Jan 29th Flashcards
what are the theories about
what primary afferents do and how the spinal cord interprets their activity
the specificity theory
nociceptors do not fire to innoculous stimuli; only when a stimulus becomes noxious does that primary afferent fibres fire
what shape does the specificity theory have
sigmoid shape
the flaw with specificity theory
other neurons respond to pain but dont have the same properties as shown in the graph
intensity theory
sam as specificity but includes other primary afferent neurons called low-threshold DRG neurons
ed perl did what
discovered nociceptors and came up with specificity theory
low-threshold DRG neurons
innocuous stim can make them fire; the more noxious a stim gets, the more they will fire
the pattern theory
says that both noxious and innocuous stim activate several types of primary afferents and they have different firing patterns for that stimulation which is figured out in the spinal cord
flaw with pattern theory
doesnt tell us how the spinal cord decodes these patterns
gate control theory
first proposed in 1965; ultimately created the field of pain research
central control is another way of saying
descending modulatory systems
what are the two types of inputs for gate control theory
L for large fibres (a-betas) and s for small fibres (a-delats and Cs)
gate control theory
what is coming in is touch info from A-betas and pain information from A-deltas and Cs. the +on the graph show excitatory synapses meaning the next neuron is more likley to fire. the - show inhibitory synapses, meaning the next neuron is less likely to fire. the big T-neuron is projection neuron or a transmission neuron. both the large and small fibres go to T neuron and excite it
the more t-neuron fires,
more pain there will be
smaller SG neuron is for
substantia gelatinosa (laminas 1 and 2)
SG does what
inhibits input from the fibres to the T neuron.
the mroe Sg fires
the less the fibres will be able to excite the T-neuron
input from the large and small fibres to the sg is what
large = excitatory
small= inhibitory
because large fibre is exciting Sg it will do what to the T neuron
it will not excite it as input from the Sg neuron will inhibit the large fibre from exciting it
because the small fibres inhibit the SG neuron, it will do what to the T-neuron
excite it.
if the transmission neuron fires
the gate is open and you get pain
if the transmission neuron is prevented from firing from large fibre input or central control
the gate is closed, you get less or no pain
microneurography
when you pole a recording electrode into the foot and directly record C fibres or A-deltas. highest level at which we can do this, as going any higher would be too invasive
there are how many types of dorsal horn/ second-order/ projection neurons in the dorsal horn
three
