Neurons.
Overview of the Brain.
Neurons.
Membrane potential.
Resting membrane potential.
Neuron as a computing unit.
Overview of the Brain.
The brain is possibly the most fascinating part of the human body.
We share a lot of DNA, with other life forms.
We share a lot of Life processes, and organs, with other life forms.
If there is one organ, which differentiates us significantly,
from other life forms, it is the brain.
Human beings are endowed with the most amazingly advanced,
version of the brain.
It is our advanced brain which makes us, the most important species in the planet.
The brain can be considered as an information processing,
and decision making centre of the human body.
All the thinking that we do, happens in the brain.
It is the seat of consciousness.
The brain also performs another critically important function.
The brain regulates and manages, all the life processes in the body.
Our breathing, our heart rate, our blood pressure etc,
are all controlled, by our brain.
This control of metabolic processes, or life processes, is automatic.
We are not conscious of the management of life processes.
For example, we don’t have to think about breathing, heart rate etc.
It happens automatically, even when we are asleep.
The fact that this process, is automatic, in no way,
reduces the importance of this function.
We need our brain to live.
We need to live, in order to think.
Animals also have brains.
Animals also think.
The thinking capability of human beings, is far superior to that of any animal.
Our intelligence is so superior, animal intelligence is not even comparable to ours.
The regions in the brain, capable of high level thinking,
is present only in the human brain.
The basic unit of a human brain, is the neuron.
All the information processing, that happens in the brain,
is done by neurons.
The brain is a collective organ, of billions of neurons.
It is estimated that the brain, has about hundred billion neurons.
Each neuron in the brain, is connected to hundreds and thousands,
of other neurons.
All the information processing that happens, in the brain,
is interrelated in some way.
It is estimated that there are about hundred trillion connections in the brain.
It is these connections, that ultimately result in a process, we call thinking.
The brain can be referred to as a connectome, of neurons.
The connectome can also be thought of as the wiring circuit of the brain.
Memory, an important functionality, is organised in the Brain.
Even a feeling, such as anger, originates in the Brain.
The states of mind, being alert, motivated, or sleepy comes from the Brain.
It is the brain which helps us understand, and solve complex problems.
It is the brain which helps us invent all the wonderful things,
which we take for granted.
It is this connectome, which endows us with our superior intelligence.
This also makes, the brain a complex organ.
There are certain areas of the brain, which are specialised, in certain functions.
For example, there are special areas to process visual information,
hearing, speech etc.
All the areas of the brain, are however closely interrelated.
This makes the brain, a fascinatingly complex organ.
It also makes it a exciting subject for studying.
The brain is connected, to our whole body, via nerves.
Just like the heart is connected to the whole body, via blood vessels,
the brain is connected to the whole body, via nerves.
Nerve fibres carry signals, or information from and to the brain.
Afferent nerve fibres, carry information, from all over the body, to the brain.
Efferent nerve fibres, carry information, from the brain, to the body.
The nerves which emanate from the spine, and reach out to all parts of the body,
constitutes the peripheral nervous system.
Using the nerves to communicate,
the brain is able to manage, all the life processes of the body.
This is also the way, that the brain, gives instructions to all our skeletal muscles.
This enables us to consciously control our skeletal muscles.
This control helps us to perform day to day activities.
It is this control which helps us walk, talk, smile, play, work and dance.
All the nerves in the body, are collectively referred to as the nervous system.
The brain works closely with, and is strongly integrated with the nervous system.
The basic unit of the nervous system, and the brain, is the neuron.
In the nervous system, the neurons play the role of carrying signals,
to and from the brain.
We can say that the neuron is the building block, of the brain and nervous system.
All the neurons in the brain, and the nervous system,
have the same basic functionality.
This makes it worth while to understand the functioning of the neuron.
Throughout this module we will use examples, to understand concepts.
The examples and the values used, will be typical.
The examples help us understand the concepts.
However, we should bear in mind, that there could be variations and exceptions.
Neurons.
The neuron, is a living cell, like other cells in the body.
The neuron is a specialised cell.
The neuron is similar in structure, to other typical cells in the body.
It has a nucleus, and the same DNA, found in other cells.
It has mitochondria, which generates energy for a cell.
The neuron requires nutrients like other cells.
It has all other basic components of a living cell.
The neuron cell specialises, in the function of the nervous system.
Information transmission, and processing are the basic functions of the nervous system.
