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Block 3 > Ascending and Descending Tracts > Flashcards

Ascending and Descending Tracts Flashcards

1
Q

What does the Meissner Corpuscle detect?

Adaptation?

A

Discriminative touch

Rapid

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2
Q

What does the Pacinian Corpuscle detect?

Adaptation?

A

Deep pressure
Vibrations

Rapid ++

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3
Q

What does the Ruffini Ending detect?

Adaptation?

A

Touch

Slow

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4
Q

What does the Merkel Disc detect?

Adaptation?

A

Light, sustained touch
(slowly adapting)

Slow

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5
Q

What do the Free Nerve Endings detect?

Adaptation?

A

Pain and temperature

Rapid

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6
Q

Where do the sensory cortexes sit?

A

Parietal lobes

Left and right

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7
Q

Where is the Primary Somatosensory Cortex?

A

Post-Central Gyrus in the Parietal lobe

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8
Q

What information does the Primary Somatosensory Cortex receive on each side?

A

Contralateral sensory input from the body (including taste)

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9
Q

Behind what sulcus does the primary somatosensory cortex sit?

A

Central sulcus

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10
Q

Why is the Superior Parietal Lobe responsible for?

A

Integration of sensory inputs

Sensory memory

Perception of contralateral self/world

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11
Q

How does somatotopic mapping differ between the sensory and motor cortex?

A

Sensory cortex is responsible for genitals

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12
Q

What is the internal capsule?

A

Dense collection of white matter (myelinated axons) that carry sensory and motor tracts to and from the cortex

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13
Q

What are the 3 types of interconnection fibres in the cortex?

A

Projection - to brainstem

Association - within hemisphere

Commissural - between hemisphere

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14
Q

What type of projection is the internal capsule?

A

Commisural

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15
Q

What type of nerves does the internal capsule carry?

A

Sensory and motor nerves

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16
Q

What does white matter contain?

A

(Myelinated) axons

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17
Q

What does grey matter contain?

A

Cell bodies

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18
Q

Where is white matter found?

A

Deep inside the cortex

Outer portion of the spinal column

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19
Q

Where is grey matter found?

A

On the surface of the cortex

Inner portion of the spinal column

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20
Q

Name the 4 regions of the internal capsule

A

Anterior limb

Genu

Posterior limb

Retrolenticular

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21
Q

What type of nerves pass through the anterior limb of the internal capsule?

A

Motor fibres from the frontal lobe to the pons or thalamus

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22
Q

What type of nerves pass through the Genu of the internal capsule?

A

Motor fibres from the head

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23
Q

What type of nerves pass through the posterior limb?

A

Motor to arm and leg

All sensory fibres

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24
Q

In which portion of the internal capsule would you see both sensory and motor damage?

A

Posterior portion

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25
Q

What type of nerves pass through the Retrolenticular portion of the internal capsule?

A

Special fibres for vision and hearing

The Putamen and Globus Pallidus basal ganglia (together form the lentiform nucleus)

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26
Q

How many chains are there in a sensory neuron tract?

A

3 neuron chain

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27
Q

Do 1st order neurons of the sensory pathway from the limbs ascend the spinal cord ipsilaterally or contralaterally?

A

Ascend ipsilaterally

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28
Q

Where do 1st order neurons from the limbs synapse with 2nd order neurons?

A

Lower medulla

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29
Q

Where do ascending sensory pathways from the limbs decussate?

A

Lower medulla

2nd order neuron decussates after synapse with 1st order neuron (see handout)

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30
Q

Where do 2nd order neurons of the ascending sensory pathway from the BODY synapse with 3rd order neurons?

A

Ventral Posterior Lateral (VPL) nucleus of the Thalamus

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31
Q

Where does a 1st order sensory neuron from the face enter the CNS?

A

Lateral body of the pons - along CN V

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32
Q

Where does a 1st order sensory neuron from the face synapse with a 2nd order neuron?

A

Pons

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33
Q

Where does a sensory neuron from the face decussate?

A

In the pons

2nd order neuron decussates after synapse with 1st order neuron (see handout)

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34
Q

Where do 2nd order neurons of the ascending sensory pathway from the FACE synapse with 3rd order neurons?

