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Summary 1.4 the human body problem 3; inside the neuron

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The Human Body 1.4

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Erasmus Universiteit Rotterdam (EUR)

in this summary you will find everything you need to know about what neurons look like (what parts they have), how they work and why we have them.

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neurons
sensory neurons
motor neurons
inside the neuron
what does a neuron look like

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1.4 the human body

€ 17,94 € 5,49 6 items

1. Samenvatting - 1.4 the human body problem 6; bon appetite!
2. Samenvatting - 1.4 the human body problem 4; drugs
3. Samenvatting - 1.4 the human body problem 3; inside the neuron
4. Samenvatting - 1.4 the human body problem 2; two sides
5. Samenvatting - 1.4 the human body problem 8; stress
6. Samenvatting - 1.4 the human body problem 7; night, night
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Notes problem 3 – lecture
membrane potential: difference in electrical charge between the inside and the outside of cell due to
unequal distribution of ions across the cell membrane. Ions are small particles with an electrical
charge in this case we use sodium ions (Na +) and potassium ions (K+). Ions can only pass the
membrane through active transport this is not easy. The membrane is made up of a layer of fatty
molecules (lipid) the extracellular space is the outside of the neuron and the intracellular space is
inside the neuron.
membrane potential during rest
this is also called the resting potential. During rest there are more sodium ions outside the neuron
and more potassium ions inside the neuron. There are more positively charged ions on the outside
this is the reason why the resting potential has a -70 mV difference inside the neuron vs outside the
neuron. The neuron is then polarized.
3 factors that influence ion distribution during rest
1. Sodium-potassium pumps
- takes 3 sodium ions out and 2 potassium into the neuron to keep de distribution polarized.
- is an active process and costs the neurons energy.

2. Electrostatic pressure
- because the charge of the neuron is negative on the inside and positive on the outside the sodium
ions want to move inside the neuron.
- the potassium ions on the inside want to stay there.
- the electrostatic pressure goes against the unequal distribution.
- the electrostatic pressure makes sure that the potassium ions stay inside the neuron.
- passive transport

3. Pressure from random motion due to the concentration gradient
- because they are able to move freely they want to move away from the highest concentration and
make the concentration equal.
- the sodium ions want to move inside the neuron because the concentration there is lower.
- the potassium ions want to go outside because there are more outside than inside.

The sodium and potassium ions can only enter the neuron through the protein molecules. This can
only happen when the protein molecules are open. During the resting state the sodium and
potassium protein molecules are closed to maintain the concentration.

The action potential – depolarization
the resting potential makes it easy for the neuron to react fast when it is stimulated. When it is
stimulated the resting potential is disturbed. The potential inside the neuron might reach a certain
point if it is stimulated enough, reaches the threshold. At this point the sodium channels and the
potassium channels open up and the electrostatic pressure and the pressure from random motion
due to the concentration gradient are pulling the sodium ions to enter the neuron. This causes the
potential to become more positive. The inside becomes more positive and the outside more
negative.

, In the beginning the neuron is at rest (-70mV) when the membrane potential reaches -55 mV the
resting potential is being disturbed and the sodium channels open and they can enter the neuron.
The inside of the neuron is way more positive (+30 mV). This phase is called the depolarization. At
the peak of the flow the sodium channels close again and they can’t enter the neuron anymore.
However the potassium channels are still open. Due to the concentration gradient of the membrane
the potassium ions flow outside of the neuron. This also happens because the inside is now positively
charged and the outside is now negatively charged. This is called repolarization. The potential inside
the neuron is now even more negative than it was in the resting phase. This is called
hyperpolarization. The sodium-potassium pumps go to work again to make the potential in the
membrane -70 mV again.

- The action potential happens at the axon.

- The action potential is an all or nothing potential, it is always the same and is not
influenced by the intensity of the stimulation.

-

Rate law: when a neuron is stimulated strongly, the frequency of the action potential rises.

How does an action potential travel across the axon membrane:
- like a domino effect, when it is started it activates the area around it.
- when the action potential is activated in a certain point it opens the sodium and potassium
channels and lets them come inside the neuron, this activates the following parts of the
neuron where the channels open up too and lets the sodium and potassium ions come in the
neuron there too. This is how the action potential travels to the dendrites at the end of the
axon and maybe transmitted to other neurons.

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