Most of the information processing takes place in the brain.
Signal transmission is taken care of by the nerves.
Communicating a signal to one or more neurons, is the most important function,
of a neuron.
Inside the neuron, the signals are electrical signals.
A neuron typically communicates with another neuron,
in the peripheral nervous system, in the body.
A neuron communicates with hundreds and thousands,
of other neurons in the brain.
A neuron does not make physical contact, with another neuron.
A gap exists between a neuron ending, and the next neuron.
This gap is called the synapse.
To communicate across the synapse, the neuron uses chemical signals.
The chemical signals, generate a new electrical signal in the next neuron.
Dendrites.
Dendrites are a series of out growths, from the cells body, or soma.
Neurons have multiple dendrites.
Each Dendrites have many branches, just like a tree.
The dendrites are the sites, for the specialised junctions, for receipt of signals.
The dendrites are the in gates, for the neuron.
The dendrites receive signals, from other neurons.
Dendrites enable many other neurons to connect with it.
The ability of one neuron to connect with many other neurons,
is critical to the functioning of the neuron, specially in the brain.
Neurons thus are specially designed, to connect with hundreds and thousands,
of other neurons.
Soma.
The cell body of a neuron, is called as the soma.
The soma is a living cell, like other cells.
It breathes in oxygen, and breathes out carbon dioxide.
It takes in nutrition, and gives out waste products.
These soma has a nucleus.
The nucleus contains the same DNA, like other cells.
The DNA along with other genetic machinery can synthesise, many proteins.
The soma has the capability to generate energy.
The currency for energy is ATP.
Energy in the form of ATP, is essential for the cell.
Even a neuron at rest, requires expenditure of energy.
The brain which is comprised mostly of neurons,
consumes a surprisingly large amount of energy.
It is estimated that about 20% of the energy we consume,
is used by the brain.
The soma is enclosed by a cell membrane.
The cell membrane comprises of a phospholipid layer.
A phospholipid is a bio chemical, with a phosphate and lipid component.
The phosphate component is water loving, or hydrophilic.
The lipid component is water averse, or hydrophobic.
The inside and outside of the soma, has watery fluids.
Two phospholipid compound join together to form the unit of a cell membrane.
The lipid components face each other, and form the inner layer, of the membrane.
The phosphate component form the outer and inner layers, of the membrane.
The outer and inner layers are comfortable with the extra cellular,
and intra cellular fluids.
The lipid middle layer of the membrane, being hydrophobic, separates the extracellular,
and intracellular fluids and organelles.
The membrane acts as a container for the cell.
The membrane is selectively permeable to certain kinds of substances.
Charged particles or ions, are called polar molecules.
The membrane is specially impermeable to polar molecules.
The membrane prevents the free movement, of ions across it.
Neuron functionality requires the transfer of ions, across the membrane.
To enable this ion transport, the membrane has embedded proteins.
These special proteins, acts as channels and mechanisms,
to transport ions, across the membrane.
The inside of the cell membrane, is the intra cellular space.
The outside of the cell membrane, is the extra cellular space.
There are more positively charged ions, in the outside, or extra cellular space.
This causes the outside to be more positive.
There are less positively charged ions, in the inside, or intra cellular space.
This causes the inside to be less positive, or relatively negative.
This results in an electrical potential, to be created, across the cell membrane.
Membrane potentials are measured, relative to the inside of the membrane.
Neurons, even at rest, have a negative electrical potential.
Membrane potential, is the key to the functioning of the neuron.
Changes in the membrane potential results in a signal being generated.
This signal is called as the action potential.
Movement of the action potential, causes the signal to be transmitted.
Neurons are involved in receiving, processing and transmitting, of electrical signals.
Neurons receive signals, from other neurons, through their dendrites.
If the incoming signal is weak, the neuron will not respond to the signal.
There is a minimum signal strength, that is required,
to activate a neuron.
This minimum level is called, as the threshold.
If the incoming signal strength, reaches threshold, or exceeds it,
the receiving neuron will get activated.
The soma receives signals from many dendrites.
Dendrites are just extensions of the soma.
Dendrites effectively increase the exposed surface area of the cell membrane,
of the soma.
This helps the neuron to receive signals from many other neurons, or cells.
The effective signal that is received, by a neuron,
is the sum of all the signals received by the neuron.
The signal strength has to reach threshold, to activate a neuron.
