Somatosensory Tracts Flashcards
complete through dorsal column need to do spinothalmic and spinocerebellum
Ascending sensory systems are usually a ___ neuronal chain.
3
1st order neuron is in:
DRG or in C.N. ganglion
2nd order neuron cell body is in:
CNS
and it crosses the midline!
3rd order neuron cell body is usually in:
thalamus
and it projects to cortex!
The “conscious” sensation division includes which system(s)?
dorsal column
spinothalmic
The “unconscious” sensation division includes which system(s)?
spinocerebellum (unconscious proprioception)
Describe dorsal column system:
MORE DISCRIMINATING: touch pressure vibration proprioception
Describe spinothalmic system:
LESS DISCRIMINATING
pain
temp
crude touch
The dorsal column system conveys information characterized by a high agree of:
spatial and temporal resolution
this is what makes it discriminating
Describe general qualities of dorsal column system receptors:
high density of receptors
small receptor fields
Describe dorsal column system modalities:
tactile discrimination vibration deep touch (pressure) 2-pt discrimination conscious proprioception (position sense)
List the receptors of the dorsal column system:
hair follicle receptors
pacinian corpusles
meissner’s corpuscles
GTO, joint receptors, muscle spindles
Where do 1st order neurons in dorsal column system enter?
fibers enter dorsal root
How do 1st order neurons in dorsal column system ascend after entering?
ascend via fascicles cuneatus and gracilis without synapsing in SC
How do fibers from lower trunk and LE (1st order neurons in dorsal column system) ascend?
in fasciulus gracilis
What happens with fibers from upper trunk and UE (1st order neurons in dorsal column system)?
form the fascicles cuneatus
2nd order neuron cell body in dorsal column system is located in the:
nucleus cuneatus: upper trunk and UE
gracilis: lower trunk and LE
2nd order neuron cell body in dorsal column system synapse and cross (decussate) in the:
caudal medulla
2nd order neuron cell body in dorsal column system ascend through brainstem as:
medial lemniscus (somatotopically organized)
3rd order neuron cell body in dorsal column system located in:
ventral posterior lateral (VPL) nucleus of thalamus
3rd order neuron cell body in dorsal column system synapse in ______ and then ascend to what destination in somatosensory cortex?
VPL nucleus of thalamus
post-central gyrus, area 3,1,2
With damage to dorsal columns, what is the implication?
- impairment but not abolition of tactile sensation
- impaired proprioception, vibration, discriminative touch
- sensory ataxia may result
What type of injury can damage dorsal columns?
severe flexion injuries - they may damage posterior spinal arteries which in turn cause damage to dorsal columns
What are the receptors involved in spinothalmic system?
free nerve endings (pain)
mechanoreceptors, thermoreceptors, chemoreceptors
nocicpetion
What modalities does spinothalmic system conduct?
pain and temperature
nondiscriminative touch
Where is cell body of 1st order neuron of the spinothalmic tract?
cell bodies in DRG
Describe the central process of 1st order neuron of the spinothalmic tract?
central process ascend/descend 2-3 segments in LISSAUER’S TRACT then enter dorsal horn
2nd order neuron of spinothalmic system cell bodies located in:
delta fibers: lamina I or lamina V
C fibers: intermediate grey or dorsal horn
Describe pathway of C fibers - of spinothalmic system:
take an indirect course
form a polysynaptic pathway through reticular formation known as spinoreticular fibers
Where does decussation occur for spinothalmic system?
both delta and C fibers decussate in anterior grey matter in SC
After decussation, spinothalmic 2nd oder neurons form what tract?
contralateral spinothalmic tract
- in anterior half of lateral funiculus
What is decussation?
crossing the midline
Cell bodies of 3rd order neuron in spinothalmic system are located in
VPL nucleus OR intralaminar nuclei
Describe the cell bodies of 3rd order neuron in spinothalmic system located in VPL:
fibers from lamina I and V
“fast” pain (A delta fibers)
Well localized, sharper, epicritic pain
Describe the cell bodies of 3rd order neuron in spinothalmic system located in intralaminar nuclei:
spinoreticular fibers
“slow” pain (C fibers)
poorly localized, dull aching, protopathic chain
VPL 3rd order neuron destination in spinothalmic system:
to somatosensory cortex
postcentral gyrus, area 3, 1, 2
Intralaminar nuclei 3rd order neuron destination in spinothalmic system:
to widespread areas of cortex
Evaluation of sensory system from periphery to sensory cortex is known as
somatosensory evoked potentials
somatosensory evoked potentials process:
stimulation distally on limb
recording on scalp
series of wave forms produced correspond to structures/synapses along sensory tracts
What modalities does unconsious proprioception to cerebellum conduct?
joint position
proprioception
What receptors are involved in unconsious proprioception to cerebellum?
GTO
muscle spindle
joint mechanoreceptors
Generally, unconsious proprioception to cerebellum system 1st order neuron is in:
DRG
Generally, unconsious proprioception to cerebellum system 2nd order neuron is in:
dorsal horn
What specific tracts are in the unconscious proprioception to cerebellum system?
dorsal spinocerebellar tract
ventral spinocerebellar tract
cuneocerebellar tract
Cerebellar trats project to?
ipsilateral Cb
Lesions of cerebellum produce?
ipsilateral deficits
Damage to spinothalmic tract results in:
contralateral loss pain and temperature
Why does most tactile sensation remain with spinothalmic lesion?
due to overlap in function with dorsal column system
Which modalities are specific to spinothalmic system?
ITCH and TICKLE
they are lost with damage to spinothalmic tract (no overlap with dorsal column like other tactile sensation)
What is thalamic pain syndrome?
chronic pain syndrome caused by dysfxn of thalamus
often as a result of CVA effecting posterior cerebral artery
