Chapter 2: Brain Development TJHSST Neuroscience Society Prepared by Usnish Majumdar

Development First neurons must be created (differentiated cells) Neurons must then migrate Axon-dendrite migration and connection occurs

3 Layers of Embryo Ectoderm (“ecto” latin = outside) Neural Tissue Skin Neural Tissue Mesoderm (“middle” latin = middle) Endoderm (“endo” latin = within) http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20102/Bio%20102%20lectures/Animal%20Diversity/Protostomes/Lophotrochozoans/Image7.gif

Neural Tube Formed 3-4 weeks after conception Two parallel ridges form from ectoderm tissue Hollow Forms spinal cord and Brain http://scienceblogs.com/retrospectacle/2007/06/neurological_defect_spotlight.php

Cell Differentiation Most embryonic cells are pluripotent stem cells A variety of chemicals signal cells to turn into specialized cells Ectodermal cells are inhibited by molecules, signalling a development into neural cells and not skin cells After neural cell determination: Sonic hedgehog – protein secreted from mesoderm Higher concentration = glial cell Lower concentration = motor neuron Even lower concentration = interneuron

More Cell Differentiation (Yes, this is important) Signals help determine the specific neurotransmitters that can be used by a neuron If neurons are cultured by themselves = norepinephrine Cultured with cardiac tissue = acetylcholine Based on different genes turning off and on

Neuronal Migration in The Brain Neurons produced in center of tube, migrate outward Ventricular zone -> Marginal zone Migration prominent in cortex Mechanisms Neurons migrate along fibers to destination inhibitory interneurons migrate tangentially External forces that can disrupt proper neuronal migration: Alcohol, Cocaine, Radiation, etc.

Connections Axons travel long distances until they find dendrites In the case of a motor neuron, axon may travel from spinal cord to foot

Axon Growth Controlled by Growth Cone Contains receptors for certain signaling proteins Signaling proteins (actually classes of proteins) Netrin Semaphorins Ephrins Possible effects Move forward Stop Recoil Change Direction Axon meets Dendrite and forms synapse Additional molecules help with target recognition Last process is the wrapping of axon in myelin

Cervical Thoracic Lumbar Sacral

Paring Back Neural network is ‘pruned’ to create a more efficient and accurate system (too many connections at first) Apoptosis: programmed cell-death AP Biology: regulated by several proteins Neuron doesn’t receive enough trophic factor to deter these proteins, it dies Each trophic factor supports a specific group of neurons Ex: nerve growth factor = sensory neuron survival

Critical Periods Important period when nervous system must obtain certain critical experiences. “use it or lose it” Enriched environments bolster brain development

Development Continues Even in your late teens, your brain is still maturing. Frontal lobe is last to become connected with myelinated axons Judgement, insight, and impulse control …college students …

Quiz: 5 minutes, 15 Questions