5 Synaptic transmission

5 Synaptic transmission - Synap&c transmission The...

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Unformatted text preview: Synap&c transmission The patellar tendon reflex Quadriceps muscle Cell body of sensory neuron in dorsal root ganglion Gray matter White matter Hamstring muscle Spinal cord (cross section) Fig. 49-3 Sensory neuron Motor neuron Interneuron The nervous system consists of two principal types of cells: neurons and glia. A typical neuron is divided into readily identifiable regions. Nervous Tissue 40 µm Dendrites Cell body Glial cells Axon Neuron Axons Fig. 40-5n Blood vessel 15 µm Dendrites S&mulus Nucleus Cell body Axon hillock These two neurons illustrate neuronal structure and introduce the Presynap&c major mechanism by which neurons transmit informa&on through the cell nervous system: synap&c transmission. Axon Synap&c cleM NeurotransmiFer Synap&c terminals Postsynap&c cell Fig. 48-4 Events at a synapse when an ac&on poten&al arrives in the presynap&c terminal: 5 Synap&c vesicles containing neurotransmiFer K+ Na+ Presynap&c membrane Ac#on poten#al! Voltage ­gated Ca2+ channel 1 Ca2+ Synap&c cleM Postsynap&c membrane 4 2 6 3 Ligand ­gated ion channels Fig. 48-15 When ion channels open in membrane of the post ­synap&c cell, ionic currents across the post ­synap&c membrane can change Vm in that cell. Vm might depolarize, but not OR enough to produce an ac#on poten#al. Terminal branch E1 E1 of presynap&c neuron E2 E2 Membrane poten&al (mV) Postsynap&c neuron Input from several presynap#c neurons might sum. Spike ­ini#a#ng zone 0 E1 E2 E2 Ac&on poten&al Threshold of axon of postsynap&c neuron I I I I E1 Ac&on poten&al Res&ng poten&al –70 E1 E1 (a) Subthreshold, no summa&on E1 E1 (b) Temporal summa&on E1 + E2 (c) Spa&al summa&on E1 I E1 + I (d) Spa&al summa&on of EPSP and IPSP Fig. 48-16 NeurotransmiFers belong to a number of different chemical groups, and their effects are complex. Some neurotransmiFers are generally excitatory (that is, they increase the likelihood of an ac&on poten&al in the postsynap&c cell. Some neurotransmiFers are generally inhibitory (that is, they decrease the likelihood of an ac&on poten&al in the postsynap&c cell). And some neurotransmiFers are excitatory at some synapses and inhibitory at other synapses. Table 48-1 ...
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