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26 Lecture Ppt

  1. 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 26 Coordination by Neural Signaling
  2. 2. Most Animals Have a Nervous System That Allows Responses to Stimuli
  3. 3. 26.1 Invertebrates reflect an evolutionary trend toward bilateral symmetry and cephalization <ul><li>Invertebrate Nervous Organization </li></ul><ul><ul><li>In simple animals, such as sponges, the most common observable response is closure of the osculum (central opening) </li></ul></ul><ul><ul><li>Hydras (cnidarians) have a nerve net that is composed of neurons </li></ul></ul><ul><ul><li>Planarians, (flatworms) have a ladderlike nervous system </li></ul></ul><ul><ul><li>In annelids (earthworm), arthropods (crab), and molluscs (squid) the nervous system shows further advances </li></ul></ul><ul><li>Cephalization - concentration of ganglia and sensory receptors in a head region </li></ul><ul><ul><li>Ganglion (pl. ganglia) - cluster of neurons </li></ul></ul>
  4. 4. Figure 26.1A Evolution of the nervous system
  5. 5. <ul><li>Figure 26.1A Evolution of the nervous system (continued) </li></ul>
  6. 6. Vertebrate Nervous Organization <ul><li>Cephalization, and bilateral symmetry, results in paired sensory receptors to gather information about environment </li></ul><ul><ul><li>Eyes, ears, and olfactory structures </li></ul></ul><ul><li>Central nervous system (CNS) </li></ul><ul><ul><li>Spinal cord and brain and develops from an embryonic dorsal neural tube </li></ul></ul><ul><ul><ul><li>Ascending tracts carry sensory information to the brain, and descending tracts carry motor commands to the neurons in the spinal cord that control the muscles </li></ul></ul></ul><ul><li>Vertebrate brain divided into three parts </li></ul><ul><ul><li>Hindbrain - most ancient part and regulates motor activity below the level of consciousness </li></ul></ul><ul><ul><li>Midbrain - optic lobes are part of the midbrain and was a center for coordinating reflexes involving the eyes and ears </li></ul></ul><ul><ul><li>Forebrain - originally dealt mainly with smell. Later, the thalamus evolved to receive sensory input from the midbrain and the hindbrain and to pass it on to cerebrum </li></ul></ul><ul><li>Cerebrum integrates sensory and motor input and is particularly associated with higher mental capabilities </li></ul>
  7. 7. Figure 26.1B Organization of the vertebrate brain
  8. 8. 26.2 Humans have well-developed central and peripheral nervous systems <ul><li>Peripheral nervous system (PNS) consists of all the nerves and ganglia that lie outside the CNS </li></ul><ul><ul><li>All signals that enter and leave the CNS travel through paired nerves </li></ul></ul><ul><ul><ul><li>Those connected to spinal cord are spinal nerves </li></ul></ul></ul><ul><ul><ul><li>Those attached to brain are cranial nerves </li></ul></ul></ul><ul><ul><li>Somatic sensory axons (fibers) send signals from the skin and special sense organs </li></ul></ul><ul><ul><li>Visceral sensory fibers convey information from the internal organs </li></ul></ul><ul><li>CNS and PNS must work in harmony to carry out three primary functions </li></ul><ul><ul><li>Receive sensory input </li></ul></ul><ul><ul><li>Perform integration </li></ul></ul><ul><ul><li>Generate motor output </li></ul></ul>
  9. 9. Figure 26.2 Organization of the nervous system in humans
  10. 10. Neurons Process and Transmit Information
  11. 11. 26.3 Neurons are the functional units of a nervous system <ul><li>Neurons (nerve cells) receive sensory information and convey information to an integration center </li></ul><ul><ul><li>Three major parts </li></ul></ul><ul><ul><ul><li>Cell body - contains a nucleus and a variety of organelles </li></ul></ul></ul><ul><ul><ul><li>Dendrites - short, highly branched processes receive signals from sensory receptors or other neurons and transmit them to cell body </li></ul></ul></ul><ul><ul><ul><li>Axon - portion of the neuron that conveys information to another neuron or to other cells </li></ul></ul></ul><ul><ul><li>Axons bundle together to form nerves and are often called nerve fibers </li></ul></ul><ul><ul><li>Axons are covered by a white insulating layer called the myelin sheath </li></ul></ul><ul><li>Neuroglia - cells that provide support and nourishment to the neurons </li></ul><ul><ul><li>Myelin sheath is formed from membranes of tightly spiraled neuroglia </li></ul></ul><ul><ul><li>In PNS, Schwann cells perform this function, leaving gaps called nodes of Ranvier , or neurofibril nodes </li></ul></ul>