A

Ventral Posterior Medial (VPM) nucleus of the thalamus

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35
Q

Which area of the thalamus contains the nuclei for somatosensory input?

A

Ventral Posterior Nucleus

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36
Q

What are the two areas of the ventral posterior nucleus?

What do they receive input from?

A

Ventral Posterior Lateral nucleus - sensory from body

(lateral = limbs)

Ventral Posterior Medial nucleus - sensory from the face

(face is medial)

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37
Q

Describe the basic structure of the spinal cord (white and grey matter)

A

Grey matter (cell bodies) surrounded by white matter (axons)

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38
Q

What are the names of the organised zones of the spinal cord?

A

Rexed Lamina

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39
Q

Why are the Rexed Lamina areas important?

A

Where ascending or descending tracts may synapse with other neurons - therefore contain cell bodies

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40
Q

Which Rexed Lamina zone contains nerve bodies associated with pain, temperature and touch?

A

Zone II

Dorsal horn of spinal cord

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41
Q

Which Rexed Lamina zone contains nerve bodies associated with pain transmission?

A

Zone II

Dorsal horn of spinal cord

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42
Q

Which Rexed Lamina zones contain lower motor neurons?

A

Zones VIII and IX

Ventral horn of spinal cord

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43
Q

How can white matter in the spinal cord be grouped?

How many groups are there?

A

Into Funiculi (bundles of more than one tract)

3 groups

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44
Q

What are the 3 funiculi called?

A

Dorsal funiculus

Lateral funiculus

Ventral funiculus

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45
Q

What type of nerves does the lateral funiculus carry?

A

Sensory and motor nerves

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46
Q

Why does the cervical region of the spinal cord have a large grey horn?

A

Grey horn = cell bodies

Large number of neurons required to innervate upper limbs

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47
Q

Why does the thoracic region of the spinal cord have a small grey horn and large white lateral horns?

A

Small grey horns - few neurons needed for segmental thoracic innervation

Large lateral horns - lateral funiculus carrying motor and sensory to the thorax

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48
Q

Why does the lumbar region have large grey horns?

A

Large number of cells bodies to innervate lower limbs

49
Q

Which portion of the spinal cord will have a large portion of white matter compared to grey matter?

A

Cervical region

Large population of neurons needed to innervate upper limbs

50
Q

Which portion of the spinal cord has a small grey horn but large white matter parts?

A

Thoracic region

Small grey horn - segmental thoracic

51
Q

DIAGRAM:

Draw out the different portions of the spinal cord (e.g. cervical, thoracic) in terms of white and grey matter

A

Look at slide 16 of ascending tracts lecture

52
Q

What are the 3 major ascending sensory pathways?

A

Dorsal column pathway

Spinothalamic tract

Spinocerebellar tracts

53
Q

Which type of sensors send information through the dorsal column pathway?

A

Meissner’s

Merkel’s

Pacinian

Ruffini

54
Q

What senses does the dorsal column pathway send?

A

Discriminative touch

Vibration

Conscious proprioception

55
Q

What are the 2 areas of the dorsal column pathway called?

A

Fasciculus Cuneatus (lateral)

Fasciculus Gracilis (medial)

56
Q

Where does the Fasciculus Cuneatus receive information from?

A

From above T6

Discriminative touch, vibration and conscious proprioception

57
Q

Where does the Fasciculus Gracilis receive information from?

A

From below T6
(graceful legs)

Discriminative touch, vibration and conscious proprioception

58
Q

Does the dorsal column pathway ascend contralaterally or ipsilaterally in the spinal cord?

A

1st order neuron ascends ipsilaterally to the medulla where it decussates

59
Q

Describe the pathway of a neuron carrying sensation of discriminative touch, vibration and conscious proprioception from the body - 1st order neuron to the cortex

A

Stimulated by either Meissner’s receptor or Merkel’s receptor.

Carries sensation via 1st order neuron

Neurons below T6 enter the spinal cord at the medial Fasciculus Gracilis of the dorsal column.
Neurons above T6 enter the spinal cord at the lateral Fasiculus Cuneatus of the dorsal column

1st order neurons ascend the spinal cord ipsilaterally

Synapse with 2nd order neuron in the nucleus gracilis (below T6) or nucleus cuneatus (above T6) of the lower medulla, where they decussate

Travel to thalamus where they synapse with 3rd order neurons that travel to the primary sensory cortex

60
Q

Which somatosensory pathway carries discriminative touch, vibration and conscious proprioception?

