Ascending Sensory Systems Flashcards
cutaneous receptors and their fnctns
- pacinian corpuscle: vibration
- meissner corpuscle: discriminative touch
- ruffini ending: pressure
- ending around hairs: touch
- merkel endings: discriminative touch, fine touch, texture
- free nerve endings: pain, temp, itch, touch
general types of fibers in ascending/descending paths
- long ascending fibers going to thalamus, cerebellum or various BS nuclei
- long, descening fibers going from cerebral cortex or various BS nuclei to SC grey matter
- short propriospinal fibers interconnecting different SC levels (help coordinate flexor refelxes)
which funiculi are ascending fibers found in?
all three
where are propriospinal fibers found?
surrounding the SC grey matter
what do somatosensory receptors do?
detect mechanical, chemical, or thermal changes
structure of somatosensory receptors
- all are pseudounipolar neurons
- cell body in DRG or CN ganglion
- central CNS process
- peripheral process w/ an ending in skin, m, or joint
fasciculus cuneatus
extends to cuneate tubercle, which is site of nucleus cuneatus
fasciculus gracilus
extends to the gracile tubercle, which is site of nucleus gracilus
caudal medulla
- spinothalamic tract, NG, FG, NC, FC
- structures similar to posterior horn = spinotrigeminal tract (Lissauer’s tract) and spinal nucleus of substantia gelatinosa
rostral medulla
- medial lemniscus: fibers from contralateral cuneate and gracile nuclei
- spinotthalamic tract (anterior position)
- NG and NC cross as internal arcuate fibers
caudal pons
- medial lemn: more oval and horizontal (info from feet = lat, cervical = medial)
- spinothalamic tract: ant lat position
5 ascending pathways
- posterior column - medial lemniscus pathway
- spinothalamic tract (anterolateral path)
- posterior spinocerebellar tract
- cuneocerebellar tract
- anterior spinocrebellar tract
discriminative touch of med lemn path
- mostly ascending large myelinated primary afferents from various mechanoreceptors
- vibratory sense
- 2 pt touch
pathway of medial lemniscus path
synapse in medulla, decussates forming medial lemniscus, goes up to BS, relays in lat thalamus (VPL), terminates in postcentral gyrus
where are cell bodies for med lemn path located?
spinal arrerents are in ipsilateral DRGs
how do fibers of med lemn path divide once they enter SC?
DRG rootlets enter cord and divide into
- medial: heavily myelinated, large diameter, enter post column and ascend BS
- lateral: finely myelinated and unmyelinated, small diameter fibers
where is FC located?
above T6 only
location of 2nd and 3rd order fibers in medial lemn path
2nd: fibers cross midline in caudal medulla and for med lemn
3rd: originate in thalamus and ascend thru internal capsule and synapse in primary somatosensory cortex in post cent gryus
clinical relevance of med lemn path injury
- impaired proprioception and discriminative touch
- tested with vibrating fork or drawing on skin
- sensory info reaches brain via multiple paths so damage to 1 rarely leads to total fnctn loss
fnctn of anterolateral path
- pain and temp (one of multiple paths)
- involved in awareness and localization of painful stimulus
pathway of anterolateral path
fibers enter cord via lat division of dorsal root, project brs to post horn, primary fibers synapse to secondary fibers in substantia gelatinosa of post horn, 3rd order cell bodies on VPL
how do fibers cross midline in anterloateral path?
diagonally and ascend with rostral inclination
what special fibers travel in anterolat pathway?
- spinomesencephalic: imp in pain control mechanisms
2. spinohypothalamic: mediate autonomic response to pain
clinical relevance of anterolat path
- damage causes loss of pain and temp (can regenerate), itch and tickle (never regenerate)
- unilat injury does not impact bladder/bowel/sexual sensation bc they ascend bilaterally
- no tactile deficit bc most infor in post column
