NSCI Exam 2 Lec 5

Explain the dorsal column pathway in a flow chart.

Sensory afferent goes into spinal cord → ascends to either the nucleus cuneatus or nucleus gracilis → crosses the midline at the medial lemniscus → ascends to the ventral posterolateral nucleus in the thalamus → goes to the somatosensory cortex

the spinothalamic tract ascends in the _______ in the spinal cord

ventral lateral funciulus

what happens if you cut the spinothalamic tract?

relieve intractable pain

Explain the spinothalamic tract pathway in a flow chart.

Primary sensory axons responding to pain, temp, and itch synapse on relay neurons in spinal cord dorsal horn → cross midline and ascend contralaterally in the ventral lateral funiculus as the spinothalamic tract → synapse in the contralateral ventral posterior lateral nucleus of the thalamus → axons of VPL ascend thru internal capsule to synapse in the contralateral primary somatosensory cortex

where does the trigeminothalamic tract project it’s axons to in the thalamus?

ventral posterior medial nucleus

pain information is projected to the primary somatosensory cortex as well as what other system? (particularly for motivation to avoid the pain)

limbic system

how is pain carried into the CNS?

by thin primary afferent axons with slow conduction velocities (this is why sometimes pain takes a second to register)

which sensory pathway carries pain?

spinothalamic pathway

which sensory pathway carries itch?

spinothalamic pathway

nociceptors signal…

tissue damage or threat of tissue damage

• mechanical injury

• heat injury

• cold

• gut distension

• chemical injury

• etc.

true or false: nociceptors are free nerve endings, meaning they are not encapsulated by other cells

true or false: nociceptors have lower thresholds than other sensory receptors

false, they have higher sensory thresholds

mechanical nociceptors

have a high threshold

• the more force put on them, the more they fire

• they have small, point-like receptive fields

heat nociceptors

respond to heat and capsaicin (from red peppers)

• thermal thresholds are at 45 degrees Celsius

cold nociceptors

respond to cold

• thresholds are roughly at 0 degrees Celsius

• their thresholds don’t overlap much with those of cooling receptors

polymodal receptors

• they respond to mechanical, heat, and chemical stimuli

• thermal thresholds are at roughly 43-45 degrees Celsius

• they have high mechanical thresholds

• also respond to chemical agents like acid

nociceptor terminal transduction proteins are sensitive to what 5 things?

heat, cold, acid, pressure, and ATP

acute pain

also known as normal pain. happens in response to injury or threat of injury. lasts as long as the stimulus and defines what’s safe to touch

persistent pain

outlasts the injury or threat of injury. related to healing. protective during healing process

chronic pain

outlasts duration of healing

inflammatory pain

most common type of persistent pain (e.g., sunburn)

• accompanies all injuries in the skin, joints, muscles, bones, and also post-surgery

it promotes healing, but also causes more pain. this decreases the likelihood of more injury to happen

what are the effects of taking NSAIDs (aspirin, ibuprofen)?

blocks the production of prostaglandins, which reduces inflammatory pain. although the effect on healing is uncertain

how does persistent pain affect nociceptors?

it sensitizes them, causing a decreased threshold and larger response. it contributes to increased pain after injury

what are the two types of nociceptor sensitizers?

activity (heat, mechanical stimulation, chemical stimulation) and inflammatory agents (prostaglandins)

what three things can chronic pain lead to?

helplessness, depression, and suicide

how much does chronic pain cost annually?

600 billion dollars (cost of treatment, and lost productivity)

neuropathic pain

type of chronic pain caused by nerve injury (nerve compression, amputation, chemotherapy, diabetes, etc)

what happens if you stimulate the periaqueductal gray (area surrounding cerebral aqueduct) in rats?

produces profound analgesia

what happens if you stimulate the rostral portion of the ventromedial medulla?

it can facilitate pain

what is the function of pain-inhibitory circuits?

mediating the analgesia caused by morphine and other drugs

can be activated to treat pain (spinal cord stimulation, transcutaneous electrical simulation, placebo analgesia)

what is the function of pain-facilitating circuits?

may mediate pain of opiate withdrawl

anesthesia

loss of all sensation

analgesia

specific loss of pain sensation

used to decrease suffering from pain

drugs can be NSAIDs or opioids

general anesthesia

causes loss of consciousness, no reaction to pain. used mostly for major surgery

local anesthesia

used for minor or (sometimes) major surgery. can be injectable. cold temperatures can also act as a local anesthetic (e.g., ice for sprains, burns). blocks action potential generation/propagation by blocking voltage-gated sodium channels

opioids

drugs derived from or related to those coming from opium (morphine, heroin, fentanyl, codeine, oxycodone, methadone)

what actions do opioids take on the brain?

• inhibit spinothalamic tract neurons

• inhibit neurotransmitter release from nociceptors

• activate prefrontal (limbic) cortex