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26 Lecture Ppt

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    26 Lecture Ppt 26 Lecture Ppt Presentation Transcript

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