Transmission of electrical impulses

The analysis of the transmission of electrical impulses through amplifiers rests on the finding by Fourier, that a periodic impulse function can be thought of as being composed of an infinite series of harmonic functions. Let f(t) be a function which repeats itself after time T, then f(t) can be expressed as 

Cj is the amplitude of the kth spectral component and 9 is its phase. In the case of a single impulse, f(t) is nonperiodic and the sum in Equation 136 is replaced by an integral. An electrical impulse is in this manner characterized by its spectral distri- 

If a step voltage, 11, is applied to the input of the amplifier (A = 1), the output voltage, Uout, will rise according to 

In order for a voltage pulse to be transmitted without distortion, the rise time of the pulse has to be longer than the rise time of the amplifier. The low limit Vj determines a fall time of the amplifier, Xf. After the output voltage has reached the value of it starts to decrease due to the fact that internal RC elements start to discharge themselves. The output voltage decreases according to 

Xf determines the length of the signal pulse which can be transmitted through the amplifier without distortion. Only for the case that v = 0 will the output voltage remain constant. Besides the amplifier itself, external resistors and capacitors form an RC-network which influences the transmission of the measurement pulse. 

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The cardiotonics affect the transmission of electrical impulses along the pathway of the conduction system of tiie heart. The conduction system of die heart is a group of specialized nerve fibers consisting of die SA node, die AV node, the bundle of His, and die branches of Purkinje (Fig. 39-2). Each heartbeat (or contraction of tiie ventricles) is tiie result of an electrical impulse tiiat normally starts in tiie SA node, is tiien received by die AV node, and travels down die bundle of His and through tiie Purkinje fibers (see Fig. 39-2). The heartbeat can be felt as a pulse at the wrist and otiier areas of die body where an artery is close to the surface or lies near a bone When the electrical impulse reaches the... 

Figure 4.4 Saltatory conduction. Transmission of electrical impulses in a myelinated axon occurs by way of saltatory conduction. Composed primarily of lipid, the myelin sheath insulates the axon and prevents generation of membrane potentials. Membrane potentials occur only at gaps in the myelin sheath, referred to as the nodes of Ranvier. Therefore, transmission of the impulse, or generation of action potentials, occurs only at the nodes.

Several factors influence synaptic transmission of electrical impulses ... 

Figure 6.4 Potential route of transmission of electrical impulses through association...

The Brain Uses Energy for Transmission of Electrical Impulses... 

Too much potassium, however, is also bad for the body. Several grams of the compound potassium chloride can actually paralyze the nervous system. The presence of too much potassium disrupts the transmission of electrical impulses. This causes all body functions to shut down, including the heart muscles, which will eventually stop beating altogether. 

Neurotransmitters and Transport Proteins in the Transmission of Electric Impulses... 

You have probably heard of electrolytes in the context of sports drinks such as Gatorade. Electrolytes in body fluids are necessary for the transmission of electrical impulses, which are critical to physiological processes such as nerve impulses and muscle contractions. In general, an electrolyte is a substance that dissolves in water to yield a solution that conducts electricity. By contrast, a nonelectrolyte is a substance that dissolves in water to yield a solution that does not conduct electricity. Every water-soluble substance fits into one of these two categories. 

Cyclic nucleotides, 3, 5 -cyclic adenosine monophosphate (cAMP) and 3, 5 -cyclic guanosine monophosphate (cGMP), function to regulate cell-to-cell communication processes (33). Cellular communication follows primarily three pathways. The first involves the transmission of electrical impulses via the nervous system. The second involves chemical messengers or hormonal secretions. The third involves de novo protein synthesis. All three processes are usually in response to some demand or stimulus and involve, at least to some extent, regulation by cyclic nucleotides ... 

The Bachmaims bundle and itemodal tracts allow the rapid transmission of electrical impulses from the SAN to the left atrium and AV node. 

It is found that the above polarity may be reversed upon addition of species which may disturb the structure of the membrane and open it for transmission of larger ions. Such is the case if a quaternary ammonium salt is introduced near the membrane surface. It would appear that the organic cations are able to penetrate the membrane faster than the inorganic ions, so that they (temporarily at least) open the membrane structure and allow freer passage of inorganic ions. Such a mechanism has been postulated as a contributory factor in the control of the transmission of electrical impulses from one nerve cell to another and from nerve to muscle cells in an organism. 

