Synapse and Reflexes

Synapse and Reflexes

What Is a Synapse?

A synapse is the tiny gap between two neurones. Signals pass across it using chemical messengers called neurotransmitters.

How Synapses Work

1. An electrical impulse reaches the end of the first neurone.
2. This triggers the release of neurotransmitters.
3. These chemicals diffuse across the synapse.
4. They bind to receptors on the next neurone, triggering a new impulse.

💡 Key Concept: Synapses allow neurones to communicate, but they slightly slow down transmission because of the chemical stage.

What Are Reflexes?

Reflexes are fast, automatic responses that help protect the body. They do not involve the conscious brain.

Why Are Reflexes Important?

✔ Prevent injury (e.g. pulling your hand away from something hot).
✔ Allow quick reactions to danger.

The Reflex Arc

The reflex arc is the pathway that an impulse takes during a reflex.

Stage

What Happens

Stimulus

Detected by a receptor (e.g. heat on skin).

Sensory neurone

Carries impulse to the spinal cord.

Relay neurone

Passes impulse across the spinal cord.

Motor neurone

Carries impulse to the effector.

Effector

Muscle contracts or gland releases a hormone.

💡 Key Fact: Reflexes are involuntary and bypass the brain, allowing a quicker response.

Examples of Reflex Actions

  • Blinking when something comes close to the eyes.
  • Pupil reflex – pupils shrink in bright light.
  • Knee-jerk when tapped below the kneecap.
  • Withdrawal reflex – pulling hand away from sharp or hot objects.

Questions 

  1. What is a synapse?
  2. What carries the signal across a synapse?
  3. What is a reflex?
  4. What is the role of a relay neurone?
  5. Why are reflexes fast?

Summary 

  • Synapses are gaps between neurones, where signals pass via neurotransmitters.
  • Reflexes are fast, automatic responses that protect the body from harm.
  • Reflex arcs include sensory, relay, and motor neurones, and bypass the brain.