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Clinical neuroscience > Development of the central nervous system > Flashcards

Development of the central nervous system Flashcards

1
Q

What is gastrulation?

A
  • Process whereby outer layer of bilaminar disc invaginates at primitive streak to produce 3 cell layers
  • Endoderm, mesoderm, ectoderm
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2
Q

What are the 2 layers of the embryonic disc?

A
  • Epiblast
  • Hypoblast
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3
Q

From where does the nervous system derive?

A
  • Ectoderm
  • Becomes skin and neural tissue, as well as neural crest
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4
Q

Which key structure develops in the midline of the mesoderm?

A
  • Notochord
  • Grows towards where head will be
  • Instructs overlying ectoderm to invaginate and form neural tube
  • Via chemical signals
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5
Q

What is neurulation?

A
  • Process of formation of neural tube
  • Induced by notochord
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6
Q

Outline the process of neurulation

A
  • Day 22
  • Elevation of neural folds
  • Surface over top of invagination needs to be sealed to create a fully formed neural tube
  • Part that fuses first corresponds to cervical level of adult spine
  • Fusion then proceeds cranially and caudally
  • When folds fuse, neural crest cells detach and migrate to their ultimate destinations
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7
Q

What are the primary brain vesicles?

A
  • Rostral neural tube displays 3 swellings which go on to form major parts of the adult brain
  • Prosencephalon - forms forebrain
  • Mesencephalon - becomes midbrain
  • Rhombencephalon - becomes hindbrain
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8
Q

What developments have occurred in the embryo by day 40 of development?

A
  • Cerebral vesicles have become very elaborate
  • Very prominent swellings and subdivisions of basic forebrain, midbrain and hindbrain have formed
  • Special sense organs have started to develop
  • PNS has started to develop
  • Sympathetic chain has formed
  • Cranial nerves have formed
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9
Q

What has happened to the forebrain by day 43 of development?

A

Forebrain is divided into telencephalon and diencephalon
- Telencephalon forms cerebral cortex, basal ganglia, hippocampus
- Diencephalon forms thalamus, hypothalamus and optic nerves

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10
Q

Outline the fundamental relationship between the sensory and motor systems

A
  • Motor structures tend to sit anteriorly
  • Sensory structures tend to sit posteriorly
  • Due to development of basal and alar plates in neural tube
  • Pattern seen at all levels of nervous system
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11
Q

Outline the development of cauda equina

A
  • Initially (at 60 days) spinal cord and vertebral column are same length
  • However, spine grows faster than spinal cord (particularly at lumbar levels)
  • Lower portions of cord are stretched, creating cauda equina
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12
Q

Why do neural tube defects predispose to hydrocephalus?

A
  • May be caused by tethering of cord at site of defect
  • As spine grows, cord cannot move within vertebral canal
  • Results in brainstem being pulled through foramen magnum and becoming occluded
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13
Q

Outline the developmental basis of neural tube defects

A
  • Failure of neural tube to zip up
  • Failure to close in cranial direction involves the brain
  • Failure to close in caudal direction caudal direction involves spine/spinal cord
  • Failure of development of posterior vertebral arches at one or more levels
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14
Q

List the different neural tube disorders from most to least severe

A
  • Craniorachischisis
  • Anencephaly
  • Myelocoele
  • Myelomeningocoele
  • Meningocoele
  • Spina bifida occulta
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15
Q

Outline craniorachischisis

A
  • Entire neural tube remains open
  • Hence failure of both brain and spinal cord to form
  • Incompatible with life
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16
Q

Outline anencephaly

A
  • Cranial neural tube fails to close
  • Hence failure of brain to form
  • Child may be born alive but does not live for long
17
Q

Outline meningomyelocoele

A
  • A CSF-filled cyst containing spinal cord
  • Transilluminates relatively poorly
  • Children may have neurological deficits - roots are stretched and damaged
  • Repair is necessary
18
Q

Outline meningocoele

A
  • Presence of a CSF filled cyst
  • Cord is sited within vertebral canal
  • Transilluminates brilliantly
  • Children tend to have a good neurological prognosis
  • Cyst requires repair as it predisposes child to infectiom
19
Q

Outline spina bifida occulta

A
  • Only anomaly is lack of posterior vertebral arch
  • May manifest a sign such as a tuft of hair or a large naevus over defect
  • Not associated with significant neurological problems
  • Occurs in about 10% of the population
20
Q

How are neural tube defects prevented?

A
  • Folic acid taken from 3 months before conception and until week 12 of pregnancy
  • Unknown reason why folate helps
21
Q

What is the neural crest?

A
  • A highly specialised population of cells that are a vertebrate innovation
  • Multifunctional, contributing to a wide range of tissues
22
Q

What forms the neural crest?

A
  • Derived from point at which neural folds fuse
  • When surface of ectoderm is reconstituted
  • Neural crest cells become detached from ectoderm and then migrate to distant targets
23
Q

What are the derivatives of the neural crest?

A
  • Sensory neurones in the PNS
  • Post-synaptic autonomic neurones
  • Enteric neurones
  • Schwann cells
  • Adrenal medulla cells
  • Melanocytes
  • Arachnoid and pia mater of meninges
24
Q

Which tissues receive a significant contribution from the neural crest?

A
  • Thymus
  • Thyroid
  • Parts of the heart e.g. spiral septum
  • Teeth
25
Q

Which disorders occur due to defects in the neural crest?

A
  • Di George syndrome
  • Hirschsprung’s disease
26
Q

How does Di George syndrome manifest?

A
  • Immunodeficiency
  • Facial anomalies
  • Heart anomalies
  • Hypocalcaemia
27
Q

How does Hirschsprung’s disease manifest?

A
  • Lack of enteric neurones in sections of large intestine
  • Leads to hypomobility and constipation
28
Q

What has happened to the hindbrain by day 43 of development?

A

Hindbrain is divided into metencephalon and myelencephalon
- Metencephalon gives rise to pons and cerebellum
- Myelencephalon gives rise to medulla

Clinical neuroscience (19 decks)

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