Section 2. Signal Transmission Between the Neurons
Section 2: Signal Transmission Between the Neurons
Neurotransmission 1. Chemical synapse(Classical Synapse) Predominates in the vertebrate nervous system 2.Non-synaptic chemical transmission 3. Electrical synapse Via specialized gap junctions Does occur. but rare in vertebrate NS Astrocytes can communicate via gap junctions
Neurotransmission 1.Chemical synapse (Classical Synapse) – Predominates in the vertebrate nervous system 2.Non-synaptic chemical transmission 3.Electrical synapse – Via specialized gap junctions – Does occur, but rare in vertebrate NS – Astrocytes can communicate via gap junctions
Chemical synapse Copyright O The MeGraw-Hit Companies, Inc, Permission required for reproduction or display. Terminal bouton is Action Axon separated from Ca2+ potentials Action Ca potential postsynaptic cell by Ca2+ Ca haptic cleft Protein kinase activates. Protein kinase Inactive Calmodulin Synaptic (inactive) vesicles phosphorylates Ⅴ esicles fuse with synapsin Docking proteins axon membrane and Synaptic cleft Fusion and nt released by Ca exocytosis" Ca2+ Neurotransmitter.. exocytosis released Ca2+ amount of nts released depends upon frequency of AP
Chemical Synapse • Terminal bouton is separated from postsynaptic cell by synaptic cleft. • Vesicles fuse with axon membrane and NT released by exocytosis. • Amount of NTs released depends upon frequency of AP
Non-synaptic chemical transmission Vesicle The postganglionic neurons innervate the ⊙ smooth muscles Smooth muscle ⊙ no recognizable endplates Intervaricose Axon segment or other postsynaptic Varicosity specializations, Mitochondrion The multiple branches are beaded with enlargements (varicosities) that are not Varicosity covered by Schwann cells and contain synaptic vesicles Terminal Fig. Ending of postganglionic autonomic neurons on smooth muscle
Non-synaptic chemical transmission The postganglionic neurons innervate the smooth muscles. • No recognizable endplates or other postsynaptic specializations; • The multiple branches are beaded with enlargements (varicosities) that are not covered by Schwann cells and contain synaptic vesicles; Fig. : Ending of postganglionic autonomic neurons on smooth muscle
Non-synaptic chemical transmission continued In noradrenergic neurons, the varicosities are about ⊙ 5μm, with up to20,000 Smooth muscle varicosities per neuron ⊙o Intervaricose Axon segment Transmitter is apparently Varicosity released at each varicosity, Mitochondrion at many locations along each axon ● One neuron innervate Varicosity many effector cells 了 Termina Fig. Ending of postganglionic autonomic neurons on smooth muscle
• In noradrenergic neurons, the varicosities are about 5m, with up to 20,000 varicosities per neuron; • Transmitter is apparently released at each varicosity, at many locations along each axon; • One neuron innervate many effector cells. Fig. : Ending of postganglionic autonomic neurons on smooth muscle Non-synaptic chemical transmission continued
Electrical Synapse Impulses can be regenerated without interruption in adjacent cells Gap junctions Adjacent cells electrically Cytoplasm s Plasma coupled through a MEmbrane of one cell channe Plasma Two cells, membrane inter- of adja Each gap junction is connected< cell/acent y gap composed of 12 connexin junctions Connexin proteins proteins Cytoplasm forming gap unctions · Examples: Smooth and cardiac muscles, brain, and glial cells
Electrical Synapse • Impulses can be regenerated without interruption in adjacent cells. • Gap junctions: – Adjacent cells electrically coupled through a channel. – Each gap junction is composed of 12 connexin proteins. • Examples: – Smooth and cardiac muscles, brain, and glial cells
Electrical Synapses Electric current flow- communication takes place by flow of electric current directly from one cell2 neuron to the other crop .No synaptic cleft or vesicles cell membranes in direct contact communication not cytoplasm Iong and Charnel forned polarized- electric current ena.1 noleculemby pores in can flow between cells in either direction
•Electric current flowcommunication takes place by flow of electric current directly from one neuron to the other •No synaptic cleft or vesicles cell membranes in direct contact •Communication not polarized- electric current can flow between cells in either direction Electrical Synapses
Microtubule Presvnaptic Presynaptic neuron Cytoplasm neuron Synaptic vesicle Mitochondrion ○○ Gar neuron junction lons flow through gap junction channels Synaptic Neurotransmitter released Presynaptic membrane icle fusing Presynaptic membrane S cleft 。 Postsynaptic neurotransmitter membrane Gap junction channels Postsynaptic receptor lons flow through membrane postsynaptic channels Electrical Synapse Chemical synapse Purves 2001
Electrical Synapse Chemical Synapse Purves, 2001
I The Chemical Synapse and Signal Transmission
I The Chemical Synapse and Signal Transmission
The chemical synapse is a specialized junction that transfers nerve impulse information from a pre synaptic membrane to a postsynaptic membrane using neurotransmitters and enzymes Cell body Dendrites Axodendritic Axosomatic synapses synapses Axoaxonal synapses Axon D BENJAMIN/CUMMINGS
• The chemical synapse is a specialized junction that transfers nerve impulse information from a pre synaptic membrane to a postsynaptic membrane using neurotransmitters and enzymes
