Biology the Study of Life

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					Chapter 26 Coordination by Neural Signaling
Chapter Outline

I. Getting a Head
        A. Not all animals have a head.
            1. Echinoderms (sea urchins) lack a head.
            2. Clams lack a head – have inactive lifestyle.
            3. Octopus has a head – active lifestyle.
                a) Also has brain, eyes and arms for hunting.
                b) Head is an advantage for predator lifestyle.
            4. Marine vertebrates have a head.
                a) Head region is indistinct from rest of body.
                b) This is an advantage for an aquatic lifestyle – streamlined.
            5. Land animals have a more definitive head.
                a) Lifestyle, feeding behaviors influence shape of head.
        B. Type of nervous system is more critical than presence of head.
            1. Hydra – only a few nerve cells present – very inactive lifestyle.
            2. Presence of brain, protective skull, nerves, sense organs – active lifestyle.
                a) Receive information from the environment, interpret, and respond.
            3. Vertebrate Brain regions include:
                a) Hindbrain.
                b) Midbrain.
                c) Forebrain.
            4. Function of regions varies among vertebrates.
                a) Fishes/amphibians – complex behaviors via midbrain.
                b) Mammals – complex behaviors via forebrain.
                    1) Human forebrain is most well-developed.

II. Most Animals Have a Nervous System That Allows Responses to Stimuli
-Critical concepts include: evolutionary trends in nervous system development, central
nervous system, peripheral nervous system, and integration of CNS and PNS.

   26.1 Invertebrates reflect an evolutionary trend toward bilateral symmetry and
   cephalization
       A. Nervous system monitors internal and external environments.
           1. Adjusts internal conditions to maintain homeostasis.
           2. Comparison of nervous system organization indicates evolutionary trends.
       B. Invertebrate Nervous Organization.
           1. Simple animals – sponges (cellular level of organization).
               a) Respond to stimuli (ex.: closure of osculum).
           2. Simple animals – hydras (tissue level of organization).
               a) Respond to stimuli with more complex movements.
                   1) Tentacle extension, body contraction.
               b) Nerve Net – Neurons in contact with each other and contractile cell.
           3. Simple animals – sea anemones, jellyfish (cnidarians).
               a) Possess two nerve nets.



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           1) Fast-acting nerve net – allows major responses to stimuli.
           2) Slow-acting nerve net – coordinates slower, delicate movements.
   4. Simple animals – planarians – flatworms.
       a) Bilaterally organized nervous system.
           1) Two ventrally located longitudinal nerve cords (nerve bundles).
           2) Extend from cerebral ganglia to posterior end of body.
           3) Transverse nerves connect the nerve cords.
           4) Transverse nerves also connect cerebral ganglia to eyespots.
       b) Represents a ladderlike nervous system.
           1) Cephalization – Concentration of ganglia and sensory receptors in
               head region.
           2) Ganglion – Cluster of neurons (ganglia).
               i) Anterior cerebral ganglia receives information from eyespots.
           3) Rapid transfer of information along nerve cords.
           4) Nerve cord connections coordinate side localized movement.
       c) Cephalization + Bilateral symmetry = evolutionary advance for nervous
           system development.
   5. Simple animals include annelids, arthropods, and molluscs.
       a) Further nervous system advances.
           1) Brain + ventral nerve cord with a ganglion in each segment.
               i) Includes the annelids and arthropods.
           2) Brain controls the activity of the ganglia and associated nerves.
           3) Well-developed brain/well-developed sense organs (eyes).
               i) Associated with crab/squid.
           4) In general – increase in the number of neurons present.
C. Vertebrate Nervous Organization.
   1. Several types of paired sensory receptors.
       a) The result of cephalization plus bilateral symmetry.
       b) Includes: eyes, ears, and olfactory structures.
   2. Paired cranial and spinal nerves – numerous nerve fibers.
   3. More neurons than invertebrates.
   4. Central Nervous System (CNS).
       a) Consists of: spinal cord and brain.
           1) Develops from embryonic dorsal neural tube.
           2) Spinal cord is continuous with brain.
           3) Ascending tracts carry information to the brain.
           4) Descending tracts carry information to neurons.
   5. Vertebrate brain regions.
       a) Hindbrain.
           1) Most ancient region.
           2) Well-developed in nearly all vertebrates.
           3) Regulates motor activity of subconscious.
               i) Heart and lung activity in humans.
       b) Midbrain.
           1) Contains the optic lobes.
       c) Forebrain.



