pain pathways Flashcards
what is a noxious stimulus
a stimulus that is damaging or threatens to damage normal tissues
what is nociception
the neural process of encoding noxious stimuli. nociceptive pain (pain from activation of nociceptors
- includes the reception, conduction nd CNS processing of nerve signals from nociceptors
- physiological process that results in the perception of pain
what is central sensitisation
increased responsiveness of nociceptive neurons in the CNS to their normal subthreshold afferent input
what is somatic pain
pain experienced from skin, muscle, bone damage/disease
what is visceral pain
pain experienced because of organ pain (abdominal or thoracic)
what is neuropathic pain
pain caused by a lesion or disease of the somatosensory nervous system (in conctrast to nociceptive pain)
what is wind up
wind up is a frequency-dependent increase in the excitability of spinal cord neurons, evoked by electrical stimulation of afferent C-fibres
what are nociceptors
- first point of pain pathway (receives signals)
- non-encapsulated nerve endings
- can be stimmulated mechanically, thermally or chemically
- some polymodal
what are A fibres
- nerves coming from nociceptor
- myelinated
- fast conduction
- good localisation
- sharp pain
what are C fibres
- nerve coming from nociceptor
- unmyelinated
- slow
- dull aching pain
- not well localised
what are the paradoxical/adverse effects of pain
- hypoglycemia
- weight loss
- impaired wound healing
- impaired immune system
- fatigue
- immobility
- weakness
- decreased lung volume leading to atelectasis and hypoxaemia
- decreased bowel motility leading to constipation
- anorexia
- ileus
- urinary retention
- decreased muscle function and spasm leading to weakness
- fear
- anxiety
- poor sleep
- PTSD
- poor coping/depression
why is nociception different from pain
pain is concious understanding and perception whereas nociception is the physiological process of pain
What are the two ascending pathways that mediate the perception of pain?
- spino(cervico)thalamic tract
- spinoreticular tract
how does spino(cervico)thalamic tract work
first order neurone synapses in the dorsal horn of the spinal cord, these synapse with second order neurones which decussate to ascend in the spinothalmic tract. a third order neurone arises in the contralateral thalamus and ascends to the cortex
- touch and superficial pain
- primary pain pathway
- discriminatory (high degree of somatotrophy)
- in carnivores there are 2 spinal projection neurones making a total of 4 rather than 3 neurones for this pathway
how does the spinoreticular tract work
primarily afferents enter spinal cord and diverge cranially and caudally (spreads over several segments) and allows intersegmental reflexes such as withdrawal. second order afferents in the dorsal horn (diffuse and bilateral) project to the reticular formation, then some pss to the thalamus
- deep pain and visceral sensations
- activates the limbic system (emotional response)
- poorly localised
- little evidense of somatotropy
- can travel in sympathetic fibres
- large overlapping receptor fields
- responds to stretch, ischaemia, dilation and spasm
- A-d to C ration is 1:10 (1:2 in spino(cervico)thalamus so much more diluted)
