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