Impulse & Membrane Potential · hard · theory
The all-or-none law of nerve impulses states that:
A. Impulses vary continuously with stimulus size
B. A stimulus above threshold produces a full-sized impulse; below threshold produces none ✓ Correct
C. Stronger stimuli give proportionally bigger impulses
D. Impulses never travel along the axon
Solution: Once threshold is reached, the action potential is of a fixed magnitude regardless of further stimulus strength.
Q6 — Nerve Impulse & Membrane Potential · hard · theory
At the peak of an action potential, the membrane potential becomes about ______, a state called:
A. +30 mV; depolarised (reversed polarity) ✓ Correct
B. −70 mV; polarised
C. −90 mV; resting
D. 0 mV; hyperpolarised
Solution: At the action potential peak the potential reverses to about +30 mV (inside positive) — depolarisation.
Q7 — Nerve Impulse & Membrane Potential · easy · numerical
In a resting neuron, the concentration gradients maintained across the axonal membrane are:
A. High Na⁺ and low K⁺ inside; low Na⁺ and high K⁺ outside
B. High K⁺ and low Na⁺ inside; low K⁺ and high Na⁺ outside ✓ Correct
C. High Na⁺ and high K⁺ inside; low ions outside
D. Equal Na⁺ and K⁺ on both sides of the membrane
Solution: At rest the axoplasm has high K⁺ and low Na⁺, while the fluid outside has high Na⁺ and low K⁺. This distribution, maintained by the Na⁺/K⁺ pump, underlies the resting potential.
Q8 — Nerve Impulse & Membrane Potential · easy · numerical
The resting membrane is far more permeable to K⁺ than to Na⁺ mainly because of the presence of:
A. Open potassium leak channels in the resting membrane ✓ Correct
B. Chloride channels that pump K⁺ inward
C. Voltage-gated sodium channels that stay open at rest
D. A high number of open sodium leak channels
Solution: At rest, K⁺ leak channels remain open, allowing K⁺ to diffuse out, while most Na⁺ channels are closed. This selective K⁺ permeability makes the inside negative (~ -70 mV).
Q9 — Nerve Impulse & Membrane Potential · easy · numerical
During the falling phase (repolarisation) of an action potential, the membrane potential is restored toward its resting value chiefly by the:
A. Influx of Na⁺ through voltage-gated sodium channels
B. Influx of Cl⁻ through leak channels
C. Efflux of K⁺ through voltage-gated potassium channels ✓ Correct
D. Immediate action of the Na⁺/K⁺ pump
Solution: Repolarisation results from opening of voltage-gated K⁺ channels and outflow of K⁺, which restores the negative interior. The Na⁺/K⁺ pump only slowly re-establishes the original ionic gradients afterwards.
Q10 — Nerve Impulse & Membrane Potential · easy · numerical
A stimulus that is below the threshold intensity fails to trigger an action potential. This illustrates that nerve conduction obeys the:
A. Principle of graded local potentials
B. Weber–Fechner law
C. All-or-none principle ✓ Correct
D. Law of summation of subthreshold stimuli
Solution: A neuron fires a full action potential only when the stimulus reaches threshold; below threshold it does not fire at all. This all-or-none behaviour means the impulse amplitude is independent of stimulus strength once threshold is met.
Q11 — Nerve Impulse & Membrane Potential · medium · numerical
Assertion (A): During the absolute refractory period a second action potential cannot be generated no matter how strong the stimulus. Reason (R): The voltage-gated sodium channels are in an inactivated state and cannot reopen until the membrane repolarises.
A. A is true but R is false
B. Both A and R are true and R is the correct explanation of A ✓ Correct
C. Both A and R are true but R is not the correct explanation of A
D. A is false but R is true
Solution: In the absolute refractory period the Na⁺ channels are inactivated and cannot reopen, so no stimulus can evoke another impulse. R correctly explains the refractoriness.
Q12 — Nerve Impulse & Membrane Potential · medium · numerical
If the Na⁺/K⁺ ATPase pump of a neuron were suddenly inhibited, the most immediate long-term consequence would be:
A. An instant and permanent rise to +30 mV
B. A sharp increase in the resting potential to -90 mV
C. Gradual loss of the ionic gradients and decay of the resting potential ✓ Correct
D. No effect because the pump has no role in the membrane potential
Solution: The pump actively maintains the Na⁺ and K⁺ gradients that create the resting potential. Blocking it lets the gradients run down over time, so the resting potential is gradually lost.
