Lecture 11: Pain and Temperature Pathway

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Nociception is what?

The detection and localization of a stimulated pain receptor

Pain is what?

The emotional or arousal aspects of such stimulation

Pain is these 3 things…

A sensory, subjective, and emotional experience

Can pain arise without nociceptor stimulation?

Yes

Nociceptors are or are not free nerve endings?

They are

Where does pain perception crossover? (Decussate)

In 2nd order spinal cord, proceeding to the thalamus

Axons that conduct pain/temp are ____ and myelinated and ____ and unmyelinated

Small, Small

What is the fastest pain fiber?

A-delta

What is the slowest pain fiber?

C fiber

What is a ganglion?

A bundle of nerve cells/fibers in the peripheral

What is a fasciculus?

A bundle of nerve cells/fibers in the central nervous system

What is a commisure?

A bundle of nerve fibers connecting through the midline

1st order pain pathway

1. Dorsal root ganglion

2. Nucleus Proprius (Via the Dorsolateral fasciculus)

3. Spinothalamic tract

What connects the nucleus proprius to the spinothalamic tract?

The anterior white commisure

Pain withdrawal reflex excites and inhibits what?

Excites flexor and opposite extensors

Inhibits extensors

What is involved in the spinothalamic tract?

Medulla → Medulla → Pons → Midbrain → Ventral Posterolateral (VPL)

Pain Neuron 3 is located in…

The ventral posterolateral of the thalamus

Axons of Neuron 3 travel in what?

The internal capsule and corona radiata to reach the cortex. Ending there

What 3 areas does the spinothalamic tract terminate in?

1. The postcentral gyrus

2. The cingulate Gyrus

3. Insula

Termination in the poscentral gyrus means

A location and duration of the pain stimulus

Termination in the cingulate gyrus and insula

Indicates unpleasant, emotional qualities of pain such as burning or throbbing

Along with the postcentral gyrus, what also detects the location of pain stimuli?

The paracentral lobule

What is this?

The insula

What is this?

The cingulate gyrus

_____descending pathways from brainstem can decrease spinothalamic tract activity. Where are they from?

Two. One from the periaqueductal gray matter and another from substantia gelantinosa.

What transmission is inhibited in these two descending pathways?

Transmission from neuron 1 to 2

Axons release ____ and _____ onto opiate interneurons that inhibit which order neuron in the pain pathway?

Serotonin, norepinephrine, 2nd neuron

Genetic Mutations such as…

Prevention of action potentials in sodium channels can prevent pain sensations

Neuropathic pain

Trauma that directly damages pain fibers, chronic pain

Hyperalgesia

Increases pain caused by mildly noxious stimulus

Allodynia

Pain caused by a stimulus that is NOT noxious

Syringomyelia

Formation of a cavity in the spinal cord

Brown-Sequard syndrome

Sensory deficits caused by injury to one half of the spinal cord

In syringomyelia, if the cavity interrupts the anterior white commissure what happens?

Both sides of the body will have affected pain sensation/temperature sensation