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                   1) Processes sensory information.
                   2) Originally limited to sense of smell.
                   3) Thalamus evolved to receive input from midbrain and hindbrain.
                   4) Hypothalamus – Involved in regulation of homeostasis.
           6. Cerebrum – Integrates sensory and motor input.
               a) Associated with higher mental capabilities.

   26.2 Humans have well-developed central and peripheral nervous systems
       A. Human CNS – Brain + spinal cord.
          1. Brain enclosed in skull.
          2. Spinal cord housed in vertebral column.
          3. Peripheral Nervous System (PNS).
              a) All nerves and ganglia outside of the CNS.
              b) Spinal Nerves – Paired nerves that connect to the spinal cord.
              c) Cranial Nerves – Paired nerves attached to the brain.
              d) Sensory pathways deliver information to the CNS.
                  1) Somatic sensory axons – Signals from skins and external organs.
                  2) Somatic motor fibers – Skeletal muscle control.
                  3) Autonomic motor fibers – Control smooth/cardiac muscle and
                      glands.
                      i) Sympathetic division.
                      ii) Parasympathetic division.
          4. CNS and PNS must coordinate for three primary functions.
              a) Receive Sensory Input.
                  1) Receptors on skin/organs detect internal/external stimuli.
                  2) Generate nerve impulses that travel to CNS.
              b) Perform Integration.
                  1) CNS collects all information from body.
              c) Generate Motor Output.
                  1) Nerve impulses from CNS to muscles and glands.
          5. Stimuli responses include muscle contractions and gland secretions.

III. Neurons Process and Transmit Information
-Critical concepts include: types of neurons, neuroglia, action potential, resting potential,
threshold, propagation of action potential, synapse, communication at synapses,
neurotransmitters, signal integration, and drug links to the CNS and PNS.

   26.3 Neurons are the functional units of a nervous system
       A. Nervous tissue is composed of two principle types of cells.
          1. Neurons – Nerve cells.
          2. Neuroglia – Cells that provide nourishment/support to neurons.
       B. Neuron characteristics and function
          1. Functional units of the nervous system.
          2. Receive and convey sensory information to brain.
          3. Conduct signals from integration center to response structures (muscles).
          4. Function dictates appearance.



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          a) Cell Body – Contains nucleus and organelles.
          b) Dendrites – Short, branched extensions.
              1) Receive signals from receptors.
              2) Transmit signals to the cell body.
          c) Axon – Extension from cell body – nerve fibers.
              1) Conveys information to other neurons/cells.
              2) Bundles of axons form nerves.
              3) Myelin Sheath – Insulating layer around axons.
   C. Neuroglia characteristics and function.
      1. Glial cells.
      2. Outnumber neurons.
      3. Different types in CNS.
          a) Microglia – Remove bacteria and debris.
          b) Astrocytes – Metabolic and structural support for neurons.
          c) Schwann cells – In PNS, form myelin sheath for axons.
              1) Nodes of Ranvier – Gaps in myelin sheath – neurofibril nodes.
          d) Oligodendrocyte – In CNS performs Schwann cell function.
   D. Types of Neurons – Classified based on function and shape.
      1. Motor (efferent) Neurons.
          a) Carry nerve impulses from CNS to muscles/glands.
          b) Have many dendrites and single axon.
      2. Sensory (afferent) Neurons.
          a) Relay impulses from receptors to CNS.
          b) Has axon connecting dendrites to cell body.
          c) Has axon also connecting cell body to CNS.
          d) Characterized by branched structures at input and output ends.
      3. Interneurons.
          a) Occur entirely within the CNS.
          b) Parallel the structure of motor neurons.
          c) Convey nerve impulses between various parts of the CNS.
              1) Connect sensory neurons and motor neurons.
              2) Connect opposite sides of spinal cord.
              3) Connect brain to spinal cord.
          d) Form pathways for processing thought, memory, and language.

