Pain Flashcards
Define ‘pain’
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
What is nocioceptive pain?
Pain felt following the activation of pain fibres
What are nociceptors?
Specialist pain fibres located throughout the body. They respond to tissue damaging stimuli.
How is neuropathic pain felt?
If pain nerve fibres are damaged. Normally a long term sensation which is difficult to acutely manage.
Define nociception in relation to nociceptive pain:
The conversion of stimuli into nerve impulses by nociceptor pain fibres
Define transmission in relation to nociceptive pain:
The movement of nerve impulses along defined pathways to reach the brain.
Define perception in relation to nociceptive pain:
The conscious experience of pain which arises through stimulation of higher brain centres
Define modulation in relation to nociceptive pain:
An increase or decrease in our perception of pain. Linked to the gate control theory.
Which system does pain arise from?
The nervous system.
Where are nociceptors located and where do they transmit signals to? (specific Lucy)
In tissues throughout the body. One end of the nociceptor is located in the skin where it detects pain stimuli. The axon of the nociceptor travels within a spinal nerve where it is taken to the spinal cord. The cell body of the nociceptor is located within the dorsal root ganglion which is a swelling in the spinal nerve close to the spinal cord. Pain fibres end in the dorsal horn where they connect with other neurons.
Which three types of stimuli activate endings of nociceptors in the skin?
- temperature- extremes
- intense pressure
- chemicals
What happens when a nociceptor is stimulated in relation to creating a nerve impulse. What is this process called?
Stimulation causes ion channels on the surface of nociceptors to open allowing sodium and calcium ions to flow through the cell membrane. The movment of these ions into the cell generates a nerve impulse. If the impulse reaches action potential the impulse is passed on. This process is called nociception.
An increase in tenderness and pain following injury is known as:
Hyperalgesia
Why does hyperalgesia occur?
Prostaglandins are released as a part of the inflammatory response which sensitise the nerve fibres making them more susceptible and responsive to pain stimuli.
How are prostaglandins formed? (3 steps)
- Prostaglandins are formed from arachidonic acid which is a componant of the phospholipid molecules which make up the cell membrane.
- Phospholipids are converted into arachidonic acid in response to inflammatory stimuli.
- Arachidonic acid is then converted into prostaglandins by cyclooxygenase enzymes.
What is the primary role of prostaglandins?
Prostaglandins bind to receptors on the nerve endings of pain fibres and lower the threshold for activation causing more pain messages to reach the brain.
What are the two types of pain fibre present in the skin? What are their functions?
A delta and C fibres.
A delta: fast response to stimuli. Produce an immediate pain sensation.
C fibres: conduct nerve impulse at a slower speed producing a dull aching pain.
In the dorsal horn, which two neurotransmitters do A delta and C fibres release? What type of neurotransmitters are they?
Glutamate and substance P which are excitatory neurotransmitters.
What happens once glutamate and substance P neurotransmitters are released in the dorsal horn?
They excite relay neurones which then travel in white matter tracts of the spinal cord to reach the brainstem and the midbrain.
What is the synapse between A delta and C fibres and relay neurons also known as?
The pain gate
What is the white matter carrying relay nerve fibres to the brainstem and the midbrain called?
The spinothalamic tract.
What happens when relay nerve fibres reach the brainstem?
The sympathetic nervous system is triggered (fight or flight response)
What does perception relate to?
The conscious experience of pain.
Where are pain signals sent once they reach the thalamus?
To higher brain centres including the anterior cingulate cortex and the somatosensory cortex. It is through the activation of these higher centres that the perception of pain occurs.
