Chemical anatomy of pain (2) Flashcards
What is the role of the ACC (Anterior Cingulate Cortex) in pain processing?
ACC Involved in emotions and attention related to pain
What is the role of the primary sensory cortex in pain processing?
Responsible for sensory discrimination of pain
What is the role of the prefrontal cortex in pain processing?
Plays a role in the cognitive aspects of pain processing
What is the role of the insula in pain processing?
Integrates sensory and motor information related to pain
What is the role of the amygdala in pain processing?
Influences emotional affect associated with pain
What is the role of the spinal cord in pain processing?
- In dorsal horn, it processes sensory input, while in the ventral horn, it’s responsible for motor output
- the grey matter is divided into 10 laminae - with different functions, including pain and touch processing
How is pain processing organized in the spinal cord’s grey matter?
- spinal cord’s grey matter consists of 10 laminae
- Pain signals, carried by A-delta & C-fiber nociceptors, are processed in specific laminae
- this segregation allows for the differentiation of pain & touch signals in spinal cord
What are peripheral cutaneous afferents?
- sensory nerve fibers that transmit info from the skin to CNS, contributing to the perception of touch, pressure, temperature, & pain
What are the peripheral cutaneous afferents associated with mechanosensation?
Merkel cells: Associated with the sense of light touch and the discrimination of shapes and textures.
Ruffini ending: Function as slowly adapting mechanoreceptors.
Meissner’s corpuscle: Mechanoreceptors that are sensitive to light touch and rapidly adaptive
What is the first step leading to the perception of innocuous touch in the somatosensory system?
- the activation of cutaneous sensory neurons known as LTMRs (Low-Threshold Mechanoreceptors)
How are cutaneous sensory neurons classified?
Cutaneous sensory neurons are classified as Ab (A-beta), Ad (A-delta), or C based on:
Cell body size
Axon diameter
Degree of myelination
Axonal conduction
What distinguishes LTMRs (Low-Threshold Mechanoreceptors)?
-LTMRs are distinguished by their activation by weak innocuous mechanical force applied to skin.
- they’re associated with specific cutaneous end organs
- LTMRs have preferred stimuli or tuning properties
What are the major types of mechanosensory end organs found in glabrous skin?
note: Glabrous skin = thick skin found over the palms, soles of the feet and flexor surfaces of the fingers that is free from hair
- Glabrous skin contains four types of mechanosensory end organs:
- Pacinian corpuscles (Pacinian c)
- Ruffini endings
- Meissner’s corpuscles (Meissner c)
- Merkel cells
What are slowly adapting receptors (SA receptors), and how are they classified?
- Slowly adapting receptors = mechanoreceptors that maintain firing during sustained indentation
- further classified into SAi and SAii types based on their specific properties. (Abraira & Ginty, 2013)
What happens in the spinal cord dorsal horn regarding LTMRs?
- the spinal cord dorsal horn receives axonal projections & terminations from every LTMR that innervates the skin.
- this convergence occurs in a somatotopic & columnar manner, and likely to be a key location for LTMR integration & processing of info (Abraira & Ginty, 2013)
Where do A-fiber axons ascend in the spinal cord, and what is their role?
- A-fiber axons ascend to the dorsal column nuclei and make contacts within the spinal cord
- their role includes carrying discriminative touch info & projecting into the cord to activate various dorsal horn interneurons
where do C fibers run?
C fibers run in Lissauer’s tract
How do innocuous and noxious inputs distribute in the spinal cord, and what are their patterns?
- Innocuous and noxious inputs exhibit distinct but overlapping distribution patterns in the spinal cord
How do low-threshold afferents contribute to sensory processing in the spinal cord?
- Low-threshold afferents project into the dorsal columns medial lemniscus system (which carries discriminative touch info)
- they also project into the spinal cord and activate a range of dorsal horn interneurons
What is the primary function of Laminae I in the spinal cord?
- associated with nociception & contains nociceptive-specific cells (primarily respond to noxious or painful stimuli)
- plays a role in processing pain-related information & has small receptive fields
What types of stimuli do wide dynamic range cells in Laminae V-VL respond to?
- wide dynamic range cells in Laminae V-VL can respond to a broad range of sensory stimuli (incl. noxious & innocuous inputs)
- have small to large receptive fields & receive input from C and Ad fibers.
What is the main function of Laminae VIII-X in the spinal cord?
- Laminae VIII-X associated with visceral nociception & contain nociceptive-specific cells
- Neurons in these layers typically have large/bilateral receptive fields & play a role in processing information related to visceral pain
What is the role of Lamina I & V(X) projection neurons in the spinal cord?
- carry nociceptive information from the spinal cord to the brain
- they transmit info related to pain & noxious stimuli to higher brain centers for further processing
How do visceral and muscle pain signals differ in terms of localization in the spinal cord?
- Visceral & muscle pain signals involve sparse C fibers in the cord, leading to poorly localized sensations
- these signals can also converge with cutaneous input, resulting in referred pain
What is referred pain?
- pain perceived at a location different from the actual site of the painful stimulus
- often occurs when visceral & muscle pain signals converge with cutaneous input
What is the nature of all projection neurons in the spinal cord, specifically in relation to neurotransmitters?
- All projection neurons in the spinal cord are thought to be excitatory, and none of them express GABA/glycine
What percentage of projection neurons express the substance P receptor NK1, particularly in rodents?
Around 80% of projection neurons express the substance P receptor NK1, at least in rodents
What is the significance of parallel ascending pathways in the anterolateral spinal system?
Parallel ascending pathways in the anterolateral spinal system are functionally different
What is the role of RVM neurons projecting onto spinal enkephalinergic neurons in nociception?
RVM neurons projecting onto spinal enkephalinergic neurons are GABAergic but facilitate nociception
Why is the dorsal horn of the spinal cord important?
crucial for:
- processing noxious inputs, integrating peripheral stimuli
- receiving descending signals from brain
It is modality-specific