A

Dorsal columns pathway

61
Q

Describe the dorsal column pathway carrying sensory innervation from the face

A

1st order trigeminal nerve sensory neurons enter PONS and synapse in CN V nucleus where they decussate

2nd order neurons ascend in trigeminal lemniscus to ventral posterior medial (VPM) nucleus of the thalamus, where it synapses with 3rd order neurons

3rd order neurons pass to primary sensory cortex

62
Q

SLIDE REVIEW

A

Slide 24 - dorsal column damage

63
Q

What senses does the spinothalamic tract carry?

A

Pain

Temperature

Simple touch

64
Q

Which sensory pathway carries pain, temperature and simple touch?

A

Spinothalamic tract

65
Q

Describe the spinothalamic pathway

A

1st order neurons from body ascend 1-2 vertebral levels (in the Tract of Lissauer) in dorsal grey matter before synapsing with 2nd order neurons

2nd order neurons decussate via (across) the anterior white commissure

2nd order neurons ascend in the spinothalamic tract to ventral posterior lateral (VPL) nucleus of thalamus

2nd order neurons synapse with 3rd order neurons in ventral posterior lateral (VPL) thalamic nucleus

3rd order neurons travel to primary sensory cortex

66
Q

Do spinothalamic nerves from the body ascend the spinal cord ipsilaterally or contralaterally?

A

Ipsilaterally 1-2 vertebral levels then decussates with 2nd order neuron via the anterior white commissure

67
Q

Which receptors carry sensation to the spinothalamic tract?

A

Free nerve endings

68
Q

Where is the spinothalamic tract situated in the spinal cord?

A

Ventral portion of the spinal cord

69
Q

Before they decussate, where do spinothalamic tract neurons ascend?

A

Ascend 1-2 vertebral levels via the Tract of Lissauer

70
Q

What is special about spinothalamic tract organisation?

A

It is organised somatotopically

Lateral –> medial

Sacral
Leg
Arm/thorax
Head & neck

71
Q

What sensation does the spinocerebellar tract carry?

A

Unconscious proprioception

72
Q

Which sensory pathway carries unconscious proprioception?

A

Spinocerebellar tract

73
Q

What are the 2 regions of the spinocerebellar tract called?

A

Dorsal spinocerebellar tract

Ventral spinocerebellar tract

74
Q

What do dorsal spinocerebellar tract neurons monitor?

A

Muscle length

Speed of contraction

Tension

75
Q

What is different about the DORSAL spinocerebellar tract compared to the spinothalamic and dorsal tract?

A

Dorsal spinocerebellar is a 2-neuron pathway

Ipsilateral pathway to the cerebellum

76
Q

Describe the pathway of the DORSAL spinocerebellar tract from the lower limb

A

Sensory innervation enters the spinal cord and synapses in Clarke’s Dorsal Nucleus

Ascends as 2nd order neuron

77
Q

What is a motor unit?

A

A lower motor neuron and the extrafusal muscle fibres it innervates

78
Q

Where is the primary motor cortex?

A

In the pre-central gyrus, anterior to the central sulcus.

In the frontal lobe

79
Q

Where is the pre-motor cortex?

A

Immediately anterior to the primary motor cortex

In the frontal lobe

80
Q

What is the pre-motor cortex responsible for?

A

Motor programme retrieval

81
Q

Where does the primary motor cortex receive input from?

A

Pre-motor cortex

Supplemental motor cortex

Cerebellum (via the ventrolateral nucleus of the thalamus)

Somatosensory nucleus

82
Q

Which Brodmann area is the primary motor cortex in?

A

Brodmann Area 4

83
Q

Which Brodmann area is the supplementary motor area (pre-motor cortex and supplementary motor area) in?

A

Brodmann Area 6

84
Q

What does damage to the pre-frontal cortex usually result in?

