Download The Nerve Impulse

The Nerve
Impulse
How are
electricity and
nerves different?
Electrochemical Impulse,
Pages 418-425
- Current travels along a wire much faster than the nerve impulse
travels along a nerve.
- Electrical wires rely on external energy to push electrons along.
Nerve Impulses rely on cellular energy (from what source?) to
generate current.
-1900, Julius Bernstein, “Nerve impulses are electrochemical
messages created by the movement of ions through the nerve cell
membrane.”
- 1939, more evidence for the theory, action potential observed
in a giant axon of a squid.
How do nerve cells
become charged?
- neurons have a rich supply of + and - ions
- the electrochemical event is caused by an
unequal concentration of positive ions across
the nerve cell membrane.
-in the resting membrane excess + ions accumulate along the
outside of the membrane, while excess - ions accumulate
along the inside of the membrane, The membrane is polarized.
- this separation of charges gives the nerve cell membrane the
potential to do work.
-upon excitation, the nerve cell membrane becomes more
permeable to sodium than potassium. Sodium gates open!
- potassium gates close, sodium diffuses into the nerve cell.
The rapid inflow of Na ions causes more + ions than - ions on
the inside of the cell. The cell is now depolarized.
- K ions move out of the cell and restore polarity. The Na-K
pump moves the K ions back inside and Na ions outside and
the membrane is repolarized.
• Lets have a look at the nerve impulse.
Nerve
Impulse
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
The Action Potential
The Synapse