Sensory receptors
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Transcript of Sensory receptors
SENSORY RECEPTORS
By: Jhon Mar L. Bellos
DMD1A
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.
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.
FOUR MAJOR TYPES OF SENSORY RECEPTORS OF
THE MASTICATORY SYSTEM
I. Muscle Spindles
II. Golgi Tendon Organs
III.Pacinian Corpuscles
IV. Nociceptors
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
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
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.