1. The Nervous System: Crossing Neural Membranes Anna Mayersohn, Hannah Medley, Alex Mitchell, and Zahra Pirani

2. Electrical Charges in a Neuron When a neuron is not being disturbed (resting), it maintains a constant electrical charge across its membrane, where the cytoplasm is negatively charged, and the extracellular fluids are positively charged. These charges are reversed by stimuli, or outside forces. When this happens, the cytoplasm becomes positively charged compared to the negative extracellular fluid. The change creates an action potential, which spreads throughout the rest of the neuron (7).

3. Electrical Charges in a Neuron Within a neuron, information is carried through action potentials, which are electrical signals. To carry information to another cell, the electrical signal needs to be converted to a chemical signal (7). http://upload.wikimedia.org/wikipedia/commons/d/d3/Neuron1.jpghttp://upload.wikimedia.org/wikipedia/commons/d/d3/Neuron1.jpg (3)

4. Chemical synapse and Neurotransmitters Chemical synapse: The narrow cleft between two neurons or between a neuron and another cell. The first neuron is the presynaptic neuron and the second is the postsynaptic neuron (7). Neurotransmitters: Signaling molecules that are packaged in vesicles at the end of the axon of the presynaptic neuron (7). Once the molecules are released, they diffuse across the chemical synapse and bind to receptors on the membrane of the cell on the other side (4, 7).. http://www.neurevolution.net/wp- content/uploads/Synapse.JPGhttp://www.neurevolution.net/wp- content/uploads/Synapse.JPG (1)

5. Neurotransmitters Acetylcholine or ACh is a type of neurotransmitter. It acts at a chemical synapse between a motor neuron and a muscle cell. ACh is released from the motor neuron, diffuses across the chemical synapse, and binds to receptors on the muscle membrane where it finally triggers action potentials which initiate muscle contraction (7). Serotonin is a neurotransmitter converted from tryptophan (an amino acid) that binds to serotonin receptor sites in the postynaptic neuron. Serotonin acts on neurons in brain regions that control sleeping and eating habits, sensory perception, temperature control, and emotions(5).

6. The Path of a Neurotransmitter Neurotransmitters start in synaptic vesicles that float in the cytoplasm of the presynaptic neuron. They require an action potential in order to diffuse out of the cell and across the synapse (7). http://www.daviddarling.info/images/neurotransmitter.jpg (2)

7. The Path of a Neurotransmitter When the action potential arrives at the end of an axon, it is converted from an electrical signal to a chemical one in the form of neurotransmitters. The synaptic vesicles that neurotransmitters are packaged in fuse with the membrane of the presynaptic neuron and are expelled from it (exocytosis). The neurotransmitters then diffuse across the synaptic cleft (7). http://www.daviddarling.info/images/neurotransmitter.jpg (2)

8. The Path of a Neurotransmitter The neurotransmitters bind to protein pumps on the dendrites of the postsynaptic neuron. The ions enter the neuron by passing through protein pumps that change shape and create a passageway when specific neurotransmitters bind to them (7). https://static.flatworldknowledge.com/sites/all/files/imagecache/book/58757/fwk-stangor- fig03_005.jpg https://static.flatworldknowledge.com/sites/all/files/imagecache/book/58757/fwk-stangor- fig03_005.jpg (8)

9. The Path of a Neurotransmitter When the neurotransmitter binds to the postsynaptic cell, it either creates (excitatory neurotransmitter) or inhibits (inhibitory neurotransmitter) an action potential in that neuron. In other words, an electrical signal (action potential) triggers the release of a chemical signal (neurotransmitter) when it reaches the output zone. If an excitatory neurotransmitter is released, it can trigger another action potential, which will run though the other neuron in a similar fashion (7).

10. The Path of a Neurotransmitter http://www.youtube.com/watch?v=HXx9qlJetSUhttp://www.youtube.com/watch?v=HXx9qlJetSU (6)

11. References 1. Chemical synapse. 8 Apr. 2007. Neurevolutions. N.p., n.d. Web. 25 Oct. 2011. http://www.neurevolution.net/wp-content/uploads/Synapse.JPG.http://www.neurevolution.net/wp-content/uploads/Synapse.JPG 2. Darling, David. Neurotransmitter. N.d. Internet Encyclopedia of Science. David Darling, n.d. Web. 25 Oct. 2011.http://www.daviddarling.info/encyclopedia/N/neurotransmitter.html.http://www.daviddarling.info/encyclopedia/N/neurotransmitter.html 3. Gorton, Nick. Neuron1.jpg. N.d. Wikipedia. N.p., 16 Aug. 2005. Web. 25 Oct. 2011. http://upload.wikimedia.org/wikipedia/commons/d/d3/Neuron1.jpg.http://upload.wikimedia.org/wikipedia/commons/d/d3/Neuron1.jpg 4. Johnson, George B., and Gary J. Brusca. Biology, Visualizing Life. Washington DC: National Academy, 1990. Print. 5. Landry, Mim J. "Serotonin and impulse dyscontrol: brain chemistry involved in impulse and addictive behavior." Behavioral Health Management Jan.-Feb. 1994: 35+. General OneFile. Web. 24 Oct. 2011.Document URL. http://go.galegroup.com/ps/i.do?&id=GALE% http://go.galegroup.com/ps/i.do?&id=GALE% 7CA15628250&v=2.1&u=mlin_m_wellhigh&it=r&p=ITOF&sw=w. Gale Document Number: GALE|A15628250 6. Neural Synapse. Youtube. jokerwe, 2 Oct. 2007. Web. 25 Oct. 2011. http://www.youtube.com/watch?http://www.youtube.com/watch? v=HXx9qlJetSU.

12. References (continued) 7. Starr, Cecie, and Ralph Taggart. "34.3 Chemical Synapses." Biology, The Unity and Diversity of Life. 9th ed. Pacific Grove: Jack C. Carey, 2001. 580-81. Print. 8. The Synapse. Introduction to Psychology. By Charles Stangor. N. pag. Flat World Knowledge. N.p., Nov. 2010. Web. 25 Oct. 2011. http://www.flatworldknowledge.com/node/285354#stangor-ch03_s01_s02_f01.http://www.flatworldknowledge.com/node/285354#stangor-ch03_s01_s02_f01