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THE FORMATION AND THE
TRANSMISSION OF MESSAGE IN
NERVOUS SYSTEM
Farbod Niazi
General information
What is a neuron and an
action potential
What is a neuron
The neuron is a nervous system cell that is designed to
transmit messages.
This cell has three parts:
1)
Dendrites
2)
Cell body
3)
Axon
The path of the message in a neuron
Signals are transmitted from dendrites to cell body
and from cell body to axon
Dendrites
cell body
axons
synaptic terminals
BACK
The resting potential

When a neuron doesn’t work, it’s at its resting
potential. At the resting potential, there is a
difference between the electric charge of inside the
cell and outside the cell. The cytoplasm of the
neuron is slightly more negative than the
extracellular fluid(-70 mV) . In fact, the membrane
of the cell is polarized because it has a positive
pole and a negative pole.
What help the cell to maintain the
resting potential
There are some channels and pumps that help the
neuron to maintain his charge:
•
Chemically-activated channels
•
Voltage-activated channels
•
Passive ion channels
•
Sodium-potassium pumps
Back
Passive ion channels

Channels with no gates that let specific ions in. At
resting potential, the cell is more permeable to
potassium ion than to sodium ions, so these channels
let more K+ in than Na+.
Neuron
channels
Sodium-potassium pumps

A pump which receives energy to make an
exchange between sodium and potassium ions. This
pump let two potassium ions in for each three
sodium ions that leave the cell.
Neuron
channels
But how a neuron creates messages
Neurons can transmit electrical signals called nerve
impulses or action potentials. Every neuron receives
signals from its dendrites and transmits it by its
axon. This flow continues until it reaches the brain or
the spinal cord.
The path of a message
through a neuron
How the action potential or the nerve
impulse is formed
When a stimulus is strong enough, it causes a difference
of membrane voltage. The cell membrane becomes
permeable to sodium ions which are positively
charged. This change can fire an action potential and
create a nerve impulse.
The creation of a nerve impulse
These
channels are
the main
reason of the
change in
membrane
potential
Details
The process of creating a
nerve impulse
The threshold level
Any stimulus that can increase the voltage of
cytoplasm to -55 mV or more causes an action
potential. When the threshold level is reached at
-55 mV, the voltage of the cytoplasm suddenly
reaches 0 and overshoots to +35 mV. In fact, the
membrane is depolarized.
The change in voltage
A stimulus can trigger the voltage-activated channels.
Voltage-activated channels are responsible for the
sudden change of voltage. There is a specific
voltage-activated channel for every ion that pass
through the membrane of a neuron. But the
potassium and sodium ions voltage-activated
channels are essential for the creation of the action
potential.
Voltage-activated channels
Sodium voltage-activated channels
These channels have two gates:
 Activation gates
 Inactivation gates
When a stimulus
is detected, the
activation gates
open and let
some sodium ions
in.
Sodium voltage-activated channels
When a certain
number of ions come
into the cell, the
threshold level is
reached, which
means that some
other gates start to
open.
The opening of sodium voltage-activated channels
Before and after the depolarization
Depolarization is stopped
When the membrane voltage reaches 35 mV, the
inactivation gates close in response to
depolarization and the sodium ions can’t enter the
cell anymore. The Na+ can only come in during a
brief period when both activation and inactivation
gates are open.
The opening and the closing of a voltage-activated
channel’s gates
Repolarization
What a neuron hates the most is when the membrane
potential is positive. That’s exactly the case of a
neuron after the depolarization. So, potassium
voltage-activated channels open and let K+ ions out
Potassium voltage-activated channels
Unlike sodium voltage-activated channels, these
channels have only one gate.
Potassium voltage-activated channels
In response to depolarization, the only gate of
potassium voltage-activated channels opens and
potassium ions rush out of the cell and the
membrane voltage reaches -70 mV again.
Repolarization
Resting potential
Threshold level
Depolarization
Repolarization
Resting potential
The flow of the nerve impulse
When an action potential is initiated, it continues
along the cell until the end of the axon where it
jumps to another neuron by neurotransmitters.
Resting potential
Depolarization
Repolarization
Resting potential
Sources
Author’s name
Date of publication
Title
Publisher or URL
Eldra P. Solomon
Linda R. Berg
Diana W. Martin
2010
Solomon biology
Life science
Crash course
2012
Eric H. Chudler
N.D
The Nervous System https://www.youtub
– Crash Course
e.com/watch?v=x4P
Biology #26
PZCLnVkA&t=574s
&list=PL3EED4C1D
684D3ADF&index=
26
Neuroscience for
kids
http://faculty.washi
ngton.edu/chudler/
neurok.html