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Clinical Neuroscience > Motor System > Flashcards

Motor System Flashcards

1
Q

What are the 2 primary components of the Somatic motor system

A

Upper and lower motor neurones

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2
Q

Describe the location of the UMNs and LMNs in relation to the CNS and PNS

How is this relevant clinically?

A
  • Entire UMN is in CNS
  • LMN cell body is in CNS
  • Proximal LMN axon is in PNS

Poorer prognosis for neurone damage if in CNS

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3
Q

Where are most UMN cell bodies found?

A

In the Primary Motor Cortex

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4
Q

Where are most LMN cell bodies found?

Where can the other be found?

A

Ventral horn of the spinal cord

Brainstem

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5
Q

Are there any upper motor neurones in the Basal Ganglia or Cerebellum?

A

No

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6
Q

What do the Cranial Nerve nuclei contains?

A

Cell bodies of lower motor neurones that distribute along the nerve

(Not CN VIII nucleus as it is purely sensory)

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7
Q

Which cranial nerves share an elongated nucleus?

Name the nucleus

A

9, 10, 11

Nucleus Ambiguus

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8
Q

Describe the Patellar Reflex

A
  • Patellar ligament stretch causes stretch of Quadriceps fibres, detected by Muscle spindles
  • Muscle spindles send impulses via 1st Order neurones to L3 level, where the neurones synapse with LMNs in the Ventral Horn
  • LMNs leave via Ventral Root to synapse with Quadriceps fibres causing knee extension
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9
Q

Describe how the Hamstrings are inhibited in the Patellar Reflex

A
  • 1st order neurones descend from L3 to L5, synapsing with inhibitory interneurons in the grey matter
  • In the Ventral Horn, inhibitory interneurones synapse with LMNs innervating the Hamstring fibres
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10
Q

How are the Descending modulatory inputs from the brain clinically relevant with regards to reflexes?

A

Damage to them (during stroke) can lead to an altered/ abnormal reflex response

  • Toe extension, rather than flexion in Babinski reflex
  • Babies have immature descending modulatory fibres so their reflexes change as the get older
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11
Q

What is the Internal Capsule?

A

A white matter pathway that runs between the Thalamus (circular) and the Lentiform Nucleus (triangular)

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12
Q

List the contents of the Internal Capsule (Convergence of the Corona Radiata)

A
  • Descending motor fibres (Axons of UMNs)
  • Ascending sensory fibres (Axons of 3rd Order neurones)

(Internal Capsule contains the Medial Lemniscus)

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13
Q

Compare the Cerebellar and Cerebral peduncles

A

Cerebral Peduncle: White matter connecting a cerebral hemisphere to the Brainstem

Cerebellar Peduncle: White matter connecting a cerebellar hemisphere to the Brainstem

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14
Q

Describe the route of the Corticospinal Tracts up-to where it decussates

A
  • Begin on Primary Motor Cortex
  • Descend through the Corona Radiata then enter and travel through the Internal Capsule
  • Continue descending to enter the Brainstem through the Cerebral Peduncle
  • Descend through the Pons, enter and pass through Medullary Pyramids, then MOST AXONS decussate at The Decussation of The Pyramids
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15
Q

Describe the topography of the Corticospinal Tracts supplying the Upper and Lower limbs

A
  • Corticospinal Tract fibres supplying the Upper Limbs lie Medially
  • Corticospinal Tract fibres supplying the Lower Limbs lie Laterally
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16
Q

The decussated Corticospinal Tract fibres descend the cord, forming the Lateral Corticospinal Tract.

Which Funiculus is this within?

A

The Lateral Funiculus

17
Q

What proportion of Corticospinal Tract fibres do not decussate at The Decussation of The Pyramids?

Where do they decussate instead?

What do they form as they descend the cord ipsilaterally ?

