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Semester 4 - Clinical Neuroscience > 2. Embryology > Flashcards

2. Embryology Flashcards

1
Q

define gastrulation

A

Gastrulation is the process whereby the outer layer of the bilayer germ disc (ectoderm) invaginates at the primitive streak to produce a three layered germ disc

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2
Q

what are the 3 layers of the germ disk after gastrulation>

A

ectoderm, mesoderm, endoderm

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3
Q

what does the ectoderm become?

A

Becomes skin and neural tissue as well as neural crest

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4
Q

what does the mesoderm become?

A

 Heart, vessels, muscles etc.

 The notochord is a crucial structure composed of endoderm

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5
Q

what is the function of the notochord?

A

It inducts the overlying ectoderm to invaginate and form the neural tube

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6
Q

what does the endoderm become?

A

Gut including accessory organs

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7
Q

describe the process of neurulation

A

Neurulation is the process of formation of the neural tube
o Induced by the notochord
o Elevation of the neural folds
o Fusion of the folds in the midline at mid cervical level with reconstitution of the surface ectoderm
o Neural tube zips up rostrally and caudally

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8
Q

what happens to neural crest cells in neurulation?

A

When the folds fuse, neural crest cells detach and migrate their ultimate destinations

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9
Q

what happens if there is failure of the neural tube to zip rostrally or caudally?

A

 If this process fails in the rostral direction can result in anencephaly
 Failure in the caudal direction can lead to spina bifida

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10
Q

what are the 3 Primary brain vesicles?

A

The rostral neural tube displays a number of swellings which will become the major parts of the adult brain

  • Forebrain (Prosencephalon)
  • Midbrain (mesencephalon)
  • Hindbrain (rhombencephalon)
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11
Q

What are the 5 secondary brain vesicles and what do they form from?

A
  • Prosencephalon forms the telencephalon and the diencephalon
  • Mesencephalon form the mesencephalon
  • Rhombencephalon form the metencephalon and the myelencephalon
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12
Q

What are the mature derivatives of the secondary brain vesicles?

A
  • Telencephalon: cerebral hemispheres
  • Diencephalon: thalamus, hypothalamus and optic nerve/retina
  • Mesencephalon: midbrain
  • Metencephalon: pons and cerebellum
  • Myelencephalon: medulla
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13
Q

what is a fundamental pattern to the organisation of the nervous system?

A

 Motor structures tend to sit anteriorly (I remember this as you ‘motor forwards)
 Sensory structures tend to sit posteriorly

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14
Q

What causes the pattern of motor anteriorly and sensory posteriorly?

A

This pattern exists due to the development of the basal (floor) and alar (roof) plates in the neural tube
• The notochord inducts the ventral (anterior) portion of the neural tube to become the basal (or floor) plate
o The basal plate gives rise to motor neurones
• The alar (or roof) plate (dorsal) forms in the absence of influences from the notochord
o Gives rise to inter- and sensory neurones

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15
Q

How is this fundamental pattern seen in the spinal cord?

A

 Dorsal roots are sensory whilst ventral roots are motor
 The dorsal horn contains sensory neurones whilst the ventral horn contains motor neurones
 The dorsal columns (a sensory tract) sit posteriorly whilst the corticospinal tract (motor) sits anteriorly

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16
Q

How is this fundamental pattern seen in the medulla?

A

The lemnisci (sensory) sit posterior to the pyramids of the medulla (motor) (contain corticospinal tracts)

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17
Q

How is this fundamental pattern seen in the midbrain?

A

The colliculi (sensory) sit posterior to the cerebral peduncles (motor)

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18
Q

How is this fundamental pattern seen in the cerebral cortex?

A

The primary sensory cortex (sensory) sits posterior to the primary motor cortex (motor)

19
Q

Why are there flexures in the CNS?

A

Growth & development at cranial NT exceeds available space linearly, so….it must fold up

20
Q

What are the 2 flexures of the CNS?

A
  • Cervical flexure (spinal cord- hindbrain)

- Cephalic flexure (midbrain region)

21
Q

what leads to the development of the cauda equina?

A

o Initially, there is a one to one correspondence between cord levels and vertebral levels (the cord fills the entire vertebral canal)
o but, the spine grows faster than the spinal cord, particularly at the lumbar levels
o so, the lower portions of the cord are stretched, drawing out the cauda equina

22
Q

How do neural tube defects predispose to hydrocephalus?

