1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 48 Nervous Systems

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Information Processing Nervous systems process information in three stages – Sensory input, integration, and motor output Figure 48.3 Sensor Effector Motor output Integration Sensory input Peripheral nervous system (PNS) Central nervous system (CNS)

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neuron Structure Most of a neuron’s organelles – Are located in the cell body Figure 48.5 Dendrites Cell body Nucleus Axon hillock Axon Signal direction Synapse Myelin sheath Synaptic terminals Presynaptic cell Postsynaptic cell

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most neurons have dendrites – Highly branched extensions that receive signals from other neurons The axon is typically a much longer extension – That transmits signals to other cells at synapses – That may be covered with a myelin sheath

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) – Form the myelin sheaths around the axons of many vertebrate neurons Myelin sheath Nodes of Ranvier Schwann cell Schwann cell Nucleus of Schwann cell Axon Layers of myelin Node of Ranvier 0.1 µm Axon Figure 48.8

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.2: Ion pumps and ion channels maintain the resting potential of a neuron Across its plasma membrane, every cell has a voltage – Called a membrane potential The inside of a cell is negative – Relative to the outside

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The concentration of Na + is higher in the extracellular fluid than in the cytosol – While the opposite is true for K + If a cell has gated ion channels – Its membrane potential may change in response to stimuli that open or close those channels

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A stimulus strong enough to produce a depolarization that reaches the threshold – Triggers a different type of response, called an action potential Figure 48.12c +50 0 –50 –100 Time (msec) 0 1 2 3 4 5 6 Threshold Resting potential Membrane potential (mV) Stronger depolarizing stimulus Action potential (c) Action potential triggered by a depolarization that reaches the threshold.

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An action potential – Is a brief all-or-none depolarization of a neuron’s plasma membrane – Is the type of signal that carries information along axons

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The generation of an action potential – – – – + + + + + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + Na + K+K+ K+K+ K+K+ K+K+ K+K+ 5 1 Resting state 2 Depolarization 3 Rising phase of the action potential 4 Falling phase of the action potential Undershoot 1 2 3 4 5 1 Sodium channel Action potential Resting potential Time Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Threshold Membrane potential (mV) +50 0 –50 –100 Threshold Cytosol Figure 48.13 Depolarization opens the activation gates on most Na + channels, while the K + channels’ activation gates remain closed. Na + influx makes the inside of the membrane positive with respect to the outside. The inactivation gates on most Na + channels close, blocking Na + influx. The activation gates on most K + channels open, permitting K + efflux which again makes the inside of the cell negative. A stimulus opens the activation gates on some Na + channels. Na + influx through those channels depolarizes the membrane. If the depolarization reaches the threshold, it triggers an action potential. The activation gates on the Na + and K + channels are closed, and the membrane’s resting potential is maintained. Both gates of the Na + channels are closed, but the activation gates on some K + channels are still open. As these gates close on most K + channels, and the inactivation gates open on Na + channels, the membrane returns to its resting state.

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 48.14 – + – + + ++ + – + – + + ++ + + – + –+++ + + – + – +++ + + – + – – –– – + – + – – –– – –– – – –– – – –– –– + + ++ + + + + – – – – + + + + – –– – – – – – ++ ++ –– – – ++ ++ Na + Action potential K+K+ K+K+ K+K+ Axon An action potential is generated as Na + flows inward across the membrane at one location. 1 2 The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K + flows outward. 3 The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon. K+K+ At the site where the action potential is generated, usually the axon hillock – An electrical current depolarizes the neighboring region of the axon membrane

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.4: Neurons communicate with other cells at synapses In an electrical synapse – Electrical current flows directly from one cell to another via a gap junction The vast majority of synapses – Are chemical synapses

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When an action potential reaches a terminal – The final result is the release of neurotransmitters into the synaptic cleft Figure 48.17 Presynaptic cell Postsynaptic cell Synaptic vesicles containing neurotransmitter Presynaptic membrane Postsynaptic membrane Voltage-gated Ca 2+ channel Synaptic cleft Ligand-gated ion channels Na + K+K+ Ligand- gated ion channel Postsynaptic membrane Neuro- transmitter 1Ca 2+ 2 3 4 5 6

