unit 3 nerve
TRANSCRIPT
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Nervous System
Dr. S. Francis
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Function of the NS
Monitors the Bodys Internal env. and the
Bodys External env.
Integrates Sensory information from all over
the body
Coordinates Voluntary and Involuntary
responses of many other Organ system
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Histology of the NS
Neural Tissue
Contains two kinds of cells
Neuroglia (glial cells):
cells that support and protect neurons
Neurons :
cells that send and receive signals
Blood vessels Connective tissue
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Neuroglia
Neuroglia
Half the volume of the nervous system
Many types of neuroglia in CNS and PNS
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Chapter 5 The Central Nervous
SystemHuman Physiology by LauraleeSherwood 2007 Brooks/Cole-
Neuroglia
Also called Glial cells support Neurons
Physically,
Metabolically,
Functionally
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Neuroglia Four Types of Neuroglia in the CNS
Astrocytes: large cell bodies with many processes
Ependymal cells: cells with highly branched processes;
contact neuroglia directly
Oligodendrocytes: smaller cell bodies with fewer
processes
Microglia: smallest and least numerous neuroglia with
many fine-branched processes
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Neuroglia
Figure 12 6a Schwann Cells and Peripheral Axons.
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Neuroglia
Figure 12 6b Schwann Cells and Peripheral Axons.
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Neuron & Neuroglia Neuroglia preserve physical and biochemical
structure of neural tissue and are essential to
survival and function of neurons Neurons perform all communication, information
processing, and control functions of the nervous
system Neurons communicate via changes in membrane
potential
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Neurons
Four Structural Classifications of Neurons Anaxonic neurons
Found in brain and sense organs Function not well known No distinguishing features
Bipolar neurons Found in special sensory organs (sight, smell, hearing)
Unipolar neurons or Psuedounipolar Neuron Found in sensory neurons of PNS Fused dendrites and axon
Multipolar neurons Most Common in the CNS Are the motor neurons that control skeletal muscle
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Neurons
Figure 12 3 A Structural Classification of Neurons.
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Functional Classes of Neuron
Afferent or Sensory Neurons Inform CNS about conditions in both the external andinternal environment
Efferent or Motor Neurons
Carry instructions from CNS to effector organs muscles and glands
Interneurons Found entirely within CNS Responsible for
Integrating afferent information and formulating anefferent response
Higher mental functions associated with the mind
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Chapter 4 Principles of Neuraland Hormonal CommunicationHuman Physiology by LauraleeSherwood 2007 Brooks/Cole-
Parts of the Neuron
Cell body Houses the nucleus and organelles
Dendrites Project from cell body and increase surface area
available for receiving signals from other nerve cells Signal toward the cell body
Dendrite and cell body serve as the neurons input zone.
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Axon Nerve fiber Single, elongated tubular extension Conducting zone of the neuron
Carries electrical signal ( action potential )from axon hillock to target
Axon structure is critical to function
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Structures of the Axon Axoplasm
Cytoplasm of axon
Contains neurotubules, neurofibrils, enzymes,
organelles
Axolemma Specialized cell membrane
Covers the axoplasm
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Structures of the Axon
Synaptic or Axon terminals Tips of telodendria
Release chemical messengers
Output zone of the neuron
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Neurons
Figure 12 1a The Anatomy of a Multipolar Neuron.
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Neurons
Major Organelles of the Cell Body Large nucleus and nucleolus Perikaryon ( cytoplasm)
Lots of Mitochondria (produce energy) Transport manufactured neurotransmitters
Nissle bodies (produce neurotransmitters) Cytoskeleton
Neurofilaments and neurotubules : in place of microfilaments andmicrotubules
Neurofibrils : bundles of neurofilaments that provide support fordendrites and axon
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Neurons
The Structure of Neurons Nissl bodies
Dense areas of RER and ribosomes
Make neural tissue appear gray ( gray matter ) Dendrites
Highly branched
Dendritic spines: many fine processes receive information from other neurons 80 90% of neuron surface area
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Neurons
Figure 12 1b The Anatomy of a Multipolar Neuron.
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Chapter 4 Principles of Neuraland Hormonal CommunicationHuman Physiology by LauraleeSherwood 2007 Brooks/Cole-
Neuron
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Transmembrane Potential
Figure 12 8 An Overview of Neural Activities.
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Chapter 4 Principles of Neuraland Hormonal CommunicationHuman Physiology by LauraleeSherwood 2007 Brooks/Cole-
Action Potentials
Two types of propagation Contiguous conduction
Conduction in unmyelinated fibers Action potential spreads along every portion of the
membrane Saltatory conduction
Rapid conduction in myelinated fibers Impulse jumps over sections of the fiber covered
with insulating myelin
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Chapter 4 Principles of Neuraland Hormonal CommunicationHuman Physiology by LauraleeSherwood 2007 Brooks/Cole-
Contiguous Conduction
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Chapter 4 Principles of Neuraland Hormonal CommunicationHuman Physiology by LauraleeSherwood 2007 Brooks/Cole-Thomson Learning
Saltatory Conduction
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Chapter 4 Principles of Neuraland Hormonal CommunicationHuman Physiology by LauraleeSherwood 2007 Brooks/Cole-
Saltatory Conduction
AP faster than contiguous conduction because
at myelinated section
Myelin
Primarily composed of lipids
Formed by oligodendrocytes in CNS Formed by Schwann cells in PNS
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The Synapse The synaptic knob
Is expanded area of axon of presynaptic neuron
Contains synaptic vesicles of neurotransmitters
Junction between two neurons or muscle cell
Its the primary means by which one neuron directlyinteracts with another neuron or muscle cell
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The Structure of Neurons The synapse
Presynaptic cell:
neuron that sends message Postsynaptic cell:
cell that receives message
The synaptic cleft:
the small gap that separates the presynaptic membrane and thepostsynaptic membrane
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Neurons
Figure 12 2 The Structure of a Typical Synapse.
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Synapses Two Types of Synapses
Electrical synapses
Direct physical contact between cells
Both pre & post synaptic cells join
Electrical signals Permitted thru gap junction
Extremely Rare
Chemical synapses Signal transmitted across a space by chemical neurotransmitters
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Synapses Two Classes of Neurotransmitters
Excitatory neurotransmitters
Cause depolarization of postsynaptic membranes
Promote action potentials
Inhibitory neurotransmitters
Cause hyperpolarization of postsynaptic membranes
Suppress action potentials
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Neurotransmitters:
are chemical messengers are released at presynaptic membrane affect receptors of postsynaptic membrane
are broken down by enzymes are reassembled at synaptic knob