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Chapter 28 Nervous Systems PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko Introduction Spinal cord injuries disrupt communication between – the central nervous system (brain and spinal cord) and – the rest of the body. © 2012 Pearson Education, Inc. Introduction Over 250,000 Americans are living with spinal cord injuries. Spinal cord injuries – happen more often to men, – happen mostly to people in their teens and 20s, – are caused by vehicle accidents, gunshots, and falls, and – are usually permanent because the spinal cord cannot be repaired. © 2012 Pearson Education, Inc. 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. Figure 28.1A Sensory input Integration Sensory receptor Motor output Brain and spinal cord Effector cells Peripheral nervous system (PNS) Central nervous system (CNS) 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands 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). © 2012 Pearson Education, Inc. 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands 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. © 2012 Pearson Education, Inc. Figure 28.1B 1 Sensory receptor 2 Sensory neuron Brain Ganglion Motor neuron Spinal cord 3 Quadriceps muscles 4 Interneuron Nerve Flexor muscles PNS CNS 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. 28.2 Neurons are the functional units of nervous systems Myelin sheaths – enclose axons, – form a cellular insulation, and – speed up signal transmission. © 2012 Pearson Education, Inc. Figure 28.2 Signal direction Cell body Nucleus Signal pathway Node of Ranvier Layers of myelin Nodes of Ranvier Myelin sheath Dendrites Cell body Schwann cell Synaptic terminals Nucleus Axon Schwann cell Figure 28.2_1 Signal direction Nucleus Nodes of Ranvier Myelin sheath Dendrites Cell body Schwann cell Axon Signal pathway Synaptic terminals Figure 28.2_2 Node of Ranvier Layers of myelin Nucleus Schwann cell NERVE SIGNALS AND THEIR TRANSMISSION © 2012 Pearson Education, Inc. 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. 28.3 Nerve function depends on charge differences across neuron membranes 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. Animation: Resting Potential © 2012 Pearson Education, Inc. Figure 28.3 Neuron Axon Plasma membrane Outside of neuron Na Na Na Na K K Na channel Na Plasma membrane Na Na Na K Na Na Na Na Na-K pump K K Na Na Na Na ATP K channel K Na K K Na Na K K Inside of neuron K K K K K K K Figure 28.3_1 Neuron Plasma membrane Axon Figure 28.3_2 Outside of neuron Na Na Na Na K K Na Na Na Na K Na Na Na Na Na Na Na Na channel Plasma membrane K Na-K pump K Na ATP K channel K Na K K Na Na K K Inside of neuron K K K K K K K 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. 28.4 A nerve signal begins as a change in the membrane potential 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. Animation: Action Potential © 2012 Pearson Education, Inc. Figure 28.4 Na Na Na Na K Additional Na channels open, K channels are closed; interior of cell becomes more positive. Na Na K 2 K 50 Membrane potential (mV) 3 Action potential 3 0 5 The K channels close relatively slowly, causing a brief undershoot. 4 50 Threshold 1 Resting potential 100 5 1 Time (msec) Sodium Potassium Na channel channel Na channels close and inactivate; K channels open, and K rushes out; interior of cell is more negative than outside. 2 A stimulus opens some Na channels; if threshold is reached, an action potential is triggered. Na 4 Outside of neuron Na Na Plasma membrane K 1 K Inside of neuron Resting state: Voltage-gated Na and K channels are closed; resting potential is maintained by ungated channels (not shown). 1 Return to resting state. Figure 28.4_s1 Membrane potential (mV) 50 Action potential 0 50 Threshold 1 100 Resting potential Time (msec) 1 Resting state: Voltagegated Na and K channels are closed; resting potential is maintained by ungated channels (not shown). Na Na Sodium Potassium channel channel Outside of neuron Plasma membrane K Inside of neuron Figure 28.4_s2 Membrane potential (mV) 50 Action potential 0 2 50 Threshold 1 100 Resting potential Time (msec) 2 A stimulus opens some Na channels; if threshold is reached, an action potential is triggered. Na Na K Figure 28.4_s3 Membrane potential (mV) 50 Action potential 3 0 2 50 Threshold 1 100 Resting potential Time (msec) 3 Additional Na channels open, K channels are closed; interior of cell becomes more positive. Na Na K Figure 28.4_s4 Membrane potential (mV) 50 Action potential 3 0 4 2 50 Threshold 1 100 Resting potential Time (msec) 4 Na channels close and inactivate; K channels open, and K rushes out; interior of cell is more negative than outside. Na Na K Figure 28.4_s5 Membrane potential (mV) 50 Action potential 3 0 2 50 Threshold 1 100 Resting potential Time (msec) 5 The K channels close relatively slowly, causing a brief undershoot. 4 5 Figure 28.4_s6 Membrane potential (mV) 50 Action potential 3 0 2 50 Threshold 1 1 100 5 Resting potential Time (msec) 1 Return to resting Na 4 Na state. K 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. Figure 28.5_s1 Action potential Na Plasma membrane Axon segment 1 Na Figure 28.5_s2 Action potential Na Plasma membrane Axon segment 1 Na Action potential Na K 2 K Na Figure 28.5_s3 Action potential Na Plasma membrane Axon segment 1 Na Action potential Na K 2 K Na Action potential Na K 3 K Na Figure 28.5 Axon Plasma membrane Action Na potential Axon segment 1 Na Action potential Na K 2 K Na Action potential Na K 3 K Na 28.5 The action potential propagates itself along the axon The frequency of action potentials (but not their strength) changes with the strength of the stimulus. © 2012 Pearson Education, Inc. 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. 28.6 Neurons communicate at synapses 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. Animation: Synapse © 2012 Pearson Education, Inc. Figure 28.6 1 Sending cell Axon of sending cell Synaptic terminal of sending cell Action potential arrives Synaptic vesicles Synaptic terminal 2 3 Vesicle fuses with plasma membrane Dendrite of receiving cell Neurotransmitter is released into synaptic cleft Synaptic cleft 4 Neurotransmitter binds to receptor Receiving cell Ion channels Neurotransmitter molecules Neurotransmitter Receptor Neurotransmitter broken down and released Ions 5 Ion channel opens 6 Ion channel closes Figure 28.6_1 1 Sending cell Axon of sending cell Synaptic terminal of sending cell Action potential arrives Synaptic vesicles Synaptic terminal 2 Vesicle fuses with plasma membrane Dendrite of receiving cell 3 Neurotransmitter is released into synaptic cleft Synaptic cleft 4 Receiving cell Neurotransmitter binds to receptor Ion channels Neurotransmitter molecules Figure 28.6_2 Neurotransmitter Receptor Neurotransmitter broken down and released Ions 5 Ion channel opens 6 Ion channel closes