Oral Somatosensory System Flashcards
What is the somatosensory system?
Part of the sensory system concerned with touch, pressure, pain, temp, position, movement, vibration which arise from muscles joints skin and fascia
Most of the discussion will be based on orofacial pain
What are the components of pain experience?
Sensory-discriminative: Localisation, intensity discrimination, quality of noxious stimulus
Moitivative-affective: Emotion, arousal and pain behavior, how the individual reacts, influenced by prior experience, expectations, possible, misconception.
*Orofacial pain is unique: Life-sustaining physiological processes
What is nociception?
Neurochemical process that detects noxious stimuli (mechanical, thermal, chemical)
What could happen to nociception on the way to the brain?
Nociception is either, amplified, reduced, or inhibited on the way to the brain
What are the 2 categories of pain?
Somatic and Visceral pain:
Somatic pain: Noxious stimuli from structures of the body. Normal and physiological, may be superficial or deep.
Visceral pain: Internal organs, diffuse and difficult to localize, tooth pulp.
What is non-nociceptive pain?
Neuropathic pain: Abnormalities of the nervous system with no need for noxious stimuli, may be spontaneous, no protective role, episodic or continuous neuropathic pain
Psychogenic pain: Patients report pain without evidence of tissue damage or physiological cause, caused by psychological stress, no neurophysiological basis for pain, exaggerated pain and unresponsive to treatment.
Watch video of trigeminal neuralgia
Very common to be seen by dentists
What are the features of neuropathic pain?
Abnormalities of the nervous system with no need for noxious stimuli
May be spontaneous
No protective role
Episodic or continuous neuropathic pain
What is orthodromic and antidromic conduction?
Orthodromic = Conduction in normal direction
Antidromic = Conduction in opposite direction
What do glial cells do?
Maintain chronicity of pain
Every year question bout the free nerve endings 3 types of nocieptors. What are they?
Thinly myelinated A-delta fibers FAST
Unmyelinated polymodal C fibers SLOWER
Silent/sleeping nociceptors PATHOLOGY
Large diameter, myelinated fibers A-alpha, A-beta and A-gamma transmite tactile and proprioceptive impulses to CNS
Which is faster of the nociceptors
Thin myelinated is faster
Unmyelinated C-fibers slower
Silent/sleeping involved in pathology
What is central sensitization?
Central sensitization causes hypersensitivty in pain. Allodynia and hyperalgesia are features of this
What is allodynia?
Allodynia = light touch hurts
How does the trigeminal system work?
Nociceptive information from head and face is transmitted to CNS via afferent fibers of trigeminal system.
Trigeminal system has mixed sensory and motor nerves
How does the trigeminal system work?
Nociceptive information from head and face is transmitted to CNS via afferent fibers of trigeminal system.
Trigeminal system has mixed sensory and motor nerves
What is the function of the thalamus?
Acts as a relay center. Acts to amplify or inhibit pain.
What does convergence of pain do to nociception?
Convergence makes pain referral possible from different teeth and so confusion is very possible in practice
What are the parts of the trigeminal brainstem complex?
3 parts:
Trigeminal main sensory nucleus
Trigeminal spinal tract nucleus
Motor nucleus of the trigeminal nerve
What kind of stimuli do A-beta fibers respond to?
Light touch. When there is inflammation and nerve injury they can transmit impulses that are perceived as pain (Allodynia)
What kind of stimuli do A-delta fibers respond to?
Intense mechanical and thermal sensations
What kind of stimuli do C-fibers respond to?
Thermal
Mechanical
Chemical
What velocity do A-beta, A-delta, and C-fibers transmit signals at?
A-beta = 40 - 70 m/sec
A-delta = 2.5 - 25 m/sec
C-fibers = 0.5 - 2.5 m/sec
What are silent nociceptors and how do they act?
They are usually dormant in healthy tissues but are sensitive to chemical release following tissue injury and then respond to mechanical stimuli.
They respond to high intensity stimuli with added input from A-delta and C-fibers
How do second-order neurones affect pain signals?
Increase in responsiveness in second-order neurones is called central sensitization
What is the difference between first and second pain?
A-delta nerve fibers transmit signal quickly leading to first pain which is short lasting and easy to localize and is sharp + stabbing pain.
C-fibers slow conduction velocity down leading to second pain which is felt as dull, deep, and burning pain
