S1) Embryology of the Nervous System Flashcards

look at pp for images

1
Q

Describe the five steps involved in the formation of the neural tube in early embryonic development

A

Gastrulation produces the notochord

Notochord induces neurulation

Neurulation induces the neural plate

⇒ Elevation of lateral edges of neural plate

⇒ Neural folds gradually approach each other in the midline and fuse, producing the neural tube

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2
Q

What is the role of the notochord during neurulation?

A

The notochord directs the conversion of the overlying ectoderm to neurectoderm

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3
Q

What is a neuropore?

A

A neuropore is a region corresponding to the opening of the embryonic neural tube in the anterior/posterior portion of the developing prosencephalon

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4
Q

Defects in closure of the neuropores underlie serious and common birth defects of the nervous system.

What are neural tube defects?

A
  • Neural tube defects are defects which result from failure of the neutral tube to close
  • Failure can occur caudally or cranially
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5
Q

What are the results of the following:

  • Cranial neural tube defect
  • Caudal neural tube defect
A
  • Cranial neural tube defect results in anencephaly
  • Caudal neural tube defect results in spina bifida
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6
Q

What is spina bifida?

A
  • Spina bifida is a type of neural tube defect occurring when the vertebrae don’t form properly around part of the baby’s spinal cord
  • It arises from the failure of neural tube closure caudally
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7
Q

Spina bifida can occur anywhere along the length of the spine.

What is the most common location?

A

Spina bifida most commonly occurs in lumbosacral region

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8
Q

What is anencephaly?

A

- Anencephaly is a neural tube defect resulting in the absence of cranial structures, including the brain

  • It results from the failure of neural tube closure cranially and is incompatible with life
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9
Q

What is rachischisis?

A

Rachischisis is a neural tube defect occuring due to the failure of neural fold elevation

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10
Q

How can one diagnose a neural tube defect?

A
  • Raised maternal serum α-fetoprotein
  • Ultrasound
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11
Q

How can a neural tube defect be prevented?

A

Folic acid pre-conceptually (3 month) and for the first trimester reduces incidence by 70%

  • given especially to woman who are obese, diabetic and epileptic ( increase 300mg to 400mg daily)
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12
Q

Most of the length of the neural tube gives rise to the spinal cord.

In four steps, explain how the cauda equina forms

A

⇒ A 3 months, the spinal cord is the same length as the vertebral column

⇒ Thereafter, the vertebral column grows faster

⇒ The spinal roots must elongate in order to exit at their intervertebral foramen

Cauda equina is formed

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13
Q

During neural fold formation three primary brain regions can be distinguished.

Identify these primary brain vesicles

A
  • Embryonic forebrain (prosencephalon)
  • Embryonic midbrain (mesencephalon)
  • Embryonic hindbrain (rhombencephalon)
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14
Q

At 5 weeks of development, the three primary brain vesicles become five secondary brain vesicles.

Identify these

A
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15
Q

Identify the mature derivatives of the following secondary brain vesicles:

  • Telencephalon
  • Diencephalon
  • Mesencephalon
  • Metencephalon
  • Myelencephalon
A
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16
Q

How are flexures formed in the embryological development of the nervous system?

A

Growth & development at the cranial neural tube exceeds available space linearly, so it must fold up to form flexures

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17
Q

Which two flexures are formed in the embryological development of the nervous system?

A
  • Cervical flexure
  • Cephalic flexure
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18
Q

Where are the cervical and cephalic flexures located respectively?

A
  • Cervical flexure – hindbrain junction
  • Cephalic flexure – midbrain region
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19
Q

What is the role of the ventricular system?

A

The ventricular system cushions the brain & spinal cord within their bony cases

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20
Q

Compare and contrast the ventricular system in development and adults

A
  • In development, it is a tubular structure of the developing CNS persisting as development proceeds
  • In the adult, it is comprised of interconnected “reservoirs” filled by CSF, produced by cells of ventricular lining
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21
Q

Relate the secondary brain vesicles to their corresponding ventricle in the ventricular system

A
  • Telencephalon → lateral ventricle
  • Diencephalon → third ventricle
  • Mesencephalon → cerebral aqueduct
  • Metencephalon & myelencephalon → fourth ventricle
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22
Q

What is hydrocephalus?

A
  • Hydrocephalus is a condition characterised by excessive accumulation of fluid in the brain
  • Is is most common in newborns with spina bifida occur due to a blockage of the ventricular system e.g. tumour, infection
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23
Q

How can hydrocephalus be treated?

A

Hydrocephalus is readily treatable by use of shunt

24
Q

Explain the early organisation of the neural tube by describing its three layers

A
  • Inner: neuroepithelial layer
  • Intermediate: mantle layer (neuroblasts)
  • Outer: marginal layer (processes)
25
Q

What is the function of the roof and floor plates of the neural tube?

