Somatosensation Flashcards
pathways carrying somatosensation for the body enter the spinal cord how and where
in a segmental fashion
over the dorsal root of each spinal nerve
somatotopic organization
-describe what this means
throughout the transfer of information from the periphery to the brain, the segmental arrangement is maintained as a topographic map within the pathways and nuclei carrying each sensation
where do we see a representation of somatotopic organization ?
in the homunculus positioned over both primary somatosensory cortex and primary motor cortex
dorsal column/medial lemniscus system
-carries what sensations
conscious
- proprioception
- discriminative touch (two-point discrimination; light touch)
- vibration
what carries proprioception, discriminative touch, and vibration for the face
CN V
DCML sensations are
- encoded by…
- enter spinal cord over what fibers
encoded by encapsulated nerve endings
enter spinal cord over Ia, Ib, and type II fibers
what is proprioception
information concerning movement and position of body parts
what are the two types of proprioception
conscious
unconscious
conscious proprioception is involved in…
-what is this?
kinesthesia
-sense of perception of movement of joints
stereognosis
- what is it
- what sensations are necessary to have it
ability to identify an object by feel
need proprioception and discriminative touch
unconscious proprioception is mediated (carried) by what tracts
spinocerebellar
DCML 1st order neuron
- cell body is where
- type of neuron
- level of peripheral processes myelination
cell body is in dorsal root ganglia from S5 through C1
pseudounipolar neurons
peripheral processes are heavily myelinated (Ia, Ib, II)
DCML 1st order neuron
- central processes level of myelination
- central processes ascend via what tracts?
high level of myelination
tracts
-fasciculus gracilis
-fasciculus cuneatus
fasciculus gracilis
-carries fibers from what segmental entry points?
S5-T7
-lower trunk and lower limb
fasciculus cuneatus
-carries fibers from what segmental entry points
T6-C1
-upper trunk and upper limb
fasciculus gracilis and fasciculus cuneatus comprise what?
dorsal (posterior) columns
fasciculus gracilis and fasciculus cuneatus spacial organization within the dorsal columns
added sequentially in a topographic fashion from medial (lower extremities) to lateral (upper extremities)
DCML 1st order neuron
-how much of it is ipsilateral and contralateral to receptor that encoded sensation
entirely ipsilateral
DCML 2nd order neuron
- location of cell bodies
- these nuclei (from 1st part of question) are located at level of…
- ascending fibers in dorsal columns synapse on…
cell bodies located in the nucleus gracilis and nucleus cuneatus, respectively
both nuclei are located at the level of the closed or caudal medulla
ascending fibers in the dorsal columns synapse on these nuclei
axons of DCML 2nd order neurons form…
-what do these do?
form the internal arcuate fibers
-these cross the midline to form the contralateral medial lemniscus
medial lemniscus
-projects to…
ventral posterolateral nucleus of the thalamus (VPL)
DCML 2nd order neuron
- cell body ipsilateral or contralateral to 1st order neuron
- what does the axon do?
ipsilateral
axon crosses the midline to eventually terminate in the contralateral thalamus
DCML 3rd order neuron
- cell body location
- axons go where?
cell bodies in VPL
axons of these neurons project through the posterior limb of the internal capsule to the primary somatosensory cortex (areas 3, 1, 2; postercentral gyrus in the parietal lobe)
DCML 3rd order neuron
- projections to the postcentral gyrus is organized how?
- what areas receive a greater representation within the cortex?
organized in a somatotopic fashion
areas of body that are most sensitive have greatest representation
3rd order neuron entirely contralateral to location of stimulus
DCML 3 neuron pathway exception
proprioception of the LE
- includes Nucleus Z (part of Nucleus Gracilis) and Clarke’s Nucleus (sipinal cord levels T1-L2)
- extra neuron is added between the dorsal root ganglion and the nucleus Gracilis
DCML alternative pathway
-what is the pathway
some large diameter 1st order fibers end in the ipsilateral dorsal nucleus of Clarke
2nd order neuron sends its axon out ipsilaterally to ascend in the dorsolateral fasciculus, adjacent to the dorsal spinocerebellar tract
-synapses in Nucleus Z
axons of nucleus Z join the internal arcuate fibers and cross to ascend as part of the contralateral medial lemniscus
rest of pathway is same as others
location of Nucleus Z
rostral end of nucleus Gracilis
DCML alternative pathway proposed purpose
possible neural pathway by which some conscious perception of proprioception for the LE is maintained when the dorsal column system is damaged due to trauma or degenerative illnesses
anterolateral or spinothalamic system
-carries what sensations?
pain
temperature
non-discriminative touch
spinothalamic system
-primary pathways
lateral spinothalamic pathway
anterior spinothalamic pathway
how are the sensations of the spinothalamic system transported in anterior 2/3 of the face, oral and nasal cavities
trigeminal nerve and its cetnral nuclei and tracts
lateral spinothalamic system carries what sensations
pain
temperature
(more localizable sensations)
lateral spinothalamic system
-how does it get its name
named for the position of the fiber bundle of axons from the 2nd neuron
lateral spinothalamic system 1st order neuron
- type of neuron
- cell body location
- peripheral receptors are what type of nerve ending
- fiber types
pseudounipolar neuron
located in dorsal root ganglia
peripheral receptors are free nerve endings
A-delta fibers (light myelinated)
lateral spinothalamic system 1st order neuron
-A-delta fibers carry what sensation
pricking pain that is fairly localizable
lateral spinothalamic system 1st order neuron
- central processes enter spinal cord where?
