Gross Anatomy Axial Development

Front 1

of what does the axial skeleton consist?

Back 1

skull
vertebral column
12 pairs of ribs
sternum

Front 2

where are the mesenchymal cells from the sclerotome of the somites found during week 4?

Back 2

around the notochord
surrounding the neural tube
in the body wall

Front 3

what does each sclerotome around the notochord consist of?

Back 3

loosely packed cells cranially
densely packed cells caudally

Front 4

what forms the intervertebral disc?

Back 4

movement of some of the densely packed cells from the sclerotome cranially

Front 5

what happens to the remaining densely packed cells in the sclerotome after intervertebral disc is formed?

Back 5

fuse with loosely arranged cells of adjacent caudal sclerotome and form mesenchymal centrum of the vertebra

Front 6

where do peripheral nerves form?

Back 6

close to intervertebral discs

Front 7

where do intersegmental arteries come to lie?

Back 7

on each side of vertebral bodies

Front 8

what do the dorsal intersegmental arteries of the thorax become?

Back 8

intercostal arteries

Front 9

what happens to the notochord?

Back 9

where it is surrounded by verterbral body, it degenerates and disappears

between vertebrae, expands to form nucleus pulposus

Front 10

what surrounds the nucleus pulposus to form the intervertebral disc?

Back 10

annulus fibrosus

Front 11

what is a chordoma?

Back 11

slow-growing neoplasm caused by persisting remnants of the notochord

most commonly at base of skull and lumbosacral region

Front 12

what happens to the mesenchymal cells around the notochord?

Back 12

form bodies of vertebrae and intervertebral discs

Front 13

what happens to the mesenchymal cells around the neural tube?

Back 13

form vertebral arch

Front 14

what happens to the mesenchymal cells in the body wall?

Back 14

form costal processes which develop into ribs in thoracic region

Front 15

when do chondrification centers appear in each mesenchymal vertebra?

Back 15

week 6

Front 16

when do the two chondrification centers from each centrum fuse?

Back 16

week 8

form cartilagenous centrum

Front 17

when do chondrification centers in the vertebral arches fuse with each other and with the centrum?

Back 17

week 8

Front 18

from what do spinous and transverse processes develop?

Back 18

extensions of chondrification centers in the vertebral arch

Front 19

when does the typical vertebrae ossify?

Back 19

begins during embryonic period

ends by year 25

Front 20

how many primary ossification centers are present in the vertebrae at the end of the embryonic period?

Back 20

3
one in the centrum
one in each half of the vertebral arch

Front 21

at birth, what does each vertebra consist of?

Back 21

3 bony parts connected by cartilage

Front 22

when do the halves of the vertebral arch fuse? in what progression?

Back 22

years 3-5

first laminae of lumbar region, and then moves cranially

Front 23

what are cartilaginous neurocentral joints?

Back 23

articulations between vertebral arch and centrum

permit vertebral arches to grow as the spinal cord enlarges

Front 24

when do the neurocentral joints disappear?

Back 24

years 3-6

when vertebral arch fuses with centrum

Front 25

where do the five secondary ossification centers appear after puberty?

Back 25

tips of spinous processes
tip of each transverse process
2 rim (annular) epiphyses (superior and inferior borders of centrum)

Front 26

when do secondary centers unite with rest of vertebra?

Back 26

year 25

Front 27

which vertebrae ossify atypically?

Back 27

C1, C2, C7
lumbar vertebrae
sacrum
coccyx

Front 28

when does the neural plate appear?

Back 28

week 3

Front 29

from what does the nervous system develop?

Back 29

neural plate

an area of embyronic ectoderm

Front 30

what induces the formation of the neural plate?

Back 30

underlying notochord and adjacent mesoderm

Front 31

what does the neural plate differentiate into?

Back 31

neural tube
neural crest

Front 32

what does the neural tube give rise to?
the neural crest?

Back 32

neural tube - CNS (brain and spinal cord)

neural crest - PNS, bones and muscles of the head, meninges, odontoblasts, pigment cells, Schwann cells

Front 33

when does the neural tube begin to form?

Back 33

early part of week 4 (22-23 days)

cranial 2/3 represents brain
caudal 1/3 represents spinal cord

Front 34

from where does the neural tube begin to form?

Back 34

region of 4th-6th pairs of somites
(future cervical region of the spinal cord)

Front 35

when do the rostral and caudal neuropores close?

Back 35

rostral - day 25
caudal - day 27

Front 36

what thickens to form the brain and spinal cord?

Back 36

walls of the neural tube

Front 37

what does the lumen of the neural tube become?

Back 37

ventricular system of brain
central canal of spinal cord

Front 38

what forms the spinal cord?