Q13 — Nerve Impulse & Membrane Potential · medium · numerical
During the rising phase of an action potential, the inside of the membrane briefly becomes positive relative to the outside. This reversal of polarity is called depolarisation and is due to:
A. Active pumping of Na⁺ into the cell by the ATPase
B. A rapid efflux of K⁺ through leak channels
C. Closure of all ion channels in the membrane
D. A rapid influx of Na⁺ through voltage-gated sodium channels ✓ Correct
Solution: At threshold, voltage-gated Na⁺ channels open and Na⁺ rushes in down its gradient, reversing the polarity so the inside becomes positive (about +30 mV). This is depolarisation.
Q14 — Nerve Impulse & Membrane Potential · medium · numerical
Which of the following statements about saltatory conduction is correct?
A. The impulse jumps from one node of Ranvier to the next, greatly increasing conduction speed ✓ Correct
B. It requires the myelin sheath itself to depolarise at each point
C. It occurs only in non-myelinated fibres where the membrane depolarises continuously
D. It slows down the impulse because of the insulating myelin
Solution: In myelinated fibres, depolarisation occurs only at the nodes of Ranvier (myelin insulates the internodes), so the impulse leaps node-to-node. This saltatory conduction is much faster than continuous conduction in non-myelinated fibres.
Q15 — Nerve Impulse & Membrane Potential · medium · numerical
The correct temporal sequence of events at one point on an axon during a single action potential is:
A. Refractory period → depolarisation → resting state → repolarisation
B. Resting polarised state → depolarisation → repolarisation → refractory period ✓ Correct
C. Repolarisation → depolarisation → resting state → refractory period
D. Depolarisation → resting state → repolarisation → refractory period
Solution: A point at rest is polarised; a threshold stimulus causes depolarisation (Na⁺ influx), then repolarisation (K⁺ efflux), followed by a brief refractory period before it can fire again.
Q16 — Nerve Impulse & Membrane Potential · medium · numerical
Two axons X and Y have identical diameters, but X is myelinated and Y is non-myelinated. The impulse in axon X travels faster mainly because:
A. Depolarisation is confined to the nodes of Ranvier, allowing the impulse to jump ✓ Correct
B. Non-myelinated fibres have no ion channels at all
C. Myelin lowers the threshold so more Na⁺ channels open along the whole length
D. The myelin sheath actively pumps Na⁺ into the axon at every point
Solution: Myelin insulates the internodal regions so current flows and depolarisation happen only at the nodes, letting the impulse skip from node to node (saltatory conduction). This is why myelinated fibres conduct faster than non-myelinated ones of the same diameter.
Q17 — Nerve Impulse & Membrane Potential · medium
In resting condition, the concentration gradient is maintained by
A. Active transport of ions
B. Sodium-potassium pump
C. All of the above ✓ Correct
D. Utilisation of ATP energy
Solution: The ionic concentration gradient at rest is maintained by the Na+-K+ pump, which is an active transport process using ATP energy.
Q18 — Nerve Impulse & Membrane Potential · easy
The electrical potential difference across the resting plasma membrane is called as the
A. Nerve impulse
B. Resting potential ✓ Correct
C. Both (2) and (3)
D. Action potential
Solution: The electrical potential difference across the resting plasma membrane is called the resting potential.
Q19 — Nerve Impulse & Membrane Potential · medium
During development of action potential in a nerve fibre, positive and negative charges on outer and inner side of axon membrane are reversed due to
A. Excretion of all K+ ions
B. All Na+ ions enter the axon
C. More Na+ ions entering the axon than K+ ions that leave the same ✓ Correct
D. More K+ ions entering than Na+ ions leaving the axon
Solution: During an action potential the membrane becomes highly permeable to Na+, so more Na+ enters than K+ leaves, reversing the polarity.