- bifurcate where?
enter spinal cord laterally
bifurcate in the Lissauer’s tract
lateral spinothalamic system 1st order neuron
-how/where do they synapse?
may ascend or descend several segments, or enter dorsal horn at that level and then synapse on neurons in substantia gelatinosa/nucleus Proprius (Lamina of Rexed II, III)
lateral spinothalamic system 1st order neuron
-what is the likely neurotransmitter in this pathway
glutamate
lateral spinothalamic system 1st order neuron
-ipsi or contra to location of stimulus
ipsi
lateral spinothalamic system 2nd order neuron
-cell body location
cell body location not known with certainty
-probably located in substantia gelatinosa and nucleus proprius
lateral spinothalamic system 2nd order neuron
- where do the axons go?
- what do they form and where
axons move across midline, through anterior white commissure, in an ascending and oblique (1-2 segments) direction to form the lateral spinothalamic tract on the contra side of cord
lateral spinothalamic system 2nd order neuron
-describe the somatotopic organization
lateral fibers carry pain and temerature sensations from lower body segments
medial fibers carry sensation from higher levels of spinal cord
lateral spinothalamic system 2nd order neuron
-where does it end?
ascends through spinal cord and brainstem to reach the ventral postolateral thalamic nucleus (VPL) and intra-laminar thalamic nuclei
lateral spinothalamic system 3rd order neuron
- cell body location
- ipsi or contra to stimulus
- somatotopic distribution
cell body is located in VPL positioned contra to stimulus somatotopic distribution -lateral: LE -medial: higher up
lateral spinothalamic system 3rd order neuron
-axon location
ascend to primary somatosensory cortex via the superior thalamic radiations (medial part of the posterior limb of the internal capsule)
location of primary somatosensory cortex
postcentral gyrus, cortical areas 3, 1, 2
lateral spinothalamic system 3rd order neuron
-due to the somatotopic organization (same representation as in other neurons), the result is a representation of the contralateral body called…
a homunculus (little man)
homunculus appearance
upside down, as if it is hanging by the lower limb with the leg representation in the midline cortex and the rest of the body on the lateral surface with the neck and head towards the lateral sulcus
lateral spinothalamic system 3rd order neuron
-loss of these will result in…
loss of localization of pain, but not the affective emotional response to pain
precision in the lateral spinothalamic system makes it useful to…
define lesion sites
possible to identify the level of a spinal cord lesion by the loss of painful stimulation
-termed anesthesia
loss of pain over half the body would be a…
hemi-anesthesia
parallel systems to the lateral spinothalamic tract
spinocervicothalamic
spinoreticulothalamic
spinomesencephalic
spinocervicothalamic pathway
- contains what that the lateral spinothalamic does not
- what does it carry
- this information is…
contains an extra neuron that originates in the dorsal horn and ascends ipsilaterally to a group of cells located at the level of the cervical dorsal horn
-these fibers joint the medial lemniscal system
carries
-modalities of conscious proprioception, discriminative touch, pain, temperature
information in this pathway is non-localizable
spinoreticulothalamic pathway
- have a synapse in the _____ of the brain stem
- pathway eventually reaches…
synapse in reticular formation of brain stem
pathway eventually reaches medial and intralaminar thalamic nuclei that project to widespread cortical areas including the limbic system
spinoreticulthalamic pathways
- limbic system connections involve…
- purpose of this connection
hypothalamus
activates or influences the ANS
spinoreticulothalamic pathway
-purpose
functions to help in analyzing the stimulus within the emotional domain
activates the SNS response
spinomesencephalic (spinotectal) pathway
- projects to…
- pathway can activate…
projects to the superior colliculus and periaqueductal gray in the midbrain
pathway can activate descending pathways that are critical for modulating incoming painful stimuli
spinoreticulothalamic and spinomesencephalic pathways
-similarities in regards to ability to activate…
can activate descending pathways originating from Raphe’ nuclei (serotonin) and locus ceruleus (norepinephrine) of the reticular formation
function of Raphe’ nuclei and locus ceruleus of the reticular formation
have descending projections to the spinal cord that function in the proposed circuitry used in the modification of the transmission of painful sensations
anterior spinothalamic pathway
- function
- 1st order neuron fiber type
- 1st order neuron neurotransmitter
carry light or non-discriminative touch and pain sensation
non-specific temperature information
C-fibers
carry sensation of burning pain, as well as thermal nociceptive impuses
neurotransmitter
-substance P
anterior spinothalamic pathway
-location of neuron cell bodies (1, 2, and 3)
same as for lateral spinothalamic tract
anterior spinothalamic pathway
-how do you demonstrate this sensation?
brush a piece of cotton across the skin
-patient is aware of being touched but is unable to identify texture or precise limits of the stimulation
anterior spinothalamic pathway
-trajectory of 2nd order neuron axon
random
-may travel up or down 10 to 12 segments before it crosses through anterior white commissure
anterior spinothalamic pathway 2nd order neuron
- once axons have crossed, they form…
- where does this go?
forms the anterior spinothalamic pathway
pathway ascends to VPL
