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• Action potential travels along an axon• Information passes from presynaptic
neuron to postsynaptic cell
Nerve impulse
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• Electrical • Rare• Pre- and postsynaptic cells are bound by
interlocking membrane proteins
General properties of synapses
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• Chemical synapses• More common• Excitatory neurotransmitters cause
depolarization and promote action potential generation
• Inhibitory neurotransmitters cause hyperpolarization and suppress action potentials
General properties of synapses
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• Release acetylcholine (ACh) • Information flows across synaptic cleft• Synaptic delay occurs as calcium influx and
neurotransmitter release take appreciable amounts of time
• ACh broken down• Choline reabsorbed by presynaptic
neurons and recycled• Synaptic fatigue occurs when stores of ACh
are exhausted
Cholinergic synapses
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Animation: Overview of a cholinergic synapsePLAY
Figure 12.19 The Function of a Cholinergic Synapse
Figure 12.19.1
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Figure 12.19 The Function of a Cholinergic Synapse
Figure 12.19.2
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• Adrenergic synapses release norepinephrine (NE)
• Other important neurotransmitters include• Dopamine• Serotonin• GABA (gamma aminobutyric acid)
Other neurotransmitters
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• Influence post-synaptic cells response to neurotransmitter
• Neurotransmitters can have direct or indirect effect on membrane potential• Can exert influence via lipid-soluble
gases
Neuromodulators
Animation: Synaptic potentials, cellular integration, and synaptic transmissionPLAY
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Figure 12.21 Neurotransmitter Functions
Figure 12.21a
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Figure 12.21 Neurotransmitter Functions
Figure 12.21b
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Figure 12.21 Neurotransmitter Functions
Figure 12.21c
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• Simplest level of information processing occurs at the cellular level• Excitatory and inhibitory
potentials are integrated through interactions between postsynaptic potentials
Information processing
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• EPSP (excitatory postsynaptic potential) = depolarization • EPSP can combine through summation
• Temporal summation• Spatial summation
• IPSP (inhibitory postsynaptic potential) = hyperpolarization
• Most important determinants of neural activity are EPSP / IPSP interactions
Postsynaptic potentials
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Figure 12.22 Temporal and Spatial Summation
Figure 12.22a
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Figure 12.22 Temporal and Spatial Summation
Figure 12.22b
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Figure 12.23 EPSP – IPSP Interactions
Figure 12.23
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• GABA release at axoaxonal synapse inhibits opening calcium channels in synaptic knob• Reduces amount of neurotransmitter
released when action potential arrives
Presynaptic inhibition
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Figure 12.24 Presynaptic Inhibition and Facilitation
Figure 12.24
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• Activity at axoaxonal synapse increases amount of neurotransmitter released when action potential arrives• Enhances and prolongs the effect of the
neurotransmitter
Presynaptic facilitation
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Figure 12.24 Presynaptic Inhibition and Facilitation
Figure 12.24
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• Neurotransmitters are either excitatory or inhibitory• Effect on initial membrane segment
reflects an integration of all activity at that time
• Neuromodulators alter the rate of release of neurotransmitters
Rate of generation of action potentials
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• Can be facilitated or inhibited by other extracellular chemicals
• Effect of presynaptic neuron may be altered by other neurons
• Degree of depolarization determines frequency of action potential generation
Rate of generation of action potentials
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You should now be familiar with:
• The two major divisions of the nervous system and their characteristics.
• The structures/ functions of a typical neuron.
• The location and function of neuroglia.• How resting potential is created and
maintained.
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You should now be familiar with:
• The events in the generation and propagation of an action potential.
• The structure / function of a synapse.• The major types of neurotransmitters and
neuromodulators.• The processing of information in neural
tissue.