Lecture 3b-ascending pathways Flashcards
In the ascending pathways, sensory info from receptors comes into the cord via what?
what are their steps after that?
peripheral nerves/spinal nerves/dorsal roots
- the info participates in spinal reflexes or
- ascends to the cerebral cortex and
- ascends to the cerebellum
in the descending pathway, motor commands issued by your brain descend to the cord to synapse wehre?
cord’s ventral horn cells
where do tracts live
white matter
many tracts have 2 part names, what does the first part tell you? what about the second?
- tells you the location of the neuronal cell bodies from which these axons originated from (aka cell bodies of origin)
- tells you the site where they terminate (aka synapse)
whta are the 3 kinds of connections that afferent info make up
- local reflex connections
- connections destined for the cerebral cortex (conscious perception)
- connections destined for the cerebellum (regulation of muscle tone and coordination of muscle function; subconscious)
what is proprioception? what can it be?
body sense
either conscious or unconscious
what do conscious sensation reach? via what?
what does unconscoius sensations refer to?
the cerebral cortex via thalamus
unconscious sensations refers to stuff that does not
what are the different subtypes of touch (tactile) stimuli?
2 point tactile discrimination
light(gross) touch
pressure
vibration
what is epicritic
what is protopathic
discriminating touch
pain and temperature
in the ascending pathway, where does the 1st order neuron always have its cell body in. why?
dorsal root ganglion
-there are no synapses in the DRG
the shortest path to the cerebral cortex is 3 neurons long, what are they?
primary afferent
neuron that crosses the midline
thalamic neuron
where does each primary afferent neuron have its cell body in?
sensory ganglion (DRG) -a peripherally directed process ending in skin, muscle, or a joint, and a central process ending in the CNS
primary afferents terminate in the CNS on…
2nd order neurons, which in turn project to 3rd order neurons and so forth.
with few exceptions, the receptive ending, cell body, and central terminals of a primary afferent are all on the…
same side
-central process ends on the side ipsilateral to the cell body
somatic sensory afferents segregate at the margin of the spinal cord.
where do large diameter heavily myelinated fibers enter? and where?
small diamter fibers? and wehre?
medially through dorsal funiculus
Mylinated=Medial
laterally through the zone of Lissauer
Lissauer’s=Later
fasciculus gracilis and cuneatus entering ____ to lissaurer’s tract;
-2 pt tactile and proprioceptive info comes in more ______ and is highly myelinated whereas pain and temp is ______ myelinated
medial
medially
thinly
what general sensations do the medial lemniscus pathway in the dorsal column carry
“conscious proprioception” from the lower extremity =>eventually lead to cerebral cortex
proprioception (joint position)
2-point tactile discrimination
pressure
vibratoin
what is the dorsal column- medial lemniscus pathway (lower extremity)?
- 1st cell body is DRG enters the cord medially
- once in dorsal columns (funiculus) rise as fasciculus gracilis
- FG synpase at nucleus gracilis (2nd CB)
- 2nd order neuron sneds out fibers (INTERNAL ARCUATE) to arc around and cross the midline to the other side of the body. aka SENSORY DECUSSATION
- fibers rise as medial lemniscus
- 3rd order fibers leaving the thalamus as sent through the internal capsule (through its post limb)
- arrive at the specific place for legs w/in somatosensory area of the parietal cortex
what are mechanoreceptors
more superficial
pacinian corpuscles (vibration)
meissner’s corpuscles (tactile discrimination)
what are proprioceptors
for position sense
more deep
muscle spindles
gogli tendon worgan
where does tactile sensation start
skin receptors
where does proprioception start out w/
specilized receptors in the muscle spindles or tendons
after leaving the receptors, what is afferent info sent via
large myelinated fast conducting nerves
same primary afferent as monosynaptic stretch reflex
where are the central branches of the axons of the primary sensory neurons for discriminative touch and proprioception located
medially located in each rootlet and bifurcate on entering the dorsal funiculus
if epicritic sensation is blocked below/before the decussation, wehre is the clinical deficit to the lesion?
what if it the lesion if above the decussation?
ipsilateral
contralateral
what is romberg sign
loss of conscious proprioception
-ex. walking requires a sense wehere you are in space, if a conscious joint position sense from the lwoer body were damaged and you close your eyes you would sway bc no sense of where you are
what is 2 point discrimination
pt asked to determine whether two points of an instrument are touching them or only 1. most accurate place is at fingertips
what is vibratory sense and deep pressure sense
to test vibratory sense a turning fork is placed against a joint
does FG ever cross over to the other side?
no
what is the dorsal column- medial lemniscus pathway (upper extremity)?
