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Neuroscience > N9 + 10 - Touch and mechanorecption > Flashcards

N9 + 10 - Touch and mechanorecption Flashcards

1
Q

what is mechanoreception?

A

detection of mechanical stimuli

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2
Q

What is the same as mechanoreceptor?

A

peripheral receptor

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3
Q

what is an adequate stimulus?

A

Mechanical distortion:

  • pressure
  • vibration
  • tension
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4
Q

what is touch and what does it involve?

A
  • The sensory experience when mechanoreceptors are excited

- CNS

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5
Q

What is the definition of exteroception?

A

Give information about things coming into contact with the body

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6
Q

what is the definition of proprioception?

A

awareness of position

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7
Q

What are the mucosal and skin receptors of exteroceptors?

A
  • Mechanoreceptors
  • Nociceptors- harmful stimuli(pain)
  • Thermoreceptors -change in temp
  • Chemoreceptors - chemcial change
  • PDL mechanoreceptors
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8
Q

what is the other type of exteroceptors?

A

PDL mechanorectors

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9
Q

Name proprioceptors?

A 
-PDL Mechanoreceptors 
 -Muscle Spindles
- Joint receptors
- Golgi tendon organs
- Inner ear
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10
Q

Describe the oro-facial mechanoreceptors.

A 
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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11
Q

what is the effect of stimulation on mechanoreceptors?

A
  • 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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12
Q

How does rubbing help pain?

A

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

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13
Q

what makes up different types of mechanoreceptors?

A

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

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14
Q

what is the difference between rapid and slow adaptation?

A
  • 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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15
Q

what is definition of receptive field?

A

The area/space where a stimulus will affect the receptor

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16
Q

what are the 4 major types of mechanoreceptors?

A

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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17
Q

Name the 4 most common mechanorecptors.

A
  • 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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18
Q

Describe RA I receptors.

A

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

19
Q

Describe RA II receptors.

A
  • Example- Pacinian corpuscles  -Deep in mucosa
  •  Large RF
  • Rapid adaptation
  •  Very low threshold
  •  Rare in oral mucosa
20
Q

Describe SA I receptors.

A

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

21
Q

Describe SA II receptors.

A
  • Ruffini endings
  •  Deep
  •  Large RF
  •  Respond to tension
  •  Low threshold
  • most commonly found in PDL
22
Q

Describe the formation of action potential.

A
  • Transduction from mechanical to electrical energy
  • stimulus causes depolarisation
  • If it reaches threshold an action potential is produced and passed to CNS
23
Q

describe the structure of the parent axon.

A

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

24
Q

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

A
  • lips and oral mucosa : 10mg

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

25
Q

what does 2-point discrimination reflect?

A
  • innervation density

- size of receptive field

26
Q

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

A
  • low 2-point thresholds
  • high innvervation density
  • small receptive fields
27
Q

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

A
  • low 2-point thresholds

- able to discriminate small objects -braille

28
Q

what role does the PDL have?

A

exteroceptive role and proprioceptive role

29
Q

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

A 
Nerve endings: – Ruffini
 Afferents:
– A‐beta axons 
– ~300 per tooth
 Cell bodies: 
– V ganglion
– mesencephalic nucleus
30
Q

How do you study PDLM properties?

A 
Animal studies:
-cat canine preparation
-localise individual receptors
-single fibre recordings
Human studies:
-Recordings from inferior alveolar nerve
-Discrete forces applied to teeth
31
Q

why is the PDL easy to localise?

A

-No branched axons between adjacent teeth

32
Q

where is innveration density highest at in the PDL?

A

apex

33
Q

what is an adequate stimulus for PDLM?

A
  • tension in the PDL due to pressure applied to tooth

- tooth moves around a fulcrum

34
Q

what does amount of PDLM activity depend on?

A

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

35
Q

what does the tooth rotate around?

A

fulcrum

36
Q

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

A
  • linked to position relative to fulcrum

- smaller stimulus nearer the fulcrum

37
Q

what type of receptors are found at apex of PDL?

A

slowly adapting and low threshold

38
Q

what type of receptors are found nearer fulcrum?

A

rapidly adapting and high threshold

39
Q

Describe the sensory pathway.

A

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

40
Q

what is dermatome?

A

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

41
Q

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

A
  • Cell bodies in: V ganglion and V mesencephalic nucleus

- eneter brainstem via trigeminal root

42
Q

where doe trigeminal pathways synapse?

A
  • mianly in main sensory nucleus

- project to spinal v nuclei as well

43
Q

where do trigeminal pathways project to?

A

sensory cortex via thalamus

44
Q

how does the body focus on individual stimuli?

A

inhibits surrounding axons (surround inhibition)

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