Somatosensory Systems & Pain

Question 1

4 attributes of a stimulus

Answer 1

1. modality
2. intensity
3. location
4. duration

Question 2

What is rate coding ?

Answer 2

the more intense the stimulus –> more action potentials

Question 3

rapidly adapting mechanoreceptors

Answer 3

respond only at the beginning and end of a stimulus, signalling the rate at which the stimulus is applied or removed

Question 4

slow adapting mechanoreceptors

Answer 4

respond throughout a continuous stimulus. As the pressure increases, the total number of APs discharged rises, leading to higher firing rates

Question 5

What is proprioception?

Answer 5

awareness of position of your body in space

Question 6

Do intrafusal muscle fibers detect signals during muscla contraction?

Answer 6

No, because it only responds to stretch or tension. They do respond to contraction but by a different mechanism

Question 7

Explain intrafusal and extrafusal muscles

Answer 7

intrafusal is the sensory muscles fibers that are parallel with the extrafusal but they have specializations.

Question 8

What type of nerves mediate fine touch and proprioception?

Answer 8

large diameter, myelinated sensory fibers

Question 9

touch and proprioception ascend through the brain ipsilaterally or contralaterally? What is the path called?

Answer 9

ipsilaterally; dorsal column/medial lemniscal system

Question 10

What is the pathway of the dorsal column/medial lemniscal system?

Answer 10

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)

Question 11

homunculi

Answer 11

representation of the body parts of the surface of the primary sensory cortex

Question 12

What gyrus is in the parietal lobe immediately behind the central sulcus?

Answer 12

primary sensory cortex

Question 13

what does the parietal association cortex do?

Answer 13

combines sensory information; awareness of our body and environment

Question 14

What is neglect syndrome? How does it occur?

Answer 14

not recognizing a side of the body as belonging to them. Can result from a lesion of the right parietal cortex

Question 15

how is pain produced?

Answer 15

produced by tissue injury but may also be produced by disturbed central sensory transmission

Question 16

paraesthesia

Answer 16

altered or abnormal sensation

Question 17

phantom limb

Answer 17

sensation that an amputated limb is still present, often with painful paraesthesia

Question 18

causalgia

Answer 18

burning pain following nerve damage that persists long after tissue healing has occurred

Question 19

plasticity

Answer 19

CNS may reorganize and not in a good way

Question 20

anesthesia

Answer 20

loss of sensation

Question 21

analgesia

Answer 21

lack of perception of pain from a normally nociceptive stimuli

Question 22

thermal anesthesia

Answer 22

loss of temperature appreciation

Question 23

referred pain

Answer 23

pain from deep structures perceived as arising from another area from the body

Question 24

allodynia

Answer 24

pain arising from what is normally a non painful stimulus

Question 25

what kind of nerve fibbers mediated nociception?

Answer 25

unmyelinated or small diameter myelinated sensory fibers

Question 26

gate theory of pain transmission

Answer 26

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

Question 27

allodynia

Answer 27

perception of pain from what would normally be non-nociceptive stimulus

Question 28

what is a consequence of dysfunctional gate control?

Answer 28

because inhibitory interneuron is not activated, the second order (ascending) spinothalamic tract neuron becomes more active

Question 29

the endogenous opioid system

Answer 29

stimulation around the cerebral aqueduct (midbrain-periaqueductal grey area) produces long lasting pain reduction

Question 30

referred pain

Answer 30

nociceptive afferents from viscera enter the spinal cord at the same spinal segment as nociceptive afferents from skin/muscle/joints –> convergences onto common neurons –> perception of pain other than the site of origin