Neuro 56: U & LMN Flashcards

1
Q

2 components of the UMN

A
  1. lateral corticospinal tract
  2. bulbospinal tract
    * *run together –> so damage will effect both & cause UMN lesion sx!
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2
Q

Lateral corticospinal tract

A
  • provides comands from the cortex to the spinal chord to allow for mvmnt of the limbs
  • starts in precentral gyrus and the associated motor areas of the cortex –> 90% cross over when they get to the spinal chord
  • supply the LMN in the ventral horn which then cause the contraction
  • DIRECT pathway from cortex to LMN
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3
Q

Bulbospinal tract

A
  • INDIRECT pthwy
  • arise from a few diff locations in the brainstem that terminate on the MN networks in the spinal chord
  • play a role in adjusting muscle tone and posture
  • get input from cortex
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4
Q

Why is there increased tendon reflexes with UMN lesions?

A

-b/c the bulbospinal signals from the brainstem are normally inhibatory to the stretch reflex of the DTR –> so since these are damaged the inhibition is taken away and the DTR will be increased

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5
Q

Location of LMN’s

A

-ventral horn (lamina IX) of the SC

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6
Q

alpha mn

A

-innervate extrafusal muscle fibers

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7
Q

gamma mn

A
  • innervate intrafusal muscle fibers

- the CNS controls the sensitivity of muscle spindles by these mns

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8
Q

Motor neurons for axial muscles

A

-located more medially in the longitudinal column of cell bodies that runs the length of the spinal cord

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9
Q

Motorneurons for limbs

A

-located more laterally in a discontinuous lateral cell column located in the cervical and lumbosacral enlargements

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10
Q

Spinal reflexes

A

-depend on local circuts w/in the sc that couple incoming sensory info to outgoing motor info

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11
Q

Origin of corticospinal T cell bodies

A
  • cell bodies are located in the frontal cortex motor areas
  • cells in the somatosensory cortex also contribute, but are not used for mvmnt
  • the amnt of cortex devoted to a body area is related to the need for fine motor control
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12
Q

Cortical motor areas

A
  • highly interconnected regions invlved in planning and initiation of voluntary mvmnt
  • divided into regions based on structural and functional differences:
    1. motor cortex
    2. pre-motor cortex
    3. supplementary motor cortex
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13
Q

Motor cortex (cortical motor area)

A
  • the precentral gyrus will stimulate a single UMN here that will activate several muscles
  • shows that UMNs encode PURPOSEFUL mvmnts rather than contraction of individual muscles
  • *lesions = weakness/paralysis
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14
Q

Premotor cortex (cortical motor area)

A
  • immediately anterior to the precentral gyrus
  • receievs info from the somatosensory and visual cortex
  • mediates mvmnts that require sSENSORY GUIDANCE –> such as tactile and visual reaching
  • *lesions = apraxia
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15
Q

Supplementary motor area (cortical motor area)

A
  • planning of self-initiates mvmnts
  • bimanual coordination (using 2 hands together)
  • *lesions = apraxia
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16
Q

Lateral corticospinal tract

A
  • terminates in the cervical and lumbosacral enlargements on mn controlling upper and lower limb muscles
  • has important role in controlling fine mvmnts in fingers and toes
17
Q

Ventral corticospinal T

A
  • crosses later in the spinal cord and influences axial mvmnts
  • only makes up 10% of the corticospinal T
  • significance is unknown
18
Q

Where do bulbospinal pathways originate?

A

3 brainstem nuclei:

  1. red nucleus
  2. reticular formation
  3. vestibular nuclei
19
Q

Rubrospinal T

A
  • origin: @ red nucleus
  • projects: CONTRALATERALLY
  • target LMN: upper limb FLEXORS
  • function = arm/forearm/wrist position
20
Q

Reticulospinal T

A
  • origin: @ reticular formation
  • projection: BILATERAL
  • target LMN: axial, proximal limb
  • function: extensor/flexor mvmnts
21
Q

Vestibulospinal T -lateral

A
  • origin: @ vestibular nuclei
  • projetions: IPSILATERAL
  • target LMN: axial, proximal limb
  • function: EXTENSOR mvmnts in body/limb
22
Q

Vestibulospinal T - medial

A
  • origin: @ vestibular nuclei
  • projetions: BILATERAL
  • target LMN: axial
  • function: EXTENSOR mvmnts in neck
23
Q

Spasticity

A
  • due to loss of inhibition from the reticulospinal T
  • caused by UMN lesions
  • causes increased tone in the upper limb flexors and the lower limb extensors