Nerve impulsesAQA A-Level Biology: Mind map

Exam questions on Nerve impulses

1. A neurone has a resting potential of −70 mV and a threshold potential of −55 mV. In an experiment, three separate stimuli depolarised the membrane to −62 mV, −50 mV and −30 mV. Only two of the stimuli produced action potentials.
   Explain why one stimulus produced no action potential and the other two produced action potentials of the same size.2 marks
2. Neurologists measure the speed of conduction along motor neurones. In a healthy adult at 37 °C the speed along one neurone is 60 m s⁻¹. In a patient with multiple sclerosis, a condition that destroys patches of the myelin sheath, the speed along the same neurone is 8 m s⁻¹.
   Explain why the speed of conduction is lower in the patient.2 marks
3. A researcher stimulates an axon repeatedly. After each action potential the axon cannot produce another for 2.0 ms, because the voltage-gated sodium ion channels are closed and the membrane potential has to return to its resting value. The researcher increases the strength of the stimulus.
   Explain the importance of the refractory period for the transmission of nerve impulses.3 marks