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Neurology > Spinothalamic, Posterior Column, Thalamo-Cortical Pathways > Flashcards

Spinothalamic, Posterior Column, Thalamo-Cortical Pathways Flashcards

1
Q

2 Systems for Somesthesis

A

1) Protopathic: anterolateral pathways

2) Epicritic: lemniscal pathway

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2
Q

Somatosensory Modalities

A

-touch, pain, temp., vibration proprioception

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3
Q

Protopathic

A
  • pain, crude touch, temperature
  • low spacial & temporal resolution
  • small, slowly conducting, lightly myelinated & unmyelinated
  • lateral Spinothalamic tract (anterolateral funiculi)
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4
Q

Epicritic

A

-form, texture, touch, pressure, slippage, vibration, position
-high spacial & temporal resolution
-large, rapidly conducting, myelinated
-Posterior & Posterolateral columns
-Medial Lemniscus
-proprioception
In spinal cord: epicritic info travels in posterior columns that becomes a tract known as the medial lemniscus in brainstem

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5
Q

Motorneuron Cell Bodies

A
  • located in the spinal cord ventral horn
  • axons exit the ventral horn in the ventral roots & travel within spinal nerves to their target muscles
  • “final common path” for motor activation & the efferent side of spinal reflexes
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6
Q

Pseudo Unipolar Sensory Neurons

A
  • how sensory receptors communicate with the CNS
  • cell bodies are located outside the spinal cord in the dorsal root ganglia (DRG)
  • action potentials continue (within dorsal roots) along the central process into the dorsal horn of the spinal cord
  • peripheral process may synapse in the dorsal horn or project up the spinal cord to the brainstem
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7
Q

Types of Sensory Receptors for Somesthesis

A
  • exteroreceptors: external events
  • proprioceptors: position of joints & muscles in space
  • Enteroreceptors: state of internal organs
  • Chemoreceptors
  • Photoreceptors
  • Thermoreceptors
  • Mechanoreceptors
  • Nociceptors (pain/noxious stimuli)
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8
Q

Pacinian Corpuscle

A
  • large, lamellar, rapidly adapting mechanoreceptor that efficiently detects gross pressure & vibratory skin stimula (250 Hz)
  • in subcutaneous skin, they are also found in joints, muscle, & mesentery
  • free nerve endings encapsulated by a series of modified Schwann cells (lamellae)
  • pressure to lamellae the corpuscle is distorted, causes AP at onset and adaptation until pressure is released, then 2nd AP happens
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9
Q

Meissner’s Corpuscle

A
  • rapidly adapting skin mechanoreceptor that is sensitive to light touch & vibration of <50 Hz
  • located in glabrous skin, right below epidermis
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10
Q

Merkel’s Disks

A
  • slowly adapting mechanoreceptors located in skin & mucosa
  • glabrous skin: these disks are found clustered beneath the ridges on the fingertips that make up fibgerprints
  • in hairy skin: they cluster into specialized epithelial structures called “touch domes” or “hair disks”
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11
Q

Ruffini Organs

A
  • slowly adapting mechanoreceptors found only in deep layers of glabrous skin
  • respond to sustained pressure & skin stretch
  • responsible for detecting objects slipping along the skin & contribute to position sense
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12
Q

Free Nerve Endings

A
  • no accessory structures associated with them to form a sense organ
  • free nerve endings are typically responsive to temperature and nociceptive stimuli
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13
Q

Adaptation

A

-a reduced response in the face of a continued, constant stimulus

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14
Q

Funiculi = Fasciculi

A

-surface feature indicating an underlying axon tract

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15
Q

Epicritic Somesthesis: Lemniscal Pathway

A
  • Pacinian Corpuscle connected to large afferent axon which projects into the dorsal horn of the spinal cord
  • axon continues into the ipsilateral posterior column of the spinal cord & ascends through the entire spinal cord to the ipsilateral brainstem (medulla)
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16
Q

Epicritic Somesthesis: Lemniscal Pathway

Synapses

A

-First Synapse: one of the posterior column nuclei in the medulla (for afferents that enter in the lumbar & sacral spinal cord, this synapse is in the Gracile Nucleus

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17
Q

Nucleus Cuneatus

A
  • serves similar function for afferents from Throacic & Cervical levels
  • for spinal cord, axons from the lumbar cord destined for the nucleus gracilis travels in the fasciculus gracilis
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18
Q

Fasciculus Cuneatus

A

-corresponding path for the throacic/cervical cord

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19
Q

What is the cut-off for gracilis?

