1,791 research outputs found
Mammalian Sperm Motility: Observation and Theory
Mammalian spermatozoa motility is a subject of growing importance because of rising human infertility and the possibility of improving animal breeding. We highlight opportunities for fluid and continuum dynamics to provide novel insights concerning the mechanics of these specialized cells, especially during their remarkable journey to the egg. The biological structure of the motile sperm appendage, the flagellum, is described and placed in the context of the mechanics underlying the migration of mammalian sperm through the numerous environments of the female reproductive tract. This process demands certain specific changes to flagellar movement and motility for which further mechanical insight would be valuable, although this requires improved modeling capabilities, particularly to increase our understanding of sperm progression in vivo. We summarize current theoretical studies, highlighting the synergistic combination of imaging and theory in exploring sperm motility, and discuss the challenges for future observational and theoretical studies in understanding the underlying mechanics.\ud
Acronyms and Definitions\ud
Acrosome: the cap of the sperm head containing enzymes allowing penetration of the zona pellucida via the acrosome reaction\ud
Adenosine triphosphate (ATP): the currency unit of chemical energy transfer in living cells\ud
Axoneme: a phylogenetically conserved structure within the eukaryotic flagellum consisting of a ring of nine microtubule doublets and a central pair, frequently referred to as 9 + 2\ud
Bending moment density: the moment per unit length associated with flagellar bending; it can be divided into a hydrodynamic moment, an elastic moment (from the flagellar bending stiffness), an active moment (generated by dyneins exerting forces between adjacent microtubule doublets), and a passive moment resisting shear\ud
Capacitation: the physiological state of a sperm required for fertilization, which is accompanied by the motility patterns associated with hyperactivation, characterized in saline by high-amplitude asymmetric beating\ud
Central pair: a pair of microtubules along the length of the axoneme, symmetrically and slightly offset from the axoneme centerline\ud
Cumulus oophorus: the outer vestment of the mammalian egg consisting of hundreds of cells radiating out from the egg embedded within a non-Newtonian hyaluronic acid gel\ud
Dynein: a molecular motor within the axoneme, attached between adjacent microtubule doublets, that exerts a shearing force to induce axonemal bending\ud
Flagellum: a motile cellular appendage that drives the swimming of sperm and other cells; this article focuses on the eukaryotic flagellum\ud
Microtubule doublet: a pair of proteinaceous filament structures running the length of the axoneme; dyneins drive their bending, which induces flagellar motion\ud
Mid-piece: the region of a sperm flagellum with a mitochondrial sheath, where ATP is generated\ud
Oocyte: the egg\ud
Outer dense fibers and fibrous sheath: accessory structures reinforcing the mammalian sperm flagellum; the combined axoneme and accessory structures are referred to as 9+9+2\ud
Resistive-force theory: an approximation for the local drag of a slender filament element in Stokes flow (or a viscoelastic generalization thereof)\ud
Rheotaxis: directed motility in response to the influence of fluid flow\ud
Shear: in the context of the flagellum, the relative movement of adjacent microtubule doublets\ud
Slender-body theory: an improved approximation for the local drag on a slender filament element in Stokes flow (or a viscoelastic generalization thereof)\ud
Zona pellucida: a tough glycoprotein coat between the human egg and the cumulus oophorus, which a sperm must penetrate for successful fertilizatio
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Functional Imaging of the Outer Retinal Complex using High Fidelity Imaging Retinal Densitometry
We describe a new technique, high fidelity Imaging Retinal Densitometry (IRD), which probes the functional integrity of the outer retinal complex. We demonstrate the ability of the technique to map visual pigment optical density and synthesis rates in eyes with and without macular disease. A multispectral retinal imaging device obtained precise measurements of retinal reflectance over space and time. Data obtained from healthy controls and 5 patients with intermediate AMD, before and after photopigment bleaching, were used to quantify visual pigment metrics. Heat maps were plotted to summarise the topography of rod and cone pigment kinetics and descriptive statistics conducted to highlight differences between those with and without AMD. Rod and cone visual pigment synthesis rates in those with AMD (v = 0.043 SD 0.019 min-1 and v = 0.119 SD 0.046 min-1, respectively) were approximately half those observed in healthy controls (v = 0.079 SD 0.024 min-1 for rods and v = 0.206 SD 0.069 min-1 for cones). By mapping visual pigment kinetics across the central retina, high fidelity IRD provides a unique insight into outer retinal complex function. This new technique will improve the phenotypic characterisation, diagnosis and treatment monitoring of various ocular pathologies, including AMD
Sustaining Educational Reforms in Introductory Physics
While it is well known which curricular practices can improve student
performance on measures of conceptual understanding, the sustaining of these
practices and the role of faculty members in implementing these practices are
less well understood. We present a study of the hand-off of Tutorials in
Introductory Physics from initial adopters to other instructors at the
University of Colorado, including traditional faculty not involved in physics
education research. The study examines the impact of implementation of
Tutorials on student conceptual learning across eight first-semester, and seven
second-semester courses, for fifteen faculty over twelve semesters, and
includes roughly 4000 students. It is possible to demonstrate consistently
high, and statistically indistinguishable, student learning gains for different
faculty members; however, such results are not the norm, and appear to rely on
a variety of factors. Student performance varies by faculty background -