Not only may this relationship confer a special susceptibility to metabolic derangements but so may also the endowment of certain axons with myelin sheaths. The intimate myelin investment of axons in segmented fashion by the specially differentiated cell membranes of Schwann cells serves to allow an increased rate of transmission of electrical impulses by virtue of saltatory conduction at the nodes of Ranvier. Since the rate of conduction of impulses in the absence of this segmental sheath is much slower, myelinated fibre function can be... 

The function of a neuron is to communicate or relay information to another cell by way of an electrical impulse. A synapse is the site at which the impulse is transmitted from one cell to the next. A neuron may terminate on a muscle cell, glandular cell, or another neuron. The discussion in this chapter will focus on neuron-to-neuron transmission. At these types of synapses, the presynaptic neuron transmits the impulse toward the synapse and the postsyn-aptic neuron transmits the impulse away from the synapse. Specifically, it is the axon terminal of the presynaptic neuron that comes into contact with the cell body or the dendrites of the postsynaptic neuron. Most neurons, particularly in the CNS, receive thousands of inputs. As will become evident, the transmission of the impulse at the synapse is unidirectional and the presynaptic neuron influences activity of the postsynaptic neuron only. 

The heart depends on the synchronous integration of electrical impulse transmission and myocardial tissue rcsponsc to cany exit its function as a pump. When the impulse is released from the SA node, excitation of the heart tis.sue takes place in an orderly manner by a spread of the impulse ihmughout the specialised autontatic fibers in the atria, the AV node, and the Purkinje fiber network in the ventricles. This spreading of impulses produces a characteristic clectro-atdiographic pattern that cun be equated to predictable myo-caidial cell membrane potentials and Nu and K fluxes In and out of the cell. 

Demyelination and axonal transection cause disruption in the transmission of nerve impulses, which leads to neurologic symptoms reflecting the area of the brain or spinal cord that is affected. De-myelinated nerve fibers have prolonged refractory periods that impair conduction of electrical impulse volleys. Maximal electrical impulse frequency may be reduced substantially before impulse conduction is interrupted entirely. A single plaque may extend across several nerve pathways, producing symptoms involving several nervous system functions. Smaller plaques may cause isolated disturbances however, typically several plaques develop at the same time, causing multiple but unrelated problems such as disturbed vision and decreased sensation. 

In nervous tissue, some neurons are connected by gap junctions through which Ions pass rapidly, thereby allowing very rapid transmission of electrical signals. Impulse transmission through these connections, called electrical synapses. Is almost a thousandfold as rapid as at chemical synapses (Chapter 7). Gap junctions are also present in many non-neuronal tissues where they help to Integrate the... 

The rate of electrical impulse conduction through different cardiac tissues is variably affected. Thus low doses increase the velocity in the atrium and ventricle but toxic doses decrease velocity, sometimes even producing a block. Digitalis affects the refractory period by shortening it in the atrium, but markedly prolonging it for atrioventricular (AV) transmission. 

Some of the functions of lipids are related to the structures they form. The micelle formation characteristic of fatty acids, detergents, and soaps in aqueous solution helps to dissolve dirt and other hydrophobic materials. Lipid bilayers play many vital roles. Liposomes are used to deliver drugs to desired tissues. A cell membrane, because of its hydrophobic core, is a substantial barrier to the passage of ions, allowing the cell interior to have concentrations of ions different from those of the extracellular environment. Bilayers are good electrical insulators, and aid in the transmission of nerve impulses along the conducting portions of nerve fibers. The importance of fipids in neural function is seen in diseases in which these insulators are lost, such as multiple sclerosis, or not properly maintained, such as Tay-Sachs disease. 

Epinephrine or adrenaline (X) is one of the well-known drugs in medicine. Only recently it was discovered to contain 10-18% norepinephrine or arterenol (IX) when prepared from beef adrenal glands (47). Both epinephrine and norepinephrine exist in levorotatory form and are hormones of the body. When sympathetic nerves are electrically stimulated, epinephrine and norepinephrine are liberated producing the characteristic responses of the visceral organs (48). This accounts for the chemical transmission of nerve impulses, and the two bases serve as mediators. Both epinephrine and norepinephrine are present in the venom of certain toads (49-52). 

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