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Biological Sciences
BISC 101
Timothy Swartz

Neurons nerve cells and synapse L7Glial cells are an important component of the CNS 15 trillion in human brainAstrocytesprovide structural support regulate extracellular concentrations of neurotransmittersMicroglia role in immune function in CNS1 All cells have a membrane potential and electrical charge difference across the plasma membrane 2Ion pumps and ion channels establish and maintain a resting membrane potential 3 in neurons transient changes in this resting membrane potential generates and action potential electrical signal 4 Propagation of the action potential along the nerve cell axon transmits information information coded in action potentials is transmitted from cell to cell at synapses 5 Plasticity of synaptic connections underlies memory and learningFormation of resting membrane potential key role of N and K1 Ion concentrations inside and outside neuron differ2 Concentration gradients exist across the membrane 3 Selectively permeable membrane kNa4 concentration gradients aremaintained by Na KpumpsHigh K and Low Na inside the cell Low K and high Na outside the cellHow1 NaK pump generates and maintains concentration gradients for Na and K transporting 3 Na out for every 2K in 2 Little net inward diffusion of Na due to few open resting Na channels3 Significant outflow of K due to large number of open resting K channelsGraded potential small change in membrane potential where magnitude varies with size of stimulusAction potential all or none constant magnitude and can regenerate along axonRole of voltagegated ion channels in generation of an action potential1Resting state a Voltagegated Na and K ion channels are closed b Nongated channels maintain resting membrane potential2Depolarization a depolarization opens some voltagegated Na channels allowing Na to diffuse in b further depolarizes membranes allowing even more Na in3Rising phase of action potentiala if depolarization reaches threshold b then all voltagegated Na channels open positive feedback cycle4Falling phase of action potential a voltagegated Na channels rapidly inactivate close b delayed voltagegated K channels open causing rapid K outflow
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