scholarly journals The Rates Of Conduction Of Nerve Fibres Of Various Diameters In Cephalopods

1938 ◽  
Vol 15 (4) ◽  
pp. 453-466 ◽  
Author(s):  
R. J. PUMPHREY ◽  
J. Z. YOUNG
Keyword(s):  
Conduction Velocity ◽  
Strong Support ◽  
Nerve Impulse ◽  
Nerve Fibres ◽  
Exact Relation ◽  
Significant Saving ◽  
Mode Of Life ◽  
The Central Nervous System ◽  
Giant Fibres ◽  
The Times

1. The rates of conduction of nerve fibres of Sepia and Loligo varying from 30 to 718µ in diameter have been estimated from records of their action potentials. The limits of conduction velocity were found to be 2.2-22.8 m./sec. at 20° C. 2. Although the fibres examined have different functions, and come from animals which differ considerably in structure and mode of life, yet the conduction rates of all of them can be approximately expressed as a single function of the diameter. These fibres, therefore, do not differ greatly from each other in any respect but size. 3. Calculation of the regression coefficient of the log. of the conduction rate on the log. of the diameter of the fibres shows that the rate increases with the power 0.614±0.027 of the diameter. On account of various sources of error however the exact relation does not necessarily lie within these limits, but it is not likely to be very far from the square root. 4. The possession of giant fibres produces a significant saving of time for the animal, it being calculated that the reaction time of a squid is about half that of a similar animal without giant fibres. 5. The presence of rapidly conducting fibres is probably also an advantage in that it decreases the discrepancies between the times of contraction of parts of the mantle at varying distances from the central nervous system. In Loligo there is a graded series of fibres with the larger in the longer nerves, and this is apparently a further device for ensuring more nearly simultaneous contraction. 6. The relative thickness of the myelin-like sheath increases from about 1% of the diameter of the axon in cephalopods to 5% in Crustacea and annelids and 25% in vertebrates: the conduction velocity of fibres of a given size also increases in the same series. This parallelism provides strong support for the view that the layer of oriented lipoids increases the velocity of propagation of the nerve impulse in proportion to its thickness.

scholarly journals The Structure and Conduction Velocity of the Medullated Nerve Fibres of Prawns

1941 ◽  
Vol 18 (1) ◽  
pp. 50-54 ◽  
Author(s):  
W. HOLMES ◽  
R. J. PUMPHREY ◽  
J. Z. YOUNG
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Conduction Velocity ◽  
Myelin Sheath ◽  
Axon Diameter ◽  
Relative Thickness ◽  
Nodes Of Ranvier ◽  
Nerve Fibres ◽  
The Central Nervous System ◽  
Myelinated Fibres

1. The structure of the myelinated fibres of prawns is described, and the homologies of the nucleated sheath which lies between the axon and the fatty layer discussed. 2. The relative thickness of the myelin sheath increases with decrease in total diameter of the fibre along a curve similar in shape to that found in vertebrates and earthworms. 3. Nodes of Ranvier are found in the sheaths of most fibres of a diameter greater than about 13µ 4. The nodes are similar to those in vertebrate nerves in that the myelin sheath is interrupted at the node. 5. The conduction velocity of fibres in the central nervous system of axon diameter 26µ and total diameter 35µ is between 18 and 23 m. per sec., a rate faster than is found in the "unmyelinated" fibres of similar size in other crustacea.

Temperature Acclimation of the Functional Parameters of the Giant Nerve Fibres in Lumbricus Terrestris L

1967 ◽  
Vol 47 (3) ◽  
pp. 471-480
Author(s):  
KARI Y. H. LAGERSPETZ ◽  
ANTTI TALO
Keyword(s):  
Action Potential ◽  
Temperature Dependence ◽  
Conduction Velocity ◽  
Nerve Cord ◽  
Lumbricus Terrestris ◽  
Temperature Acclimation ◽  
Nerve Fibres ◽  
The Difference ◽  
Giant Fibres ◽  
Q10 Values

1. Temperature dependence of the conduction velocity and the duration of the rising and falling phase of action potential was studied in the median and lateral giant fibres of the nerve cord of earthworms acclimated to 13° or 23° C. 2. Compensatory acclimation of the conduction velocity was found at all temperatures studied from 6° to 32° C. However, the effect was statistically significant only at 6° C. 3. The temperature coefficient (Q10) of the conduction velocity was lower at all temperatures for the cold-acclimated animals. The difference was significant only for the temperature interval from 6° to 13° C. 4. The compensatory acclimation of the duration of the rising and falling phases of the spike was statistically significant at 6° and 13° C. The corresponding Q10 values were lower for the cold-acclimated animals. 5. The duration of the falling phase of the action potential showed the most efficient compensatory acclimation of the parameters studied.