A

 This may be caused by tethering of the cord at the site of the defect
 Thus, as the spine grows the cord cannot move within the vertebral canal, resulting in the brainstem (containing the fourth ventricle) being pulled down through foramen magnum and becoming occluded

23
Q

What do neural tube defects result from?

A

Failure of the neutral tube to close

- can occur cranially or caudally

24
Q

What do cranial neural tube defects result in?

A

Anencephaly

25
Q

What is anencephaly?

A

Failure of NT closure cranially
• Absence of cranial structures, including brain
• Incompatible with life

26
Q

What do caudal neural tube defects result in?

A

Spina bifida

27
Q

What is spina bifida?

A

A birth defect in which there is incomplete closing of the spine and membranes around the spinal cord during early development in pregnancy

28
Q

What are the different severities of spina bifida from most severe to least?

A
  • myelomeningocele
  • meningocele
  • spina bifida occulta
29
Q

what are the different neural tube disorders from severe to least severe

A 
Craniorachischisis
Anencephaly
Myelocoele
Myelomeningocoele
Meningocoele
Spina bifida occulta
30
Q

what is Craniorachischisis

A
  • The entire neural tube remains open
  • Hence failure of both brain and spinal cord to form
  • Incompatible with life
31
Q

what is Anencephaly?

A
  • The cranial neural tube fails to close
  • Hence failure of the brain to form
  • These children may be born alive but do not live for long
32
Q

what is Myelocoele?

A
  • The spinal cord fails to develop ( i.e. the lumen of the neural tube is exposed to the outside world), usually associated with a CSF filled cyst
  • These children frequently have neurological deficits and are susceptible to meningitis due to the presence of exposed neural tissue
33
Q

which conditions appear to have a normal neural tube, but there is failure of development of the posterior vertebral arch?

A

Myelomeningocoele
Meningocoele
Spina bifida occulta

34
Q

what is Myelomeningocoele?

A
  • A CSF-filled cyst containing the spinal cord
  • Transilluminates relatively poorly (due to [presence of solid tissue in the cyst)
  • These children may have neurological deficits (less likely than disorders listed above)
  • Repair is necessary
35
Q

what is a Meningocoele?

A

o Presence of a CSF filled cyst
o The cord is sited within the vertebral canal
o Transilluminates brilliantly
o These children tend to have a good neurological
prognosis
o However, the cyst will need repair as it does
predispose to infection

36
Q

what is Spina bifida occulta?

A

o The only anomaly is the lack of the posterior vertebral arch
o May manifest a sign such as a tuft of hair or a large naevus over the defect
o Not associated with significant neurological problems
o Occurs in about 10% of the population!

37
Q

how can nuerual tube defects be prevented?

A

folic acid
o 400 micrograms daily, to be taken before from
around 3 months before conception and until week
12 of pregnancy

38
Q

what does the neural tube form?

A

brain and spinal cord

39
Q

what does the neural crest form ?

A

 All neurones whose cell bodies are in the peripheral nervous system
• Primary sensory neurones
• Autonomic postganglionic neurones
• Enteric neurones
 Schwann cells
 Cells of the adrenal medulla
 Melanocytes
 The leptomeninges (i.e. the arachnoid and pia)
 Head mesenchyme, which contributes to many tissues such aspharyngeal arches

40
Q

what is the neural crest?

A

o Derived from the point at which the neural folds fuse when the surface ectoderm is reconstituted
o They become detached from the ectoderm and then migrate to their distant targets

41
Q

which tissues receive a significant contribution from neural crest?

A

 Thymus
 Thyroid
 Parts of the heart (e.g. spiral septum)
 Parts of the teeth

42
Q

what are the 2 disorders of the neural crest?

A

Di George syndrome

Hirschprung’s disease

43
Q

what is Di George syndrome

A

• Immunodeficiency (due to involvement of the thymus)
• Facial anomalies (due to contribution of neural crest to
facial development)
• Heart anomalies
• Hypocalcaemia (involvement of parathyroids)

44
Q

what is Hirschprung’s disease

A
  • Lack of enteric neurones in sections of the large intestine
  • This leads to hypomotility and constipation

Semester 4 - Clinical Neuroscience (19 decks)

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