1 Psychology 304: Brain and Behaviour Lecture 17

2 Development of the Nervous System 1. What are the phases of prenatal neurodevelopment?

3 Announcements 1. This morning, Naghmeh informed me that she made an error in scoring the labels for version 2 of the exam. She is in the process of correcting the scores. I will post the revised grades on the course website as soon as they are available. 2. Students who are absent from class and/or exams due to illness are now required by the University to indicate their absence using the online reporting system available through the Student Service Centre.

4 3. As a consequence of my absence due to illness, we will not be able to discuss chapter 11 (Motor Control and Plasticity) in class. As a result, this chapter will not be included on the final exam.

5 What are the phases of prenatal neurodevelopment? Prenatal neurodevelopment is marked by a number of discrete phases: 1. Development of the neural plate and neurogenesis.  Within 1 week of conception, the embryo shows three cell layers: The ectoderm, mesoderm, and endoderm. The nervous system develops from the ectoderm, often referred to as the neural plate.

6 Formation of Neural Tube

7 Electron Micrograph of Neural Tube Closure

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9 Neural Tube

10 Embryonic Neural Tube Development

11  The anterior end of the neural tube ultimately develops into the forebrain, midbrain, and hindbrain.  The posterior end of the neural tube ultimately develops into the cerebral ventricles and central canal of the spinal cord.  Once formed, the cells that line the inner surface of the neural tube—that is, the ventricular zone—divide and proliferate.

12 Forebrain Midbrain Hindbrain Spinal cord CNS Development from the Neural Tube

13 2. Cell migration  Once cells have developed in the ventricular zone, they migrate to target locations.  Migration occurs in two directions: radial migration and tangential migration.

14 Directions of Migration

15  Cells migrate via two processes: somal translocation and glia-mediated migration.  Cell migration is guided be cell-adhesion molecules.

16 Processes of Migration

17 Glial-Mediated Migration

18 3. Cell differentiation  Once cells have reached their target locations, they differentiate into region-specific neurons and glial cells.  Cell differentiation is determined by genetic programs and cell-cell interactions.

19 4. Axon growth and synaptogenesis  Once cells have differentiated into region-specific neurons, axons and dendrites begin to grow from them.  Axonal and dendritic growth are directed at appropriate targets.  Filopodia and lamellipodia extend and retract from growth cones, in search of appropriate targets.  Chemoattractants and chemorepellents guide axonal growth.

20 Growth Cone with Filopodia

21 Filopodia and Lammelipodia

22 Development of the Nervous System 1. What are the phases of prenatal neurodevelopment?