Lecture on Reflex Action

What is a Reflex Action?

• Reflex Action: An immediate, involuntary response to a stimulus.
• It provides a fast reaction to a stimulus without involving thought, and does not engage the brain’s conscious areas.
• Example: Quickly pulling your hand back when you touch something hot.

Reflex Arc

• Pathway on which a reflex action travels.
• It is called an arc because it is a pathway that forms a curve.
• A specialised pathway for the involuntary response that occurs in reflex action.

Role of Neurons

• Sensory Neurons: Located in the finger, detect the stimulus.
• Heat-sensitive Receptors: Detect heat.
• Ganglion: Where many cell bodies are collected.
• Spinal Cord: The signal travels to the spinal cord.
  • White Matter: Made of axons and myelin sheath.
  • Grey Matter: Made of cell bodies.
• Interneurons: Located in the grey matter.
• Motor Neurons: Carry the signal to the effector.

Reflex Action Pathway

1. Stimulus Detection: Sensory neurons in the finger detect the stimulus.
2. Creation and Travel of Impulse: Impulse travels from dendrites to axons.
3. Travel from Ganglion: Signal reaches the spinal cord from the ganglion.
4. Processing in Spinal Cord: Signal reaches interneurons in the grey matter.
5. Motor Response: Motor neurons carry the signal to the muscles.
6. Muscular Response: Biceps/triceps muscles contract/relax, causing the hand to retract.

Additional Signal

• A signal also travels to the brain, informing about the action taken.

Important Points

• Reflex action is an immediate involuntary response, mostly occurring through the spinal cord.
• It does not involve the brain’s conscious part, although the brain is informed.
• The pathway is called a reflex arc, involving sensory neurons, interneurons, and motor neurons.