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Year 2 C&M Clinical Symposia > Somatosensory physiology > Flashcards

Somatosensory physiology Flashcards

1
Q

What are the 4 main classes of receptors in the somatosensory system?

A

1) Tactile (innocuous - not painful)
2) Nociceptive
3) Proprioceptive
4) Thermal

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2
Q

What are the 4 types of innocuous tactile receptors?

A

1) Merkel
2) Ruffini
3) Meissener
4) Pacinian

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3
Q

What are the 3 types of proprioceptive receptors?

A

1) Muscle (spindle) - in muscles
2) Golgi tendon receptors - in joints
3) Some inputs from cutaneous mechanoreceptors

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4
Q

How are thermal sensations mediated?

A

Mediated by thermoreceptors localized to discrete zones that exhibit hot and cold sensitivity

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5
Q

By what 3 receptors are nociceptive (painful) sensations mediated?

A

1) Mechanical nociceptors
2) Thermal nociceptors
3) Polymodal nociceptors

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6
Q

What are the 5 types of sensory receptors in the skin, where is each located?

A

1) Meissener’s corpuscle - Just beneath epidermis (between papillae)
2) Merkel’s discs - Just beneath the epidermis (aligned with papillae)
3) Pacinian corpuscles - in the subcutaneous tissue
4) Ruffini’s corpuscles - deep in the dermis

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7
Q

What is the morphology of Meissener’s corpuscles?

A

Looping axon terminals that intertwine supporting cells

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8
Q

What is the morphology of Merkel discs?

A

Dome structure atop axon terminals

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9
Q

What is the morphology of pacinian corpuscles?

A

Sensory axon surrounding by fluid filled capsule, onion shaped appearance

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10
Q

What is the morphology of Ruffini endings?

A

Nerve terminals intertwined with collagen fibrils

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11
Q

What is the morphology of nociceptors?

A

Free nerve endings that penetrate epithelial cells, no morphological specialization

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12
Q

Which type of cutaneous sensory receptor has the smallest receptive field?

A

Merkel discs

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13
Q

Which type of sensory receptor has the largest receptive field?

A

Pacinian corpuscles

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14
Q

Which cutaneous sensory receptors are rapidly adapting?

A

Meissener’s corpuscles and pacinian corpuscles

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15
Q

Which cutaneous sensory receptors are slow adapting?

A

Merkel’s discs and Ruffini endings

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16
Q

Which 2 types of cutaneous sensory receptors have a small receptive field?

A

Meisseners and merkels discs

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17
Q

Which 2 types of cutaneous sensory receptors have a large receptive field?

A

Pacinian corpuscles and Ruffini endings

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18
Q

What is the role of Merkel cells in perception?

A

Detect pressure, form and texture

19
Q

What is the role of Meissener’s corpuscles in perception?

A

Detect flutter and motion

20
Q

What is the role of Ruffini corpuscles in perception?

A

Detect skin stretch

21
Q

What is the role of Pacinian corpuscles in perception?

A

Detect vibration (250-350 Hz)

22
Q

Which type of cutaneous sensory receptor is involved in reading braille?

A

Merkel afferents

23
Q

In terms of 2 point discriminatory thresholds across the body, what is sensitivity correlated with?

A

Density of sensory innervation

24
Q

What are the 2 areas of high sensitivity (small 2 point discriminatory threshold)?

A

1) Fingertips

2) face

25
Q

What are the 2 areas of low sensitivity (large 2 point discriminatory threshold)?

A

1) Torso

2) limbs

26
Q

What are the 4 ‘types’ of temperatures that different thermoreceptors respond to?

A

1) Cold pain
2) Cold
3) Warm
4) Hot pain

27
Q

Temperatures ranging from noxious heat to noxious cold activate several members of which family of receptors?

A

The Trp family of receptors

28
Q

Which receptor does menthol activate?

A

Trpm8

29
Q

Which receptor does capsaicin activate?

A

Trpv1

30
Q

How does capsaicin produce the pungent burning sensation in the mouth?

A 
Belongs to a group of chemicals known as vanilloids 
Acts on thermal receptors (class of nociceptor)
VR1 is expressed in cultured cells
Capsaicin causes an inward Ca2+ current which is dose dependent according to 'hotness of the pepper' - this receptor is also activated by heat
31
Q

What proprioceptor is found in muscles, what does it do?

A

Muscle spindles

Provide sensory feedback from muscle fibres on body position and movement

32
Q

What proprioceptor is found in joints?

A

Golgi tendon organ

Regulate muscle tension or force of contracting and prevent muscle overloading

33
Q

Conduction velocity of a nerve fibre is positively correlated with what?

A

Axon diameter

34
Q

Large diameter, rapidly conducting afferents are associated with which type of somatosensory receptor?

A

Low threshold mechanoreceptors

35
Q

Small diameter, slow conducting afferents are associated with what 2 types of somatosensory receptor?

A

1) Nociceptors

2) Thermoreceptors

36
Q

How can the Herpes Zoster Virus enable us to visualise dermatomes?

A

Virus lurks in primary sensory neurones then can reactivate as shingles - get inflammation and blistering on skin of area of affected dorsal root/sensory neuron

37
Q

Innocuous sensitivities are carried through the CNS by which pathway?

A

Dorsal column pathway

38
Q

Noxious and thermal sensitivities are carried through the CNS by what pathway?

A

Spinothalamic pathway

39
Q

What are Brodmann areas of the brain?

A

47 areas within the cerebral cortex which subserve different physiological functions

40
Q

Where does the secondary somatosensory cortex lie?

A

Adjacent to the primary somatosensory cortex (S1) along the lateral sulcus

41
Q

What is the function of the secondary somatosensory cortex?

A

Plays a key role in sensory and motor integration
Receives corpus callosum inputs to form a ‘joined-up’ body image
Build info from multiple body areas and form a body image

42
Q

Where are the association areas localized to, what is there function?

A

Localised to the posterior parietal cortex

Play a role in integration of multimodal senses

43
Q

Damage to the posterior parietal cortex (ie the association areas) leads to what 2 unusual neurological disorders?

A

1) Astereoagnosia - the inability to identify objects on basis of touch alone - would only be able to confirm what it was by using other sense eg. vision
2) Neglect syndrome - body part or visual field is disregarded

44
Q

After passing through the ventrobasal complex in the thalamus and to the post central gyrus what areas does somatosensory info then pass to?

A

Passes to the posterior parietal (secondary association area) then from there to:

1) Motor system
2) Polysensory association areas
3) Limbic system (learning and memory)

Year 2 C&M Clinical Symposia (21 decks)

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