Sensory receptors

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SENSORY RECEPTORS By: Jhon Mar L. Bellos DMD1A

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Transcript of Sensory receptors

Page 1: Sensory receptors

SENSORY RECEPTORS

By: Jhon Mar L. Bellos

DMD1A

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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.

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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.

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FOUR MAJOR TYPES OF SENSORY RECEPTORS OF

THE MASTICATORY SYSTEM

I. Muscle Spindles

II. Golgi Tendon Organs

III.Pacinian Corpuscles

IV. Nociceptors

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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

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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