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91 Cards in this Set

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What is the dorsal column system?
The sensory pathway for touch and discrimination.
4 Specific things detected by the dorsal column system:
-light touch
-2pt tactile discrimination
-vibration
-proprioception
Where is the first place in the CNS that sensory information goes?
To the spinal cord.
How many spinal segments?
31
How many cervical spinal segments?
-Thoracic?
-lumbar?
-Sacral?
Cervical = 8
Thoracic = 12
Lumbar = 5
Sacral = 5
Coccygeal = 1
What is a Dermatome?
The section of skin and muscle innervated by a single spinal segment.
What does each dorsal root originate from? What is the effect?
SEVERAL different peripheral nerves - effect is that dermatomes overlap.
How is pain relieved in a dermatome?
By cutting 2-3 adjacent dorsal roots.
What is the upper arm dermatome?
Thumb?
Middle finger?
Little finger?
Upper arm = C5
Thumb = C6
Middle finger = C7
Little finger = C8
What is the nipple dermatome?
Umbilicus?
nipple = T4
umbilicus = T10
What is the big toe dermatome?
Heel?
Back of thigh?
Big toe = L5
Heel = S1
Back of thigh = S2
What will result if you cut a peripheral cutaneous nerve?
Loss of sensation from the entire receptive field of that nerve.
What will result if you cut just one dorsal root nerve at the spinal cord?
Loss of only part of the receptive field since some info is still transmitted by adjacent nerve roots that mix.
What is the gray matter in the spinal cord?
Spinal neuron cell bodies
What are nuclei in the spinal cord made up of?
Clusters of cell bodies that connect to functional systems.
What are spinal TRACTS?
Bundles of axons that project carrying similar functional information. The white matter.
2 major sensory tracts:
-Dorsal columns
-Anterolateral columns
Dorsal column components:
-Fasciculus cuneatus
-Fasciculus gracilis
What do the dorsal columns convey?
-Touch
-Tactile discrimination
-Pressure
-Proprioception
what do the anterolateral tracts convey?
Pain and temp
What does the dorsal horn recieve?
Sensory input
What does the ventral horn do?
Sends out efferent output to muscles.
Where are the Rexed laminae?
In gray matter
What Rexed laminae recieve pain and temp input from dorsal roots?
Laminae 1/2
What Rexed laminae recieve tactile and vibration input from dorsal roots?
Laminae 3/4
2 Characteristics that make the Cervical Spinal Cord distinct:
-Lots of white matter
-Distinct dorsal columns
2 Characteristics that make the Lumbar Spinal Cord distinct:
-Lots of gray matter
-Big ventral horns
What are Rexed laminae 1/2 associated with?
-Substantia gelatinosa
-Marginal zone
So the dorsal column pathways ascend in:
Dorsal column funiculi
What type of receptors give input to the dorsal columns?
All mechanoreceptors (deep or superficial)
What is the First place that mechanoreceptor afferent information goes? What type of fibers carry it there?
Goes to the Dorsal root ganglion -Carried by Abeta axons
Where does the central process of the DRG for Dorsal tracts enter the spinal cord gray matter?
Enters in the medial division of the dorsal root, then into Rexed laminae 3/4
Where does the primary neuron go in the spinal cord?
Based on whether it's lower or upper sensory afferent, to Fasciculus cuneatus or gracilis
At what spinal cord levels do mechanoreceptor afferents enter the Fasciculus gracilis?
T7 and below
At what spinal cord levels do mechanoreceptor afferents enter the Fasciculus cuneatus?
T6 or above
What do MOST mechanoreceptor axons do once they enter the spinal cord?
Ascend the ipsilateral side they came in on.
What do SOME do?
Synapse in the dorsal horn (rexed laminae 3/4) and send axons contralaterally to the anterolateral tract.
So what is the result of cutting the dorsal columns?
A little crude touch remains in the anterolateral tracts.
What is the somatotopy of the dorsal columns in the spinal cord?
Medial to Lateral:
Legs to Neck
How high up do cervical nerves add to fasciculus cuneatus?
Up to C2 - there is no c1 dermatome
What is the result of a lesion to the dorsal column at the spinal cord level?
Loss of tactile discrimination pressure, touch, & propriocept.
-on the SAME SIDE
-BELOW the level of lesion.
Where do the dorsal columns terminate and synapse onto 2ndry neurons?
In nucleus cuneatus/gracilis in the caudal medulla.
Where do the 2nd order neurons project?
Across the sensory decussation to turn and ascend in the Medial Lemniscus.
How are the synapses in the dorsal column Nuclei in the medulla organized?
