N9 + 10 - Touch and mechanorecption Flashcards
what is mechanoreception?
detection of mechanical stimuli
What is the same as mechanoreceptor?
peripheral receptor
what is an adequate stimulus?
Mechanical distortion:
- pressure
- vibration
- tension
what is touch and what does it involve?
- The sensory experience when mechanoreceptors are excited
- CNS
What is the definition of exteroception?
Give information about things coming into contact with the body
what is the definition of proprioception?
awareness of position
What are the mucosal and skin receptors of exteroceptors?
- Mechanoreceptors
- Nociceptors- harmful stimuli(pain)
- Thermoreceptors -change in temp
- Chemoreceptors - chemcial change
- PDL mechanoreceptors
what is the other type of exteroceptors?
PDL mechanorectors
Name proprioceptors?
-PDL Mechanoreceptors -Muscle Spindles - Joint receptors - Golgi tendon organs - Inner ear
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
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)
How does rubbing help pain?
Huge low level afferent (sensory ) input which blocks out pain from tissue damage
what makes up different types of mechanoreceptors?
Physiological classification:
-Adaption properties
-Receptive field size
Anatomical classification
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
what is definition of receptive field?
The area/space where a stimulus will affect the receptor
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
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)
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)
