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BRAIN AND BEHAVIOUR > Histology: Spinal Cord > Flashcards

Histology: Spinal Cord Flashcards

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1
Q

Name the six types of glial cells

A

1) Ependymal cells
2) Astrocytes
3) Microglia
4) Oligodendrocytes
5) Schwann cells
6) Satellite cells

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2
Q

Define ‘glia’

A

the connective tissue of the nervous system, consisting of several different types of cell associated with neurons.

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3
Q

Name the 4 types of glia in the central nervous system

A

Ependymal cells, astrocytes, microglia, oligodendrocytes

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4
Q

Name the 2 types of glia in the peripheral nervous system

A

Schwann cells and satellite cells

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5
Q

What are ‘autonomic ganglia’?

A

Cell bodies of the neurones in the autonomic nervous systems

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6
Q

Describe the location and function of ependymal cells

A

They line fluid-filled cavities of CNS (e.g. spinal cord central canal and brain ventricles) and are involved in the circulation of CSF

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7
Q

Describe ependymal cells histologically

A

They are ciliated and the cilia movement circulates CSF through hollow spaces . They look like epithelia without a basement membrane

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8
Q

Describe the location and function of astrocytes

A

Most common glial cell in CNS, surround neurones. Function: structural and metabolic support, help form BBB, regulate K+/Ca2+ conc., regulate pH and neurotransmitter availability (can mop-up excess transmitter) and form scars in areas of damage

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9
Q

Describe astrocytes histologically

A

Are star shaped and can be distinguished from neurones by presence of glial fibrillary acid protein (GFAP)

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10
Q

Describe the location and function of microglia

A

Distributed throughout the CNS. In development release GFs and act like macrophages to pick up debris from apoptosis, in adults they are surveillance cells and in injury they change shape and revert to phagocytic macrophages known as reactive microglia.

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11
Q

Describe microglia histologically

A

They are small cells in the CNS which have long spiny processes

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12
Q

Describe oligodendrocytes histologically

A

Have a small number of processes

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13
Q

Describe the location and function of oligodendrocytes

A

Insulate axons of the CNS (myelinate). Each cell can myelinate up to 60 axons and their cell bodies lie between those axons

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14
Q

Describe the location and function of Schwann cells

A

Myelinate axons of the PNS, though only myelinate a single axon segment.

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15
Q

Describe Schwann cells histologically

A

Cell bodies are close to the myelin sheath and the sheath is covered by external lamina

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16
Q

Describe the location and function of satellite cells

A

Found in the space around ganglion cells in the PNS and have a supportive function similarly to astrocytes in the CNS.

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17
Q

Describe satellite cells histologically

A

Oval-nuclei cells which surround cell bodies of ganglionic cells.

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18
Q

What is the primary neurotransmitter used by sensory neurones?

A

Glutamate

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19
Q

What other neurotransmitters may sensory neurones use?

A

Neuropeptide substance P, CGRP or somatostatin as a co-transmitter

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20
Q

Why may some dorsal root ganglion cells have a role in detecting tissue damage?

A

Some are selectively responsive to ATP which is found in higher concentrations in damaged tissue

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21
Q

Explain what is meant by ‘myelination’

A

Where a single Schwann cell or oligodendrocyte process wraps itself round a segment of axon, forming layers of tightly wrapped plasma membrane

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22
Q

What is the function of the regions of cytoplasm within myelinating cells?

A

Maintains cell constituents

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23
Q

What types of neurones are associated with non-myelinating Schwann cells?

A

small-diameter sensory C fibres or postganglionic autonomic efferents

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24
Q

Why are some axons referred to as unmyelinated?

A

They are only wrapped with one fold of their plasma membrane - by non-myelinating Schwann cells

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25
Q

What are remack bundles?

A

collections of axons supported by the same Schwann cell

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26
Q

How are axons separated in remack bundles?

A

By thin extensions of the Schwann cell body

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27
Q

Define ‘mesaxon’

A

a pair of parallel plasma membranes of a Schwann cell, marking the point of edge-to-edge contact by the Schwann cell encircling the axon

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28
Q

What is the role of the perineurium?

A

A selective barrier to restrict passage to the nerve fibres in the endoneurium and forms part of the BBB

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29
Q

Define ‘epineurium’

A

The outermost layer of dense irregular connective tissue surrounding a peripheral nerve. It usually surrounds multiple nerve fascicles as well as blood vessels which supply the nerve

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30
Q

Define ‘perineurium’

A

The sheath of connective tissue surrounding a bundle (fascicle) of nerve fibres within a nerve.

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31
Q

Define ‘endoneurium’

A

A layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber

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32
Q

Describe the contents of the axonal cytoplasm and their function

A

Numerous mitochondria to power Na+/K+ pump, and microtubules (appear as dots in cross-section) which work to maintain axon shape and guide products of the soma to the axon terminal. Axon cytoplasm generally bland-looking.

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33
Q

What is the role of the dorsal roots?

A

To receive sensory information from the periphery

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34
Q

What is the role of the ventral roots?

A

To carry motor and autonomic information from the spinal cord to the periphery

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35
Q

What is the role of the dorsal root ganglion?

