Transcript Threshold Stimulus

• Stimulus must be sufficient to make the neuron respond and cause complete
depolarization. __________ stimuli do not cause depolarization.
• “_________________________ principle” - neuron depolarizes to its maximum
strength or not at all
• Strong stimuli cause numerous sodium channels open, which creates a WAVE OF
DEPOLARIZATION
• Conduction of the Action Potential —spreading wave of opening Na+ channels
in sufficient numbers to allow sodium influx and depolarization
• Wave of Depolarization = Conduction of Action Potential = Nerve Impulse
Threshold Stimulus
Neuron Function: Action Potential Propagation
• Time period when sensitivity
of neuron is reduced
—Cell is still in depolarization/early
repolarization
• _____________ refractory period
- during Na+ influx and early K+
outflow
• No amount of stimulus can cause
depolarization
• ____________ refractory period -
during end of repolarization period
• Strong stimulus can cause
depolarization
Refractory Period
Saltatory Conduction
• RAPID means of conducting an action potential (more rapid than
in unmyelinated axons)
• Depolarization in myelinated axons can only take place at
_______________________________
• Myelin sheath prevents sodium ions from entering the cell.
• The depolarization wave is able to skip from one NOR to the next,
accelerating the rate at which the wave moves from the cell body to the
end of the axon
http://www.blackwellpublishing.com/matthews/actionp.html
Local Anesthetics
• Work by blocking the
propagation of the action
potential
• Blocks _______ channels
• Sodium cannot flow into the
cell, so threshold is not
achieved
• Example: Lidocaine
• ____________ – junction between two neurons or a neuron and target
cell
• ___________ ________– gap between adjacent neurons/effector cell
• Presynaptic neuron - neuron bringing the depolarization wave to the
synapse
• Releases _______________________
• Postsynaptic neuron - contains receptors for the neurotransmitter
Synaptic
Transmission
Neurons: synapses
• The axon of the presynaptic neuron ends as
a branched structure (________________).
• Synaptic knob/synaptic end
bulb/terminal bouton- slightly enlarged
bulb at end of axon
• Vesicles contain neurotransmitter (a
chemical)
• When depolarization wave reaches axon
terminal, calcium channels open and cause
vesicles to fuse with cellular membrane
and release neurotransmitter into the
synapse
Synaptic
Transmission
Synaptic Transmission
• Neurotransmitters diffuse across synaptic cleft toward postsynaptic
membrane
• Receptors on postsynaptic membrane bind neurotransmitter
• Receptors are VERY
specific for each
neurotransmitter
(similar to a lock and
key)
Types of Neurotransmitters
• ______________ neurotransmitters (acetylcholine, norepinephrine,
dopamine)
• Usually cause an influx of Na+; postsynaptic membrane moves toward
threshold (more positive)
• _______________ neurotransmitters (acetylcholine, norepinephrine,
dopamine, GABA, glycine)
• Move the charge of postsynaptic cell farther away from threshold (more
negative)
• May open K+ channels/Cl- channels
Recycling the Neurotransmitter
• Acetylcholinesterase -
found on postsynaptic
membrane; breaks down
acetylcholine
• Monoamine oxidase (MAO)
- breaks down
epi/norepinephrine
• Catechol-O-methyl
transferase (COMT) - breaks
down epi/norepinephrine that
is not reabsorbed