nerve impulse

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

• Action potential travels along an axon• Information passes from presynaptic

neuron to postsynaptic cell

Nerve impulse


• Electrical • Rare• Pre- and postsynaptic cells are bound by

interlocking membrane proteins

General properties of synapses


• 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


• 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


Animation: Overview of a cholinergic synapsePLAY

Figure 12.19 The Function of a Cholinergic Synapse

Figure 12.19.1


Figure 12.19 The Function of a Cholinergic Synapse

Figure 12.19.2


• Adrenergic synapses release norepinephrine (NE)

• Other important neurotransmitters include• Dopamine• Serotonin• GABA (gamma aminobutyric acid)

Other neurotransmitters


• 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


Figure 12.21 Neurotransmitter Functions

Figure 12.21a



Figure 12.21b



Figure 12.21c


• Simplest level of information processing occurs at the cellular level• Excitatory and inhibitory

potentials are integrated through interactions between postsynaptic potentials

Information processing


• 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


Figure 12.22 Temporal and Spatial Summation

Figure 12.22a


Figure 12.22 Temporal and Spatial Summation

Figure 12.22b


Figure 12.23 EPSP – IPSP Interactions

Figure 12.23


• GABA release at axoaxonal synapse inhibits opening calcium channels in synaptic knob• Reduces amount of neurotransmitter

released when action potential arrives

Presynaptic inhibition


Figure 12.24 Presynaptic Inhibition and Facilitation

Figure 12.24


• Activity at axoaxonal synapse increases amount of neurotransmitter released when action potential arrives• Enhances and prolongs the effect of the

neurotransmitter

Presynaptic facilitation


Figure 12.24 Presynaptic Inhibition and Facilitation

Figure 12.24


• 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


• 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


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.


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.

nerve impulse

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