Nerve impulse transmission in insects PDF

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There are strong differences in ion concentration between the outside and inside of the cell. Outside the concentration of Na + and Ca2 + it is very high compared to that of the cytosol, on the contrary for K +.

The difference in charge outside and inside the cell must be balanced to ensure the correct functionality of the cell and since the cell has negative charges for the nucleic acids present, the cations can neutralize this charge.

| cations passively move through the membrane protein ion channels following the electrochemical magnitude, or to balance the charge and the concentration.

| cations are actively transported through membrane protein transporters and this occurs against the gradient of concentration and requires energy obtained from the hydrolysis of ATP which phosphorylates the transporter.

One such transporter is the sodium-potassium pump.

At the level of the synapses there are normally closed ion channels. The opening of them is managed by control systems:

1 potential difference on the membrane

2 non-covalent conformational modulation with the ligand

3 mechanical stress

There are channels of loss of K that oscillate between "closed" and "open" without any induction or stimulus that determines it: the potassium present inside the cell escapes by diffusion, but leaves compensated negative electrical charges, therefore such cations are recalled until electro-chemical equilibrium is reached, when there is no more net flow. Such a situation of

equilibrium is established when there is a potential difference (calculated with Nest's equation) inside the nerve cell of -75mVolt, typical of the rest condition.

Some ion channels such as those for Na + are potential-controlled, that is, as long as the cell has the membrane with the rest potential difference, they are closed. But if there is an input stimulus, a Nat ion, the channel opens for the action of a neurotransmitter (which is the ligand that modulates the opening) and positive charges begin to enter which raise the difference in membrane potential, therefore the channels open even more as the potential is still rising and consequently they enter other Na + cations. Thus the potential rises to become positive.

This is how the ion channels of the K + always in potential control come into play; but delayed: they open beyond a certain value higher than potential and then release the K + until the membrane repolarizes returning to the basal condition at -7SmVolt. At that point the Na + channels close.

This ordered sequence of potential oscillations causes the stimulus to be progagated only in sense unidirectional from the body of the neuronal cell along the axon: In fact, the depolarization wave moves in a univocal direction, given that the ion channels upstream of the input stimulus (given by the Na +) are inactivated and therefore the process described always proceeds downstream.

This is the electrical transmission of the nerve impulse. When it comes to the axon termination of the presynaptic cell for pass to the postsynaptic cell, there is a communication at the level of the synapse. The wave of depolarization causes that in the part terminal, the potential-controlled channels for Ca2 + present at that point open and the entry of this cation induces the release of synaptic vesicles containing a neurotransmitter molecule, such as acetylcholine. This molecule released in the synaptic space, reaches the postsynaptic cell and opens a ligand-controlled channel, the opening of which is modulated by the

non-covalent bond with a ligand that is the neurotransmitter, at that point the depolarization wave is generated which allows the transmission of the nerve stimulus.

The functioning just described is that of the excitatory synapses; there are also synapses of the inhibitory type.

In this case the ion channels of the CI- are involved, very concentrated outside the cell. This channel has been open since neurotransmitter, gamma aminobutyric acid GABA, so chlorine enters and the potential of rest conditions from -75mVolt is lower it until it becomes more and more negative. Then the input stimulus of Na + to generate a depolarization wave it must be more consistent.

In addition to neurotransmitters, there are molecules that function as neuromodulators with a slow and lasting effect on the synaptic transmission and others that function as neurormones released in the hemolymph that function like hormones....