Lecture 12 -ascending tracts Flashcards
label the parts
a. dorsal horn
b. dorsal root ganglion
c. grey matter
d. white matter
Name the three ascending pathways
- dorsal column medial lemniscus pathway
- spinothalamic
- spinocerebellar
define ascending pathways
carry sensory information from peripheries to cerebral and/or cerebellar cortex
what are the 3 neurons present in ascending pathways and describe where they travel.
- first order/primary afferent: go from the periphery to the spinal cord
- second order - goes from spinal cord/brainstem to thalamus
- third order - travels from the thalamus to the primary sensory cortex
what is decussates mean and which neuron is responsible for this?
it means crosses the midline and is performed by the second order neuron.
what are the types of sensory receptors and what do they respond to?
- mechanoreceptor - tactile, vibration, proprioception
- nociceptors - pain (pin prick or tissue damage)
- thermoreceptors - cold/warm
what does this image represent?
the peripheral nerve distribution
name the 3 areas in the spinal cord where we can expect to see variation in white and gray matter regions:
- cervical enlargements (brachial plexus)
-lateral horns (thoracic region)
-lumbar enlargements
organization of the tracts to corresponding body parts in the spinal cord is known as _______.
somatotopy
what corresponds to 1a&b and 3a&b?
1 dorsal column-medial lemniscus
a) cuneate fasciculus (C&T)
b) fasciculus gracilis (L&S)
3 anterolateral spinothalamic tracts
a) lateral spinothalamic tract
b) anterior spinothalamic tract
peripheral nerves travel in bundle to spinal cord and form one or more
_____ _____ ______.
spinal nerve roots
what is a dermatome?
the area of skin innervated by a spinal nerve
why is the peripheral nerve distribution and spinal nerve distribution clinically significant?
based on symptoms (numbness/tingling) in what regions, can help to determine if lesion occurred in the periphery or at the level of the spinal nerve
what are two important things that can help to facilitate clinical reasoning of lesion location?
- peripheral nerve distribution
- somatotopy
what 4 sensations ascend via DCML?
vibration, light touch, conscious proprioception, discrimminative touch
how would you assess each sensation ascending the DCML?
- vibration = tuning fork
- light touch = Qtip or cotton ball
- proprioception = mechanical movement of joints, patient eyes opened then closed
- discriminative touch = 2 point discrimination tool
where does the DCML 1st order neuron travel?
mechanoreceptors to the medulla (doesn’t terminate in the spinal cord)
where does the DCML 2nd order neuron travel? what is it called at this stage?
cross in the medulla and travel to thalamus. as the medial lemniscus
where does the DCML 3rd order neuron travel? what does it travel as?
from the ventral posterolateral (VPL) nucleus in the thalamus to the primary somatosensory cortex as the thalamocortical fibers
do DCML tracts for cervical region travel medial or lateral to tracts of the lumbar region?
lateral goes: cervical-thoracic-lumbar-sacruum.
what 4 sensations ascend via the spinothalamic tracts
pain, temperature, crude/non-discriminative touch, pressure
how would you assess each sensation ascending the spinothalamic?
- pain - broken Qtip, dull side vs sharp side
- crude/non-discriminative touch - have them close their eyes, can they feel where you are touching
- temperature - test tubes of hot versus cold liquids
- pressure - by using a pressure algometer
what type of sensory receptors are present in the spinothalamic tract?
nociceptors and thermoreceptors
what is significant about the 1st order neurons in the spinothalamic tract?
they bifurcate at the spinal cord and one branch synapses on the dorsal horn at the same level and the other branch ascends or descends 1-2 levels in the spinal cord via the lissauer’s fasciculus
Ascending pathways are also called
Somatosensory pathways
The primary afferent covers specific areas of the body that….
are similar person to person
Somas of second order afferents (spinothalamic tract) are found in the…
dorsal horn (gray matter)
Axons of second order afferents travel in bundles called
tracts (white matter)
Label what the missing parts represent
Whats a name for this image
Homunculus
If a lesions was found at the top cerebrum, what might we see
Sensory changes to lower extremities
If the person presented sensory changes to the ulnar border of the hand and 4-5th fingers what might we suspect
A lesion to the ulnar nerve
If a person presented with sensory changes to the ulnar border of the hand and forearm, and 4th-5th fingers, what might we suspect
Lesion to C8 nerve root
where does the second order neuron cross over In the spinothalamic tract?
at the spinal level along the anterior white commissure
Where are the somas for the primary, 2nd and 3rd order afferents located for DCML
1st = DRG
2nd = medulla
3rd = VPL of thalamus
Where does the DCML pathway decussate
Medulla
Why is bifurification of the spinothalamic tract 1st order neuron important
To preserve sensation if there is damage to the tract
Describe the path of the first order neuron of the spinothalamic tract
nociceptors, thermoreceptors enter spinal cord and bifurcates
Describe the path of the second order neuron in the spinothalamic tract
From dorsal horn it decussates at the spinal cord at the anterior white commissure and travels to the medulla where the anterior and lateral tracts merge to form the spinal lemniscus and then innervate the VPL of the thalamus
What sensory info does the lateral tract of the spinothalmic second order neuron transmit
pain and temperature
what are the 2 tracts of the spinothalamic 2nd order neuron as it travels to the medulla and what are they responsible for?
anterior tract; crude touch, pressure
lateral tract: pain, temperature
What sensory info does the anterior tract of the spinothalamic second order neuron transmit
crude touch and pressure
Describe the pathway of the 3rd order neuron of the spinothalamic tract
Travels from VPL to primary somatosensory cortex and elsewhere (eg. reticular formation, frontal cortex, etc.)
when the ST 2nd order tracts merge in the medulla they form the:
spinal lemniscus
what is the pathway of the ST 3rd order neuron?
ventral nuclues in thalamus (VPL) to the primary somatosensory cortex and elsewhere (front cortex, reticular formation, etc.)
Where are the somas for 1st, 2nd and 3rd order afferents of spinothalamic tract
1st = DRG
2nd = Dorsal horn of spinal cord
3rd = VPL in thalamus
where does the pathway of the spinothalamic tract decussate?
spinal cord at the white commissure
Where does the pathway decussate in the spinothalamic tract
Spinal cord in the white commissure
do tracts for cervical region travel medial or lateral to tracts from lumbar region in the spinothalamic tract?
medial
what are the most common NT’s in the nociceptive processing system?
glutamate and substance P
a delta fibers are responsible for transmitting signals of:
fast, well-localized pain
