Neurones and nerve impulsesEdexcel A-Level Biology A: Mind map

Exam questions on Neurones and nerve impulses

1. A student touches a hot kettle and pulls her hand away before she feels any pain. The withdrawal reflex involves three types of neurone linking the receptors in her skin to the muscles in her arm.
   Describe the role of Schwann cells in the myelination of an axon.2 marks
2. A student studies the giant axon of a squid using microelectrodes. The potential difference across the axon membrane is -70 mV at rest. When the axon is stimulated, the potential rises rapidly to +40 mV and then falls back, dipping below -70 mV briefly before returning to its resting value.
   A weak stimulus fails to produce an action potential. Explain why.2 marks
3. Motor neurones carry impulses from the spinal cord to the muscles of the foot, a distance of 0.84 m. In a myelinated motor neurone, the action potential travels at 70 m s⁻¹. In an unmyelinated neurone of the same length the action potential travels at 1.4 m s⁻¹.
   Calculate the time taken, in milliseconds, for an action potential to travel along the myelinated neurone, and state how many times faster this is than in the unmyelinated neurone.3 marks