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Neurophysiology
Neurophysiology of Nerve Impulses
2 major physiological properties of neurons:
Excitability: the ability to respond to stimuli and convert it to nerve impulses
Conductivity: the ability to transmit the impulse to other neurons, muscles or
glands
In a resting neuron, the outside is more positive than the inside
Resting membrane potential: the difference in electrical charges that results in a
voltage across the plasma membrane
Polarized: a neuron at its resting membrane potential
In the resting state, the predominant intracellular ion is K, Na is
extracellular
Resting membrane potential is maintained by the Na-K pump that
transports Na and K in and out of the cell
The Nerve Impulse
Threshold stimulus: the membrane at the axon hillock becomes more permeable
to Na ions when a neuron is activated by a stimulus of adequate
intensity
Depolarization: the interior becomes less negative, exterior becomes less positive
Action potential: when depolarization reaches a certain point so that the
membrane polarity changes
Repolarization: within a millisecond Na and K return to their original state and
the resting membrane potentil is restored
Absolute refractory period: when the Na gates are open and the neuron is totally
insensitive to additional stimuli
Relative refractory period: if a very strong stimuli is able to reactivate the neuron
after repolarization, it is called the relative refractory period
Once an action potential begins, it is self propagating… it is
NEVER PARTIALLY TRANSMITTED!
Is an all or non response
Nerve impulse: propagation of the action potential in neurons
When a nerve impulse reaches the axon terminals, they release neurotransmitters
that act to stimulate or inhibit the next neuron in the chain