Node of Ranvier length as a potential regulator of myelinated axon conduction speed

Myelination speeds conduction of the nerve impulse, enhancing cognitive power. Changes of white matter structure contribute to learning, and are often assumed to reflect an altered number of myelin wraps. We now show that, in rat optic nerve and cerebral cortical axons, the node of Ranvier length varies over a 4.4-fold and 8.7-fold range respectively and that variation of the node length is much less along axons than between axons. Modelling predicts that these node length differences will alter conduction speed by ~20%, similar to the changes produced by altering the number of myelin wraps or the internode length. For a given change of conduction speed, the membrane area change needed at the node is >270-fold less than that needed in the myelin sheath. Thus, axon-specific adjustment of node of Ranvier length is potentially an energy-efficient and rapid mechanism for tuning the arrival time of information in the CNS

Ethnocracy without groups: Conceptualising ethnocratiser states without reifying ethnic categories

This article advances a non-groupist understanding of the foundation, operation and self-perpetuation of states that scholars have hitherto labelled ethnocracies or ethnic democracies. Such states create and ignite zero-sum internal conflicts between portions of their populations. They do so by demarcating the population into ethnic categories. They apply labels to individuals and hierarchically order the categories to which they are deemed to belong, awarding one cohort more privilege than the other. Existing literature on such states has obscured the processes by which states reify and institutionalise identity, instead presenting it through groupist frames in which ethnicity is a pre-existing variable. Re-conceptualising the doing of ethnicity as a process enables us to study internal dissent against ethnic privilege and consider its transformational capacity in inspiring new nationalist discourses

Electrical coupling of neuro-ommatidial photoreceptor cells in the blowfly

A new method of microstimulation of the blowfly eye using corneal neutralization was applied to the 6 peripheral photoreceptor cells (R1-R6) connected to one neuro-ommatidium (and thus looking into the same direction), whilst the receptor potential of a dark-adapted photoreceptor cell was recorded by means of an intracellular microelectrode. Stimulation of the photoreceptor cells not impaled elicited responses in the recorded cell of about 20% of the response elicited when stimulating the recorded cell. This is probably caused by gap junctions recently found between the axon terminals of these cells. Stimulation of all 6 cells together yielded responses that were larger and longer than those obtained with stimulation of just the recorded cell, and intensity-response curves that deviated more strongly from linearity. Evidence is presented that the resistance of the axon terminal of the photoreceptor cells quickly drops in response to a light flash, depending on the light intensity. Incorporating the cable properties of the cell body and the axon, the resistance of the gap junctions, and the (adapting) terminal resistance, a theoretical model is presented that explains the measurements well. Finally, it is argued that the gap junctions between the photoreceptor cells may effectively uncouple the synaptic responses of the cells by counteracting the influence of field potentials.

Is immunisation education in midwifery degrees adequate?

© 2018, © 2018 The Author(s). Published with license by Taylor & Francis Group, LLC. Maternal and childhood vaccination decisions begin during pregnancy, and midwives are an important information resource. Their role is set to increase with the expansion of maternal immunisations into new jurisdictions, and new maternal vaccines in development. Meanwhile, other health providers are orienting parents towards vaccine acceptance, using strategies at odds with midwifery norms around information provision and maternal autonomy. To better understand and address the implications of these developments, we conducted a pilot study to ascertain how midwifery students in Australian universities are taught about immunisation, including dedicated time, assessment, who teaches it, and when. We also analysed teaching materials, looking for messaging regarding the importance of vaccination and whether midwives should be advocating for it. We found that education on immunisation comprises less than four hours of the degree, and encountered the norm of midwives informing about rather than recommending vaccination. The considerations we brought to our small project, and what it illuminated, suggest that midwifery university education is an important arena for developing future vaccine advocates. However, midwifery ideology and professional practice mean that such efforts will be challenging, and must commence from a position of respect for the values midwives hold

Consequences of converting graded to action potentials upon neural information coding and energy efficiency

Information is encoded in neural circuits using both graded and action potentials, converting between them within single neurons and successive processing layers. This conversion is accompanied by information loss and a drop in energy efficiency. We investigate the biophysical causes of this loss of information and efficiency by comparing spiking neuron models, containing stochastic voltage-gated Na+ and K+ channels, with generator potential and graded potential models lacking voltage-gated Na+ channels. We identify three causes of information loss in the generator potential that are the by-product of action potential generation: (1) the voltage-gated Na+ channels necessary for action potential generation increase intrinsic noise and (2) introduce non-linearities, and (3) the finite duration of the action potential creates a ‘footprint’ in the generator potential that obscures incoming signals. These three processes reduce information rates by ~50% in generator potentials, to ~3 times that of spike trains. Both generator potentials and graded potentials consume almost an order of magnitude less energy per second than spike trains. Because of the lower information rates of generator potentials they are substantially less energy efficient than graded potentials. However, both are an order of magnitude more efficient than spike trains due to the higher energy costs and low information content of spikes, emphasizing that there is a two-fold cost of converting analogue to digital; information loss and cost inflation

