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Neurons transmit nerve impulses between parts of the nervous system. ... The central nervous system (CNS) is made up of the spinal cord and the brain. ...

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Chapter 12 l.jpg

Chapter 12

Nervous System


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Outline

  • Nervous Tissue

  • The Nerve Impulse

    • Action Potential

  • Central Nervous System

    • The Spinal Cord

    • The Brain

  • Peripheral Nervous System

    • Nerves and Ganglia

  • Drug Abuse

  • Degenerative Nervous System Diseases


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Nervous Tissue

  • Nervous Tissue contains two types of cells.

    • Neurons transmit nerve impulses between parts of the nervous system.

    • Neuroglia support and nourish neurons.


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Neuron Structure

  • Neurons are classified according to function.

    • Sensory neurons take impulses from a sensory receptor to the CNS.

    • Interneurons receive input from sensory neurons, and other neurons, and then communicate with motor neurons.

    • Motor neurons take nerve impulse away from the CNS to an effector that carries out responses to environmental change.


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Neuron Structure

  • Neurons contain three basic parts.

    • Cell body contains nucleus and other organelles.

    • Dendrites receive signals from sensory receptors or other neurons.

    • Axon conducts nerve impulses.



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Myelin Sheath

  • Some axons are covered by a protective myelin sheath.

    • Formed by Schwann cells containing myelin in plasma membranes.

    • Nodes of Ranvier are gaps on the axon with no myelin sheath.



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The Nerve Impulse

  • The nervous system uses the nerve impulse to convey information.

    • Resting potential is the voltage level when an axon is not conducting an impulse.

  • Sodium-potassium pump causes greater concentration of Na+ outside the axon, and greater concentration of K+ inside the axon.

    • Unequal ion distribution causes inside of axon to be negative relative to the outside.


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Action Potential

  • An action potential is a rapid change in polarity across an axomembrane as the nerve impulse occurs.

    • All-or-none once threshold is reached.

      • Sodium gates open, allowing Na+ to move inside the axon.

      • Potassium gates open, allowing K+ to move outside the axon.


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Transmission across a Synapse

  • Transmission across a synaptic cleft is carried out by neurotransmitters stored in synaptic vesicles.

    • Depending on the neurotransmitter and the receptor, the response of the postsynaptic neuron can be towards excitation or inhibition.

      • Integration is the summing of signals received by a postsynaptic neuron.



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The Central Nervous System

  • The central nervous system (CNS) is made up of the spinal cord and the brain.

    • Both are wrapped in protective membranes, meninges, with spaces between meninges filled with cerebrospinal fluid.

  • CNS is composed of two types of nervous tissue.

    • Gray matter – Short, nonmyelinated fibers.

    • White matter - Myelinated axons.


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The Spinal Cord

  • The spinal cord extends from the base of the brain through the foramen magnum into the vertebral canal.


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Functions of the Spinal Cord

  • The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord, and is a center for reflex actions.


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The Brain

  • The Cerebrum.

    • The cerebrum, telencephalon, is the largest portion of the human brain.

      • Communicates with, and coordinates activities of, other parts of the brain.

      • Divided into left and right cerebral hemispheres.

        • Divided by longitudinal fissure.



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The Brain

  • Gray matter of cerebrum consists of cerebral cortex and basal nuclei.

    • Cerebral cortex is a highly convoluted outer layer that covers the cerebral hemispheres.

    • Basal nuclei are masses located deep within white matter.

  • White matter consists of long myelinated axons organized into tracts.



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The Brain

  • Diencephalon is made up of hypothalamus and thalamus, and circles the third ventricle.

  • Cerebellum is separated from the brain stem by the fourth ventricle.

  • The brain stem contains the midbrain, pons, and medulla oblongata.

    • Reticular formation is a complex network of nuclei and fibers extending the length of the brain stem.



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The Limbic System

  • Limbic system is a complex network of tracts and nuclei.

    • Blends primitive emotions and higher mental functions into a united whole.

    • Composed of hippocampus and amygdala.



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Higher Mental Functions

  • Memory is the ability to hold a thought in mind or to recall events from the past.

    • Short-term versus long-term.

    • Skill memory.

  • Learning takes place when we retain and utilize past memories.

  • Language and speech depends on motor centers in the occipital and temporal lobes.



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Language and Speech

  • Left and right brain have different functions.

    • Left Hemisphere:

      • Verbal, Logical, Analytical, Rational.

    • Right Hemisphere:

      • Nonverbal, Intuitive, Creative.


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Peripheral Nervous System

  • Composed of nerves and ganglia.

    • Cranial nerves take impulses to and from the brain.

    • Spinal nerves take impulses to and from the spinal cord.



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Somatic System

  • Somatic system includes nerves that take sensory information from external sensory receptors to the CNS and motor commands away from the CNS to the skeletal muscles.

    • Reflexes are automatic responses to a stimulus.



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Autonomic System

  • Autonomic system regulates the activity of cardiac and smooth muscles and glands.

    • Sympathetic division brings about fight or flight responses.

    • Parasympathetic division brings about relaxed responses.


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Drug Abuse

  • Drugs that affect the nervous system have two general effects.

    • Impact limbic system.

    • Promote or decrease action of a particular neurotransmitter.

  • Drug abuse is apparent when a person takes a drug at a dose level and under circumstances that increase the potential for a harmful effect.



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Drug Abuse

  • Alcohol.

  • Nicotine.

    • Causes neurons to release dopamine.

      • Excess dopamine has reinforcing effect that leads to dependence.

  • Cocaine.

    • Prevents synaptic uptake of dopamine.

      • Continued use causes body to produce less dopamine.


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Drug Abuse

  • Heroin.

    • Binds to receptors meant for endorphins.

      • Continued use causes body to produce fewer endorphins.

  • Marijuana.

    • Binds to receptor for anandamide.

      • Brain impairment?


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Homeostasis

  • Governance of internal organs and the regulation of blood and tissue fluid usually takes place below the level of consciousness.

    • Heart Rate.

    • Breathing Rate.


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Degenerative Nervous System Diseases

  • Alzheimer disease.

    • Presence of abnormal neurons.

      • Plaques.

      • Neurofibrillary tangles.

  • Parkinson disease.

    • Overactive basal nuclei due to the degeneration of dopamine-releasing neurons in the brain.


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Review

  • Nervous Tissue

  • The Nerve Impulse

    • Action Potential

  • Central Nervous System

    • The Spinal Cord

    • The Brain

  • Peripheral Nervous System

    • Nerves and Ganglia

  • Drug Abuse

  • Degenerative Nervous System Diseases


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