Summers

Neurobiology

text: Principles of Neural Science - Kandel, Schwartz and Jessell: Read pages 1017-1086 for this lecture end

V. Development of Neural Systems 			back to III. Cortical Lobes and Behavior

	A. Origins of the Nervous System



		1. Neurulation: Neural tube gives rise to the 6 brain regions

								      

			a. tube develops from neural plate of ectoderm		        



				i. cavity of tube becomes ventricles + central canal of CNS



				ii. tube = neuroepithelium become neurons and glial cells of the CNS



				iii. neural crest cells from the ends of the neural plate and dorsal
				    tube migrate in with, and then away from neural tube



					(1) become sensory and autonomic neurons
					    (+ other non-neural structures)



	B. Regional Differentiation of the Brain



		1. rostral tube forms 3 vesicles: prosencephalon (pro=front, encephalon=head; or
		   forebrain), mesencephalon (mes=middle; or midbrain), and rhombencephalon
		  (rhomb = lozenge-shaped; hindbrain)      
 												

											        

		2. forebrain (a+b) and hindbrain (c+d) subdivide			        



			a. telencephalon (endbrain) becomes the cerebral cortex, basal ganglia,
			   hippocampal formation and amygdala



			b. diencephalon (betweenbrain, lies between the cerebral hemispheres) gives rise
			   to the thalamus, hypothalamus and retina



				i. hypothalamus connects with sac (Rathke's pouch) from the roof of the
				   mouth to form the pituitary



			c. the metencephalon (afterbrain) develops into the pons and cerebellum



			d. the myelencephalon (myel=fibers) becomes the medulla



		3. the most caudal portion of the neural tube remains undivided and becomes the
		   spinal cord



	C. Functional Development of Spinal cord and Brain               



		1. embryonic spinal cord and brain have similar and contiguous elements: 2 zones of
		   proliferating cells



			a. alar plate: becomes somatic and visceral sensory neurons in the brain



				i. ascending sensory neurons and interneurons  of dorsal spinal cord



			b. basal plate: motor control of visceral and somatic function in brain



				i. motor neurons and interneurons in spinal cord



				ii. basal plate neurons in the spinal cord also become autonomic neurons



	D. C shape of cerebral hemispheres, basal ganglia (caudate
	  nucleus), limbic and lateral ventricles come from rapid cell division:		



		1. first rostrally (frontal lobes), then dorsally (parietal), finally posterior and
		   inferiorly (occipital and temporal)



	E. Gross anatomical structure emerges from steps of  Neuronal development

												

		1. cell differentiation or neurogenesis follows proliferation of precursor cells


		2. neurons migrate to final location and begin to grow axons, dendrites and in size



			a. mechanisms of axonal growth also stimulate direction of growth and synapse
			   formation



				i. final function depends on competition among synapse connections
				   and death of unnecessary neurons



					(1) more neurons are made than needed because, with few
					    exceptions, they cannot be replaced



						(a) replacement axons and synapses can be made



	F. Neurotrophic factors control the migration, growth, directional axon development,
	   synapse formation and regeneration of damaged axons and synapses

									      

		1. GH and growth factors (IGFs, PDGF, EGF) stimulate proliferation of precursor
		   cells



		2. Nerve Growth Factor (NGF) and other neurotrophins (BDNF, NT3,4,5,
		 IL1, EGFs, FGFs ) control growth of neurons but also, directional growth
		 of axons, synaptogenesis, and which cells will eventually survive



	G. Determination of Neurotransmitter


		1. surrounding cells can induce production of appropriate neurotransmitter


			a. eg: sympathetic cells alone in vitro produce NE


				i. cultured with somatic or heart cells produce ACh


		2. neurotrophins may play a role in this induction (since they create synaptic
		   connections)

VI. Nerves, Neurons and Glia

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