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Biopsych year 2 > somatosensory system > Flashcards

somatosensory system Flashcards

1
Q

what is the somatosensory system?

A
  • system that allows us to feel things things & determine where our body is.
  • composed of 3 interacting systems:
    a) exteroceptive system = external stimuli (sensation onthe skin)
    b) proprioception = where body is in space
    c) interoceptive system = internal stimuli (temperature)
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2
Q

what is transduction?

A

the membrane potential of receptor cells changes generating a receptor potential (cell converts one kind of signal or stimulus into another)

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3
Q

basic pathway of stimulation to cns

A

membrane potential of membrane of receptor changes - receptor potential - transduction —–> receptor potentials converted to action potentials in the afferent nerve (in the dorsal root) —–> goes to cortex via dorsal column medial route OR anterolateral system

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4
Q

organisation of the sensory system

A

hierarchical: Rees et al 2002
receptors - cutaneous mech, thermo, nociceptors
thalamus - sorting room
primary sensory cortex - first to receive
secondary sensory cortex - organisation
association cortex - connects & coordinates secondary areas

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5
Q

perception

A

higher process of integrating, reorganising & INTERPRETING a complete pattern of sensation

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6
Q

sensation

A

Stimulation of a sense organ - detection of

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7
Q

Most of the sensory receptors in the somatosensory system are…

A

mechanoreceptors (mechanical energy - association with motion & position of object)

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8
Q

term for identifying objects by touch?

A

Stereognosis

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9
Q

2 point discrimination task: what & used for?

A

2 pin pricks at the same time; the more receptors th
more likely to see that its two pins.
Used: diagnose tactile agnosia

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10
Q

afferent axons

a) what?
b) enter via which spinal route

A

a) Sensory info to cns from the sensory receptor

b) Dorsal route

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11
Q

the axons would be X and X for the fastest conduction

A

myelinated & thick in diameter

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12
Q

dermatome

A

The area of skin innervated by the right and left dorsal root is called a dermatome

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13
Q

Dorsal column-medial lemniscal pathway

what? what Info?

A

ONE system by which somatosensory info from each side of the body ascends to the cortex
- caries info relating to: light touch, vibration, pressure & position of the body

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14
Q

Dorsal column-medial lemniscal pathway: route?

A 
(Watson, 2010)
sensory receptors 
enters spinal cord via dorsal route  
ascends IPISLATERALLY  via dorsal column 
synapse at dorsal column nuclei (@medulla) 
axons cross over to other side of brain 
thalamus 
somatosensory cortex
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15
Q

primary somatosensory cortex

Where, what & organisation

A

Lies on the postcentral gyrus
Receives info from thalamus & is sensitive to somato info
Homunculus: larger the size - more important & more sensory receptors

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16
Q

Posterior parietal cortex

What?

A

area involved in the integration of somatosensory info with other sensory info

17
Q

pain receptors: what? & function?

A

nociceptors; Woolf & Ma (2007) primary sensory neurons are specialized to detect intense stimuli and represent, the first line of defense against any potentially threatening or damaging environmental inputs

18
Q

nociceptors actvated how?

A

by stimuli which may cause tissue damage(extremes in temp, harmful chems etc)

19
Q

types of nociceptors

A

unimodal: respond to ONE type of stimulus
polymodal: respond to more than one

20
Q

unimodal nocieptors

A

lower threshold

short lasting response

21
Q

polymodal nociceptors

A

higher threshold

longer lasting response

22
Q

Nociceptors are classified according to…

A

the type of stimulation they respond to

i.e mechanical, thermo

23
Q

what fibres are the fastest at pain transmission & what fibres are slower at pain transmission

A

A delta fibres; short lasting & sharper pain

thermal & mechanical stimuli

24
Q

pain vs nociception

A 
pain = perception
nociception = the sensory process that triggers pain
25
Q

spinothalamic pain pathway what & function

A

Preece (2012)
dorsal route - ducussate - up spinal cord through pons,medulla, midbrain etc (no synapsing) - goes to ventral posterior nucleus of thalamus - primary somatosensory area
~~ Function - localisation of painful stimuli
(suppoted by evidence of their neurons being distinct & modally differentiated – lamina 1 neurones; produce distinct physiological systems for the spread of pain and temperature (Almedia & Tufik, 2004)

