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Clinical Neuroscience > Development of the nervous system > Flashcards

Development of the nervous system Flashcards

1
Q

What is gastrulation?

A

Process where outer layer of bilaminar disc (epiblast) invaginates at the primative streak to produce a three layered germ disc (trilaminar)

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2
Q

3 layers after gastrulation and what they become

A

Ectoderm - skin, neural tissue, neural crest

Mesoderm - heart, vessels, muscles, somites

Endoderm - gut and it’s accessory organs

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3
Q

Where does the notocord originate from?

A

Mesoderm

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4
Q

What is neuralation?

A

Formation of neural tube
Somites lie either side of tube and skin ectoderm overlies

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5
Q

What induces neuralation?

A

Notocord - underlies ectoderm in mesoderm

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6
Q

What happens in neuralation?

A

Elevation of neural folds (neuroectoderm)
Folds fuse in midline
Skin ectoderm overlies

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7
Q

What happens when the folds of the neural tube fuse?

A

Neural crest cells detach and migrate elsewhere all around the body

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8
Q

How does the rest of the neural tube close?

A

Zips up caudally (to bum) and rostrally (to head)
Leaving openings at top and bottom

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9
Q

What happens if zipping of the neural tube fails rostrally?

A

Anencephaly - no brain forms

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10
Q

What happens if zipping of neural tube fails caudally?

A

Spina bifida

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11
Q

What are the 3 swellings on the rostral neural tube known as?

A

Primary brain vesicles - will become major parts of adult brain

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12
Q

3 swellings on rostral neural tube and what they will become

A

Prosencephalon - will become forebrain (write prose with forebrain)

Mesencephalon - becomes midbrain (mes = middle)

Rhombencephalon - will become hindbrain (fourth ventricle from this region is shaped like a rhombus)

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13
Q

What does the prosencephalon (future forebrain) get subdivided into and what do these become?

A

Telencephalon - becomes most of cerebral hemisphere (telo = end like telomere)

Diencephalon - becomes thalamus, hypothalamus and optic nerve/retina

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14
Q

What does mesencephalon get divided into?

A

Stays same as boundary of forebrain and hindbrain (midbrain)

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15
Q

What does rhombencephalon get subdivided into and what do these become?

A

Metencephalon - forms pons and cerebellum (met = after, pons and cerebellum sit behind cerebrum)

Myelencephalon - forms medulla (myelo = spinal cord and medulla joins this)

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16
Q

Motor structures vs sensory structures layout

A

Motor structures tend to sit anteriorly (eg ventral horn of spinal cord, precentral gyrus motor cortex)

Sensory structures sit posterioly (eg post central gyrus, dorsal horn)

17
Q

Why are motor structures anteriorly and sensory posteriorly?

A

Basal (floor) and alar (roof) plates form in neural tube

Notocord inducts the ventral (anterior) portion of tube to become basal (floor) plate which becomes motor neurones

Alar (roof) forms in absence of the notocord and becomes sensory neurones

18
Q

Why does the cauda equina develop?

A

Spine grows faster than spinal cord (particularly the lumbar levels)
Therefore lower spinal cord is stretched

19
Q

Why is it they think that neural tube defects can cause hydrocephalus?

A

Cord is tethered at site of defect
As spine grows, cord cannot move with vertebral canal resulting in brainstem being pulled through foramen magnum (fourth ventricle now squished and occluded)

20
Q

What is spina bifida, spina dysraphism/neural tube defects?

A

All the same thing
Spina bifida means double spine - used as you can palate bony ridges either side of midline where dorsal vertebrae failed to fuse
Only severe forms have obvious neural tube defects

21
Q

What causes spina bifida?

A

Failure of closure of the neural tube in the caudal direction
with Posterior vertebral arches failure - incorrect migration of sclerotomes from somites can happen too (neural tube is partly responsible) leading to unfused arches

22
Q

Most severe to least severe neural tube defects

A

Craniorachischisis
Anencephaly
Myelocoele

23
Q

Disorders with normal neural tube but failure of posterior vertebral arch

A

Myelomeningocele
Meningocele
Spina bifida occulta

24
Q

What is craniorachischisis?

A

Entire neural tube remains open - failed to zip caudally and rostrally
Failure of brain and spinal cord to form
Incompatible with life

25
Q

Anencephaly - what is it?

A

‘Without brain’
Cranial neural tube fails to close
Children born alive but not live for long

26
Q

Myelocoele what is it?

A

Myelo - spinal cord
Coele - cyst

Spinal cord fails to develop (lumen of neural tube exposed to the outside world
Usually associated with CSF filled cyst
Neurological deficit and susceptible to meningitis

27
Q

What is a myelomeningocoele?

A

CSF filled cyst containing spinal cord
Transilluminates poorly due to solid tissue in cyst
Neurological deficits likely
Repair needed

28
Q

What is a meningocoele?

A

CSF filled cyst
Cord still within vertebral canal
Transilluminates very well
Good neurological prognosis - no cord in cyst
Cyst will need repairing as predisposes infection

29
Q

What is spina bifida oculta?

A

Lack of posterior vertebral arch
Tuft of hair over defect
No neurological problems
10% of population

30
Q

Preventing neural tube defects

A

Folic acid 400micrograms daily 3 months before conception until week 12

31
Q

What are neural crest cells?

A

Highly specialised population of cells
Multifunctional, contribute to lots of tissues
Derived from neural folds fusing, detach from ectoderm and migrate

32
Q

Cells derived from neural crest cells

A

All neurones in PNS - primary sensory neurones, autonomic post ganglionic neurones, enteric neurones
Schwann cells
Cells of adrenal medulla - postganglionic neurones
Melanocytes
Leptomeninges (arachnoid and pia)
Head mesenchyme - eg pharyngeal arches

33
Q

Tissues recieving significant contribution from neural crest

A

Thymus
Thyroid
Heart
Teeth

34
Q

As neural crest cells migrate from the dorsal part of the embryo, populations get left behind at certain points, what are these? Dorsal to ventral

A

Dorsal root ganglia (sensory neurones)
Sympathetic ganglia (sympathetic postganglionic neurones)
Pre-aortic ganglia (sympathetic postganglionic neurones receiving input from splanchnic nerves
Adrenal medulla (chromaffin cells, which are sympathetic post ganglionic neurones)
Enteric nervous system

35
Q

What are some disorders caused by failure of neural crest cells?

A

DiGeorge Syndrome
Hirschprungs disease

36
Q

What can DiGeorge syndrome manifest as?

A

Immunodeficiency (due to thymus involvement)
Facial anomalies - facial development contribution
Heart anomalies
Hypocalcaemia (too little PT producing PTH involved)

37
Q

What is Hirschprungs disease?

A

Lack of enteric neurones in sections of large intestine
= hypomobility and constipation
Presenting particulary in young children

38
Q

What is the worse form of spina bifida?

A

Rachischisis

Clinical Neuroscience (24 decks)

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