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 does nociceptive transmission work?
- nociception occurs (detection of painful stimuli)
- transmission of nociceptor action potential to CNS
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)
How can nociception occur without pain?
- nociception refers to neural encoding of impending or actual tissue damage (noxious stimulation), pain refers to the subjective experience of actual or impending harm
- animal can receive noxious stimuli, but may not perceive it as painful
What is the main point of pain pathways?
not every animal is going to perceive the same pain stimulus in the same way due to genetics, experience, anxiety, etc.
