Neuroanatomy & Neurobiology Flashcards
(42 cards)
1
Q
What organs have pruritus sensation?
A
skin, cornea, mucosa
2
Q
What nerve cells in skin, superficial to deep
A
- Merkel cells
- Meissner’s corpuscle
- Ruffini corpuscle
- Pacinian corpuscle
- Hair Follicles
3
Q
What do merkel cells do?
A
- light touch
- slowly adopting AB sensory fiber
- high resolution to stimuli…can feel the small stuff (needle poke moving closer together, eventually feels like one point
- ability to feel two needs = merkel cell sensations!
4
Q
What do Meissner’s corpuscle accomplish?
A
- Touch (dynamic skin deformation)
- rapidly adapting AB sensory fiber
- seen at the end of the peripheral nerves
5
Q
What do Ruffini corpuscle do?
A
- Stretch
- slowly adapting AB sensory fiber
- further from the end of the nerve fiber
- feel “stretch” and can balance movement based on sensation of skin stretch
6
Q
What do Pacinian corpuscle do
A
- High pressure, vibration
- rapidly adapting AB sensory fiber
- onion-like structure
7
Q
What new somatosensory organ may be seen in dogs?
A
- nonencapsulated naked nerve bundles
- similar to Meissner’s corpuscles
- Located near the tip of nose/nasal planum? within the dermis leading to the epidermis
- described in 2019 in humans….maybe not in dogs?
8
Q
What are the properties of “Hair follicles” sensation/mechanoreceptors?
A
- Light touch
- (low frequency vibration)
- all types of sensory fibers
- may be coupled with Merkel cells
9
Q
What sensations do Dermal and epidermal free nerve endings capture?
A
- innocuous touch
- nociceptive touch
10
Q
What type fo intraepidermal nerve endings are present?
A
- b3T
- recently published 2017 in dogs
- cool, because these are infiltrating the keratinized layer!!!
11
Q
How do thermoreceptors work? (briefly describe the category and way it works)
A
- (transient receptor potential)
- An intramembrane cation channel
- Calcium cations cause depolarization after stimulation to the nerves
- heat/cold can stimulate sensation
12
Q
What are the types of thermoreceptors?
A
- TRPA1
- TRPM8
- TRPV4
- TRPV3
- TRPV1
- TRPV2
13
Q
Tell me about:
Transient receptor potential ankyrin 1 (TRPA1)
A
- senses cold temperatures (<17 °C)
- chemical stimuli
- pungent taste of mustard, horseradish, and wasabi
- causing thermal hypersensitivity. It also
- responds to mechanical stimuli via membrane stress
- expressed on Aδ and C fibers.
14
Q
Describe classification of cutaneous sensory nerve fibers
A
- A-beta/II = should be fastest given largest diameter and conduction velocity
- A-gamma
- C/IV = no myelin, very slow, smaller diameter
15
Q
Describe the pathway of stimuli from skin to spinal cord
A
- various stimuli via sensory receptors, depolarized sensory neurons contribute to synaptic activities
- cell bodies of sensory neurons reside in dorsal root ganglia (DRGs) that are found justoutside the spinal cord or trigeminal ganglia (TGs) the base of the skull.
- Neurons are “pseudo-unipolar” with no dendrite
- single axon that bifurcates, creating one branch projecting to the periphery and another branch projecting into the central nervous system (CNS) at the level of the spinal cord (DRGs) and brainstem (TGs).
- impulses ascend through the spinal cord and finally reach the brain where “somatosensation” is
- finally imaged and interpreted.
16
Q
Describe the Gate Control Theory?
A
This is why rubbing a painful area helps decrease pain sensation….perhaps helps with itch sensation too??
The gate theory states that
- stimulation of nerves carrying non-painful sensations (Aβ nerve fibers) closes a neurological “gate” in the spinal cord that reduces transmission from pain (and must somehow include itch) nerves (Aδ and C nerve fibers) to the brain.
- In this theory, simultaneously-stimulated large myelinated Aβ fibers can activate interneurons that modulate the firing of secondary spinal neurons associated with primary afferent pain fibers.
- (YouTube => https://www.youtube.com/watch?v=oQLFfvGM7nI)
17
Q
What correctly describes characterizes C nerve fibers?
A
Unmyelinated, small diameter, slow conduction velocity
18
Q
What is itch?
A
- text book def: an unpleasant sensation which causes and intense desire to scratch
Also consider:
- itch on primary inflamed skin
- infection, ectoparasite, allergy, immune-mediated, skin cancer
- itch on primary, non-inflamed skin
- neuropathic, systemic, psychogenic
- itch on secondary scratch lesions
- itch-scratch cycle
19
Q
Describe Transient receptor potential melastatin 8 (TRPM8)
A
TRPM8 is notable for detecting cold temperature (8-26 °C) and contributing to the cooling sensation by chemicals such as menthol and icillin (synthetic TRPM8 agonist). TRPM8 is expressed on Aδ and C fibers.
20
Q
Describe Transient receptor potential vanilloid 1 (TRPV1)
A
TRPV1 is also known as a capsaicin receptor (capsaicin is one of the vanilloids). Temperature greater than 43 °C, low pH (< 6.0), capsaicin (chili peppers), endocannabinoids, or other substances can induce TRPV1 activation leading to burning sensation and pain. TRPV1 is highly expressed on Aδ and C fibers.
