IB BIOLOGY 6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron

6.5.5Explain how a nerve impulse passes along a

non-myelinated neuron

NERVE IMPULSE

• An electrical current which carry information that travels along dendrites and axons of a neuron

NON-MYELINATED NEURON

• Neuron without myelin sheath

RESTING POTENTIAL

• 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 membrane.

• The voltage-gated channels are the sodium and potassium channels, which means that they can open and close depending on the voltage across the membrane.

• 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 sodium-potassium pumps.

• 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.

ACTION POTENTIAL

• The potential difference produced across the plasma membrane of nerve cell when it is stimulated.

• 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 charge.

• The membrane is said to be “depolarized”. The resting potential is reversed from -70mV to +40mV. ~

• 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 opened.

• This causes the rapid flow of K + ions out of the membrane and thus, “repolarizing” the membrane.

• So, the inside is again negatively charged and the outside is positively charged.

• The resting potential of the membrane is restored.