  12. 12. Types of Neurons <ul><li>Motor (efferent) neurons carry nerve impulses from CNS to muscles or glands </li></ul><ul><ul><li>Have many dendrites and a single axon </li></ul></ul><ul><ul><li>Cause muscle to contract or glands to secrete </li></ul></ul><ul><li>Sensory (afferent) neurons take nerve impulses from sensory receptors to the CNS </li></ul><ul><ul><li>Sensory receptors may be the end of a sensory neuron itself (a pain or touch receptor), or may be a specialized cell that forms a synapse with a sensory neuron </li></ul></ul><ul><li>Interneurons (association neurons) occur entirely within the CNS </li></ul><ul><ul><li>Parallel the structure of motor neurons and convey nerve impulses between various parts of the CNS </li></ul></ul>
  13. 13. Figure 26.3A Motor neuron
  14. 14. Figure 26.3B Sensory neuron
  15. 15. Figure 26.3C Interneuron
  16. 16. 26.4 Neurons have a resting potential across their membranes when they are not active <ul><li>Voltage, in millivolts (mV), is a measure of the electrical potential difference between two points </li></ul><ul><ul><li>In the case of a neuron, the two points are the inside and the outside of the axon </li></ul></ul><ul><li>Membrane potential - w hen an electrical potential difference exists between the inside and outside of a cell </li></ul><ul><li>When a neuron is not conducting an impulse, its resting potential is about −65 mV </li></ul><ul><ul><li>Negative sign indicates that the inside of the cell is more negative than the outside </li></ul></ul><ul><li>Potential is created by an unequal distribution of ions </li></ul><ul><ul><li>Due to the activity of the sodium-potassium pump, which moves three sodium ions (Na + ) out of the neuron for every two potassium ions (K + ), it moves into the neuron </li></ul></ul>
  17. 17. Figure 26.4 Resting potential: More Na + outside the axon and more K + inside the axon. Inside is −65 mV, relative to the outside
  18. 18. 26.5 Neurons have an action potential across axon membranes when they are active <ul><li>Action potential - rapid change in polarity across axonal membrane as nerve impulse occurs </li></ul><ul><li>An action potential uses two types of gated ion channels in the axon membrane </li></ul><ul><ul><li>First, a gated ion channel allows sodium (Na + ) to pass into the axon </li></ul></ul><ul><ul><li>Another gated ion channel allows potassium (K + ) to pass out of the axon </li></ul></ul><ul><li>If a stimulus causes the axon membrane to depolarize to threshold , an action potential occurs in an all-or-none manner </li></ul>
  19. 19. Figure 26.5A An action potential can be visualized as voltage changes over time
  20. 20. Depolarization and Repolarization <ul><li>Sodium Gates Open </li></ul><ul><ul><li>When an action potential begins, the gates of the sodium channels open, and Na + flows into the axon </li></ul></ul><ul><ul><ul><li>Membrane potential changes from −65 mV to +40 mV </li></ul></ul></ul><ul><ul><li>Called depolarization because inside axon changes from negative to positive </li></ul></ul><ul><li>Potassium Gates Open </li></ul><ul><ul><li>Gates of potassium channels open, and K + flows out of axon </li></ul></ul><ul><ul><ul><li>Action potential changes from +40 mV back to −65 mV </li></ul></ul></ul><ul><ul><li>Called repolarization because inside of axon becomes negative again as K + exits the axon </li></ul></ul>
  21. 21. Figure 26.5B Action potential begins: Depolarization to +40 mV as Na + gates open and Na + moves to inside the axon
