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B3 CAI > Spinal Cord, Descending Tracts and Reflexes > Flashcards

Spinal Cord, Descending Tracts and Reflexes Flashcards

1
Q

what is somatotopic mapping?

A

the motor cortexes on both the right and left side of the brain have body regions mapped onto them in a specific pattern

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2
Q

what is the amount of cortical surface area that a region gets proportional to (somatotopic mapping)?

A

the body part and the amount of motor fibres that that body part requires in order to function

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3
Q

where do descending motor fibres begin?

A

the primary motor cortex

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4
Q

what does the primary motor cortex receive input from?

A

the pre-motor cortex and the supplementary motor cortex, which lie anterior to the primary motor cortex

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5
Q

what is the organisation of the internal capsule and what does it contain?

A

the internal capsule is somatotopically organised and contains ascending/descending white matter tracts

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6
Q

describe the path of motor fibres as they descend from the motor cortex

A

they descend through the corona radiata and into and through the internal capsule

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7
Q

what does the genu hold?

A

the motor fibres descending from the motor cortex heading out towards the face

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8
Q

what does the posterior limb contain?

A

additional motor fibres travelling from the cortex to the spinal cord as the corticospinal tract

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9
Q

what is the corticospinal tract?

A

the major descending motor tract which innervates skeletal muscles in the arms and legs

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10
Q

what will damage to large parts of the internal capsule lead to?

A

widespread contralateral motor and/or sensory symptoms

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11
Q

what neurons do descending motor tracts contain?

A

an upper and lower motor neuron (2 neuron chain)

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12
Q

where is the upper motor neurone in the descending motor tract found?

A

in the CNS

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13
Q

where is the lower motor neurone in the descending motor tract found?

A

begins in the CNS but is found in the PNS

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14
Q

6 regions where UMN lesions can occur

A

cortex, corona radiata, internal capsule, descending tracts, brainstem, spinal cord

When identifying which motor neuron symptoms are present (UMN or LMN) you can locate the level of damage and the tracts/neurons involved.

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15
Q

4 regions where LMN lesions can occur

A

spinal cord (at the level of LMN cell body), spinal nerve, cauda equina, peripheral nerve damage

When identifying which motor neuron symptoms are present (UMN or LMN) you can locate the level of damage and the tracts/neurons involved.

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16
Q

5 UMN lesion symptoms

A

spastic paralysis, hyper-reflexia, no muscle wasting, clonus, extensor plansar response

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17
Q

4 LMN lesion symptoms

A

flaccid paralysis, hypo-reflexia, muscle wasting, fasciculations

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18
Q

what happens following damage to an UMN?

A

initially the patient will present with flaccid paralysis and loss of tone (LMN symptoms), but over time UMN symptoms will take over (this initial damage after an UMN lesion is known as spinal shock)

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19
Q

what makes up a motor unit?

A

motor unit = LMN + the extrafusal muscle fibres it innervates

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20
Q

give an example of a muscle that has a large number of muscle fibres per motor unit

A

unrefined powerful muscles e.g. knee extensors

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21
Q

give an example of a muscle that has few muscle fibres per motor unit

A

muscles with fine control e.g. hand digit movement

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22
Q

what allows the hand to have fine control of movement?

A

the fact that it has few muscle fibres per motor unit

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23
Q

5 possible causes of damage to the motor system

A

spinal cord lesions, motor neuron disease, Parkinson’s disease, MS, ALS

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24
Q

what does ALS stand for?

A

amyotrophic lateral sclerosis

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25
Q

what is another term for ALS?

A

Lou Gehrig disease

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26
Q

what is ALS?

A

motor neuron diseases - a progressive disease involving the death of neurons responsible for controlling voluntary muscle movement, with degeneration of the corticospinal tracts and the ventral horn of the spinal cord.

degeneration of UMN and LMN - they stop sending signals to muscles. eventually the brain will lose its ability to initiate and control voluntary movement. most people will die from respiratory failure.

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27
Q

where are symptoms first seen with ALS?

A

UMN and LMN symptoms are seen together, with limb onset often first before spread to the rest of the body

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28
Q

give some symptoms of ALS

A

fasciculations, spasticity/cramps, weakness (limbs, neck, diaphragm), dysarthria, dysphagia, dyspnoea

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29
Q

give an example of a lower motor neurone disease

A

polio, which can lead to muscle weakness, wasting, hypo-reflexia and fasciculations

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30
Q

define plegia

A

paralysis

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31
Q

define paresis

A

weakness

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32
Q

define monoplegia

A

one limb paralysed

33
Q

define hemiplegia

A

both limbs on one side paralysed

34
Q

what are fasciculi?

A

bundles that axons in white matter are organised into

35
Q

what are the 3 major descending motor pathways?

A

lateral corticospinal tract, ventral corticospinal tract, lateral vestibulospinal tract

36
Q

where does the lateral corticospinal tract travel?

A

from the cortex to the spine laterally in the spinal cord

37
Q

where does the ventral corticospinal tract travel?

A

from the cortex to the spine ventrally in the spinal cord

38
Q

why is the lateral corticospinal tract considered the major motor fibre tract in the body?