A
  • 15%
  • At the level of their corresponding LMN, in the Ventral Horn
  • The Ventral Corticospinal Tract
18
Q

Describe the fibres of the Corticospinal Tract that leave the CS pathway and synapse within the Brainstem

A
  • These are the fibres of the Corticonuclear Pathway

- They supply LMNs present in the Cranial Nerve nuclei

19
Q

What are the 2 components of the Corticospinal System?

Which is larger?

A
  • Lateral Corticospinal Tract
  • Ventral Corticospinal Tract
  • Lateral is larger
20
Q

Compare the musculature supplied by the Lateral and Ventral Corticospinal Tracts

A

Lateral: Supplies distal muscle (fine movements, such as hand/ foot/ arm/ leg)

Ventral: Supplies proximal muscle (such as at limb girdles)

21
Q

Do the Cranial Nerve motor nuclei receive a Bilateral or Unilateral innervation from the Cerebral cortex?

A

Bilateral

Except facial nerve nucleus, whose upper half ONLY has a bilateral innervation

22
Q

The Facial Nerve motor nuclei are split into 2 halves.

Compare the area innervated by each half

A

Upper half supplies upper face

Lower half supplies lower face

23
Q

Describe the innervation of the Upper half of the Facial Nerve nuclei.

What is its clinical significance?

A
  • Bilateral innervation, one UMN from each Cerebral Cortex

- In stroke, upper half of face is spared

24
Q

Describe the innervation of the Lower half of the Facial Nerve nuclei.

What is its clinical significance?

A
  • Only receives innervation from the Contralateral Cerebral cortex
  • In stroke, lower half of face is not spared
25
Q

List the 3 visible parts of the Internal Capsule on a transverse view (V shaped)

A
  • Anterior Limb
  • Genu (the ‘bend’)
  • Posterior Limb
26
Q

List the contents of the Anterior Limb of the Internal Capsule

A
  • Fibres from Thalamus to Frontal Lobe (in Anterior Thalamic Radiation)
  • Fibres connecting the Lentiform and Caudate nuclei
  • Fibres connecting the Cortex and Corpus Striatum
27
Q

List the contents of the Posterior Limb of the Internal Capsule

A
  • Corticospinal fibres
  • Sensory fibres (in Superior Thalamic Radiation)
  • A few Corticobulbar fibres
28
Q

List the contents of the Genu of the Internal Capsule

A
  • Corticobulbar fibres (Between Brainstem and Cortex)
29
Q

Where are the Facial Nerve Nuclei found, with reference to the Internal Capsule?

A

Found in the Corticobulbar Tract, within the Genu of the Internal Capsule

30
Q

Compare UMN and LMN lesion with regards to;

  • Power in muscles innervated
  • Tone
  • Rigid/ flaccid
A

UMN;

  • Reduced (No input to LMN)
  • Increased (as most are actually inhibitory)
  • Rigid (due to increased tone due to decreased inhibition)

LMN;

  • Reduced (No ACh at end-plate)
  • Decreased
  • Flaccid
31
Q

Compare Fasciculations and Fibrillations

A

Fasciculations;
- Visible

Fibrillations;
- Detectable using electromyography

33
Q

Other than impulses what is delivered to muscle fibres by LMNs?

A

Growth factors (hence can atrophy in LMN lesion)

34
Q

An UMN lesion can lead to Hypertonia.

How may this present?

A

Spasticity

35
Q

In Upper Limb during Hypertonia, why do we get a Flexed posture?

A

Flexors are more powerful than extensors, but both are affected equally

36
Q

Compare UMN and LMN lesion with regards to;

  • Reflexes
  • Presence of fasciculations/ Fibrillations
  • Atrophy
A

UMN;

  • Increased (after Spinal Shock-after initial period of decreased reflex activity)
  • Both are absent (as LMN is spared)
  • Mild if present (majorly due to disuse)

LMN;

  • Decreased/ absent
  • Both are present (possibly due to aberrant activity/ AChR changes)
  • Present

Clinical Neuroscience (19 decks)

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