ACTION POTENTIALS Chapter 11 Part 2 HONORS ANATOMY & PHYSIOLOGY.
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Transcript of ACTION POTENTIALS Chapter 11 Part 2 HONORS ANATOMY & PHYSIOLOGY.
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ACTION POTENTIALSChapter 11 Part 2
HONORS ANATOMY & PHYSIOLOGY
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Key terms
• action potential: A short-term change in the electrical potential that travels along a cell (such as a nerve or muscle fiber); the basis of neural communication.
• neural impulse: The signal transmitted along a nerve fiber, either in response to a stimulus (such as touch, pain or heat), or as an instruction from the brain (such as causing a muscle to contract).
• Plasticity: The ability to change and adapt over time.
• Polarity: The spatial differences in the shape, structure, and function of cells.Almost all cell types exhibit some sort of polarity, which enables them to carry out specialized functions.
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The Brain and Behavior
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•Reuptake: The reabsorption of a neurotransmitter by a neuron after the transmission of a neural impulse across a synapse.
•Depolarization: the act of depriving of polarity, or the result of such action; reduction to an unpolarized condition
•resting potential: The membrane potential of inactive cells. The voltage that exists across plasma membranes during the resting state of excitable cells; ranging from:
• -90 to -20 millivoltsFree to share, print, make copies and changes. Get yours at www.boundless.com
The Brain and Behavior
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Neurons use pulses of electrical current to
receivetransmitregulate
the flow of information over long distances w/in the body
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Neuron Organization
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Types of Neurons Sensory Neurons
transmit information (senses) from body brain
are afferent specialized dendrites that initiate action
potential when stimulated
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Types of Neurons2. Motor Neurons transmit signals to muscle fibers &
glands are efferent
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ACTION POTENTIALSnerve impulsesoccur in neurons only
neurons are electrically excitable communicate with one another using 2 types
of electrical signals:1. graded potentials (short distances only)2. action potentials (short or long distances)
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Synapse junction between axon terminal & next cell
(another neuron, muscle fiber, gland cell)
neurotransmitters are chemical messengers released @ most synapses that pass action potential to receiving cell
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Synapse presynaptic cell: cell releasing
neurotransmitter & passing on action potential
postsynaptic cell: receiving neurotransmitter
synaptic cleft: physical space between the 2; neurotransmitter released into this space & diffuses across it attaching to receptors on postsynaptic cell
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Synapse
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Ion Pumps
ions unequally distributed across plasma membrane
inside of cell slightly (-) compared to outside cell
source of potential nrg
called the membrane potential
resting potential: the membrane potential of neuron @ rest =
-60 to –80 mV
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Resting Potential
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Formation of Resting Potential Na+/K+ pump generates & maintains the
ionic gradients of membrane potential 1 turn of pump
1 ATP 3 Na+ out 2 K+ in
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Membrane Potential
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Ion Channels pores that span the membrane allowing ions
to diffuse across (in or out)
membranes are selectively permeable and variations in how easily any particular ion can cross a membrane depends on the # of channels & how often they are open
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Types of Ion Channels
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Action Potentials neurons have gated ion channels that open or
close in response to stimuli open/close changes permeability for that ion
neurons have K+ channels when open K+ diffuses out of cell changes resting potential from: -60 mV to -90 mV
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Hyperpolarization
when K+ channels open & resting potential decreases to -90 mV inside of cell becoming more (-) than normal resting potential called:
hyperpolarization
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K+ Ion Channels in Neurons
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Depolarization when Na+ ion channels open Na+ diffuse
into cell making inside less (-) compared to outside cell
membrane potential shifts toward (+) mv this reduction in magnitude of
membrane potential called depolarization
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Graded Potentials any shift in membrane potential
magnitude of shift varies with strength of stimulus
induce a small electrical current that flows along the membrane leaking out of the cell
so only lasts short distance from source
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Action Potential electrical signal that propagates along the
membrane of a neuron as a nongraded (all or nothing) depolarization
have a constant magnitude & can regenerate in adjacent regions of the membrane
travel long distances
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Voltage-Gated Ion Channels ion channels that open/close based on
membrane potential passing a particular level
Na+ channels in neurons are voltage gated: open when depolarization occurs Na+ diffuses into cell becomes more depolarized more Na+ channels open (+ feedback)
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Threshold Action potentials occur when a depolarization
increases the membrane voltage to a particular value (the threshold)
for mammals the threshold is a membrane potential ~ -55mV
once started the action potential has a magnitude independent of the strength of triggering stimulus
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+ feedback loop of depolarization & channel opening triggers an action potential whenever the membrane potential reached the threshold
membrane depolarization opens both Na+ & K+ channels but Na+ opens faster initiating the action potential
Na+ channels become inactivated as action potential proceeds (gates close) & remain so until after membrane returns to resting potential
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Refractory Period (-) membrane potential restored by
inactivation of Na+ channels, which increases K+ outflow
This is followed by a refractory period: no matter how strong the stimulus to initiate next
action potential is cannot initiate one during refractory period
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Conduction of Action Potentials
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Action Potentials An electrical impulse travels along the
axon via depolarized voltage-gated ion channels in the membrane, and can either "jump" along a myelinated area or travel continuously along an unmyelinated area.
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http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
http://www.sumanasinc.com/webcontent/animations/content/action_potential.html
https://www.youtube.com/watch?v=U0NpTdge3aw
https://www.youtube.com/watch?v=ifD1YG07fB8