Gates + Potentials Do Now: Review 1. What is a synapse? 2. What are the two different ways that neurons communicate with each other? 3. What is the difference between an excitatory neurotransmitter and an inhibitory nt? 4. List the excitatory nt.
5. Are you a light sleeper or a heavy sleeper? A little more: Synaptic Transmission When the action potential arrives at the axon terminal (end of the axon), the electric signal opens calcium channels. These calcium channels open to allow the vesicles with neurotransmitters to bind to
the cell membrane and enter the synaptic cleft. http://highered.mcgraw-hill.com/sites/0072 495855/student_view0/chapter14/animatio n__transmission_across_a_synapse.html Which are you? Key Players Sodium Ions
Potassium Ions Calcium Ions Gates/Channels Leak Channels: Allow things to pass through all the time Voltage gated Ion channels: Open when the membrane has a certain potential Calcium Channels: Open in response to an electrical stimulus Sodium/Potassium pumps: pumps 3 Na out of the cell, 2 K into cell
Leak Channels Many more of these for K+ and Clthan for Na+. K+ are in higher concentration on inside than out, they move out. Always open and responsible for permeability when membrane is at rest. Specific for one type of ion although not absolute. 11-7
Leak Channels 11-8 Gated Ion Channels Gated ion channels. Gated ion channels open and close because of some sort of stimulus. When they open, they change the permeability of the cell membrane.
Ligand-gated: open or close in response to ligand such as ACh binding to receptor protein. Receptor proteins are usually glycoproteins. E.g., acetylcholine binds to acetylcholine receptor on a Na+ channel. Channel opens, Na+ enters the cell. 11-9 Voltage Gated Ion Channels Voltage-gated: open or close in
response to small voltage changes across the cell membrane. At rest, membrane is negative on the inside relative to the outside. When cell is stimulated, that relative charge changes and voltage-gated ion channels either open or close. Most common voltage gated are Na+ and K+. 11-10
Resting Potential The normal state of things Potential: like a difference Charge: -70 mV Establishing the Resting Membrane Potential Number of charged molecules and ions
inside and outside cell nearly equal Concentration of K+ higher inside than outside cell, Na+ higher outside than inside Potential difference: unequal distribution of charge exists between the immediate inside
and immediate outside of the plasma membrane: -70 to -90 11-12 mV What happens when someone messes up your rest? Changing the Resting
Membrane Potential: K + Depolarization: Potential difference becomes smaller or less polar Hyperpolarization: Potential difference becomes greater or more polar K+ concentration gradient alterations If extracellular concentration of
K+ increases: less gradient between inside and outside. Depolarization If extracellular ion concentration decreases: steeper gradient between inside and outside. Hyperpolarization 11-14
11-15 Action Potential Threshold: -55mV If threshold is reached, an action potential occurs. Gates open and close to allow ions to flow across the membrane, changing the charge of the membrane. Continues all the way down the axon until
the end, where the nt is released and the signal is sent to the next neuron Practice 1. Describe the events that occur at the synapse. 2. Summarize how a nerve fiber becomes polarized. 3. What is a potential? 4. What is the difference between a leak channel
and a voltage gated ion channel? 5. What is the difference between the resting potential and an action potential? 6. Describe the difference between hyperpolarization and depolarization. Action Potentials Depolarization phase followed by repolarization phase.
Depolarization: more positive Repolarization: more negative (may get afterpotential [slight hyperpolarization]) Series of permeability changes when a graded potential causes depolarization of membrane. A large enough graded
potential may cause the membrane to reach threshold. Then get action potential. All-or-none principle. No matter how strong the stimulus, as long as it is 11-18
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