Lecture Notes: Neural Pathways and Reflexes

Overview

• Neural pathways: Communication routes within the body.
• Reflex arc: A neural pathway that does not reach the brain.

Reflex Arc

• Reflex: A rapid, involuntary response to a stimulus.
  • Does not require conscious thought.
  • Integration occurs in the spinal cord, allowing for faster responses.
• Protective function: E.g., pulling hand away from a hot surface.
• Components:
  • Sensory receptor: Responds to stimuli.
  • Sensory neuron: Conducts info to the integrating center.
  • Integrating center: Located in the spinal cord, can be an interneuron or direct synapse.
  • Motor neuron: Sends motor output to effector.
  • Effector: Typically muscles or glands.

Classification of Reflexes

1. Based on origin:

   • Innate reflex: Inborn, e.g., Moro reflex in babies.
   • Acquired reflex: Learned, e.g., riding a bike.

2. Based on integration center location:

   • Cranial reflex: In the brain stem, e.g., eye movements.
   • Spinal reflex: In the spinal cord, e.g., limb movements.

3. Based on response nature:

   • Visceral reflex: Involves organs, e.g., pupil constriction.
   • Somatic reflex: Involves skeletal muscles, e.g., stretch reflex.

4. Based on laterality:

   • Ipsilateral reflex: Same side of the body.
   • Contralateral reflex: Opposite sides of the body.

5. Based on synapses involved:

   • Monosynaptic reflex: One synapse.
   • Polysynaptic reflex: Multiple synapses.

Specific Reflexes

Stretch Reflex

• Function: Causes contraction of a skeletal muscle in response to stretching.
• Example: Patellar reflex (knee-jerk).
• Process:
  • Tap tendon > stretches muscle > muscle spindles detect > sensory neuron > motor neuron > muscle contracts.
  • Can be mono or polysynaptic.

Tendon Reflex

• Function: Protects muscles/tendons by forcing relaxation before damage.
• Receptors: Golgi tendon organs detect tension changes.
• Example:
  • Strong contraction > tension detected > sensory neuron > interneuron > motor neuron > muscle relaxes.
  • Can cause antagonist muscle to contract to balance tension.

Crossed Extensor Reflex

• Function: Balance maintenance during reflex actions.
• Example: Stepping on something sharp.
• Process:
  • Painful stimulus > withdraw leg > other leg extends to maintain balance.
  • Characteristics: Contralateral, polysynaptic, spinal, and somatic reflex.

Summary

• Reflexes are essential protective and quick-response mechanisms.
• Understanding reflex pathways aids in grasping nervous system functions and responses.