IB BIOLOGY 6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron
Explain how a nerve impulse passes
along a non-myelinated neuron
• An electrical current which carry information
that travels along dendrites and axons of a
• Neuron without myelin sheath
• The potential difference across a nerve cell membrane
when it is not stimulated. (-70mV)
• A nerve impulse is an electrical current that travels
along dendrites or axons due to ions moving through
voltage-gated channels in the neuron’s plasma
• The voltage-gated channels are the sodium and
potassium channels, which means that they can open
and close depending on the voltage across the
• When the neuron is not sending an impulse,
the charge difference is maintained inside and
outside of the axon cell. This is called the
resting potential where it is polarized.
• The resting potential is due to the active
transport of Na+ ions and K + ions through
• The pumps sends Na+ ions out of the axon cell
and brings K + ions in.
• There are negatively charged ions (Cl-) located
permanently in the cytoplasm of the axon.
This leads to the net positive charge outside
the axon membrane and a net negative charge
inside the axon membrane.
• The potential difference produced across the
plasma membrane of nerve cell when it is
• Due to the diffusion of ions from outside the
axon to the inside and from the inside of axon
to the outside.
• Action potential is triggered by a stimulus
received at a receptor or sensitive nerve ending
causes a sodium channel to open.
• The Na+ ions which is actively transported out
diffused into the membrane. This causes the local
region inside the membrane to have net positive
charge while the outside having net negative
• The membrane is said to be “depolarized”. The
resting potential is reversed from -70mV to
• This area of axon then initiates the next area
of the axon to open up the other sodium
channels. (Domino effect)
• Therefore, the moving depolarization is called
an action potential.
• After a short while, the sodium channels
closed, and the potassium channels are
• This causes the rapid flow of K + ions out of the
membrane and thus, “repolarizing” the
• So, the inside is again negatively charged and
the outside is positively charged.
• The resting potential of the membrane is