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MSU CHMY 121IN - Action Potential

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CHMY 121 1st Edition Lecture 2Review- Nervous System- Organized so that adjacent neurons send info. to adjacent muscles.- Organized so that adjacent neurons receive info. from adjacent areas.- Not all body areas are allocated the same amount of “real estate” in the cortex.- Right vs. left Symmetry- right primary motor cortex controls movements on theleft side of body- left primary motor cortex controls movements on theright side of body- touch sensations from right side of body go to leftsomatosensory cortex- touch sensations from left side of body go to rightsomatosensory cortex- Right vs. Left Asymmetry- Left has a lot to do with speech- Right has a lot to do with visual processing- Link between the two is the corpus callosumTodays Lecture• Wernicke’s Area• located in left temporal lobe• helps people understand words and choose from memory the words needed to convey information• Wernicke’s Aphasia• fluent aphasia• language comprehension & production is hurt• use lots of little words (of, on, the, from, a, but) but many nouns get replaced by pronouns and many verbs get replaced by wrong verb• person can’t come up with the correct words from memory• Synaptic TransmissionThese 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 synapse is the gap between two neurons so synaptic transmission is when a neuron sends a message to another neuron across the synapse.• The transmission of information across the synapse is done via chemicals. •• Synaptic Transmission• Membrane of a neuron is semipermeable• Keys• Presynaptic membrane• Axon terminal• Neurotransmitters• Locks• Presynaptic membrane• Axon terminal• Neurotransmitters• Many charges inside and outside of the membrane but there are more negative on the inside then positive. So we say there is a negative charge across the membrane• Fast Synaptic Transmission• Excitatory• Opens sodium (Na+) channels• Results in partial depolarization• Makes the charge of the post synaptic neuron morepositive (from -70mv to -60mv or -50mv etc.)• Makes the post synaptic neuron more likely to fire orrespond• Inhibitory • Opens chloride (Cl-) channels or• Opens potassium (K+) channels• Makes receiving neuron more negative (from -60mvto -70mv to -80ms, etc.) • Post synaptic neuron is now less likely to fire orrespond• Synaptic transmission recap• Neurotransmitters go across the synapse to change the charge across the membrane of the postsynaptic neuron.• So the charge across the membrane is constantly fluctuating in response to neurotransmitters.• Question- So how does the signal get from the dendrites and cell body to the end of the axon so that it can be passed on• Answer- Action Potential(occurs on an axon)• The Action Potential• The neuron at rest• The major players:• inside the axon• amino acids (A-)• potassium (K+)• outside the axon• sodium (Na+)• chloride (Cl-)• the situation is everyone is chillin’ at -70 millivolts• Action potential continued• Depolarization• depolarization is started whenever the charge in the front end of the axon hits a certain threshold (for instance -40 mv)• depolarization of the front end causes depolarization further along the axonand so on and so on until the end (the axon terminal)• What causes depolarization?• Sodium (Na+) channels open up• Na+ moves into the axon• Inside the axon the charge goes from -70 mv to -60 mv to -50 mv...• Repolarization• Sodium (Na+) channels close so no more Na+ moving in• Potassium (K+) channels open&K+ starts moving out• What is The Result?• The charge goes from -10 mv to -20 mv to -40 mv to -70mv• Sequencerestdepolarizationrepolarizationrestdepolarizationrepolarization etc.• Depolarization followed by repolarization• After repolarization the Na+ and the K+ are on the wrongsides of the axon membrane• Sorting things out after repolarization• Sodium Potassium Pump• moves sodium (Na+) out of axon• moves potassium (K+) into axon• requires lots of energy• What affects speed of the signal?• Bigger Axon Diameter & ThickerMyelin• Both cause faster signals• Once the axon terminalreceives a transmissionfrom the axon, it mustsend the signal (inchemical form) to thedendrites (or other cells) itis connected to.Action Potential(Axon) Graded Potential(Dendrites)Message from one end of the neuron to the otherMessage from one to the nextAll or NoneGraded  not all or noneDepolarization Partial


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