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Medneuro M2-3 > Somatosensory system > Flashcards

Somatosensory system Flashcards

1
Q

somatosensory cells…

a. mechanoreceptors have small cell body and are lightly to not myelinated and nociceptors are myelinated with large cell body
b. nociceptors have small cell body and are lightly to not myelinated and mechanoreceptors have large cell body and long axons
c. both nociceptors and mechanoreceptors have the same developmental origin
d. the axon of nociceptors has a large diameter because they need to transmit signal over very long distances

A

B.

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2
Q

what types of somatosensory fibres are there?

A

A-alpha and ß fibres- myelinated, fast signal transduction, can be nociceptors and mechanoreceptors. these nociceptors deliver the 1st pain (spike very shortly after painful stimulus)
A-gamma fibres - all nociceptors, thinly myelinated, small to medium diameter, responsible for mechanical, chemical, thermal sensation; deliver the ‘2nd pain’ which comes later after stimulus.
C fibres- the vast majority of nociceptors, unmyelinated fibres with very small diameter. these fibres are activated much later and are responsible for long lasting 2nd pain

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3
Q

types of mechanoreceptors?

A

slow adapting mechanoreceptors (SA) - 50% of mechanoreceptors, respond to static phase of nociception
rapidly adapting (RA)- respond during the movement phase of stimulus
D-hair- dawn of animals (but we have that too); the most sensitive mechanoreceptors

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4
Q

types of nociceptors?

A

Amechanic nociceptors (AM)- pricking pain, respond to static phase of stimulus ‘ electric fence’ (~12%)
C-fibres-mechano-heat-nociceptors - respond to heat and temperature changes (spike starts when kin reaches temp of 43-45º); polymodal response to 2 different types of stimuli and some respond to cold temps. (~40%)
C-fibres-mechanociceptors- respond only to mechanical stimuli.

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5
Q

sensory mechanotransduction…

a. is slow (takes seconds to reach peak)
b. is extremely fast and sensitive (in the nm range)
c. can be fast or slow, depending on the type of fibre
d. is dependent on TrkB receptors

A

B

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6
Q

mechanical stimuli…(which statement is WRONG?)

a. initiate the opening of a channel (depending on stimulus intensity)
b. follow transduction–>spike initiation–>propagation
c. generate a second messenger response

A

C

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7
Q

characteristics of slowly adapting mechanoreceptors (SAM)

A

55% of all Aß fibres innervating the skin and ~12% of all DRG neurons innervating the skin
sensation of touch, skin indentation and slip
response (and AP) persist and remains constant from the start of the stimulus
neurons responding only to movement, not to amplitude (intensity)
2 types: I- innervate merkel cells; II- respond to ruffini corpuscles

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8
Q

characteristics of rapidly adapting mechanoreceptors (RAM)

A

45% of all Aß fibres innervating the skin and ~10% of all DRG neurons innervating the skin
sensation of touch, skin indentation and slip
response rapidly changes, firing does not respond to movement
response is a mix between skin indentation and velocity (unlike SAM)
2 types: I- Meisner’s corpuscles; II- Puccini corpuscles

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9
Q

what is the advantage of the spider slit preparation in the study of mechanoreceptors?

A

one can stimulate the receptor ending and record both the receptor AP and receptor current, because the organ has a distinct morphology, with the slit at the end and the cilium at the joint.

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10
Q

why has the study of mechanoreceptors in C.elegans contributed to the study of sensation?

A

the organism is very simple and yet still has nociceptors and mechanoreceptors
there is similar transduction currents in both C.elegans and mammals (highly conserved mechanism)

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11
Q

mechanosensitive neurons in C.elegans… (which answer is WRONG?)

a. each neuron is sufficient to show behaviour
b. has 15 genes which code for mechanosensitive neurons
c. all genes code for ion channels and are necessary for response
d. only 2 out of 15 genes code for mechanosensitive ion channels and the rest code for domains and membrane proteins
e. the channels on their own are not mechanosensitive but when combined with other genes/domains they become mechanosensitive

A

C.

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12
Q

deletion of Mec4 and 10 in C.elegans….

a. abolishes transduction (loss of mechanosensitive current)
b. decreases mechanosensation but does not abolishes it
c. is important for touch –> loss of tactile sensation
d. does not change response to mechanical stimulus

A

A.

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13
Q

STOML3 KO mice…

a. died
b. survived but were not sensitive to mechanical stimuli
c. had increased mechanosensation
d. did not change mechanosensation

A

B.

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14
Q

the morphology of Piezo2?

A

located at terminal endings of mechanoreceptors
fast mechanotransduction
located at hail follicles: hair moves–> pushes nerve ending –> channel activation

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15
Q

deletion of Piezo2…(which statement is wrong?)

a. abolishes mechanosensitivity of Aß mechanoreceptors
b. can only work as a conditional KO
c. can be done in embryonic cells
d. only required for mechanical response of Aß fibres (not in nociceptors)
e. preserves pain reaction but decreases dynamic response

A

C.