This threshold can be reached, by the sum of all the individual signals.
A number of weak signals, receive together, can create a signal strong enough,
to activate the receiving neuron.
This is an important concept, in understanding the functioning of a neuron.
It responds to sum of all the signals, that it receives.
By doing this summation, the neuron is exhibiting,
some of its most basic processing capability.
Axon.
The axon is like the out gate of the neuron.
Signals are received by the dendrites, of the neuron.
Signals are sent out, through the axon of the neuron.
The axon is a long extension, from the neuron cell body.
A typical nerve has only one axon.
The neurons are designed to receive multiple signals,
but send out only one signal.
If the sum of the signals, received from the dendrites are strong enough,
the neuron will generate a signal,
which it will send out via the axon.
This functionality of many signals in, and a single signal out,
is central to functioning of a neuron.
The soma of the neuron, sums up all the signals,
that it receives, in the cell membrane.
The net signal travels to a point, in the soma, where the axon emanates from the soma.
This point is known as the axon hillock.
The axon hillock is the starting point of the axon.
This is the point at which, the decision is taken,
whether the neuron will respond to the incoming signals.
If the sum of the incoming signals, at the axon hillock,
does not reach a threshold value, a new signal, will not be generated.
If the sum of the incoming signals, reach or exceed, a threshold value,
a new signal will be generated, in the axon hillock.
Once a signal is generated, at the axon hillock,
the signal will propagate, along the entire length of the axon.
Processing and propagating signals, are essential functions,
in the brain and nervous system.
The basis of this function, starts in the neuron,
when it decides to generate a new signal, based on the signals, it receives.
A long axon can be called as a nerve fibre.
A bundle of nerve fibres, is called as a nerve.
The nerves, some of which are visible to us, comprises of large number of axons,
or nerve fibres.
A neuron can have a short axon, or a long axon.
In the brain, a neuron may connect, to an adjacent neuron.
It may also connect using a longer axon to a neuron,
in another part of the brain.
In the peripheral nervous system many of the neurons have long axons.
This is because the neuron near the spinal cord,
has to reach out to a distant part of the body.
For example, an axon might extend from near the spine, all along the leg,
to the little toe in our feet.
Axons enable the brain, to send signals to all parts of the body.
The end of the axon, has typically many branches.
This enables a single neuron to send signals,
to hundreds and thousands of other neurons.
The end of the axon branch is the axon terminal.
The signals carried by the axons are electrical signals.
If sum of the signals in the soma of a neuron, is of sufficient strength,
it will generate a signal in the axon.
The signal will propagate, all along the axon, however long it is,
to the axon terminal.
If a signal is generated by a neuron in the spinal cord,
the axon will carry it all the way, to the toe.
Axon terminal.
The axon terminal is the physical end of the axon.
The axon does not make physical contact, with the dendrite of a neuron.
The axon terminates in a junction, called as synapse,
just before the dendrite of the next neuron.
The axon of the neuron, communicates with the dendrite of another neuron,
via the synapse.
Signals from the axon terminal, to the dendrite, is chemically transported.
Myelinated axons.
Some axons do not have any covering sheath.
These are called un-myelinated axons.
Signals can travel in an un-myelinated axon.
But they cannot travel very far.
To enable long distance travel, many axons are myelinated .
Myelinated axons, have a sheath, covering the axon.
Myelin is a fatty substance.
The myelin sheath acts like a insulation, for the axon.
These axons are called myelinated axons.
Myelinated axons are used for long distance transmission, of signals.
The myelin sheath, gives a white colour to the axon.
In the nervous system, it is common to call, the myelinated axons,
as white matter.
This is in contrast to the soma of the cell, which is called grey matter.
We note that the same neuron, has a soma, which is grey,
and has an axon, which is white.
In the brain and in the spinal cord, there are clusters of soma,
referred to as grey matter.
Other areas in the brain, and spinal cord, have clusters of axons,
which are called white matter.
Nodes of Ranvier.
The myelin sheath does not cover the entire length of the axon.
There are gaps between the myelin sheath covering.
The gaps are called nodes of Ranvier.
The areas covered by the myelin sheath, does not allow ions,
to travel across the cell membrane.
In the gaps, or the nodes of Ranvier, there are channels,
which allow the ions to cross the cell membrane.
In the peripheral nervous system, the myelin sheath, comprises of Schwann cells.
