Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

neuro - yr 2 > somatosensory pathways > Flashcards

somatosensory pathways Flashcards

1
Q

what is somatosensory function

A

the ability to interpret bodily sensations - mechanical, thermal, proprioceptive, nociceptive (encoding of noxious stimuli, not necessarily painful)

gives lots of info about touch - pressure, where, speed, of it is a threat, know when stimulus ends

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what does the somatosensory system compose of

A

sensory receptors in skin, tissues and joints

nerve cells and tracts in the spinal cord

brain centres that process and modulate sensory info

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

list the somatosensory modalities *

A

touch

thermoception

nociception

proprioception

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

define the different somatosensory modalities *

A

touch - sense light mechanical stim, pressure and vibration

thermoception - temperature

nociception - noxious/potential damaging stimulation - much more susceptible to contextual influences than other modalities

proprioception - mechanical displacement of muscles or joints

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what sensory modality uses free nerve endings *

A

thermoreeptors and nociceptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what sensory modality uses enclosed nerve endings *

A

mechanoreceptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

how do receptors differ within a sensory modality *

A

structure

location

size of receptor feild

the tactile info that they encode for

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe the classification of sensory neurons *

A

AB fibres - large and fast, because big diameter and high myelin - for innocuous mechanical stimulation

Adelta - moderate speed, smaller but still myelinated - noxious mechanical and thermal stimulation

(therefore info about touch reaches cortex before info about pain)

C fibres - no myelin = slow - noxious mechanical, thermal and chemical stimulation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

define the term receptor *

A

sensory receptors are transducers that convert energy from the environment into neuronal action potentials

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

describe thermoreceptors *

A

Ad and C fibres

free nerve endings

senstive to temperature because of membrane mechanisms, they can percieve small differences in temperature

temperature sensation is not uniformly distributed - some areas sensitive to cold and some to warm - depends on the type of ion channel:

TRPV1-4 - activated by heat 43degrees (temp that is painful)

TRPM8 and TRPA1 - aactivated by 15degrees which is painful cold

30degrees is neutral

cold is relayed by Ad, heat by C fibres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

describe the effects of capsaicin *

A

bind to TRPV1 for a long time - cause painful heat response

because bonded for a long time, it decreases the ability of other stimuli to cause painful response

therefore used as a topical analegic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

4 different types of mechanoreceptor and what they relay *

A

meissner’s corpuscle - fine discriminitive touch, low freq vibration

Merkel cells - light touch and superficial pressure

pacinian corpusle - detects deep pressure, high freq vibration and tickling

Ruffini endings - continuous pressure or touch and stretch

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how can you clinically induce stretch

A

use monofilaments that deform the tissue underneath

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is the clinical benefit of testing mechanoreceptors

A

see the somatosensory function from receptor to interpretation `

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

define stimulus threshold *

A

a threshold is the point of intensity at which the person can detect the presence of a stimulus 50% of the time (absolute threshold)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

define stimulus intensity *

A

encoded by how quickly the neuron fires

increased stimulus strength and duration = increased NT release = increased intensity of response to stimulus

usually firing freq is related to Log(stim intensity) ie stim increase 10 fold mean firing frequency doubles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

describe adaption in relation to tonic receptors *

A

they detect a continuous stimulus strength

they continue to transmit impulses to the brain as long as the stimulus is present - keeping brain informed of the status of the body

Merkel cells - slowly adapt allowinhg for superficial pressure and fine touch to be percieved, burst at the start and end of the stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

describe adaption in terms of phasic receptors *

A

they detect a change in stimulus strength

transmit an impulse at the start and end of stimulus - when a change is taking place

pacinian receptor - sudden pressure excites the receptor, transmits a signal again when the signal is released

they adapt quickly to a constant stimulus and turn off, firing only when the stimulus is turned off

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

define receptive field *

A

the region on the skin which causes activation of a single sensory neuron when activated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

describe the differences in size of the receptive field *

A

large receptive fields on the back allow fewer cells to detect changes over a wider area, but this is less precise

small receptive fields allow for detection of fine detail over small areas - precise but requires more cells

fingers have very densly packed mechanoreceptors with small receptive fields

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

define 2 point discrimination *

A

minimum distance that 2 points are percieved as separate

related to teh size of the receptive field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how can you use 2 point discrimination clinically

