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Transcript of Pages 234-239. 2495855/student_view0/chapter14/animatio n__the_nerve_impulse.html .
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The Nerve Impulse and Reflex Arcs
Pages 234-239
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http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
Nerve impulse animation
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Neurons have two functional properties
◦ Irritatability – respond to a stimulus and convert it into a nerve impulse
◦ Conductivity – ability to transmit the impulse to other neurons, muscles, or glands
Functional Properties of Neurons
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When neurons are in a “resting” state:◦ They are polarized
inside the plasma membrane is more negative than outside more potassium (K) inside the cell More sodium (Na) outside the cell
a gradient is created
the cell stays at rest
Waiting for a nerve impulse…
[Na+]
[K+]
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A stimulus depolarizes the neuron’s membrane
The membrane is now permeable to sodium sodium channels open sodium (Na) diffuses into the membrane the inside becomes more positive
This is how an action potential can be initiated
The potential for a nerve impulse…
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A nerve impulse (action potential) is generated: If the stimulus is strong enough If sodium influx great enough
If enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon
Action potential generation
Na+
Na+
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© 2015 Pearson Education, Inc.
the nerve impulse is propagated or it is not There are no partial impulses
Repolarization: the membrane is restored to resting potential
Negative inside, positive outside The sodium-potassium pump restores resting potential
using energy supplied by ATP Another impulse cannot take place until the entire
membrane has been repolarized
All-or-none response
K+
K+
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© 2015 Pearson Education, Inc.
When the action potential reaches the axon terminal:1. calcium channels open2. vesicles containing neurotransmitters fuse with
the axonal membrane3. neurotransmitters diffuse across the synapse
and bind to receptors on the membrane of the next neuron
The amount of neurotransmitter released will determine if the action potential will continue ◦ This is known as graded potential
The Synaptic Events
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Actionpotentialarrives.
Figure 7.10 How neurons communicate at chemical synapses.
Axon oftransmittingneuron
1
Receivingneuron
Dendrite
Axon terminal
Vesicles
Synapticcleft
Slide 2
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Figure 7.10 How neurons communicate at chemical synapses.
Transmitting neuron Vesiclefuses withplasmamembrane.
Synapticcleft Ion
channelsNeurotransmittermolecules
Receiving neuron
Slide 3
2
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Figure 7.10 How neurons communicate at chemical synapses.
Transmitting neuron Vesiclefuses withplasmamembrane.
Neurotrans-mitter isreleased intosynaptic cleft.
Synapticcleft Ion
channelsNeurotransmittermolecules
Receiving neuron
Slide 4
2
3
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Figure 7.10 How neurons communicate at chemical synapses.
Transmitting neuron Vesiclefuses withplasmamembrane.
Neurotrans-mitter isreleased intosynaptic cleft.
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane.
Synapticcleft Ion
channelsNeurotransmittermolecules
Receiving neuron
Slide 5
2
34
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The transmission of a nerve impulse down neuron is electrical
The transmission of a nerve impulse to next neuron is chemical
Signal transmission is electrochemical
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Somatic reflexes◦ Reflexes that stimulate the skeletal muscles◦ Example: pulling hand away from a hot object
Autonomic reflexes◦ Regulates smooth muscles, heart, and glands◦ Example: regulation of blood pressure, glands,
digestive system
The Reflex Arc
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Reflexes are rapid, predictable, involuntary responses to a stimulus
A reflex arc can include:1. Sensory receptor—reacts to a stimulus2. Sensory neuron—carries message to
integration center3. Integration center (CNS) –
processes information directs motor output
4. Motor neuron —carries message to an effector 5. Effector organ —muscle or gland to be
stimulated
The Reflex Arc and its components
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Figure 7.11a Simple reflex arcs.
1
23
45
Stimulus at distalend of neuron
Skin
Receptor
Effector
Sensoryneuron
Motor neuron
Spinal cord(in cross section)
Integrationcenter
Interneuron