PSYC 1100 1nd Edition Lecture 6 Outline of Last Lecture I Early Idea of the Nervous System II Reflex III The Neuron Outline of Current Lecture I Nerve Impulse II Communication across the Synapse Current Lecture I Nerve Impulse A nerve impulse is an action potential a change in voltage The inside of the cell is more negative than the outside do to Cl inside and NOT outside of the cell 1 Starts with an electrical RESTING POTENTIAL negative environment inside potential compared to the outside 2 Stimulation of neurons lets Na into neuron which makes the inside more positive 3 When enough Na get in neuron for the potential to be reduced to 55mV suddenly the ion gates to the cell membrane are flung open allowing Na to rush in 4 So much Na enters that the potential doesn t just go to 0mV it shoots all the way up to 40mV so the inside is now positive relative to the outside The ACTION POTENTIAL 5 Ion pumps work to reduce potential back to 70mV by pushing positive ions out K get pushed out because it goes faster than Na then another pump gradually puts Na back out and K back in Note that 55mV is a threshold below that voltage there is no action potential firing is all or nothing More intense stimulation doesn t cause a more intense action potential just more frequent ones up to 1000 sec and more neurons These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute The action potential travels down the length of the axon by depolarizing neighboring areas and travels NOT at the speed of the electrical current in a wire but rather at about 50 to 100 m sec II Communication Across the Synapse 1 The Synapse is a gap between two neurons the presynaptic and the postsynaptic cleft 2 Terminal buttons contain little sacs vesicles of chemicals neurotransmitters at the action potential vesicles burst and release neurotransmitters into the synapse 3 Receptor molecules on the membrane of dendrites are like little locks to be opened neurotransmitters are the keys and this is what opens ion gates to allow Na inside in the first place The shape of the neurotransmitter and receptor molecule is important the shape of both must match in order for the gate to open