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Neurophysiology > Spinal cord > Flashcards

Spinal cord Flashcards

1
Q

How is the spinal cord the main effector of all behavioural responses

A

The spinal cord must relay info from diverse receptors in the PNS to the CNS, where higher brain centres may perceive it, and cause voluntary or reflex behavioural response

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2
Q

What is the central core and surround of the spinal cord

A

Central core of nerve cells (grey matter) surrounded by fibre tracts (white matter) rich in myelinated axon tracts
Also a central CSF filled canal

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3
Q

How is the grey matter of the spinal cord divided

A

Dorsal horn (posterior) that is sensory in function, and a ventral horn that is motor in function

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4
Q

How is the white matter of the spinal cord divided

A

Dorsal, lateral and anterior (ventral) columns/funiculi

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5
Q

What surrounds the spinal cord

A

The 3 layers of meninges- the thick dura, the fine arachnoid, the surface covering of pia mater

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6
Q

Where does the spnial cord receive sensory (afferent) info

A

From central axons of the dorsal root ganglion neurons, that enter the spinal cord through the dorsal spinal nerve roots

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7
Q

Where does the spinal cord provide motor (efferent) output from MAINLY

A

Motor neurons in the ventral horn leave the spinal cord through the ventral spinal nerve roots to gp skeletal muscles

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8
Q

Where does the spinal cord provide motor (efferent) output from as well as the ventral horn

A

Ouput from lateral horn sympathetic preganglionic neurons (in T1-L2), and parasympathetic pre-ganglionic neurons (in S2-4) to blood vessels, glands, and viscera

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9
Q

Summarise how the neural tube is formed in development

A

The neural plate forms from the ectoderm at gastrulation- the edges of the neural plate roll up to form the neural tube

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10
Q

What is the result of failure to form the neural tue

A

Spina bifida

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11
Q

What cues determine the patterning of the spinal cord

A

Diffusible inductive cues called Morphogens which form cross repressive interactions

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12
Q

What is the Sonic hedgehog (Shh) protein

A

A protein in the notochord that specifies floor plate and induces the ventral horn of the neural tube (Mcmahon et al, 1993)

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13
Q

What are bone morphogenetic proteins (BMPs)

A

Proteins from the ectoderm that overlies the notochord and specifies the roof plate, inducing the dorsal horn formation (Urist, 1965)

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14
Q

What are the Morphogens that control the patterning of the spinal cord

A

Sonic hedgehog (Shh) protein and bone morphogenetic proteins (BMPs)

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15
Q

Study showing the role of the notochord as a signalling centre- what was the proce

A

Holtfreter (1933)- transplanted a notochord into a different animal at the side of the spinal cord, found an ectopic floor plate and third set of motor neurons was developed at the side of the spinal cord, and in the animal with no notochord no motor neurons are formed

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16
Q

Study showing the role of Shh protein in ventral identity

A

Briscoe et al (2000)- Shh protein acts in a concentration dependent manner to specify a range of different motor related interneurons and motor neurons

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17
Q

What is the node

A

Another early patterning centre of the spinal cord that secretes signals to lead to the rhythmic clock creation of somites in early development

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18
Q

What do the somites so

A

Control segmental outgrowth of axons in peripheral nerve roots, prevent axon growth through their posterior halves and regulate the development of a segmentally arranged pattern of spinal nerves (Tannahill et al, 1997)

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19
Q

What reflects the somite-induced segmentation of outgrowing spinal nerves

A

Dermatomes

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20
Q

What are dermatomes

A

Areas of skin supplied by the right and left sensory neurons from a single spinal nerve ganglion

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21
Q

What are the applications of dermatomes for C section

A

Can assess sensory limits of regional anaesthesia

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22
Q

What are the applications of dermatones in radiculopathy

A

Can assess level of spinal cord injury from trauma to radiculopathy by working out which spinal nerve ganglions are implicated based on sensation in different dermatomes

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23
Q

Where is the end of the spinal cord in adults

A

Situated at the level of lumbar vertebrae L1-L2

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24
Q

What 4 regions is the spinal cord divided into

A

Cervical, thoracic, lumbar and sacral

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25
Q

In which spinal cord regions is the grey matter largest at and why

A

Cervical and lumbar enlargements, reflecting the larger no of ventral motor efferents to the limbs, and sensory interneurons and projection afferent neurons (dorsal) from the limbs

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26
Q

Where in the spinal cord is the amount of white matter the largest

A

Rostral end of the cord

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27
Q

How does the size of the ascending tracts change as one moves up the cord

A

As one moves up the cord, more sensory fibres are added, so the ascending tracts increase in size as one moves up