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Direct Synaptic Transmission The process of direct synaptic transmission – Involves the binding of neurotransmitters to ligand-gated ion channels Neurotransmitter binding – Causes the ion channels to open, generating a postsynaptic potential

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings After its release, the neurotransmitter – Diffuses out of the synaptic cleft – May be taken up by surrounding cells and degraded by enzymes

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Major neurotransmitters Table 48.1

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.5: The vertebrate nervous system is regionally specialized In all vertebrates, the nervous system – Shows a high degree of cephalization and distinct CNS and PNS components Figure 48.19 Central nervous system (CNS) Peripheral nervous system (PNS) Brain Spinal cord Cranial nerves Ganglia outside CNS Spinal nerves

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The brain provides the integrative power – That underlies the complex behavior of vertebrates The spinal cord integrates simple responses to certain kinds of stimuli – And conveys information to and from the brain

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The PNS can be divided into two functional components – The somatic nervous system and the autonomic nervous system Peripheral nervous system Somatic nervous system Autonomic nervous system Sympathetic division Parasympathetic division Enteric division Figure 48.21

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The somatic nervous system – Carries signals to skeletal muscles The autonomic nervous system – Regulates the internal environment, in an involuntary manner – Is divided into the sympathetic, parasympathetic, and enteric divisions

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The sympathetic division – Correlates with the “fight-or-flight” response The parasympathetic division – Promotes a return to self-maintenance functions The enteric division – Controls the activity of the digestive tract, pancreas, and gallbladder

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Brainstem The brainstem consists of three parts – The medulla oblongata, the pons, and the midbrain medulla oblongata pons midbrain

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The medulla oblongata – Contains centers that control several visceral functions The pons – Also participates in visceral functions The midbrain – Contains centers for the receipt and integration of several types of sensory information

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cerebellum The cerebellum – Is important for coordination and error checking during motor, perceptual, and cognitive functions

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Diencephalon The embryonic diencephalon develops into three adult brain regions – The epithalamus, thalamus, and hypothalamus

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The epithalamus – Includes the pineal gland and the choroid plexus The thalamus – Is the main input center for sensory information going to the cerebrum and the main output center for motor information leaving the cerebrum

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The hypothalamus regulates – Homeostasis – Basic survival behaviors such as feeding, fighting, fleeing, and reproducing

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cerebrum The cerebrum – Develops from the embryonic telencephalon

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In humans, the largest and most complex part of the brain – Is the cerebral cortex, where sensory information is analyzed, motor commands are issued, and language is generated A thick band of axons, the corpus callosum – Provides communication between the right and left cerebral cortices

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.6: The cerebral cortex controls voluntary movement and cognitive functions Each side of the cerebral cortex has four lobes – Frontal, parietal, temporal, and occipital Frontal lobe Temporal lobeOccipital lobe Parietal lobe Frontal association area Speech Smell Hearing Auditory association area Vision Visual association area Somatosensory association area Reading Speech Taste Somatosensory cortex Motor cortex Figure 48.27

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lateralization of Cortical Function The left hemisphere – Becomes more adept at language, math, logical operations, and the processing of serial sequences The right hemisphere – Is stronger at pattern recognition, nonverbal thinking, and emotional processing

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Memory and Learning The frontal lobes – Are a site of short-term memory – Interact with the hippocampus and amygdala to consolidate long-term memory

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Schizophrenia About 1% of the world’s population – Suffers from schizophrenia Schizophrenia is characterized by – Hallucinations, delusions, blunted emotions, and many other symptoms Available treatments have focused on – Brain pathways that use dopamine as a neurotransmitter

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Depression Two broad forms of depressive illness are known – Bipolar disorder and major depression Bipolar disorder is characterized by – Manic (high-mood) and depressive (low-mood) phases In major depression – Patients have a persistent low mood

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Treatments for these types of depression include – A variety of drugs such as Prozac and lithium

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alzheimer’s Disease Alzheimer’s disease (AD) – Is a mental deterioration characterized by confusion, memory loss, and other symptoms

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A successful treatment for AD in humans – May hinge on early detection of senile plaques

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parkinson’s Disease Parkinson’s disease is a motor disorder – Caused by the death of dopamine-secreting neurons in the substantia nigra – Characterized by difficulty in initiating movements, slowness of movement, and rigidity There is no cure for Parkinson’s disease – Although various approaches are used to manage the symptoms