Antibiotics online: digital pharmacy marketplaces and pastiche medicine

The internet enables access to information and the purchasing of medical products of various quality and legality. Research and regulatory attention have focused on the trafficking of illicit substances, potential physical harms of pharmaceuticals, and possibilities like financial fraud. However, there is far less attention paid to antibiotics and other antimicrobials used to treat infections. With online pharmacies affording greater access, caution around antibiotic use is needed due to the increasing health risks of antimicrobial resistance (AMR). The COVID-19 pandemic has helped to normalise digital healthcare and contactless prescribing, amplifying the need for caution. Little is known of how antibiotics are consumed via digital pharmacy and implications for AMR prevention. To expand insight for AMR prevention policy in Australia and internationally, we use digital ethnographic methods to explore how digital pharmacies function in the context of health advice and policy related to AMR, commonly described as antimicrobial stewardship. We find that digital pharmacy marketplaces constitute 'pastiche medicine'. They curate access to pharmaceutical and information products that emulate biomedical authority combined with emphasis on the 'self-assembly' of healthcare. Pastiche medicine empowers the consumer but borrows biomedical expertise about antibiotics, untethering these goods from critical medicine information, and from AMR prevention strategies. We reflect on the implications of pastiche medicine for AMR policy, what the antibiotics case contributes to wider critical scholarship on digital pharmacy, and how medical humanities research might consider researching online consumption in future

Global and regional brain metabolic scaling and its functional consequences

Background: Information processing in the brain requires large amounts of metabolic energy, the spatial distribution of which is highly heterogeneous reflecting complex activity patterns in the mammalian brain. Results: Here, it is found based on empirical data that, despite this heterogeneity, the volume-specific cerebral glucose metabolic rate of many different brain structures scales with brain volume with almost the same exponent around -0.15. The exception is white matter, the metabolism of which seems to scale with a standard specific exponent -1/4. The scaling exponents for the total oxygen and glucose consumptions in the brain in relation to its volume are identical and equal to $0.86\pm 0.03$, which is significantly larger than the exponents 3/4 and 2/3 suggested for whole body basal metabolism on body mass. Conclusions: These findings show explicitly that in mammals (i) volume-specific scaling exponents of the cerebral energy expenditure in different brain parts are approximately constant (except brain stem structures), and (ii) the total cerebral metabolic exponent against brain volume is greater than the much-cited Kleiber's 3/4 exponent. The neurophysiological factors that might account for the regional uniformity of the exponents and for the excessive scaling of the total brain metabolism are discussed, along with the relationship between brain metabolic scaling and computation.Comment: Brain metabolism scales with its mass well above 3/4 exponen

AMPK:a nutrient and energy sensor that maintains energy homeostasis

AMP-activated protein kinase (AMPK) is a crucial cellular energy sensor. Once activated by falling energy status, it promotes ATP production by increasing the activity or expression of proteins involved in catabolism while conserving ATP by switching off biosynthetic pathways. AMPK also regulates metabolic energy balance at the whole-body level. For example, it mediates the effects of agents acting on the hypothalamus that promote feeding and entrains circadian rhythms of metabolism and feeding behaviour. Finally, recent studies reveal that AMPK conserves ATP levels through the regulation of processes other than metabolism, such as the cell cycle and neuronal membrane excitability

Dietary iron and the elite dancer

Dancers are an athlete population at high risk of developing iron deficiency (ID). The aesthetic nature of the discipline means dancers potentially utilise dietary restriction to meet physique goals. In combination with high training demands, this means dancers are susceptible to problems related to low energy availability (LEA), which impacts nutrient intake. In the presence of LEA, ID is common because of a reduced mineral content within the low energy diet. Left untreated, ID becomes an issue that results in fatigue, reduced aerobic work capacity, and ultimately, iron deficient anaemia (IDA). Such progression can be detrimental to a dancer’s capacity given the physically demanding nature of training, rehearsal, and performances. Previous literature has focused on the manifestation and treatment of ID primarily in the context of endurance athletes; however, a dance-specific context addressing the interplay between dance training and performance, LEA and ID is essential for practitioners working in this space. By consolidating findings from identified studies of dancers and other relevant athlete groups, this review explores causal factors of ID and potential treatment strategies for dancers to optimise absorption from an oral iron supplementation regime to adequately support health and performance

Dietary iron and the elite dancer

Dancers are an athlete population at high risk of developing iron deficiency (ID). The aesthetic nature of the discipline means dancers potentially utilise dietary restriction to meet physique goals. In combination with high training demands, this means dancers are susceptible to problems related to low energy availability (LEA), which impacts nutrient intake. In the presence of LEA, ID is common because of a reduced mineral content within the low energy diet. Left untreated, ID becomes an issue that results in fatigue, reduced aerobic work capacity, and ultimately, iron deficient anaemia (IDA). Such progression can be detrimental to a dancer’s capacity given the physically demanding nature of training, rehearsal, and performances. Previous literature has focused on the manifestation and treatment of ID primarily in the context of endurance athletes; however, a dance-specific context addressing the interplay between dance training and performance, LEA and ID is essential for practitioners working in this space. By consolidating findings from identified studies of dancers and other relevant athlete groups, this review explores causal factors of ID and potential treatment strategies for dancers to optimise absorption from an oral iron supplementation regime to adequately support health and performance