A

To contain the cell bodies of visceral and somatic sensory neurones

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36
Q

How many pairs of spinal nerves are there?

A

31

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37
Q

How many spinal nerves project from each of the spinal segments?

A 
Cervical - 8
Thoracic - 12
Lumbar - 5
Sacral - 5
Coccygeal - 1
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38
Q

At which points of the spinal cord do the spinal nerves intermingle to form mixed nerves?

A

At cervical and lumbar enlargements of the spinal cord, the nerve fibres intermingle in the brachial and lumbosacral plexi to form peripheral nerves with multiple nerve roots.

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39
Q

Where are the cell bodies of postganglionic sympathetic neurones found?

A

sympathetic chain ganglia (T1-L3)

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40
Q

Where are the cell bodies of preganglionic sympathetic neurones found?

A

Thoracic cord (stemming from lateral horn)

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41
Q

Where is the sympathetic chain ganglia found?

A

It runs from T1-L3

42
Q

Where is the white matter in the spinal cord?

A

In the spinal cord white matter surrounds the grey matter

43
Q

Where is the white matter in the brain?

A

In the brain, grey matter surrounds the white matter

44
Q

What does spinal cord grey matter contain?

A

Neuronal cell bodies and terminals of primary sensory afferents

45
Q

Where are lateral horns present?

A

Thoracic and sacral levels

46
Q

What are lateral horns involved with?

A

Autonomic outflow

47
Q

What is the lateral horn of T1-L3 involved with?

A

Contains preganglionic sympathetic neurones (thoracic cord)

48
Q

What is the lateral horn of the sacral level involved with (sacral cord)?

A

Contains preganglionic parasympathetic fibres

49
Q

Where are preganglionic parasympathetic fibres found?

A

Sacral cord

50
Q

What is the function of the substantia gelatinosa and where is it found?

A

Has few myelinated fibres passing through it and caps the dorsal horn in lamina II, and as many nociceptive C fibres terminate here, it’s very important in the regulation of pain sensitivity

51
Q

What is meant by ‘ventral horn enlargement’?

A

In segments that control a limb, the motor neurones are large and numerous which causes the ventral horns to enlarge

52
Q

Which areas of the spinal cord illustrate ventral horn enlargement and why?

A

In lower cervical sections (C5-C8) and lower lumbar sections (and some lower sacral) - so if ventral horn enlargement is present you have to distinguish between cervical and lumbar generally.

53
Q

Which 3 things help to distinguish parts of the spinal cord?

A

overall shape, ventral horn enlargement and amount of grey matter: white matter

54
Q

Why does the amount of white matter appear to change as you move down the spinal cord?

A

Amount of white matter relative to grey matter decreases as the upper segments are still carrying most of the ascending and descending fibres, whereas in the more caudal regions, most of the nerve fibres have exited the cord, so it has little white matter

55
Q

Describe the gross anatomy of the cervical spinal cord

A

Wide, flat cord with lots of white matter (has ventral horn enlargements in lower sections)

56
Q

Describe the gross anatomy of the thoracic spinal cord

A

Has pointed tips of the lateral horns (which sticks out between the small dorsal and ventral horns)

57
Q

Describe the gross anatomy of the lumbar spinal cord

A

It is a round (circular) cord with ventral horn enlargements

58
Q

Describe the gross anatomy of the sacral spinal cord

A

It is a small, round cord with almost no white matter

59
Q

How many laminae is the dorsal horn split into, and on what basis is this done?

A

6, on the basis of cell size

60
Q

What are laminae I-II known as?

A

Superficial dorsal horn

61
Q

Describe the input to the superficial dorsal horn

A

Receives info from C and Adelta fibres (mainly nociceptor fibres). Lamina I from cutaneous, muscle and visceral nociceptors, lamina II from primarily cutaneous input

62
Q

What is Lissauer’s tract and what is it’s function?

A

It caps and merges with lamina I of the dorsal horn and allows integration of nociceptive reflexes on a broader area

63
Q

Where do sensory C fibres primarily terminate?

A

Laminae I-II

64
Q

Where do low-threshold cutaneous A-beta fibres terminate?

A

Laminae III-VI

65
Q

Where do high-threshold A-delta fires terminate?

A

Lamina I and IV/V

66
Q

Which laminae is in the ventral horn?

A

Laminae VII-IX

67
Q

How are motor neurones arranged in the ventral horn?

A

Motor neurones to distal muscles are more lateral, to proximal muscles are more medial. Motor neurones to extensors are more ventral, motor neurones to flexors are more dorsal.

68
Q

Which enzyme makes acetylcholine?

A

Choline acetyl transferase

69
Q

Which neurotransmitter is used by somatic motor neurones in the ventral horn?

A

ACh

70
Q

Which neurotransmitter is used by sympathetic preganglionic neurones of the lateral horn?

A

ACh

71
Q

Name the 3 ascending (sensory tracts) of the spinal cord

A

dorsal column medial lemniscus (DCML), spinothalamic, spinocerebellar tracts

72
Q

What information does the DCML tract carry?