A

because it takes up more space than the ventral corticospinal tract and carries about 90% of the motor fibres

39
Q

what happens to most (80-90%) of the neurons in the corticospinal tract?

A

they decussate in the caudal medulla, in the pyramids (pyramidal decussation) and descend as the lateral corticospinal tract, where they synapse with a LMN

40
Q

what happens to 10-15% of neurones in the corticospinal tract?

A

they descend ipsilaterally as the ventral corticospinal tract and decussate close to termination at the level of the LMN synapse

41
Q

what forms the two anteriorly bulging pyramids on the anterior medulla?

A

the decussation of the fibres of the lateral corticospinal tract

42
Q

what provides the major motor pathway to the face?

A

the corticobulbar tract

43
Q

what does the corticobulbar tract initially run next to as it descends from the motor cortex?

A

the corticospinal tract

44
Q

describe the path of the corticobulbar tract

A

it descends down as an UMN through the corona radiata and genu of the internal capsule, and passes into the brainstem where the UMN will decussate and terminate at any number of motor nuclei that are spread across the brainstem

45
Q

how do the LMN of the corticobulbar tract get to the face?

A

they travel with cranial nerves to the muscles of the head and neck

46
Q

describe the innervation to the left side of the face from the corticobulbar tract

A

primary UMN innervation to the left face comes from the right (contralateral) cortex, but it does get minor innervation from the left as well

47
Q

why is the lateral vestibulospinal tract unique?

A

it doesn’t start in the motor cortex, instead starting from nuclei in the brainstem (pons and medulla), and these tracts also do not decussate

48
Q

where will the UMN synapse onto an LMN in the lateral vestibulospinal tracts?

A

it will synapse at the level that it wants to exit

49
Q

what are the effects on LMN of UMN in the lateral vestibulospinal tracts?

A

it excites extensor LMN and inhibits flexor LMN

50
Q

what is Brown-Sequard syndrome? What does it result in?

A

when you have a hemi-section of the spinal cord at a particular level

51
Q

what is a hemi-section of the spinal cord?

A

when half of the spinal cord is knocked out at a specific level

52
Q

what is the myotatic reflex?

A

the muscle stretch reflex e.g. patellar tendon reflex

if a muscle stretches, it will then contract in response to bring it back to original shape/size.

53
Q

how does the myotatic reflex work?

A
  1. a passive muscle stretch is sensed by muscles spindles
  2. reflex arc stimulates a contraction of the stretched muscle
  3. reflex arc inhibits antagonist muscle from contracting (relaxes the opposing muscle)
54
Q

what is the inverse myotatic reflex?

A

the opposite of the myotatic reflex, with an example being the golgi tendon reflex

55
Q

how does the inverse myotatic reflex work?

A

golgi tendon organs (GTO) detect stretch in tendons and initiate a tendon-protective reflex, whereby as muscle tension increases, GTOs inhibit muscle fibres of the agonist muscle

56
Q

what is the effect of the inverse myotatic reflex on antagonists muscles?

A

the reflex arc stimulates contraction of the antagonist muscle

57
Q

when will the inverse myotatic reflex override the myotatic reflex?

A

when tension is great enough in the tendon

58
Q

what is the flexor reflex?

A

quick withdrawal of a limb from a painful (noxious) stimuli (e.g. touching a hot stove)

59
Q

what does the flexor reflex stimulate and inhibit?

A

stimulates ipsilateral flexors of limb, and inhibits ipsilateral extensors of limb

60
Q

what is the crossed extensor reflex?

A

activation of the flexor reflex in a weight bearing limb (e.g. stepping on something sharp)

61
Q

what does the crossed extensor reflex lead to?

A

ipsilateral flexor withdrawal and contralateral extensor activation

62
Q

What does damage here cause?

A
63
Q

What does damage here cause?

A
64
Q

What does damage here cause?

A
65
Q

What is the motor homunculus? Draw it out

A

The motor homunculus is a map along the cerebral cortex of where motor processing for different parts of the body is processed.

66
Q

Where is primary motor cortex located?

A

On the precentral gyrus (frontal lobe).

67
Q

what are some causes of infarction?

A
  • emboli that has passed there
  • atheroma formed within that vessel
  • tumour or trauma that has compromised blood supply
68
Q

define diplegia

A

same limb on both sides paralysed

69
Q

define paraplegia

A

paralysis of the legs and lower body

70
Q

define quadriplegia

A

paralysis of all four limbs

71
Q

What are each of the descending tracts responsible for?

A
72
Q

Where are the 3 descending tracts located on the spinal cord?

A
73
Q

Describe and draw out the lateral corticospinal tract

A
74
Q

Describe and draw out the ventral corticospinal tract

A
75
Q

What does damage here cause?

A
76
Q

What does damage here cause?

A
77
Q

What does damage here cause?

A
78
Q

Describe and draw out the lateral vestibulospinal tract

A
79
Q

Where does the lateral vestibulospinal tract decussate?

A

this tract do not decussate

B3 CAI (13 decks)

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