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28
Q

How does the size of the descending tracts change as one moves down the cord

A

As one moves down the cord, descending tracts diminish, as fibres from the descending tracts diminish in the grey matter

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29
Q

What are the size of dorsal/ventral/lateral horns of the thoracic cord

A

Smaller dorsal and ventral horns, reflecting sparese innervation to trunk
More prominent lateral horn

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30
Q

What does the lateral horn of grey matter contain

A

Sympathetic preganglionic neurons, and neurons of Clarke’s column

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31
Q

Where is the cervical enlargement

A

C3-T2 vertebrae

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32
Q

Where is the lumbar enlargement

A

L1-S2 enlargements

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33
Q

Where are the sympathetic autonomic pregangionic neurons

A

T1-L2

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34
Q

Where are the parasympathetic autonomic pregangionic neurons

A

In the sacral region

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35
Q

What are the gracile and cuneate fasiculus

A

Gracile from lumbar region, cuneate from upper limbs

Dorsal column nuclei, relay the dorsal column fibres up to the higher order brain centres

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36
Q

What are the size of the ventral/dorsal horns in the cervical cord

A

Dorsal horns are prominent reflecting the importance of the hand as a sensory structure
Ventral horns also large, with large diameter motor neurons supplying arm and hand muscles

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37
Q

At which region of the spinal cord are white matter tracts the largest

A

Cervical cord

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38
Q

What are the size of the ventral/dorsal horns in the lumbar enlargement

A

Big due to innervation of lower limb- dorsal horns at their largest as most sensory info is concerned with reflexes keeping us upright, ventral horn as largest motor neurons with long axons to innervate foot and leg muscles

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39
Q

How are motor neurons organised at the coronal (separates dorsal and ventral) axis of spine

A

Motor neurons and associated interneurons are arranged in an orderly fashion reflecting their targets in the limb

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40
Q

How do fine unmyelinated axons enter the dorsal horn

A

Lissauer’s tract, a fine outer tract containing Aδ, C, noci-, and thermal fibres- enters laterally and projects across several segments

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41
Q

How do large diameter axons enter the dorsal horn

A

Aalphas and Abetas from proprio- and mechanoreceptors enter medially and possess ascending collaterals

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42
Q

What are the 3 main functional zones of the dorsal horn

A

Marginal zone, substatia gelatinosa, ‘main sensory nucleus’

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43
Q

3 main functional zones of the dorsal horn- marginal zone?

A

Lamina I- area of grey matter where many nociceptive fibres end (Aδ)

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44
Q

3 main functional zones of the dorsal horn- substantia gelatinosa

A

Lamina II- interneurons, primarily innervated by C fibres

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45
Q

3 main functional zones of the dorsal horn- what makes up the main sensory nucleus

A

Nucleus proprius (lamina 3,4,5,6)- consists of projection neurons which send axons that descend the cord in the anterolateral column of grey matter

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46
Q

3 main functional zones of the dorsal horn- what does the main sensory nucleus receive info from

A

Aδ and interneurons, as well as alpha and beta fibres

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47
Q

How are motor neurons gruoped in the ventral horn

A

Motor neurons that supply a single muscle are grouped into ‘motor pools’ which may extend several segments of the cord- these pools are arranged in vertical antagonistic pairs

48
Q

Where do motor neurons that supply distal vs axial muscle lie in the ventral horn

A

Motor neurons supplying axial muscles- medial

Motor neurons supplying distal limb muscles- lateral

49
Q

Where do motor neurons that supply flexors vs extensors lie

A

Motor neurons pools supplying flexors- dorsal

Motor neuron pools supplying extensors- ventral

50
Q

What provides the largest part of the synaptic input onto motor neurons

A

Groups of excitatory and inhibitory interneurons they are associated with

51
Q

What is local circuity in the spinal cord

A

Links sensory input to motor input via various spinal cord reflexes, has intrinsic motor programmes that combine motor neurons/surrounding interneurons/sensory feedback

52
Q

What are distal projections in the spinal cord

A

Project sensory information to higher centres via ascending tracts, receive receive descending tracts

53
Q

Examples of the distal projections of the spinal cord

A

Corticospinal tract, anterior lateral system, spinocerebellar tract

54
Q

What are the different types of afferent fibres

A

Large diameter fibres- Aalpha and Abeta

Small diameter fibres- Aδ (delta) and C fibres

55
Q

How fast can Aalpha and Abeta fibres conduct and why

A

Thickly myelinated and thick diameter means they conduct action potentials very quickly, 120m/s

56
Q

What do Aalpha and Abeta fibres provide info for

A

Online adjustment of movement and locomotor behaviour

57
Q

What do Aalpha fibres do

A

Primarily proprioceptors of skeletal muscle, immediate feedback reflex arcs
Sensory innervation to muscle spindles

