Somatosensory System Flashcards
dorsal/posterior column pathway
spinothalamic tract pathway
DORSAL: carries pressure, proprioception, two point sensation
- sensation enters the DRG, goes up the spinal cord in its cuneus or gracilis pathway to the medulla
- crosses and synpases at the medulla to the contralateral side of brain then enters the cortex
SPINOTHALAMIC: carries pain and temperature sensation
- carries sensation into the DRG: then IMMEDIATELY synpases and crosses over at the SC level, travels up the contralateral side of the SC to cortex
- - anterior and lateral pathways
lesions above the deccasaion will have contrlateral effects, lesions below will have ipsilateral effects
where in the medulla is the location of decussaion for motor and dorsal sensory
- both decussations are in the lower medulla
the ventral white commisure: carries the information along the decusaation: the area of cross over for the sensory information and cross for LMN to get to target
since the decussaion is low in the BS: lesions to the brainstem will mostly have contralateral affects (likelihood of the injury being above this cross over is high)
orientation of the BS sensory nerve tracts & the cranial nerve tracts
where are the CN exiting the BS
Sensory nerves: running dorsal (posterior) of the BS
Cranial Nerves = are peripheral nerves
- thus lesions of the CN are essentailly Peripheral nerve lesions, which reseult in ipsilateral loss of function
- they cross over right before/at their nuclei
- so anything above (like a cortex lesion, etc.) will have contralater effects, but anything thats impacting in hte BS will have ipsilateral effects at theri specific CN level
MIDBRAIN : leaving
- CN III (lesions = down and out eye, ptosis, loss of light pupillary reflex so itll be dilated)
- CN IV
PONS: leaving
- CN VI (lesion = inability to abduct eye)
- CN VII (lesion = facial muscle paralysis: no smile)
MEDULLA: leaving
- CN XII (lesion = tongue deviates to side of lesion)
Lesions of the SC: results
MS: transverse myelitis
- will effect either the motor or the dorsal or the spinothalamic tracts
where do they run
motor = anterior (ventrally)
spinothalmaic/anteriolateral = laterally (blood = anterior spinal artery)
dorsal tract = dorsally (blood = posterior spinal artery)
Anterior Cord Syndrome
infarction of teh anterior spinal artery
- therefore impacting the spinothalamic tract & motor tract
- dorsal column is preserved
Tabes Dorsalis (neurosyphilis)
damage to the dorsal roots and columns
so pain and temperature unaffected but other sensation is
Symptoms
- pain is first to occur; because of the irritation at the dorsal sensory area
- anesthesaid as the dorsal roots are destroyed
lost dorsal: therefore lost proprioception
- loss of position sense: borad based gait of walking
- slap and stomp feet: to eleict pain to feel the sensation of walking
Syringomyelia
- a softening or cavitation of the middle of the SC
resultsin in BILATERAL loss of pain and temperature (since the spinothalamic tracts are sitting right there alterally)
- often impacting the hands
if it occurs in the medulla: think Arnod Chiarai malformation
Combined System Disease: pernicious anemia (B12 loss)
Dorsal Column impacted: lost postion in space = broad based gait
corticospinal tracts impacted: UMN lesions - paralysis
what nerve pathway sends sensory information about the head back to the brain and how
the Trigeminal Nerve: sends sensory information about the head back to the brain
Areas it is in control of sensation
- cranial cavity’s meninges
- paranasal sinuses
- nasal cavity and nasopharynx
- oral cavity
- also the superfiscial skin of the face!!! sensation
- also muscles of mastication
- orbital cavity too
the trigeminal nerve crosses at different locations = trigeminothalamic tract
pain fibers
type A delta: myleinated
- fast fibers for pain
- sharp, stabbing pain
- pain is sent to the sensory cortex: 3,1,2
type C: unmyleinated
- c for chronic pain
- slow, dull, achy and diffuse
- pain to the reticular formation
remeber the reticular formation is conencted to the limbic system, the thalamus too so it has an emotioanl compontne to thebrain and pain
reticular formation + vomiting center
the reticular formation has the vomiting center in teh RF location in the medulla
VOMITING CENTER
- in teh RF of the medulla
- information from the vestibular system (cholenergic and hsitaminergic)
- information from teh postrema (for toxins in teh blood)
CTZ: chemo trigger zone
- a hole in the BBB: capillaries and fenistrated ehre and montiro the blood for toxins and will trigger vomiting
- this is called teh areas postrema
- which is connected to the RF too and vomiting center
modulation of pain
opioids
analgesics
Endogenous opioids
- endorphins
- enkephalins
- dynorphins
narcotic (sleep) or analgesic (pain relief)
nociceptive path = pain pathway
antinociceptive path = anti-pain path
pain modulation
- can be presynpatic or possynpatic modulation
- presynaptic = inhibition of teh CA++ channel opening to let the NT release to the cleft
- post-synaptic = via the same mechanisim of blocking Ca (?)
postsynaptic inhibiton of tehe pain pathway can be from higher levels of the CNS
Headaches
pain from= meninges, dural venous sinsuses, arteries, upper cervical nerves
supratentoral compartments = via trigeminal nerve
infratentororal compartments: IX, X and cervical N
Migraine
- the Trigem enrve becomes activeated and the nerve and vascualtre interplay occure
- neurogenic hypotehsis (retrograde axon transport that causes inflamamtion of tissue and stimaultes pain)
Cluster HA
- trigeminovascualr system: vascualr, neurologic : dialted intracrainal arteris on the location of the pain
- autnomic symptoms (lacrimantion, conj. redness, etc.) shows hypothalamus interplay = giving O2 stops the pain
- +/- horners because lack of sympathetic innervation can occur (constriction pupil, ptsos, and lack of sweating)