Back 38

neural tube (caudal to somites 4)

Front 39

when does the central canal of the spinal cord form?

Back 39

week 9 or 10

Front 40

what is the ventricular zone (ependymal layer) and what does it give rise to?

Back 40

pseudostratified columnar neuroepithelium in the walls of the neural tube caudal to somites 4

gives rise to all neurons and macroglial cells (astroglia and oligodendroglia) in spinal cord

Front 41

what is the marginal zone and what does it give rise to?

Back 41

outer parts of neuroepithelial cells in walls of neural tube caudally to somites 4

gives rise to white matter of spinal cord as axons grow into it from neurons in the spinal cord, spinal ganglia and brain

Front 42

what gives rise to neurons?

Back 42

neuroblasts, differentiated from neuroepithelial cells in the ventricular zone

(form intermediate zone between ventricular and marginal)

Front 43

when do glioblasts differentiate from neuroepithelial cells?

Back 43

after neuroblast formation has stopped

(migrate from ventricular zone into intermediate and marginal zones)

Front 44

what happens to the remaining neuroepithelial cells after neuroblast fomation has stopped?

Back 44

some become astroblasts and then astroglia (astrocytes)

some become oligodendroblasts and then oligodendroglia (oligodendrocytes)

rest become ependymal cells lining central canal of spinal cord

Front 45

when do microglia, derived from mesenchymal cells, invade nervous system?

Back 45

late in fetal period
(after penetration of blood vessels)

Front 46

what is the sulcus limitans?

Back 46

shallow, longitudinal sulcus that appears in the lateral walls of the spinal cord and separates dorsal alar plate from ventral basal plate

Front 47

what forms from the alar plates?

Back 47

dorsal horns of spinal cord

afferent functional neurons

Front 48

what forms from the basal plates?

Back 48

ventral and lateral horns

efferent functional neurons

(axons grow out of the spinal cord to form the ventral roots)

Front 49

from what are dorsal root ganglia formed?

Back 49

neural crest cells
(axons enter the spinal cord to form th dorsal roots)

Front 50

what forms the meninges?

Back 50

mesenchyme surrounding the neural tube condensing to form primitive meninx

outer layer thickens to form dura mater

inner layer remains thin and forms pia and arachnoid mater

Front 51

why does the spinal cord become shorter than the vertebral canal?

Back 51

spine and dura mater grow more rapidly than the spinal cord

Front 52

at what level does the end of the spinal cord lie in month 6 of gestation?
in newborn infant?
in adult?

Back 52

month 6 - S1
newborn - L3
adult - L2/3

Front 53

what causes most of the congenital malformations of the spinal cord?

Back 53

defective closure of caudal neuropore at end of week 4

Front 54

what is spina bifida?

Back 54

congenital malformations involving spinal cord and vertebral arches

(nonfusion of the vertebral arches)

Front 55

spina bifida occulta

Back 55

defect in vertebral arch resulting from failure of halves to grow normally and fuse in medial plane

at L5 or S1 in 10% of population

small dimple with tuft of hair
no clinical symptoms

Front 56

spinal dermal sinus

Back 56

dimple of the skin caused by incomplete closure of caudal neuropore at the end of week 4

dimple may be connected by fibrous cord to dura mater

Front 57

intramedullary dermoids

Back 57

tumors arising from surface ectodermal cells incorporated into the neural tube during closure of the neuropore

Front 58

spina bifida cystica

Back 58

protrusion of the spinal cord and/or meninges through defective neural arch

1/1000 births

may result in loss of sensation in corresponding dermatome, complete or partial skeletal muscle paralysis, sphincter paralysis (with lumbar mengomyeloceles) and saddle anesthesia

Front 59

what is a meningocele?

Back 59

meninges & CSF protrude through a defective neural arch

Front 60

what is a meningomyelocele?

Back 60

protrusion of CSF, spinal cord and meninges through a defective neural arch

marked neurological deficits inferior to sac (neural tissue incorporated into wall of sac)

usually occurs in lumbar region, possibly associated with craniolacunia

Front 61

what is craniolacunia?

Back 61

defective calvarium

Front 62

what is a myeloschisis?

Back 62

myelocele

meninges and CSF in sac
open spinal cord due to failure of neural folds to fuse
spinal cord is flattened mass in this area

Front 63

what is meroanencephaly?

Back 63

absence of part of the brain

Front 64

how can you suspect spina bifida cystica or meroanencephaly?

Back 64

high levels of alpha-fetoprotein in amniotic fluid or in maternal blood serum

amniocentesis or ultrasound at about week 10 when vertebral column becomes visible

Front 65

anencephaly

Back 65

absence of brain