Neurons, Synapses, & Signaling Campbell and Reece Chapter 48.
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Transcript of Neurons, Synapses, & Signaling Campbell and Reece Chapter 48.
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Neurons, Synapses, & Signaling
Campbell and ReeceChapter 48
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Neurons
nerve cells that transmit information within the body
communication between neurons consists of:◦long distance electrical signals◦short distance chemical signals
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Neurons
use pulses of electrical current toreceivetransmitregulate
the flow of information over long distances w/in the body
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Neuron Organization
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Nervous System
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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 Neurons
2. Motor Neurons transmit signals to muscle fibers
& glandsare efferent
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Types of Neurons
3. Interneurons majority of neurons in brain
◦ form local circuits connecting neurons
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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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Glial Cells
cells that support neuronsGreek: glueaka neuroglianourish neuronsinsulate axonsregulate ECF surrounding neurons
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Ion Pumps
ions unequally distributed across plasma membrane
inside of cell slightly (-) compared to outside cell
source of potential nrgcalled the membrane potentialresting 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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K+ Ion Channels in Neurons
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Resting & Action Potentials
http://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swf
http://www.dnatube.com/video/1105/Understanding-Action-Potential-and-Nerve-Impulses
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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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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 potentialmagnitude of shift varies with
strength of stimulusinduce 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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http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
Interactive site to try at home:
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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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Myelin Sheaths
glial cells oligodendrocytes (CNS) and Schwann cells (PNS) form layers of electrical insulation along length of axons
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Saltatory Conduction
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Neurotransmitters
>100 neurotransmitters belonging to 5 groups:
1. Acetylcholine2. Amino Acids3. Biogenic Amines4. Neuropeptides5. Gases
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