Pain and Thermosensation Flashcards
What are the 3 types of pain?
nociceptive pain; inflammatory and pathological
What are nociceptors?
specific peripheral primary sensory afferent neurones normally activated preferentially by intense noxious stimuli
Where are the cell bodies of nociceptors located?
dorsal root ganglia and trigeminal ganglia
What type of fibre are nociceptors?
Ad and C
What is the difference between the type of pain that Ad and C fibres carry?
Ad mediate first or fast pain whereas C fibres mediate slow pain
What type of sensations is first pain?
stabbing; pricking
What type of sensation is slow pain?
bruning; throbbing; cramping; aching
What type of stimuli do nociceptive Ad fibres respond to?
noxious mechanical and thermal stimuli
What ytpe of stimuli do nociceptive C fibres respond to?
all noxious stimuli- polymodal
What is frequency coding?
rate of AP discharge correlates with the intensity of the applied stimulus
What are the types of nociceptive Ad fibres?
type 1 (HTM) and type 2
What is the difference between the thresholds of heat required to activate type 1 and type 2 Ad fibres?
type 1- >53 whereas type 2 43-47
What type of fast pain do type 1 fibres mediate?
mechanical
What type of fast pain do type 2 fibres mediate?
heat
What happens to type 1 Ad fibres in response to prolonged stimuli?
show sensitisation
What are the types of C fibre?
C-MH; C-M; C-H and CMiHi
What are the features of C-MH fibres?
shows sensitisation to repeated stimuli and contributes to location of stimulus
What are the features of C-H fibres?
mediates heat hyperalgesia; acquires sensitivity to mechanical stimuli in inflammation
What are C-MiHi fibres?
normally insensitive to both mechanical and heat stimuli but acquires sensitivity through inflam mediators
How does the peripheral terminal of nociceptors influence local tissue environment?
releases molecules eg substance P and CGRP
What does substance P do?
vasodilation and extravasation of plasam proteins
What is CGRP?
calcitonin gene related peptide- vasodilation
Where do nociceptors terminate in the spinal cord?
laminae of Rexed
What do C and Ad fibres synapse with in the spinal cord?
nociceptive specific cells
What type of fibre do wide dynamic range neurones receive input from?
Ab; Ad and C
Where are the soma of the sensory neurones of the trigeminal system located?
trigeminal sesnory ganglion
What modality synapses in the chief sensory nucleus?
general tactile stimuli
What modality synapses in the spinal nucleus?
pain and temperature
How do peptides participate in neurotransmission?
cause a slow and prolonged epsp facilitating activation of NMDA receptors by relieving voltage-dependent blokc by magnesium
When do peptides mainly take part in neurotransmission?
during high frequency stimulation
Whta are the 2 types of sensisation of the nociceptive pathway following tissue damage?
peripheral and central
What mediates peripheral sensitisation?
nociceptors at the site of injury/tissue inflam
How does peripheral sensitisation cause primary hyperalgesia?
via reduced threshold and amplified response
What type of stimuli is peripheral sensitisation mainly involved in?
heat, to lesser extent mechanical
What mediates central sensitisation?
an increase in CNS neurone activity and properties
How does central sensitisation cause secondary hyperalgesia and allodynia?
recruitment of novel inputs to nociceptive pathways (eg Ab fibres) and abnormal processing of sensory input
What type of stimuli is central sensisation mainly involved in ?
mechanical sensitivity
How do visceral afferents from nociceptors reach the dorsal horn?
follow sympathetic pathways
What are the two nociceptive tracts i nthe spinal cord?
spinothalamic and spinoreticular
What type of pain does the spinothalamic tract carry?
fast fibre Ad pain and wide dynamic range
What does pain perception require in the spinothalamic tract?
simultaneious firing in both the Ad fibres and wide dynamic range neurones
What type of pain does the spinoreticular tract carry?
slow C-fibre pain
Where does the SRT connect?
reticular nuclei in the brainstem eg periaqueductal grey
What response to pain is the spinoreticular tract involved in?
autonomic respones to apin- arousal, emotional and fear
Where does the Spinoreticular tract relay information to after the thalamus?
limbic areas of the forebrain (cingulate and insular cortices and amygdala)
Where does the spinothalamic tract take pain signals after the thalamus?
primary sensorimotor cortices
How can pain evoked by acitivty in nociceptors be reduced?
simulatneous activity in LTMs (Ab fibres)
What is the gate control theory?
projection neurones to the spinothalamic tract receive inhibitory input from Ab and excitatroy input from C/Ad fibres- if both are Ab and Ad/C fibres are excited dont get pain
What area of the dorsal horn does the gate control theory take place?
substantia gelaninosa
What type of info does the ventral horn deal with ?
motor
How does TENS work?
Ab fibres can be activated by high freq, low intensity electrical stimulation through the skin, reducing the pain felt
What are thermoreceptors?
neurones specialised to respond to small changes in temperature
