Lecture on Reflex Actions

Overview

• Discussion on the reflex actions demonstrated through four videos.
• Key observations: Involuntary responses to stimuli.

Key Concepts

Stimulus

• Defined: A change in the environment that affects the body.
• Examples:
  • Temperature change affecting the finger.
  • Light intensity affecting the pupil.
  • Change in the nasal environment causing a sneeze.
  • Pressure change at the knee.

Response to Stimuli

• In all cases, a response occurs:
  • Moving the hand away from heat.
  • Pupils constricting due to light.
  • Sneezing to expel irritants.
  • Leg raising due to knee pressure.

Reflex Action

• Defined: An involuntary response to a stimulus.
• Different from other involuntary processes (e.g., heartbeat, breathing) as it requires a stimulus.

Mechanism of Reflex Actions

Neurons Involved

• Involves three neurons:
  • Sensory Neuron: Detects the stimulus and converts it to an electrical signal.
  • Relay Neuron (Interneuron): Transfers the signal to the motor neuron.
  • Motor Neuron: Acts on the muscle causing contraction.

Pathway

• Reflex Arc: The pathway consisting of the sensory neuron, relay neuron, and motor neuron.
• Reflex actions bypass the brain to provide a quick response to stimuli, essential for survival.

Reflex Arc

• Sensory neurons detect stimulus and send signals to the spinal cord.
• Signals are transferred via relay neurons without waiting for brain command.
• Motor neurons execute the action.

Importance of Reflex Actions

• Provides immediate response to potentially dangerous stimuli to prevent damage.
• Evolved before complex brain structures, crucial for survival.

Diagram Notes

• Sensory Neuron: Looped structure represents body of neuron, enters the spinal cord from the back.
• Motor Neuron: Exits the spinal cord from the front.
• Reflex arcs may vary:
  • Some may have only sensory and motor neurons (e.g., knee reflex).

Recap and Recall

• Define: Reflex action and reflex arc.
• Identify: Sensory, relay, and motor neurons and their roles.
• Practice: Drawing the reflex arc to aid memory retention.