B.D.S, Human Anatomy, Medical updates

Masticatory Reflexes or Jaw Reflexes

Reflex is a highly stereotyped automated response to a specific stimulus
Masticatory reflexes are type of stretch reflexes brought about by activation of muscle spindles in the muscles
Types of Jaw Reflexes:
  1. Jaw Closing Reflex / Jaw Jerk Reflex
  2. Jaw Opening Reflex
  3. Jaw Unloading Reflex
  4. Tooth Contact Reflexes
  5. Horizontal Jaw Reflexes
Jaw Closing Reflex / Jaw Jerk Reflex:
  • A stretch reflex similar to knee jerk reflex
  • It is a monosynaptic reflex generated by stretching muscle spindles in the masseter muscle
  • Latency period 7-12ms
  • Demonstration: A sharp downward tap on the chin when the mandible is held loosely in the rest position results in contraction of the masseter muscle to bring the teeth into occlusion
Jaw Opening Reflex:
  • Polysynaptic reflex
  • Occurs as a result of mechanical or electrical stimulation of the lips, oral mucosa or teeth
  • A slight opening movement occurs due to inhibition of activity in the mandibular elevators without simultaneous contraction of the depressors

Jaw Unloading Reflex:

  • It is a protective reflex that occurs when the jaw is suddenly unloaded
  • Eg: When a stone comes inside mouth with food while mastication.
  • On sudden encounter with the hard object, mastication is stopped.
  • This is due to reflex inhibition of elevators & reflex excitement of jaw depressors
  • Due to receptors in periodontal ligament
  • Protects teeth from damage

Tooth Contact Reflex:

  • Reflex changes that occur in the elevator muscles when the upper & lower teeth are snapped together
  • There is transient activation followed by a silent period & then a phase of increased & decreased activity in the elevators
  • No effects on the depressors

Horizontal Jaw Reflexes:

  • Lateral, protrusive & retrusive reflex mandibular reflexes

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