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Embryology > Lect. 2: Neurulation/Musculoskeletal Development > Flashcards

Lect. 2: Neurulation/Musculoskeletal Development Flashcards

1
Q

What leads to the formation of the neural plate?

A

appearance of the notochord and prechordal mesoderm induces the overlying ectoderm to thicken and form the neural plate

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2
Q

When does the notochord form?

A

around day 18 after fertilization

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3
Q

What is the neuroectoderm?

A

cells of the neural plate

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4
Q

When does the neuroectoderm acquire a “neural groove” and start forming “neural folds”?

A

week 3

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5
Q

What is the fate of the neuroectoderm?

A

they will eventually fuse and the whole neural tube will pinch off

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6
Q

Explain the trend of fusion of the neural folds?

A

they fuse from in the cervical region and then passes cranially and caudally

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7
Q

When do the neural folds complete fusion? Is this fusion complete?

A

around day 21, not a complete fusion, leave open cranial and caudal neuropores

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8
Q

What do the cranial and caudal neuropores allow?

A

leads to a temporary communication between the neural tube and the amnion

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9
Q

Where are neural crest cells originally?

A

they are initially on the neural folds but detact form the neural tube as the folds fuse

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10
Q

What meninges of the brain do the neural crest cells form?

A

arachnoid and pia maters

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11
Q

What sort of cells exist within the neural tube?

A

once the neural tube forms, neuroepithelium exists within the tube (pseudostratified columnar epithelium)

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12
Q

Explain the formation of neuroblasts.

A

Some of the cells from the neuroepithelium differentiate into neuroblasts. These cells leave the neuroepithelium and take up residence in the “mantle layer”

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13
Q

What do neuroblasts differentiate into? What do these form?

A

the neuroblasts differentiate into neurons and pass out their processes to form the “marginal layer”

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14
Q

What is the function of the sulcus limitans?

A

widening of the central canal that divides the developing spinal cord into a dorsal and ventral halves

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15
Q

What does the dorsal region of the mantle layer form?

A

alar plate

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16
Q

What does the ventral region of the mantle layer form?

A

basal plate

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17
Q

What does the alar plate form in the developed human?

A

the alar plate forms the dorsal sensory horn of the central gray matter

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18
Q

What does the basal plate form in the developed human?

A

ventral horn of gray matter and intermediolateral horn of the gray matter

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19
Q

What do the processes of the neurons that were sent into the marginal layer form in a mature human?

A

white matter

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20
Q

What does the ependymal layer (where the original neuroblasts came from) form in a mature human?

A

ependymal lining of the central canal

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21
Q

What communicates between the lateral ventricles of the brain?

A

3rd ventricle

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22
Q

What is the cerebral aqueduct?

A

communication between the 3rd and 4th ventricles of the brain

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23
Q

Where does the 4th ventricle extend?

A

into the spinal canal

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24
Q

What are the walls of the 3rd ventricle?

A

thalamus, hypothalamus, and the pituitary gland

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25
Q

Where is CSF made? What is its path of circulation?

A

in lateral ventricle and 3rd ventricle. It then passes to cerebral aqueduct and into the 4th ventricle which has small holes that allow for the passage of the CSF into the subarachnoid space until it comes up to superior surface of brain and goes into superior sagittal sinus of the dura mater

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26
Q

Where is the 4th ventricle?

A

anterior to cerebellum and posterior to pons

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27
Q

What are the 3 primary vesicles of the neural tube?

A

1) prosencephalon (forebrain)
2) mesencephalon (midbrain)
3) rhombencephalon (hindbrain)

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28
Q

What does the prosencephalon divide into?

A

1) telencephalon (2 of these)

2) diencephalon

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29
Q

What does the mesencephalon divide into?

A

NOTHING, it remains as the mesencephalon or midbrain

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30
Q

What does the rhombencephalon divide into?

A

1) metencephalon

2) myelencephalon

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31
Q

What does the telencephalon become?

A

cerebral hemispheres (lateral ventricles)

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32
Q

What does the diencephalon become?

