Somatosensory Ascending Pathway - Part III Flashcards
Explain axonal reflex
-1st axonal terminal in one receptive area: afferent
- AP conducted back to the spinal cord/brainstem: orthodromic
However…
- AP conducted to other axonal terminals: antidromic
- release neurotransmitters: efferent
- Directly causes inflammation through mast cells
What do mast cells release when activated?
histamine
Where are free nerve endings?
EVERYWHERE
- from epidermis to internal organs
- ONLY SENSORY SYSTEM in epidermis
What do free nerve endings detect?
pain with noxious stimuli
What kind of axons are free nerve endings?
small, slow conduction
What are the two types of fibers in free nerve endings?
A delta and C-fiberss
What should we know about A-delta fibers?
poorly myelinated
SLOW CONDUCTION
What should we know about C-fibers?
none myelinated
SLOW
What are the functions of free nerve endings?
crude touch, temperature, noxious stimuli, itch and flavor
What do mechanoreceptors detect?
crude touch
What are the two parameters of mechanoreceptors / crude touch?
- duration
- intensity (increased AP frequency)
What is important about intensity of stimuli?
- initiate receptor potential
- defined by amplitude
- push harder = more stimulation transformed by nerve ending trigger zone, initiate AP
- push harder = higher amplitude of receptor potential, transform into AP increase the frequency
What are some modality specific receptors?
- cutaneous mechanoreceptors
- cutaneous thermoreceptors
- cutaneous nociceptors
What are some polymodal receptors?
1 free nerve ending can detect different types of stimuli
- other cutaneous nociceptors such as neat, cold, chemo, etc.
What kind receptors are most free nerve endings?
polymodal
- 2 levels of receptors
- protein complex on cell membrane interact with stimuli
- axonal terminals, interact with environment to detect stimuli
What are high threshold nociceptors?
pain initiated, above 45 degrees celsius
- A-delta = pain, fast
What are low threshold thermoreceptors?
when the hand gets closer to the bulb - low threshold themoreceptors activated
What happens when thermoreceptors are plateaued?
- elongated refractory phase
Pain is caused above this temperature?
45 degrees celcius
- thermal receptors have much longer absolute refractory period
- above 40 degrees increases temp but wont increse AP
In between what temperatures we CAN feel cold and hot?
17 to 45 degrees Celsius
When do we feel pain? Above and below what temperatures?
above 45 degrees celsius and below 17 degrees celsius
What detects hot and cold between 17 and 45 degrees celsius?
thermoreceptors
What detects pain above and below 45 and 17 degees celsius?
nociceptors
How many polymodal receptors are there in CN V3?
6
- still thermoreceptors
How can we detect taste/ What CN play a part?
V3/CN IX/CNX
What does flavors?
chemoreceptors?
What does V3 supply?
the face, like visceral, detects flavor
- anterior 2/3 of tongue where we detect different flavors
What does CNIX detect that helps with taste?
- posterior 1/3 of the tongue
- flavor
What does CN X detect that helps with taste?
- epiglottis
- also detect flavor
What can cold thermoreceptors detect?
menthol to the pungency of garlic
What can hot themoreceptors detect?
spicy pepper, pungency of garlic too
What is the first level of polymodality?
single receptor, different stimuli
- all can open/activate ion channel
What is the second level of polymodality?
different receptors on the same axonal terminal
- FNE neuron in dorsal root ganglion has only one axon, one axon can have hundreds of axonal terminals
- Recognize histamine, prostaglandin, ATP, serotonin, H+ ions, etc. bc in receptive area of axonal terminal has a bunch of protein complexes as receptors, can detect different types of stimuli
What detects sour food?
Hydrogen ions
What is out side and inside of the VR-1 receptor for spicy food?
temperature outside, sour food inside
What is polymodal receptor for?
not for a nerve, only for a single free nerve ending
Which sensory modalities project to Brodmann areas 3a, 3b, and 2 plus 1?
- 3a: proprioception from Ia and Ib
- 3b and 2: fine/crude touch, sharp pain, temp
- 1: proprioception from joint capsules
Where is 3a?
posteiror to central sulcus, impoportant for motor functions
- anterior bank: Betz cells
- directly control LMN in spinal cord
- in charge of all fine motor control functions develop after birth
What kind of receptors and in plus 1?
Ruffini type or Pacinian type
- all Aa
What kind of fibers are in 3b and 2?
- AB, C-fibers, do NOT project
What is hyperalgesia?
literally “more pain”, over reaction to noxious stimuli
What are the two mechanisms of hyperalgesia?
- increased rest membrane potential: sensitized (takes less to get above threshold with stimuli, initiate AP with less)
- Activated silent nociceptors: high threshold (bc of inflammatory reactions, transfers receptors onto FNE axon terminals= more receptors detect stimuli)
- or both
What can cause hyperalgesia usually?
acute injury
What is allodynia?
Burning pain, nociplasticity, change peripheral membrane, central processor axon terminal overgrow
- after injury, more receptors express or get out onto the axonal terminal membrane, inside central processes overgrow, spread out in spinal cord = allodynia
What should we know about sympathetic nervous system?
- always active, tonic, constricts blood vessels, maintains BP
What should we know about the parasympathetic nervous system?
only when we need it, aphasic
What is the afferent axonal reflex?
- AP along the peripheral process to the central process to the spinal cord
= pain
What is the efferent axonal reflex?
- AP to other peripheral processes
- blood vessels: leaking, thus pain and swelling
- Mast cells: amplify swelling/itchy etc.
What nociceptors do muscle pain?