A myelinated axon, with intermittent nodes,
help in long distance transmission of signals.
Myelinated axons, also result in faster transmission, of electrical signals.
Myelinated axons, are like fast channels.
It is interesting to note that more evolved animals, like human beings,
have more myelinated axons.
This among other things, help them to perform,
very fast skilful synchronised, and co-ordinated complex actions,
like playing football, or classical dancing.
Membrane potential.
Membrane potential plays the key role in neuron functioning.
The membrane is a thin phospholipid bilayer, which separates the inside of the cell,
from the outside.
The membrane is very thin.
It is typically only about 3.5 nanometers thick.
Ions are charged particles.
A molecule which is short in electrons, will be positively charged.
A positively charged ion, is called as a cation.
A molecule which has extra electrons, will be negatively charged.
A negatively charged ion, is called as an anion.
It is possible that ions, collects as a thin layer outside the membrane.
This layer is typically, only a few molecules thick.
Similarly, ions can collect, in a thin layer, inside the cell.
These ion layers, inside and outside the membrane,
can cause a potential difference, across the membrane.
Membrane potential is conventionally measured,
relative to the inside of the cell membrane.
Membrane potentials are measured in millivolts.
If there are more positive ions, in the outer layer of the membrane,
relative to the inner layer, there will be a negative potential difference, or voltage.
If there are more positive ions, in the inner layer of the membrane,
relative to the outer layer, there will be a positive voltage.
If the ions can somehow be moved, from the inner to the outer layer,
or vice versa, a voltage change is generated.
This transport of ions, in and out of the membrane, is the basic mechanism,
that neurons use to generate electrical signals.
Membrane transport.
The cell membrane, by its design, is impermeable to ions.
To move ions, across the membrane, we need special mechanisms.
Proteins are the special molecular machines, that perform the function of transporting,
ions across the membrane.
These special proteins are embedded in the cell membrane.
They facilitate the regulated movement of ions, across the membrane.
We will discuss three of these special protein mechanisms.
- Potassium diffusion channel.
- Sodium diffusion channel.
- Sodium potassium pump.
Potassium diffusion channel.
This is also called as a potassium leak channel.
Special proteins are embedded in the membrane,
which allows potassium ions to pass through.
Proteins are coiled up, long chains of amino acids.
By changing its shape or conformation, proteins can allow a selected substances,
to move inside a channel, in its coiled conformation.
This protein acts like a revolving gate.
It allows the potassium ion, to enter from one side,
and exit from another side.
For example, potassium can exit the cell via potassium diffusion channel.
This will happen, if the concentration of potassium, inside the cell,
is higher than the concentration of potassium, outside the cell.
Sodium diffusion channel.
This is also called as a sodium leak channel.
This is similar protein machinery to the potassium leak channel.
This allows sodium ions, to move across the membrane.
For example, sodium can enter the cell, via the sodium diffusion channel.
This will happen if the concentration of sodium, outside the cell,
is higher, than inside the cell.
Concentration gradient.
If two solutions of varying concentration, are separated by a membrane,
there will be a concentration gradient, across the membrane.
If the membrane is permeable, substances will try to move across the membrane.
For example, let us take a chamber, separated by a permeable membrane.
Let us have a solution with high concentration of sodium chloride on one side,
and a low concentration on the other side.
Sodium chloride will tend to move, from the highly concentrated solution,
to the low concentration solution.
This process is called diffusion.
The greater the difference, between the concentration, of the solutions,
the greater will be the tendency, for sodium chloride to diffuse.
The difference in the concentration, is called as the concentration gradient.
A larger concentration gradient, results in a larger diffusion force.
The diffusion force acts in a direction,
from a higher concentration to a lower concentration.
A similar concept applies to ions also.
Ions will diffuse from a area of higher concentration,
to an area of lower concentration.
The inside of a cell has a higher concentration, of potassium ions.
Potassium ions, have a tendency to diffuse, out of the cell.
Sodium ions have a higher concentration outside the cell.
Sodium ions, have a tendency to diffuse, into the cell.
Sodium potassium pump.
The sodium potassium pump is a very interesting protein machinery.
It transports three sodium ions, from inside the cell to outside the cell.
It transports two potassium ions, from outside the cell, to inside the cell.
We can visualise this as a special revolving gate.
The gate pumps out three sodium ions , in half a revolution,
and pumps in two potassium ions, in the next half a revolution.
