Somatosensation II Flashcards
What are the 2 major pathways of the somatosensory system?
- Dorsal columnar-medial lemniscal system
- Spinothalamic tract
Where does the dorsal columnar-medial lemniscal system receive its input from?
Receives input from large diameter myelinated afferent
-Include tactile afferents
Where does the spinothalmic tract receive input from?
Receives input from small diameter, thinly unmyelinated axons
What is the spinothalamic tract for?
Its for crude touch, pain and temperature sensitivity
Where do the DCML and STT cross?
DCML and STT cross the midline at different sites
Whats the ascending pathway mediating sensory aspect of pain for body and face?
2nd order neurons decussate and project to ventral posterior nuclear complex of thalamus
- VPL for body
- VPM for face
What is pain?
- It is a sensory discriminate
- It is a sensation
What are nociceptors?
They are neurons that detect painful stimuli
What is the TRPV1 receptors involved in?
The TRPVI receptor is involved in transduction of noxious heat
What are TRPV1 receptors present on?
Present on A-delta and C fibers
What is a TRPV1 receptor?
It is an ion channel to allow depolarization (Ca2+,Na+)
What is the TRPV1 also activated by?
Also activated by capsaicin
What are the 2 types of nociceptor fibers?
A delta and c fibers
What do both types of nociceptor fibers contribute to?
Both contribute to different aspects of pain sensation
What is the a delta fiber for in terms of pain?
A delta fiber is for the fast and first pain
What is the C fiber for in terms of pain?
C fiber is for second and slower pain
How do we ensure the maintenance of nociceptor activity after injury?
Following tissue injury, we get an inflammatory soup of cytokines, prostaglandins and small signalling molecules
-These maintain depolarisation and sensitivity of C fiber terminals after original stimulus
Where are dorsal horn inter neurons located?
Located in superficial and deep layers of dorsal horn
What is the synaptic input for dorsal horn interneurons?
Synaptic input from C and A-delta fibers
What does it mean by some dorsal horn interneurons being multimodal?
Means it receive convergent nociceptive and non-nociceptice inputs
Where do some dorsal horn interneurons receive convergent inputs from?
Some receive convergent inputs from visceral afferents
What is referred pain?
It is pain perceived at a location other than the site of the painful stimuli
What is the cause of referred pain?
Happens because of afferents converging with dorsal horn interneurons
Why is the cortical representation of pain complex?
-STT projects to S1 via VP nuclei of thalamus
-However STT and DCML axons do not converge on the same thalamic neurons as the pathways are
parallel
-S1 is necessary for the localisation of pain but stimulation of S1 gives rise to tactile sensations
What is the pain system known as?
The pain system is the anterolateral system
What can the pain system be divided into and where does this divergence of afferents occur?
Can be subdivided into a lateral and medial pain system
-This divergence of afferents occurs at the level of thalamus
What is the lateral pain system responsible for?
Responsible for sensory-discriminate aspect of pain
What does the lateral pain system project via?
Project via specific somatosensory thalamic nuclei
What is the medial pain system responsible for?
Responsible for effective-motivational aspect of pain
Where does the medial pain system project via to different cortical area ?
Project to different cortical areas via midline thalamic nuclei
What is the most effective painkiller known?
opioids
What are examples of treatment for pain?
- Opiate drugs
- NSAIDS
How do NSAID’s work?(Aspirin)
- Aspirin inhibits prostaglandin synthesis by blocking the activity of the precursor enzyme cyclo-oxygenase
- This reduces the inflammatory response that sustains C fiber firing
- Also acts on the hypothalamus and inhibits the generation of pain impulses