58
Q

What is proprioception

A

A sense of body position, essential for locomotion and balance

59
Q

Where do Aalpha and Abeta form synapses

A

In the dorsal horn and on motor neurons (for stretch reflex)

60
Q

Where do Aalpha and Abeta send collateral branches

A

Collateral branches ascend in the dorsal columns to inform higher centres for conscious proprioception

61
Q

What are the 4 classical mechanoreceptors

A

Meissner’s corpuscle and Merkel cells (superficial), Pascianian corpuscle and Ruffini endings (deep)

62
Q

What do Abeta fibres fo

A

Touch- carry info from cutaneous receptors (in epi/dermis), and static proprioceptors

63
Q

Which fibres control dynamic vs static proprioception

A

Aalpha fibres- dynamic

Abeta fibres- static

64
Q

How do the terminations of dorsal root ganglion cells differ

A

Differ for each type of fibre ie sensory modality- each dorsal root ganglion axon branches in a discrete region of the dorsal horn at multiple sequential levels

65
Q

What is the myelination of Adelta vs C fibres

A

Adelta are thinly myelinated, C fibre is not myelinated, so velocity is a lot slower

66
Q

What is the velocity of C fibres

A

0.5-2m per second

67
Q

What do Adelta and C fibres do

A

Both convey pain and temp info, C fibres convey itch info

68
Q

Where do Adelta and C fibres terminate

A

In the dorsal horn, form distinct layers of innervation

69
Q

Where are the dorsal root ganglia located

A

Lie outside the spinal cord and in the invertebral foramen central to where the dorsal and ventral nerve roots join

70
Q

What are the dorsal columns involved in

A

Touch

71
Q

Where do DRG large fibres synapse in the grey matter (as well as sending branches that ascend the dorsal columns)

A

Synapse on neurons in the substantia gelatinosa, main sensory nucleus, intermediate zone (on interneurons), directly to motor neurons in the ventral horn for the monosynaptic stretch reflex

72
Q

What forms the dorsal columns

A

The ascending collateral branches of the primary afferent fibres (largely from mechanoreceptors) form the dorsal columns

73
Q

Where are the dorsal columns in the lower body vs upper body

A

Lower body- gracile fasciculus

Upper body- cuneate fasciculus

74
Q

How are the dorsal columns organised in the spinal cord

A

Uncrossed tracts- their fibres are somatotopically organised

75
Q

Where do the dorsal columns terminate

A

On relay neurons of the dorsal column nuclei in the medulla, that give rise to the medial lemniscus, which projects to the contralateral thalamus which projects to the cerebral cortex

76
Q

What is the anterolateral system involved in

A

Pain (nociception) and temperature

77
Q

How does Lissauer’s tract amplify nociceptive afferent input in the anterolateral system

A

Innervates multiple cells as fibres travel a short distance up and down it, more likely to get through conscious reception and recruit reflex pathways

78
Q

How do fine fibres mediating nociception and temp enter the cord in the anterolateral system

A

Enter the cord and send short ascending and descending collaterals in Lissaur’s tract, which run to adjacent spinal levels, then synpse on cells in the substantia gelatinosa

79
Q

What complex network of interconnections is formed in the anterolateral system

A

Complex interconnections betwee the cells of the substantia gelatinosa and the afferent fibres supplying the marginal zone and main sensory nucleus

80
Q

What indirect ascending nociceptive tracts are there

A

Projection (second order) fibres from the marginal zone and main sensory nucleus cross the midline as the anterior white commissure and ascend in the anterolateral columns

81
Q

What is the anterolateral system composed of

A

Composed largely of crossed tracts due to the anterior white commissure, and includes the spinothalamic tract that relays info directly to the thalamus

82
Q

Where do the fibres of the anterolateral system terminate

A

Many terminate in the reticular formation of the medulla, pons and midbrain, but some ascend to the thalamus (lateral and anterior spinothalamic tract) for relay to the cerebral cortex

83
Q

What are the spinal-cerebelllar tracts involved in

A

Proprioception

84
Q

What are the spino-cerebellar tracts formed of

A

Arise from cells of the intermediate grey matter- proprioceptive afferents from the leg ascend to thoracic levels and axon collateral synapse onto neurons in Clarke’s column

85
Q

What is the larger diamater spino-cerebellar tract

A

The uncrossed dorsal spino-cerebellar tract originates in neurons of Clarke’s column, which relat info up to the ipsilateral cerebellum

86
Q

Where are the spino cerebellar tracts situated

A

Lateral funiculus

87
Q

What are the main ascending tracts

A

Dorsal columns, spinothalamic tract and Lissauer’s tract (of anterolateral system), spino-cerebellar tracts

88
Q

What type of systems is parallel processing a useful feature of

A

Where it is advantageous to keep info sensed by each receptor sub-class separate and therefore maximise the detailed information received by the brain

89
Q

Dorsal column vs anterolateral system- ipsilateral or contralateral?

