Affect (pain, reward, fear)

Question 1

where do nocioceptors input to (in the ascending pathway)

Answer 1

the dorsal horn of the spinal cord

Question 2

ascending pain pathway through the spinal cord from upper body (excluding face)

Answer 2

starts in the dorsal horn of cervical spinal cord, crosses to contralateral side, ascends through the spinothalamic tract to the ventral posterior lateral nucleus of the thalamus, then to cerebrum & primary somatic sensory cortex

Question 3

ascending pain pathway through the spinal cord from lower body

Answer 3

starts in the dorsal horn of lumbar spinal cord, crosses to contralateral side, ascends through the spinothalamic tract to the ventral posterior lateral nucleus of the thalamus, then to cerebrum & primary somatic sensory cortex

Question 4

where does pain perception occur

Answer 4

the cerebrum

Question 5

types of pain

Answer 5

Nociceptive (actual or threatened pamage to non-neural tissue, activation of nociceptors)

Inflammatory (mediators either activate nociceptors or change their sensitivity)

Neuropathic (lesion or disease of somatosensory system that changes circuit sensitivity or CNS connections)

Question 6

Axon classification of nociceptors

Answer 6

Have un-specialised, free nerve endings

Classified according to conduction of axons:
Aδ-fibre = thinly myelinated, fast & sharp pain

C-fibre = unmyelinated, slow burning pain

Question 7

Modality classification of nociceptors

Answer 7

Mechanical
Thermal
Polymodal (including chemicals and inflammatory mediators)

Specific combinations of ion channels and receptors can be involved in transduction for each nociceptor

Question 8

Mechanisms of pain modulation

Answer 8

1. Sensitization: increased responsiveness (peripheral or central)
2. Neurogenic inflammation: peripheral nociceptors release inflammatory mediators
3. Descending systems can inhibit pain signal as it passes through dorsal horn

Question 9

Descending inputs modulating pain in dorsal horn

Answer 9

From somatosensory cortex, hypothalamus or amygdala to midbrain periaqueductal gray. Then to either raphe nuclei, parabrachial nucleus, medullary reticular formation or locus coeruleus to dorsal horn of spinal cord.

Synapse with interneurons that then inhibit nociceptors

Question 10

what is the anterolateral system

Answer 10

refers to a collection of ascending pathways that carry pain and temperature–as well as related touch–sensations from the spinal cord to the brainstem or thalamus. The anterolateral system is generally considered to contain the spinothalamic tract, spinoreticular tract, and spinomesencephalic tract

Question 11

where does the anterolateral tract crossover & how does this

Answer 11

At the level of the spinal cord

Question 12

what does the crossing of anterolateral vs dorsal column-medial lemniscal systems tell us about predicting pain loss

Answer 12

As anterolateral tract crosses in the spinal cord but the dorsal column-medial lemniscal system crosses in the brainstem, if you lose touch/pressure on one side (lemniscal system), you’ll lose pain on the contralateral side (anterolateral system)

Question 13

Categories of common analgesics

Answer 13

1. NSAIDS: reduce prostaglandins which activate & sensitise peripheral nociceptors
2. Paracetamol: inhibits COX in brain?
3. Opiods: act supraspinally on opiod receptors which enhances descending inhibition, can also act in dorsal horn by inhibiting excitatory NT release
4. local anaesthetics: inhibit action potential propagation of sensory neurons

Question 14

pathway for emotional expression vs volitional movement

Answer 14

Emotional: Extrapyramidal (involuntary) projections from medial forebrain and hypothalamus -> called a Duchenne smile

Voluntary: both pyramidal and extrapyramidal from motor cortex and brainstem -> called a pyramidal smile

Question 15

the limbic lobe

Answer 15

5 or less layered cerebral hemisphere on the medial part.
Includes: cingulate gyrus, parahippocampal gyrus

Question 16

patient SM

Answer 16

Urbach-Wiethe disease cause amygdala to degrade (hippocampus still intact)

Had no capacity to recognise fear (didnt respond to it) and no conception of fear (couldnt draw it)

Question 17

Result of too much activation of fear circuitry

Answer 17

Generalised anxiety disorder
Panic attack/disorder
Phobias
OCD
PTSD

Question 18

Approaches to normalising fear responses

Answer 18

1. re-learning associations
2. pharmacological intervention with GABA (inhibitory NT)

Question 19

brain areas involved in addition (dopaminergic pathway)

Answer 19

The VTA (ventral tegmental area) of the midbrain
Projects to: 1. prefrontal cortex (meso-cortical)
2. limbic cortex, nucleus accumbens and anterior temporal regions (meso-limbic)

Question 20

where does cocaine act

Answer 20

enhances transmission in the nucleus accumbens

Question 21

where do heroin and nicotine act

Answer 21

In the ventral tegmental area (VTA) to enhance transmission to cerebral cortex via basal medial forebrain projection

Question 22

dopamine system

Answer 22

VTA -> frontal lobe
Substantia nigra -> striatum (then basal ganglia)

Question 23

best model for dopamine release from VTA outcome

Answer 23

the accuracy, or error associated with, the likelihood of reward.

Question 24

parts of the limbic cortex

Answer 24

caudate
putamen
nucleus accumbens (ventral striatum) -> gets input from VTA and substantia nigra

Question 25

how does dopamine influence the limbic loop

Answer 25

1. Dopamine increases transmission from cortex (anterior cingulate) and amgydala to the ventral striatum = increase activation of striatal neurons
2. this increases the inhibition of neurons in the ventral pallidum
3. less activation of ventral pallidum neurons = less inhibition of thalamus
4. greater activation of thalamus leads to more excitation of the limbic cortex

Overall: dopamine enhances activity of limbic cortex, allows emotional reinforcement to help structure our behaviour

Question 26

what is the relationship between dopamine and pleasure/reward?

Answer 26

Dopamine ≠ pleasure
Dopamine increases association between cortical inputs (eg from prefrontal cortex) and the accumbens (in the limbic cortex)
-> is released in proportion to the accuracy to which reward is predicted

Question 27

reward prediction error

Answer 27

RPE = actual reward now + discounted predicted reward later* - predicted reward now

*reward now is more valuable than reward later