26.4 Neurons have a resting potential across their membranes when they are not
active
    A. Neurons can be studied using excised axons and a voltmeter.
       1. Voltage (millivolts: mV) – Measure of electrical potential difference
           between two points.
       2. Two points of neuron – inside and outside of the axon.
       3. Membrane Potential – Electrical potential difference across the
           membrane.
       4. Polarity – Unequal distribution of electrical charges.
           a) Ex.: Positive charge on one side of membrane, negative charge on
               other.



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      5. Resting Potential – State where no impulse is conducted = ~-65mV.
   B. Membrane potential can be correlated to differences in ion distribution.
      1. This reflects changes in sodium-potassium pumps.
          a) Move three sodium ions out for every two potassium ions into axon.
          b) Membrane is more permeable to K+ than Na+.
              1) Potassium leaks out faster than sodium leaks in.
      2. Large negatively charged proteins present in axon cytoplasm.
   C. Neurons alter membrane potential to send nerve impulses.

26.5 Neurons have an action potential across axon membranes when they are
active
    A. Action Potential.
        1. Rapid change in polarity across an axonal membrane.
        2. Associated with nerve impulse.
        3. Can visualize as plot of voltage changes against time.
    B. Two types of gated ion channel proteins are used.
        1. Sodium specific gated ion channel.
            a) Allows Na+ ions to pass membrane.
            b) Functional during first part of action potential.
        2. Potassium specific gated ion channel.
            a) Allows K+ ions to pass membrane.
            b) Functional following the activity of first gated channel.
            c) Gated ion channels are stimulated to open and close.
                 1) Signal from neuron may be the stimulus.
    C. Threshold – Critical point of action potential.
        1. Referred to as an all-or-none-manner.
        2. Is the result of axonal membrane depolarization.
    D. Strength of an action potential does not change.
    E. Intense stimulus changes rate of axon firing (initiation of axon potential).
    F. The Sodium Gates Open scenario.
        1. Action potential begins with these gates open.
        2. Na+ flows into axon.
        3. Membrane potential changes from -65mV to + 40mV.
            a) Referred to as depolarization.
            b) Charge inside axon changes from negative to positive.
            c) Polarity reversal closes the sodium channel.
            d) Polarity reversal opens the potassium channel.
    G. The Potassium Gates Open scenario.
        1. K+ moves in through open potassium channels.
        2. K+ moves to outside the axon.
        3. Action potential changes from +40mV to -65mV.
            a) Referred to as repolarization.
            b) Returns to internal charge state.

26.6 Propagation of an action potential is speedy
    A. Nonmyelinated Axon impulse transfer.



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      1. Action potential travels one section at a time
          a) Speed ~ 1 m/second
          b) Refractory Period – Na+ gates are unable to open.
              1) Occurs when action potential moves out of section.
              2) Inhibits reverse travel of action potential.
              3) Action potential is forced toward terminal region.
              4) End of refractory period – ion distribution is restored.
   B. Myelinated Axon impulse transfer.
      1. Gated ion channels concentrated at nodes of Ranvier.
          a) Speeds up action potential transfer.
          b) Saltatory Conduction.
              1) Action potential “jumps” from node to node.
              2) Speeds up to 200m/second (450 mph).
   C. Multiple sclerosis – symptoms due to demyelination of axons.

26.7 Communication between neurons occurs at synapses
    A. Axon Terminals – Small swellings at tips of axon branches.
       1. Lie close to dendrite or cell body of another axon.
       2. Synapse – Region of close proximity of axon terminals.
           a) Presynaptic Membrane – Membrane of first neuron.
           b) Postsynaptic Membrane – Membrane of next neuron.
           c) Synaptic Cleft – Small gap between neurons.
       3. Nerve impulses cannot cross the synaptic cleft.
           a) Neurotransmitters – Molecules that transfer impulse across cleft gaps.
           b) Stored in synaptic vesicles.
       4. Gated calcium (Ca+2) channels open when impulse reaches terminal.
           a) Opens calcium gates, Ca+2 enter terminal.
               1) Increase in Ca+2 stimulates synaptic vesicles to merge with
                   presynaptic membrane.
               2) Neurotransmitters are released into the synaptic cleft.
               3) Neurotransmitters diffuse to postsynaptic membrane.
               4) Neurotransmitters bind to specific receptor proteins.
               5) Types of receptors dictate response – activation or inhibition of
                   response.
               6) Finally, neurotransmitter needs to be removed quickly from cleft.
               7) This prevents continuous stimulation or inhibition.

