Generator action

Regenerative braking If the motor be run beyond synchronous speed by some external means it will work as a generator and feed back useful energy to the supply system. It will draw only the necessary excitation current, / , for the generator action from the source of supply. In such a condition, the motor... 

Descending loads may overspeed the motor and iwerexcite the capacitor when connected across the motor due to motor generator action above the synchronous speed (Section 6.21). Such a situation may damage the motor as w ell as the capacitor and ntust be avoided. 

Normal rhythmic activity is the result of the activity of the sinus node generating action potentials that are conducted via the atria to the atrioventricular node, which delays further conduction to the His-Tawara-Purkinje system. From the Purkinje fibres, action potentials propagate to the ventricular myocardium. Arrhythmia means a disturbance of the normal rhythm either resulting in a faster rhythm (tachycardia, still rhythmic) or faster arrhythmia (tachyarrhythmia) or slowed rhythm (bradycardia, bradyarrhythmia). 

The LVA channels are expressed in a wide variety of tissues. In the cardiac sinus node and the thalamus, activation of LVA channels seems to be necessary to generate action potentials upon depolarising the membrane. 

Voltage-dependent sodium channels are a family of membrane proteins that mediate rapid Na+ influx, in response to membrane depolarization to generate action potentials in excitable cells. 

The primary role of the sodium channels is to generate action potentials in excitable cells. In case of neurons, the sodium channel density is high at axon hillocks or axon initial segment where action potentials start to propagate. The sodium channels are also present in dendrites. The sodium channels contribute to amplifying synaptic inputs (particularly those distally located) and are actively involved in back propagation of action potentials into dendrites. Subtle differences in properties of sodium channels influence the dendritic processes of synaptic integration in and complex ways. 

Neurons are very sensitive to changes in the pH of the interstitial fluid surrounding them. Normally, the pH of arterial blood is 7.4. Under conditions of alkalosis, in which pH increases, the excitability of neurons also increases, rendering them more likely to generate action potentials. This inappropriate stimulation of the nervous system may lead to seizures, particularly in epileptics predisposed to them. Under conditions of acidosis, in which pH decreases, the excitability of neurons is depressed, rendering them less likely to generate action potentials. This lack of nervous system stimulation may lead to a comatose state. Severe diabetic acidosis or acidosis associated with end-stage renal failure will often lead to coma. 

As its name implies, the neurohypophysis is derived embryonically from nervous tissue. It is essentially an outgrowth of the hypothalamus and is composed of bundles of axons, or neural tracts, of neurosecretory cells originating in two hypothalamic nuclei. These neurons are referred to as neurosecretory cells because they generate action potentials as well as synthesize hormones. The cell bodies of the neurosecretory cells in the supraoptic nuclei produce primarily antidiuretic hormone (ADH) and the cell bodies of the paraventricular nuclei produce primarily oxytocin. These hormones are then transported down the axons to the neurohypophysis and stored in membrane-bound vesicles in the neuron terminals. Much like neurotransmitters, the hormones are released in response to the arrival of action potentials at the neuron terminal. 

Action potentials are generated in single-unit smooth muscle. Simultaneous depolarization of 30 to 40 smooth muscle cells is required to generate a propagated action potential the presence of gap junctions allows this to occur readily. Because single-unit smooth muscle is self-excitable and capable of generating action potentials without input from the autonomic nervous system, it is referred to as myogenic. In this muscle, the function of the autonomic nervous system is to modify contractile activity only. Input is not needed to elicit contraction. 

Skeletal muscle is neurogenic and requires stimulation from the somatic nervous system to initiate contraction. Because no electrical communication takes place between these cells, each muscle fiber is innervated by a branch of an alpha motor neuron. Cardiac muscle, however, is myogenic, or self-excitatory this muscle spontaneously depolarizes to threshold and generates action potentials without external stimulation. The region of the heart with the fastest rate of inherent depolarization initiates the heart beat and determines the heart rhythm. In normal hearts, this "pacemaker region is the sinoatrial node. 

Neurons are specialized to integrate selected extracellular signals, both spatially and temporally. In addition to generating action potentials and, through synaptic activity, signaling other cells, structural modifications are initiated... 

Taste cells have multiple types of ion channels. TRCs are electrically excitable and capable of generating action-potentials voltage-dependent channels for Na+, Ca2+ and K+, similar to those in neurons, have been detected in vertebrate TRCs. The surface distribution of these channels... 

Somljo Some of you may remember that there was an old-fashioned drug called TEA (tetraethyl ammonium chloride). When this was applied to smooth muscle that normally didn t generate action potentials, it caused beautiful action potentials and rhythmic contractions. I don t think this was physiological. 

Fry But ion channels don t always have to generate action potentials to be useful. You measured them as an expression of an action potential, but they might produce slow waves and still produce a function. 

Studied in both an experimental and theoretical manner. The link between glycolytic oscillations and the pulsatile secretion of insulin in pancreatic p cells [53] is another topic of current concern. Models for the latter phenomenon rely on the coupling between intracellular metabolic oscillations and an ionic mechanism generating action potentials. Such coupling results in bursting oscillations of the membrane potential, which are known to accompany insulin secretion in these cells [54, 55]. 

Resting potentiai the membrane potential maintained by a cell when it is not generating action potentials. 

A third project which the team helped start was FRODA (Friends and Relatives of Drug Abusers), a self-help group which meets on a regular basis to help its members to cope with their burden and occasionally generate action from statutory services. 

Lithium is closely related to sodium in its properties. It can substitute for sodium in generating action potentials and in Na + -Na+ exchange across the membrane. It inhibits the latter process that is, Li+-Na+ exchange is gradually slowed after lithium is introduced into the body. At therapeutic concentrations (around 1 mmol/L), it does not significantly affect the Na + -Ca2+ exchanger or the Na +, K+ ATPase pump. 

Lithium is closely related to sodium in its properties. It can substitute for sodium in generating action potentials and in Na+-Na+ exchange across the membrane. It inhibits the latter process, ie,... 

Once the neurotransmitter is released from the presynaptic terminal it diffuses across the synaptic cleft. On the postsynaptic side it complexes with a membrane-bound macromolecule, its receptor. In synapses that have to generate action potentials within microseconds of neurotransmitter release, the receptors must be clustered in the postsynaptic membrane at high density, close to where the neurotransmitter is released. Such a synapse exists at the neuromuscular junction, where acetylcholine is the neurotransmitter. Acetylcholine is released from the presynaptic nerve terminal within 50 nm of the postsynaptic muscle membrane that contains densely arrayed acetylcholine receptors ( 10,000 acetylcholine rcccptors/pm2). There is a steady turnover of receptors, with newly synthesized receptors replacing those that are periodically degraded or not being utilized. 

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