Transcript 9.5-9.9 Notes

9.5-9.9 Notes
https://www.youtube.com/watch?v=
XdCrZm_JAp0
Biology 2
1/15
HW-finish reading guide for Friday
Agenda: Action Potentials
-notes first
-online activity next
1. Take out 9.5 reading guide
2. Take out online activity.
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Cell Membrane Set-up
• Membrane is polarized.
-large amounts of negative charges on
the inside of the membrane
-large amounts of positive charges on the
outside of the cell
• Overall makes inside the cell negatively chargedTHIS IS POLARIZED
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CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ions move during Rest Time
• Channels in membranes are permeable
– Potassium moves easier than sodium
• More potassium moving out that
sodium coming in
– Move through diffusion
• Helps create negative charge inside
• Sodium Potassium Pump-ATP is used to
pump sodium and potassium ions across
membrane
– Maintains polarization
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Resting Potential
• Active Transport allows for potassium to
move out faster than sodium moving in.
• This separation of charge, or potential
difference, is called the resting potential.
• Cell is at -70 millivolts
Things happen to the membrane:
• When a neurotransmitter is picked up by a
dendrite, it will stimulate the membrane.
• An action potential can occur: 2 things must
happen
– Repolarization
– Depolarization
Depolarization
• Inside of the membrane becomes less
negative (insides becomes more positive)increase in volts
• Sodium channels open and potassium
channels close
• Stimulation must reach a certain point
(threshold) before the neuron continues
on.
Repolarization
• potassium channels open and sodium closes
• Inside of the membrane becomes negative
• Refractory period-time when the neuron
cannot respond to a second stimulus (time
when the graph dips below resting potential)
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CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dip in graph after repolarization:
• Hyperpolarization (at refractory period
time)-a deep below the -70 mv occurs
because gates are closed and chlorine
comes into the cell. So the cell negativity
drops more.
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Impulse Conduction
MYELINATED VS UNMYELINATED
• Unmyelinated fibers conduct impulses over their
entire membrane surface-SLOW
• Myelinated fibers conduct impulses from node of
Ranvier to node of Ranvier, a phenomenon called
saltatory conduction.
– Saltatory conduction is many times faster than
conduction on unmyelinated neurons.
• http://www.blackwellpublishing.com/matthews/a
ctionp.html
AXON DIAMETER
• The greater the diameter, the faster it travels.
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All-or-None Response
• If a nerve fiber responds at all to a stimulus, it
responds completely by conducting an impulse
(all-or-none response).
• Greater intensity of stimulation triggers more
impulses per second, not stronger impulses.
• Complete depolarization must take place for a
neuron to travel along the axon
• How does an action potential move from one
neuron to the next?
•
http://www.execulink.com/~ekimmel/mixed_flash.htm
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The Synapse
http://outreach.mcb.harvard.edu/animations/synap
tic.swf
• The junction between two communicating
neurons is called a synapse
• There exists a synaptic cleft between them across
which the impulse must be conveyed.
• Presynaptic neuron-carries pulse
• Postsynaptic neuron-receives it
• When the impulse reaches the synaptic knobs
(also known as axon terminal), neurotransmitters
must be released from synaptic vesicles into the
synaptic cleft.
• The nts are released because of the influx of
calcium.
• Recycled, deactivated, or attach to receptors
LABEl
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Excitatory and Inhibitory Actions
• Neurotransmitters that increase postsynaptic
membrane permeability to sodium ions may trigger
impulses and are excitatory.
– Acetylcholine, epinephrine, norepinephrine, serotonin,
amino acids
• Decrease membrane permeability to sodium ions,
reducing the chance that it will reach threshold, and are
inhibitory.
– GABA, dopamine
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Impulse Processing
•
•
How impulses are processed is dependent upon
how neurons are organized in the brain and
spinal cord.
Neuronal Pools
– Neurons within the CNS are organized into neuronal
pools with varying numbers of cells.
– Each pool receives input from afferent nerves and
processes the information according to the special
characteristics of the pool.
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Facilitation
• A particular neuron of a pool may receive
excitatory or inhibitory stimulation; if the
net effect is excitatory but subthreshold,
the neuron becomes more excitable to
incoming stimulation (a condition called
facilitation).
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Convergence
• A single neuron within a pool may receive
impulses from two or more fibers
(convergence), which makes it possible for
the neuron to summate impulses from
different sources.
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Divergence
• Impulses leaving a neuron in a pool may be
passed onto several output fibers (divergence), a
pattern that serves to amplify an impulse.
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Reflex Arc
• Sensory neuron---interneuron in spinal
cord---motor neuron
• Autonomic
• Homeostasis and survival (withdraw reflex)