Flashcards in 26 Pain and touch Deck (33):
Why do people with congenital neuralgia tend to die early (around 22 years old)?
Cardiac failure caused by the strain of multiple blood infections. If you don't know you're hurt, you don't change behaviour to allow infection to heal.
How did Hardy et al. (1952) show relationship between pain and tissue damage?
The experiment showed that level of pain was not necessarily related to level of tissue damage, but to potential for tissue damage if noxious stimulus is allowed to proceed.
Heated probe to different temperatures - 45 C and 49 C.
At 45 C probe would cause damage in several hours.
At 49 C probe would cause damage in several minutes.
Skin of individuals was heated to these temperatures for only a few seconds. 49 C resulted in more pain than 45 C although neither caused tissue damage.
Pain can thus be correlated with potential for tissue damage, as well as actual tissue damage.
What are the sensory-informative functions of pain?
- Tells you where injury occurred
- How serious the injury is
What are the behavioural-motivational functions of pain?
- Immediate response is aggression and fear
- Acute response is recuperative behaviours
What are the cognitive functions of pain?
- Our cognitive powers are pulled towards appraising source and meaning of pain
- Inform behavioural responses
- Learn from experience, avoid similar situations
Why do chili peppers seem hot?
Because they contain capsaicin, which stimulates heat receptors
What are the primary afferent nerves involved in touch?
The Aβ myelinated fibre controls fine touch (reaching in bag and naming object by feeling with fingers).
The Aδ myelinated fibre causes a wide dynamic range signals – from touch (OK) to heavy touch (painful).
The NON-myelinated C-fibres carry protopathic pain.
What accounts for the delay between immediate pain and slow pain?
Difference in conduction speeds between myelinated Aδ-fibres and non-myelinated C-fibres
What is the difference in organisation of white/grey matter between spine and brain?
Brain has grey matter on the outside, white matter on the inside.
Spine has white (axons) on outside, grey on inside (where nerves come in from the body).
What are the four levels of the spinal cord from top to bottom
Where do touch fibres (Aβ, Aδ, C) connect to the spinal column?
At the dorsal horn, where they synapse with ascending neurons which go up to the brain.
What is the spino-thalamic tract?
The pathway from the spinal cord to the thalamus to the somatosensory cortex
What is the formal definition of pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What areas of the brain does the thalamus project to when pain is experienced?
A variety of areas, in particular...
The medulla, responsible for alertness - which is why pain wakes you up. Rugby players slap each other before games.
Parabrachial nucleus and amygdala - involved in stress response - affective areas
Hypothalamus, important for autonomic, sympathetic responses
Insular cortex - feelings of disgust
What is hyperalgesia?
Hyperalgesia is an exaggerated response to noxious stimuli, caused by sensitization of nociceptors.
It can occur after an injury. Hit thumb with hammer, for days after that thumb is more sensitive to stimulation. Repeated stimulation sensitizes nociceptors - wind-up of neural activity.
How does LTP influence chronic pain?
When constant information of pain coming through, neurons transmitting this information wire together through LTP - activity dependent plasticity – and make it more likely this signal will be transmitted.
What is secondary hyperalgesia?
NMDA-receptor mediated strengthening of synapses to pain transmission neurons
When neurons of CNS become more sensitive to pain information through LTP.
What will blocking NMDA receptors at time of injury do later?
Block neuroplasticity effects related to pain, such as phenotypic changes to neurons
What longer-term neuroplasticity effects can occur if pain persists?
Changes in phenotype of neurons - start to express NTs and receptors that wouldn't normally be expressed.
Silent neurons start making new pain receptors and responding to pain.
Aβ-fibres (touch neurons) start releasing NTs in the spinal cord that are normally only released by C-fibres (pain neurons).
What changes in dorsal horn occur with chronic pain?
Touch fibres in dorsal horn start to wire themselves to the pain fibres and vice versa. Touch becomes associated with pain, and pain with touch - system loses integrity.
How can changes in neural wiring in spinal cord cause referred pain?
Signals get confused in spinal cord. Signals from kidney start to talk to neurons usually associated with skin.
What is Allodynia?
Touch becomes painful - shirt on back hurts.
What is Paraesthesia?
Pins and needles - often severe and constant
What morphological changes/rewiring are associated with secondary hyperalgesia?
– Aβ (touch) fibres start to connect to ascending pain transmission neurons (touch = pain)
– Spreading of pain fibres to more ascending pain transmission neurons (wider painful area)
– Referred pain
How do glial cells enable secondary hyperalgesia?
They stop regulating glutamate at the synapses, and so allow spreading of activation from one synapse to another.
What affective disruptions occur in secondary hyperalgesia?
Activation increases in anterior cingulate cortex, responsible for affective aspect of pain, and people become hypersensitive to emotion of pain.
Activation increases in parabrachial nucleus and amygdala - people become hypervigilant and stressed.
What causes phantom limb syndrome?
Activation of adjacent areas in somatosensory cortex. People who pucker lips feel phantom sensation in fingers - adjacent areas. Similarly, genitals and toes.
How did Ramachandran use a mirror to treat phantom limb pain?
Subjects with a missing arm would position mirror so it appeared they had two arms. Visual percept of two healthy arms appeared to override pain response.
What happens when blind people read braille?
Stimulates visual cortex (if person lost sight at young age)
Describe the endogenous opioid system
Three opioid receptors: mu, delta, kappa
Three important opioid peptides: endorphin, enkephalin, dynorphin
How can the endogenous opioid system reduce pain?
Interneurons release endogenous opiods that can regulate the transmission of pain at level of spinal cord (induced by neurons from above, or locally)
Also see this at thalamus, medulla and cortices.
What is Gate Theory of Pain?
Touch afferents (Aδ fibres) activate enkephalin releasing interneurons in spinal cord, which inhibit both pain (C fibres) and touch. This is why when you rub your thumb after hitting it with a hammer the pain goes away.