Oral Receptors Flashcards
Why is it important to know about receptors in dentistry?
1) Malocclusion:
- CNS will detect + correct
- both upper and lower jaw
2) Bruxism:
- awareness of where jaw is
- drugs, iatrogenic
3) Orthodontics:
- chewing pattern must be re- programmed
You have to move teeth and do things so slowly, not only because you may destroy structure but your brain needs time to reprocess that.
4) TMJ disorders:
- trigeminal (sensory V3)
5) Pain!
- oral cavity a common site for pain
What are exteroreceptors, proprioceptors, and interoceptors?
Classified depending on their physical location throughout the body
Exteroceptors - just beneath the skin
Proprioceptors - within muscles and joints
Interoceptors - within the viscera
Exteroceptors - 1° for pain, touch temperature and pressure (nociceptor, mechanoreceptor, thermoreceptor)
Proprioceptors - position & movement, vibration and pressure, pain
Interoceptors - pressure (distention), pain
All of them can transmit pain.
Fastest neurotransmition for proprioceptors, NOT FASTEST FOR PAIN
How are receptors differentiated?
Receptors are differentiated on the basis of whether they are encapsulated or not
Encapsulated
Meissner's (mechanoreceptors) Pacinian (mechanoreceptors) Ruffini's (mechanoreceptors) Golgi Tendon (proprioceptors) Muscle spindle (proprioceptors)
Non-encapsulated
Merkel’s Disks (mechanoreceptors)
Free nerve endings
How are peripheral nerves classified?
Characteristics of peripheral nerves: They are classified according to different criteria: size conduction velocity whether possess a myelin covering
Basic Rule
Fibres that are required to transmit important information do so at much faster rates
Applies to both sensory and motor nerves
What are the motor and sensory neurons?
Only sensory nerves get numeric names (e.g. type 2 affterent)
If you’re using alphabetic it can be either motor or sensory.
Group 1 is faster because it has more myelin.
C type fibers have no myelin so they’re the slowest.
Most autonomic fibers are B type fibers, they are all motor (they aren’t on this chart!!!!!)
ABC motor and sensory. A alpha (Group I) is proprioceptors of skeletal muscle.
Abeta (group II) is mechanoreceptors of skin.
Adelta (Group III) is pain, temperature
C (group IV) are temperature, pain, and itch. Unmyelinated and therefore the slowest.
So once again Sensory fibres from the soma (Somatic afferents) have been classified according to where the information comes from (basically this is a physiological distinction), so what do types I - IV deliver?
Type I - muscle spindle / Golgi tendon endings
Type II - m. spindle / touch / pressure receptors
Type III - myelinated pain / temperature receptors
Type IV - unmyelinated pain / temp. receptors
What are the fastest transmitting fibers?
Muscle spindle and golgi tendon organ are the fastest transmitting.
What is the motor system and what is it divided into?
There is also a system that conveys motor information
This motor division is subdivided into
somatic efferent (muscles) and
visceral efferents (controlling glands, smooth muscle)
What is an example of a visceral efferent motor nucleus that is important for dentistry?
Inf. / Sup. Salivatory Nucl.
What is the most complicated/complex receptor and why?
The most complicated / complex receptor is the muscle spindle
This is because it has both a sensory component and a motor component
All other receptors have only the sensory component
What do neuromuscular spindles provide sensory data for?
Provide sensory data for
- reflex adjustments of muscle tonus
- contribution of cerebellum to motor function
- sensory / motor integration at cortical level
What is the organization of a muscle spindle?
Organization:(Fig 5 -1)
- C.Tissue capsule surrounding a group (2 - 10) of specialized muscle fibres (intrafusal fibres)
- Spindles exist in the body of the muscle itself amongst the extrafusal fibres (in parallel)
- Each spindle is expanded at its central region into a fluid filled bag
- have both motor input and sensory output
What are the two types of intrafusal fibers?
