CNS Development

Question 1

What is the time period of the development of the brain?

Answer 1

Begins in the 3rd post conception week…

and continues well into late adolescence/early adulthood and beyond

Question 2

Is brain development influenced by genes or environment?

Answer 2

Both!

Question 3

What role do genes play in development of the brain?

Answer 3

Genes carry the information which when decoded will determine:

1. The correct sequence and evolution of the brain from conception to neuronal proliferation, migration and reorganisation
2. Development of dendritic and axonal interconnections
3. They also determine the development of synapses, complex chemical structures called receptors and chemical messaging substances called neurotransmitters

Question 4

What environmental factors influence development of the brain?

Answer 4

INTRAUTERINE ENVIRONMENT

• maternal health and disease (maternal PKU)
• insults which may be continuous throughout pregnancy/episodic
  
  • alcohol exposure
  • cytomegolovirus
  • infection
• placental function and fetal nutrition

EXTRAUTERINE ENVIRONMENT

• physical factors such as nutrition, environmental toxins
• emotional and social factorrs e.g. neglect and lack of stimulation
• exposure to drugs, alcohol and other related substances

Question 5

How is the embryonic period defined?

Answer 5

Conception to Week 9

Question 6

What occurs during the embryonic period in regards to brain development?

Answer 6

• 2 layered embryo: epiblast and hypoblast
• primitive streak AND a primitive node
• migration of cells through streak –> and then rostral-caudal migration
• determined by nodal signalling

Question 7

1st Year Revision…

What is gastrulation?

Answer 7

Results in the development of a three layered embryo

• Ectoderm –> skin, nails, hair and neural tissue
• Mesoderm –> muscle, bone, cartilage and vascular system
• Endoderm –> gut and respiratory system

Question 8

Discuss the neural tube

Answer 8

• First well defined neural structure to form
• Occurs at day 20-27
• Neural progenitor cells form the neural plate
• Neural groove
• Neural tube formation

Question 9

Discuss the neural tube again this time drawing a diagram of its formation

Answer 9

Question 10

What is the relevance of the neural tube to development of the brain?

Answer 10

The neural progenitors line the inside of the neural tube- termed the ventricular zone

• the HOLLOW CENTRE of the tube will become the VENTRICULAR SYSTEM and the central channel of the SPINAL CORD
• the anterior/ROSTRAL tube will become the brain
• CAUDAL tube will become the spinal cord

Question 11

How many primary brain vesicles are there? At what stage of embyronic development are they present?

Answer 11

There are 3 primary brain vesicles:

1. Prosencephalon (forebrain)
2. Mesencephalon (midbrain)
3. Rhombencephalon (hindbrain)

They’re seen in a 3-4 week embryo

Question 12

How many secondary brain vesicles are there? At what stage of embryonic development would you expect to see them appear?

Answer 12

There are 5 secondary brain vesicles:

1. Telencephalon
2. Diencephalon
3. Mesencephalon
4. Metencephalon
5. Myelencephalon

These 5 secondary brain vesicles are seen in a 5 week embryo

Question 13

Draw out the development of the brain vesicles

Answer 13

Question 14

Define ‘neocortex’.

Answer 14

‘the largest and evolutionarily most recent portion of the cerebral cortex, composed of complex, layered tissue the site of most of the higher brain functions.’

-Dictionary.com

Question 15

Explain neocortical patterning

Answer 15

The mature neocortex has distinct functional and structural ‘areas’

Signalling molecules:

• Emx2 and Pax6
• High conc. Pax6 with low conc. of Emx2 induce progenitor to differentiate into motor neurons
• Low conc. Pax6 and high conc. Emx2 induce visual cortical neurons