This pump is always working in the neuron.
Pumping sodium out, increases the sodium concentration outside the cell membrane.
This causes a sodium concentration gradient.
Sodium ions build up, to have a higher concentration, outside the cell.
Sodium ions have a tendency, to move inside the cell.
Pumping potassium in, increases the potassium concentration inside the cell.
This causes a potassium concentration gradient.
Potassium ions build up, to have a higher concentration, inside the cell.
Potassium ions have a tendency, to move out of the cell.
The sodium potassium pump is always working, to maintain the concentration gradient.
This concentration gradient, is crucial for the functioning of the neuron.
Resting membrane potential.
When a neuron is not transmitting any signal, it is said to be at rest.
Even at rest, the neuron maintains a potential difference, across its membrane.
This potential difference is called, as the resting membrane potential.
The membrane of the neuron, has more positively charged ions, in a thin layer,
outside the membrane.
It has more negatively charged ions, in a thin layer, inside the membrane.
The potential difference between the outer layer,
and the inner layer, can be measured.
This difference is typically around minus 70 millivolts.
There are some differences in voltage levels for different neurons.
For the purpose of our discussion, we will use some typical values.
The resting membrane potential, of a neuron is around minus 70 millivolts.
There are 3 main mechanisms, which play a role,
in creating and maintaining the resting membrane potential.
Sodium potassium pump.
Potassium diffusion channel.
Sodium diffusion channel.
The sodium potassium pump, pumps in 2 potassium ions,
and pumps out 3 sodium ions.
This creates a larger concentration of potassium inside the neuron,
and a larger potassium concentration, in the outer layer of the neuron membrane.
When there is a concentration gradient, the natural tendency of the ions,
is to try and equalise the concentration.
Since the cell membrane, is not fully permeable to ions,
the concentration gradient, creates diffusion forces.
The sodium concentration gradient, results in sodium, trying to enter the cell.
Sodium has a diffusion force, acting from outside to inside.
Sodium ions are always trying to diffuse into the neuron.
The potassium concentration gradient, results in potassium, trying to exit the cell.
Potassium has a diffusion force, acting from inside to outside.
Potassium ions are always trying to diffuse out of the neuron.
Sodium potassium pump, is working against the concentration gradient.
It pumps sodium, out of the cell, where the sodium concentration,
is already high.
It pumps potassium, into the cell, where the potassium concentration,
is already high.
It requires energy to do this.
For every pumping cycle, the sodium potassium pump, uses one unit of ATP.
ATP is the currency of energy, in the cell.
The sodium potassium pump, is always at work, even when the neuron is at rest.
Energy is continuously spent, by the neuron to maintain the concentration gradient.
Maintaining the concentration gradient, of sodium and potassium,
is a basic function of a living neuron.
The neuron requires a constant supply of energy, in the form of ATP to function.
The brain does not do any physical work.
A surprisingly large amount of energy is consumed by the brain.
The sodium potassium pump, consumes a significant portion of this energy.
The sodium potassium pump, pumps out 3 sodium ions,
for every two potassium ions, that it pumps in.
The sodium and potassium ions are positively charged.
3 positively charged sodium ions are pumped out.
2 positively charged potassium ions are pumped in .
This causes the inside of the cell membrane, to be negatively charged,
relative to the outer layer of the membrane.
This causes a small potential difference to be created, across the cell membrane.
A small part of the resting membrane potential, of minus 70 millivolts,
is contributed by the action of the sodium potassium pump.
The sodium potassium pump maintains a concentration gradient,
of sodium and potassium, across the neuron membrane.
The membrane is not permeable to ions.
Sodium and potassium ions cannot diffuse, through the membrane.
The membrane has many potassium diffusion channels.
Potassium has a higher concentration, inside the cell.
Potassium ions diffuses out through the diffusion channels.
This leads to a larger number of positively charged ions,
to be present in the outer layer of the membrane.
The outer layer becomes more positively charged.
The inner layer becomes relatively more negative.
As the inner layer becomes more negative, it starts to attract,
the positively charged potassium ions.
This causes an electrical force from the outside to the inside.
The electrical force, acts against the diffusion force,
which acts from inside to outside.
The diffusion force, tends to push the potassium ions, out of the cell.
The electrical force, tends to push the potassium ions, into the cell.
At some point the electrical force, balances the diffusion force.
At this point equilibrium is reached.
This point is known as the potassium equilibrium point.