  22. 22. Figure 26.5C Action potential ends: Repolarization to −65 mV as K + gates open and K + moves to outside the axon
  23. 23. 26.6 Propagation of an action potential is speedy <ul><li>In nonmyelinated axons, action potential travels down an axon one section at a time, at a speed of about 1 m/second </li></ul><ul><ul><li>As soon as an action potential has moved on, the previous section undergoes a refractory period , during which the Na + gates are unable to open </li></ul></ul><ul><ul><ul><li>The action potential cannot move backward and instead always moves down an axon toward its terminals </li></ul></ul></ul><ul><ul><li>After refractory period, the sodium potassium pump restores the previous ion distribution by pumping Na + to outside the axon and K + to inside the axon </li></ul></ul><ul><li>In myelinated axons, gated ion channels that produce action potential are concentrated at the nodes of Ranvier </li></ul><ul><ul><li>Ion exchange only at the nodes makes the action potential travel faster in nonmyelinated axons called saltatory conduction </li></ul></ul>
  24. 24. Figure 26.6 Saltatory conduction
  25. 25. 26.7 Communication between neurons occurs at synapses <ul><li>Every axon branches into many fine endings, tipped by a small swelling, called an axon terminal </li></ul><ul><ul><li>Each terminal lies very close to the dendrite (or the cell body) of another neuron </li></ul></ul><ul><li>Region of close proximity is called a synapse </li></ul><ul><ul><li>At synapse, membrane of first neuron is pre synaptic </li></ul></ul><ul><ul><li>The membrane of the next neuron is the post synaptic </li></ul></ul><ul><ul><li>Small gap between the neurons is the synaptic cleft </li></ul></ul><ul><li>A nerve impulse cannot cross a synaptic cleft </li></ul><ul><ul><li>Transmission across a synapse is carried out by molecules called neurotransmitters , which are stored in synaptic vesicles </li></ul></ul>
  26. 26. Figure 26.7 Synapse structure and function
  27. 27. 26.8 Neurotransmitters can be stimulatory or inhibitory <ul><li>Acetylcholine (ACh) and norepinephrine (NE) are well-known neurotransmitters in both the CNS and the PNS </li></ul><ul><ul><li>In the PNS, ACh excites skeletal muscle but inhibits cardiac muscle </li></ul></ul><ul><ul><li>ACh has either an excitatory or inhibitory effect on smooth muscle or glands </li></ul></ul><ul><li>In the CNS, NE is important to dreaming, waking, and mood </li></ul><ul><ul><li>Serotonin, another neurotransmitter, is involved in thermoregulation, sleeping, emotions, and perception </li></ul></ul><ul><li>Clearing of Neurotransmitter from a Synapse </li></ul><ul><ul><li>Once a neurotransmitter has been released into a synaptic cleft and has initiated a response, it is removed from the cleft </li></ul></ul><ul><ul><li>Short existence of neurotransmitters at a synapse prevents continuous stimulation (or inhibition) of postsynaptic membranes </li></ul></ul>
  28. 28. 26.9 Integration is a summing up of stimulatory and inhibitory signals <ul><li>A single neuron can have many synapses all over its dendrites and the cell body </li></ul><ul><ul><li>A neuron is on the receiving end of many excitatory and inhibitory signals </li></ul></ul><ul><ul><ul><li>An excitatory neurotransmitter produces a signal that drives the neuron closer to threshold </li></ul></ul></ul><ul><ul><ul><li>An inhibitory neurotransmitter produces a signal that drives the neuron further from threshold </li></ul></ul></ul><ul><li>Integration is the summing up of excitatory and inhibitory signals </li></ul><ul><ul><li>If a neuron receives many excitatory signals the axon will transmit a nerve impulse </li></ul></ul><ul><ul><li>If a neuron receives both inhibitory and excitatory signals, the summing up of these signals may prohibit the axon from reaching threshold and firing </li></ul></ul>
  29. 29. Figure 26.9 Synaptic integration