A

see if there is normal 2 point discrim and therefore if normal sensory perception in periphery

in hand can be used to check that the median, ulnar and radial nerves are in tact

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

describe somatosensory dermatomes

A

each spinal nerve has a specific dermatome on the skin

dermatomes provide mapping system to see where sensory info is percieved on the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

list the main dermatomes

A

C5 - clavical

C6 - thumb and index finger

T4 - nipple

T10 - umbilicus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

where are the cell bodies for the face and body

A

face - trigeminal ganglia

body - dorsal root ganglia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

describe the pathway from the limbs to the cortex *

A

from lower limbs nerve enter lumbar spinal cord

primary neurons travel in the cuneate and gracile fasiculus and synapse in the medulla in the gracile and cuneate nuclei

the secondary neurons are called internal articulate fibres and cross at the medulla forming the medial lemniscus tract

they synapse in the thalamus in the ventral nuclei

tertiary neurons relay to the primary somatosensory cortex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

describe the pathway from the face to the cortex *

A

nerves enter in the pons

synapse in the trigeminal nucleus

enter thalamus - synapse

3rd order neurons go to the somatosensory cortex

28
Q

describe the neurons in the dorsal horn *

A

divided into projection neurons (axons project to the brain) and interneurons (axons stay in spinal cord)

Ad and C fibres are superficial and are in lamina 1 and 2 of the dorsal horn

AB fibres are deep, in lamina 3 4 and 5

29
Q

define lateral inhibition *

A

the difference between adjacent inputs is enhanced by lateral inhibition

30
Q

describe lateral inhibition *

A

a receptive field can overlap with another receptive field - so difficult to distinguish between 2 receptive fields

lateral inhibition prevents this, it is mediated by inhibitory interneurons in the dorsal horn, and allows enhanced senssory perception and pinpoint accuracy in location of a stimulus

31
Q

describe the ascending pathway for touch and proprioception *

A

dorsal column, for innocuous mech stimuli (fine discriminitive touch, vibration)

AB fibres enter the dorsal horn - enter ascending dorsal columns (gracile tract from lower limbs)

travel ipsilaterally

synapse in the gracile/cuneate nucleus

2nd order neurons decussate in the caudal medulla and form the contralateral medial leminiscus tract

they terminate in the ventral posterior lateral nucleus of the thalamus

3rd order neurons from the VPL project to the somatosensory nucleus

thee size of the somatotropic areas is proportional to the number of sensory receptors in that area - eg hands and lips are big

32
Q

describe the acending pathway for pain temp and crude touch *

A

spinothalamic pathway

pain and temp in lateral spinothalamic tract, crude touch in anterior spinothalamic tract

1st order neurons terminate when enter spinal cord

2nd decussate immediately forming the spinothalamic tract, teminate in the ventral posterior lateral nucleus

3rd order go to the somatosensory cortex for analysis of localisation and intensity of the noxious sytimulus

collatoral branches go to brainstem and convey info to forebrain structures fo teh pereption of pain - affective pathway

branches to periaqueductal grey of the midbrain inhibit pain - central inhibition pathway

33
Q

key differences between the spinothalamic and dorsal column tracts *

A

spinothalamic decussate in spinal cord before medulla, dorsal synapse in medulla

dorsal is for light touch, vibration and 2 point discrimination

spinothalamic is for pain, temp and course touch

34
Q

define crude touch

A

a sensory modality that allows teh subject to sense that ssomething has touched them, without being able to localise it

35
Q

what is quantitative sensory testing *

A

where the stimulus and pt response are quantified

you detect small abnormalities in sensation adn compare these to normal values

can test temperature pain sensation, light touch using glass monofilaments, sharp/blunt sensation using pin pricks, whether innocuous stim is painful usng a brush, normal and abnormal vibration stimuli using graded tuning fork, and normal/abnormal perception of pain using a graded pressure algometer

psychophysical - going to depend on mental capacity of pt oe if they are tired it will affect how they interpret pain

36
Q

clinical signigicance of 2 point discrimination test to assess posterior column patency *

