When a fly lands on a horse, the horse's skin shivers - OCR Gateway - GCSE Biology - Question 21 - 2022 - Paper 1

Stimulus Detection: When a fly lands on the horse's skin, sensory receptors in the skin are activated. These receptors detect the presence of the fly.

Signal Transmission: The sensory neurons transmit the signal from the skin receptors to the spinal cord. This transmission occurs via electrical impulses.

Integration Process: Within the spinal cord, the sensory neurons connect to interneurons which process the information and generate a response without needing to travel to the brain, showcasing the reflex nature of the action.

Motor Neuron Activation: The interneurons then activate motor neurons that transmit signals back to the muscles responsible for making the skin shiver.

Response Execution: The motor neurons stimulate the muscles in the skin to contract rapidly, causing the shivering response, which helps to dislodge the fly, or improve the horse's comfort.

Reflex Arc: This entire process exemplifies a reflex arc, which involves the pathway from the sensory receptor to the spinal cord (integration center) and back out to the effector (muscles) for a rapid, involuntary response.