The Physiology of Pain Flashcards
Where do pain signals originate
Nociceptors
where are pain signals transmitted to
Pain signals are transmitted from nociceptors in the peripheral nervous system to the brain in the central nervous system.
Which parts of the central nervous system receive pain signals
The brain including the higher centres and the somatosensory cortex.
Why is pain difficult to assess
Because it is subject to experience and often has a psychological component
What are two conditions in which peripheral pain sensation can be lost
- Leprosy
- Diabetes
(Neuropathic diseases)
What are the consequences of the loss of pain sensation
The natural instinct to remove the part of your body from the source of the pain or to not use that part of the body is lost which can lead to further damage.
What is an example of a situation where there is loss of sensation in joints which are damaged
This leads to a Charcot joint where there is complete disruption to the joint architecture as the patient continues to use the joint even though it is damaged.
What other symptoms may pain also be associated with
Anxiety, depression, insomnia, anorexia.
What are the 5 different kinds of pain
- Physiological
- Inflammatory
- Vascular
- Neuropathic
- Psychogenic
What are two other names for physiological pain
Visceral and somatic.
Where does somatic sensation come from
Somatic sensation is sensation that occurs around the periphery of the body.
Where does visceral sensation come from
Visceral sensation relates to the nociceptors which sense pain in the internal organs.
What are the features of physiological pain
Physiological pain tends to be acute, transient and heals over a period of time.
How does inflammatory pain come about
Inflammatory mediators released in inflammation can trigger activity in nociceptors.
What is an example of condition which causes inflammatory pain
Rheumatoid Arthritis.
How does vascular pain come about
When the blood supply is cut off this leads to lack of oxygen supply, ischaemia, overproduction of lactic acid and death of cells. This can trigger nociceptors and subsequently painful responses.
What is an example of a type of vascular pain
Migraine. This results from an instability of the vascular supply around the head.
What triggers neuropathic pain
Neuropathic pain does not come from nociceptors but from damage to nerves themselves.
Give examples of things that can cause neuropathic pain
- Phantom limb pain in amputee
- Slipped disc
- Neuralgia
- Stroke
- Diabetes
What is psychogenic pain
Pain which is related to a psychological disorder
What is acute pain
A short term natural defence reaction that prevents further damage to the body. Acute pain disappears once tissue damage resolves.
What is chronic pain
This is pain that goes on for a long period of time, persisting for weeks, months or years. It is often associated with a chronic disease process.
What is referred pain
This is pain experienced in one part of the body related to physical damage in another part of the body.
What is an example of referred pain
Pain in the left arm due to angina as a result of starvation of oxygen to the myocardium.
What are the four stages of pain perception
1) Pain “sensing”
2) Pain transmission to the spinal cord
3) Impulses to the brain
4) Analysis of information
What is the process of pain perception
First nociceptors are activated in response to physical damage in the peripheral tissues. This response leads to pain transmission through afferent nerve fibres to the spinal cord from the periphery. In the spinal cord impulses are carried up ascending tracts to the brain. Information is then analysed in higher brain centres and an action can be initiated.
What can inhibit the transmission of pain through ascending tracts in the spinal cord
Descending inhibitory tracts.
What is the location of nociceptors
Nociceptors are present in somatic locations such as the skin, joints, tongue, teeth etc. and in visceral locations like in internal organs - heart, gut etc.
What is the difference in pain localisation in visceral nociceptors compared to somatic nociceptors
Somatic nociceptors are good at localising pain and locating exactly where it is coming from. Visceral nociceptors are not good at localising where pain is coming from. Pain is often diffuse and can be referred.
What are the four reasons why some people are more susceptible to pain than others
- Genetics affects the way sodium channels on nociceptors respond
- Opioid receptor differences
- Experience
- Family attitude.
