N9 + 10 - Touch and mechanorecption Flashcards by Emma Williams

what is mechanoreception?

detection of mechanical stimuli

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What is the same as mechanoreceptor?

peripheral receptor

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what is an adequate stimulus?

Mechanical distortion:

pressure
vibration
tension

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what is touch and what does it involve?

The sensory experience when mechanoreceptors are excited

- CNS

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What is the definition of exteroception?

Give information about things coming into contact with the body

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what is the definition of proprioception?

awareness of position

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What are the mucosal and skin receptors of exteroceptors?

Mechanoreceptors
Nociceptors- harmful stimuli(pain)
Thermoreceptors -change in temp
Chemoreceptors - chemcial change
PDL mechanoreceptors

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what is the other type of exteroceptors?

PDL mechanorectors

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Name proprioceptors?

-PDL Mechanoreceptors 
 -Muscle Spindles
- Joint receptors
- Golgi tendon organs
- Inner ear

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Describe the oro-facial mechanoreceptors.

Mucosa (and skin):
-food texture
-important for mastication
Periodontal ligament:
-forces on teeth
Muscles:
-Muscle spindles-muscle length
Joint receptors:
-joint position and movement

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what is the effect of stimulation on mechanoreceptors?

sensation of touch
Reflexes e.g. jaw muscle reflex, salivary reflex
Interact/ modulate other sensory modalities e.g. effect of rubbing a painful area (gate control)

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How does rubbing help pain?

Huge low level afferent (sensory ) input which blocks out pain from tissue damage

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what makes up different types of mechanoreceptors?

Physiological classification:
-Adaption properties
-Receptive field size
Anatomical classification

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what is the difference between rapid and slow adaptation?

Rapid - the firing is for a short period of time

- Slow - receptors continue firing as long as there is a stimulus

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what is definition of receptive field?

The area/space where a stimulus will affect the receptor

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what are the 4 major types of mechanoreceptors?

RA I - small receptive field/ rapid adaptation
RA II- large receptive field/ rapid adaptation
SA I- small receptive field/ slow adaptation
SA II- large receptive field/ slow adaptation

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Name the 4 most common mechanorecptors.

Meissner’s corpuscle- RA I- (myelinated axons, found deep in tissues)
Pacinian corpuscle- RA II - (multilayered, myelinated, single receptor in the middle, deep in tissues)
Merkel cells - SA I -( non hairy skin, sits just above basement membrane -epidermis)
Ruffini ending- SA II - (multiple terminals-wide area of skin , responds to tension not pressure)

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Describe RA I receptors.

-Example -Meissner corpuscles
- Small receptive fields (RF).  -Low threshold
-rapid adaptation
 Present in:
– Oral mucosa
– Vermillion border. – Mucosa of lip
– Hard palate

Describe RA II receptors.

Example- Pacinian corpuscles  -Deep in mucosa
 Large RF
Rapid adaptation
 Very low threshold
 Rare in oral mucosa

Describe SA I receptors.

-Merkel cell neurite complexes - In basal epithelium
- Small RF
- Low threshold – as low as 1mg 
Present in:
– Tongue – Lips
– cheeks

Describe SA II receptors.

Ruffini endings
 Deep
 Large RF
 Respond to tension
 Low threshold
most commonly found in PDL

Describe the formation of action potential.

Transduction from mechanical to electrical energy
stimulus causes depolarisation
If it reaches threshold an action potential is produced and passed to CNS

describe the structure of the parent axon.

A‐beta large myelinated fibres – fast (33‐75m/s)

what are the touch thresholds for lips/ oral mucosa/ teeth.

lips and oral mucosa : 10mg

- teeth - 0.01N (1g) - strong enough to cause the tooth to move in the socket

what does 2-point discrimination reflect?

- innervation density | - size of receptive field

Describe 2-point discrimination threshold in tip of tongue and lips.

- low 2-point thresholds - high innvervation density - small receptive fields

Describe the 2-point discrimination threshold in the finger tips.

- low 2-point thresholds | - able to discriminate small objects -braille

what role does the PDL have?

exteroceptive role and proprioceptive role

what are the nerve endings, afferents and cell bodies of the PDLMs?

``` Nerve endings: – Ruffini  Afferents: – A‐beta axons – ~300 per tooth  Cell bodies: – V ganglion – mesencephalic nucleus ```

How do you study PDLM properties?

``` Animal studies: -cat canine preparation -localise individual receptors -single fibre recordings Human studies: -Recordings from inferior alveolar nerve -Discrete forces applied to teeth ```

why is the PDL easy to localise?

-No branched axons between adjacent teeth

where is innveration density highest at in the PDL?

apex

what is an adequate stimulus for PDLM?

- tension in the PDL due to pressure applied to tooth | - tooth moves around a fulcrum

what does amount of PDLM activity depend on?

-Direction of applied force - magnitude of force - Adaptation properties - Threshold of the receptors - Position of receptors in PDL

what does the tooth rotate around?

fulcrum

with the same receptor, why is their differences in properties ?

- linked to position relative to fulcrum | - smaller stimulus nearer the fulcrum

what type of receptors are found at apex of PDL?

slowly adapting and low threshold

what type of receptors are found nearer fulcrum?

rapidly adapting and high threshold

Describe the sensory pathway.

Stage 1: Mechanoreception – Transduction of stimulus – Propagation along primary afferent nerve  Stage 2: Processing at first synapse – Trigeminal nuclei (or Spinal nuclei)  Stage 3: Processing in thalamus  Stage 4: Conscious perception – Somatosensory cortex

what is dermatome?

the area of skin innervated by the : – Trigeminal division or – Single spinal segment

where are trigeminal afferent nerve cell bodies found and where do they enter the brainstem?

- Cell bodies in: V ganglion and V mesencephalic nucleus | - eneter brainstem via trigeminal root

where doe trigeminal pathways synapse?

- mianly in main sensory nucleus | - project to spinal v nuclei as well

where do trigeminal pathways project to?

sensory cortex via thalamus

how does the body focus on individual stimuli?

inhibits surrounding axons (surround inhibition)