Lecture 3: Pain

finished 9/8

What are nociceptors? What type of nociceptors do we have? What is their function?

Nociceptors are sensory receptors that detect signals from damaged tissue.

free nerve endings - A delta (pain and temp), C (pain, temp, itch)

Fast pain

myelinated (A delta) fibers

Slow pain

unmyelinated C fibers

Difference between Type I and Type II A delta fibers

Type I respond to dangerously intense mechanical and chemical stimulation and have high heat threshold.

Type II have low heat thresholds, but high thresholds for mechanical stimulation.

What is the touch pathway called?

Dorsal column-medial lemniscus system

What is the pain pathway called?

Anterolateral system

In the anterolateral system, the first order neuron is the

dorsal root ganglia

pain pathway: decussation point

at spinal cord

Describe the ascending and descending pain pathway

Descending systems modulate transmission of ascending pain signals. Ascending pain pathways carry pain signals from the site of the injury to the brain.

How can we locate a unilateral spinal cord lesion?

by seeing which functions are lost (taking note of what crosses where) on which sides.

Trigeminothalamic tract

face/head/teeth pain. crosses at medulla, trigeminothalamic tract to VPM

Describe the visceral pain pathway

dorsal root ganglion cells to spinal cord. crosses at medulla, medial lemniscus to VPM.

What is referred pain?

visceral pain misperceived as cutaneous pain

Explain the gate theory of pain.

there are inhibitory neurons between A delta and C fibers. activation of A delta fiber (mechanoreceptor) activates the inhibitory neurons and take away from the C fiber (nociceptor) pain. So rubbing a pain can help lower perceived pain.

What is the function of pain?

it works as an alarm that something is wrong

peptides that bind to the same postsynaptic receptors as opium

endogenous opioids