Neurons, Synapses and Signaling

Dendrites Stimulus Axon hillock Nucleus Cell body Presynaptic cell Figure 48.4 Dendrites Stimulus Axon hillock Nucleus Cell body Presynaptic cell Axon Signal direction Synapse Synaptic terminals Figure 48.4 Neuron structure and organization. Synaptic terminals Postsynaptic cell Neurotransmitter

Table 48.1 Ion Concentrations Inside and Outside of Mammalian Neurons

Sodium- potassium pump Figure 48.7 Key Na K Sodium- potassium pump OUTSIDE OF CELL Potassium channel Sodium channel Figure 48.7 The basis of the membrane potential. INSIDE OF CELL

140 mM KCl 150 mM NaCl Inner chamber  90 mV Inner chamber  62 mV Figure 48.8 Inner chamber  90 mV Inner chamber  62 mV Outer chamber Outer chamber 140 mM KCl 5 mM KCl 15 mM NaCl 150 mM NaCl Cl K Na Cl Potassium channel Sodium channel Artificial membrane Figure 48.8 Modeling a mammalian neuron. (a) Membrane selectively permeable to K (b) Membrane selectively permeable to Na EK  62 mV  90 mV ENa  62 mV  62 mV

Strong depolarizing stimulus Figure 48.10 Stimulus Stimulus Strong depolarizing stimulus 50 50 50 Action potential Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Threshold Threshold Threshold 50 50 50 Resting potential Resting potential Resting potential Hyperpolarizations Depolarizations 100 100 100 Figure 48.10 Graded potentials and an action potential in a neuron. 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 6 Time (msec) Time (msec) Time (msec) (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K (b) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to Na (c) Action potential triggered by a depolarization that reaches the threshold

Falling phase of the action potential 3 Figure 48.11-5 Key Na K 4 Falling phase of the action potential 3 Rising phase of the action potential 50 Action potential 3 Membrane potential (mV) Threshold 4 2 50 1 1 5 2 Depolarization Resting potential 100 Figure 48.11 The role of voltage-gated ion channels in the generation of an action potential. Time OUTSIDE OF CELL Sodium channel Potassium channel INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot

Axon Plasma membrane Action potential 1 Cytosol Action potential 2 Figure 48.12-3 Axon Plasma membrane Action potential 1 Cytosol Na Action potential K 2 Na Figure 48.12 Conduction of an action potential. K Action potential K 3 Na K

Nucleus of Schwann cell Axon Myelin sheath Figure 48.13 Node of Ranvier Layers of myelin Axon Schwann cell Schwann cell Nodes of Ranvier Nucleus of Schwann cell Axon Myelin sheath Figure 48.13 Schwann cells and the myelin sheath. 0.1 m

Presynaptic cell Synaptic cleft Figure 48.15 Presynaptic cell Postsynaptic cell Axon Synaptic vesicle containing neurotransmitter 1 Postsynaptic membrane Synaptic cleft Presynaptic membrane 3 Figure 48.15 A chemical synapse. K Ca2 2 Voltage-gated Ca2 channel Ligand-gated ion channels 4 Na

Figure 48.17 Summation of postsynaptic potentials. Terminal branch of presynaptic neuron E1 E1 E1 E1 E2 E2 E2 E2 Postsynaptic neuron Axon hillock I I I I Threshold of axon of postsynaptic neuron Action potential Action potential Membrane potential (mV) Resting potential Figure 48.17 Summation of postsynaptic potentials. 70 E1 E1 E1 E1 E1  E2 E1 I E1  I Subthreshold, no summation (a) (b) Temporal summation (c) Spatial summation Spatial summation of EPSP and IPSP (d)

Concentration That Blocked Naloxone Binding 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 Concentration That Blocked Naloxone Binding Figure 48.18 INQUIRY: Does the brain have a specific protein receptor for opiates? Drug Opiate Morphine Yes 6  109 M Methadone Yes 2  108 M Levorphanol Yes 2  109 M Phenobarbital No No effect at 104 M Atropine No No effect at 104 M Serotonin No No effect at 104 M

Membrane potential (mV) Figure 48.UN01 Action potential 50 Falling phase Rising phase Membrane potential (mV) Threshold (55) 50 Resting potential Figure 48.UN01 Summary figure, Concept 48.3 70 Depolarization Undershoot 100 1 2 3 4 5 6 Time (msec)

Figure 48.UN03 Appendix A: answer to Figure 48.10 legend question

Figure 48.UN04 Figure 48.UN04 Appendix A: answer to Test Your Understanding, question 7