nervous system ii

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.