Embryology

Question 1

what embryonic layer develops into the nervous system?

Answer 1

ectoderm

Question 2

what does thickening of the ectoderm anterior to the primitive node form?

Answer 2

neural plate

Question 3

the edges of the ectoderm thicken and move upwards in the 3rd week forming what?

Answer 3

neural folds

Question 4

what is formed when the neural folds migrate towards each other and fuse in the midline?

Answer 4

the neural tube

Question 5

when does the anterior neuropore close?

Answer 5

18-20 somite stage (25 days)

Question 6

when does the posterior neuropore close?

Answer 6

day 27

Question 7

describe neural tube closure

Answer 7

> initiated at several pints along the AP axis
proceeds in cranial and caudal directions
begins at day 18

Question 8

when is neural tube closure completed?

Answer 8

by the end of the 4th week

Question 9

how may closure sites of the neural tube are in humans?

Answer 9

up to 5

Question 10

name some conditions arising from neural tube defects

Answer 10

> anencephaly
encephalocoele
spina bifida

Question 11

what causes meroencephaly?

Answer 11

failure of the anterior neuropore to close so the skull fails to form and the brain tissue degenerates

Question 12

what is craniorachischisis?

Answer 12

failure of the neural tube closure along the entire neuroaxis

Question 13

what causes encephalocoele?

Answer 13

failure in closure of rostral neural tube

Question 14

what is the effect of encephalocoele?

Answer 14

herniation of cerebral tissue through a defect in the skull with a variable degree of neurological deficits

Question 15

what part of the skull is encephalocoele most frequent?

Answer 15

the occipital region

Question 16

in spina bifida where is the closure of the neural tube defective?

Answer 16

the causal end

Question 17

what is the effect of spina bifida?

Answer 17

> affects tissues overlying the spinal cord
can affect the neural tissue
severity ranges from minor to major clinical symptoms

Question 18

define spina bifida

Answer 18

non fusion of the vertebral arches

Question 19

describe the cause of spina bifida occulta

Answer 19

failure of the embryonic halfs of vertebral arches to grow normally and fuse.

Question 20

at what vertebral level does spina bifida occulta normally occur?

Answer 20

L5 and L6

Question 21

what are the effects of spina bifida occulta?

Answer 21

> usually no clinical symptoms

> may result in a small tuft of hair

Question 22

what is spina bifida cystica?

Answer 22

protrusion of spinal cord and/or meninges through the defect in the vertebral arches

Question 23

what is spina bifida meningocele?

Answer 23

> rarest form

> protrusion of meninges and cerebral spinal fluid

Question 24

what is spina bifida meningomyelocle?

Answer 24

> nerve roots and/or spinal cord involved
neurological deficit (sensation loss and paralysis)
associated with hydrocephalus

Question 25

what is the most severe form of spina bifida cystica?

Answer 25

spina bifida myeloschisis

Question 26

describe spina bifida myeoschisis

Answer 26

the spinal cord in the affected area is open due to failure of the neural folds to fuse

Question 27

how is spina bifida incidence decreased in the UK

Answer 27

> folic acid supplements > maternal blood screening > amniocentisis > ultrasound

Question 28

describe maternal blood screening in spina bifida

Answer 28

> high levels of alpha-fetoprotein in serum | > best detected at1 16-20 weeks

Question 29

what are the risk factors for spina bifida?

Answer 29

> genetic predisposition > nutritional (too little foliate, too much vitamin a) > environmental (hyperthermia, drugs)

Question 30

when does brain vesicle development begin?