entry at T6 or above
Lumar entry
- 1st cell body is DRG enters the cord medially
- once in dorsal columns (funiculus) rise as fasciculus cuneatus
- FG synpase at nucleus cuneatus (2nd CB)
- 2nd order neuron sneds out fibers (INTERNAL ARCUATE) to arc around and cross the midline to the other side of the body. aka SENSORY DECUSSATION
- fibers rise as medial lemniscus
- 3rd order fibers leaving the thalamus as sent through the internal capsule (through its post limb)
- synapses on post-central gyrus in parietal complex arrive at the specific place for legs w/in somatosensory area of the parietal cortex
what is the somatotopic map in the somatosensory cortex called
sensory homunculus
why is there no dorsal intermediate sulcus below T6?
bc there is no fasciculus cuneatus below T6
dorsal columns in the cord (ffasciculus gracilis and cuneatus) are what?
internal arcuates in the brainstem do what?
medial lemniscus is waht to the receptors?
uncrossed
cross
contralateral
where is the cell body of origin for the fasciculus gracilis?
fasciculus cuneatus?
medial lemniscus?
DRG
DRG
nucleus gracilis/cuneatus
what tracts make up the anterolateral system
spinothalamic
spinotectal
spinoreticular
spinoolivary
what is the lateral spinothalamic tract for?
what is the ventral spinothalamic tract for?
- conscious: convey info about pain and temp
- light touch
eventually make its way to cerebral cortex by way of the thalamus bc its conscious
what are nociceptors?
what is the NT?
what will they enter the dorsal root entry zone as?
what will they synapse on?
free nerve endings of A-delta and C fibers (small myelinated and unmyelinated fibers)
- substance P
- lissaurer’s tract (just lateral to the large-diameter fibers of the DCML pathway)
- substantia gelatinosa (cap of the dorsal horn gray)
what is the pathway of the anterolateral system: lateral spinothalamic tract
- small diameter pain and temp fibers enter the spinal cord via the dorsal root entry zone as lissauer’s tract
- lissauer’s tract synapses on substantia gelatinosa in the dorsal horn gray
(sometimes synapses again on an unamed interneuron in the dorsal horn) - these 2nd order fibers are now called the lateral spinothalamic tract and decussate beneath the central canal in the ventral white commisure
- then rises as the lateral spinothalamic tract in a somatotopic way (legs lateral, arms medial-opp to the dorsal columns) all the way until it synapses onto VPL thalamus
- from tehre, it travels in PLIC (post limb of the internal capsule) to reach the post central gyrus in the parietal cortex
Lissaur’s tract can do what before synapsing? and the lateral spinothalamic tract can do what before finding the anterolateral funiculus
rise obliquely for 1-2 segments
*by the time you see the spinothalamic tract in the cord’s anterolateral funiculus, it has already risen 1-2 segments to get there
lesion of the spinothalmic tract results in….
contralateral loss of pain and temperature (and light touch) sensation starting at a level 1-2 segments below the level of lesion
why do clinical symptoms of a lesion begin 1-2 segments below the level of the lesion
bc of the oblique rise of the STT in the ventral white commissure (and/or the rise of Lissaurer’s tract over 1-2 segments)
ex. if you lesion the lateral spinothalmic tract at T6 on left, you lose pain and temp info from appro T8 and cont. on down on the right side
what does a lesion of the ventral white commissure give you? why?
bilateral segmental loss of pain and temperature bc the STT is crossing over from the right and left sides; so you lesion both at once
what happens when a tumor is pressing where the spinothalamic tract runs in the cord (anterolateral cord)
since that area of cord is carrying pain and temp info that has already decussated, starting from about 1-2 lvls down…then the clinical deficit would be contralateral to the tumor and 1-2 segments below.
- deficit would cont all the way down the right lower extremity.
- lost at all levels below
what happens if there is a lesion at Lissaurer’s tract?
since it is before/below the decussation, the clinical deficit would be ipsilateral to the side of the lesion
- ipsilateral loss of pain and temp (and light touch)
- “segmental loss” you lose sensation at a patch of skin corresponding to 1-2 segments below the lesion on the ipsilateral side
where does decussation happen in the lateral spinothalamic tract
in the cord, near entry level, at the ventral white commissure
what does the spinothalamic tract carry?
pain, temperature, and light touch
what is somatotopic organization?
legs-lateral and post
arms-medial and ant
what are the 4 general somatic sensations
pain
temp
touch (tactile)
proprioception
sensory ascending pathways start out far apart in the cord, once they get to the middle of the brainstem, they do what?
what could this do
get much closer together.
cord lesions selevtively affect just the DCML or the STT modalities, lesions in the higher brainstem might cuase a loss of all conscious somatic sensory info
a lesion in the higher brainstem is after the decussations for both DCML and STT so would cuase a loss from the _____ body
in a cord lesion, it would affect the DCML before the decussatoin..but the STT after its decussaion so what does it cuase the loss of?
contralateral
cord lesion would cause loss of DCML sensory modaltiies ipsilaterally while causing loss of STT modalities contralaterally