26.8 Neurotransmitters can be stimulatory or inhibitory
    A. Neurotransmitters include:
       1. Acetylcholine.
       2. Norepinephrine.
       3. Dopamine.
       4. Serotonin.
       5. GABA (gamma aminobutyric acid).
    B. Various drugs influence impulse transmission via:
       1. Enhance or block the release of neurotransmitters.



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       2. Mimic the action of neurotransmitters.
       3. Block the receptor.
       4. Interfere with removal of neurotransmitter from synaptic cleft.
   C. Acetylcholine (Ach) and Norepinephrine (NE).
       1. Well-known neurotransmitters of CNS and PNS.
       2. ACh deficiency in CNS is associated with Alzheimer disease.
       3. PNS ACh associated with:
           a) Excitation of skeletal muscle.
           b) Inhibition of cardiac muscle.
           c) Botulin toxins block the release of ACh at skeletal muscle synapses.
               1) 6 hours to 8 days post poisoning (via contaminated food) – death.
                   a) Due to inhibition of respiratory muscles.
               2) Toxin used on facial muscles to paralyze them – reduces wrinkles.
       4. CNS NE – Involved in dreaming, waking, and mood.
       5. Serotonin – Involved in thermoregulation, sleeping, emotions, perception.
           a) Reduced levels of NE and serotonin – associated with depression.
               1) Prozac – Drug, blocks removal of serotonin from a synapse.
       6. Dopamine and GABA – Primarily in CNS.
           a) Dopamine – Involved in emotions, control of motor function, attention.
               1) Lack of dopamine associated with Parkinson disease.
           b) GABA – Inhibitory neurotransmitter in CNS.
               1) Valium binds to GABA receptors – increases effects.
   D. Neuromodulators – Molecules that block the release of neurotransmitters.
       1. Caffeine – Interferes with inhibitory neurotransmitters in the brain.
       2. Substance P – Neuromodulator.
           a) Released in response to pain.
       3. Endorphins – Neuromodulator.
           a) Block the release of substance P – inhibits perception of pain.
           b) Associated with “runners high.”
           c) Opiates (codeine, heroin, morphine) bind endorphin receptors.
               1) Reduce pain and produce feeling of well-being.
   E. Clearing of Neurotransmitter from a Synapse.
       1. Occurs following binding and response initiation.
       2. Removal prevents continuous stimulation/inhibition of postsynaptic
           membrane.
       3. Enzymes rapidly inactivate neurotransmitters in some synapses.
           a) Acetylcholinesterase (AChE) degrades acetylcholine.
           b) GABA transaminase inactivates GABA.
       4. Presynaptic membranes can reabsorb neurotransmitters in some synapses.
           a) Repacked into vesicles or broken-down.

26.9 Integration is a summing up of stimulatory and inhibitory signals
    A. A single neuron can have many synapses.
        1. Found covering the cell body and dendrites.
        2. Up to 10,000 synapses.
    B. Excitatory neurotransmitters produce a signal.



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         1. This drives neuron closer to action potential.
             a) Polarizing effect.
     C. Inhibitory neurotransmitters produce a signal.
         2. Results in driving neuron further from an action potential.
             a) Hyperpolarizing effect.
     D. Integration – Summing of inhibitory and excitatory signal.
         1. Opposite signals can cancel each other out.
         2. Dominant signal influences output.

