L3: Development of the spinal cord (finished) Flashcards
1
Q
what are the segments of the spinal cord?
A
cervical thoraic lumbar sacral coccygeal
2
Q
what does the cervical region support?
A
head and neck
3
Q
what does each segment contain?
A
neurons
4
Q
what do the neurons in each segment do ?
A
control or sense their related body segment
5
Q
neurones are arranged in _____ regions depending on _______
A
specific
function
6
Q
Different neuron clusters within a segment may control what?
A
different muscle groups
7
Q
where does the notochord form from?
A
forms from the mesoderm cells soon after gastrulation is complete
8
Q
Signals from the notochord cause uneven ______ and closing of the _____ _____
A
proliferation
neural plate
9
Q
At early stages the neural tube is still in close proximity to what?
A
the mesoderm somites and notochord and also the epidermal cells of the ectoderm.
10
Q
Cells of the neural tube form a __________ epithelium with the nuclei of dividing cells located at the _______ surface
A
pseudostratified
luminal
11
Q
pseudostratified layer of cells include what?
A
neural stem cells or precursor cells
12
Q
where is the luminal surface located ?
A
middle of the neural tube
13
Q
exterior cells deliver _____ to the cord
A
signals
14
Q
what happens to the cells receiving less signals?
A
they are are unspecified until they receive specifying signals as they migrate outwards
15
Q
where do cells differentiate?
A
Cells differentiate as they migrate outwards, eventually the cells at the luminal border will also differentiate
16
Q
what stem ependyma ?
A
the thin membrane of glial cells lining the ventricles of the brain and the central canal of the spinal cord.
17
Q
what forms the ependyma ?
A
ependymal cells
18
Q
what 3 layers become visible?
A
ventricular layer, mantle layer, marginal layer
19
Q
what is the ventricular layer?
A
undifferentiated, proliferating cells
20
Q
what is the Mantle layer ?
A
differentiating neurons (form grey matter)
21
Q
what is the marginal layer?
A
contains nerve fibres (form white matter)
22
Q
what does the alar plate form?
A
the sensory area (dorsal horn)
23
Q
what does the basal plate form?
A
the motor area (ventral horn)
24
Q
what happens to Neuroblasts ?
A
start large but decrease in size and become multipolar
25
Neural tube develops in different ways along what?
along the rostrocaudal axis such that cells in different regions of the neural tube will start to acquire regional identities.
26
formation of the different early brain regions and also the spinal cord are mediated by what?
patterned signalling which drive cells to different fates
27
signalling which drive cells to different fates, comes form where?
the surrounding mesoderm and by the endoderm
28
what happens when cells respond to signal that choose their fate?
cells change their transcriptional profile so that it is different in different areas of the neural tube.
29
what happens when cells change their transcriptional profile?
restrict/define what these cells will become and what they can respond to.
30
what protein is important in early regionalisation ?
Wnt proteins
31
what happens with Wnt proteins across the rostral caudal axis?
There is a gradient of Wnt activity, probably mediated by Wnt inhibitors along the rostral caudal axis.
32
does the rostral region have high or low Wnt signalling ?
low
33
what region has high levels on ant signalling ?
caudal region
34
what does the caudal region become?
hindbrain and spinal cord
35
what does the rostral region become?
fore and mid brain
36
dorsoventral patterning is first mediated by what?
signals from the surrounding tissue
37
mesoderm and ectoderm are close to what?
close to the dorsal or ventral parts of the neural tube
38
what establishes ventral signals?
Ventral signals are established intially by the notochord
39
whats the notochord?
a long region of mesoderm running parallel to the neural tube
40
the disoventral patterning signals are eventually transferred to where via what?
to the neural tube through the floor plate
41
Dorsal signals are initiated by ? and are passed on to where?
Dorsal signals are initiated by epidermal/ectoderm cells and are passed on to the roof plate within the neural tubes itself.
42
dorsal signalling will generate what?
dorsal neurons
43
ventral signalling will generate what?
ventral neurons
44
How are Ventral horn neurons specified?
by Shh signalling
45
where is Shh released from?
released Initially from the notochord
46
what does Shh do?
instigates ventral neural tissue characteristics
47
where does the signalling go after rSh is released from the notocho?
signalling is later passed to the floor plate
48
Shh is highly concentrated where?
at the most ventral part of the developing SC
49
where does Shh diffuse towards?
towards to the more dorsal part
50
Sonic hedgehog is a what?
a morphogen
51
what does being a morphogen mean?
This means that it can instigate different cell responses along a gradient of concentration.
52
At different concentration levels of Shh cells responds...
differently, there a number of types of cell response which are distinct from eachother
53
How does Shh cause different types of cell responses depending on concentration?
by switching on/off expression of different transcription factors when the cells are exposed to higher and higher concentrations.
54
where is the highest concentration of Shh?
most ventral part of the cord the floor plate
55
how many and which transcription factors are expressed at the floor plate?
Two, Nkx2.2 and Nkx6.1. other 5 repressed
56
shh has a _____ effect at the furthest point away which means ___ TF are on
minimal
| 5
57
what do these tf control?
genes which will set the cell on a path towards a certain specification of neurons.
