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Unformatted text preview: 1 Outline 3: How Neurons work : I. Properties of Neuronal Membranes A. Membranes consist of a lipid bilayer studded with proteins. These proteins form ion channels and receptors 1. Ion channels- pores formed by membrane spanning proteins that permit specific ions to enter and exit the cell 2 types of ion channels: Passive ion channels are always "open". The flow of ions through passive channels is determined by concentration and electrical gradients (described below). Gated ion channels open and close in response to specific signals. 2 types of gated ion channels: voltage-gated channels- these open or close in response to changes in the electrical state (voltage) of the neuron chemically-gated channels- these open or close in response to neurotransmitters binding to receptors 2. Receptors- membrane proteins that bind with neurotransmitters and result in the opening or closing of ion channels. *More on this below*. B. Membrane potential 1. In most living cells, the inside of the cell is negatively charged relative to the outside of the cell. - This results from a greater concentration of negatively charged ions inside the cell compared with outside the cell. -The difference in the charge, inside versu outside, is called the transmembrane potential difference or sometimes "membrane potential" for short. 2 2. Resting membrane potential . In neurons at rest, the transmembrane potential difference tends to be around -55 to -75 mV (difference inside versus outside). C. What causes the resting membrane potential difference? 1.The inside of the cell is more negatively charged than the outside of the cell because of the unequal distribution of certain types of negatively and positively charged ions: The extracellular fluid is rich in sodium ( Na+ ) and chloride ( Cl- ) ions The intracellular fluid is rich in potassium ( K+ ) and large negatively charged protein ions ( A- ) 2. This unequal distribution is maintained by the following pressures: a. concentration gradients and electrical gradients (aka electrostatic pressure) Concentration gradients cause ions to move from areas of high concentration to low concentration....
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- Spring '08