Reflexes Overview

• Definition: Reflexes are automatic responses to changes in the environment, typically integrated in the gray matter of the spinal cord.

Types of Reflexes

• Somatic Reflexes: Involved in voluntary movements.

  • Examples: Knee-jerk reflex (patellar reflex), biceps reflex.

• Autonomic or Visceral Reflexes: Control involuntary functions.

  • Examples: Increased heart rate when scared, slowed digestion.

Cranial Nerve Involved Reflexes

• Corneal Reflex (Cranial Nerves V & VII)

  • Automatic blinking when an object touches the eyeball.

  • Sensory input from Cranial Nerve V; motor output via Cranial Nerve VII.

• Oculo-cardiac Reflex (Cranial Nerves V & X)

  • Slowing of heart rate upon applying pressure to the eyeball.

• Pupillary Reflex (Cranial Nerves II & III)

  • Pupil constricts in response to light.

  • Sensory input from Cranial Nerve II; motor output via Cranial Nerve III.

Reflex Arc Components

1. Sensory Receptor: Detects stimulus (e.g., pain from a pinprick).

2. Sensory Neuron: Transmits information to spinal cord.

3. Integrating Center: Processes information via association neurons.

4. Motor Neuron: Sends signals to muscles for action.

5. Effector: Muscle or gland that responds to the motor neuron signal.

Somatic Spinal Reflexes

• Stretch Reflex

  • Example: Patellar reflex (knee-jerk reaction).

  • Mechanism: Stretch at the muscle spindle activates motor neurons, causing quadricep contraction and leg extension; involves reciprocal inhibition to the hamstrings (Sherrington's law).

• Golgi Tendon Organ Reflex

  • Example: Lifting a heavy weight (e.g., leg extensions).

  • Mechanism: Tension sensed by Golgi tendon organs, leading to inhibitory signals to the contracted muscle (quads) and excitatory signals to antagonistic muscles (hamstrings) to prevent injury.

• Flexor Reflex (Withdrawal Reflex)

  • Example: Pulling hand away from a hot surface.

  • Mechanism: Sensory receptors detect pain, signal sent via sensory neurons to spinal cord; motor neurons cause flexor muscles to contract rapidly to withdraw limb.

• Crossed Extensor Reflex

  • Function alongside the flexor reflex.

  • Mechanism: When one leg withdraws (flexor reflex), the opposite leg extends to maintain balance.

  • Involves sensory input for one side and motor output to extensors on the opposite side.