A

Roof & floor plates regulate dorsal & ventral patterning

26
Q

Describe the modality of the alar and basal plates respectively

A
  • Alar plate = sensory
  • Basal plate = motor
27
Q

Describe the location and function of neural crest

A
  • Location: cells of the lateral border of the neuroectoderm tube
  • Function: become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition
28
Q

Identify 8 neural crest derivatives in the nervous system

A
  • Cranial nerve ganglia
  • Spinal root ganglia
  • Sympathetic ganglia (chain & pre-aortic)
  • Parasympathetic ganglia
  • Schwann cells
  • Glial cells
  • Leptomeninges (arachnoid & pia)
  • Connective tissue & bones of the face & skull
29
Q

Identify 3 neural crest derivatives in the head, neck and midline

A
  • Odontoblasts
  • Dermis (face & neck)
  • C cells of the thyroid gland
30
Q

Identify 3 miscellaneous neural crest derivatives

A
  • Conotruncal septum (heart)
  • Melanocytes
  • Adrenal medulla
31
Q

what is neurolation?

A
  • formation of the neural tube
  • induced by the notochord
  • fusion of the folds in the midline at around the neck level
  • once folds fuse, neural crest cells detach and ,migrate
32
Q

what direction does the neural zip close up

A
  • rostrally and caudally
33
Q

what two parts does the forebrain split into?

A
  • telencephalon → becomes most of cerebral hemisphere
  • diencephalon → thalamus, hypothalamus an optic nerve
34
Q

what does the rhombencephalon split into?

A
  • metencephalon → pons and cerebellum
  • myelencephalon → medulla
35
Q

what is the relationship between the sensory and motor neurones

A
  • motor structures sit anteriorly and sensory sit posteriorly
  • due to the neural tube making the floor give rise to motor neurones and roof sensory
36
Q

give some examples of the relationship of sensory and motor neurone’s

A

Medulla
The medial lemniscus (sensory) sit posterior to the

pyramids of the medulla (motor)

o Midbrain

The colliculi

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

37
Q

development of the caudal equina

A
  • initially spinal chord and spine grow at same pace
  • soon spine grows faster at lumbar level
38
Q

what can happen to the caudal equine to cause hydrocephalus?

A
  • tethering of chord at sight of defect
  • as spine grows the cord can’t
  • 4th ventricle gets pulled down foramen magnum and becomes occluded
39
Q

what is a meningomyelocoele?

A
  • failure of somite to form bone precursors around neural tube (neural tube still fully developed)
  • cyst filled with CSF
  • spinal chord gets stretched and pulled and damaged
  • transilluminates poorly due to solid tissue in cyst
40
Q

what is a meningocele?

A
  • failure of somite to form a bone precursor around the neural tube
  • here spinal cord isn’t being pulled and is in correct position
  • presence of a cyst full of CSF
  • transilluminates well
  • good prognosis
41
Q

what is a myelocoele?

A
  • neural tube fails to develop
  • neural tube exposed to outside world
  • susceptible to meningitis
42
Q

what is spinal bifida occulta

A
  • lack of posterior vertebral arch
  • manifest with hair tuft on back
  • no significant neurological problems
43
Q

neural crest cells

A
  • highly specialised
  • multifunctional and give rise to wide range of tissues
  • derived when the neural folds fuse
44
Q

what are some of the derivatives of neural crest cells

A
  • sensory neurones in the PNS
  • enteric neurones
  • Schwann cells
  • cells of adrenal medulla
  • head mesenchyme
45
Q

which tissues receive a significant contribution from neural crest cells

A
  • thymus
  • thyroid
  • parts of heart and teeth
46
Q

As streams of neural crest cells migrate from the dorsal part of the embryo, defined populations become left behind at certain points

A

from dorsal to ventral:

  • The dorsal root ganglia (sensory neurones)
  • The sympathetic ganglia (sympathetic postganglionic

neurones)

  • The preaortic ganglia (sympathetic postganglionic

neurones that receive input from splanchnic nerves)

  • The adrenal medulla (chromaffin cells, which are

homologous to sympathetic postganglionic neurones)

The but wall (enteric nervous system)

47
Q

Di George syndrome

A
  • disorder of the neural crest cells:
  • Immunodeficiency (due to involvement of the thymus)
  • Facial anomalies (due to contribution of neural crest to

facial development)

  • Heart anomalies
  • Hypocalcaemia (involvement of parathyroids)
48
Q

Hirschprung’s disease

A
  • disorder of neural crest cells

Lack of enteric neurones in sections of the large intestine → no peristalsis inside parts of the colon

This leads to hypomotility and constipation

49
Q

what does the term meningo refer to

A

CSF

50
Q

what does the term myelo refer to

A

cord

51
Q

what other tissue does the CNS share embryological origin

A

it derives from ectoderm same as the skin

52
Q

what organ develops from the same origin as the nervous system

A

skin, from ectoderm

53
Q

what is another name for cerebral peduncles

A

crus cerebri

54
Q

which part of the brainstem lies directly at the level of the tenotrium cerebellum

A

midbrain

55
Q

the falx cerebri is composed of which meningeal layer

A

meningeal dura