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  • 10/5/16

    1

    Nervous System - Neurons

    Biol 105 Chapter 7

    Copyright © 2009 Pearson Education, Inc.

    Outline

    I.  Nervous system function II.  Central and peripheral nervous system III.  Nervous system cells IV.  Myelinated neurons V.  Nerve signal transmission VI.  Nerve Synapse

    Copyright © 2009 Pearson Education, Inc.

    Nervous Tissues

    §  Nervous tissue functions to conduct messages throughout the body.

    §  When nerve cells are stimulated, an electrical signal quickly travels through the nerve cell to the nerve ending, triggering events.

    Copyright © 2009 Pearson Education, Inc.

    Nervous System §  Includes nervous tissue and sensory organs.

    §  Nervous system functions to:

    § Sense the environment – it receives information from both outside and inside the body.

    § Process the information it receives.

    § Respond to information – send out orders.

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    Two Parts of the Nervous System 1.  Central Nervous System (CNS)

    §  Brain and Spinal Cord.

    2.  Peripheral Nervous System (PNS) §  Nervous tissue outside brain and

    spine. §  Sense organs.

    Copyright © 2009 Pearson Education, Inc.

    Central Nervous System

    Peripheral

    Copyright © 2009 Pearson Education, Inc.

    Figure 8.1 The nervous system

    Copyright © 2009 Pearson Education, Inc.

    Nervous System Cells

    §  Two types of nervous tissue cells.

    § Neurons – The cells that are responsible for transmitting messages.

    § Neuroglial Cells – Cells that support the neurons.

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    Copyright © 2009 Pearson Education, Inc.

    Neuroglial Cells

    §  Microglia – Immune system cells, engulf bacteria and cellular debris.

    §  Astrocytes – Provide nutrients to neurons.

    §  Oligodenrocytes and Schwann Cells – Form myelin sheaths.

    Copyright © 2009 Pearson Education, Inc.

    Copyright © 2009 Pearson Education, Inc.

    Parts of a Neuron

    §  Cell body – contains the nucleus, main body of cell.

    §  Dendrites – projections from the cell body that carry messages to the cell body.

    §  Axon – one projection that carries messages away from the cell body (can be very long).

    Copyright © 2009 Pearson Education, Inc.

    Neurons Have Dendrites, a Cell Body, and an Axon

    Figure 7.2

    The cell body integrates input from other neurons.

    Dendrites receive information from other neurons or from the environment.

    The cell body controls the cell’s metabolic activities.

    An axon conducts the nerve impulse away from the cell body.

    Axon endings release chemicals called neurotransmitters that affect the activity of nearby neurons or an effector (muscle or gland).

    Receiving portion of neuron

    Sending portion of neuron

    Cell body

    Axon endings

    Nucleus

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    Copyright © 2009 Pearson Education, Inc. 12-12 Copyright © 2009 Pearson Education, Inc.

    Neurons of the Peripheral Nervous System

    §  Neurons in the PNS are either carrying messages to or from the CNS.

    §  Afferent = Sensory neurons = Neurons carrying messages to the CNS.

    §  Efferent = Motor neurons = Neurons carrying messages from the CNS.

    Copyright © 2009 Pearson Education, Inc.

    Interneurons in the Central Nervous System

    §  Interneurons are located between sensory and motor neurons within the CNS.

    §  Interneurons integrate and interpret sensory signals.

    Copyright © 2009 Pearson Education, Inc.

    Figure 8.1 The nervous system

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    Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc.

    Sensory Neurons

    §  The afferent or sensory neuron cell bodies are located in dorsal root ganglion.

    Copyright © 2009 Pearson Education, Inc.

    Motor Neurons

    §  The efferent or motor neuron cell bodies are located in the gray matter of the spinal cord.

    §  Their axons leave the CNS and go to the skeletal muscles.

    Copyright © 2009 Pearson Education, Inc.

    The cell bodies of these neurons are located in the dorsal root ganglion

    M oto

    r

    Se ns

    or y

    50%50% 1.  Motor 2.  Sensory

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    Copyright © 2009 Pearson Education, Inc.

    The cell bodies of these neurons are located in the dorsal root ganglion

    M oto

    r

    Se ns

    or y

    50%50% 1.  Motor 2.  Sensory

    Copyright © 2009 Pearson Education, Inc.

