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18

There is a very different mechanism for generation (and detection) of ultraviolet, visible and infrared light vs radio waves. For the first, it is possible to generate it using chemical reactions (that is, chemiluminescence, bioluminescence) with a typical energy of order of 2 eV (electronovolts). Also, it is easy to detect with similar means - coupling to ...


9

There are two factors that need to be taken into account here: 1. Myelination decreases membrance capacitance. The rate at which sodium influx through a node can depolarize the axon at the next node is related to both the current and capacitance across the membrane (in addition to a few other factors). So while adding a new node to the axon would indeed ...


7

The carriers of the charge are ions and they get repelled from each other well enough. Other than their charge there is only the size in which they differ (for all practical purposes). This means, as long as we are talking about membrane potential, the actors are just a mix of 1+ ions which don't come near each other. When size matters, for example in an ion ...


5

I don't want to comment about the nature of electric signals in neurons (as I know only little about physiology and neurophysiology). But here is a short answer that may already help you. Neuronal electric signals are called action potential. If you register the voltage at a given location on the axon of a neuron through time you will see something like ...


5

This phenomenon is called depolarization block and it occurs in real membranes in current-clamp experiments. The key mechanism is that the membrane has not been allowed to repolarize sufficiently to relieve the inactivation of sodium channels. The Hodgkin-Huxley model reflects this in the "inverted" voltage-dependence of the h gate (sodium inactivation ...


4

(I probably ought to have a pat answer to this on the tip of my mind, but since I don't I'm going to wing it. This is probably just an opportunity to make an utter fool of myself. Please treat everything that follows with extreme suspicion.) I think this is effectively an artefact of the model. That may not be true in the strictest sense -- it is possible ...


4

While Luke's answer is perfectly correct, the answer can be given in a more intuitive manner. First, the main point is that it is increased positive voltage (inside the axon) that opens the sodium ion channels to propagate the action potential. The question is: how fast can this voltage get to the sodium channels? In an unmyelinated axon, the movement of ...


4

Good question. Just to set some stuff straight: In contrast to a comment placed earlier, there is definitely a current flow between electrodes in neural tissue, as long as the impedance is not too high. The potential difference between the electrodes and impedance determines how much current flows, basically following Ohm's law: I = U/R. As to your ...


3

High sodium extracellularly means an increased sodium concentration gradient across the membrane. This means there is a larger driving force for sodium to enter the cell once the sodium channels open at the start of the action potential, and hence a larger depolarization takes place increasing the action potential amplitude. The enhanced depolarization leads ...


3

Let's start with the basics. The inside of the cell contains predominantly positive potassium ions, and negative phosphate ions, and other negative ions (e.g. from amino acids). The outside of the cell contains predominantly positive sodium ions, and negative chloride ions. The cell however sets up a resting membrane potential, due to the cell's ...


3

These statements are not true, simply speaking. Currents as little as few microampers can kill a person if, for example, applied directly next to the heart. A few seconds of 220V can kill a person even if the current is in miliamper range (Biksom, cited below, mentions 4s at 120mA). However, it is true that it is not the voltage alone that kills, that there ...


3

Essentially all animal cells maintain an ionic balance causing a resting potential of about -70 mV in order to maintain their internal environment including pH, ion concentrations, osmotic pressure and volume. (Lodish, Molecular Cell Biology) Neurons developed from existing types of cells and it's unlikely that the cost of maintaining resting potential in ...


3

Electroencephalography has a good time resolution (milliseconds) but poor spatial resolution (several centimers). The usual estimated figure is that at least 50000 neurons need to fire simultaneously so that the activity can picked up by EEG. The answer provided by @Jeremy Kemball is not very accurate. The reason why the spatial resolution of EEG is poor is ...


3

I am not sure that kind of action would be a "significant influence", but the general understanding is that LFP and spike frequency are inter-correlated (1, 2). An interesting recent publication on the topic (3), however, doubts this correlation as the nature of LFP recording and signal processing might introduce some artifacts to the recordings. It would ...


2

Every atom produces a magnetic field, so the formally correct answer would be "yes" (assuming that viruses belong to the tree of life, which is disputed -- otherwise, one would not use the prefix 'bio'). However, biomagnetism as a science (and not pseudoscience) is concerned with more measurable effects. The biomagnetism of a virus will be negligible ...