faculty involved in, or informed by physics education research, consistently
post higher student learning gains than less-informed faculty. Student
performance in these courses also varies by curricula used - all semesters in
which the research-based Tutorials and Learning Assistants are used have higher
student learning gains than those semesters that rely on non-research based
materials and do not employ Learning Assistants.Comment: 21 pages, 4 figures, and other essential inf
Nonlinear instability in flagellar dynamics: a notel modulation mechanism in sperm migration
Throughout biology, cells and organisms use flagella and cilia to propel fluid and achieve motility. The beating of these organelles, and the corresponding ability to sense, respond to and modulate this beat is central to many processes in health and disease. While the mechanics of flagellum–fluid interaction has been the subject of extensive mathematical studies, these models have been restricted to being geometrically linear or weakly nonlinear, despite the high curvatures observed physiologically. We study the effect of geometrical nonlinearity, focusing on the spermatozoon flagellum. For a wide range of physiologically relevant parameters, the nonlinear model predicts that flagellar compression by the internal forces initiates an effective buckling behaviour, leading to a symmetry-breaking bifurcation that causes profound and complicated changes in the waveform and swimming trajectory, as well as the breakdown of the linear theory. The emergent waveform also induces curved swimming in an otherwise symmetric system, with the swimming trajectory being sensitive to head shape—no signalling or asymmetric forces are required. We conclude that nonlinear models are essential in understanding the flagellar waveform in migratory human sperm; these models will also be invaluable in understanding motile flagella and cilia in other systems
Autistic Traits Mediate Reductions in Social Attention in Adults with Anorexia Nervosa
Anorexia nervosa (AN) is associated with difficulties in social and emotional functioning. A significant proportion of individuals with AN show autistic traits, which may influence social attention. This study examined attention to faces and facial features in AN, recovered AN (REC), and healthy controls, as well as relationships with comorbid psychopathology. One hundred and forty-eight participants’ eye movements were tracked while watching a naturalistic social scene. Anxiety, depression, alexithymia, and autistic traits were assessed via self-report questionnaires. Participants with AN spent significantly less time looking at faces compared to REC and controls; patterns of attention to individual facial features did not differ across groups. Autistic traits mediated the relationship between group and time spent looking at faces
Autistic traits mediate reductions in social attention in adults with anorexia nervosa
Anorexia nervosa (AN) is associated with difficulties in social and emotional functioning. A significant proportion of individuals with AN show autistic traits, which may influence social attention. This study examined attention to faces and facial features in AN, recovered AN (REC), and healthy controls, as well as relationships with comorbid psychopathology. One hundred and forty-eight participants’ eye movements were tracked while watching a naturalistic social scene. Anxiety, depression, alexithymia, and autistic traits were assessed via self-report questionnaires. Participants with AN spent significantly less time looking at faces compared to REC and controls; patterns of attention to individual facial features did not differ across groups. Autistic traits mediated the relationship between group and time spent looking at faces
The Structure of IR Luminous Galaxies at 100 Microns
We have observed twenty two galaxies at 100 microns with the Kuiper Airborne
Observatory in order to determine the size of their FIR emitting regions. Most
of these galaxies are luminous far-infrared sources, with L_FIR > 10^11 L_sun.
This data constitutes the highest spatial resolution ever achieved on luminous
galaxies in the far infrared. Our data includes direct measurements of the
spatial structure of the sources, in which we look for departures from point
source profiles. Additionally, comparison of our small beam 100 micron fluxes
with the large beam IRAS fluxes shows how much flux falls beyond our detectors
but within the IRAS beam. Several sources with point- like cores show evidence
for such a net flux deficit. We clearly resolved six of these galaxies at 100
microns and have some evidence for extension in seven others. Those galaxies
which we have resolved can have little of their 100 micron flux directly
emitted by a point-like active galactic nucleus (AGN). Dust heated to ~40 K by
recent bursts of non-nuclear star formation provides the best explanation for
their extreme FIR luminosity. In a few cases, heating of an extended region by
a compact central source is also a plausible option. Assuming the FIR emission
we see is from dust, we also use the sizes we derive to find the dust
temperatures and optical depths at 100 microns which we translate into an
effective visual extinction through the galaxy. Our work shows that studies of
the far infrared structure of luminous infrared galaxies is clearly within the
capabilities of new generation far infrared instrumentation, such as SOFIA and
SIRTF.Comment: 8 tables, 23 figure
Study of bound states in 12Be through low-energy 11Be(d,p)-transfer reactions
The bound states of 12Be have been studied through a 11Be(d,p)12Be transfer
reaction experiment in inverse kinematics. A 2.8 MeV/u beam of 11Be was
produced using the REX-ISOLDE facility at CERN. The outgoing protons were
detected with the T-REX silicon detector array. The MINIBALL germanium array
was used to detect gamma rays from the excited states in 12Be. The gamma-ray
detection enabled a clear identification of the four known bound states in
12Be, and each of the states has been studied individually. Differential cross
sections over a large angular range have been extracted. Spectroscopic factors
for each of the states have been determined from DWBA calculations and have
been compared to previous experimental and theoretical results
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