How Biology Impacts Our Lives:
 26.10 Drugs that interfere with neurotransmitter release or uptake may be abused
     A. Drug Abuse – Use of drug at dose level under harmful conditions.
     B. Addiction – Requirement of higher levels of drug to get same effect.
         1. Withdrawal Symptoms – Occur when drug levels are reduced.
     C. Alcohol.
         1. Most socially accepted – regular consumption by 65% of US adults.
         2. Depressant – Affects neurotransmitters in the brain.
             a) Increases the action of GABA – inhibits motor neurons.
             b) Increase levels of endorphins – natural pain killers.
             c) Sensations include relaxation, lowered inhibitions, impaired
                 concentration, impaired coordination, slurred speech, and vomiting.
             d) Excessive blood levels of alcohol can result in coma or death .
         3. Chronic consumption effects:
             a) Damage frontal lobes.
             b) Decrease brain size.
             c) Increase size of ventricles.
             d) Permanent memory loss, amnesia, confusion, apathy, disorientation.
             e) Permanent damage to the liver.
     D. Nicotine.
         1. Tobacco smoking delivers nicotine to CNS (midbrain).
         2. Bind neurons – release of dopamine.
             a) Promotes sense of pleasure.
         3. Stimulant – Increases heart rate, blood pressure, muscle activity.
             a) Mimics acetylcholine.
         4. Addiction rate is high – 70% of smokers.
         5. Withdrawal symptoms include:
             a) Irritability, headache, insomnia, weight gain, poor cognitive ability.
         6. Methods of quitting.
             a) Application of nicotine skin patches.
             b) Chewing nicotine gum.
             c) Oral drugs that block the actions of acetylcholine.
             d) Therapy success varies.
     E. Club and Date Rape Drugs.
         1. Methamphetamine – Meth or speed.
             a) Synthetic drug has a methyl group added to amphetamine.
             b) Simple process that uses many toxic chemicals.



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        c) Over 9 millions people have used it in the U.S.
        d) Mimics dopamine in structure.
        e) Mimics cocaine in stimulatory effects.
        f) Symptoms:
            1) Reverses fatigue – maintains wakefulness.
            2) Elevates user’s mood temporarily.
            3) Initial rush followed by irritability and violent behavior.
            4) Chronic – amphetamine psychosis – paranoia, hallucinations,
                aggressive, erratic behavior.
            5) Excessive use can result in hyperthermia, convulsions, and death.
    2. Ecstasy – Methylenedioxymethamphetamine.
        a) Similar effects to methamphetamine.
        b) Taken as a pill.
        c) Over-production of serotonin – elevates mood.
        d) Increases body temperature – potentially fatal.
    3. Date rape/predatory drugs.
        a) Rohypnol (roofies).
        b) Gamma-hydroxybutyric acid (GHB).
        c) Ketamine (special K).
        d) Cause relaxation, amnesia, and disorientation.
            1) Abusers use to assault victims.
        e) Used in conjunction with other drugs to enhance their effects.
F. Cocaine.
    1. Alkaloid derivative from the plant Erythroxylon coca.
    2. 35 million Americans users– sniffing, snorting, injection, and smoking.
    3. Powerful stimulant of CNS.
        a) Interferes with re-uptake of dopamine at synapses.
        b) Enhances mood for 5-30 minutes.
    4. Symptoms include insomnia, tremors, and cocaine psychosis (paranoid
        schizophrenia).
    5. Withdrawal causes fatigue, depression, irritability, memory loss,
        and confusion.
    6. Crack – Processed cocaine for smoking.
        a) Name refers to sound made when smoking.
        b) Smoking increases dose that reaches the brain – immediate rush.
        c) Long-term brain damage expected.
    7. Highly addictive.
        a) Death associated with cardiac and respiratory arrest.
G. Heroin.
    1. Derived from resin/sap of opium poppy plant.
    2. Highly addictive.
    3. Depressant.
    4. Drugs derived from opium are opiates.
        a) Includes morphine and codeine – painkilling effects.
    5. Most abused opiate.
    6. Converted to morphine in brain – generates feeling of euphoria.



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           7. Dangers associated with needle use – HIV/AIDS, hepatitis, bacterial
               infections.
           8. Users inject, snort, or smoke.
       H. Marijuana.
           1. Cannabis sativa flowering tops, leaves and stems (Indian hemp).
           2. THC – tetrahydrocannabinol – Resin that covers plant organs.
           3. Typically smoked (joint).
           4. Some medical applications.
           5. Mimics actions of anandamide.
               a) Class of chemicals – cannabinoids
               b) Receptors located in hippocampus, cerebellum, basal ganglia, cerebral
                   cortex – important for memory, balance, perception.
           6. Experience mild euphoria and alterations in vision and judgment.
               a) Hallucinations, depression, anxiety, paranoia, psychosis.
       I. Treatment for Addictive Drugs.
           1. Behavior modification is main treatment.
           2. Some chemical treatments – heroin – synthetic opiate compounds.
           3. Antibodies that block effects of cocaine/methamphetamine.
               a) Inhibit possible relapse by addicted users.