21
Q
What is a pruitogen
A
- any substance that causes pruritus
- Histaminergic itch vs. non-histaminergic itch
- histamine = mast cells, basophils
- acute itch????
- non-histaminergic = mucunain, such as with cowage (velvet beans) tiny spines (cactus itch!)
- chronic itch????
- histamine = mast cells, basophils
- future study: classify the differences between these two pathways? the neruons for each pathway are seperated from each other…..and different in the brain!!! super cool….probably not testable ;-)
22
Q
Histamine - describe pruritogen ability
A
- Histamine is predominantly released from mast cells and basophils.
- It can directly stimulate itch sensory neurons in the skin to cause acute itch.
- In contrast, the evidence suggests that histamine- induced itch does not substantially contribute to chronic itch such as atopic dermatitis (AD).
23
Q
Describe Substance P (SP) pruritogen properties
A
- neuropeptide secreted from the free nerve endings in the skin as well as from keratinocytes and various inflammatory cells.
- SP has been suggested to be an important itch mediator in AD.
- Although the receptors of SP, neurokinin 1 receptors (NK-1Rs) and mas- related G protein-coupled receptors (Mrgprs), are both expressed on the terminates of non- histaminergic itch-mediating sensory neurons, a recent mouse study has shown that only Mrgprs are responsible for SP-induced itch.
24
Q
Describe the pruritogen properties of Nerve growth factor
A
- Nerve growth factor (NGF)
- neurotrophin mainly produced by keratinocytes.
- NGF promotes the growth of nerve endings in the skin, which is partly responsible for neuronal sensitization of itch seen in AD patients.
- NGF up-regulates other neuropeptides, especially SP, thereby further promoting itch indirectly.
25
Do protease induce pruritus in dogs?
* questionable (in dogs)
* if so, very mild
26
Which cytokine has been shown to cause itch in dogs and cats and horses?
* IL-31
**other** cytokines in _humans/mice_ include: IL-2 (not in dogs though)
27
What cells produce IL-31 in dog skin
TH2 cells
28
which cells receive IL-31 signals?
* Two structures of receptor IL31RA receptors
* IL31R-alpha and OSMR-beta…must have both parts for signaling
* found in dorsal root ganglion!!!
* keratinocytes expressed in canines, increased after AD flare
* IL-31Ralpha constitutively expressed on keratinocytes
* in cats….expressed extremely low in skin :-(
29
which molecule is responsible for neurogenic inflammation?
substance P
30
Nerugogenic vs. neuropathic itch?
* neurogenic = itch induced by pruritogens in the absence of neural damage
* itch on inflamed skin
* neuropathic itch = itch associated with damaged neurons
* itch on non-inflamed skin
31
Canine syringomyelia (SM) - what pruritogen is present in CKCS skin?
significant difference of SP in symptomatic dogs
32
Acral mutilation syndrome
* autosomal recessive sensory neuropathy (diminution of pain perception)
* CS: sudden intense licking → auto-amputation
* breeds: GSHP, Eng springer spaniel, Eng/french Spaniel
* mean age = 4 mo
* dx via clinical signs
* GDNF (glial cell derived neurotrophic factor) mutation AND….
* SNP mutations at LincRNA (long noncoding RNA) **upstream** of GDNF = GDNF-AS
* perhaps the regulator of expression of the GDNF area
33
Tail Dock Neuroma
64% of piglets with docked tails :-(
no difference based on location of docking
34
What is Radiculopathy? (humans - extrapolte to dogs)
* HUMAN definitions/cut offs:
* Focal NI Syndrome
* Trigeminal trophic syndrome (CNV)
* Brachioradical pruritus (C5-6)
* Notalgia paresthetica (T2-6)
35
FEHV-Associated Dermatits and neurogenic/-pathic itch?
* causes: facial pruritus
* neuropathic itch? We know that herps hides in trigeminal nerve ganglia of humans….possibly in cats
* trigeminal ganglia…innervating facial nerve, and ciliary ganglia, cranial cervical ganglia
36
Acral Lick Dermatitsi
* Causes: allergy, orthopendic, neurologic, neoplasia, focal infection, behavioral
* prevalence: 50% behavioral???? not convinced
37
Describe Feline Psycogenic Alopecia
* causes: stress related overgrooming
* prevalence = 1.2 to 4.7% itchy cats
* breeds: Siamese, Abyssinian, asian cats (over-diagnosis?)
* age: no predilections
* diagnosis: by exclusion
* study: 21 presented to behaviorist, only 2 had psychogenic, 16 had medical causes, 3 had combo of psychogenic and medical
38
Describe Feline Idiopathic Ulceration
* self-induced, stress?
* CS: non-healing ulceration at dorsal neck and shoulder
* Dx: by exclusion
* 2018 study found possible correlation with stress
* clinician looked at environment and evaluated….found that enrichment and caused improvement within 15 days???? (or where these cats herpes cats that resolved b/c reduction in stress…I have questions re: this study)
39
What is the name of gene associated with acral mutilation dermatitis in German short haired pointer
GDNF
40
Mu-opioid reeptor agonist effect on pruritus
increase itch
41
How does maropitant have antipruritic effects?
Acts as to NK-1R inhibitor
This is also the receptor for Substance P
42
Gabapenin MOA
Decrease release of pruritogens and decrease effects