A

Discriminative touch (touch, pressure, vibration) and where our limbs are in space (conscious proprioception)

73
Q

Describe the DCML tract

A

Comprises of the dorsal columns of the gracile and cuneate fasciculi in the dorsal funiculus, decussates at the medulla and travels to the thalamus and then to the somatosensory cortex.

74
Q

What information does the gracile nuclei carry?

A

Information about the lower body (and is the most medial anatomically)

75
Q

What information does the cuneate nuclei carry?

A

Information about the upper body (and is the most lateral in the dorsal funiculus)

76
Q

What information does the spinothalamic tract carry?

A

Pain and temperature (+ itch and tickle)

77
Q

Describe the spinothalamic tract

A

Decussates in the spinal cord where primary afferent synapses with second order neurone in the dorsal horn which then sends axon to opposite side through ventral funiculus about one segment above origin of entry.

78
Q

Describe the location of the 4 main tracts in the spinal cord

A

DCML - in the dorsal funiculus
STT - most ventral, lies below corticospinal
SCT - most lateral
CST - circular and dorsal

79
Q

What information does the spinocerebellar tract carry?

A

Unconscious proprioceptive information to the cerebellum for continuous feedback

80
Q

Describe the spinocerebellar tract

A

It doesn’t decussate as the cerebellum works on an ipsilateral basis, and provides continuous feedback from muscles to allow coordinated movement.

81
Q

What information does the corticospinal tract carry?

A

Motor innervation to the periphery to allow voluntary movement and reflexes

82
Q

Describe the corticospinal tract

A

Tract begins in precentral gyrus (mainly motor cortex) and 80% of axons decussate at medulla, forming lateral corticospinal tract, 20% do not and decussate just prior to periphery which they innervate (anterior corticospinal tract). ACST travels in the ventral funiculus and innervates more medial motor neurones.

83
Q

What happens if a lesion affects a dorsal root/horn?

A

Sensory input from dermatome affected, though there is overlap so multiple damage may have to occur before noticeable

84
Q

What happens if a lesion affects a ventral root or motor neurone?

A

No input to muscles, causing them to be weak or completely flaccid; this is a lower motor neurone lesion

85
Q

What happens if a lesion affects the CST?

A

This is an upper motor neurone lesion which inhibits muscle reflexes and causes loss of tone, as well as weakness (paresis) or paralysis alongside spasticity and hyperactive reflexes

86
Q

What is a Babinski sign?

A

In baby stroking of foot plantar surface causes dorsiflexion and toe-spread, in adults should cause plantarflexion. Babinski sign is indicative of infant response instead of adult (normal)

87
Q

When is a Babinski sign displayed?

A

If the corticospinal tract is lesioned

88
Q

What is Brown-Sequard Syndrome?

A

It is a complete hemisection of the spinal cord

89
Q

What are the symptoms of Brown-Sequard syndrome?

A

Contralateral loss of pain and temp sensation, ipsilateral loss of discriminative touch, spastic paresis below lesion, flaccid paralysis at lesion level, Babinski sign, hyper-reflexia below lesion, ipsilateral loss of all sensory modalities below lesion level

90
Q

What is anterior spinal artery occlusion?

A

The loss of blood and an infarction at a spinal/segmental level

91
Q

What are the symptoms of anterior spinal artery occlusion?

A

Bilateral loss of pain and temperature sensation, spastic paresis below lesion, flaccid paralysis at level of lesion, Babinski sign, hyper-reflexia below lesion

92
Q

What is Tabes Dorsalis?

A

Infection with treponema pallidum (tertiary syphilis)

93
Q

What are the symptoms of Tabes Dorsalis?

A

Bilateral loss of discriminative touch and proprioceptive sensation

94
Q

What is Amyotrophic Lateral Sclerosis?

A

motor neurone disease

95
Q

What are the symptoms of Amyotrophic Lateral Sclerosis?

A

spastic paresis below lesion level, flaccid paralysis at lesion level, Babinski sign, hyper-reflexia below lesion

96
Q

Describe the two stages of spinal cord damage

A

Primary damage results from initial trauma e.g. compression which occurs on injury, secondary damage is initiated by the trauma but occurs gradually and involves physiological alterations to trauma

97
Q

What is meant by spinal shock?

A

A state of shock whereby there is temporary loss of function in the spinal cord which is often produced initially as a result of severe spinal cord injury

98
Q

Outline the stages of spinal shock

A

To start, all functions and reflexes below lesion are depressed or absent giving flaccid paralysis and sensation loss, then few days/weeks neurones regain excitability slowly so flaccid paralysis –> spastic paresis, then flexion reflexes begin to reappear then after several months, muscle tone and tendon reflexes may occur

99
Q

Describe the histology of spinal cord trauma

A

over weeks, grey matter becomes necrotic, leading to macrophage infiltration and removal of degenerative debris. Over more time there is infiltration by fibroblasts and associated collagenous fibrosis occurs to repair.

100
Q

What is present in the endoneurium?

A

Collagen fibres

101
Q

What is present around a Schwann cell?

A

External lamina

102
Q

Where does cavitation often occur in spinal cord injury?

A

Ventral part of dorsal column

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