unit 3 nerve

8/10/2019 Unit 3 Nerve

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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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Copyright 2009 PearsonEducation, Inc., publishing asPearson Benjamin Cummings

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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Neuron


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Transmembrane Potential

Figure 12 8 An Overview of Neural Activities.


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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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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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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

unit 3 nerve

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