A

Paresis (weakness) on contralateral postural muscles

Due to influence on the reticulospinal tract

85
Q

Name the 3 types of ascending pathways

A

Dorsal column

Spinothalamic

Spinocerebellar (dorsal and ventral)

86
Q

Name the 2 types of lower motor neurons

A

Alpha

Gamma

87
Q

What does an alpha motor neuron innervate?

A

Motor units of extrafusal fibres

88
Q

What does a gamma motor neuron innervate?

A

Intrafusal muscle fibres of muscle spindles

89
Q

What does a muscle spindle measure?

A

Muscle strength and contraction.

Tells the brain how much strain the muscle is under.

90
Q

Describe an alpha motor neuron

A

Large myelinated axons

Innervates muscle units, making muscle bellies contract

91
Q

Describe a gamma motor neuron

A

Small diameter axons

Innervates intrafusal fibres of muscle spindles

Help to monitor stretch and contraction

92
Q

What does the suffix ‘plegia’ mean?

A

Paralysis

93
Q

What does the suffix ‘paresis’ mean?

A

Weakness

94
Q

Describe the blood supply to the spinal cord

A

2 posterior spinal arteries

1 anterior spinal artery

95
Q

Name the 3 descending pathways

A

Lateral Corticospinal Tract

Lateral Vestibulospinal Tract

Ventral Corticospinal Tract

96
Q

Apart from the 3 main descending pathways, what is another descending pathway to be aware of?
What does it do?

A

Reticulospinal tracts

Helps inhibit lower motor neurons so you don’t have overactive spasticity

97
Q

Where does the lateral corticospinal tract receive output from?

A

Primary motor cortex

Supplementary motor area

98
Q

What is the lateral corticospinal tract responsible for?

A

Major voluntary, skilled motor movement

99
Q

Which descending pathway is responsible for major voluntary, skilled motor movement

A

Lateral Corticospinal Tract

100
Q

Where does the lateral vestibulospinal tract receive output from?

A

Vestibular nuclei of pons and medulla

101
Q

What is the lateral vestibulospinal tract responsible for?

A

Extensor muscle control (anti-gravity action)

102
Q

Which descending tract is responsible for extensor muscle control (anti-gravity action)

A

Lateral Vestibulospinal Tract

103
Q

Where does the ventral corticospinal tract receive output from?

A

Primary motor cortex

104
Q

What is the ventral corticospinal tract responsible for?

A

Minor motor movement

To a lesser extent than the lateral corticospinal tract

105
Q

Which descending pathway is responsible for minor motor movement?

A

Ventral Corticospinal Tract

106
Q

Where do descending neurons from the lateral corticospinal tract decussate?

A

In the medulla

107
Q

Where do descending neurons from the ventral corticospinal tract decussate?

A

At the level of synapse with lower motor neuron (spinal level of exit)

108
Q

Where do motor nerves exit the spinal cord from?

A

Ventral grey horn

109
Q

What 4 symptoms would you see with an Upper Motor Neuron lesion?

A

Spastic paralysis
Hyper-reflexia
No muscle wasting
Extensor plantar response

110
Q

What 4 symptoms would you see with an Lower Motor Neuron lesion?

A

Flaccid paralysis
Hypo-reflexia
Muscle atrophy (wasting)
Fasciculations

111
Q

What would result from a hemi-section of the spinal cord?

Injury and symptoms

A

At the level of the injury the patient would experiences LMN symptoms (where the UMN synapses with a LMN)

Below the level of injury there would be UMN symptoms, because the UMN carries on past the first synapse

112
Q

What is the corticobulbar tract?

A

Major motor pathway to the face

113
Q

What is the major motor pathway to the face?

A

Corticobulbar tract

114
Q

Where do motor nerves to the face decussate?

A

Higher in the medulla. Leave via CN V or CN VII

115
Q

What effect would a brainstem lesion have on motor movement?

A

Ipsilateral LMN loss to the face.

Contralateral UMN loss to the body below the level of the lesion

116
Q

Which descending pathway never decussates?

A

Lateral vestibulospinal tract

117
Q

What has an important influence on LMN?

A

Reticulospinal tract - acting on Renshaw cells

Can influence cells that live in ventral horn of the spinal cord

118
Q

What cells does the reticulospinal tract activate?

A

Renshaw Cells

Inhibitor cells of the LMN

Block 3 (14 decks)

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