PTRS 852 Pain Pathways

· What are the three dimensions of pain

o Sensory discrimination (sensation, location, duration, quality)
o Motivational affective (emotions associated w/, anxiety, depression)
o Cognitive evaluative (past trauma/experiences impact on current pain)

· What aspect of the pain pathways add to the pain experience, especially in patients with chronic pain

Output (descending) pathways

· How long does pain need to last in order to be considered chronic

3 months

· Sensory receptors in free nerve endings of A-delta and C fibers that convert noxious stimuli into electrical signals

Nociceptors

· Primary afferent fibers refer to what

o Nerves that carry signals from stimuli to spinal cord
o i.e. A-delta and C fibers

· What type of primary afferent fiber transmits sharp pain, noxious mechanical, and thermal stimulation

A-delta

· What type of primary afferent fiber has a low threshold and has a fast conduction speed

A-delta

· The lateral pain system involves which type of primary afferent fiber

A-delta

· What type of primary afferent fiber transmits dull pain, thermal, noxious mechanical, and chemical stimulation

C fibers

· What type of primary afferent fiber has a high threshold and a low conduction speed

C fibers

· The medial pain system involves which type of primary afferent fiber

C fibers

· ____ pain system processes immediate sharp pain sensation following an injury that indicates location of pain

Lateral pain system

· ____ pain system processes dull, burring, throbbing ache followed by sharp pain that is not well localized

medial pain system

· Detection of stimulus refers to what

Transduction

· Conversion of stimulus into an electrical signal refers to what

Transmission

· Increase or decrease in electrical signal refers to what

Modulation

· How we as a person senses/feel about the stimulus

Perception

· What is sensitization

o Increased responsiveness or decreased threshold of nociceptors
o Increased sensitivity to input

· Peripheral sensitization indicates what

Dysfunction in the PNS

· Central sensitization indicates what

Dysfunction in the CNS

· What changes are occurring with peripheral sensitization

o Up-regulation of ion & glutamate receptors
o Plasticity of nociceptors results in a change in function
o Decreased threshold for AP
o Increased synaptic activity
o Increased responsiveness

· 1st order neurons are responsible for what actions

Transduction and transmission

· 2nd order neurons are responsible for what

Modulation

· 3rd order neurons are responsible for what

Perception

· Where are 1st, 2nd, and 3rd order neurons located

o 1st - periphery
o 2nd - spinal cord
o 3rd - brain/brain stem

· What are the 3 types of dorsal horn neurons

o Projection
o Interneurons
o Wide dynamic range

· Projection neurons are excitatory or inhibitory?

Excitatory

· Interneurons are excitatory or inhibitory?

Inhibitory

· Wide dynamic range neurons are excitatory or inhibitory?

Both

· What chemical are released by primary afferent fibers to create an excitatory response

Glutamate and Substance P

· How is pain information communicated between 1st order and 2nd order neurons happen

o Pain comes in form periphery via A-delta or C fibers
o Glutamate and Substance P are released to synapse with afferent fibers of the dorsal horn (rexed lamina of the gray matter)

· What is the importance of Wide dynamic range neurons

o Integrate painful and non-painful information (receives input bilaterally)
o 1st place that communication b/w nociceptors and non-nociceptors
o Has both contralateral and ipsilateral ascending pathways

· Wide dynamic range neurons that cross contralaterally form which part of the pain system?

Medial pain system

· In which rexed lamina do A-delta fibers terminate?

Lamina I

· In which rexed lamina do C fibers terminate?

o Lamina II (conscious pain) and V

· Wide dynamic range neurons are found in which rexed lamina?

Lamina V

· Why are wide dynamic range neurons able to confuse the brain?

o Located bilaterally
o Receive noxious and non-noxious stimuli

· Which neuron is responsible for referred pain and chronic pain?

Wide dynamic range neurons

· Wide dynamic range neurons' function is biased towards _________ of pain when they are functioning properly

inhibition

· (T/F) When functioning correctly, wide dynamic range neurons are excitatory. When functioning incorrectly, they can be inhibitory.