A

Anterolateral system- contralateral

Dorsal column- axons mostly arise from a single peripheral receptor and ascend ipsilaterally

90
Q

What is the main descending spinal cord pathway

A

Corticospinal tract

91
Q

What is the role of the corticospnial tract

A

Voluntary movement

92
Q

Where does the corticospnial tract travel

A

Arises from somatosensory and motor cortex, descends to the caudal medulla where most axons cross to the contralateral side to form the lateral corticospinal tract

93
Q

What is the composition of the lateral corticospinal tract

A

50% comes from primary motor cortex, other sources are the supplementary motor area, premotor cortex and sensory areas

94
Q

What is the larger ventral uncrossed pathway of the corticospinal tract

A

Anteriori corticospinal tract

95
Q

Descending tracts- rubrospinal tract?

A

Motor tract arising from the red nucleus, involved in voluntary movement, flexion distal arm muscles

96
Q

Descending tracts- tectospinal?

A

Mot tract arising from the tectum, controls reflex postural movements of the head in response to visual and auditory stimuli

97
Q

Descending tracts- vestibulospinal tract?

A

Motor tract arising from lateral vestibular nucleus, controls upright posture and balance, conscious realisation of spatial orientation and motion

98
Q

Descending tracts- descending analgesic pathways

A

Arises from brainstem reticular formation- involved in maintaining balance and posture, especially during body movements

99
Q

Name the 4 additional descending motor tracts

A

Rubrospinal tract, tectospinal tract, vestibulospinal tract, analgesic pathways

100
Q

How is the dorsal horn divided structurally

A

Divided into 6 roughly parallel layers, Rexed’s laminae

101
Q

Where do smaller fibres project to when joining to dorsal columns

A

Project onto to the cord itself, and ascending fibres are derived from second-order neurons

102
Q

Evidence that the anterolateral system carries pain info

A

Dissection of the anterolateral system causes complete peripheral analgesia for both pricking and burning pain

103
Q

What is the reticular formation

A

Consists of axons and dendrites weaving together with long branching axons going upwards to the midbrain and forebrain, and down to the spinal cord

104
Q

What are upward projections of the reticular formation concerned with

A

Regulation of the level of brain activity including attention, sleep, arousal

105
Q

What are downward projections of the reticular formation concerned with

A

Generating patterns of response that can often be stereotypeed eg control of visceral activity, and timing more clearly motor functions

106
Q

What are the reticulospinal tracts

A

Two large descending tracts that go down from the reticular formation to the spinal cord, mediate movement

107
Q

How long are the neurons of the corticospinal tract

A

Its neurons are some of the longest in the body, running from the cerebral cortex to the bottom of the spinal cord

108
Q

What happens to the fibres at the upper end of the corticospinal tract

A

Fibres fan out into a sheet called the internal capsule , in order to squeeze past the thalamus and basal ganglia

109
Q

How many pairs of dorsal and ventral roots are there down the human spinal cord

A

30 pairs

110
Q

What is the effect when a dorsal root is cut

A

The corresponding dermatome on that side of the body does not lose all sensation, as the adjacent dorsal roots innervate overlapping areas- to lose all sensation in one dermatone, 3 adjacent dorsal roots must be cut

111
Q

Shingles as evidence of dermatomes

A

The skin innervated by the axons of one dorsal root is revealed by shingles, where the neurons of a single dorsal root ganglion become infected with a virus

112
Q

How does the spinal cord continue below the lumbar vertebra 1-2

A

The bundles of spinal nerves streaming down within the lumbar and sacral vertical column are the caudal equina, contained within a sack of dura filled with CSF

113
Q

What are second-order sensory neurons

A

Neurons that receive sensory input from primary afferents, most lie within the dorsal horns

114
Q

What info does the spinothalamic pathway convey

A

Info about pain and temp

115
Q

How wide of an area do spinothalamic tract axons synapse over in the brain

A

A wider region of the thalamus than those of the medial lemniscus do

116
Q

What are lower motor neurons

A

Somatic motor neurons in the ventral horn of the spinal cord that innervate the somatic musculature, called lower to distinguish them from the higher order upper motor neurons of the brain that supply input to the spinal cord

117
Q

How do spinal nerves exit the spinal cord

A

Notches in the vertebra

Neurophysiology (23 decks)

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