Download nerve impulse

PowerPoint® Lecture Slide Presentation
by Patty Bostwick-Taylor,
Florence-Darlington Technical College
The Nervous
System
7
PART A
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
 Neurons = nerve cells
 Cells specialized to transmit messages
 Major regions of neurons
 Cell body—nucleus and metabolic center
of the cell
 Processes—fibers that extend from the
cell body
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
 Cell body
 Nissl substance
 Specialized rough endoplasmic reticulum
 Neurofibrils
 Intermediate cytoskeleton
 Maintains cell shape
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
Figure 7.4
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
 Cell body
 Nucleus
 Large nucleolus
 Processes outside the cell body
 Dendrites—conduct impulses toward the cell
body
 Axons—conduct impulses away from the cell
body
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
Figure 7.4
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
 Axons end in axonal terminals
 Axonal terminals contain vesicles with
neurotransmitters
 Axonal terminals are separated from the next
neuron by a gap
 Synaptic cleft—gap between adjacent neurons
 Synapse—junction between nerves
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
 Myelin sheath—whitish, fatty material covering
axons
 Schwann cells—produce myelin sheaths in jelly
roll–like fashion
 Nodes of Ranvier—gaps in myelin sheath along
the axon
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
Figure 7.5
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Neuron Cell Body Location
 Most neuron cell bodies are found in the central
nervous system
 Gray matter—cell bodies and unmyelinated
fibers
 Nuclei—clusters of cell bodies within the white
matter of the central nervous system
 Ganglia—collections of cell bodies outside the
central nervous system
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Neuron Classification
Figure 7.6
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Structural Classification of Neurons
 Multipolar neurons—many extensions from the
cell body
Figure 7.8a
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Structural Classification of Neurons
 Bipolar neurons—one axon and one dendrite
Figure 7.8b
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Structural Classification of Neurons
 Unipolar neurons—have a short single process
leaving the cell body
Figure 7.8c
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nerve Impulses
 Resting neuron
 The plasma membrane at rest is polarized
 Fewer positive ions are inside the cell than
outside the cell
 Depolarization
 A stimulus depolarizes the neuron’s
membrane
 A depolarized membrane allows sodium (Na+)
to flow inside the membrane
 The exchange of ions initiates an action potential
in the neuron
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nerve Impulses
Figure 7.9a–b
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nerve Impulses
 Action potential
 If the action potential (nerve impulse) starts, it
is propagated over the entire axon
 Impulses travel faster when fibers have a
myelin sheath
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nerve Impulses
Figure 7.9c–d
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nerve Impulses
 Repolarization
 Potassium ions rush out of the neuron after
sodium ions rush in, which repolarizes the
membrane
 The sodium-potassium pump, using ATP,
restores the original configuration
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nerve Impulses
Figure 7.9e–f
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of a Signal at Synapses
 Impulses are able to cross the synapse to another
nerve
 Neurotransmitter is released from a nerve’s
axon terminal
 The dendrite of the next neuron has receptors
that are stimulated by the neurotransmitter
 An action potential is started in the dendrite
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of a Signal at Synapses
Axon of
transmitting
neuron
Axon
terminal
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Synapse
Transmitting neuron
Vesicle
fuses with
plasma
membrane
Neurotransmitter is released into
synaptic cleft
Neurotransmitter
molecules
Synaptic cleft
Ion channels
Neurotransmitter binds
to receptor
on receiving
neuron’s
membrane
Receiving neuron
Neurotransmitter
Receptor
Neurotransmitter
broken down
and released
Na+
Na+
Ion channel opens
Ion channel closes
Figure 7.10
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of a Signal at Synapses
Axon of
transmitting
neuron
Axon
terminal
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Synapse
Figure 7.10, step 1
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of a Signal at Synapses
Axon
Axon of
transmitting terminal
neuron
Vesicles
Action
potential
arrives
Synaptic
cleft
Receiving
neuron
Synapse
Transmitting neuron
Vesicle
fuses with
plasma
membrane
Synaptic cleft
Ion channels
Receiving neuron
Figure 7.10, step 2
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of a Signal at Synapses
Axon of
transmitting
neuron
Axon
terminal
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Synapse
Transmitting neuron
Vesicle
fuses with
plasma
membrane
Synaptic cleft
Ion channels
Neurotransmitter is released into
synaptic cleft
Neurotransmitter
molecules
Receiving neuron
Figure 7.10, step 3
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of a Signal at Synapses
Axon of
transmitting
neuron
Axon
terminal
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Transmitting neuron
Vesicle
fuses with
plasma
membrane
Synaptic cleft
Ion channels
Neurotransmitter is released into
synaptic cleft
Synapse
Neurotransmitter binds
to receptor
on receiving
neuron’s
membrane
Neurotransmitter
molecules
Receiving neuron
Figure 7.10, step 4
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of a Signal at Synapses
Axon of
transmitting
neuron
Axon
terminal
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Transmitting neuron
Vesicle
fuses with
plasma
membrane
Neurotransmitter is released into
synaptic cleft
Neurotransmitter binds
to receptor
on receiving
neuron’s
membrane
Neurotransmitter
molecules
Synaptic cleft
Ion channels
Synapse
Receiving neuron
Neurotransmitter
Receptor
Na+
Ion channel opens
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 7.10, step 5
Transmission of a Signal at Synapses
Axon of
transmitting
neuron
Axon
terminal
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Transmitting neuron
Vesicle
fuses with
plasma
membrane
Neurotransmitter is released into
synaptic cleft
Neurotransmitter binds
to receptor
on receiving
neuron’s
membrane
Neurotransmitter
molecules
Synaptic cleft
Ion channels
Synapse
Receiving neuron
Neurotransmitter
Receptor
Na+
Ion channel opens
Neurotransmitter
broken down
and released
Na+
Ion channel closes
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 7.10, step 6
Transmission of a Signal at Synapses
Axon
terminal
Axon of
transmitting
neuron
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Synapse
Transmitting neuron
Vesicle
fuses with
plasma
membrane
Neurotransmitter is released into
synaptic cleft
Neurotransmitter
molecules
Synaptic cleft
Ion channels
Neurotransmitter binds
to receptor
on receiving
neuron’s
membrane
Receiving neuron
Neurotransmitter
Receptor
Na+
Ion channel opens
Neurotransmitter
broken down
and released
Na+
Ion channel closes
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 7.10, step 7