Neurophysiology of Nociception: Sensory Transduction Flashcards
The processing of nociceptive information is accomplished via?
electrochemical reactions that occur along specific nociceptive pathways
Can the perception of pain occur without nociception?
YES
What are the 4 distinct neurophysiological events of nociception?
Transduction
Transmission
Modulation
Perception
What is transduction?
converting noxious stimuli into electrochemical impulses
What is transmission?
transmitting electrochemical impulses along afferent fibers to various nervous system regions
What is modulation?
altering the perception of noxious stimuli by peripheral or central mechanisms
What is perception?
the conscious experience of pain created by the interpretation of nociceptive information by higher centers of the CNS
What is sensory transduction?
the process in which information from various forms of noxious stimuli (chemical, thermal and/or mechanical) is transformed into electrochemical energy by sensory nerve ending (nociceptors)
Nociceptors are free nerve endings of what?
specialized afferent fibers
Nociceptors respond to?
intense, noxious stimuli
The primary cell bodies of neurons carrying noxious info from the body are located where?
in dorsal root ganglia (DRG)
Primary cell bodies of neurons carry noxious info from the face are located where?
trigeminal ganglia
All nociceptive neurons utilize what as primary neurotransmitters?
glutamate and substance P
What are the properties of peripheral nociceptor fibers?
myelinated A delta and unmyelinated C fibers
Myelinated nociceptors (20%)
- A delta fiber group
- Large myelinated axons
- conduct at ~20 m/s
- Bimodal: respond to noxious mechanical & thermal stimuli
- Small receptive fields (clusters of sensitive spots)
- Project to lamina I of spinal cord grey
Unmyelinated nociceptors (80%)
- C fiber group
- Small axons in remak bundles
- Conduct at ~2 m/s
- Polymodal: respond to mechanical, thermal and chemical stimuli
- Large receptive fields
- Project to lamina II and III of spinal cord grey
Myelinated bimodal nociceptors (A delta):
What is the adequate noxious stimuli for activation?
Mechanical: > 10 grams of pressure
Thermal: Heat (>45 C); Cold (11° C)
Unmyelinated polymodal nociceptors (C fiber):
What is the adequate noxious stimuli for activation?
Mechanical: >10 grams of pressure
Thermal: Heat (>45 C); Cold (11° C)
Chemical: numerous substances
What is the perception of first and second pain?
pain perception has been described:
- A first sharp pain and a more delayed diffuse and longer-lasting second pain
What fiber will be activated when intensity of a stimulus initially reaches the threshold of nociception?
Fast-conducting A-delta fibers
- producing a sharp painful sensation (first pain)
If a noxious stimulus persists which fibers are then activated? and what is there response?
Slowly adapting C-fibers will be activated
- producing a less well-localized pain of a dull quality
How fast do A-delta and C-fibers deactivate?
- A-delta fibers rapidly deactivate
- C-fibers deactivate slowly –> extending sensation of dull pain
Somatosensory quality (modality) processing form?
Receptor type (transduction) - i.e. temp, pressure, pain
Somatosensory intensity (magnitude) processing form?
Impulse (frequency)
- i.e. light or heavy pressure
