somatosensory system

Question 1

what is the somatosensory system?

Answer 1

• 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)

Question 2

what is transduction?

Answer 2

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

Question 3

basic pathway of stimulation to cns

Answer 3

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

Question 4

organisation of the sensory system

Answer 4

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

Question 5

perception

Answer 5

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

Question 6

sensation

Answer 6

Stimulation of a sense organ - detection of

Question 7

Most of the sensory receptors in the somatosensory system are…

Answer 7

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

Question 8

term for identifying objects by touch?

Answer 8

Stereognosis

Question 9

2 point discrimination task: what & used for?

Answer 9

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

Question 10

afferent axons

a) what?
b) enter via which spinal route

Answer 10

a) Sensory info to cns from the sensory receptor

b) Dorsal route

Question 11

the axons would be X and X for the fastest conduction

Answer 11

myelinated & thick in diameter

Question 12

dermatome

Answer 12

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

Question 13

Dorsal column-medial lemniscal pathway

what? what Info?

Answer 13

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

Question 14

Dorsal column-medial lemniscal pathway: route?

Answer 14

(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

Question 15

primary somatosensory cortex

Where, what & organisation

Answer 15

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

Question 16

Posterior parietal cortex

What?

Answer 16

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

Question 17

pain receptors: what? & function?

Answer 17

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

Question 18

nociceptors actvated how?

Answer 18

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

Question 19

types of nociceptors

Answer 19

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

Question 20

unimodal nocieptors

Answer 20

lower threshold

short lasting response

Question 21

polymodal nociceptors

Answer 21

higher threshold

longer lasting response

Question 22

Nociceptors are classified according to…

Answer 22

the type of stimulation they respond to

i.e mechanical, thermo

Question 23

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

Answer 23

A delta fibres; short lasting & sharper pain

thermal & mechanical stimuli

Question 24

pain vs nociception

Answer 24

pain = perception
nociception = the sensory process that triggers pain

Question 25

spinothalamic pain pathway what & function

Answer 25

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)

Question 26

gate control theory of pain

Answer 26

- 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)

Question 27

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

Answer 27

central factors i.e. emotion

Question 28

secondary pathway of gate theory

Answer 28

substantia gelatinosa

Question 29

Periaqueductal grey area (PAG) (4)

Answer 29

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

Question 30

Endorphins

Answer 30

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

Question 31

anterolateral system: consists of? &

Answer 31

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

Question 32

spinotectal tract what & function

Answer 32

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

Question 33

spinoreticular tract what & function

Answer 33

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)

Question 34

evidence in support of these systems

Answer 34

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)

Question 35

gate control theory

Answer 35

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

Question 36

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

Answer 36

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)

Question 37

Cognition & mediation of pain | - what according to gate theory

Answer 37

- signals descending from CNS can activate neural gating mechanisms in spinal cord - can block pain signals

Question 38

support for cogintion in pain suppressing

Answer 38

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