Embryology

Question 1

Where does fertilisation happen?

Answer 1

Ampulla of the uterine tubes

Question 2

What are the key events in the first 7 days post fertilisation?

Answer 2

D1: Fertilised and becomes a zygote
D3: Becomes a morula (ball of cells)
D4: Enters uterus as a blastocyst
D7: Trophoblast (edge) cells implant into uterus and surround inner cell mass

Question 3

What does the inner cell mass split into between wk 1-2?

Answer 3

Epiblast (becomes amniotic fluid)
Hypoblast (becomes yolk sac)
Between these is the embryonic disc which becomes the embryo

Question 4

What key event happens 3 weeks into development?

Answer 4

Primative streak forms (from caudal to rostral end). The three germ layers form

Question 5

What is the notochord from and what does it do?

Answer 5

Notochord forms from the mesoderm, it secretes proteins to differentiate ectoderm tissue:
No inhibition from notocord proteins: Cell becomes skin
Inhbition from notochord proteins: Cell becomes neural

Question 6

What is the role of sonic hedgehog protein? Where is it produced from?

Answer 6

Secreted from mesoderm, cells which receive:
High conc: Become specialised glial cells
Med conc: Become motor neurons
Low conc: Become interneurons

Question 7

Sonic hedgehog binds to a receptor on neural cells coded for by which gene?

Answer 7

PTCH1

Question 8

Where are neurons produced in the embryo?

Answer 8

Produced in central canal of neural tube and travel from ventricular (inner) zone to the marginal (outer zone) where they grow and migrate to the brain

Question 9

How do cells move in the primiative streak?

Answer 9

Migrate along glial fibres from caudal (tail) end to rostral (head) end

Question 10

How can cocaine/ alcohol/ radiation affect embryo growth?

Answer 10

Prevent nerve cell migration = misplacement of cells = retardation/ epilepsy

Question 11

By what process do axons grow?

Answer 11

Growth cones (neural cell outgrowings) search for signal molecules and causes advancement/ turning/ pausing

Question 12

How does the brain remove improper connections?

Answer 12

Initially a child has double the number of neurons and adult has. Sculpting action removes improper or redundant connections as nerves need constant presence of trophic factors (nerve growth factor) to survive

Question 13

Why is childhood critical to development?

Answer 13

Physical/ social deprevation = Less neurons made

Stimulation = More neurons made

Question 14

Where does myelination take place?

Answer 14

From back of brain to front (so frontal lobe often not fully myelinated til 20’s)

Question 15

Where does the neural plate form from?

Answer 15

Ectodermal tissue just opposite the primitive streak

Question 16

What is neurulation?

Answer 16

At D20 the edges of the neural plate begin to elevate, forming neural folds, the groove formed is the neural tube- this becomes the brain and spinal cord

Question 17

When does the neural tube close?

Answer 17

Rostral (head) end: D25

Caudal (tail) end: D27

Question 18

What are the three primary vesicles formed at 3wks?

Answer 18

Proencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)

Question 19

From which brain regions does the cerebrum originate embryologically?

Answer 19

Proencephalon > telencephalon > cerebrum

Question 20

The diencephalon consists of what and forms from which primary vesicle at 3wks?

Answer 20

Thalamus, hypothalamus, epithalamus

From proencephalon > diencephalon

Question 21

Where does the midbrain (brainstem) originate embryologically?

Answer 21

Mesencephalon

Question 22

What forms from the metencephalon?

Answer 22

Rhombencephalon > metencephalon > pons + cerebellum

Question 23

Where does the medulla oblongata originate from embryologically?

Answer 23

Rhombencephalon > myelencephalon > medulla oblongata

Question 24

Which primary and secondary vesicles does the cerebellum come from embryologically?

Answer 24

Rhombencephalon > metencephalon > pons + cerebellum