26
Q

gate control theory of pain

A
  • sensory input is stronger than pain
  • Rubbing (sensory) will activate the inhibitory neurons, which will not allow projection of pain to the brain (gate closed)
  • When only pain, then the inhibitory neurons are inactive which projects pain (gate open)
27
Q

as well as peripheral factors (touch) what else can influence gating mechanism

A

central factors i.e. emotion

28
Q

secondary pathway of gate theory

A

substantia gelatinosa

29
Q

Periaqueductal grey area (PAG) (4)

A

Electrical stimulation of this area is found to suppress pain (analgesic effects)

PAG receives input from many brain areas including ones that relate to emotional status (central regulation)

PAG neurons descend into regions of medulla (top of stem) - particularly the raphe nuclei

These medullary neurons then project down into the dorsal horn of the spinal cord- thus, suppressing the painful response

30
Q

Endorphins

A

Especially concentrated in the areas that modulate pain (e.g., PAG, raphe nuclei, dorsal horn)

dont suppress touch

31
Q

anterolateral system: consists of? &

A 
3 systems -->
1) spinothalamic
2) spinoreticular
3) spinotectual 
Tracts relating to pain & temp
organised hierarchically, functionally separate & parallel processing (Goldstein, 2009)
32
Q

spinotectal tract what & function

A

Preece (2012)
dorasl route - dessucate - up spinal cord through medulla - synapses at tectum
Function - directs attention to stimuli

33
Q

spinoreticular tract what & function

A

Preece (2012)
dorsal - dessucates - up spinal cord - synapses at the reticular formation in medulla - through RF which finishes at tectum - projection to parafascicular nucleus of thalamus - S1
Function - facilitation of alertness in response to pain - ivolved in the motivational characteristic responses i.e. to descend suppression (Almedia & tufik, 2004)

34
Q

evidence in support of these systems

A

Mark et al. (1962)

  • lesions to ventral posterior nuclei (spinothalamic tracts & DCML) reduces sensitivity to touch, changes in temperature and sharp pain (parallel systems- functionally separated) BUT not to chronic pain (Sternbach, 2013)
  • lesions to parafascicular nuclei reduces deep chronic pain while leaving other sensations in tact (parallel systems & functionally separated) (Munn et al. 2009)
35
Q

gate control theory

A

Melzack & Wall (1965)
- A beta & c fibres synapse at projection neurone – activation = perception of pain
- ALSO synapse at inhibitory neurone - decreases chances of P firing
Stimulation of C fibres impedes inhibitory cells, thus allowing transmission. A beta cells excite the inhibitory neurone thus, this blocks c fibres transmission IF ENOUGH

36
Q

Mendell (2014) For (1) & against (3) gate control

A

for: relief from pain has come from stimulation of dorsal columns which is compromised of LARGE MYELINATED afferent fibres (Shealy et al. 1967)
Against:
1) spinal neurones activation become more prolonged in response to each consecutive c fibre stimulation –> seeby theory as ‘wind up’ BUT ITS NOT its peptide release from afferents which prolongs the potential (Kumazawa & Perl, 1978)
2) wasnt much consideration for high threshold afferents when theory considered – now nociceptors been discovered (Burgess & Perl 1967)
3) Peripheral pain (McMachon et al. 1993)

37
Q

Cognition & mediation of pain

- what according to gate theory

A
  • signals descending from CNS can activate neural gating mechanisms in spinal cord
  • can block pain signals
38
Q

support for cogintion in pain suppressing

A

1) emotional state, anxiety, attention & memories = affect pain sensation (Ossipov, Dussor & Porreca, 2010)
2) PAG – morephine injected into rat PAG - pain relief BUT not placebo controlled
3) PAG & amygdala - provides emotional - affective modulation of cog functions in pain (decison making etc)
- when amygdala neurones sensitized - chronic pain
- when inhibited - pain & anxiety stops

Biopsych year 2 (9 decks)

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