IV. The Vertebrate Central Nervous System (CNS) Consists of the Spinal Cord and
Brain
-Critical concepts include: spinal cord, brain ventricles, cerebral hemispheres, cerebral
cortex, basal nuclei, regions of the brain, reticular activating system, limbic system,
learning, and memory.

   26.11 The human spinal cord and brain function together
       A. CNS = spinal cord + brain.
           1. Protected by bone: skull (brain) and vertebrae (spinal cord).
           2. Protected by meninges.
               a) Three protective membranes surrounding structures.
               b) Meningitis – Inflammation of the meninges.
                   1) Disorder caused by bacteria or viruses.
               c) Cerebrospinal Fluid – Liquid that fills the spaces between meninges.
                   1) Cushions and protects the CNS.
                   2) Also contained within central canal of spinal cord – reservoir.
       B. Spinal Cord.
           1. Bundle of nervous tissue enclosed in the vertebral column.
           2. Extends from base of brain to vertebrae below rib cage.
           3. Two main functions.
               a) Center for reflex actions
                   1) Automatic responses to external stimuli.
               b) Communication between brain and spinal nerves that exit spinal cord.
           4. Cross section of spinal cord.
               a) Central portion = gray matter.
                   1) Cell bodies and unmyelinated fibers.



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              2) Two dorsal (posterior) horns.
              3) Two ventral (anterior) horns.
              4) Horns surround a central canal.
              5) Contains portions of sensory neurons and motor neurons.
              6) Also contains short interneurons that connect sensory/motor
                  neurons.
          b) Peripheral region = white matter.
              1) Tracts – Myelinated long fibers in bundles.
              2) Connect spinal cord to brain.
              3) Dorsal tracts primarily ascending – info to the brain.
              4) Ventral tracts primarily descending – info from the brain.
              5) Tracts cross:
                  i) Left brain controls right side of body.
                  ii) Right brain controls left side of body.
      5. Paralysis results from severing the spinal cord.
          a) Injury in cervical (neck) region usually paralyzes the four limbs.
              1) Quadriplegia.
          b) Injury in thoracic region may paralyze lower body.
              1) Paraplegia.
   C. Brain Ventricles.
      1. Four interconnected chambers called ventricles.
      2. Two Lateral Ventricles – Located inside the cerebrum.
      3. One ventricle is surrounded by the diencephalon.
      4. One ventricle lies between the cerebellum and the pons.
      5. Cerebrospinal fluid continuously produced in the ventricles.
          a) Flows between ventricles.
          b) Flows out of ventricles into meninges.

26.12 The cerebrum performs integrative activities
    A. Cerebrum – Largest portion of human brain.
       1. Coordinates the activities of other parts of the brain.
    B. Cerebral Hemispheres – Two halves of the cerebrum.
       1. Longitudinal Fissure – Groove that divides the right and left hemispheres.
       2. Right Hemisphere.
           a) Associated with:
               1) Artistic and musical ability.
               2) Emotion.
               3) Spatial relationships.
               4) Pattern recognition.
       3. Left Hemisphere.
           a) Associated with:
               1) Mathematics.
               2) Language.
               3) Analytical reasoning.
       4. Corpus Callosum – Bridge connecting right and left hemispheres.
       5. Sulci – Shallow grooves that divide hemispheres into lobes.



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      6. Frontal Lobe – Controls motor control, memory, reasoning, and judgment.
          a) Broca Area – Region on left side of lobe that controls speech.
      7. Parietal Lobes – Control sensory reception and integration and taste.
          a) Primary Taste Area – Accounts for taste sensations.
      8. Temporal Lobe – Primary auditory area – receives info from ears.
      9. Occipital Lobe – Most posterior lobe associated with sight.
          a) Primary Visual Area – Receives information from eyes.
   C. The Cerebral Cortex – Thin, convoluted layer of gray matter surrounding the
      cerebral hemispheres.
      1. Increase surface area of cerebral cortex enhances neuron connections.
      2. Primary Motor Area.
          a) Located in frontal lobe, ventral to central sulci.
          b) Controls voluntary movements to skeletal muscles.
          c) Size of area related to precision of motor control.
              1) Face and hand take up large portions of area.
      3. Primary Somatosensory Area.
          a) Dorsal to central sulci in parietal lobe.
          b) Receives sensory information from skin and skeletal muscle.
   D. Basal Nuclei.
      1. Masses of gray matter embedded in the white matter.
      2. Integrate motor commands – coordination of muscle groups.
      3. Huntington Disease and Parkinson Disease.
          a) Due to malfunctioning basal nuclei.

