Glossary of Owch 2

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What are the two ascending pathways associated with pain?
1. Dorsal columns
2. Spinothalamic tract
What is the perception of unpleasant or aversive stimulation?
What is one of the main functions of pain?
Warns of injury
Is pain always identical to nociception
What are peripheral free endings of primary sensory neurons originating from the dorsal root ganglion and trigeminal ganglia neurons?
What activates nociceptors?
Harmful stimuli
What type of fibers typically make up nociceptors?
C Fibers
What are three classes of nociceptors?
1. Thermal nociceptors - extreme temperature (below 5 and above 45) - Alpha-delta fibers (sharp pain)

2. Mechanical - intense pressure

3. Polymodal - combinations of listed - C Fibers
What type of fiber is the least myelinated in the Alpha family?
What type of fiber is associated with polymodal nociceptors?
C Fibers (unmyelinated)
What two categories can pain be divided into and which is detected first?
1. Sharp - 1st
2. Dull prolonged - 2nd
Name four substances that are released after tissue damage and what do they do?
1. Histamine and Bradykinin - directly stimulates nerve endings
2. Potassium - depolarization and sensitization
3. Substance P
What happens when Substance P is released?
Hyperalgesia which is caused by the relase of histamine from mast cells and histamine acts on nerve endings. Also Substance P will cause vasodilation and inflammation.
Substances released from damaged cells act how?
They don't actually cause a full blown nociceptive response but instead they sensitize the endings of nerves.
What is the action of arachidonic acid?
After converted to PGE2 by cyclooxygenase it causes sensitization.
How does bradykinins act?
After being released from the damaged cells, it causes the production of more prostaglandins which helps increase the inflammatory response.

It also acts directly on C Fibers and Alpha-delta fibers.
Substance P is a transmitter of what type of fibers?
C Fibers
What releases Substance P?
Activated nociceptive terminals
What type of fibers does histamine activate?
C Fibers (polymodal)
What type of fibers MIGHT be involved in sensorimotor reflexes?
Alpha-alpha and Alpha-beta fibers
As a generalization, what fibers synapse on the more superficial layers of the dorsal horn?
Alpha-delta and C fibers
Where do C fibers typically synapse?
Substantia gelatinosa - lamina II
Where do alpha-delta fibers typically synpase? Where can they also synapse?
1. Marginal layer - lamina I
2. Layer V
(Superficial/Deep) layers tend is where most of the pain information is coming in
What type of fibers synapse in layers III and IV? What type of stimulis actiavtes them?
1. Alpha-beta
2. Non-noxious
What type of fibers synapse in layer V?
Alpha-beta, alpha-delta and C fibers
What type of fibers synapse in layer VI?
Muscle joint input/ Alpha-beta
What type of fibers synapse in layer VII/VIII?
Polysynaptic nociceptive
Where does most pain ascend in relation to the injury?
Which two types of fibers are heavily myelinated and propagate signals the fastest? How fast are the signals they propagate?
1. Alpha-alpha and alpha-beta
2. 100 m/s
Which fiber type is myelinated, but not to the same extent as the other myelinated fibers?
Which fibers are not myelinated and are responsible for slow burning pain?
C - fibers
What two types of transmitters do C fibers use?
1. Glutamate - AMPA
2. Substance P
What type of vesicles do you find glutamate residing in? What type of response do you need for the release of glutamate from C Fibers?
1. Small clear coat
2. Single action potential
What type of vesicle is Substance P in? What type of stimulus do you need to cause the release from C Fibers?
1. Large dense-core vesicle
2. Repetitive stimulation
What exactly does Substance P do to enhance the action of Glutatmate on AMPA receptors?
Depolarizes the post-synaptic membrane by activating G-Protein Coupled Receptors.
What type of receptor is specific for temperature in thermoreceptors?
Capsaicin receptor
What family of receptors does Capsaicin belong to?
When do mechanoreceptors become activated?
When there is pressure that causes damage or potentially could cause damage.
What is the term that refers to increased sensation of pain to stimuli that shouldn't cause that level of pain?
What is the term that refers to pain from stimuli that shouldn't cause pain?
Describe the action involved with "winding up".
Severe persistent injury causes C Fibers to fire repetitively, releasing large amounts of Glutamate that active NMDA receptors in the dorsal horn.
What was found to reduce phantom pain in amputation patients?
Applying an anesthetic in the spinal cord instead of just applying peripherally
What part of the anterolateral system is associated with laminae I, V, and VII?
What part of the anterolateral system is associated with laminae VII and VIII?
Spinoreticular tract
What part of the anterolateral system is associated with laminae I and V?
Spinomesencephalic tract
What part of the anterolateral system is associated with the reticular system of the brainstem? Where does it end up in the cortex? Does this tract cross or not?
1. Spinoreticular system
2. Somatosensory cortex
3. Crossed and uncrossed fibers
Which anterolateral tract does not go to the Thalamus? Where does it go instead? Crossed or uncrossed?
1. Spinomesencephalic tract
2. Periaquaeductal grey matter then hypothalamus and limbic system
3. Crossed
Are there any pain fibers in the dorsal column system?
Yes a few
What nuclei within the thalamus are considered neospinothalamic?
Lateral nuclear group (VPL/VPM and posterior nuclei)
Where does the lateral nuclear group of the thalamus project its neurons?
Primary somatosensory cortex
Where does the medial nuclear group of the thalamus project its neurons?
Diffuse projections in the cortex
What are the three cortical areas of pain processing?
1. Anterior insular cortex
2. Anterior cingulated cortex
3. Primary somatosensory cortex
What is the anterior insular cortex associated with?
Visceral/autonomic component of pain
What is the anterior cingulated cortex associated with? What projects to this area?
1. The emotion of pain
2. Intralaminar nucleus of the medial thalamus
What does the concept of gating refer to?
Basically it is the ability to either strengthen or diminish the output of the projection neuron by the stimulation of other types of neurons (ie vibration neurons).

For example along with excitation carried by C Fibers a few Alpha-beta fibers carrying vibration information might activate an inhibitory interneuron diminishing the activation of the projection neuron.
Describe the descending pain control phenomenon.
The periaquaductal grey matter receives pain information and will actually send signals back down through other areas (raphe nucleus, locus ceruleus spinal cord) to modify signals synapsing on the dorsal horn
What type of cells do descending neurons act on?
Opioid containing cells
What are the two possible modes of action when descending neurons act on the dorsal horn?
1. Presynaptically - shortens AP so there is less of a chance NT will be released
2. Post-synaptically - hyperpolarization is slowed by the action of G Proteins
What happens with the phenomenon of referred pain?
Pain from deep within the viscera enter in the dorsal horn and get mixed up with afferent fibers from different parts of the skin.

As a result, when you are having a herat attack the signals from the heart might get mixed up with the ones from your left arm so you think your left arm hurts.

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