58
Sonic hedgehog signalling drives what?
ventral neuron patterning
59
Neurons experience different levels of ___ which leads to ____ transcription factor expression
Shh
| different
60
what does Transcription factor pattern dictate?
neurone identity
61
each part of the ventral horn has a specific transcription factor profile, what does this establish?
establishes the specific cell types found at these locations.
62
there is a specific profile of transcription factors for every type of cell example...
cells can be pushed towards motor neurones
63
early on motor neurone cells are referred to as what?
(progenitor) pMN which then lead to mature motor neurons
64
transcription factors ______ their opposite transcription factor.
repress
65
ventral horn, contains what and receives input form what?
lower motorneurones
| higher motorneurones
66
input from MN are sent t the VH how?
direct from cortex OR others are polysynaptic via the red nucleus and from vestibular nuclei.
67
striated muscle is what type of muscle?
voluntary
68
what do ventral neurones produce ?
axons
69
what do axons produced by ventral neurones do?
- grow out along ventral roots to innervate striated (voluntary) muscle.
- innervate autonomic ganglia.
70
when are all major ventral columns visible?
14 weeks
71
what type of neurones are dorsal neurones?
Dorsal neurons are the sensory neurons and are often somatotopically arranged
72
in the dorsal region what drives regionalisation?
BMP signalling
73
length of exposure to BMP is a ?
regulating factor
74
dorsal horn neurones are derived form where?
from the alar plate
75
many dorsal horn neurones become what?
many become interneurones receiving input from sensory neurones
76
At the end of the 4th week, axons grow in from ____ ____ ______ to synapse with them
dorsal root ganglion
77
Dorsal column neurones produce ____ that ascend the _____ ___ by the end of the ____ ____.
axons
spinal cord
3rd month
78
during developement of the dorsal horn what happens by the fifth month?
spino-thalamic and spino-cerebellar fibres have ascended to the brain, carrying sensory information from the spinal cord at all levels.
79
Antiparallel signalling gradient precisely dictates what?
cell specification
80
how are spinal cord motor neurones arranged?
in pools
81
each section of motor neurones have what?
have specific muscular targets
82
LMC motor neurons innervate the?
limbs
83
what are some pools of motor neurones?
PMC = Phrenic motor column; LMC = Lateral motor column; PGC = Preganglionic column; MMC = Medial motor column
84
How are the neurons specified to these pools?
using Hox genes
85
what are the steps to how neurones are specified to these pools?
- During development neural tubes is exposed to graded levels of morphogens
- Cells exposed to different levels of retinoic acid and FGF8 will express different Hox genes
- expression of Hox gene determines what motor neurone class is generated.
86
These transcription factors switch on specific genes - some of which specify what?
axonal guidance
87
Hox expression profile specifies what?
which muscle group motor neurons will target
88
Hox profile also controls what?
axonal guidance receptor expression. E.g. Ephrin receptors
89
Specific ephrin receptors bind specific ephrins which act as ___ ___
repulsive cues
90
How are axons guided in the lumbar column?
In the lumbar column, axons are guided to ventral or dorsal muscles depending on Ephrin A or B receptor expression
91
Higher EphA receptor =
repulsion from ventral area where there is a high level of EphA
92
Following fusion of the neural folds, what happens to neural crest cells?
neural crest cells leave the dorsal aspect of the developing spinal cord.
93
Many of the neural stem cells leaving the dorsal aspect of the developing spinal cord move to form ?
the sensory neurons of the spinal (dorsal root) ganglia.
94
How do Cells in the dorsal root ganglia extend sensory fibres ?
extend sensory fibres both centrally and peripherally
95
motor axons grow out from the neurons in the?
basal plate.
96
where do Oligodendrocytes (myelinate nerve fibres) appear from ?
from ventral and dorsal regions of the spinal cord
97
WHAT ARE Ventrally derived oligos directed by?
Shh signalling
98
______ appear latest in development from ventricular regions of the spinal cord
Astrocytes
99
where do astrocytes populate?
Populate all areas of spinal cord (grey and white matter)
100
Microglia invade the CNS apparently with ______
vascularisation
101
true or false, All spinal cord nerve fibres are initially unmyelinated.?
true
102
what are Dorsal and ventral nerve roots myelinated by?
Schwann cells (arising from the neural crest) at 5 months.
103
where do schwann cells come from?
from the neural crest
104
Axons within the spinal cord are myelinated by ?
oligodendrocytes.
105
Most descending fibres are myelinated at ?
nine months.
106
some descending fibres are not myelinated until?
one year after birth.
107
Many ascending neurons remain unmyelinated.
| , true or false?
true
108
Most spinal cord defects are a result form what?
abnormal closure of the neural folds in the 3rd and 4th week
109
whats the most common neural tube defect?
spina bifida
110
what enrol tube defect is Occulta?
vertebrate provides incomplete coverage
111
what is Meningocele?
– meninges herneate
112
what is Myelomeningocele ?
- Spinal cord herneates
113
Dorsal horn is specified by ?
BMP Signalling
114
Glial cells develop after what?
neurogenesis
115
Dorsal root ganglia are derived from where?
the neural crest