2

Because the intermediate stages are not evolutionarily favoured. That's why. Sound and light perception are useful without any generative capability. An organism with a tiny amount of perception for either of these things has an advantage over those without; and an organism with a tiny amount more has an advantage over those with a tiny bit less. This ...


2

Actually, electromagnetic communication is used by certain fish, the mormyrids and the gymnotids. Pulse modulated in the former and amplitude modulated in the latter. However, the frequencies used are not much greater than 1Khz, which is not what we ordinarily consider to be in the radio frequency spectrum. There is, too, another biological species in ...


2

A quick comparison between light and sound vs. Radio Light: Wavelength 380 nm -740 nm Sound: 17 mm - 17 m Radio: 1mm - 10e5 km From the Planck relation, the energy of a wave is inversely proportional to the wavelength. As a result light is stronger than sound which is stronger than FM radio which is stronger than AM radio. Very likely, the energy ...


2

The smallest area that the EEG can measure is related to the electrode density. Even with research setups with 100s of electrodes, the smallest measurable region is on the order of a square centimeter or so on the skull surface. Brain regions deeper in the brain produce a 'blurred' signal that shows up on several electrodes at once. fMRI, on the other hand, ...


2

A LFP can be measured at any point in space and is just the sum of all the fields generated by nearby charges. Conventionally, it's assumed to be some distance from a cluster of neurons, but you technically could measure the LFP near the external surface of a neuron (but that would bias your signal towards the reading of that one neuron). LFP's are ...


2

The His-Purkinje fiber system is a network of one type of specialized conducting cardiac cells that carry an action potential in the heart. There are other cells which perform this function in different parts of the heart. The initiation time, shape, and duration of the action potential are distinctive for different parts of the heart, reflecting their ...


2

According to Wikipedia Electric shock, the Magnitude of electric shock to a body is mainly due to current as well as voltage. Various factor of the environment will also play a major role in damaging the body while under contact. The following quote explains it: The minimum current a human can feel depends on the current type (AC or DC) and frequency. A ...


2

Since the action potential question has already been answered, I will attempt to answer I'm sure this differs based on genetics and all sorts of other factors, but what are the general power ratings for the central nervous system? How much Watts/Volts/Amps travel with these signals? Are there standard ranges? You are right in that there is a large ...


2

Not different from @ChrisStronks answer. Just in different words. Just for everyone's knowledge — you are referring to the Voltage-clamp experiment. Situation 1: Sodium is depleted in the ECF. Despite the fact that Na+ conductance is much less than that of K+ and the equilibrium membrane potential (hyperpolarized) is closer to Nernst potential of K+, ...


1

Most importantly, the whole Goldman-Hodgkin-Katz model is, well, a model. It is a way we would like to find and explain phenomena, given pen and paper. Often, scientists build models in order to explain data in hand, but even then, they will have to add something from their imagination. For example, early astronomers saw planets moving differently from ...


1

On the wiki they are called cardiac action potentials. As the generation of the action potentials in the sinoatrial node is mediated by muscle cells, as is the conduction of the action potentials through the purkinje network (see wiki), the action potentials are not neural in nature, but cardiac.


1

Excellent question! The difference is the fact that the rheobase is an example of a threshold measure. The threshold, as you correctly suggest, is the minimal energy (typically current level and not voltage as you suggest) to excite neural tissue. The threshold applies only under the specific experimental parameter settings used. These parameters include the ...


1

Very nice question! I'll go through your three questions sequentially. Q1: Why does lower capacitance increase "the effectiveness of nearby nodes" or allow the depolarizing voltage to "travel not by ion diffusion, but as an electric field"? A: Capacitance basically results in sequestering of charge of opposite polarities along the cell membrane, which ...


1

The Hodgkin-Huxley model: $$I=C_m\frac{dV}{dt} + g_k(V_m - V_k) + g_{Na}(V_m - V_{Na}) + g_l(V_m- V_l)$$ Where $C_m$ is membrane capacitance per unit area and $g_i$ are membrane conductances. Reducing the number of channels does not affect capacitance; it basically reduces membrane conductance. Myelination causes reduction of number of channels ...


1

This article deals with the issue in detail.



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