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1. SENSORY RECEPTORS
By: Jhon Mar L. Bellos
DMD1A

2. SENSORY RECEPTORS
 They are neurologic structures or organs located in all body tissues
that provide information to the CNS by way of the afferent neurons
regarding the status of these tissues.
 They are located in throughout the tissues that make up the
masticatory system.

3. SENSORY RECEPTORS
 Specialized sensory receptors provide specific information to the
afferent neurons and thus back to the CNS.
 E.g
• Nociceptors – specific for discomfort and pain.
• Procioceptors – provides information regarding the position and
movement of the mandible and associated oral structures.
• Interoceptors – carry information regarding the status of the internal
organs.

4. FOUR MAJOR TYPES OF
SENSORY RECEPTORS OF
THE MASTICATORY SYSTEM
I. Muscle Spindles
II. Golgi Tendon Organs
III. Pacinian Corpuscles
IV. Nociceptors

5. MUSCLE SPINDLES
 Are specialized receptor organs found in the muscle tissues.
 A connective tissue sheath where a bundle of intrafusal muscle fibers
are bound.
Terminologies:
 Intrafusal fibers – muscle fibers which are only minutely contractile.
 Extrafusal fibers – muscle fibers which are contractile and make up a
bulk of the muscle

6. MUSCLE SPINDLES
 They primarily monitor tension within the skeletal muscle. They
are interspersed throughout the muscles and aligned parallel with the
extrafusal fibers.
 Arrangements of the intrafusal fibers within each spindle:
• 1. Chainlike – Nuclear chain type.
• 2. Clumped – Nuclear bag type

7. MUSCLE SPINDLES
 Afferent nerves that supply the intrafusal fibers:
• 1. Larger Fiber
- conduct impulses at a higher speed and have lower thresholds.
- end in the central region of the intrafusal fibers and are said to be the
primary endings.
• 2. Smaller Fiber
- end in the poles of the spindle and are secondary endings.

8. MUSCLE SPINDLES
 When the muscles are stretched, the intrafusal fibers are also
stretched because it is parallel to the extrafusal fibers.
• This stretch is monitored at the nuclear chain and nuclear bag region.
• The annulospiral (primary) and flower spray (secondary) endings are
activated by the stretch., and the afferent (sensory) neurons carry
these neural impulses to the CNS.
• The afferent neurons originating in the muscle spindles have their cell
bodies in the trigeminal mesencephalic nucles..
• TMN - involved in proprioception of the face.

9. MUSCLE SPINDLES
 The intrafusal fibers receive efferent (motor) innervation by the
way of fusimotor nerve fibers. They are given the alphabetical order
of “gamma” to distinguish them from “alpha” nerve fibers, which
supply the extrafusal fibers.
 Y-efferent fibers originate from the CNS and causes the
contraction of intrafusal fibers when stimulated.

10. MUSCLE SPINDLES
 Initiation of afferent activity.
• 1. Y-efferent is stimulated.
• 2. Intrafusal fibers contract.
• 3. Nuclear Chain and Nuclear Bag areas are stretched.
• 4. Stretching of NC and NB areas are registered as though the entire
muscle were stretched.
• 5. Afferent activity is initiated.

11. MUSCLE SPINDLES
 Two manners in which the afferent fibers of the muscle spindles
can be stimulated:
• 1. Generalized stretching of the entire muscle. (Extrafusal fibers)
• 2. Contraction of the intrafusalfibers by way of y-efferents.
*The muscle spindles can only register the stretch; they cannot
differentiate between these two activities. Therefore, the activities are
recorded as the same activity by the CNS.

12. MUSCLE SPINDLES
 The extrafusal muscle fibers receive innervation by the way of the
a-efferent motor neurons. Most of these have their cell bodies at the
trigeminal motor nucleus. Stimulation of these neurons therefore
causes the group of extrafusal muscle fibers to contract.

13. MUSCLE SPINDLES
 Gamma efferent system – believed to act as a mechanism to
sensitize the muscle spindles.
- without this, there will be a total
shutdown of spindle fiber activity

14. GOLGI TENDON ORGAN
 They are located in the muscle tendon between the muscle fibers
and their attachment to the bone.
 They are more sensitive and active in reflex regulation during
normal function.
 They primarily monitor tension.

15. GOLGI TENDON ORGAN
 They occur in series with the extrafusal muscle fibers and not in
parallel as with muscle spindles.
 They consist of tendinous fibers surrounded by lymph spaces
enclosed within a fibrous capsule.
 Afferent (sensory) fibers enter near the middle of the organ and
spread out over the extent of the fiber.

17. GOLGI TENDON ORGAN
 Tension on the tendon stimulates the receptors in the Golgi
Tendon Organ.
 Contraction of the muscle also stimulates the organ.
 Overall stretching of the muscle creates tension in the tendon and
stimulates the organ.

18. PACINIAN CORPUSCLES
 They are large oval organs made up of concentric lamellae of
connective tissues.
 They are widely distributed .
 They are considered to serve principally for the perception of
movement and firm pressure.

19. PACINIAN CORPUSCLE
 At the center of each cell is a core containing the termination of a
nerve fiber.
 Locations: Tendons, joints, periosteum, tendinous insertions,
fascia, and subcutaneous tissue.
 Pressure applied deforms the organ and stimulates the nerve fiber.

22. NOCICEPTORS
 Generally, they are stimulated by injury and transmit injury
information to the CNS by way of the afferent fibers.
 They are located throughout most of the tissues in the masticatory
system.

23. NOCICEPTORS
 Types:
• 1. Responds exclusively to noxious mechanical and thermal stimuli.
• 2. Responds to a wide range of stimuli, from tactile sensations to
noxious injury
• 3. Low-threshold receptors specific for light touch, pressure or facial
movement.
• 4. Mechanoreceptors – responds to mechanical pressure or
distortion.

24. NOCICEPTORS
 Primarily functions to monitor the condition, position, and
movement of the tissues in the masticatory system.
 When conditions exist that are either potentially harmful or
actually causes injury to the tissue, the nocireceptors relay this
information to the CNS as sensation of pain or discomfort.