  30. 30. APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 26.10 Drugs that interfere with neurotransmitter release or uptake may be abused <ul><li>Alcohol </li></ul><ul><ul><li>Acts as a depressant on many parts of the brain where it affects neurotransmitter release or uptake </li></ul></ul><ul><ul><ul><li>Increases the action of GABA, which inhibits motor neurons, and increases the release of endorphins </li></ul></ul></ul><ul><li>Nicotine </li></ul><ul><ul><li>Binds to neurons, causing the release of dopamine, neurotransmitter that promotes a sense of pleasure and is involved in motor control </li></ul></ul><ul><ul><li>In the PNS, nicotine is a stimulant by mimicking acetylcholine increasing heart rate, blood pressure, and muscle activity </li></ul></ul><ul><li>Club and Date Rape Drugs </li></ul><ul><ul><li>Structure of methamphetamine is similar to that of dopamine, and its stimulatory effect mimics that of cocaine </li></ul></ul><ul><ul><li>Ecstasy has an overstimulatory effect on neurons that produce serotonin, which, like dopamine, elevates our mood </li></ul></ul><ul><li>Cocaine </li></ul><ul><ul><li>Powerful stimulant in CNS, interferes with re-uptake of dopamine at synapses </li></ul></ul><ul><ul><li>Result is a rush of well-being that lasts from 5 to 30 minutes </li></ul></ul>
  31. 31. Heroin, Marijuana and Treatment for Addictive Drugs <ul><li>Heroin </li></ul><ul><ul><li>Highly addictive drug that acts as a depressant in the nervous system </li></ul></ul><ul><ul><li>Come from opium poppy plant, thus called opiates </li></ul></ul><ul><ul><ul><li>Opiates depress breathing, block pain pathways, cloud mental function, and cause nausea </li></ul></ul></ul><ul><li>Marijuana (THC) </li></ul><ul><ul><li>THC may mimic the actions of anandamide, a neurotransmitter </li></ul></ul><ul><ul><li>When THC reaches CNS, person experiences euphoria, with alterations in vision and judgment </li></ul></ul><ul><ul><ul><li>In heavy users, hallucinations, anxiety, depression, body image distortions, paranoia, and psychotic symptoms can result </li></ul></ul></ul><ul><li>Treatment for Addictive Drugs </li></ul><ul><ul><li>Mainly consists of behavior modification </li></ul></ul><ul><ul><li>Heroin addiction can be treated with synthetic opiate compounds, such as methadone that decrease withdrawal symptoms and block heroin’s effects </li></ul></ul><ul><ul><li>New treatment techniques include the administration of antibodies to block the effects of cocaine and methamphetamine </li></ul></ul>
  32. 32. Figure 26.10 Drug use
  33. 33. The Vertebrate Central Nervous System (CNS) Consists of the Spinal Cord and Brain
  34. 34. 26.11 The human spinal cord and brain function together <ul><li>CNS consists of the spinal cord and the brain, where sensory information is received and motor control is initiated </li></ul><ul><ul><li>Spinal cord and brain are wrapped in three protective membranes known as meninges </li></ul></ul><ul><ul><ul><li>Spaces between meninges filled with cerebrospinal fluid that protects CNS </li></ul></ul></ul><ul><li>Spinal Cord - bundle of nervous tissue enclosed in vertebral column </li></ul><ul><ul><li>Extends from base of the brain to the vertebrae just below the rib cage </li></ul></ul><ul><ul><li>Two main functions </li></ul></ul><ul><ul><ul><li>Center for many reflex actions , automatic responses to external stimuli </li></ul></ul></ul><ul><ul><ul><li>Provides a means of communication between the brain and the spinal nerves, which leave the spinal cord </li></ul></ul></ul><ul><ul><li>Central portion of gray matter and a peripheral region of white matter </li></ul></ul><ul><ul><ul><li>Gray matter consists of cell bodies and unmyelinated fibers </li></ul></ul></ul><ul><ul><li>Myelinated long fibers of interneurons that run together in bundles called tracts give white matter its color </li></ul></ul><ul><ul><ul><li>Tracts connect the spinal cord to the brain </li></ul></ul></ul><ul><li>Brain Ventricles - brain contains four interconnected chambers called ventricles </li></ul><ul><ul><li>Two lateral ventricles are inside the cerebrum </li></ul></ul><ul><ul><li>Third ventricle is surrounded by the diencephalon, and the fourth ventricle lies between the cerebellum and the pons </li></ul></ul>
