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Transcript
Pg. 109 Resting Potentials Think back to chemistry! Opposites attract! Potentials Key Point #1: All cells exhibit a membrane potential Difference in electrical charge Cytoplasm (-) and ECM (+) Represent this as voltage Resting Potential Key Point #2: The resting potential of the cell (inside) is the membrane potential when NOT transmitting signals -70 mV Sodium/potassium pumps maintains the potential Active transport ATP AGAINST the gradient Key Point #3: At rest, Na+ and K+ are constantly moving The membrane is more permeable to K+ Key Point #4: Ion Channels K+ and Na+ move through ungated ion channels (free flowing) Gated ion channels- open/close in response Ligand-gated At synapses Open/close when a specific chemical binds Voltage gated axons Open/close when the potential changes 30 second break Find a classmate and ask them what their favorite book is and why. Pg. 110 Action Potentials Key Point #1: Action potential A response/impulse All or none Generated at the axon hillock Carry information along the axons Very brief- lasting only 1-2 milliseconds. This allows neurons to produce them at high frequency Generation of Action Potentials: A Closer Look Key Point #2: At resting potential Voltage-gated Na+ and K+ channels are closed Key Point #3: When an action potential is generated Voltage-gated Na+ channels open first and Na+ flows into the cell K+ Decrease in voltage- depolarization From -70 mV to -60 mV Key Point #3 continued Na+ influx causes more Na+ channels to open and diffuse into the cell Causes further depolarization -60 mv to -50 mv POSITIVE FEEDBACK! Key Point #4: Threshold The voltage needed for an action potential to fire. Action Potential Action potentials propagate impulses along neurons. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes. In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized. Na+/K+ pumps, powered by ATP, work to maintain membrane potential. 15 Label the graph of the action potential as we go through the next several slides. 16 Key Na K Membrane potential (mV) 50 0 50 2 Depolarization OUTSIDE OF CELL INSIDE OF CELL Inactivation loop 1 Resting state 100 Sodium channel Potassium channel Threshold 2 1 Resting potential Time KP#5: Once the threshold is met, Na+ continues to rush inside the cell, raising the voltage into the positive region (~+40) Key Na K 50 Rising phase of the action potential Membrane potential (mV) 3 Action potential 50 2 Depolarization OUTSIDE OF CELL INSIDE OF CELL Inactivation loop 1 Resting state 100 Sodium channel Potassium channel 3 0 Threshold 2 1 Resting potential Time Key Na K 50 Rising phase of the action potential Membrane potential (mV) 3 Depolarization OUTSIDE OF CELL INSIDE OF CELL Inactivation loop 1 Resting state Potassium channel 3 0 100 Sodium channel Falling phase of the action potential Action potential 50 2 4 Threshold 2 4 1 Resting potential Time Key Point #6: When the neuron’s voltage is high enough, the Na+ channels will close During the falling phase, voltage-gated K+ channels open, and K+ flows out of the cell Repolarizing the cell Making the cell negative again Key Na K 50 Rising phase of the action potential Membrane potential (mV) 3 Depolarization OUTSIDE OF CELL 3 0 100 Sodium channel Falling phase of the action potential Action potential 50 2 4 Threshold 2 4 1 5 Resting potential Time Potassium channel INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot 1 KP#7: Undershoot More K+ flows out the cell, making the cell even more negative (-75 mV) Eventually the K+ channels close to restore the resting potential (homeostasis) Figure 48.11a 50 Membrane potential (mV) Action potential 3 0 2 50 4 Threshold 1 5 Resting potential 100 Time 1 Refractory Period During the refractory period after an action potential, a second action potential cannot be initiated KP #8: The refractory period is a result the closing of Na+ channels and a second impulse cannot be fired. Axon Action potential 1 Na Plasma membrane Cytosol Axon Plasma membrane Action potential 1 Na K 2 Cytosol Action potential Na K Axon Plasma membrane 1 KP#9: Impulses travel Na in one directiontowards the synapses.Action potential Moves down the axon K in a wave like motion 2 Na to prevent K diminishing. Cytosol K 3 K Action potential Na Sequence the following in order of occurrence Depolarization Resting state Repolarization Hyperpolarization Resting state Depolarization Hyperpolarization Repolarization Resting state 50 ? Membrane potential (mV) 3 0 Resting state 2 Depolarization 50 Hyperpolarization 1 Repolarization Resting state 100 Time 4 5 1 Tell me what you know! a. increase; increase b. increase; decrease c. decrease; increase d. decrease; decrease Tell me what you know! Adding a poison that specifically disables the Na+/K+ pumps to a culture of neurons will cause: a. the resting membrane potential to drop to 0 mV. b. the inside of the neuron to become more negative relative to the outside. c. the inside of the neuron to become positively charged relative to the outside. d. sodium to diffuse out of the cell and potassium to diffuse into the cell. Homework Read and outline 48.4 Synapses Neurotransmitters-next slide Homework In most animals, transmission across synapses involves chemical messengers called neurotransmitters: Choose one Acetylcholine Epinephrine Norepinephrine Dopamine Serotonin