26.13 The other parts of the brain have specialized functions
    A. Diencephalon – Region that surrounds the third ventricle.
       1. Hypothalamus.
           a) Forms floor of third ventricle.
           b) Integration center.
           c) Maintains homeostasis.
           d) Regulates hunger, sleep, thirst, body temperature, and water balance.
           e) Controls the pituitary gland – links nervous and endocrine systems.
       2. Thalamus.
           a) Gray matter – sides and top of third ventricle.
           b) Receives all sensory input except smell.
           c) Integrates information (from nerves and tracts).
           d) Conveys information to correct regions of cerebrum.
               1) Referred to as the “Gatekeeper” of sensory information.
           e) Participates in higher brain function – memory and emotions.
       3. Pineal Gland – Located within the diencephalon.
           a) Secretes melatonin (hormone).
               1) Melantonin may have roles in jet lag, insomnia, and puberty.
    B. Cerebellum.
       1. Located under occipital lobe of cerebrum.
       2. Largest part of hindbrain.
       3. White matter connections link two separate portions of cerebellum.



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      4. Receives sensory input from eyes, ears, joints, and muscles.
          a) Integrates information.
          b) Relays information to muscles via brain stem.
          c) Maintains balance and coordination.
      5. Important in judging the passage of time.
   C. Brain Stem.
      1. Contains the midbrain, pons, and medulla oblongata.
          a) Midbrain.
               1) Relay area for tracts between cerebrum/spinal cord/cerebellum.
               2) Tracts cross in the brain stem.
          b) Pons – Bridge between cerebellum and CNS.
               1) Reflex center for visual, auditory, and tactile responses.
               2) Assists in regulating breathing rate.
          c) Medulla Oblongata.
               1) Reflex centers regulate: heartbeat, breathing, and blood pressure.
               2) Reflex centers for coughing, sneezing, vomiting, and hiccupping.
               3) Located just above the spinal cord.
   D. The Reticular Activating System.
      1. Network of nuclei and nerve fibers.
      2. Extend the length of brain stem.
      3. Reticular Formation – Receives/relays sensory signals to higher centers.
      4. Arouses the cerebrum via thalamus – causes alertness.
      5. Filters out unnecessary sensory stimuli.
      6. Activated with sudden stimulus – cold water.
      7. Deactivated with removal of stimuli.
      8. A severe injury to the RAS can cause a person to be comatose.

26.14 The limbic system is involved in memory and learning as well as in emotions
    A. Limbic System – Blends higher mental functions/primitive emotions.
        1. Network of tracts and nuclei.
        2. Incorporates cerebral lobes, basal nuclei, and diencephalon.
        3. Accounts for pleasure associated with sex or eating.
        4. Hippocampus.
            a) Seahorse shaped structure located in temporal lobe.
            b) Recognizes past experiences stored in sensory areas.
        5. Amygdala.
            a) Associates experiences with emotional response.
    B. Learning and Memory.
        1. Memory – Ability to hold a thought or recall past events.
        2. Learning takes place when we retain and use past memories.
        3. Frontal lobe is active for short term memory.
        4. Long-term memory.
            a) Combination of semantic and episodic memory.
            b) Semantic Memory – Numbers and words.
            c) Episodic Memory – Persons and events.
            d) Skill Memory – Independent of episodic – perform motor activities.



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               e) Long-term information stored in sensory area of cerebral cortex.
                   1) Hippocampus gathers this information.
                   2) Info used by the frontal lobe.
                   3) Amygdala activity associates strong emotion with memory.
           5. Long-Term Potentiation.
               a) Enhanced response at hippocampus synapses.
               b) Essential to memory storage.
               c) Over stimulation can cause cell death.
               d) Excitotoxicity – Cell death (apoptosis) due to over stimulation.
                   1) Due to action of glutamate (neurotransmitter).
                   2) Glutamate binds to the postsynaptic membrane.
                   3) Underlying cause of Alzheimer disease (AD).

