Reflexes Lecture Notes

Introduction to Reflexes

• Reflexes are not just a song by Duran Duran, but important neural pathways.
• Reflexes are neural pathways that control automatic reactions to stimuli.
• Example: Commonly tested during medical exams, such as the knee-jerk reflex.

Reflex Arc

• Definition: A neural pathway that controls a reflex.
• Key Feature: Allows reflexes to occur without brain involvement, speeding up the process.
• Components of a Reflex Arc:
  1. Receptor: Stretch receptor stimulated by the stretching of a muscle tendon, activating the muscle spindle.
  2. Afferent Pathway: Carries information to the spinal cord; pseudo-unipolar sensory neuron.
  3. Synapse: Integration site between sensory and motor pathways, usually within the spinal cord.
  4. Efferent Pathway: Carries command back to the effector; involves a motor neuron.
  5. Effector: Causes a reflex action, such as muscle contraction.

Patellar Reflex

• Process:

  • Muscle spindle in quadriceps detects patellar ligament movement.
  • Sensory neuron sends information to the spinal cord.
  • Motor neuron induces contraction of quadriceps muscle.

• Neural Details:

  • Sensory Neuron: Afferent, pseudo-unipolar, resides in the dorsal root ganglion (PNS).
  • Motor Neuron: Efferent, multipolar, located in the CNS.
  • Monosynaptic Reflex: Involves a single synapse; no interneuron.

Importance of Stretch Reflex

• Spinal Reflex Example: Patellar reflex, crucial for proprioception and balance.
• Function:
  • Maintains posture and balance without conscious effort.
  • Enables rapid response to muscle stretch, allowing compensation through contraction.
• Application:
  • Maintains upright posture by countering shifts in body position.
  • Rapid adaptation to changes in ground surface or added loads.

Neural Circuitry

• The reflex arc involves a loop from muscle to spinal cord and back.
• Conscious movements involve cerebral processing but reflexes bypass this for speed.
• Motor neurons travel in a loop from the spinal cord to muscles.

These notes summarize the key points about reflexes, focusing on the reflex arc and the patellar reflex, their components, and their physiological importance.