Somatosensory And Pain Systems Flashcards
What is the difference between nociception and pain?
Nociception is the perception (detection) of noxious events in our environment.
Pain is the feelings associated with nociception.
Pain is alway subjective, a learned experience and unpleasant
How does the perception of pain involve the Peripheral and Central Nervous Systems working together?
Detection of noxious events (nociception) involves PNS which relays information to the CNS (specifically spinal dorsal horn).
Interpretation of noxious inputs takes place in the CNS (specifically the brain)
What are the types of Primary Afferent Fibres (PAFs)?
Simplest classification defines according to size and state of myelination.
A-beta: Largest diameter, myelinated, terminate in lamina III, IV, V; highest conduction velocity; convey light touch/pressure/vibration; ATP and Glutamate as neurotransmitters
A-delta: Medium diameter, less myelinated, not as thick but still saltatory conduction; terminate in laminae I and V; Convey sense of touch/sharp pain/temperature; Glutamate and ATP as NTs
C: Smallest diameter, unmyelinated, terminate in lamina II and V; high threshold information; slow, dull pain (takes to long and NTs hang around a long time); detect itch/nocuous temperature/significant pressure/dull pain; Glutamate, ATP and neuropeptides as NTs
Describe how the spinal cord dorsal horn nociceptive laminae are functionally distinct
- Nociception
C and Ad input from skin, viscera, muscle
Projection neurones: specific modalities - nociceptive specific, polymodal, temperature, itch; Projects to ventro-medial posterior nucleus of thalamus - Substantia gelatinosa - nociception
C fibre input from skin
Many modulatory interneurones; few projection neurones
Descending modulation from PAG, RVM - Nociception and low threshold
C (polysynaptic) and Ad (monosynaptic) inputs
Wide dynamic range - some nociceptive specific neurones
Describe the pathway of signals from peripheral nociceptors to descending neurones
Peripheral nociceptors
Primary Afferent Neurones
Intrinsic Spinal dorsal horn neurones
Ascending projection neurones
Higher centre neurones
Descending neurones
Describe the efferent (effector) functions of nociceptive afferents.
Afferent = towards CNS
Efferent = away from CNS
Neurogenic inflammatory response called axon reflex
Mast cell - histamine and SP release
Triple response of redenning, flare and wheal (oedema)
What are some examples of chronic pain and altered pain sensations?
Chronic pain isn’t useful pain, maladaptive
Hyperalgesia = increased responsiveness to a normally noxious stimulus
Allodynia = Pain or unpleasant sensation evoked by normally non-painful stimulation
Spontaneous pain = pain with no obvious immediate cause
Changes in perception arise through changes in neuronal properties
What’s the difference between Primary and Secondary hyperalgesia?
Primary:
- Thermal (heat and cold) and mechanical hyperalgesia and allodynia
- Small region surrounding injury within minutes
- Peripheral neuronal changes
Secondary:
- Mechanical hyperalgesia and allodynia
- Larger region within minutes/hours
- CNS changes
What are the types of dorsal horn neurones?
Projection (convey information to the brain)
Spinal Interneurons (relay/integrate noxious information to projection or MN, other areas of SC)
Describe the effects of mediators of inflammation and tissue damage on nociceptors.
Chemicals released in inflammation that change primary sensory neurones are prostaglandins, ATP, H+ and NGF
Most commonly used treatment = non-steroidal anti-inflammatory drugs (NSAIDS) e.g. ibuprofen
How does information travel through the brain?
Arrives at Thalamus and sends information to primary somatosensory cortex then secondary somatosensory cortex.
Thalamus sends information to prefrontal cortex and anterior cingulate cortex
Main ascending tract in emotional pain is spinoparabrachial tract from lamina I and II to parabrachial nucleus which has a big output to the amygdala.
Amygdala may send information to basal ganglia.
Thalamus sends information to Insula
Cerebellum involved in pain and controlling SC
What is the Mid-brain periaqueductal grey (PAG)?
Next to aqueduct in midbrain
Involved in descending pain modulation
Following noxious stimulation during PAG stimulation in rats, pain behaviours are absent
Could be possible treatment for humans with chronic pain but PAG is also very important in modulating autonomic processes e.g. BP, HR
Gets information from DH of SC, Cingulate cortex, frontal cortex, amygdala, nucleus accumbens, hypothalamus, locus coeruleus.
Dorsal part is more in autonomic functions
Ventral part is pain modification
Sends information to rostral ventral medulla (also nucleus raphe magnus - NRM)
Sends projections down to SC
Can make pain better (inhibiting DH) or worse (exciting DH)
PAG complicated without any typical neurones