A

thalamus, etc. (third ventricle)

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33
Q

What does the mesencephalon become?

A

midbrain (aqueduct)

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34
Q

What does the metencephalon become?

A

pons and cerebellum (upper part of 4th ventricle)

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35
Q

What does the myelencephalon become?

A

the medulla (brain stem) (lower part of the 4th ventricle)

36
Q

Do the alar and basal plates always maintain a dorsal: ventral relationship?

A

no, when the neural tube folds open and the roof of the 4th ventricle expands, the alar plates become lateral and the basal plates become medial

37
Q

What is the relationship of motor and sensory nuclei in the brainstem?

A

sulcus limitans divides the sensory (lateral) and motor nuclei (medial)

38
Q

When does the mesoderm begin to thicken around midline and divide into paraxial and lateral plate mesoderm?

A

day 19 after fertilization

39
Q

Where is the paraxial mesoderm?

A

medial, close to notochord, running the entire length of the embryo

40
Q

What is the mesoderm called that lies lateral to the paraxial mesoderm?

A

lateral plate mesoderm

41
Q

Describe the placement of the lateral plate mesoderm.

A

lateral plate mesoderm communicates with the mesoderm over the amnion (somatic extraembryonic mesoderm) and the mesoderm that surrounds the yolk sac (splanchnic extraembryonic mesoderm)

42
Q

What is another name for the somatic extraembryonic mesoderm?

A

parietal extraembryonic mesoderm

43
Q

What is another name for the splanchnic extraembryonic mesoderm?

A

visceral extraembryonic mesoderm

44
Q

Why do the somatic and splanchnic extraembryonic mesoderms change name?

A

cavities develop in the lateral plate that make intraembryonic parietal mesoderm and intraembryonic visceral mesoderm, and as the embryo continues to develop, lateral folds develop that pull the amnion down and extend the lateral plate mesoderm (so you have lots of intraembryonic mesoderm)

45
Q

What are somites?

A

organization of the paraxial mesoderm that consists of little blocks of tissue that begin in the cervical region and extend cranially and caudally as the neural tube zippers off

46
Q

In the cranial region, are their somites?

A

No, in the cranial region, there are somitomeres (less organized)

47
Q

What are the 3 regions of a somite?

A

1) sclerotome
2) dermatome
3) myotome

48
Q

What is a sclerotome?

A

medial region of a somite- sclerotomes migrate out of somites and surround the neural tube and notochord to form the bone (of axial skeleton and cranial vault) and cartilage of the vertebral column

49
Q

What is a dermatome?

A

region of a somite gives rise to the dermis of the skin

50
Q

What is a myotome?

A

cells that leave the somite and migrate down to become the muscles of the region (intrinsic back)

51
Q

What is unique about the muscles that come from myotome?

A

these muscles always keep their segmental innervation–there is one somite for each segment served by a spinal nerve and as the cells migrate to form the muscles they retain this innervation.

52
Q

Do named muscles typically originate from one somite?

A

no, named muscles often have more than one segment of myotome that gives rise to them

53
Q

How does the sclerotome form the vertebrae?

A

to form a vertebral body, the caudal half of one sclerotome fuses with the cranial half of another sclerotome

54
Q

Where do the intervertebral discs come from?

A

intervertebral disc (between the vertebrae) comes from sclerotome tissue left behind after the fusion of the caudal half and cranial half of adjacent vertebrae.

55
Q

What is the origin of the 2 portions of the intervertebral discs?

A
  • Circular arrangement of fibers (annulus fibrosis)- from sclerotome cells.
  • Center (nucleus pulposus)-from notochord.
56
Q

What is the origin of bones of the face?

A

cranial neural crest cells

57
Q

What is the origin of more posterior cranial bones (parietal, occipitalis, petrosal portion of the temporal bone, etc.)?

A

sclerotome portion of the paraxial mesoderm (occipital somites and their less organized counterparts in the head region (somitomeres)

58
Q

What is the failure of closure of the caudal neuropore?

