BIOLOGY WITH HAMZA · MDCAT REVISION
Coordination & Control
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
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Learning targets
- Explain how ion gradients create the resting membrane potential.
- Trace depolarisation, repolarisation and the refractory period.
- Describe chemical synaptic transmission and one-way signalling.
Core notes
- Resting potential depends on ion gradients and selective permeability.
- Voltage-gated sodium entry causes depolarisation; potassium exit restores negativity.
- Refractory periods support one-way propagation.
- Calcium entry links an arriving impulse with neurotransmitter release.
Read, cover and redraw
Ion gradients and leak permeability maintain negativity.
Sufficient depolarisation opens Na⁺ channels.
Rapid Na⁺ entry makes the inside positive.
Na⁺ channels inactivate and K⁺ leaves.
Channels reset before normal excitability returns.
Written recall
1. Why does the sodium–potassium pump not directly create the rapid rising phase of an action potential?
2. Why is transmission across a typical chemical synapse one-way?
Apply the idea
1. Which label belongs at X in the simplified withdrawal reflex pathway?
- Skin receptor
- X
- Spinal cord relay
- Motor neuron
- Muscle
- Sensory neuron
- Photoreceptor
- Endocrine gland
- Motor neuron
My answer: _____ Reason: ____________________________________
2. An impulse travels 0.8 m along an axon in 0.02 s. What is its average conduction speed?
- 0.016 m s⁻¹
- 40 m s⁻¹
- 4 m s⁻¹
- 400 m s⁻¹
My answer: _____ Reason: ____________________________________
3. An action potential reaches a presynaptic terminal, but its voltage-gated calcium channels are blocked. What should decline first?
- Neurotransmitter receptor synthesis throughout the body
- Action potential amplitude in every sensory neuron
- Vesicle fusion and neurotransmitter release
- Myelin thickness along the postsynaptic neuron
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. The rising phase is produced by rapid sodium flow through voltage-gated channels. The pump works more slowly to maintain the gradients that make that flow possible.
2. Transmitter vesicles and release machinery are presynaptic, while the relevant receptors are on the postsynaptic membrane.
Applied questions
1. A — The sensory neuron carries impulses from the receptor towards the spinal cord. A motor neuron carries the output towards the effector.
2. B — Speed = distance ÷ time = 0.8 ÷ 0.02 = 40 m s⁻¹. The units are metres per second, not seconds per metre.
3. C — Calcium entry at the terminal triggers vesicle fusion. Blocking that entry reduces transmitter release even though the impulse has reached the terminal.