Download Nervous System II

SBI4U
2
types of synapses: Chemical & Electrical
 Neurotransmitter-Receptor
vs. Gap junctions
 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
Membrane 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
 Membrane
potential changes during an
electrical impulse.
 All or nothing principle : frequency of AP not
magnitude (a greater stimulus  faster AP
not bigger)
 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
 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.