A

-T6
gracilis (below T6)
cuneatus (above T6)

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20
Q

Gracile

A

-thin

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21
Q

Cuneate

A

-“wedge shaped”

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22
Q

Decussation

A

-crossing the midline

23
Q

Protopathic Somesthesis: Spinothalamic Pathway

A
  • free nerve endings (axons are small and slowly conducting
  • afferents from skin of leg enter spinal cord in the lumbar or sacral spinal cord
  • axons synapse in the ipsilateral dorsal horn (1st synapse)
  • a second order neuron sends its axon across the mid-line at the same level of the spinal cord to the contralateral anterolateral funiculus
  • axon turns & ascends in the anterolateral spinal cord through the brainstem to the VPL thalamus (synapse #2)
  • third order neuron projects ipsilaterally to somatosensory cortex (post central gyrus, synapse #3)

-entry: pathway decussates in anterior commissure of spinal cord & rest of pathway is in contralateral to peripheral receptor

24
Q

Posterior Column - Medial Lemniscal Pathway

A
  • First Synapse: Nucleus Cuneatus or Nucleus Gracilis, the nuclei are in the caudal medulla
  • decussation of axons from these nuclei occurs in caudal medulla (internal arcuate fibers)
  • in rostral medulla, the medial lemniscus (axons of controlateral posterior column nuclei) runs near the midline, towards the anterior medulla
  • as medial lemniscus travels rostrally its path takes it gradually away from the midline, through the pons & midbrain on its way to VPL
  • Projections from VPL to cortex travel through the posterior limb of the internal capsule
25
Q

Rexed’s Laminae

A

I-V = dorsal horn
VI, VII = intermediate zone
VIII & IX = ventral horn

26
Q

A(alpha)(lambda)(pi).. afferents

A
  • from the muscle receptors (spindles and Golgi tendon organs)
  • project to ventral horn as well as deep layers of dorsal horn
27
Q

A(beta)(e)()(alpha) fibers

A
  • include many cutaneous & joint receptors (secondary spindle organs)
  • these project mostly to dorsal horn
28
Q

Protopahtic Imputs:

A
  • synapse immediately in ipsilateral dorsal horn and the second order projection is to the contralateral spinothalamic tract
  • some axons travel a short way in Lissauer’s Tract before synapsing in the dorsal horn
  • takes 2-3 spinal cord segments for all afferents entering at a given level to cross to the contralateral cord
  • lesions at given spinal cord level therefore result in loss of inputs from 2-3 segments below lesion
29
Q

Spinocerebellar Tracts

A
  • collection of axons that originate in spinal cord & terminate in cerebellum (ipsilateral)
  • conveys info about limb & joint position to the cerebellum
  • input from muscle spindle organs & Golgi tendon organs
  • 4 Components: dorsal spinocerebellar tract, ventral spinocerebellar tract, cuneocereballar tract, rostral spinocerebellar tract
30
Q

Dorsal Spinocerebellar Tract

A
  • conveys info from spindles & GTOs from ipsilateral leg & body
  • afferents pass via fasiculus gracilis & synapse in Clarke’s Nucleus, these neurons in turn project to the cerebellum via the inferior cerebellar peduncle
  • afferents in cuneocerebellar tract synapse in accessory cuneate nucleus
  • second order neurons project to the ipsilateral cerebellum via the inferior cerebellar peduncle
31
Q

Ventral Spinocerebellar Tract

A
  • conveys info from GTO’s from ipsilateral leg & body
  • afferents synapse in layer VII of the spinal cord (L3-S3)
  • cells project over to the contralateral lateral funiculus to synapse with neurons in the region of the superior cerebellar peduncle
  • some projections from the superior cerebellar peduncle cross the midline again, ending on the ipsilateral cerebellum
32
Q

Cuneocerebellar Tract

A

-conveys info from spindles & GTOs from the ipsilateral arm

33
Q

Rostral Spinocerebellar Tract

A
  • conveys info from GTOs from the ipsilateral arm
  • afferents synapse in layer VII of the spinal cord (L4 for Rostral)
  • the tract synapses at the dorsal horn of the spinal cord & ascends ipsilaterally to the cerebellum through the inferior cerebellar peduncle
34
Q

Clarke’s Nucleus (Column)