Nuclear - bag
Nuclear – bag
Thicker
3 - 4 nuclei clustered in the bag region
more centrally located within spindle
Nuclear - chain
Nuclear – chain
Thin
Nuclei distributed down the equatorial plane of each cell
more peripherally located in spindle
What is an intrafusal fiber?
But What is an Intrafusal fibre?
It is a specialized muscle / receptor cell, shaped like a spindle that has contractile regions on either end and a relatively more central region that is contacted by sensory nerve fibres and is non-contractile
What are the two different types of sensory nerve endings associated with the intrafusal fibers?
primary endings (annulospinal); and
secondary endings (flowerspray)
Report the length of muscle spindle back to the CNS
- under resting conditions, these sensory axons send ongoing information to the CNS that is mostly unconscious
these axons increase their firing rate when the muscle spindle is stretched )
Difference between the two endings is that the annulospinal are faster than the flowerspray.
What are primary endings in neuromuscular spindles?
Primary endings
Also called annulospiral endings
Classified as Type Ia afferent endings - very rapid conduction velocities
Associated with the central portions of both the nuclear - bag and nuclear - chain fibres
Annulospiral Endings - Ia afferents - Very rapid conduction velocities of sensory information – more centrally located and innervates both bag and chain
What are secondary endings in neuromuscular spindles?
Secondary endings
Also called flowerspray endings
Classified as Type II afferent endings - fast conduction velocities
Associated mainly with the peripheral portions of the nuclear - chain fibres
Flower Spray Endings – Type II afferents - Rapid conduction velocities of sensory information-
Peripheral and primarily associated with chain
Associated with the intrafusal fibres there are also different types of motor nerve endings
called?
Gamma motor fibers (may be up to 4 different types)
What are group Agamma efferent fibers (of gamma motor fibers)?
Gamma motor fibres- Group Agamma efferent fibres
- rapid conduction velocities
- maintain tone in muscle
Subdivided into
dynamic gamma and beta: enhance sensitivity of Ia fibres to respond to activities that require rapid changes in muscle length
static gamma and beta: posture, slow movements
What is the summary of extrafusal and intrafusal muscle fibers?
Extrafusal muscle fibres Aα motor efferent = innervates the muscle
Intrafusal muscles fibres sensory and motor
Sensory: 1 = Group Ia = annulospiral
2 = Group II = flowerspray
Motor: Group Aγ motor fibres: fusimotor
- dynamic vs. static
What are the very sensitive receptors located within the tendon of muscle?
These are also very sensitive receptors
- located within the tendon of muscle
- encapsulated receptor
- spindle shaped
- comprised of many collagen fibres
How are these golgi tendon organs arranged?
Anatomical arrangement of up to 50 GTO’s at the junction between a muscle and its joining tendon
Differences (cf neuromuscular spindle)
- organized in series with a muscle, location
- no contractile element in the receptor
- innervated by a single large-diameter sensory (afferent) nerve - Type Ib
(still very fast conduction)
What do golgi tendon organs do?
GTO in tendon (to muscle border)
Ib sensory fibres weave btwn the collagen fibres of the GTO
- pull on capsule = tension created btwn tendon and muscle fibre b/c axons squeezed = axons activated, myelinated as leaves GTO)
Tension or looseness is detected by the axons.
Basic Action -
When skeletal muscle fibres (extrafusal) contract, they shorten and cause a tension increase in the collagen bundles
This leads to a compression of the unmyelinated nerve which ramifies throughout the encapsulated ending
What does the amount of firing of the golgi tendon organ depend on?
Basic Action -
The size of the generator potential and the frequency of action potential discharge is proportional to the rate and magnitude of the applied force
(Fig 5 - 7)
The amount of force required to generate a response varies due to stiffness/elasticity of the connective tissue capsule of the GTO
As you get older and the collagen gets stiff, you can activate it easily.
Are golgi tendon organs referred to as an “on/off switch”?
More stretch force = more AP’s for a longer time and a greater difference in voltage