V. The Vertebrate Peripheral Nervous System (PNS) Consists of Nerves
-Critical concepts include: peripheral nervous system, cranial nerves, spinal nerves,
somatic system, reflex arc, autonomic system, and parasympathetic and sympathetic
divisions.

   26.15 The peripheral nervous system contains cranial and spinal nerves
       A. Lies outside of the central nervous system.
       B. Contains nerves – bundles of axons.
           1. Axons within nerves are called nerve fibers.
           2. All nerves transfer impulses to and from the CNS.
           3. Cranial nerves arise from the brain.
               a) Sensory nerves contain only sensory nerve fibers.
               b) Motor nerves contain only motor fibers.
               c) Mixed nerves contain both sensory and motor nerves.
               d) Associated primarily with head, neck, and facial regions of the body.
               e) Vagus Nerve – Branches from medulla oblongata to pharynx, larynx
                   and most internal organs.
           4. Spinal nerves arise from the spinal cord.
               a) Attached to spinal cord via two short branches (roots).
               b) Separates sensory neuron axons from motor neuron axons.
                   1) Dorsal root contains sensory neuron axons.
                   2) Ventral root contains motor neuron axons.
                   3) Roots join to form spinal nerve.
               c) All spinal nerves are mixed nerves – sensory and motor together.
               d) Each spinal nerve serves a specific region of the body.

   26.16 In the somatic system, reflexes allow us to respond quickly to stimuli
       A. PNS has two divisions – somatic and autonomic systems.
       B. Somatic System.
           1. Nerves serve the skin, joints, and skeletal muscles.
           2. Nerves take info from external sensory receptors to CNS.
           3. Relay info from CNS to skeletal muscles.
           4. Acetylcholine is active in this system.



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          5. Voluntary control – Originates in the brain.
          6. Involuntary responses – Reflexes – involve brain or spinal cord.
              a) Enable reaction of body to stimuli.
          7. The Reflex Arc.
              a) Hand touches a sharp pin.
              b) Sensory receptors generate nerve impulse.
              c) Impulse transferred through axons, dorsal root ganglion to spinal cord.
              d) Signal passes on to interneurons of spinal cord.
              e) Interneurons synapse with motor neurons.
              f) Nerve impulses travel along motor axons to effector  response.
              g) Response may include withdrawal of hand from pin.

   26.17 In autonomic system, the parasympathetic and sympathetic divisions control
   the action of internal organs
       A. Autonomic System – Regulates the activity of glands, cardiac, and smooth
           muscle.
       B. Activation of two different systems:
           1. Parasympathetic.
           2. Sympathetic.
       C. Similarities of the two different systems include:
           1. Function automatically in involuntary manner.
           2. Innervate all internal organs.
           3. Utilize two neurons and one ganglion for each impulse.
               a) 1st neuron  cell body within the CNS + preganglionic fiber.
               b) 2nd neuron  cell body within ganglion and postganglionic fiber.
       D. Parasympathetic Division.
           1. Cranial nerves and axons coming from the last portion of spinal cord.
           2. Called the “housekeeping division.”
           3. Associated with relaxed state.
               a) Digestion, pupil contraction, heartbeat retardation.
           4. Utilizes acetylcholine.
       E. Sympathetic Division.
           1. Axons arise from the spinal cord.
           2. Important for emergency situations.
           3. Associated with the fight or flight response.
               a) Accelerates heartbeat.
               b) Dilates bronchi.
               c) Inhibits digestive system.
           4. Utilizes norepinephrine (similar to epinephrine).

VI. Connecting The Concepts
      A. Three functions for human nervous system:
         1. Sensory input.
         2. Integration.
         3. Motor output.
      B. Nerve impulses are physically the same for all neurons.



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C. Central nervous system integrates incoming information.
D. Brain allows perception of environment.
E. Motor output occurs post assimilation of information.
    1. Muscles and glands are effectors that respond to stimuli.
F. Peripheral nervous system link CNS to muscles and glands.
G. Cranial nerves serve the face, teeth, and mouth.
    1. Vagus nerve is only cranial nerve below the head.
H. Spinal nerves control all body movements.
    1. Paralysis typically follows spinal injury.
I. Only spinal nerves (except vagus nerve) make up the autonomic system.
    1. Autonomic system controls the internal organs.




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