UCSD BILD 2 - Lecture (19 pages)

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Lecture



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Lecture

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Pages:
19
School:
University of California, San Diego
Course:
Bild 2 - Multicellular Life
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LE 48 13 5 Na Na Na Na K K Rising phase of the action potential Falling phase of the action potential Na Na Membrane potential mV 50 Action potential 0 50 Threshold K 100 Depolarization Resting potential Time Na Na Extracellular fluid Na Potassium channel Activation gates K Plasma membrane Cytosol Resting state Undershoot Sodium channel K Inactivation gate After the depolarization of an action potential repolarization occurs due to the A closing of sodium activation and inactivation gates B opening of sodium activation gates C refractory period in which the membrane is hyperpolarized D delay in the action of the sodium potassium pump E opening of voltage gated potassium channels and the closing of sodium channels LE 48 5 Dendrites Cell body Nucleus Axon hillock Axon Presynaptic cell Signal direction Synaptic Myelin sheath terminals Synapse Postsynaptic cell Concept 48 4 Neurons communicate with other cells at synapses In an electrical synapse current flows directly from one cell to another via a gap junction The vast majority of synapses are chemical synapses In a chemical synapse a presynaptic neuron releases chemical neurotransmitters stored in the synaptic terminal LE 48 16 Synaptic terminals of presynaptic neurons 5 m Postsynaptic neuron When an action potential reaches a terminal the final result is release of neurotransmitters into the synaptic cleft Animation Synapse LE 48 17 Presynaptic cell Postsynaptic cell Synaptic vesicles containing neurotransmitter Na K Presynaptic membrane Neurotransmitter Postsynaptic membrane Ligandgated ion channel Voltage gated Ca2 channel Postsynaptic membrane Ca2 Synaptic cleft Ligand gated ion channels Direct Synaptic Transmission Direct synaptic transmission involves binding of neurotransmitters to ligand gated ion channels Neurotransmitter binding causes ion channels to open generating a postsynaptic potential Postsynaptic potentials fall into two categories Excitatory postsynaptic potentials EPSPs Inhibitory postsynaptic potentials IPSPs After release the neurotransmitter diffuses out of the synaptic cleft It may be taken up by surrounding cells and degraded by enzymes Summation of Postsynaptic Potentials Unlike action potentials postsynaptic potentials are graded and do not regenerate Most neurons have many synapses on their dendrites and cell body A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron LE 48 18 Terminal branch of presynaptic neuron Postsynaptic E1 neuron E1 E2 E1 E1 I Membrane potential mV Axon hillock 0 Action potential Action potential Threshold of axon of postsynaptic neuron Resting potential 70 E1 E1 Subthreshold no summation E1 E1 Temporal summation E1 E2 Spatial summation E1 I E1 I Spatial summation of EPSP and IPSP 6 Neurotransmitters categorized as inhibitory would not be expected to A bind to receptors B open K channels C open Na channels D open Cl channels E hyperpolarize the membrane If two EPSPs are produced in rapid succession an effect called temporal summation occurs In spatial summation EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together Through summation an IPSP can counter the effect of an EPSP Indirect Synaptic Transmission In indirect synaptic transmission a neurotransmitter binds to a receptor that is not part of an ion channel This binding activates a signal transduction pathway involving a second messenger in the postsynaptic cell Effects of indirect synaptic transmission have a slower onset but last longer Neurotransmitters The same neurotransmitter can produce different effects in different types of cells


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