Neuroembryology

Question 1

Bilaminar Embryo - before & during implantation the intracellular mass starts to form two epithelial layers

Answer 1

Epiblast - external layer, forms embryo & amnion

Hypoblast - internal layers

Question 2

Primary germ layers & what they form

Answer 2

Ectoderm - outer layer of skin (epidermis) & all structures associated with the skin + The CNS
Mesoderm - supporting tissues of the body; deeper layers of the skin (dermis & hypodermis); CT, muscles etc. ; Immune system; kidneys & reproductive system
Endoderm - forms the hollow organs - lungs, digestive system, inner layer of bladder

Question 3

Why ectoderm give rise to epidermis & CNS?

Answer 3

The skin serves as the interface between external& internal environmental stimuli - essential that changes in the external environment are detected & communicated to the body so that it can adjust accordingly to maintain homeostasis. Epidermis contains receptors that detect these changes in environment and enables info to be transmitted from the skin to the brain to make appropriate changes - closely linked to execute their function well.

Question 4

Notochord

Answer 4

Central axis & lies in mesoderm

Essential for vertebrae development - source of midline signals

Question 5

Neuroectoderm

Answer 5

Derived from ectoderm
Develops into neural tube
Lies superior to notochord

Question 6

Neurulation (22-23 days after fertilization)

Answer 6

Neural tube formation

neural tube –> brain & SC

Question 7

Primary Neurulation

Answer 7

• Multi-site initiation of neural tube closure
• Neuroectodermal tissues differentiate from the ectoderm & thickens into the neural plate
• Neural plate border separates the ectoderm from the neural plate
• Neural plate bends dorsally with 2 end eventually joining at the neural plate borders –> now neural crest
• Closure of the neural tube disconnects the neural crest from the epidermis
• Neural crest cells differentiate to form most of the PNS
• Notochord degenerates & only persists as nucleus pulposus of the intervertebral disc
• Other mesoderm cells differentiate into somites (precursors of axial skeletion & skeletal muscles)

Question 8

Secondary Neurulation

Answer 8

• neural ectoderm & some cells from the mesoderm form the medullary cord
• medullary cord condenses, separates & forms cavities
• Cavities merge to form a single tube –> forms conus medullaris, cauda equina, filum terminale, distale to S2
• Tubes from primary & secondary neurulation eventually connect

Question 9

Formation of neural crest cells

Answer 9

NCC - embryonic tissue that develops in association with dorsal neural tube. Migrate extensively throughout embryo - multipotent & pluripotent
Settle & form multiple cell types - occurs after neural tube closure

Question 10

Neuroectoderm forms the:

Answer 10

Neural tube-->
CNS
Retina
Pineal Gland
Posterior part of pituitary gland

Question 11

SC - Sensory neurons in the

Answer 11

Dorsal horn

Question 12

SC - Motor Neurons in the

Answer 12

Ventral Horn

Question 13

Lateral/immediate Horn

Answer 13

Visceral Afferent
Visceral efferent
=> info about how full is stomach, bladder
(closer to the sulcus limitans)
- neurons involved in ANS

Question 14

What is a dermatome?

Answer 14

Dermatome –> map of the body: areas of skin connected by a single spinal nerve, creates a surface map of body
Damage to spinal nerve can cause symptoms in corresponding dermatome

Question 15

Cranial End of neural tube develops three primary vesicles:

Answer 15

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

Question 16

Five secondary vesicles:

Answer 16

Prosencephalon (forebrain) -->
1. Telencephalon - cerebral hemispheres
2. Diencephalon - Thalami 
Mesencephalon (midbrain) --> 
3. Mesencephalon - midbrain: brainstem 
Rhombencephalon -->
4. Metencephalon - pons & cerebellum 
5. Myelencephalon - medulla oblongata

Question 17

Prosencephalisation in primates

Answer 17

Development of the forebrain - prosencephalon gives rise to the diencephalon & telencephalon

Question 18

Treacher-Collin’s syndrome

Answer 18

Irregularities to head - prevalent in CT

Question 19

Agnathia

Answer 19

Absence of mandible, with low-set ears

Question 20

Anatomy of cauda equina relates to performing a lumbar puncture

Answer 20

Conus medullaris - at L1/2

Spinal needle is usually inserted between L3/4. Not in neonates because conus medullaris is at L3/4

Question 21

Difference between grey & white matter

Answer 21

Grey matter - neuronal cell bodies, axon terminals & dendrites
White matter - composed of long-range myelinated axons, part of neurons which transmit electrical impulses