Noesis
Level 2 — RecallNervous System

Nervous System

printable — key stays hidden on paper

Level 2 (Recall & Understanding)

Time: 30 minutes | Total Marks: 40

Answer all questions. Use diagrams where helpful.

Q1. Label the three main structural parts of a neuron and state the function of each. (6 marks)

Q2. Distinguish between sensory neurons, motor neurons, and interneurons by stating the direction in which each carries impulses. (3 marks)

Q3. The resting membrane potential of a typical neuron is about −70 mV-70\text{ mV}. (a) State what is meant by "resting membrane potential." (2 marks) (b) Name the pump that maintains this potential and state the ratio of ions it moves. (2 marks)

Q4. Place the following stages of an action potential in the correct order and give the approximate membrane voltage at each: repolarisation, depolarisation, resting, hyperpolarisation, threshold. (5 marks)

Q5. Explain saltatory conduction. In your answer, refer to myelin, nodes of Ranvier, and the effect on conduction speed. (4 marks)

Q6. Describe the sequence of events in synaptic transmission from the arrival of an action potential at the presynaptic terminal to the response in the postsynaptic neuron. (5 marks)

Q7. Complete the comparison table between the Central Nervous System (CNS) and Peripheral Nervous System (PNS). (4 marks)

Feature CNS PNS
Components (i) (ii)
Main role (iii) (iv)

Q8. State the main function of each brain region: (a) cerebellum, (b) medulla oblongata, (c) hypothalamus. (3 marks)

Q9. Draw or list, in order, the five components of a reflex arc. (5 marks)

Q10. For each situation, state whether the sympathetic or parasympathetic division is dominant: (a) sprinting from danger, (b) resting after a large meal, (c) pupil dilation. (3 marks)

End of Paper

Answer keyMark scheme & solutions

Q1. (6 marks)

  • Dendrites — receive signals/impulses from other neurons and carry them toward the soma. (1 name + 1 function)
  • Soma (cell body) — contains the nucleus and organelles; integrates incoming signals and maintains cell metabolism. (1 + 1)
  • Axon — conducts the impulse away from the soma to the axon terminals. (1 + 1) Why: these three regions define the input–integration–output flow of a neuron.

Q2. (3 marks)

  • Sensory (afferent): carry impulses from receptors → CNS (1)
  • Motor (efferent): carry impulses from CNS → effectors (muscles/glands) (1)
  • Interneurons: lie within the CNS, connecting sensory and motor neurons (1)

Q3. (4 marks) (a) The voltage difference across the membrane of a non-firing neuron, inside negative relative to outside (~−70-70 mV). (2) (b) The sodium–potassium pump (Na⁺/K⁺ ATPase) (1); moves 3 Na⁺ out for every 2 K⁺ in (1). Why: unequal ion pumping plus selective K⁺ leak keeps the inside negative.

Q4. (5 marks) — 1 mark each, correct order:

  1. Resting (~−70-70 mV)
  2. Threshold (~−55-55 mV)
  3. Depolarisation (rises to ~+30+30 / +40+40 mV, Na⁺ influx)
  4. Repolarisation (falls back toward −70-70 mV, K⁺ efflux)
  5. Hyperpolarisation (~−80-80 mV briefly) Why: Na⁺ channels open first (depolarise), then K⁺ channels (repolarise + overshoot).

Q5. (4 marks)

  • Myelin sheath is an electrical insulator covering the axon (1)
  • Gaps in myelin are the nodes of Ranvier, where voltage-gated Na⁺ channels are concentrated (1)
  • The action potential "jumps" from node to node rather than travelling continuously (1)
  • This greatly increases conduction speed (and saves energy) (1)

Q6. (5 marks) — 1 mark each:

  1. Action potential arrives at presynaptic terminal; voltage-gated Ca²⁺ channels open, Ca²⁺ enters.
  2. Ca²⁺ triggers synaptic vesicles to fuse with membrane.
  3. Neurotransmitter released by exocytosis into synaptic cleft.
  4. Neurotransmitter diffuses across cleft and binds receptors on postsynaptic membrane.
  5. Ion channels open → postsynaptic potential change (excitation/inhibition); transmitter then removed (reuptake/enzyme).

Q7. (4 marks) — 1 mark each:

Feature CNS PNS
Components (i) Brain + spinal cord (ii) Nerves + ganglia outside CNS
Main role (iii) Integration/processing & coordination (iv) Carry info between CNS and body

Q8. (3 marks) (a) Cerebellum — balance, posture, coordination of movement (1) (b) Medulla oblongata — controls involuntary vital functions (heart rate, breathing) (1) (c) Hypothalamus — homeostasis (temperature, hunger, thirst, hormone control) (1)

Q9. (5 marks) — 1 mark each, in order: Receptor → Sensory (afferent) neuron → Integration centre (interneuron/spinal cord) → Motor (efferent) neuron → Effector (muscle/gland).

Q10. (3 marks) (a) Sympathetic (1) (b) Parasympathetic (1) (c) Sympathetic (1) Why: sympathetic = "fight or flight," parasympathetic = "rest and digest."

[
  {"claim":"Na/K pump ratio 3 out : 2 in gives net +1 charge exported per cycle","code":"na_out=3; k_in=2; net_charge=na_out-k_in; result=(net_charge==1)"},
  {"claim":"Depolarisation voltage change from rest -70mV to peak +30mV is 100mV","code":"rest=-70; peak=30; delta=peak-rest; result=(delta==100)"},
  {"claim":"Threshold -55mV is 15mV above resting -70mV","code":"rest=-70; thr=-55; result=(thr-rest==15)"},
  {"claim":"Reflex arc has 5 ordered components","code":"arc=['receptor','sensory','interneuron','motor','effector']; result=(len(arc)==5)"}
]