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Sophie - The Nervous System - Year 2 > 21.3 Upper Motor Neurons > Flashcards

21.3 Upper Motor Neurons Flashcards

1
Q

What are the different upper motor descending pathways?

A

*Corticospinal |(sensory and motor components)
*Vestibulospinal
*Reticulospinal
*Rubrospinal
*Tectospinal

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2
Q

What are descending tracts?

A

Pathways by which motor signals are sent from the BRAIN to the SPINAL CORD
(aka motor tracts)

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3
Q

What are the two major functional descending tract groups?

A

Pyramidal tracts - originate in the motor cortex; carry motor fibres to the spinal cord and brainstem
Extrapyramidal tracts - originate in the brain stem; carry motor fibres to the spinal cord

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4
Q

Which classification of descending tracts are responsible for voluntary motor movement?

A

Pyramidal tracts (originate in motor cortex)
innervate striated muscles of body and face

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5
Q

Which classification of descending tracts are responsible for involuntary motor movement?

A

Extrapyramidal tracts (originate in the brainstem)
Automatic control of muscle tone, posture and balance

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6
Q

Which pathways are part of the pyramidal system? Are they lateral or medial?

A

Corticospinal (anterior and lateral)
Corticobulbar (does not travel in spinal cord-synpases in the brainstem)

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7
Q

What is each descending tract formed by?

A

2 interconnecting neurons:
-First order (upper motor neurons-from cerebral cortex or brainstem to spinal cord anterior gray horn)
-Second order (lower motor neurons-from spinal cord to skeletal muscle)

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8
Q

What is meant by the medial and lateral descending systems? What is the function of each?

A
  • Lateral descending system (top left in red) -> These are the descending tracts that innervate distal limb muscles.
  • Medial descending system (bottom left in red) -> These are the descending tracts that innervate axial and proximal limb muscles.

This is easy to remember because the lateral descending system innervates more lateral muscles.

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9
Q

What are the medial and lateral descending systems made up of?

A

Lateral:

  • Lateral corticospinal tract
  • Rubrospinal tract
  • Reticulospinal tract (medullary)

Medial:

  • Anterior corticospinal tract
  • Reticulospinal tract (pontine)
  • Vestibulospinal tract
  • Tectospinal
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10
Q

Compare the medial and lateral descending systems in terms of what they connect to and their function.

A

Lateral:

  • Decussate
  • Often end on α motor neurons
  • Control distal limb muscles for precision grip and palpation

Medial:

  • End, bilaterally, on interneurons
  • Very few monosynaptic endings on α motor neurons
  • Control posture, locomotion, and proximal components of reaching movements via supplying the mainly axial and proximal muscles
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11
Q

For the corticospinal tract, state:

  • Origins
  • Course (inc. decussation)
  • Terminations
  • Functions
A
  • Origins: Motor cortex (area 4) and premotor cortex (and also somatosensory area for modulation)
  • Course: Internal capsule -> Crus cerebri -> Pons -> Pyramids of medullary pyramids -> Spinal cord
  • Decussation at the bottom of the medulla:
    • Lateral corticospinal tract decussates and descends as the contralateral lateral funiculus (90% of fibres)
    • Anterior corticospinal tract doesn’t decussate and descends as the anterior funiculus (10% of fibres)
  • Terminations and functions:
    • Lateral corticospinal tract -> Terminates mostly on alpha motor neurons and controls distal limb muscles
    • Anterior corticospinal tract -> Terminates mostly on interneurons and controls axial muscles bilaterally
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12
Q

What are the two divisions of the corticospinal tract and what are their functions?

A
  • Lateral corticospinal tract (90%) -> Controls distal limb muscles
  • Anterior corticospinal tract (10%) -> Controls axial muscles bilaterally
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13
Q

What is decerebration?

A

*loss of cortex, cerebellum, and mid-brain (so only brainstem remains)

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14
Q

Describe decerebrate posturing.

A

everything is extended.

only vestibulospinal/ reticulospinal tracts remain –> more input to extensor muscles (anti-gravity functions)

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15
Q

What is decortication? What does decorticate posturing look like?

A

*Loss of cortex
*arms bent w/ clenched fists and straight legs

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16
Q

For the vestibulospinal tract, state:

  • Origin
    *Decussation
  • Function
A

Origin: Vestibular nuclei of brainstem
Decussation: Mostly no (medial VST is bilateral)
Function: Extensor tone to respond to changes in head position

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17
Q

For the tectospinal tract, state:

  • Origin
    *Decussation
  • Function
A

Origin: Superior Colliculus
Decussation: In the midbrain (dorsal tegmental decussation)
Function: Head movement to visual and auditory stimuli

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18
Q

For the reticulospinal tract, state:

  • Origin
    *Course
  • Function
A

Origin: Reticular formation (brainstem)
Course: Mostly ipsilateral, anterior cord
Function: Modulates reflexes, integrates inputs for coordinate movement e.g locomotion

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19
Q

For the rubrospinal tract, state:

  • Origin
    *Course
  • Function
A

Origin: Red nucleus (midbrain)
Course: Decussates in the midbrain, lateral cord
Function: Flexor tone to upper limbs

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20
Q

For the corticobulbar tract, state:

  • Origins
  • Course (inc. decussation)
  • Terminations
  • Functions
A
  • Origins: Primary motor cortex
  • Course (inc. decussation): Passes through the corona radiata and the internal capsule to the cerebral peduncle of the midbrain
  • Terminations: Motor nuclei of cranial nerves V, VII, IX, XI
    (indirectly with III and IV, VI all for eye movement )
  • Functions
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21
Q

Where is the red nucleus found?