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16
Q

How come does deletion of Piezo2 not changes nociceptive response, if both Piezo2 AND C-fibres use RAM to generate their response?

A

Piezo2 makes rapidly adapting mechanoreceptors (RAM) which is why its deletion abolishes mechanosensitivity of Aß mechanoreceptors. C-fibres, indeed have rapidly adapting response too, however, they potentially have other channels other than Piezo to preserve pain reaction

17
Q

STOML3…

a. increases the response of Piezo2 to increase touch sensitivity
b. is enhanced by Piezo2 to increase touch sensitivity
c. is down-regulated by Piezo2 to increase sensitivity of Piezo2
d. inhibits the activity of Piezo2 shortly after presentation of mechanical stimulus
e. depends on Mec2 activity

A

A.

18
Q

patients who don’t have touch sensation…

a. don’t have STOML3
b. don’t have Piezo2
c. don’t have Mec4 and 10
d. have hyperactive STOML3 channels

A

B.

19
Q

describe the microneurographic technique. What are the advantages of the method?

A

first invented in 1965
a single tungsten metal electrode is inserted to contact a single afferent fibre
the electrode is connected to an amplifier to record the activity of a single fibre
advantages:
- one can record from a single receptor and this map out the characteristics of different receptor types.

20
Q

type I SA…(which of the following statements is/are correct?)

a. respond to Merkel cells
b. have vey large receptive fields
c. have very small receptive fields
d. change dramatically across species
e. are edge sensitive and are most dense in the fingertips

A

a, c, e

22

21
Q

type I RA…(which of the following statements is/are correct?)

a. respond to Merkel cells
b. respond to Meisner’s corpuscles
c. have very small receptive fields
d. highly conserved across species
e. are edge sensitive and are most dense in the fingertips

A

b, c, d, e

22
Q

type II SA…(which of the following statements is/are correct?)

a. respond to Merkel cells
b. respond to Ruffini’s corpuscles
c. respond to skin stretching
d. have a small innervating density each corpuscle is innervated by a single axon
e. are edge sensitive and are most dense in the fingertips

A

b, c, d

23
Q

type II RA…(which of the following statements is/are correct?)

a. respond to Puccini corpuscles
b. respond to Ruffini’s corpuscles
c. respond to skin stretching
d. have large and obscure borders
e. are very sensitive

A

a, d, e

24
Q

describe the organisation of fibres in the spinal cord

A

the spinal cord is somatotopically organised.
the synapses in the spinal cord are organised and branched in a columnar fashion.
the synapses in the spinal cord originate from specific collaterals (e.g. the medial collaterals give rise to afferents that produce the receptive fields…)
each receptor type has a specifically mapped spatial organisation
sensitivity of the receptor is dependent on the height of the afferent.

25
Q

what is the difference between sub modality segregation and sub modality convergence?

A

Study These Flashcards
A
sub-modality segregation:
each mechanoreceptor is responsible for different information type (texture, shape, motion…). according to this model:
- SA1 cells deliver information about texture and shape
- RA cells deliver information about grip control and motion
- PC deliver information about vibration
sub modality convergence:
each receptor type contributes to each of the aspects of sensation on different levels:
- PC are most sensitive to vibration and grip control because they sense the smallest change in stimulus.
- shape of objects and motion is mostly sensed by SA1 and RA.

26
Q

heat-hyperalgesia…

a. is completely peripheral
b. depends on TRPV1
c. only occurs when skin temperature exceeds 43º
d. occurs after thalamic lesions

A

B

27
Q

describe the axon reflex response

A

in axon reflex response, the stimulus doesn’t need to be processed in the CNS, but elicits a strong peripheral response. the stimulus can travel not only along the axon, but flares out also to its branches.
Axon is activated–>activating C-fibres –> C-fibres release peptides –> produce peripheral flare response

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28
Q

NGF hyperalgesia…

a. adult mice develop heat hyperalgesia and mechanical hyperalgesia after injection of NGF which lasts several days
b. adult mice develop heat hyperalgesia and mechanical hyperalgesia after injection of NGF which permanent
c. heat hyperalgesia develops after mechanical hyperalgesia after injection of NGF
d. NGF cures hyperalgesia
e. infant mice develop heat hyperalgesia and mechanical hyperalgesia after injection of NGF which lasts several days

A

a

29
Q

NGF hyperalgesia…(which answer is WRONG?)

a. induction of heat- and mechanical hyperalgesia after injection of NGF
b. can be treated with TrkB to prevent sensitisation if the tissue
c. can be treated with TrkA to prevent sensitisation if the tissue
d. NGF injection leads to release of BDNF which increases amounts of TrkB and NMDA receptors and causes central sensitisation

A

B

30
Q

what are the causes for neuropathic pain?

A

diabetes
HIV
Herpes zoster
toxins/channelopathy
trauma
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Medneuro M2-3 (4 decks)

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