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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 48 Neurons, Synapses, and Signaling Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Overview: Lines of Communication • The cone snail kills prey with venom that disables neurons • __________________are nerve cells that transfer information within the body • Neurons use two types of signals to communicate: _____________(long-distance) and ___________________ (short-distance) © 2011 Pearson Education, Inc. Figure 48.1 • Interpreting signals in the nervous system involves sorting a complex set of ____________ _____________________ • Processing of information takes place in simple clusters of neurons called ____________ or a more complex organization of neurons called a ____________ © 2011 Pearson Education, Inc. Concept 48.1: Neuron organization and structure reflect function in information transfer • The __________ possesses extremely large nerve cells and has played a crucial role in the discovery of how neurons transmit signals © 2011 Pearson Education, Inc. Introduction to Information Processing • Nervous systems process information in three stages:_______________________________ ________________________ © 2011 Pearson Education, Inc. Figure 48.2 Nerves with giant axons Ganglia Brain Arm Eye Nerve Mantle • Sensors detect external stimuli and internal conditions and transmit information along ______________________ • Sensory information is sent to the brain or ganglia, where _______________ integrate the information • Motor output leaves the brain or ganglia via ___________________ , which trigger muscle or gland activity © 2011 Pearson Education, Inc. • Many animals have a complex nervous system that consists of – A ______________________________where integration takes place; this includes the brain and a nerve cord – A _______________________________, which carries information into and out of the CNS – The neurons of the PNS, when bundled together, form ____________ © 2011 Pearson Education, Inc. Figure 48.3 Sensory input Integration Sensor Motor output Effector Peripheral nervous system (PNS) Central nervous system (CNS) Neuron Structure and Function • Most of a neuron’s organelles are in the ______ _____________ • Most neurons have ______________, highly branched extensions that receive signals from other neurons • The ________ is typically a much longer extension that transmits signals to other cells at _____________ • The cone-shaped base of an axon is called the ________________ © 2011 Pearson Education, Inc. Figure 48.4 Dendrites Stimulus Axon hillock Nucleus Cell body Presynaptic cell Axon Signal direction Synapse Neurotransmitter Synaptic terminals Postsynaptic cell Synaptic terminals • The __________________ of one axon passes information across the synapse in the form of chemical messengers called _______________ • A ________________ is a junction between an axon and another cell © 2011 Pearson Education, Inc. • Information is transmitted from a ____________ _______________ (a neuron) to a __________ _____________ (a neuron, muscle, or gland cell) • Most neurons are nourished or insulated by cells called ____________ © 2011 Pearson Education, Inc. Figure 48.5 Dendrites Axon Cell body Portion of axon Sensory neuron Interneurons Motor neuron Figure 48.6 80 m Glia Cell bodies of neurons Concept 48.2: Ion pumps and ion channels establish the resting potential of a neuron • Every cell has a voltage (difference in electrical charge) across its plasma membrane called a ________________________ • The ________________ is the membrane potential of a neuron not sending signals • Changes in __________________ act as signals, transmitting and processing information © 2011 Pearson Education, Inc. Formation of the Resting Potential • In a mammalian neuron at resting potential, the concentration of ___ is highest inside the cell, while the concentration of ____ is highest outside the cell • _______________________ use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane • These concentration gradients represent ______________________ © 2011 Pearson Education, Inc. • The opening of _______________in the plasma membrane converts ______________ potential to ______________ potential • A neuron at resting potential contains many open ____ channels and fewer open ___channels; ___ diffuses out of the cell • The resulting buildup of ____________________ within the neuron is the major source of membrane potential © 2011 Pearson Education, Inc. Table 48.1 Figure 48.7 Key Na K Sodiumpotassium pump OUTSIDE OF CELL Potassium channel Sodium channel INSIDE OF CELL Modeling the Resting Potential • Resting potential can be modeled by an artificial membrane that separates two chambers – The concentration of KCl is higher in the ______ chamber and lower in the outer chamber – ____ diffuses down its gradient to the outer chamber – Negative charge (___) builds up in the inner chamber • At equilibrium, both the electrical and chemical gradients are balanced © 2011 Pearson Education, Inc. Figure 48.8a Inner chamber 90 mV 140 mM KCl Outer chamber 5 mM KCl K Potassium channel Cl Artificial membrane (a) Membrane selectively permeable to K EK 62 mV 90 mV • The _____________________is the membrane voltage for a particular ion at equilibrium and can be calculated using the __________ equation Eion = 62 mV (log[ion]outside/[ion]inside) • The equilibrium potential of K+ (EK) is ________, while the equilibrium potential of Na+ (ENa) is _____________ © 2011 Pearson Education, Inc. • In a resting neuron, the currents of K+ and Na+ are ________________, and the resting potential