Cell
Physiology
Simone D’Agostino
Academic Year 22/23
, Simone D’Agostino
CELL PHYSIOLOGY
Introduction
We will talk about properties of neurons, because neurons are the best cells that we can use
as a model in order to explain the behaviour of every other cell and we will see that the
proprieties of several cells can be explained through the proprieties of neural cells. When
we talk about communication, signal transduction, modulation of acceptability we are
talking about neurons. All this course will be concentrated on the study of neurons.
Paramecium
It is a unicellular organism, which swims in water and explores the environment. With a
normal ciliary beat the paramecium moves in a specific direction. When the paramecium
hits an obstacle there are calcium channels in the membrane that are opened by this
mechanical stimulus. When these channels open the calcium enters into the cell and the
calcium interacts with the proteins that are related to the ciliary beat. These interactions
induce a change in the direction and then calcium concentrations get lower so that the
paramecium can start to move again in the same direction.
This paramecium is not so different from one single neuron. The complexity of our nervous
system doesn’t depend on the complexity of one single neuron, but studying cell physiology
we are using a reductionist approach, analysing a complex mechanism through its simpler
components. That’s why neurosciences are divided into Molecular, Cellular, Systems,
Behavioural and Cognitive neuroscience.
What does cell physiology study?
• how a cell keeps a steady/rest state. In case of a cell, you can say even resting is quite
demanding task. So, even when a cell is just in the steady state, it is working quite a lot in
order to maintain this steady state. Why is it so important to set a proper steady state?
Because when we alter this resting condition, they are able to generate intracellular
communication to generate signal cascade at the level of the cells or the single cell.
• how an alteration of the steady state induces inner communication. This
innercommunication will allow to produce a signal travelling along the axon.
• how an intra-cellular communication becomes a "trans”-cellular communication, namely
the connection between neurons (the synapses).
Energy requirement, equilibrium and homeostasis
Any change in the form of energy, or exchange of energy between two systems, is bound to
increase the overall amount of “unusable” energy (entropy). These are consequences of the
second law of thermodynamics. Any change in a system that implies a loss of free energy
(and an increase in entropy) –exergonic change– can occur spontaneously. So, any real
spontaneous state of equilibrium can only exist when
a system is in its minimum free energy state so when
the entropy of the system is at the maximum level.
This kind of equilibrium would not be compatible with
life, so we need a continuous input of free energy in
order to maintain this steady state, in order to keep
this internal order and to prevent the deviation
towards a disordered state. This dynamic equilibrium
is the way in which we can define the steady state,
just like your room gets disordered easily and needs
time and effort to be put back in order. we cannot
think to a system that once the steady state is set can
stop working, it is necessary to continuously check
changes in the relationship between the cell and the external world
and to the regulatory systems that allow to keep the steady state and to balance
perturbation coming from both the external environment and the intracellular site. This
capability is called Homeostasis. Homeostasis has also many clinical and technological
implications.
1
, Simone D’Agostino
Control systems
Homeostasis implies the necessity to have control systems, that are able to correct
deviations from this range. We have to main ways of control:
• feed-back systems, that are based on the analysis and interpretation of the output of a
process and then that will be able to influence this process according to the output. Some
examples are pH, glucose in the blood, and blood pressure.
• feed-forward systems, that instead will not need to analyze the output of the process, but
that will be programmed independently to the output, so they are control systems that
are already present before the perturbation of the system occurs.
As regards feedback systems (the most common in
homeostasis), we can distinguish:
•negative feed-backs, in which the interpretation of
the output gives an inhibition of the process that
produces this output. Consider the example of
pressure: when it’s low, the heart rate increases to
minimize the perturbation. in order to grant this
feed-back controls. We have sensors, in the case of
the pressure we will have pressure receptors that
are required in order to measure the variation of
the parameter you want to control. Then we have
integrating centers that are able to compare the
value that is coming from the sensor to the ideal
point. Then, we will need an effector acting on it.
•positive feedbacks, in which the interpretation of
the output will strengthen the effect (like the
coagulation cascade)
•symmetrical feedbacks, in which we can have both
increasing or decreasing of the effect, like the
regulation of the level of glucose in blood.
The postural control is an instance of integration between feedback and feed forward
control system. When we perform a movements, we generate a perturbation on our body.
As a consequence, we will have mechanisms (like the ones in our ear) able to detect such
perturbations, the cerebellum will act as an integrating center and impulses will be sent to
answer the mechanical stress. This is of course a feedback system, but before starting the
movement our brain already knows that it will generate a variation in the posture and
therefore an anticipatory postural control is put in actions which is a feed forward
mechanism (independent from the output, namely the perturbation in our posture).
A feedback control has to be scaled properly both in time and gain. The intensity of the
command should be proportional to the error and the variation that we want to correct,
and an impairment can lead to disease like tremors (Holmes, dystonic or Parkingson).
Feedback stimuli also have to be kept under control and neurotransmitters like dopamine
play an essential role in this process.
