BIOLOGY 5090 · STRUCTURED PRACTICE
The diagram illustrates a cross-section of the human spinal cord and the neural pathway of a withdrawal reflex arc in response to touching a sharp object.
Identify the structures labelled P, Q, and R in the reflex arc diagram.
Describe the sequence of events that occurs at the synapse between neurone Q and neurone R when an electrical impulse arrives at the presynaptic terminal.
State two defining characteristics of a reflex action, and suggest one survival benefit of the withdrawal reflex.
A local anaesthetic drug reversibly blocks voltage-gated sodium channels in sensory neurone axons. Predict and explain the effect of applying this drug to the sensory nerve before the finger touches the sharp pin.
Total: 10 marks