across the membrane remains steady © 2011 Pearson Education, Inc. Figure 48.8b Inner chamber 15 mM NaCl 62 mV Outer chamber 150 mM NaCl Cl Na Sodium channel (b) Membrane selectively permeable to Na ENa 62 mV 62 mV Concept 48.3: Action potentials are the signals conducted by axons • Changes in membrane potential occur because neurons contain __________________ that open or close in response to stimuli © 2011 Pearson Education, Inc. Hyperpolarization and Depolarization • When gated ________________ open, K+ diffuses________, making the inside of the cell more negative • This is__________________, an increase in magnitude of the membrane potential © 2011 Pearson Education, Inc. Figure 48.10a (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K Stimulus Membrane potential (mV) 50 0 50 Threshold 100 Resting potential Hyperpolarizations 0 1 2 3 4 5 Time (msec) • Opening other types of ion channels triggers a _________________, a reduction in the magnitude of the membrane potential • For example, depolarization occurs if ________ ___________________ and Na+ diffuses into the cell © 2011 Pearson Education, Inc. Figure 48.10b (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na Stimulus Membrane potential (mV) 50 0 50 Threshold 100 Resting potential Depolarizations 0 1 2 3 4 5 Time (msec) Graded Potentials and Action Potentials • ___________________ are changes in polarization where the magnitude of the change varies with the strength of the stimulus • These are not the nerve signals that travel along axons, but they do have an effect on the generation of nerve signals © 2011 Pearson Education, Inc. • If a depolarization shifts the membrane potential sufficiently, it results in a massive change in membrane voltage called an ________________ • Action potentials have a constant magnitude, are ____________, and transmit signals over long distances • They arise because some ion channels are ____________________, opening or closing when the membrane potential passes a certain level © 2011 Pearson Education, Inc. Figure 48.10c (c) Action potential triggered by a depolarization that reaches the threshold Strong depolarizing stimulus Membrane potential (mV) 50 Action potential 0 50 Threshold Resting potential 100 0 1 2 3 4 5 6 Time (msec) Generation of Action Potentials: A Closer Look • An action potential can be considered as a series of stages • At ___________________ 1. Most voltage-gated sodium (Na+) channels are _____________; most of the voltage-gated potassium (K+) channels are also __________ © 2011 Pearson Education, Inc. Figure 48.11-1 Key Na K Membrane potential (mV) 50 0 Threshold 50 100 OUTSIDE OF CELL INSIDE OF CELL Inactivation loop 1 Resting state Sodium channel Potassium channel 1 Resting potential Time • When an _________________ is generated 2. Voltage-gated Na+ channels ________ and Na+ flows __________________ 3. During the ________, the threshold is crossed, and the membrane potential _____________ 4. During the ____________, voltage-gated Na+ channels become _____________; voltagegated K+ channels _________, and K+ flows _________________ © 2011 Pearson Education, Inc. 5. During the _____________, membrane permeability to _____is at first higher than at rest, then voltage-gated K+ channels close and ___________________ is restored © 2011 Pearson Education, Inc. Figure 48.11-5 Key Na K Membrane potential (mV) Action potential OUTSIDE OF CELL 100 Sodium channel 3 0 50 2 Depolarization 4 Falling phase of the action potential 50 3 Rising phase of the action potential Threshold 2 1 4 5 Resting potential Time Potassium channel INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot 1 Figure 48.11a Membrane potential (mV) 50 Action potential 3 0 50 100 2 4 Threshold 1 Resting potential Time 5 1 • During the ________________ after an action potential, a second action potential cannot be initiated • The refractory period is a result of a temporary inactivation of the __________________ © 2011 Pearson Education, Inc. Conduction of Action Potentials • At the site where the action potential is generated, usually the axon hillock, an electrical current _________________ the neighboring region of the axon membrane • Action potentials travel in only one direction: toward the ____________________ © 2011 Pearson Education, Inc. • _______________________ behind the zone of depolarization prevent the action potential from traveling backwards © 2011 Pearson Education, Inc. Figure 48.12-3 Axon Plasma membrane Action potential 1 Na K 2 Cytosol Action potential Na K K 3 Action potential Na K Evolutionary Adaptation of Axon Structure • The speed of an action potential increases with the ___________________ • In vertebrates, axons are insulated by a ______ ________________, which causes an action potential’s speed to increase • Myelin sheaths are made by glia— ____________________in the CNS and _____________________in the PNS © 2011 Pearson Education, Inc. Figure 48.13 Node of Ranvier Layers of myelin Axon Schwann cell Axon Myelin sheath Nodes of Ranvier Schwann cell Nucleus of Schwann cell 0.1 m • Action potentials are formed only at ________ _______________, gaps in the myelin sheath where voltage-gated Na+ channels are found • Action potentials in myelinated axons jump between the nodes of Ranvier in a process called _______________________ © 2011 Pearson Education, Inc. Figure 48.14 Schwann cell Depolarized region (node of Ranvier) Cell body Myelin sheath Axon Concept 48.4: Neurons communicate with other cells at synapses • At __________________, the electrical current flows from one neuron to another • At __________________, a chemical neurotransmitter carries