A
  • a column of relay neuron cell bodies within the medial gray matter within the spinal cord b/w T2-L2
  • located in lamina VII of the intermediate zone of the spinal cord, involved in unconscious proprioception
  • proprioceptive afferents from the lower body terminate within Clarke’s nucleus in spinal intermediate zone
  • origin of dorsal spinocerebellar tract (axons from cell bodies in the dorsal nucleus of Clarke travel through the ipsilateral lateral funiculus via the resiform body on their way to the cerebellum
  • primary input to cerebellum from spinal cord proprioceptive afferents
35
Q

Substantia Gelatinosa

A
  • Lamina I & II of the spinal cord gray matter

- site of first modulation of pain & temperature information

36
Q

Lissauer’s Tract

A

(posterlateral fasiculus)

  • composed of sensory fibers carrying pain & temperature that ascend or descend several spinal cord levels before synapsing in the dorsal horn
  • also contains short axons of projections of neurons from laminae I & II
37
Q

Spinothalmic/Protopathic Pathway

A
  • free nerve ending in cervical spinal cord
  • central process of associated DRG neuron enters the dorsal horn via the dorsal root
  • 1st synapse: ipsilateral dorsal horn (layers I & V)
  • second order neuron has body in ipsilateral dorsal horn, crosses mid-line at same cord level as the afferent entered, turns and ascends in the anterolateral part of the contralateral cord
  • 2nd synapse: VPL thalamus (contralateral to afferent)
  • Third order neuron (thalamic relay neuron) projects to primary somatosensory cortex (postcentral gyrus) via posterior limb of the internal capsul
38
Q

Spinothalamic Tract:

A
  • important for discriminative aspects of pain

- spinothalamic axon collaterals synapse in the brainstem

39
Q

Spinoreticular Pathway

A
  • synapses with neurons in the reticular formation in the pons and medulla
  • fibers come from neurons in all layers of the dorsal horn
  • generate arousal & emotional aspets of pain & the spinomesencephalic pathway is important for activating descending, efferent pathways that modulate pain
40
Q

Spinomesencephalic Tract

A
  • in mesencephalon, connections to the periaqueductal gray

- fibers come form cells in layer I and V or dorsal horn

41
Q

C fibers

A
  • smallest axons & associated with second pain - a duller, less localizable aspect of pain
  • synapse in substantia gelatinosa (Layer I) and these layer I neurons send their axons across the midline & up the cord
42
Q

Chief Sensory Nucleus

A

posterior column nuclei

43
Q

Mesencephalic Nucleus

A

analogous to displaced DRG (in brainstem)

44
Q

Spinal Nucleus

A

dorsal horn (substantia gelatinosa)

45
Q

Trigeminal Ganglion

A

-dorsal root ganglia for the spinal cord

46
Q

Muscle Receptors for Mastication

A
  • cell bodies for the afferents are located in the mesencephalic nucleus of V, within the brainstem rather than in the trigeminal ganglion
  • central processes of these cells project bilaterally to the motor nucleus of V
47
Q

Fine Touch (Epicritic)

A
  • afferents project to chief sensory nucleus of V (1st synapse is here)
  • second order axons cross to the contralateral VPM (thalamus)
  • this pathway is the trigeminal lemniscus, VPM projects in turn to primary somatosensory cortex
48
Q

VPL

A

-ventral posterolateral nucleus
In: medial lemniscus, spinothalamic tract
Out: post central gyrus (cortex: 3, 1, 2)
somatosensory thalamus for body

49
Q

VMP

A

-ventral posteromedial nucleus
In: trigeminal lemniscus, trigeminothalamic (also taste)
Out: post central gyrus (cortex: 3,1,2)
somatosensory thalamus for head (trigeminal system)

50
Q

Primary Somatosensory Cortex

A

-S1: originally described as most sensitive to fine touch

51
Q

S2

A
  • unimodal association cortex where further processing of information concerning somesthesis
  • located in parietal operculum
52
Q

Cortex

A

-required for perception of fine touch, vibration, pain, temperature

53
Q

Brodmann’s Aread

A
  • in cortex
    3a: muscle, nociceptive, Proprioception & pain from thalamus
    3b: SA & RA cutaneous from the thalamus, Tactile, vibratory, thermal sensation
    1: SA & RA cutaneous from 3b, texture perception
    2: cutaneous from 3b, nociceptive from 3a
  • position & edge detection size perception

Neurology (18 decks)

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