Q20 — Nerve Impulse & Membrane Potential · easy
Depolarisation of nerve cell involves
A. Influx of K+
B. Influx of Ca2+ and Cl-
C. Efflux of Na+
D. Influx of Na+ ✓ Correct
Solution: Depolarisation is caused by the rapid influx of Na+ into the axon.
Q21 — Nerve Impulse & Membrane Potential · medium
Transmission of nerve impulse is unidirectional due to
A. Neurotransmitter released only at dendrite ends
B. Sodium pump starts from cyton and proceeds to axon end
C. Insulation of nerve fibre by medullary sheath
D. Neurotransmitter released only at axon ending ✓ Correct
Solution: Neurotransmitter is released only at the axon ending (presynaptic side), so impulses cross a synapse in only one direction.
Q22 — Nerve Impulse & Membrane Potential · easy
A polarised neuron is the one that is
A. At resting potential ✓ Correct
B. Having action potential
C. Conducting stimulus
D. None of the above
Solution: A polarised (resting) neuron is one at resting potential, not conducting an impulse.
Q23 — Nerve Impulse & Membrane Potential · easy
During conduction of nerve impulse
A. Ca2+ moves into axoplasm
B. Na+ moves out of axoplasm
C. K+ moves into axoplasm
D. Na+ moves into axoplasm ✓ Correct
Solution: During impulse conduction (depolarisation), Na+ moves into the axoplasm.
Q24 — Nerve Impulse & Membrane Potential · medium
At resting stage nerve cell has
A. Low K+ outside and high Na+ inside
B. High K+ inside and high Na+ outside ✓ Correct
C. High K+ inside and low Na+ outside
D. High K+ outside and low Na+ inside
Solution: At rest the axoplasm has high K+ inside while the extracellular fluid has high Na+ outside.
Q25 — Nerve Impulse & Membrane Potential · easy
Different types of ion channels are present on the
A. Nuclear membrane
B. Synaptic vesicles
C. Axoplasm
D. Neural membrane ✓ Correct
Solution: Different ion channels selectively permeable to ions are present on the neural (axonal) membrane.
Q26 — Nerve Impulse & Membrane Potential · medium
When a neuron is not conducting any impulse, i.e., resting, the axonal membrane is
A. Freely permeable to sodium ions (Na+) and potassium ions (K+)
B. Comparatively more permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+) ✓ Correct
C. Comparatively more permeable to sodium ions (Na+) and nearly impermeable to potassium ions (K+)
D. Equally permeable to sodium ions (Na+) and potassium ions (K+)
Solution: At rest the axonal membrane is comparatively more permeable to K+ and nearly impermeable to Na+.
Q27 — Nerve Impulse & Membrane Potential · easy
The axoplasm inside the axon contains high concentration of
A. Na+ and positively charged proteins
B. K+ and negatively charged proteins ✓ Correct
C. K+ and positively charged proteins
D. Na+ and negatively charged proteins
Solution: The axoplasm contains a high concentration of K+ and negatively charged proteins.
Q28 — Nerve Impulse & Membrane Potential · easy
At resting stage, the sodium-potassium pump transports
A. 3Na+ outwards for 2K+ into the cell ✓ Correct
B. 2Na+ outwards for 3K+ into the cell
C. 3Na+ outwards for 2H+ into the cell
D. 3H+ outwards for 2K+ into the cell
Solution: The Na-K pump transports 3Na+ outwards for every 2K+ moved into the cell.
Q29 — Nerve Impulse & Membrane Potential · easy
At resting stage, the outer surface of the axonal membrane possesses
A. Both positive and negative charge
B. Negative charge
C. Positive charge ✓ Correct
D. No charge
Solution: At rest the outer surface of the axonal membrane is positively charged and the inner surface negatively charged.
Q30 — Nerve Impulse & Membrane Potential · medium
Read the following statements. i. The ion channels present on axonal membrane are selectively permeable to different ions. ii. The axonal membrane is permeable to negatively charged proteins present in the axoplasm. iii. The axoplasm inside the axon contains low concentration of Na+. iv. At resting stage, the inner surface of axonal membrane is negatively charged. How many statements are incorrect?
A. Three
B. Two
C. One ✓ Correct
D. Four
Solution: Only statement ii is incorrect; the axonal membrane is impermeable to the negatively charged proteins in the axoplasm.