Somatotopically AND physiologically - the same receptor types remain together.
Physiological organization?
Merckel's with merckel's
Pacinians with Pacinians
What happens to the physiological organization as fibers ascend in the medial lemniscus?
They remain that way.
What happens to the dorsal column pathway as it ascends from the medulla to the thalamus?
It crosses to the contralateral side of the body.
Lesions of the medial lemniscus produce:
Contralateral deficits in fine touch, 2pt discrimination, vibration, and joint position.
Where does the Medial lemniscus terminate?
In the VPL of the thalamus.
What is the somatotopy seen at the VPL of the thalamus?
Flipped
Legs are Lateral at the VPL
(L's go together here!)
Where is face/head information relative to the body information at the VPL?
MEdial - in the VPM.
How do the 3' axons that project from the VPL get to the sensory cortex?
Via the POSTERIOR LIMB of the internal capsule
And what feeds bloodsupply to the posterior limb of the internal capsule?
Anterior choroidal artery from ICA.
What happens to the Posterior limb of the internal capsule on its way to the cortex?
It fans out as Corona Radiata
Where does the Corona Radiata terminate?
In the S1 somatosensory cortex.
Where is the somatosensory cortex?
In the postcentral gyrus
What happens to somatotopy of the dorsal column pathway as it projects to the cortex?
It FLIPS again!! In the end the legs end up medial, face/trunk is lateral.
Lesions of the SI cortex result in:
Contralateral loss of sensation
What happens to sensory nerve fibers as they ascend to the cortex from periphery?
Convergence - so one cortical neuron may recieve input from 300-400 sensory receptors!
How is specificity retained and ambiguuity minimized in spite of this convergence?
By population response
What are the 4 specialized areas in the S1 somatosensory cortex?
3a, 3b, 1, 2
What are these areas called?
Brodmann's areas
What does area 3b recieve input from?
Slowly and RAPIDLY adapting receptors
What information is derived at area 3b?
Info about fine details of edges and surface texture - this would be MERKEL'S (texture and slowly adapting) and Meisner's (rapid)
What information is derived at area 1?
Information from cutaneous RAPIDLY adapting receptors about motion processing and direction of movement.
So what type of receptors would supply Area 1?
Meissner's (cutaneous and rapidly adapting)
What type of info does area 2 recieve?
Complex touch from skin and deep tissue information.
What does area 2 tell you?
About an object's 3D shape
What does area 3a tell you?
About limb movement (kinesthesis).
Function of area 3a:
Limb movement info
Function of area 3b:
Fine detail of objects and surface texture
Function of area 1:
Motion processing and direction of movement
Function of area 2:
Object's 3D shape
What does each area within the S1 cortex contain?
A complete map of the body surface - topographically arranged!
Where do neurons in all four areas of S1 project?
To SII cortex
Where do SII neurons project?
To the insular cortex (taste sensation!! thank you dr neitz)
Where does the insula project?
To the temporal lobe
What is the function of the SI->SII->Insula->Temporal circuit?
Tells you WHAT you are touching
What do projections from primary somatosensory cortex to the Posterior Parietal Cortex tell you?
WHERE you are and WHERE you are touching
What important skill we develop in kindergarten is derived from the Posterior parietal cortex?
Hand-eye coordination
What could cause the rare selective lesions of the dorsal columns in the spinal cord?
Secondary syphilis
What nerves carry primary afferent information for fine touch and discrimination from the Face and head?
-Trigeminal branches:
-Opthalmic, maxillary, and mandibular
Where do most mechanoreceptor afferents for the trigeminal system synapse on 2ndry neurons?
In the chief nucleus of CN V on the ipsilateral side.
What happens to 2ndry neurons after the Chief nucleus of V?
(2 options)
-Most cross over to the opposite side of the pons to then ascend.
-Some descend ipsilateral in the Spinal tract of V
Where do descending 2ndary neurons synapse?
At the spinal nucleus of V
What happens after the spinal nucleus of V?
Axons crossover to the other side to ascend back to the VPM via the Trigeminothalamic tract.
Regardless of where they enter what side of the brain does sensation from the face end up on?
The contralateral side - either it crosses in the pons upon entry, or after the spinal nucleus synapse in the cord.
What is the somatotopic arrangement of the VPM?
Retained; tongue is medial to the face (remember the little body diving down)
Where do 3rd order neurons from the VPM project?
To the posterior limb of internal capsule.
Where does the posterior limb of the internal capsule project?
Fans out as corona radiata.
Where do Trigeminal fibers in corona radiata end up?
In the LATERAL aspect of S1 cortex near the lateral fissure.