Neurons and Synapses

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Biological Sciences
BISC 101
Tony Williams

Chapter 4849 Neurons nerve cells and Synapses Neuron Structure and organization y Interneuron motor neuron sensory neuron y D CBA flow of action potential y Synapse and NTs Key concepts y All cells have a membrane potential an electrical charge differenceacross the PM y In neurons changes in this resting membrane potential generates an action potential electrical signal y Propagation or movement of the action potential along a neuron transmits information y Information coded in action potential is transmitted from cell to cell at synapses y Plasticity of synaptic connections underlines memory and learningFormation of resting membrane potential key role of Na and K y Ion concentrations differ outside and inside the neuron y Concentration gradients exist across the membrane y Selectively permeable membrane is more permeable to K than Na y Concentration gradients are maintained by NaK pumps y Resting membrane potential 60 mV to 80 mVFormation of resting membrane potential NaK pumps and ion channels y Sodiumpotassium pump generates and maintains concentration gradients for both Na and K o 3 Na OUT for every 2 K IN net loss of 1 charge y Little net inward diffusion of Na due to few open resting Na channels y Significant outflow of K due to large number of K channels openCan measure changes in membrane potential of neurons due to voltagegated ion channels y Hyperpolarization increase in K permeability inside becomes more negative y Depolarization increase permeability to Na inside becomes more positive y Action potential triggered by depolarization that reaches the thresholdAchieving action potential 1 At resting potential most voltagegated sodium channels are closed 2 Depolarization some sodium channels open allowing Na to diffuse 3 Rising phase of action potential Na channels stay open if depolarization reaches threshold positive feedback cycle 4 Falling phase of action potential Na channels inactivate K channels slowly open rapid outflow of K ions
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