The Synapse: A tiny gap between two neurones where electrical signals cannot cross directly as electricity.
Chemical Messengers: When an impulse reaches the end of the first neurone, it triggers the release of neurotransmitters from vesicles.
Diffusion: These chemicals diffuse across the synaptic cleft and bind to specific receptor sites on the membrane of the next neurone.
Signal Regeneration: The binding of neurotransmitters initiates a new electrical impulse in the second neurone, allowing the signal to continue its journey.
| Feature | Reflex Action | Voluntary Action |
|---|---|---|
| Control | Involuntary | Conscious |
| Speed | Very Rapid | Relatively Slower |
| Coordinator | Spinal Cord / Unconscious Brain | Conscious Brain (Cerebral Cortex) |
| Pathway | Reflex Arc | Sensory -> Brain -> Motor |
Direction of Impulse: Always double-check that your diagram labels show the impulse moving from the receptor to the CNS and then to the effector.
Labeling Accuracy: Be prepared to identify the sensory, relay, and motor neurones on a spinal cord cross-section; the sensory neurone enters through the dorsal root.
Effectors: Do not assume the effector is always a muscle. If the response involves a chemical change, the effector is a gland.
Bypassing the Brain: In exam questions, emphasize that the impulse goes to the spinal cord rather than the conscious brain to explain the speed of the reflex.
Misconception: Brain Involvement: A common error is thinking the brain 'chooses' to react. While the brain is notified, it is not part of the decision-making loop for a reflex.
Synapse Delay: Students often forget that every synapse introduces a slight delay because chemical diffusion is slower than electrical conduction.
Stimulus vs. Receptor: Ensure you distinguish between the environmental change (stimulus) and the cell that detects it (receptor).
Homeostasis: Many homeostatic mechanisms, such as the regulation of blood pressure or pupil size, rely on internal reflex arcs.
Reaction Time: While reflexes are fixed, the overall reaction time for voluntary tasks can be influenced by factors like age, fatigue, or drugs.
Neurobiology: The study of reflexes provides a foundation for understanding more complex neural circuits and the evolutionary development of the nervous system.
