1. Presentation 24 Neural Development
Lecturer: Dr Lucy Patston

2. Overview of this PPT and Learning Objectives
Fetal brain development
Neural tube formation
Understand and be able to reproduce (Ha!) the process of brain development during the three stages of fetal development

3. Introduction
Genetic and environmental influences act on cells throughout development of nervous system
Processes: cell growth, migration, differentiation
Even cell death, axonal retraction help to create the mature brain
Some processes completed in utero, others in first years after birth (by no means “ready to go” at birth! Gazelle anecdote)

4. Developmental Stages in Utero
We will only be considering the brain development of babies
Humans undergo 3 developmental stages:
Pre-embryonic
Embryonic
Fetal (Major brain development occurs very early in this stage)

5. Pre-embryonic Stage Conception to day 14
Fertilization (usually fallopian tube)
Cell begins divisions -> solid sphere cells
Blastocyst (D) opens into a cavity
Outer layer becomes placenta, inner cell mass becomes embryo
Implants in uterus (day 7), inner cell mass forms embryonic disk of ectoderm and endoderm (future brain)!

7. Embryonic Stage Day 15 to end of 8th week (Organs are formed)
Ectoderm develops into sensory organs, epidermis and nervous system
Mesoderm develops into dermis, muscles, skeleton, excretory and circulatory systems
Endoderm develops into gut, liver, pancreas and respiratory system

8. Fetal Stage Beginning of 9th week to birth
Nervous system develops more and myelination begins

9. Formation of Nervous System
During embryonic stage nervous system tissue coalesces to form a neural tube running down the back of the embryo
When tube closes (right to the ends) brain formation begins
Neural tube formation (Day 18-27)
Brain formation (Day 28 ->)

10. Neural tube formation (Day 18-27)
Nervous system begins as longitudinal (head to “tail”) thickening of ectoderm – the neural plate

11. Neural tube formation
Midline of neural plate moves toward interior, creating the neural groove
Somites begin to form

12. Neural tube formation When folds touch, neural tube is formed
The neural crest separates from the tube and from the remaining ectoderm
The neural crest is a mass of tissue that differentiates into: dorsal root ganglia, spinal nerves, ganglia of cranial nerves, cranial nerves, ganglia of ANS, adrenal medulla and meninges

14. Neural tube formation
Neural tube first closes in cervical region then “zips up” front to back, leaving open ends (neuropores)
(Superior (head) neuropore closes Day 27, inferior (tail) neuropore Day 30)

16. Somites (developing structures)
Somites spherical clusters of cells adjacent to mesoderm
Anterior part (sclerotome) becomes vertebrae and skull (e.g., “somite 1” becomes occipital bone; “somite 10” becomes C6)
Posterior part (myotome) becomes skeletal muscle
Lateral part (dermatome) becomes dermis

17. Developing Structures
By Day 26 the neural tube differentiates into:
Mantle layer: which will become gray matter
Marginal layer: which will become axons of cells in mantle layer and glial cells
Ependymal layer: which will become the lining of the central canal of spinal cord and ventricles
(the hole in the tube becomes the ventricles and the central canal)
When tube and crest have developed both move inside embryo, remaining overlying ectoderm will become skin
Ependymal layer

18. Developing Structures
Cells of mantle (middle) layer proliferate inside neural tube and start to separate into dorsal and ventral sections (look familiar?!)
Axons from cells in motor plate grow out of neural tube and innovate myotome region of a somite
Neurons with cell bodies in motor plate become motor neurons (innervate muscles) and interneurons
Motor plate becomes ventral horn of the mature spinal cord
Association plate becomes dorsal horn of mature spinal cord

19. Fetal nervous system
Somite
Adult nervous system

20. Developing Structures
Neural crest separates into two columns (each side of tube)
Some neural crest cells become peripheral sensory neurons and grow two “processes”, one connects to spinal cord, one to dermatome of somite

21. Developing Structures
As foetus develops the spinal column grows faster than the cord
Cauda equina: The collection of lumbosacral nerve roots that extend inferior to the end of the spinal cord
Filum terminale: A continuation of the dura, pia, and glia connecting the end of the spinal cord with the coccyx