On the relation between fibre diameter and conduction velocity in myelinated nerve fibres

1982 ◽  
Vol 217 (1206) ◽  
pp. 29-35 ◽  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Conduction Velocity ◽  
Fibre Diameter ◽  
Nerve Fibres ◽  
Myelinated Nerve ◽  
Fibre Size ◽  
Central Nervous Systems ◽  
The Central Nervous System ◽  
Myelinated Fibres

Myelinated fibres less than 1 μm in diameter are rare in the peripheral nervous system; but fibres down to 0.2 μm in diameter exist in the central nervous system. These observations are consistent with Rushton’s theory on the effects of fibre size on conduction in myelinated nerve when the different processes of myelination in the peripheral and central nervous systems are taken into account.

scholarly journals Ketamine’s effect on inflammation and kynurenine pathway in depression: A systematic review

2021 ◽  
pp. 026988112110264
Author(s):  
Emma Kopra ◽  
Valeria Mondelli ◽  
Carmine Pariante ◽  
Naghmeh Nikkheslat
Keyword(s):  
Systematic Review ◽  
Animal Studies ◽  
Bipolar Depression ◽  
Strong Support ◽  
Kynurenine Pathway ◽  
Future Research ◽  
Downstream Effects ◽  
Tnf Α ◽  
The Central Nervous System ◽  
Anti Inflammatory

Background: Ketamine is a novel rapid-acting antidepressant with high efficacy in treatment-resistant patients. Its exact therapeutic mechanisms of action are unclear; however, in recent years its anti-inflammatory properties and subsequent downstream effects on tryptophan (TRP) metabolism have sparked research interest. Aim: This systematic review examined the effect of ketamine on inflammatory markers and TRP–kynurenine (KYN) pathway metabolites in patients with unipolar and bipolar depression and in animal models of depression. Methods: MEDLINE, Embase, and PsycINFO databases were searched on October 2020 (1806 to 2020). Results: Out of 807 initial results, nine human studies and 22 animal studies on rodents met the inclusion criteria. Rodent studies provided strong support for ketamine-induced decreases in pro-inflammatory cytokines, namely in interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α and indicated anti-inflammatory effects on TRP metabolism, including decreases in the enzyme indoleamine 2,3-dioxygenase (IDO). Clinical evidence was less robust with high heterogeneity between sample characteristics, but most experiments demonstrated decreases in peripheral inflammation including in IL-1β, IL-6, and TNF-α. Preliminary support was also found for reduced activation of the neurotoxic arm of the KYN pathway. Conclusion: Ketamine appears to induce anti-inflammatory effects in at least a proportion of depressed patients. Suggestions for future research include investigation of markers in the central nervous system and examination of clinical relevance of inflammatory changes.

Conduction Velocities and Their Temperature Coefficients in Sensory Nerve Fibres of Cockroach Legs

1967 ◽  
Vol 46 (1) ◽  
pp. 63-84
Author(s):  
K. M. CHAPMAN ◽  
J. H. PANKHURST
Keyword(s):  
Conduction Velocity ◽  
Periplaneta Americana ◽  
Sensory Nerve ◽  
Point Of View ◽  
Conduction Delay ◽  
Nerve Fibres ◽  
Impulse Frequency ◽  
Temperature Coefficients ◽  
Conduction Velocities ◽  
Sensory Encoding

1. Conduction velocities of individual afferent nerve fibres from tactile spines and proprioceptive campaniform sensilla have been measured in situ over the temperature range 5-42° C., in leg preparations of the cockroach Periplaneta americana. 2. Conduction velocities at 20° C. (u20) averaged 3.3±1.4 m./sec., ranging from 1.6 to 11.0 m./sec. 3. Temperature coefficients, expressed as Q10 for the interval 20-30° C., averaged 1.7±0.24, ranging from 1.3 to 2.6. 4. The length of the propagated disturbance is about 2-3 mm., and is nearly temperature-independent. 5. Fibre diameters, estimated from conduction velocity, must be about 10 µ. 6. There is no correlation between conduction velocity and distance from the sensillum to the thoracic ganglion. Conduction delays in fibres conducting within one standard deviation of mean u20 range from about 2 to 15 msec., from the most proximal to the most distal tactile spines. 7. The effect of conduction delay on temporal and spatial sensory encoding is probably unimportant from a behavioural point of view. It contributes a factor of the form exp(-sd/u) to the sensory transfer function, and may be appreciable at upper physiological frequencies of impulse frequency modulation.

Propagation of electrical signals along giant nerve fibres

1952 ◽  
Vol 140 (899) ◽  
pp. 177-183 ◽  
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
High Concentration ◽  
Nerve Fibres ◽  
Giant Fibre ◽  
Electrical Signals ◽  
Small Fibre ◽  
The Central Nervous System ◽  
Good Conductor ◽  
Ionic Movement

In this part of the discussion we shall attempt to describe the way in which electrical signals are propagated along the giant nerve fibres of squids and cuttlefish. These fibres consist of cylinders of protoplasm, 0.2 to 0.6 mm in diameter, and ire bounded by a thin membrane which acts as a barrier to ionic movement. The protoplasm, or axoplasm as it is commonly called, is an aqueous gel which is a reasonably good conductor of electricity. It contains a high concentration of K + and a low concentration of Na + and Cl - , this situation being the reverse of that in the animal’s blood or sea water. Axons which are left in sea water slowly lose potassium and gain sodium. This process takes about 24 hours and is roughly 80 000 times slower than the diffusion of ions out of a cylinder of gelatin of the same size. The interchange of sodium and potassium is very greatly accelerated by stimulating the fibres. Experiments with tracers, such as those made by Keynes & Lewis (1951) or Rothenberg (1950), allow the interchange to be measured quantitatively, and there is general agreement that the impulse is associated with an entry of 3 to 4 µ µ mol of Na + through 1 cm 2 of membrane and an exit of a corresponding quantity of K + . These quantities are very small compared with the total number of ions inside the fibre. In the giant axon of the squid the quantity of potassium lost in each impulse corresponds to only about 1 millionth if the total internal potassium. One would therefore expect that a giant fibre should be able to carry a great many impulses without recharging its batteries by metabolism. On the other hand, a very small fibre such as a dendrite in the central nervous system should be much more dependent on metabolism since the ratio of surface to volume may be nearly 1000 times greater.

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