A

you can evaluate loss or gain to normal thermal or mechanical stimuli

test pain and temp in different areas to test the integrity of the spinothalamic tract

test discriminitive touch to see patency of the dorsal column

37
Q

what would be the effect of an anterior spinal cord lesion on 2 point discrimination *

A

a blocked anterior spinal artery = ischemic damage ot anterior part of spinal cord

this will damage the spinothalamic tract = pain and temp loss below the level of the lesion

however you will still have touch and vibration 2 point discrimination becasue the dorsal columns are in tact - therefore ensure you test different stimuli so you know what part of the spinal cord is affected

38
Q

what is pain *

A

an unpleasant sensory and emotional experience assoictated witha ctual or potential tissue damage, or described in terms of such damage

emotional pain has a similar inprint to physical pain

39
Q

describe the different types of nociceptors *

A

Ad mediate sharp, intense or 1st pain - type 1 = noxious mechanical, type 2 = noxious heat

C fibres - medaite dull, aching or second pain, noxious chemical (bradykinin/histamine), mechanical or thermal stimuli - polymodal

40
Q

how can we test teh nociceptors *

A

with pin prick, heat or pressure - see their patency and response to 1st pain and 2nd pain

41
Q

describe teh 1st synapse in the pain pathway *

A

glutamate synapse- excitatory NT - released from sensoruy afferents in response to acute or persistant painful stimuli.

this is in the superficial dorsal horn, in lamina 1/2

42
Q

describe pain as a multidimentional experience *

A

sensory, emotional and learning experience

lateral spinothalamic tract is the sensory component,

the spinoreticular tract is the emotional component

43
Q

describe the pain matrix *

A

fMRI has shown there is a cerebral signiture for pain

in the cortex it involves: S1, SII, insula cortex, anterior cingulate cortex, prefrontal cortex

amygdala

cerebellum

brainstem

however these areas are also involved in other functions

44
Q

what are the 5 tenants of pain *

A

it is subjective - only self-report can represent its existance

pain threshold is variable - failure to detect pain on fMRI is not an absence of pain

there is pain regardless of intesnity or complexity

no exclusive, specific dedicated pain spots in brain

salience and pain are intertwined and share neural representation

45
Q

describe the gate control theory *

A

peripheral inhibition

by rubbing a painful area you activate the AB fibres which through a projection fibre blocks input from the C fibres so it doesnt procede to the somatosensory cortex and reduces the pain

happens in the superficial levels of the spinal horn - substantia gelatinosa

46
Q

how can descending control pathways be altered to change pain *

A

strong emotions can inhibit pain

electrical analgesia reduces pain by affecting the descending pain pathway from the cortex

the descending pathways can be affected by fascilitation or inhibition

monoamines ie serotonin/NA inhibit the spinothalamic tract and reduce function in the C fibres

opiods sihbit stimulation at the periaqueductal grey (PAG) and the RVM

placebos also activates descending inhibition in humans - there is activation of the opiodergic descending pain control system and spinal cord involvement in placebo analgesia

47
Q

what is chronic pain

A

pain for 3 or more months

48
Q

describe the categories of pain *

A

nociceptive - noxious stimulation of a nocieptor (somatic or viscera) affecting skin, mucles, ligaments, joints, bones or viscera eg arthritis, fractures, burns or headache

neuropathic - lesion or disease of thee somatosensory system - sciatica, diabetic neuropathy, trauma, chemo, post-surgical, infection

mixed - osteoarthritis/lower back pain

49
Q

describe peripheral sensitisation *

A

inflammatory soup eg NT (Glutamate), peptides, lipids, cytokines, proteases, peptide C and bradykinin make nociceptors more sensitive - reduce the threshold to peripheral stimuli at site of injury - therefore have primry hyperalgesia here and around this econdary hyperalgesia