- A delta
- C-fibers
What is the purpose of A-delta?
muscle pain
- stretch or contraction after exertion
What is the purpose of C-fibers?
muscle pain
- ischemia or after injury
What condition caused by C-fibers causes patients not to be able to walk more than 200m due to blood vessels being blocked?
intermitentent claudcation
- ischemia by C-fibers!
What can A delta and C-fibers cause?
chronic low back pain
- PT doesn’t solve
What causes joint pain?
A delta and C-fibers responding to inflammation, peripheral sensitization
What can cause inflammation?
axonal reflex, receptors activated = pain
- like with OA
Why do our joints not hurt all day everyday?
A delta and C-fibers are usually latent, why we dont feel pain in joints
- joints under stress all day
What joint pain is the result of A-delta and c-fibers responding to inflammation?
Osteoarthritis/RA, etc
- inflammatory response
What does viscera pain?
- Mainly polymodal C-fibers
What is an example of mechanical stimuli causing pain?
bowel obstruction
What is ALWAYS c-fibers?
ISCHEMIA
What causes a tummy ache?
endogenous compounds
What is unique about viscera pain?
diffuse and always has referral patterns
Where is gallbladder referred pain?
c-fibers
- phrenic nerve
- somatic pain conducted back to C3,C4, C5
- Right shoulder pain
What is a dermatome?
- segmental distribution of a spinal nerve
- pain, crude touch, temperature
What are multiple sensory neurons called?
large receptive field
Why are overlapping peipheral and central processes impportant for healing?
- less sensitive to functional loss
- better chance to gain sensation back
What are tests for A-delta for spinal nerve or spinal cord injury?
- pinprick: sharp pain
- crude touch: cotton ball
- Temperature: test tubes with hot and cold water
What is the dermatome for the umbilicus?
T10
What is the dermatome for the nipple line?
T4
What is the first order neuron of the ascending anterolateral system?
- dorsal root ganglion
What is the 2nd order neuron of the ascending anterolateral system?
Lissauer’s tract in the dorsal horn
Only ______ axons get to spinal cord through Lissauer’s tract?
free nerve endings
What does NOT cross Lissauer’s tract, goes directly to dorsal column and then branches in at the same level or ascends or descend?
mechanoreceptors
What lamina are C-fibers?
I, II, and V
What causes central sensitization?
axons over-sprout in the lamina II of C-fibers
What lamina are A-delta?
Lamina I and V
What causes allodynia?
A delta axons sprout into lamina II , central sensitization
What lamina does chronic pain come from?
II, substantia gelatinosa
How can a single free nerve ending in the tongue detect different sensory stimuli?
- Different receptors for different stimuli in the same axonal terminal
- A single receptor with multiple sites to detect different stimulants
What does the anterolateral system of Adelta do?
localized sharp pain/temperature/crude touch
What does the neospinothalamic pathway ascend through?
lateral funiculus
Where does the anterolateral system Adelta decussate?
P+2 = L
- 2 levels higher
- ex. cut at T12 complain of numbness at L2?
What is the anterolateral system aDelta 3rd order neurons located?
Ventral posterolateral nucleus (VPL)
What is the S1, Brodmann area 3b,1 located?
medial postcentral gyrus
What is 3b and 2 for?
crude touch, sharp pain, temp
What does diffuse pain?
somatic C-fibers
What is diffuse pain?
2nd pain, bilateral projection
What is the pathway for diffuse pain?
paleospinothalamic pathway
What does the paleospinothalamic pathway ascend through?
anterior funiculus
Where does the paleospinothalamic pathway project to?
reticular formation in the thalamus
Where does diffuse pain come form in the brain?
- intralaminal/centromedian nuclei
- insula/anterior cingular gyrus, frontal lobe
- why we have emotions with pain
What lamina does the anterior funiculus project to?
Lamina I, II, V
What are the first-order neurons for the spinal trigeminal pathway for a-delta?
CN V: trigeminal ganglia for face
CN VII: geniculate ganglion
CN IX: inferior ganglion
CN X: inferior ganglion
What are the second order neurons for the spinal trigeminal pathway for A-delta?
spinal trigeminal nucleus
What crosses over in the spinal trigeminal pathway for a delta?
- decussation 2nd order neuron axons
What is the 2nd order neuron spinal trigeminal nucleus?
mid-pons to the C2
What is the concentric distribution of the spinal trigeminal nucleus?
mouth as the center 1-5, not the cervical spinal cord level
- 5 outermost
- 1 innermost around the mouth close to the medulla oblongata
What is the third-order neuron for the spinal trigeminal pathway for A-delta?
anteroposterior medial nucleus
Where does the 3rd order neuron for the spinal trigeminal pathway A-delta?
to lateral (inferior) postcentral gyrus with somatotopy maintained
What is the largest axon?
Aalpha
What is the fastest axon?
A-ALPHA
What axon is “medium myelinated”?
A-gamma
What axons are small myelinated?
A- Beta
which axons are unmyelinated?
C-fibers
What are the largest and fastest afferent axons?
Ia and Ib for spindles and GTO
What are the medium myelinated axons for the afferent axons?
AB and II
What axon does pain management such as e-stimulant (TENS)?
- a-beta activated (fast) blocks “highway” so others cant reach
What does muscle stimulation such as NMES do?
reactivate muscle fibers (especially post-surgery)
Locate the 1st, 2nd, and 3rd order neurons convey the sharp/1st pain to the S1?
1st order neuron: dorsal root ganglion
2nd order neuron: lamina I and V
3rd order neuron: above C2 level: VPL; below C2 level: VPM
Why does someone with a syrinx in the upper cervical spinal cord complain of circular pain in the face?
spinal trigeminal nucleus to C2 spinal cord level, syrinx compromises spinal trigeminal tracts