What can activate nociceptors
- Release of chemicals by local cells - histamine and bradykinin
- Mechanical forces
- Temperature - hot or cold
- Tissue injury
- Nerve damage
What is the role of prostaglandins in pain
Prostaglandins do not directly activate nociceptors but increase their sensitivity to pain.
What is neurogenic inflammation
Neurogenic inflammation in the phenomena by which pain can lead to an enhanced inflammatory process.
How does neurogenic inflammation come about
A peripheral afferent nerve which senses pain can lead to inflammation in subsequent nerve endings. The nerve cell is activated as a result of activation of nociceptors but nerve endings from the same neuron can respond by releasing inflammatory mediators in another area.
What are the two types of peripheral afferent pain fibres
Myelinated A delta fibres and unmyelinated C fibres.
What kind of pain is experienced with transmission of impulses through myelinated A delta fibres
Nerve impulse through myelinated A delta fibres is extremely rapid. The pain experience is sharp, fast and intense.
What kind of pain is experienced with transmission of impulses through unmyelinated C fibres
Nerve impulse through unmyelinated C fibres is slow. The pain experience is a dull, slow, throbbing, aching pain.
Pain transmitted though which type of afferent nerve fibre - Myelinated A delta or unmyelinated C - is easier to localise
Pain which is transmitted through A delta fibres is easier to localise and identify the source.
What is the location of the cell bodies for peripheral nerve fibres
The dorsal root ganglion.
What are three key groups of excitatory neurotransmitters which act at the synapse between afferent fibres and the ascending nociresponsive neurons
- Amino acids - glutamate
- Neurokinins - Substance P
- Other neuropeptides
What is the synapse between the peripheral afferent neuron and the ascending nociresponsive neuron influenced by
Descending nerves, particularly those that release metenkephalin and beta endorphin.
What do metenkephalin and beta endorphin do
They influence the transmission of neurotransmitters glutamate and substance P.
Other than metenkephalin and beta endorphin, what else inhibits cord pain sensitivity
Noradrenaline, 5-HT (serotonin), GABA and glycine.
What is spinal “wind up”
Spinal wind up is the chronic potentiation of depolarisation in spinal neurons due to repetitive activation of C fibres. There is a prolonged response to a stimulus. This leads to hypersensitivity/hyperalgesia.
What is the gate theory of pain
Simple sensory input at the same level of the spinal cord as the pain input can dampen down pain sensation. This is why you may rub something if you have injured it - the rubbing sensation dampens down the pain sensation.
How can the gate theory of pain be used in chronic pain patients
Transcutaneous electrical nerve stimulation can be used over the skin where pain is being sensed to reduce this pain.
Where is spinal cord transmission of pain signals
The contralateral spinothalamic tracts.
Where do pain impulses travel in the brain from the spinal cord
They travel to higher brain centres - first the thalamus and then the cerebral cortex to bring about an appropriate cognitive response. They also activate the limbic system to bring about an emotional response.
Why is pain often an emotional experience
Because pain impulses from the spinal cord stimulate the limbic system as well as other areas of the brain. This brings about an emotional response.
Where are opioid receptors found in the body
Opioid receptors are found throughout the nervous system.
What do opioid receptors respond to
Opioid receptors respond to endogenous stimuli such as metenkephalin but also respond to exogenous opioids.
What two things can affect pain impulses (the gate control theory of pain)
- Descending nerve impulses from the thalamus and cerebral cortex
- Other sensory input, e.g. from rubbing the painful area.
Why do interventions such as imagery and distraction give some relief from pain
This provides nerve impulses from the brain which inhibit ascending nerve impulses.
What are the excitatory neurotransmitters in the spinal cord
Substance P and Glutamate
What are the inhibitory neurotransmitters in the spinal cord
GABA and glycine
What are the inhibitory neurotransmitters if the descending pathway
Serotonin, noradrenaline, encephalin.
What do inhibitory neurotransmitters of the descending pathway such as encephalin act as
Analgesics.
What are algogens
Antagonists which block the substances which initiate pain.