  35. 35. Figure 26.11 The human brain
  36. 36. 26.12 The cerebrum performs integrative activities <ul><li>Cerebrum - largest portion of the brain in humans </li></ul><ul><ul><li>Last center to receive sensory input and carry out integration before commanding voluntary motor responses </li></ul></ul><ul><li>Cerebral Hemispheres - brain is divided into two halves </li></ul><ul><ul><li>Each hemisphere receives information from and controls the opposite side of the body </li></ul></ul><ul><ul><li>The two are connected by a bridge of tracts within the corpus callosum </li></ul></ul><ul><li>The Cerebral Cortex </li></ul><ul><ul><li>A thin, but highly convoluted, outer layer of gray matter that covers the cerebral hemispheres </li></ul></ul><ul><ul><ul><li>Primary motor area is in the frontal lobe and is where voluntary commands to skeletal muscles begin </li></ul></ul></ul><ul><ul><ul><li>Primary somatosensory area is in the parietal lobe and sensory information from the skin and skeletal muscles arrives here </li></ul></ul></ul><ul><li>Basal Nuclei </li></ul><ul><ul><li>Integrate motor commands, ensure proper muscle groups activated </li></ul></ul><ul><ul><li>Huntington disease and Parkinson disease are believed to be due to malfunctioning basal nuclei </li></ul></ul>
  37. 37. Figure 26.12 The lobes of a cerebral hemisphere
  38. 38. 26.13 The other parts of the brain have specialized functions <ul><li>Hypothalamus and thalamus are in the diencephalon , a region that encircles the third ventricle </li></ul><ul><ul><li>Hypothalamus forms the floor of the third ventricle </li></ul></ul><ul><ul><li>Thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle </li></ul></ul><ul><ul><ul><li>It is on the receiving end for all sensory input except smell </li></ul></ul></ul><ul><ul><li>Pineal gland , which secretes the hormone melatonin, is located in the diencephalon </li></ul></ul><ul><ul><li>Cerebellum lies under the cerebrum and is separated from the brain stem by the fourth ventricle </li></ul></ul><ul><ul><ul><li>Receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts, and it also receives motor output from the cerebral cortex </li></ul></ul></ul><ul><li>Brain stem contains the midbrain, the pons, and the medulla oblongata </li></ul><ul><ul><li>Midbrain acts as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum </li></ul></ul><ul><ul><ul><li>Pons contains bundles of axons traveling between cerebellum and rest of CNS </li></ul></ul></ul><ul><ul><ul><li>Medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and blood pressure </li></ul></ul></ul>
  39. 39. Figure 26.13 The reticular activating system
  40. 40. 26.14 The limbic system is involved in memory and learning as well as in emotions <ul><li>Limbic system - complex network of tracts and nuclei that incorporates portions of the cerebral lobes, the basal nuclei, and diencephalon </li></ul><ul><ul><li>Blends higher mental functions and primitive emotions </li></ul></ul><ul><ul><li>Two significant structures </li></ul></ul><ul><ul><ul><li>Hippocampus - well situated in brain to make the frontal lobe aware of past experiences stored in various sensory areas </li></ul></ul></ul><ul><ul><ul><li>Amygdala - in particular, adds emotional overtones </li></ul></ul></ul><ul><li>Learning and Memory </li></ul><ul><ul><li>Memory is the ability to hold a thought in mind or recall events from the past </li></ul></ul><ul><ul><ul><li>Frontal lobe is active during short-term memory </li></ul></ul></ul><ul><ul><li>A gradual extinction of brain cells, particularly in the hippocampus, appears to be the underlying cause of Alzheimer disease (AD) </li></ul></ul>
  41. 41. Figure 26.14 The limbic system (in purple)
  42. 42. The Vertebrate Peripheral Nervous System (PNS) Consists of Nerves