information across the gap junction • Most synapses are ______________synapses © 2011 Pearson Education, Inc. • The presynaptic neuron synthesizes and packages the neurotransmitter in _________ _____________located in the synaptic terminal • The action potential causes the release of the ___________________ • The neurotransmitter diffuses across the ____________________and is received by the postsynaptic cell © 2011 Pearson Education, Inc. Figure 48.15 Presynaptic cell Postsynaptic cell Axon Synaptic vesicle containing neurotransmitter 1 Postsynaptic membrane Synaptic cleft Presynaptic membrane 3 K Ca2 2 Voltage-gated Ca2 channel Ligand-gated ion channels 4 Na Generation of Postsynaptic Potentials • Direct synaptic transmission involves binding of neurotransmitters to _____________________ in the postsynaptic cell • Neurotransmitter binding causes ion channels to open, generating a _______________________ © 2011 Pearson Education, Inc. • Postsynaptic potentials fall into two categories – ____________________________________ are depolarizations that bring the membrane potential toward threshold – ____________________________________ are hyperpolarizations that move the membrane potential farther from threshold © 2011 Pearson Education, Inc. • After release, the neurotransmitter – May diffuse out of the __________________ – May be ___________ by surrounding cells – May be degraded by _________________ © 2011 Pearson Education, Inc. Summation of Postsynaptic Potentials • Most neurons have ______________on their dendrites and cell body • A single EPSP is usually ________________ to trigger an action potential in a postsynaptic neuron © 2011 Pearson Education, Inc. • If two EPSPs are produced in rapid succession, an effect called ____________________occurs © 2011 Pearson Education, Inc. Figure 48.17a Terminal branch of presynaptic neuron E1 E2 E2 Postsynaptic neuron Membrane potential (mV) E1 Axon hillock I I 0 Action potential Threshold of axon of postsynaptic neuron Resting potential 70 E1 E1 (a) Subthreshold, no summation E1 E1 (b) Temporal summation • In________________, EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together • The combination of EPSPs through ________ and _______________ summation can trigger an action potential © 2011 Pearson Education, Inc. Figure 48.17b E1 E1 E2 E2 I I Action potential E1 E2 (c) Spatial summation E1 I E1 I (d) Spatial summation of EPSP and IPSP • Through summation, an IPSP can ___________ the effect of an EPSP • The ________________ of EPSPs and IPSPs determines whether an axon hillock will reach threshold and generate an action potential © 2011 Pearson Education, Inc. Modulated Signaling at Synapses • In some synapses, a neurotransmitter binds to a receptor that is ___________________ • In this case, movement of ions through a channel depends on one or more ___________ _________________ © 2011 Pearson Education, Inc. • Binding of a neurotransmitter to a metabotropic receptor activates a signal transduction pathway in the postsynaptic cell involving a ___________ _________________ • Compared to ligand-gated channels, the effects of second-messenger systems have a _________________ but _______________ © 2011 Pearson Education, Inc. Neurotransmitters • There are more than ______________________, belonging to five groups: acetylcholine, biogenic amines, amino acids, neuropeptides, and gases • A single neurotransmitter may have more than a ____________ different receptors © 2011 Pearson Education, Inc. Table 48.2 Acetylcholine • ____________________ is a common neurotransmitter in vertebrates and invertebrates • It is involved in muscle stimulation, memory formation, and learning • Vertebrates have two major classes of acetylcholine receptor, one that is ___________ and one that is _________________ © 2011 Pearson Education, Inc. Amino Acids • ____________________________are active in the CNS and PNS • Known to function in the CNS are – ______________________________ – ______________________________ – _______________ © 2011 Pearson Education, Inc. Biogenic Amines • _____________________include – ________________ – ________________ – ________________ – ________________ • They are active in the CNS and PNS © 2011 Pearson Education, Inc. Neuropeptides • Several ________________, relatively short chains of amino acids, also function as neurotransmitters • Neuropeptides include substance P and _________________, which both affect our perception of pain • ________________ bind to the same receptors as endorphins and can be used as painkillers © 2011 Pearson Education, Inc. Figure 48.18 EXPERIMENT Radioactive naloxone 1 Radioactive naloxone and a test drug are incubated with a protein mixture. Drug Protein mixture 2 Proteins are trapped on a filter. Bound naloxone is detected by measuring radioactivity. RESULTS Drug Opiate Concentration That Blocked Naloxone Binding Morphine Yes 6 109 M Methadone Yes 2 108 M Levorphanol Yes 2 109 M Phenobarbital No No effect at 104 M Atropine No No effect at 104 M Serotonin No No effect at 104 M Figure 48.18a EXPERIMENT Radioactive naloxone 1 Radioactive naloxone and a test drug are incubated with a protein mixture. Drug Protein mixture 2 Proteins are trapped on a filter. Bound naloxone is detected by measuring radioactivity. Figure 48.18b RESULTS Drug Opiate Concentration That Blocked Naloxone Binding Morphine Yes 6 109 M Methadone Yes 2 108 M Levorphanol Yes 2 109 M Phenobarbital No No effect at 104 M Atropine No No effect at 104 M Serotonin No No effect at 104 M Gases • Gases such as ________________and ______ _____________are local regulators in the PNS © 2011 Pearson Education, Inc.