Sensory receptors

Copyright of Jhon Mar Lopez Bellos

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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 Muscle Spindles Golgi Tendon Organs Pacinian Corpuscles 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 e ach 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 .

16. 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.

17. 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.

18. 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 .

19. 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.

20. 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.

21. 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 i njury to the tissue, the nocireceptors relay this information to the CNS as sensation of pain or discomfort .