False - When functioning correctly, wide dynamic range neurons are INHIBITORY. When functioning incorrectly, they can be EXCITATORY.

· (T/F) Wide dynamic range neurons are one of the first places that pain modulation occurs in the spinal cord.

True

· What feature of the somatosensory cortex allows us to locate pain

Homunculus organization

· What ascending pain pathway is found in the lateral pain system?

Lateral spinothalamic

· What ascending pain pathways are found in the medial pain system

o Anterior spinothalamic (spinoreticular and spinomesncephalic)

· Describes the Lateral Spinothalamic Tract

o Nociceptors (A-delta fibers) sends pain info to dorsal horn (lamina I)
o Crosses SC at dorsal horn (lamina I)
o Goes up Lateral Spinothalamic tract to VPL of thalamus
o Synapses to the primary and/or secondary somatosensory cortex

· The lateral spinothalamic pathway is responsible for transmitting what aspect of pain?

o Sensory discrimination
o Location, duration, quality, and intensity of pain

· The anterior spinothalamic pathway is responsible for transmitting what aspect of pain?

o Motivational affective
o Dull, aching, and temperature related to pain

· Describe the anterior spinothalamic pathway

o Nociceptors (c fibers) sends pain info to dorsal horn (lamina II & V)
o Some info stays in ipsilateral tract and some crosses to contralateral tract to travel to thalamus
o Synapses at intralaminar thalamic nucleus

· Which ascending pain pathways are bilateral

Medial pain pathways

· Which ascending pain pathway has somatotopic organization in the somatosensory cortex

Lateral spinothalamic tract

· What are the 2 pathways in the anterior spinothalamic tract that are responsible for modulating emotional pain and activating descending pain pathways

o Spinoreticular
o Spinomesencephalic

· The spinoreticular tract projects to the ___________ and may interfere with ______

o Brainstem (Reticular formation)
o Sleep

· The spinomesencephalic tract projects to the ________

o Midbrain (PAG: periaqueductal grey area)

· The spinoreticular tract and spinomesencephalic tract terminate in the _________ and _________ respectively. Because of this they can also activate the ____________ pathways, helping to modulate pain

o Reticular formation (brain stem) and PAG (midbrain)
o Activate the descending inhibitory pathways

· (T/F) the anterior spinothalamic tract can help modulate pain

o True - by means of the spinoreticular and spinomesencephalic tracts activating the descending inhibitory pathways

· The spinolimbic pathway is responsible for what type of pain sensations?

o Visceral pain
o Emotional and autonomic reactions to pain

· Describe the Spinolimbic tract

o Nociceptors (C fibers) send pain info to dorsal horn (lamina II and V)
o Tract is multi synaptic so info can ascend ipsilateral tract or cross SC and ascend contralateral tract
o Synapses at the medial and intralaminar thalamic nucleus
o Synapse to anterior cingulate, insular cortex, and amygdala

· What does the pain matrix refer to

Any region of the brain that processes pain

· Sensory discrimination is processed in what areas of the brain

o Thalamus
o Somatosensory Cortex

· Motivational affective pain is processed in what areas of the brain (6)

o Insular cortex
o Cingulate cortex
o Prefrontal cortex
o Amygdala
o Hypothalamus
o Thalamus: intralaminar nuclei

· Cognitive pain is processed in what area of the brain

o Prefrontal cortex (DLPFC)

· Descending pain pathways are controlled by what area of the brain?

o Midbrain and brain stem

· What is the main descending pain pathway?

PAG-RVM

· Where do descending pain pathways terminate?

o Dorsal horns of the spinal cord

· How do descending pathways inhibit pain signals in the dorsal horn?

o They synapse on the nociceptor and dorsal horn afferents causing neurotransmitter release from opioid, serotonin, and GABA receptors to inhibit pain signaling up to the brain

· What 2 things increase excitatory output from descending pain pathways?

o Glutamate
o Tissue damage

· What 3 things increase inhibitory output from descending pain pathways?

o ESTIM
o Exercise
o Opioid meds