  43. 43. 26.15 The peripheral nervous system contains cranial and spinal nerves <ul><li>The peripheral nervous system (PNS) lies outside the central nervous system and contains nerves, bundles of axons </li></ul><ul><ul><li>Cranial nerves are attached to the brain </li></ul></ul><ul><ul><ul><li>Some are motor nerves that contain only motor fibers, and others are mixed nerves that contain both sensory and motor fibers </li></ul></ul></ul><ul><ul><li>Spinal nerves are attached to spinal cord </li></ul></ul><ul><ul><ul><li>A spinal nerve separates the axons of sensory neurons from the axons of motor neurons </li></ul></ul></ul><ul><ul><ul><li>Cell body of a sensory neuron is in the dorsal root ganglion </li></ul></ul></ul><ul><ul><ul><li>Each spinal nerve serves the particular region of the body in which it is located </li></ul></ul></ul>
  44. 44. Figure 26.15A Anatomy of a nerve
  45. 45. Figure 26.15B Ventral surface of brain showing the attachment of the cranial nerves (yellow)
  46. 46. 26.16 In the somatic system, reflexes allow us to respond quickly to stimuli <ul><li>Somatic system nerves serve the skin, joints, and skeletal muscles </li></ul><ul><ul><li>Includes nerves that take </li></ul></ul><ul><ul><ul><li>Sensory information from external sensory receptors in the skin and joints to the CNS </li></ul></ul></ul><ul><ul><ul><li>Motor commands away from the CNS to the skeletal muscles </li></ul></ul></ul><ul><ul><li>Acetylcholine (ACh) active in somatic system </li></ul></ul><ul><li>Reflexes - involuntary responses to stimuli </li></ul><ul><ul><li>Involve either the brain or just the spinal cord </li></ul></ul><ul><ul><li>Enable the body to react swiftly to stimuli that could disrupt homeostasis </li></ul></ul>
  47. 47. Figure 26.16 A reflex arc showing the path of a spinal reflex
  48. 48. 26.17 In the autonomic system, the parasympathetic and sympathetic divisions control the actions of internal organs <ul><li>Autonomic system - automatically and involuntarily regulates the activity of glands and cardiac and smooth muscle </li></ul><ul><li>Divided into parasympathetic and sympathetic </li></ul><ul><ul><li>Parasympathetic Division </li></ul></ul><ul><ul><ul><li>Includes a few cranial nerves as well as axons that arise from the last portion of the spinal cord </li></ul></ul></ul><ul><ul><ul><li>Promotes all the internal responses we associate with a relaxed state </li></ul></ul></ul><ul><ul><ul><ul><li>Example: causes the pupil of the eye to constrict, promotes digestion of food, and retards the heartbeat </li></ul></ul></ul></ul><ul><ul><li>Sympathetic Division </li></ul></ul><ul><ul><ul><li>Axons arise from portions of the spinal cord </li></ul></ul></ul><ul><ul><ul><li>Important during emergency situations and is associated with fight or flight </li></ul></ul></ul><ul><ul><ul><ul><li>Example: accelerates the heartbeat and dilates the bronchi, while at the same time it inhibits the digestive tract </li></ul></ul></ul></ul>
  49. 49. Figure 26.17 Autonomic system
  50. 50. Connecting the Concepts: Chapter 26 <ul><li>The human nervous system has just three functions: sensory input, integration, and motor output </li></ul><ul><li>The central nervous system (CNS) carries out the function of integrating incoming data </li></ul><ul><ul><li>The brain allows us to perceive our environment, to reason, and to remember </li></ul></ul><ul><ul><li>After sensory data have been processed by the CNS, motor output occurs </li></ul></ul><ul><ul><li>Muscles and glands are the effectors that allow us to respond to the original stimuli </li></ul></ul><ul><li>The human peripheral nervous system (PNS) contains nerves that carry sensory input to the CNS and motor output to the muscles and glands </li></ul><ul><li>There is a division of labor among the nerves </li></ul><ul><ul><li>The cranial nerves serve the face, teeth, and mouth; below the head, there is only one cranial nerve, the vagus nerve </li></ul></ul><ul><ul><li>All body movements are controlled by spinal nerves, and this is why paralysis may follow a spinal injury </li></ul></ul>

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