50
Q

describe central sensitisation *

A

reduce the threshold to peripheral stimuli at an adjacent site to the injury

hypersensitivity of C fibres in the periphery which causes plasticty in the proijection neurons in the dorsal horn affecting near cells - adjacent Ad fibre becomes sensitised in the dorsal horn

expansion of the receptive field

spontaneous pain

51
Q

what is allodynia *

A

pain due to a stimulus that doesnt normally invoke pain

52
Q

what is hyperalgesia *

A

increased pain from a stimulus that normally provokes pain - primary or secondary

shift to the L in pain intenstity related to stimulus intensity

53
Q

describe the diagnosis of neuropathic pain

A

need to have 3 things to classify as neuropathic pain:

have to have underlying disease or injury to somatosensory system

the symptoms have to be present in an area consistant with somatosensory involvement

there needs to be sensory loss or gain

(need to do questionnaires and somatosensory tests to make a diagnosis)

54
Q

describe the variability in neuropathic pain sensory profiles *

A

vary within condition - this is a driver for the low efficacy of pharmacology

using quantitive sensory testing there are 3 neuropathic pain clusters - sensory loss, thermal hyperalgesia and mechanical hyperalgesia

knowing this you can identify subsets of pts that respond to certain pharmacology

55
Q

what are SSRIs and what is there effectiveness in treating pain

A

serotonin selective re-uptake inhibitor

have low analgesic efficacy compared to TCAs or dual NA serotonin inhibitors

pharm in general is not very efficace

56
Q

describe the effect of NA and serotonin for treating pain

A

NA is protective because it is inhibitory

serotonin is a fascilitator so is not as useful at treating pain - it is harmful

57
Q

described conditioned pain modulation *

A

free of cortical influence

pain inhibits pain

it is a psychophysial measure of endogenous pain inhibitory pathway - the pt has participate

induce pain in pt and get them to rate it, then give different pain to different site, then give same pain to 1st sight and get them to rate it - it will have decreased becasue threshold will have increased or pain will have decreased. This info is being relayed through PAG and the RVM

then can use this to see if pt groups have deficient conditioned pain modulation and if this is a driver for their pain eg in people with chronic pancreatitis

CPM can be rescued pharmacologically

58
Q

describe neuromodulation in chronic pain patients *

A

non-invasive primary moror cortex stimulation - activates endogenous analgesic systems in the brain - PAG and the anterior cingulate cortex

there is a drive for this because of ineffective and SE of pharm

59
Q

describe mechanoreceptors *

A

all receptors for touch and proprioception are mechanoreceptors

they transduce mechanical stimulus into electrical ones

modified terminals of the peripheral axons of primary sensory neurons

60
Q

what does teh function of mechanoreceptors depend on *

A

degree of specialisation - from free nerve endings to elaborate accessory structures

location - eg in various layers of skin, around hari shaft, in muscles and in tendons

physiological properties - activation threshold determines sensitivity - all touch and proprioception receptors are low threshold - may be slow or fast adapting

61
Q

what is the axon type for sensory neurons *

A

muscle spindles and tendon organs are innervated by type 1 axons

most otehr mechanoreceptors are innervated by type II/A B axons

all are fast conducting

62
Q

describe somatosensation in the cortex *

A

touch and proprioceptive stimuli only become a conscious localised sensation when it reaches the cortex

response of neurons in somatosensory 1 (S1) varies - some respond to stimulus properties eg pressure, vibration and some to abstarcted properties eg movement and object shape

S2 recieves intracortical signals from S1

posterior parietal cortex - necessary for the interpretation of spatial relationships

63
Q

summaries sensory deficits *

A

injury to the pathway anywhere form the cortex to periphery may cause anaethesia or parathesia

some degenerative disorders affect the somatosensory system predominantly - eg peripheral neuropathies

64
Q

describe the somatosensory path for visceral pain *

A

carried peripherally by the ANS

centrally in the spinothalamic and dorsal column pathways

referred to skin at same spinal level

65
Q

describe the effective pathway of the spinothalamic tract *

A

axons send collatoral branches to the brainstem (reticular formation), thalamus (intralaminar nuclei), hypothalamus and some cortex (cingulate gyrus, insula)

the pathway triggers increase in awareness

and registers the unpleasantness of the stiumulus

66
Q

describe nociceptive dysfunction *

A

disruption of the pathway may reduce pain but predisposes to increased injury

some changes may exacerbrate pain eg windup in dorsal horn, thalamic syndrome, phantom pain

67
Q

sensory adaption definition *

A

a change over time in the responsiveness of the sensory system to a constant stimulus.

neuro - yr 2 (24 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions