1. Chapter 28 Nervous system

2. NERVOUS SYSTEM STRUCTURE AND FUNCTION © 2012 Pearson Education, Inc.

3. 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands  The nervous system –obtains sensory information, sensory input, –processes sensory information, integration, and –sends commands to effector cells (muscles) that carry out appropriate responses, motor output. © 2012 Pearson Education, Inc.

4.  The central nervous system (CNS) consists of the –brain and –spinal cord (vertebrates).  The peripheral nervous system (PNS) –is located outside the CNS and –consists of –nerves (bundles of neurons wrapped in connective tissue) and –ganglia (clusters of neuron cell bodies). 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands © 2012 Pearson Education, Inc.

5.  Sensory neurons –convey signals from sensory receptors –to the CNS.  Interneurons –are located entirely in the CNS, –integrate information, and –send it to motor neurons.  Motor neurons convey signals to effector cells. 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands © 2012 Pearson Education, Inc.

6. Sensory receptor 2 1 3 4 Sensory neuron Brain Spinal cord Interneuron CNS PNS Nerve Flexor muscles Quadriceps muscles Ganglion Motor neuron

7. 28.2 Neurons are the functional units of nervous systems  Neurons are –cells specialized for carrying signals and –the functional units of the nervous system.  A neuron consists of –a cell body and –two types of extensions (fibers) that conduct signals, –dendrites and –axons. © 2012 Pearson Education, Inc.

8.  Myelin sheaths –enclose axons, –form a cellular insulation, and –speed up signal transmission. 28.2 Neurons are the functional units of nervous systems © 2012 Pearson Education, Inc.

9. Figure 28.2 Signal direction Nucleus Myelin sheath Schwann cell Dendrites Cell body Axon Nodes of Ranvier Signal pathway Node of Ranvier Synaptic terminals Nucleus Schwann cell Cell body Layers of myelin

10. Figure 28.2_1 Signal direction Nucleus Myelin sheath Schwann cell Dendrites Cell body Axon Nodes of Ranvier Signal pathway Synaptic terminals Structure of a myelinated motor neuron

11. (c) Oligodendrocytes in central nervous system Axon Oligodendrocyte Nodes of Ranvier Myelin sheath

12. Schwann cell Node of Ranvier Cytoplasm (b) Schwann cells in peripheral nervous system Axon Nucleus Figure 4-13b p127

13. NERVE SIGNALS AND THEIR TRANSMISSION © 2012 Pearson Education, Inc.

14. 28.3 Nerve function depends on charge differences across neuron membranes  At rest, a neuron’s plasma membrane has potential energy—the membrane potential, in which –just inside the cell is slightly negative and –just outside the cell is slightly positive.  The resting potential is the voltage across the plasma membrane of a resting neuron. © 2012 Pearson Education, Inc.

15.  The resting potential exists because of differences in ion concentration of the fluids inside and outside the neuron. –Inside the neuron –K + is high and –Na + is low. –Outside the neuron –K + is low and –Na + is high. 28.3 Nerve function depends on charge differences across neuron membranes © 2012 Pearson Education, Inc. Animation: Resting Potential

16. 28.4 A nerve signal begins as a change in the membrane potential  A stimulus is any factor that causes a nerve signal to be generated. A stimulus –alters the permeability of a portion of the membrane, –allows ions to pass through, and –changes the membrane’s voltage. © 2012 Pearson Education, Inc.

17.  A nerve signal, called an action potential, is –a change in the membrane voltage, –from the resting potential, –to a maximum level, and –back to the resting potential. 28.4 A nerve signal begins as a change in the membrane potential © 2012 Pearson Education, Inc. Animation: Action Potential

18. Figure 28.4 Na  KK Additional Na  channels open, K  channels are closed; interior of cell becomes more positive. Na  2 KK A stimulus opens some Na  channels; if threshold is reached, an action potential is triggered. Na  KK 1 Resting state: Voltage-gated Na  and K  channels are closed; resting potential is maintained by ungated channels (not shown). Sodium channel Potassium channel Outside of neuron Plasma membrane Inside of neuron Action potential Threshold Resting potential Time (msec) Membrane potential (mV)  50 0  50  100 2 3 1 3 4 5 1 Na  KK 4 Na  channels close and inactivate; K  channels open, and K  rushes out; interior of cell is more negative than outside. Na  KK The K  channels close relatively slowly, causing a brief undershoot. 5 1 Return to resting state.

19. Figure 28.4_s1 Action potential Threshold Resting potential Time (msec) Membrane potential (mV)  50 0  50  100 1 Resting state: Voltage- gated Na  and K  channels are closed; resting potential is maintained by ungated channels (not shown). 1 Na  KK Sodium channel Outside of neuron Plasma membrane Inside of neuron Potassium channel

20. Figure 28.4_s2 Action potential Threshold Resting potential Time (msec) Membrane potential (mV)  50 0  50  100 1 2 Na  A stimulus opens some Na  channels; if threshold is reached, an action potential is triggered. Na  KK 2

21. Figure 28.4_s3 Action potential Threshold Resting potential Time (msec) Membrane potential (mV)  50 0  50  100 1 2 3 3 Na  KK Additional Na  channels open, K  channels are closed; interior of cell becomes more positive.

22. Figure 28.4_s4 Na  KK Na  channels close and inactivate; K  channels open, and K  rushes out; interior of cell is more negative than outside. Na  Action potential Threshold Resting potential Time (msec) Membrane potential (mV)  50 0  50  100 1 2 3 4 4

23. Figure 28.4_s5 Action potential Threshold Resting potential Time (msec) Membrane potential (mV)  50 0  50  100 1 2 3 4 5 5 The K  channels close relatively slowly, causing a brief undershoot.

24. Figure 28.4_s6 Action potential Threshold Resting potential Time (msec) Membrane potential (mV)  50 0  50  100 1 2 3 4 5 1 1 Na  KK Return to resting state.

25. 28.5 The action potential propagates itself along the axon  Action potentials are –self-propagated in a one-way chain reaction along a neuron and –all-or-none events. © 2012 Pearson Education, Inc.

26. Figure 28.5_s1 Plasma membrane Axon segment Action potential Na  1

27. Figure 28.5_s2 Na  1 KK KK Action potential 2 Plasma membrane Axon segment Action potential

28. Figure 28.5_s3 Na  1 KK KK Action potential 2 Plasma membrane Axon segment Action potential Na  KK KK 3

29. 28.6 Neurons communicate at synapses  Synapses are junctions where signals are transmitted between –two neurons or –between neurons and effector cells. © 2012 Pearson Education, Inc.

30.  Electrical signals pass between cells at electrical synapses.  At chemical synapses –the ending (presynaptic) cell secretes a chemical signal, a neurotransmitter, –the neurotransmitter crosses the synaptic cleft, and –the neurotransmitter binds to a specific receptor on the surface of the receiving (postsynaptic) cell. 28.6 Neurons communicate at synapses © 2012 Pearson Education, Inc. Animation: Synapse

31. Figure 28.6 Axon of sending cell Synaptic terminal of sending cell Dendrite of receiving cell Sending cell Synaptic vesicles Synaptic terminal Synaptic cleft Vesicle fuses with plasma membrane Action potential arrives Neurotransmitter is released into synaptic cleft Neurotransmitter binds to receptor Neurotransmitter molecules Neurotransmitter broken down and released Ion channel closes Ions Receptor Receiving cell Neurotransmitter Ion channels Ion channel opens 5 6 4 3 2 1

32. Figure 28.6_1 Axon of sending cell Synaptic terminal of sending cell Dendrite of receiving cell Sending cell Synaptic vesicles Synaptic terminal Synaptic cleft Vesicle fuses with plasma membrane Action potential arrives Neurotransmitter is released into synaptic cleft Neurotransmitter molecules Receiving cell Ion channels Neurotransmitter binds to receptor 1 2 3 4

33. Figure 28.6_2 Neurotransmitter broken down and released Ion channel closes Neurotransmitter Ion channel opens Ions Receptor 6 5