Download Nervous Impulse

THE NATURE OF NERVE IMPULSE
• Nerve impulses are caused by the
movement of electrically charged
ions. **sodium, potassium**
• These messages are caused by a
potential or a difference between
the inside and outside of the
membrane of the neuron
RESTING POTENTIAL
Organic negative protein
- Gives overall negative
charge inside neuron
To prevent diffusion
•
When neuron is at
rest
•
More Na+ ions
outside
•
More K+ ions inside
Uses ATP for active
transport to
maintain
concentration
difference
ACTION POTENTIAL – UP SWING
• aka Depolarization
• Nerves stimulated by
electric shock   pH
• Membrane becomes
permeable to Na+ ions
Na+ gates open and
Na+ diffuses in
ACTION POTENTIAL - DOWNSWING
• aka Repolarization
• Restores negative
potential
- K+ gates open (membrane becomes
permeable)
- K+ diffuses out
Na+ Gates close
RECOVERY PHASE
• Aka refractory period
• Na+ and K+ gates
unable to open 
ensures action
potential doesn’t
move backwards
• As soon as action
potential has moved
to next portion of
neuron, previous
portion undergoes
refractory period.
(Draw Picture from board)
• This process
requires 1/1000
sec.
ALL OR NOTHING LAW
The “All or Nothing” Law states that if the
threshold is reached an impulse is carried,
but if the threshold is not reached then
there will be no impulse. It doesn’t matter
how strong the stimulus. The same impulse
is sent regardless of strength. The
sensitivity to mild or severe pain depends
on the number of neurons stimulated as
well as the frequency of their stimulation.
Repolarization
Depolarization
ACTION POTENTIAL GRAPH
Refractory
Hyperpolarization
SPEED OF CONDUCTION
Action potential occurs at one small section of a neuron at a time
Non myelinated neuron
- Usually occurs in invertebrates/small animals
- Action potential moves slowly (0.5m/sec)
MYELINATED AXON
Action potential moves
up to 200m/sec
In myelinated neurons action potential concentrated at nodes
of Ranvier = saltatory conduction.
Action potential jumps from node to node
Causes “flip-flop” flow of charge
Animation
ACTION POTENTIAL REVIEW
Animation