A

Rostral Midbrain

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22
Q

Which tract is highlighted?

A

Rubrospinal tract

23
Q

What is 1a?

A

Lateral corticospinal tract

24
Q

What is 1b?

A

Anterior corticospinal tract

25
Q

What is 2a?

A

Rubrospinal tract (lateral motor system)

26
Q

What is 2b?

A

Reticulospinal

27
Q

What is 2c?

A

Vestibulospinal tract

28
Q

Which tract is highlighted?

A

Tectospinal tract

29
Q

What tract is highlighted?

A

Vestibulospinal tract

30
Q

How would an upper motor neuron lesion present?

A

*Spastic paralysis
*Hyperreflexia
*Babinski reflex positive

31
Q

How do lower motor neuron lesions present?

A

*Flaccid paralysis
*Atrophy of muscles
*Fasciculations
*Loss of reflexes

32
Q

What are upper and lower motor neuron lesions?

A

Upper motor neuron = descending motor pathways are damaged at the level of motor cortex or at any point of the descending pathway prior to the final synapse with the motor neurons of the spinal cord or cranial nerve nuclei.
Lower motor neuron = affects nerves LEAVING anterior horn of spinal cord/ cranial motor nuclei of relevant muscles

33
Q

Name some causes for upper motor neuron lesions?

A

Vascular (haemorrhage, thrombosis)
Trauma affecting cerebral cortex or internal capsule

34
Q

What is the effect of a lesion in a?

A

CONTRALATERAL paresis (weakness) of hand or arm
(affects corticospinal tract which decussates)

35
Q

What is the effect of lesion in b?

A

CONTRALATERAL spastic hemiplagia (paralysis of one side of the body)
Corticospinal tract fibres converge in internal capsule

36
Q

What is the effect of a lesion at c?

A

Peduncle lesion
CONTRALATERAL spastic hemiplegia (constant contraction on opposite side)
May be associated with ipsilateral paralysis of oculomotor nerve

37
Q

Which tracts favour flexor motor neurons?

A

Corticospinal tract and rubrospinal tract

38
Q

Which tracts favour extensor alpha motor neurons?

A

Vestibulospinal
Pontine recticulospinal

39
Q

What is the Babinski sign?

A

Extensor plantar response due to dominant engagement of extensors over flexors

40
Q

What does the Babinski sign indicate?

A

Lesion in corticospinal tract (supplies lower limb flexors over extensors)
More dominant engagement of extensors. Pontine reticulospinal and vestibulospinal biased extension tracts win in lower limb

41
Q

What is meant by hemiplegia?

A

Loss of control in ONE side of the body (lesion of corticospinal tract above decussation)

42
Q

What is meant by hemiparasis?

A

Weakness or inability to move one side of the body (less severe than hemiplegia)

43
Q

What is paraplegia?

A

Paralysis of the lower half of the body

44
Q

Which spinal cord injury will lead to paraplegia?

A

Anything above L1

45
Q

What would be the symptoms of the following lesion?

A

Full head and neck movement with normal muscle strength. Normal shoulder movement. * Full use of arms, wrists and fingers. * Complete paralysis of lower body and legs. * Reasonable upper body strength and balance

46
Q

What is the difference in the cause of spasticity and rigidity?

A

Spasicity = pyramidal tract damage (velocity dependent increase in tonic stretch reflexes)
Rigidity = dysfunction of extrapyramidal tract pathways (increase in muscle tone at rest)

47
Q

Where is the primary motor cortex located?

A

Precentral gyrus

48
Q

What is the Brodmann area for primary motor activity?

A

Area 4

49
Q

What are the main cortical areas directly involved in motor control?

A
  • Prefrontal cortex -> Important for decisions, planning, initiative, motivation, conscience, moral sense, social skills
  • Posterior parietal cortex -> Important for body (superior lobule) and space (inferior lobule) representation.
  • Supplementary motor cortex (medial area 6) -> Linked to the basal ganglia and thus involved in internally generated/ guided movements, sequencing of actions
  • Premotor cortex (lateral area 6) -> Linked to cerebellum and involved in the sensory guidance of movement
  • Motor cortex (precentral gyrus - area 4) -> Other areas convergence on this and it is involved in fine control of fingers (corticospinal tract) and face
  • Frontal eye fields -> Voluntary eye movements
50
Q

What are the principle inputs to the motor cortex?

A

Supplementary motor area, premotor and somatosensory cortex, ventral anterior and ventral lateral thalamus (from cerebellum and basal ganglia)

51
Q

What are the principle outputs of the motor cortex?

A

Corticospinal tract, corticostriate (caudate and putamen), corticobulbar (pons, cranial nerve nuclei, colliculus, reticular formation, red nucleus)

52
Q

What are the premotor cortical areas? Where are they located?

A

*Premotor cortex (Lateral area 6)
*Supplementary motor cortex (area 6)

53
Q

What is the function of the premotor cortex?

A

For sensory guidance of movements and postural adjustments

54
Q

What is the function of the supplementary motor cortex?

A

For planning spontaneous and bimanual movements.

Sophie - The Nervous System - Year 2 (46 decks)

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