Nerve Impulses

By: Melissa M., Wisam S., and Reem S.

Resting Membrane Conditions

a) Neurons, due to molecules called anions, are negatively charged. When an axon is at rest it has a negative charge and potassium and sodium pumps are closed which keeps the positively charged sodium and potassium ions inside. This state is known as the resting potential because of the positive-negative difference inside and outside the neuron.

b) A neuron's plasma membrane very permeable to K+ and less permeable to Na+.

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Generation of a Nerve Impulse

a) A neuron responds to stimuli like touch, sounds, lights, etc. and communicate and send impulse through the cell membrane.

b) Depolarization generates nerve impulses if its depolarization graded potential is large enough to travel through the channels then to the outside of the membrane. Permeability helps with generating nerve impulses. An increase of sodium leads to the opening of the sodium ion channels, allowing sodium to go in and get depolarized.

c) When the sodium has decreased its permeability as a result of action potential, the gates close after passing because of the increased positive charge.

d) The protein channel uses energy from ATP to pump three sodium ions out of the cells and two potassium ions in.

Conduction of the Nerve Impulse

a) Action potential is an exchange of ions that runs along the length of the axon.

b) At first, the sodium gates are opened allowing many sodium ions into the cell causing the charge of the cell to reverse; the inside of the cell is positive and the outside is negative.

Then, potassium gates open and sodium gates close allowing the potassium ions to leave causing the cell's charge to go back to negative on the inside and positive on the outside. When the action potential reaches the axon ending, it causes calcium ions to enter the cell which causes the tiny bubbles full of neurotransmitters to release their contents into the synaptic gap.

c) The ions have to pass through the protein channels to get through the membrane.

d)The myelin sheath speeds up the process of action potential.

action potential

One Neuron to Another

a) After the impulse has gone through, the axon of a neuron and reaches the axon terminals, it jumps to the dendrites of neuron next to it.

b) As the signal jumps, it passes the gap between the neurons called the synapse.

c) During the process of going to the next neuron, neurotransmitters, or chemicals that transmit signals across the synase, are released.

d)These neurotransmitters bind with the proteins receptors of the following neurons. Different proteins are receptors for different neurotransmitters. The impulse travels through the axon of the neuron and the process repeats.

Active Transport vs. Passive Transport

Active Transport

Because it requires ATP, the process of moving sodium and potassium ions across the cell membrane is an active transport. Na+ moves outward against its concentration

gradient while K+ moves inward. There is an exchange of three sodium ions for every two potassium ions.

Passive Transport

An ion that is in high concentration in one area will diffuse to an area of lower concentration if the membrane is permeable to it.

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Chemical vs. Electrical


The release of neurotransmitters


Transmission of a nerve impulse along a neuron