Flashcards in Somatosensory Systems & Pain Deck (30)
4 attributes of a stimulus
What is rate coding ?
the more intense the stimulus --> more action potentials
rapidly adapting mechanoreceptors
respond only at the beginning and end of a stimulus, signalling the rate at which the stimulus is applied or removed
slow adapting mechanoreceptors
respond throughout a continuous stimulus. As the pressure increases, the total number of APs discharged rises, leading to higher firing rates
What is proprioception?
awareness of position of your body in space
Do intrafusal muscle fibers detect signals during muscla contraction?
No, because it only responds to stretch or tension. They do respond to contraction but by a different mechanism
Explain intrafusal and extrafusal muscles
intrafusal is the sensory muscles fibers that are parallel with the extrafusal but they have specializations.
What type of nerves mediate fine touch and proprioception?
large diameter, myelinated sensory fibers
touch and proprioception ascend through the brain ipsilaterally or contralaterally? What is the path called?
ipsilaterally; dorsal column/medial lemniscal system
What is the pathway of the dorsal column/medial lemniscal system?
sensory receptor --> peripheral nerve --> dorsal root --> axon collateral projects to ipsilateral dorsal column --> ascend in dorsal column to nuclei in medulla --> synapse 2nd order neuron crosses --> becomes medial lemniscus --> projects to thalamus and synapses --> thalamic neuron projects to primary sensory cortex (post central gyrus)
representation of the body parts of the surface of the primary sensory cortex
What gyrus is in the parietal lobe immediately behind the central sulcus?
primary sensory cortex
what does the parietal association cortex do?
combines sensory information; awareness of our body and environment
What is neglect syndrome? How does it occur?
not recognizing a side of the body as belonging to them. Can result from a lesion of the right parietal cortex
how is pain produced?
produced by tissue injury but may also be produced by disturbed central sensory transmission
altered or abnormal sensation
sensation that an amputated limb is still present, often with painful paraesthesia
burning pain following nerve damage that persists long after tissue healing has occurred
CNS may reorganize and not in a good way
loss of sensation
lack of perception of pain from a normally nociceptive stimuli
loss of temperature appreciation
pain from deep structures perceived as arising from another area from the body
pain arising from what is normally a non painful stimulus
what kind of nerve fibbers mediated nociception?
unmyelinated or small diameter myelinated sensory fibers
gate theory of pain transmission
activity in non-nociceptive afferents activates inhibitory interneurons that inhibit ascending spinothalamic tract neurons and decrease transmission through the nociceptive pathway
eg. acupuncture activates large diameter sensory fibers which activates inhibitory neurone decreases pain
perception of pain from what would normally be non-nociceptive stimulus
what is a consequence of dysfunctional gate control?
because inhibitory interneuron is not activated, the second order (ascending) spinothalamic tract neuron becomes more active
the endogenous opioid system
stimulation around the cerebral aqueduct (midbrain-periaqueductal grey area) produces long lasting pain reduction