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Nervous System II. SBI4U. Synaptic Transmission. Synaptic Transmission. 2 types of synapses: Chemical & Electrical Neurotransmitter-Receptor vs. Gap junctions. Electrical signals & electical synapse. Plasma membrane of presynaptic and postsynaptic cell are in direct contact. - PowerPoint PPT Presentation
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NERVOUS SYSTEM II
SBI4U
SYNAPTIC TRANSMISSION
SYNAPTIC TRANSMISSION
2 types of synapses: Chemical & Electrical
Neurotransmitter-Receptor vs. Gap junctions
ELECTRICAL SIGNALS & ELECTICAL SYNAPSE Plasma membrane of presynaptic and
postsynaptic cell are in direct contact. Current flows directly (unbroken
transmission of electrical signal) Faster neural transmission than
chemical synapse
RESTING MEMBRANE POTENTIALMembrane potential: imbalance between
charges outside and inside the membrane that causes an electrical (electrical difference between Na+ and K+)
- 3 Na+ for every 2K+ ions pumped in(Na+/K+ active transport pump)
- An unstimulated neuron has a resting membrane potential where the voltage difference in the nerve cell is – 70mV
ACTION POTENTIAL Membrane potential changes during an
electrical impulse. All or nothing principle : frequency of AP
not magnitude (a greater stimulus faster AP not bigger)
ACTION POTENTIAL IN CHEMICAL SYNAPSE
ACTIVITY-QUESTIONS What is all-or-none response? What is the difference between chemical
and electrical synapse? Which area of the graph indicates the
opening of Na+ channels and their diffusion into nerve cells? And when does repolarisation occur ?explain
Pg.529 Q1-3
ANSWERS 1. A certain threshold stimulus is required to
trigger an AP along a nerve. However, once the threshold has been reached further increase in stimulus will not increase nerve response. It is all-or-none response. A nerve or muscle fibre responds completely to a stimulus or it does not at all.
2- Electrical transmission faster, diminish as it travels, and uses excitation energy to push elecrons.
Chemical: slower, impulse remain strong, uses cellular energy to generate current
3. During depolarization of the membrane . As it is depolarized the sodium ions rush into the cell causing the membrane potential to increase. Repolarisation occurs when K+ ions diffuses out of the axon. This diffusion lowers the membrane potential of the nerve cell.