Explain the components and function of a reflex arc, including the role of neurons and the synapse, and calculate the time taken for a reflex action given distance and speed.

Distance ($d$) = $1.5 \text{ m}$
Speed ($v$) = $75 \text{ m} \cdot \text{s}^{-1}$

The time taken for this reflex action to occur is $\boxed{\text{0.02 s}}$.

• 2.7 Neuron A is a sensory neuron (specifically, a pseudounipolar neuron). A labelled diagram of neuron A would show:
  • A cell body (soma) containing a nucleus.
  • A single process extending from the cell body that then branches into two:
    • One branch acting as a dendrite (or peripheral axon) with receptor endings to detect stimuli.
    • The other branch acting as an axon (central axon) extending towards the spinal cord.
  • The axon would be covered by a myelin sheath (formed by Schwann cells) with gaps called Nodes of Ranvier.
  • The end of the axon would have axon terminals (synaptic knobs).