    Neurons of the Nervous System

    Figure 7.1

    Interneuron

    Sensory receptor for pain

    Muscle (effector)

    Motor neuron

    Sensory neuron Cell body

    Impulse direction

    12-5 Copyright © 2009 Pearson Education, Inc.

    These neuroglial cells provide nutrients to neurons

    M icr

    og lia

    A str

    oc yte

    s

    O lig

    od en

    ro cy

    tes

    Sc hw

    an n c

    ell s

    25% 25%25%25%1.  Microglia 2.  Astrocytes 3.  Oligodenrocytes 4.  Schwann cells

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    Copyright © 2009 Pearson Education, Inc.

    These neuroglial cells provide nutrients to neurons

    M icr

    og lia

    A str

    oc yte

    s

    O lig

    od en

    ro cy

    tes

    Sc hw

    an n c

    ell s

    25% 25%25%25%1.  Microglia 2.  Astrocytes 3.  Oligodenrocytes 4.  Schwann cells

    Copyright © 2009 Pearson Education, Inc.

    These are projections of the neuron cell body that carry messages to the cell body

    A xo

    ns

    D en

    dr ite

    s

    50%50% 1.  Axons 2.  Dendrites

    Copyright © 2009 Pearson Education, Inc.

    These are projections of the neuron cell body that carry messages to the cell body

    A xo

    ns

    D en

    dr ite

    s

    50%50% 1.  Axons 2.  Dendrites

    Copyright © 2009 Pearson Education, Inc.

    Which of the following type of neuron would alert the brain that you had touched a hot object?

    ef fer

    en t n

    eu ro

    n

    af fer

    en t n

    eu ro

    n

    50%50% 1.  efferent neuron 2.  afferent neuron

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    Copyright © 2009 Pearson Education, Inc.

    Which of the following type of neuron would alert the brain that you had touched a hot object?

    ef fer

    en t n

    eu ro

    n

    af fer

    en t n

    eu ro

    n

    50%50% 1.  efferent neuron 2.  afferent neuron

    Copyright © 2009 Pearson Education, Inc.

    What type of neuron is the arrow pointing to?

    Se ns

    or y

    M oto

    r

    50%50% 1.  Sensory 2.  Motor

    Copyright © 2009 Pearson Education, Inc.

    What type of neuron is the arrow pointing to?

    Se ns

    or y

    M oto

    r

    50%50% 1.  Sensory 2.  Motor

    Copyright © 2009 Pearson Education, Inc.

    Myelinated Neurons

    §  Neurons that have axons covered with neuroglial cells that contain the protein myelin are called myelinated neurons.

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    Copyright © 2009 Pearson Education, Inc.

    Functions of Myelin Sheaths

    1.  The main benefit of myelin sheaths is that myelinated neurons are able to carry messages faster than non-myelinated neurons.

    2.  Myelin sheaths from Schwann cells also help regenerate injured PNS neuron axons.

    Copyright © 2009 Pearson Education, Inc.

    Two Types of Cells Myelinate neurons

    §  Schwann cells and Oligodenrocytes are wrapped around neuronal axons.

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    Myelinated Neurons

    §  Schwann cells are found in the PNS.

    §  Oligodendrocytes are found in the CNS.

    §  Nodes of Ranvier are spaces on the axon between the glial cells.

    Copyright © 2009 Pearson Education, Inc.

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    Copyright © 2009 Pearson Education, Inc.

    Myelin Sheath

    Figure 7.3b Copyright © 2009 Pearson Education, Inc.

    Myelin Sheath

    Figure 7.3c

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    Myelinated Neurons

    Figure 7.3a

    (a)

    Cell body

    Dendrites

    Myelin sheath

    Node of Ranvier

    Nucleus

    Schwann cell

    In saltatory conduction, the nerve impulses jump from one node of Ranvier to the next.

    Copyright © 2009 Pearson Education, Inc.

    Multiple Sclerosis (MS)

    §  Caused by the destruction of the myelin sheath that surrounds axons found in the CNS.

    §  Can result in paralysis and loss of sensation, including loss of vision.

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    Nerves

    §  Nerves contain Neuron axons that are bundled together.