At the equilibrium point, the net movement of the potassium ions,
across the membrane is zero.
The membrane potential at this point is, negative.
Sodium is more concentrated outside the cell.
The concentration gradient tends to push the sodium ions, into the cell.
The membrane has a limited number of sodium diffusion channels.
Through these channels, a small amount of sodium, diffuses into the cell.
This causes the inside to become more positive, or relatively less negative.
In this sense sodium does the opposite of what potassium does.
The amount of sodium ions, diffusing into the cell,
is very much less, compared to the potassium ions, diffusing out.
The impact of sodium ion diffusion is relatively very small,
on the membrane potential.
The membrane potential tends to be closer,
to the equilibrium potential of potassium.
The actions of,
the sodium potassium pumps,
the potassium diffusion channels,
and the sodium diffusion channels,
combine to produce a resultant membrane potential.
These three major bio mechanisms, work together to maintain,
and equilibrium potential of minus 70 millivolts.
This is called as the resting membrane potential.
Nature has designed an elegant and sophisticated mechanism,
to maintain, a resting membrane potential of about minus 70 millivolts.
When a neuron maintains, a resting membrane potential,
of minus 70 mili volts, it is said to be polarised.
Any charge movement, which causes the voltage, to become less negative,
is said to be depolarisation.
For example, positive charges entering the neuron, will cause it to depolarise.
Any charge movement, which causes the voltage, to be more negative,
is said to be hyper polarisation.
For example, positive ions, leaving the neuron, will cause it to depolarise.
The polarisation and de polarisation creates electrical signals.
The basic function of neurons is to receive and transmit electrical signals.
The neuron generates electrical signals by changes in electrical potential,
caused by ion movement, across cell membrane.
Electrical signals, in a neuron is basically, movement of ions across the membrane.
We may wonder, why nature takes so much trouble,
to maintain a resting membrane potential, of minus 70 millivolts.
This is equivalent to maintaining a battery, in a charged condition.
A charged battery is ready to use.
A neuron with a resting membrane potential, is like a charged battery.
It is always ready to fire.
It is sensitive to all the incoming electrical signals,
and if warranted, ready to fire, an outgoing electrical signal.
The neuron spends energy, to maintain itself in a charged state,
even while it is at rest.
This is the reason that we are immediately able to sense,
what we see, smell, hear and touch.
We are able to take a sharp catch, in a game,
because we are able to receive incoming signals,
process them and send out, outgoing signals in a flash.
This is possible, because all the related neurons were charged, and ready to act.
Neuron as a computing unit.
A neuron receives electrical signals from hundreds of other neurons.
A typical incoming signal will be a charged ion, entering the dendrite of a neuron.
A neuron can receive signals from hundreds of other neurons.
All these signals are summed up, within the neuron.
This is called spatial summation.
An incoming signal can be strong or weak.
A strong signal will have, a high frequency signal.
The strength of the incoming signals is also summed up, by the neuron.
This is called temporal summation.
An incoming signal can be positive or negative.
These signals are called excitatory, or inhibitive signals.
These signals are also summed up by the neuron
.
If the net result increases the membrane potential, to say, minus 55 millivolts,
It generates, a signal or action potential.
This is called the threshold level.
If the sum of the signals, does not reach threshold, no action potential is generated.
The site at which the decision is made, is the axon hillock.
If the threshold of minus 55 millivolts, is reached an action potential is generated.
This action potential is communicated to other neurons.
This is the fundamental principle, of the functioning of a neuron.
There is an interesting, and important property of a neuron.
A neuron takes a binary decision,
to fire an outgoing signal, or not to fire an outgoing signal.
This is like a true or false, or “all or none” response.
There is no in-between.
There are no intermediate signals.
When a neuron fires, it generates a signal called the ‘action potential’.
If the sum of the resultant incoming signals, is not strong enough,
the neuron will not fire an action potential.
If the sum of the resultant incoming signals, is strong enough,
the neuron will fire, an outgoing action potential.
In taking this decision, by the summation of the incoming signals,
the neuron is acting like a complex bio transistor.
This micro intelligence is built into the neuron.
In a sense, we can consider, that the neuron is the basic bio computing unit,
of our brain and nervous system.
It is billions of these neurons, acting together,
that constitutes our complex brain and nervous system.
The basic principles of the functioning of the neuron,
is the same for all species of animals, including humans.