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24

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 ...


6

The pacemaker potential is interesting (to a biologist) as it involves your typical Na/K channels, Ca channel, as well as a funny current (If) or alternatively called hyperpolarization-activated current. The funny current is a mixed sodium-potassium current that activates upon hyperpolarization at voltages in the diastolic range (normally from ...


5

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 ...


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 ...


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

I was able to do some reading and research and I found some interesting information that was a). news to me. And b). the answer is yes... And no. A spasm can be the cause of a heart attack by causing the coronary artery to contract. When that artery contracts, it causes a dramatic decrease in blood flow to the heart. When the heart looses access to ...


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

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 ...


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 ...


4

Representative ion concentrations are shown in Fig. 1: The membrane is mainly permeable to K+. Because the Na+,K+-ATPase pumps K+ inside of the cell, it tends to diffuse outward again, thereby taking positive charge outside the cell and making it negative inside (extracellular space is pretty much devoid of charge due to its vastness). Because the ...


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

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

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 ...


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

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 ...


3

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 ...


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

A microelectrode is quite literally a small electrode and they come in a variety of shapes. The glass pipette electrode you are specifically referring to is mostly used for patch clamp experiments. Patch clamp experiments are performed using various configurations: Source: Leica So basically there is the cell-attached configuration, where a patch of ...


3

First bump is called P point, middle is QRS wave (as in Q-down, R-up, S-down), and last bump is T. Every feature is representation of electrical activity in certain region of heart. E.g. P bump is contraction of atrium. See more here. Bumps are P/QRS/T. The reason why you see so many different recordings is that it was taken with many-lead ECG. Heart has ...


3

In Wolff-Parkinson-White syndrome, the normal Q wave is usually masked by the preexcitation action potential which produces the delta wave. Despite this, missing Q wave is not a diagnosis criteria of the syndrome, and up to 70 percent of the patients show a negative delta wave which causes differential diagnosis problems because it is confused with Q, ...


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

Just to clarify your ion/electron question - a neutral atom or molecule becomes ionized when it either loses one or more electrons, becoming positively charged, or gains electron(s), becoming negatively charged. Since the negatively charged phosphate (PO42-) ions have a surplus of electrons, they (the electrons) are free to flow "up" the wire and to the ...


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

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

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 ...


2

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 ...


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

Action potentials of single neurons (APs) are the building blocks of compound action potentials (CAPs). While each of the individual APs is a yes-or-no response with a clear-cut defined threshold, CAPs are not. CAPs are build up of hundreds or thousands of neuronal contributions in, e.g., the auditory nerve. Decreased responsiveness as well as ...



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