A

spina bifida

59
Q

What might indicate that a fetus has spina bifida?

A

increased alpha-fetoprotein (AFP) levels in mother’s serum and amniotic fluid

60
Q

What is the failure of closure of the cranial neuropore?

A

anencephaly (no brain)

61
Q

What might indicate that a fetus has anencephaly?

A
  • increased AFP levels

- polyhydramnios (too much amniotic fluid)

62
Q

What is the main skeletal problem of spina bifida? (very general)

A

arch of the vertebrae fail to close posteriorly

63
Q

What is the mildest form of spina bifida?

A

spina bifida occulta

64
Q

What is spina bifida occulta?

A

arch of the vertebrae is not present, no disturbance of the nervous system but no protection of the spinal cord–often tuft of dark hair growing on lower back

65
Q

What is spina bifida cystica?

A

more serious form of spina bifida where distrubances of the nervous system occur. many types

66
Q

What is spina bifida cystica with meningocele?

A

spina bifida cystica subtype where the meninges are protruding from, and are in a bulb on, the back

67
Q

What is spina bifida cystica with meningomyelocele?

A

spina bifida cystica subtype where the spinal cord and meninges are outside in a bulb

68
Q

What is spina bifida cystica with rachischisis (myeloschisis)?

A

spina bifida cystica subtype where the neural tube never closed and remains as a flat plate or slightly folded plate (MOST severe neurological disorders at caudal point of spinal cord (paralysis is likely))

69
Q

Where do neurological deficits occur in spina bifida cystica?

A

below the point of the spinal cord where the protrusion occurs

70
Q

Why does hydrocephaly occur with spina bifida?

A

blockage of circulation of CSF, ventricular system expands, CSF cannot get out, and the spinal cord gets hung up on the vertebral column, pulling the cerebellum into the foramen magnum of the skull. Tissue squeezes CSF where it cannot get out into the subarachnoid space, so infant’s skull expands to fit the fluid (can lead to a big skull).

71
Q

What can prevent spina bifida and anencephaly?

A

400 micrograms of folic acid per day starting 3 months before pregnancy

72
Q

What causes anencephaly?

A

cranial vault does not form because cranial neuropore does not cloes. The brain of the developing embryo is exposed to amniotic fluid so it degenerates and leads to no brain.

73
Q

What are the 2 divisions of the myotome?

A

1) epimere

2) hypomere

74
Q

What does the epimere give rise to?

A

extensor muscles of the spine

75
Q

What does the hypomere give rise to?

A

thoracic, abdominal, and limb muscles

76
Q

How do the limb muscles form?

A

cells of hypomere migrate into limb buds with the segmented innervation

77
Q

Where to limb bones and the pelvic/shoulder girdle originate from?

A

from parietal mesoderm (somatic layer of lateral plate mesoderm) in the region of the limbs

78
Q

How do the paddles become hands?

A

programmed cell death to dissolve tissue between digits

79
Q

What are dermatomes (of skin)?

A

Dermatomes: segmental innervation also applies to the skin, and becomes more complicated as the limbs start to turn. Overlap to prevent complete loss of sensation from areas if a nerve is severed.

80
Q

What is amelia?

A

complete absence of one or more limbs

81
Q

What is meromelia?

A

partial absence of one or more limbs

82
Q

What caused a massive outbreak of amelia and meromelia?

A

Thalidomide (widely used in Europe as a morning-sickness cure for anti-nausea)

83
Q

What is syndactly?

A

fused digits (if programmed cell death to paddles does not occur)

84
Q

Where do the serous membranes that line the peritoneal, pleural, and pericardial cavity originate? (general)

A

lateral plate mesoderm

85
Q

Where does the parietal layer of the serous membranes that line the peritoneal, pleural, and pericardial cavity originate?

A

somatic mesoderm

86
Q

Where does the visceral layer of the serous membranes that line the peritoneal, pleural, and pericardial cavity (and smooth muscle of gut and heart) originate?

A

splanchnic mesoderm

Embryology (6 decks)

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