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Chapter 28. Nervous Systems. 0. Communication Between Neurons: Synaptic Transmission . 0. © 2012 Pearson Education, Inc. Signal must be passed to another cell The synapse: Relay point between neuron and an effector cell Another neuron Muscle cell Endocrine cell.
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Chapter 28 Nervous Systems 0
Communication Between Neurons: Synaptic Transmission 0 © 2012 Pearson Education, Inc.
Signal must be passed to another cell The synapse: Relay point between neuron and an effector cell Another neuron Muscle cell Endocrine cell What happens when an action potential reaches end of neuron? 0 © 2012 Pearson Education, Inc.
Electrical synapses: Electrical signals directly passes from neuron to receiving cell Ex: heart, smooth muscle of digestive tract Chemical synapses: Action potential of neuron converted to a chemical signal (neurotransmitter) Neurotransmitter triggers response in effector cell 28.6 Neurons communicate at synapses 0 Animation: Synapse © 2012 Pearson Education, Inc.
Figure 28.6 (Pre-synaptic cell) SENDING CELL 1 Actionpotentialarrives Axon ofsending cell Synapticvesicles Synapticterminalof sendingcell Synapticterminal 2 3 Vesicle fuseswith plasmamembrane Neurotransmitteris released intosynaptic cleft Dendriteof receiving cell SYNAPTICCLEFT 4 Neurotransmitterbinds to receptor RECEIVINGCELL Neurotransmittermolecules Ion channels Neurotransmitter Neurotransmitter brokendown and released (Post-synaptic cell) Receptor Ions Ion channel opens Ion channel closes 6 5
Figure 28.6_1 AP reaching end of pre-synaptic cell triggers increase in intracellular Ca2+, which triggers release of NT 1 Sending cell Actionpotentialarrives Axon ofsending cell Synapticvesicles Synapticterminalof sendingcell Synapticterminal 2 3 Vesicle fuseswith plasmamembrane Neurotransmitteris released intosynaptic cleft Dendriteof receiving cell Synapticcleft 4 Neurotransmitterbinds to receptor Receivingcell Neurotransmittermolecules Ion channels
Figure 28.6_2 Neurotransmitter either broken down by enzymes Or Recycled back to sending cell Neurotransmitter Neurotransmitter brokendown and released Receptor Ions Ion channel opens Ion channel closes 6 5
Excitatory Trigger Na-gated channels to open and receiving cell starts to depolarize toward threshold Stimulate action potential in receiving cell Inhibitory Trigger K-gated channels to open and receiving cell hyperpolarizes Inhibits action potential from occurring in receiving cell Neurotransmitters May be Excitatory or Inhibitory 0 © 2012 Pearson Education, Inc.
Figure 28.7 Synaptic terminals Inhibitory Excitatory Dendrites Myelinsheath Receivingcell body Axon Synapticterminals
Figure 28.7_1 Synapticterminals
Examples of Neurotransmitters Acetylcholine in the brain and at synapses between motor neurons and muscle cells. Causes skeletal muscle contraction Serotonin and dopamine are important neurotransmitters in the CNS affect sleep, mood, and attention Epinephrine Involved in involuntary nervous system Flight or fright response 0 © 2012 Pearson Education, Inc.
Many drugs and toxins act at chemical synapses Many psychoactive drugs act at synapses and affect neurotransmitter action. Caffeine counters the effect of inhibitory neurotransmitters. Nicotine acts as a stimulant by binding to acetylcholine receptors. Alcohol is a depressant. 0 © 2012 Pearson Education, Inc.
Many drugs and toxins act at chemical synapses • Botox • Produced by many bacteria such as Clostridium botulinum • Inhibits release of acetylcholine from synaptic vesicles • Prevents skeletal muscle contraction • Snake Venoms • Inhibit acetylcholinesterase - the enzyme that breaks down acetylcholine • Can’t turn off induction of skeletal muscle contraction • Results in uncontrolled muscle contractions (tetany)
