CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 37 Neurons, Synapses, and Signaling

© 2014 Pearson Education, Inc. Overview: Lines of Communication  Neurons - nerve cells  Processing Centers  ganglia - simple clusters of neurons  brain - complex organization of neurons

© 2014 Pearson Education, Inc. Figure 37.1

© 2014 Pearson Education, Inc. Figure 37.2 Dendrites Nucleus Stimulus Axon hillock Cell body Axon Signal direction Presynaptic cell Synapse Neurotransmitter Synaptic terminals Postsynaptic cell Synaptic terminals

© 2014 Pearson Education, Inc. Neuron Structure and Function  cell body – contains most organelles  Dendrites - highly branched extensions, receive signals  Axon long extension, transmits signals to other cells Video: Dendrites

© 2014 Pearson Education, Inc. Figure 37.2 Dendrites Nucleus Stimulus Axon hillock Cell body Axon Signal direction Presynaptic cell Synapse Neurotransmitter Synaptic terminals Postsynaptic cell Synaptic terminals

© 2014 Pearson Education, Inc.  Synapse – junctions at branched ends of axons transmit chemical signals (neurotransmitters) to other cells

© 2014 Pearson Education, Inc.  glial cells – Nervous system support cells  In the mammalian brain, glia outnumber neurons 10- to 50-fold

© 2014 Pearson Education, Inc. Figure 37.3 Cell bodies of neurons Glia 80  m

© 2014 Pearson Education, Inc. Introduction to Information Processing  3 stages of Nervous information processing  Sensory input  Integration  Motor output

© 2014 Pearson Education, Inc. Figure 37.4 Sensory input Motor output Sensor Effector Processing center Integration

© 2014 Pearson Education, Inc.  Sensory neurons transmit information from sensors  Interneurons in brain or ganglia integrate information  Other Neurons trigger activity  Ex. motor neurons

© 2014 Pearson Education, Inc.  Central nervous system (CNS)  Brain  Spinal cord  Peripheral nervous system  Nerves that thread through the body

© 2014 Pearson Education, Inc. Figure 37.5 Dendrites Axon Cell body Portion of axon InterneuronsSensory neuronMotor neuron

© 2014 Pearson Education, Inc. Resting Potential -70millivolt Charge difference across membrane of neuron (Negative Inside)

© 2014 Pearson Education, Inc. Ion Concentrations at Resting Potential Potassium (K + ) –Higher inside than outside Sodium (Na + ) –Higher outside than inside

© 2014 Pearson Education, Inc. outside plasma membrane inside K+K+ K+K+ Na + p.577

© 2014 Pearson Education, Inc. How Ions Move across Membrane Passive transporters with open channels Passive transporters with voltage-sensitive gated channels Active transporters Lipid bilayer of neuron membrane Interstitial fluid CytoplasmNa + /K + pump Figure 34.7 Page 577

© 2014 Pearson Education, Inc. Pumping and Leaking Interstitial fluid Plasma membrane Cytoplasm Na + leaks in Na + pumped in Na + pumped out Na + leaks out K + leaks out Figure 34.7 Page 577

© 2014 Pearson Education, Inc. Figure 37.6 OUTSIDE OF CELL INSIDE OF CELL Key Na  KK Sodium- potassium pump Potassium channel Sodium channel

© 2014 Pearson Education, Inc. Figure 37.7 Inner chamber Outer chamber 140 mM KCI 5 mM KCI −90 mV Inner chamber Outer chamber 15 mM NaCI 150 mM NaCI  62 mV Cl− Potassium channel Artificial membrane KK Na  Sodium channel (b) Membrane selectively permeable to Na  (a) Membrane selectively permeable to K  E K  62 mV  −90 mV log 5 mM 140 mM E Na  62 mV   62 mV log 150 mM 15 mM

© 2014 Pearson Education, Inc. Action Potential Temporary reversal in membrane potential Voltage change causes voltage-gated channels to open Inside neuron becomes more positive than outside

© 2014 Pearson Education, Inc. Figure 37.9 Ions Change in membrane potential (voltage) (b) Gate open: Ions flow through channel. (a) Gate closed: No ions flow across membrane. Ion channel

© 2014 Pearson Education, Inc. Action Potential Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K Figure 34.8a-d Page

© 2014 Pearson Education, Inc. All or Nothing All action potentials are same size Stimulation below threshold level, no action potential Above threshold level, always same size

© 2014 Pearson Education, Inc. Repolarization Movement of Na + out repolarizes cell back to resting potential

© 2014 Pearson Education, Inc. Figure 37.10c (c) Action potential triggered by a depolarization that reaches the threshold Resting potential Time (msec) Threshold −100 −50 0  50 Membrane potential (mV) Strong depolarizing stimulus Action potential

© 2014 Pearson Education, Inc. 1 Figure Key Na  KK Action potential Threshold Resting potential Time −100 −50 0  50 Membrane potential (mV) Rising phase of the action potential Depolarization Falling phase of the action potential Resting state Undershoot Sodium channel Potassium channel Inactivation loop OUTSIDE OF CELL INSIDE OF CELL

© 2014 Pearson Education, Inc. Figure Axon Plasma membrane Cytosol Action potential Na  1 1

© 2014 Pearson Education, Inc. Figure Axon Plasma membrane Cytosol Action potential Action potential KK KK Na  1 12

© 2014 Pearson Education, Inc. Figure Axon Plasma membrane Cytosol Action potential Action potential Action potential KK KK KK KK Na  123

© 2014 Pearson Education, Inc. Evolutionary Adaptations of Axon Structure  Vertebrate axons insulated by a myelin sheath of Schwann cells  gaps in the myelin sheath are called nodes of Ranvier

© 2014 Pearson Education, Inc. Figure Axon Myelin sheath Schwann cell Nodes of Ranvier Nucleus of Schwann cell Schwann cell Node of Ranvier Layers of myelin Axon 0.1  m

© 2014 Pearson Education, Inc. Figure Cell body Schwann cell Depolarized region (node of Ranvier) Myelin sheath Axon

© 2014 Pearson Education, Inc. Concept 37.4: Neurons communicate with other cells at synapses  At electrical synapses, the electrical signal flows from one neuron to another  Most synapses are chemical synapses, chemical neurotransmitter carries information from presynaptic to the postsynaptic cell

© 2014 Pearson Education, Inc. Figure Presynaptic cellPostsynaptic cell Axon Synaptic vesicle containing neurotransmitter Synaptic cleft Postsynaptic membrane Ca 2  KK Na  Ligand-gated ion channels Voltage-gated Ca 2  channel Presynaptic membrane

© 2014 Pearson Education, Inc. Generation of Postsynaptic Potentials  neurotransmitters bind to ligand-gated ion channels in the postsynaptic cell  causes ion channels to open, generating a postsynaptic potential

© 2014 Pearson Education, Inc.  Postsynaptic potentials  Excitatory postsynaptic potentials (EPSPs) bring the membrane potential toward threshold  Inhibitory postsynaptic potentials (IPSPs) move the membrane potential farther from threshold