Information processing
2
Physiology
Simone D’Agostino
Academic Year 22/23
, Simone D’Agostino
CELL PHYSIOLOGY
Introduction
We will talk about properties of neurons, because neurons are the best cells that we can use
as a model in order to explain the behaviour of every other cell and we will see that the
proprieties of several cells can be explained through the proprieties of neural cells. When
we talk about communication, signal transduction, modulation of acceptability we are
talking about neurons. All this course will be concentrated on the study of neurons.
Paramecium
It is a unicellular organism, which swims in water and explores the environment. With a
normal ciliary beat the paramecium moves in a specific direction. When the paramecium
hits an obstacle there are calcium channels in the membrane that are opened by this
mechanical stimulus. When these channels open the calcium enters into the cell and the
calcium interacts with the proteins that are related to the ciliary beat. These interactions
induce a change in the direction and then calcium concentrations get lower so that the
paramecium can start to move again in the same direction.
This paramecium is not so different from one single neuron. The complexity of our nervous
system doesn’t depend on the complexity of one single neuron, but studying cell physiology
we are using a reductionist approach, analysing a complex mechanism through its simpler
components. That’s why neurosciences are divided into Molecular, Cellular, Systems,
Behavioural and Cognitive neuroscience.
What does cell physiology study?
• how a cell keeps a steady/rest state. In case of a cell, you can say even resting is quite
demanding task. So, even when a cell is just in the steady state, it is working quite a lot in
order to maintain this steady state. Why is it so important to set a proper steady state?
Because when we alter this resting condition, they are able to generate intracellular
communication to generate signal cascade at the level of the cells or the single cell.
• how an alteration of the steady state induces inner communication. This
innercommunication will allow to produce a signal travelling along the axon.
• how an intra-cellular communication becomes a "trans”-cellular communication, namely
the connection between neurons (the synapses).
Energy requirement, equilibrium and homeostasis
Any change in the form of energy, or exchange of energy between two systems, is bound to
increase the overall amount of “unusable” energy (entropy). These are consequences of the
second law of thermodynamics. Any change in a system that implies a loss of free energy
(and an increase in entropy) –exergonic change– can occur spontaneously. So, any real
spontaneous state of equilibrium can only exist when
a system is in its minimum free energy state so when
the entropy of the system is at the maximum level.
This kind of equilibrium would not be compatible with
life, so we need a continuous input of free energy in
order to maintain this steady state, in order to keep
this internal order and to prevent the deviation
towards a disordered state. This dynamic equilibrium
is the way in which we can define the steady state,
just like your room gets disordered easily and needs
time and effort to be put back in order. we cannot
think to a system that once the steady state is set can
stop working, it is necessary to continuously check
changes in the relationship between the cell and the external world
and to the regulatory systems that allow to keep the steady state and to balance
perturbation coming from both the external environment and the intracellular site. This
capability is called Homeostasis. Homeostasis has also many clinical and technological
implications.
1
, Simone D’Agostino
Control systems
Homeostasis implies the necessity to have control systems, that are able to correct
deviations from this range. We have to main ways of control:
• feed-back systems, that are based on the analysis and interpretation of the output of a
process and then that will be able to influence this process according to the output. Some
examples are pH, glucose in the blood, and blood pressure.
• feed-forward systems, that instead will not need to analyze the output of the process, but
that will be programmed independently to the output, so they are control systems that
are already present before the perturbation of the system occurs.
As regards feedback systems (the most common in
homeostasis), we can distinguish:
•negative feed-backs, in which the interpretation of
the output gives an inhibition of the process that
produces this output. Consider the example of
pressure: when it’s low, the heart rate increases to
minimize the perturbation. in order to grant this
feed-back controls. We have sensors, in the case of
the pressure we will have pressure receptors that
are required in order to measure the variation of
the parameter you want to control. Then we have
integrating centers that are able to compare the
value that is coming from the sensor to the ideal
point. Then, we will need an effector acting on it.
•positive feedbacks, in which the interpretation of
the output will strengthen the effect (like the
coagulation cascade)
•symmetrical feedbacks, in which we can have both
increasing or decreasing of the effect, like the
regulation of the level of glucose in blood.
The postural control is an instance of integration between feedback and feed forward
control system. When we perform a movements, we generate a perturbation on our body.
As a consequence, we will have mechanisms (like the ones in our ear) able to detect such
perturbations, the cerebellum will act as an integrating center and impulses will be sent to
answer the mechanical stress. This is of course a feedback system, but before starting the
movement our brain already knows that it will generate a variation in the posture and
therefore an anticipatory postural control is put in actions which is a feed forward
mechanism (independent from the output, namely the perturbation in our posture).
A feedback control has to be scaled properly both in time and gain. The intensity of the
command should be proportional to the error and the variation that we want to correct,
and an impairment can lead to disease like tremors (Holmes, dystonic or Parkingson).
Feedback stimuli also have to be kept under control and neurotransmitters like dopamine
play an essential role in this process.
Information processing
2
