# Where are these connections "anatomically" located in the HH model?

• somasimple
In summary, the conversation discusses the famous electric circuit of the HH model and the anatomical locations of its connections marked in red. The picture shows a circuit diagram representing how membrane currents and voltages are affected by the ions and transmembrane conductances. The subscripts "n" and "L" represent the different ion species, while "p" represents a current meter. The diagram is not physically correct, but serves as a helpful analogue for the form of the equations. The capacitor represents the membrane, the resistor and battery represent the current through the membrane channel driven by the combined reversal potentials of the ions, and the resistance is variable with open and closed states. The concentration difference of ionic species is maintained by active transport using ATP.

#### somasimple

Gold Member
Hi,

Here is a basic picture of the famous electric circuit of the HH model.
Can someone please tell me the anatomical locations of the connections marked in red in the cell?
Thanks.

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• Hodgkin-Huxley_01.png
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Could not enlarge picture. Please post anew one.

Since it has something to do with Hogkin-Huxley its probably a circuit based on membrane components.

The capacitor I can make out. It represents the membrane capacitance. Charges on ether side of the membrane act as if they are charges on either side of a capacitor.
The battery symbols represents the reversal potential for each species of ion, which drives the currents of each different ion species.
Can't tell what the other symbols are. Picture is too small. Can't read the text.

Overall it is a circuit diagram representing how membrane currents and voltages are affected by the ions and transmembrane conductances.

OK, the picture is working for me now.
What do the subscripts "n" and "L" mean based on where this can from?
The round thing at the right seems to be a current meter, with the subscript "p". What does "p" mean?

Hi,
The picture comes from there
https://en.wikipedia.org/wiki/Hodgkin–Huxley_model
Normally the resistors (ion channels) which are symbolised here are connected between the external medium and the inside of the cell because they are enclosed in the membrane.
The capacity, too.
The battery is created by a gradient between the outside and the inside (Nernst), isn't it?
So for me, the diagram doesn't fit.

The points in red do not correspond to an anatomical location in the cell. It is the combination of the resistor and the battery in series that represents an ion channel, since opening an ion channel decreases the membrane resistance and also generates a voltage. So the circuit diagram is not physically correct in a fundamental sense, but is a helpful analogue to the form of the equations (derived by considering the physics of the Nernst equation).

Incidentally, the HH equation is also different in form from the GHK equation (which is probably more correct in term of fundamental physics), but the HH equation has a more convenient analytical form and is an extremely good approximation in most of the physiological range.

However, there are times when the GHK equation is more accurate.

The capacitor is the membrane, which separates the different charges on either side of the electrically polarized membrane.
The resistor (don't know why its in a box) combined with the battery represent the current through the membrane channel (composed of certain ions) that is driven by the combined reversal potentials of the ions that can go through that particular channel. The resistance is variable in that it has open or closed states.

I'm at risk of repeating what others have said here, but there might be a couple of extra points I can make. The capacitance is essentially due to the lipid bilayer of the membrane, which allows charge to accumulate on either side. The resistance/conductance is essentially determined by the ion channels through which certain ions can flow. The battery is caused by a concentration difference across the membrane (of multiple different ionic species). Ions flow both due to voltage and concentration differences across the membrane, and different channels have different permeability to different ions. Finally, the concentration difference of the various ionic species is maintained by active transport of ions across the membrane by specialised proteins, which use ATP as an energy source.

BillTre

## 1. What is the HH model?

The HH model, or the Hodgkin-Huxley model, is a mathematical model that describes the behavior of neurons in terms of their electrical properties. It was developed by Alan Hodgkin and Andrew Huxley in the 1950s and is widely used in neuroscience to understand how neurons produce and transmit electrical signals.

## 2. What are "connections" in the HH model?

"Connections" in the HH model refer to the interactions between neurons. These connections can be either excitatory, meaning they increase the likelihood of a neuron firing, or inhibitory, meaning they decrease the likelihood of a neuron firing. These connections are crucial for understanding how groups of neurons work together to produce complex behaviors.

## 3. How are these connections located in the HH model?

In the HH model, the locations of these connections are determined by the anatomical structure of the neurons. Neurons have specialized structures called dendrites and axons, which allow them to send and receive signals from other neurons. The specific location of these connections depends on the positioning and branching of these structures.

## 4. Are these connections physically present in the brain?

Yes, these connections are physically present in the brain. The HH model is based on the anatomy and physiology of real neurons, so the connections described in the model are reflective of the actual connections between neurons in the brain.

## 5. Can these connections change over time?

Yes, these connections can change over time through a process called plasticity. In the brain, plasticity refers to the ability of neurons to form new connections and strengthen or weaken existing connections in response to experiences and learning. The HH model can be used to study how plasticity affects the behavior of networks of neurons.