Chemical changes in the adductor muscle of the cheliped of the crayfish in relation to the double motor innervation

Work from this laboratory has shown that a number of the striated muscles of the legs of the crayfish show a typical motor innervation (1). Such muscles are innervated by two motor fibers only, each causing a different type of contraction. One of these, resulting from stimulation of the thicker fiber, is termed the "fast" contraction, while the other is called the "slow." Both anatomical evidence and physiological experiments indicate that each muscle fiber is innervated by these two axons and that both contractions occur in the same muscle fibers (2, 3). The most striking difference between the two contractions is found in the adductor muscle of the cheliped of the crayfish. In this case, a single impulse in the thicker motor fiber causes a twitch-like contraction, and the system behaves in almost all respects as does a single motor unit of a vertebrate muscle: single shocks of different strengths give twitches of a considerable strength and a constant height, and during tetanic contraction the action currents are all of the same magnitude. In contrast to this, single shocks given to the thinner fiber produce no visible response in the muscle, but faradic stimulation causes action currents which grow in height and a contraction with a long latent period. The action currents in this case are always much smaller than those of the fast contraction. The chemical changes occurring in the adductor muscle of the cheliped of the crayfish Cambarus clarkii during these two types of contraction were investigated in order to obtain evidence on two possible mechanisms by which the two contractions might occur in the same muscle fiber. In the first place, two contractile substances might be present, a "phasic" and a "tonic" one, analogous to those supposed by Botazzi (4) in the vertebrate striated muscle, or the same substance might contract in both cases, the difference between the contractions being due solely to differences in the transmission mechanism between the nerve impulse and the contractile substance. Methods were devised for the rapid removal of the stimulated cheliped to liquid air and for the analysis of the frozen muscle tissue. The changes in phosphate and in lactic acid content were used as indices of the chemical changes occurring

OvoTesticular Disorder of Sex Development in Southern Africa

The patient with OT-DSD may present to the medical practitioner for a variety of reasons, but most likely for the investigation of the gender ambiguity which is the main feature of the DSD state. The classification of DSD has been based on the three main types. This thesis is about children born with a gender anomaly and specifically about those with OT-DSD. It is based on research done over a period of 23-years (1984-2006) on patients managed by the Department of Paediatric Surgery, University of KwaZulu- Natal, Durban, South Africa. The patients who were referred to our clinics came from KwaZulu-Natal, Eastern Cape, Lesotho and Swaziland, thereby constituting a Southern African group. This document is a collection of updated retrospective articles, the originals being presentations to scientific bodies and papers published in peer review journals over the period of study. The original papers presented an increasing number of patients over the years. By updating the information, the thesis presents a single cohort and allowed a re-evaluation of the aims of study. The thesis describes the studies done on patients with OT-DSD, which is generally regarded as uncommon condition among the disorders of sex development elsewhere in the world. Locally this condition is seen commonly, the reasons for the locally high incidence remain unknown

A universal ionization threshold for strongly driven Rydberg states

We observe a universal ionization threshold for microwave driven one-electron Rydberg states of H, Li, Na, and Rb, in an {\em ab initio} numerical treatment without adjustable parameters. This sheds new light on old experimental data, and widens the scene for Anderson localization in light matter interaction.Comment: 4 pages, 1 figur

THE INTERACTION BETWEEN THE SYNAPSES OF A SINGLE MOTOR FIBER

It has been shown that stimulation of synapses of the giant motor fibers of the third roots of Cambarus clarkii can block transmission at other synapses located on the same fiber. Peripherally located synapses block most synapses which are more centrally located. The reverse is true in a small number of cases. Possible reasons for this difference are discussed. It was further found that the two medial giant fibers in fresh, carefully dissected, preparations show a functional connection in the brain. It is probable that, under natural conditions, both medial giant fibers are always active at the same time

Perspectives and recent advances in super-resolution spectroscopy: Stochastic and disordered-based approaches

Spectroscopic applications are characterized by the constant effort to combine high spectral resolution with large bandwidth. A trade-off typically exists between these two aspects, but the recent development of super-resolved spectroscopy techniques is bringing new opportunities into this field. This is particularly relevant for all applications where compact and cost-effective instruments are needed such as in sensing, quality control, environmental monitoring, or biometric authentication, to name a few. These unconventional approaches exploit several strategies for spectral investigation, taking advantage of concepts such as sparse sampling, artificial intelligence, or post-processing reconstruction algorithms. In this Perspective, we discuss the main strengths and weaknesses of these methods, tracing promising future directions for their further development and widespread adoption. Published under an exclusive license by AIP Publishing