CNS Anatomy

Question 1

Explain the layers and stages of Gastrulation.

Explain the layers and stages of Neurulation.

Answer 1

Look at posters

Question 2

What is patterning & why is it important?

Answer 2

Signalling produces the different structures of the spinal cord and brain.

Expression (or repression) of specific transcription factors ultimately decides the fate & formation of parts of those structures.

Patterns of transcription factors provides a specific genetic pattern for a group of cells within the neural tube (D/V or AP).

It allows differential formation of precursors.

Question 3

Explain how patterning result in the spinal cord.

Answer 3

1. First a signalling molecule gradient forms (dorso-ventral patterns)
2. Sonic hedgehog (from notochord & floor plate)- SHH
3. Bone morphogenetic proteins (from the forsal region)- BMP’s

Opposing gradients created by these signalling molecules result areas of differential gene expression.

Question 4

Identify where the:
1. Dorsal horn
2. Intermediate zone
3. Ventral horn

are located in spinal grey matter.

Where in those regions can you find the sensory neurons, interneurons & motor neurons.

Answer 4

check image on slide 8

neurons= dorsal horn
interneurons= intermediate zone
motor neurons= ventral horn

Question 5

What is retinoic acid

Answer 5

RA is a signalling molecule implicated in Hox gene expression & petterning

it is a powerful teratogen
used in acutane & in general for treatment in acne

Question 6

where is the main source of RA found?

Answer 6

RA is found in the mesoderm immediately adjacent to the neural tube

it diffuses into the tube to form a gradient of RA which drives differential gene expression

Question 7

what does Retinoic Acid bind to? & what do the act like?

Answer 7

RA receptors. They act as transcription factors to activate specific genes.

Question 8

Describe & explain the influence of ventral midline signals on spinal cord expression.

Describe the formation of different cell types within spinal cord- SHH/ BMP gradients affecting gene expression.

Answer 8

check slide 10

check slide 11

Question 9

What does inappropriate or blocked signalling cause?

Answer 9

Alterations to closure of neural tube and differentiation of nervous system

• Spina bifida
• Anencephaly
• Holoprosencephaly (initial formation of seperate cerebral hemispheres are distrupted
• Folic acid deficiency
• Alcohol
• Teratogens (e.g. thalidomide)

Question 10

Describe slide 13

Answer 10

Embryonic brain:
1. Prosencephalon -> Telencephalon & Diencephalon
2. Mesencephalon
3. Rhombencephalon -> Metencephalon & Myelencephalon
4. Spinal chord

1. Telencephalon -> Cerebral cortex & basal ganglia, hippocampus, olfactory bulb, basal forebrain [lateral ventrical]
2. Diencephalon -> dorsal thalamus & hypothalamus [third ventricle]
3. Mesencephalon-> midbrain [cerebral aqueduct]
4. Metencephalon -> cerebellum & pons [fourth ventricle]
5. Myelencephalon -> medulla [fourth ventricle]
6. Spinal chord -> spinal cord [central canal]

Question 11

Describe & explain the nervous system development in stages.

Answer 11

Slide 14 &15

Question 12

Describe & explain hindbrain and hox genes

Answer 12

Rhombomeres- Repeating subunits in hindbrain

• Hox genes – expressed in banded patterns – expression borders (IT coincide with rhombomere boundaries)

• Creates segmental formation similar to Drosophila
• Formation of the cranial nerves (focus on motor nerves)
• Deletion or misexpression of Hox gene(s) may lead to loss of cranial nerves (but there is some redundancy)
• Knocking out all Hox genes  rhombomere 1 only (ground state)
• Retinoic acid – signalling molecule implicated in Hox gene expression

Question 13

Describe & explain hindbrain patterning

Answer 13

Knocking out HOX gen removes rombomere 4&5 resulting in abducent nerve not attaching & the facial nerve not attaching correctly like normal either (it is squished)

r2&3- trigeminal nerve
r4- facial nerve
r5- abducent nerve
r6- glossopharyngeal nerve

Question 14

Describe & explain knockout Hox 1a

Question 15

What are the midbrain-hindbrain boundaries?

Answer 15

1. Local organising centre- needed for development of midbrain and cerebellum
2. grafting of organiser & signalling molecules can produce ectopic MB-HB
3. FGF8-principal signalling molecule
4. Otx-2 (forebrain to midbrain) & Gbx-2 (anterior hindbrain to cerebellum)- oppose each other across boundary
5. Produce clearly defined border- where Otx2 and Gbx2 cross-inhibit, FGF8 is expressed