Answer 30

with the closure of anterior neuropore

Question 31

name the 3 primary brain vesicles

Answer 31

> prosencephalon (forebrain) > mesencephalon (midbrain) > rhombencephaon (hindbrain)

Question 32

name the 5 secondary brain vesicles

Answer 32

``` > telencephalon > diencephalon > mesencephalon > metencephalon > myelencephalon ```

Question 33

where is the cephalic flexure?

Answer 33

between the midbrain (mesencephalon) and the hindbrain (rhombencephalon)

Question 34

where is the cervical flexure?

Answer 34

between the hindbrain and the spinal cord

Question 35

where is the pontine flexure?

Answer 35

in the hindbrain between the metencephalon and myelencephalon

Question 36

what makes up the forebrain (prosencephalon)?

Answer 36

> telencephalon (hemispheres, hippocampus and basal ganglia) > diencephalon (thalamus, pituitary, diencephalon, pineal) > mesencephalon (superior and inferior colliculi)

Question 37

what makes up the rhombencephalon- hindbrain?

Answer 37

> metencephalon (cerebellum, pons) | > myelencephalon (medulla)

Question 38

when does CSF begin to form?

Answer 38

during the 5th weeks

Question 39

where is CSF produced?

Answer 39

by the choroid plexus in the 3rd and 4th lateral ventricles

Question 40

what is hydrocephalus?

Answer 40

accumulation of CSF resulting in an enlarged brain and cranium. it is frequently due to a blocked aqueduct preventing CSF from the lateral and 3rd ventricles passing into the 4th ventricle

Question 41

what can cause hydrocephalus?

Answer 41

> genetic > prenatal viral infection > intra-ventricular haemorrhage > spina bifida cystica

Question 42

what cells initially make up the neural tube?

Answer 42

a single layer of neuroepithelial cells

Question 43

what do neuro-epithelial cells differentiate into?

Answer 43

> neurons > astrocytes > oligodendrocytes

Question 44

what forms microglia?

Answer 44

mesenchymal cells that migrate into the CSF

Question 45

what two processes does the neural crest extend?

Answer 45

> peripheral process (body) | > central process (dorsal horn of spinal cord)

Question 46

describe the positional changes in the spinal cord

Answer 46

> 3rd month it extends the entire length of the vertebral column > vertebral column and dura mater grow more rapidly so spinal cord is at progressively higher levels spinal nerves become elongated forming cauda equina

Question 47

what form the terminal filum?

Answer 47

pia mater

Question 48

what are the sympathetic and parasympathetic ganglia formed by?

Answer 48

neural crest cells

Question 49

describe the formation of the sulci and gyri

Answer 49

brain surface is initially smooth but rapid growth results in the development of sulci and gyri, the pattern becomes more complex as the brain develops

Question 50

what is lissencephaly?

Answer 50

> smooth brain where the gryi and sulci fail to develop | > rare disorder

Question 51

what causes lissencephaly?

Answer 51

defective neural migration

Question 52

what is the result of lissencephaly?

Answer 52

> severe mental impairment > failure to thrive > seizures > abnormal muscle tone

Question 53

what is polymicrogyria?

Answer 53

excessive number of small gyri resulting in a variable degree of neurological problems (mental retardation, seizures, motor deficits)

Question 54

what is the effect of microcephaly?

Answer 54

``` > intellectual impairment > delayed motor and speech function > hyperactivity > seizures > balance problems ```

Question 55

what are the effects of aegenesis corpus callosum?

Answer 55

``` > cognitive and social difficulties > intellectual impairment > seizures > hypotonia > can range from subtle to severe ```

Question 56

what is porencephaly?

Answer 56

CSF filled cysts or cavities from a postnatal stroke or infection

Question 57

what is the effect of porencephaly?

Answer 57

> delayed growth and development > seizures > hypotonia > intellectual impairment

Question 58

what is schizencephaly?

Answer 58

large clefts or slits in the brain due to genetics, in utero stroke or infection

Question 59

what is the effect of schizencephaly?

Answer 59

> paralysis > seizures > intellectual impairment > developmental delay

Question 60

what is diastematomyelia?

Answer 60

where the spinal cord is split longitudinally into 2 pairs and bony/cartilaginous process fixes the cord in place

Question 61

what is the effects of diastematomyelia?

Answer 61

``` > scoliosis > weakness of extremities > hairy patch over lower back > foot deformities > loss of sensation ```

Question 62

what are some causes for intellectual impairment when there is no gross brain defect?

Answer 62

``` > genetic > radiation > infectious agents > birth trauma > postnatal insults > maternal alcohol abuse ```