Neuroanatomy of Pain Pathways Flashcards
What is pain?
arises in the brain:
- a conscious experience
- a complex sensation
What does the nervous system is plastic mean?
- strength of synaptic connections w/in the CNS is changeable
- pain pathways are especially plastic
What is nociception?
- SENSORY (AFFERENT) information that is relayed via ASCENDING pathways:
1. transduction
2. conduction
3. transmission
4. modulation
5. perception - there are different synapses that happen along the way & different drugs impact different locations in the pain pathway
What pathways make up the peripheral nervous system?
both motor (efferent) and SENSORY (AFFERENT)
Where is nociceptive information relayed?
- nociception is SENSORY (AFFERENT) information that is relayed via ASCENDING pathways
What are the different types of sensory neurons in the PNS?
- proprioception: ability to sense movement, action, and location
- exteroception: ability to sense environment (touch, temperature, & pressure)
- nociception: ability to sense noxious stimuli (extremes of cold, heat, mechanical, & chemical stimuli)
What is nociception?
detection of noxious stimuli by a subset of sensory neurons, termed nociceptors (A-δ, C fibres)
compared to other sensory neurons, nociceptors are:
- smaller in size
- much more numerous
What tissues and organs do nociceptors supply?
- head: meninges, cranial blood vessels, cornea, tooth pulp
- skin: epidermis, dermis
- viscera: cardiac muscle, GI tract, urogenital tract
- muscle: fascia, tendons
- bone: periosteum, perivascular
- joints: synovium, ligaments, periosteum
- basically everywhere but the CNS
What noxious stimuli do nociceptors detect?
anything that could damage tissues:
- mechanical stimuli
- thermal (heat or cold) stimuli
- chemical (normally detect acidic change) stimuli
How do nociceptors detect noxious stimuli?
multiple ION CHANNEL RECEPTORS in the cell membrane which are sensitive to:
- mechanical stimuli
- thermal (heat or cold) stimuli
- chemical (H+) stimuli
How many types of noxious stimuli can nociceptors respond to?
more than 1 type (they are polymodal)
What is the threshold for nociceptors?
have a high threshold, under resting physiological conditions
What are the characteristics of nociceptors?*
- numerous and ubiquitous
- polymodal
- high threshold
How does noxious stimuli reach the brain?
spinal transmission of information about noxious stimuli
What type of fibres convey noxious stimuli?
A-delta and C axons
How is the action potential related to nociception?
- voltage gated sodium channels are essential for propagation of the action potential
- local anesthetics block voltage-gated sodium channels
What does the state of excitability in the pain relay neuron determine?
- how much information about the noxious stimuli is transmitted to the brain
How do axons from spinal pain relay neurons travel?
In many white matter tracts.
So a large spinal lesion is required to remove all pain sensation caudal to the injury.
What are the brain regions involved in the experience of pain?
- cerebrum
- midbrain (extremely important in processing this info along w/ pons & medulla)
- cerebellum (has areas that are responsible for memory & perceiving those unconscious stimuli)
- thalamus (all pain pathways come in here & all motor pathways come out)
- diencephalon (lesion here may mean the animal has difficulty processing pain or extreme response to “pain”
- brainstem (partially responsible for maintaining animal’s consciousness)
Where else do pain pathways send info to?
- areas of conscious decision-making (cerebral cortex)
- offshoot to the hypothalamus (dilated pupils, increased respiration and heart rate, increase in core body temperature; involuntary; also neuroendocrine responses)
- offshoot can go to limbic system (these will activate memories & fear centers; activates fear & anxiety response to the stimulus they are receiving)
