RESUMEN
Because the white matter of the cerebral cortex contains axons that connect distant neurons in the cortical gray matter, the relationship between the volumes of the 2 cortical compartments is key for information transmission in the brain. It has been suggested that the volume of the white matter scales universally as a function of the volume of the gray matter across mammalian species, as would be expected if a global principle of wiring minimization applied. Using a systematic analysis across several mammalian clades, here we show that the volume of the white matter does not scale universally with the volume of the gray matter across mammals and is not optimized for wiring minimization. Instead, the ratio between volumes of gray and white matter is universally predicted by the same equation that predicts the degree of folding of the cerebral cortex, given the clade-specific scaling of cortical thickness, such that the volume of the gray matter (or the ratio of gray to total cortical volumes) divided by the square root of cortical thickness is a universal function of total cortical volume, regardless of the number of cortical neurons. Thus, the very mechanism that we propose to generate cortical folding also results in compactness of the white matter to a predictable degree across a wide variety of mammalian species.
Asunto(s)
Corteza Cerebral/anatomía & histología , Sustancia Gris/anatomía & histología , Neuronas/citología , Sustancia Blanca/anatomía & histología , Animales , Artiodáctilos/anatomía & histología , Artiodáctilos/fisiología , Corteza Cerebral/citología , Corteza Cerebral/fisiología , Conectoma , Sustancia Gris/citología , Sustancia Gris/fisiología , Humanos , Neuronas/fisiología , Tamaño de los Órganos/fisiología , Especificidad de Órganos , Primates/anatomía & histología , Primates/fisiología , Roedores/anatomía & histología , Roedores/fisiología , Escandentios/anatomía & histología , Escandentios/fisiología , Sustancia Blanca/citología , Sustancia Blanca/fisiologíaAsunto(s)
Encéfalo/irrigación sanguínea , Arteria Carótida Interna/fisiología , Primates/fisiología , Escandentios/fisiología , Animales , Encéfalo/anatomía & histología , Arteria Carótida Interna/anatomía & histología , Filogenia , Primates/anatomía & histología , Primates/sangre , Escandentios/anatomía & histología , Escandentios/sangreAsunto(s)
Encéfalo/irrigación sanguínea , Arteria Carótida Interna/fisiología , Primates/fisiología , Escandentios/fisiología , Animales , Encéfalo/anatomía & histología , Arteria Carótida Interna/anatomía & histología , Filogenia , Primates/anatomía & histología , Primates/sangre , Escandentios/anatomía & histología , Escandentios/sangreRESUMEN
Supplying the central nervous system with oxygen and glucose for metabolic activities is a critical function for all animals at physiologic, anatomical, and behavioral levels. A relatively proximate challenge to nourishing the brain is maintaining adequate blood flow. Euarchontans (primates, dermopterans and treeshrews) display a diversity of solutions to this challenge. Although the vertebral artery is a major encephalic vessel, previous research has questioned its importance for irrigating the cerebrum. This presents a puzzling scenario for certain strepsirrhine primates (non-cheirogaleid lemuriforms) that have reduced promontorial branches of the internal carotid artery and no apparent alternative encephalic vascular route except for the vertebral artery. Here, we present results of phylogenetic comparative analyses of data on the cross-sectional area of bony canals that transmit the vertebral artery (transverse foramina). These results show that, across primates (and within major primate subgroups), variation in the transverse foramina helps significantly to explain variation in forebrain mass even when variation in promontorial canal cross-sectional areas are also considered. Furthermore, non-cheirogaleid lemuriforms have larger transverse foramina for their endocranial volume than other euarchontans, suggesting that the vertebral arteries compensate for reduced promontorial artery size. We also find that, among internal carotid-reliant euarchontans, species that are more encephalized tend to have a promontorial canal that is larger relative to the transverse foramina. Tentatively, we consider the correlation between arterial canal diameters (as a proxy for blood flow) and brain metabolic demands. The results of this analysis imply that human investment in brain metabolism (â¼27% of basal metabolic rate) may not be exceptional among euarchontans.
Asunto(s)
Encéfalo/anatomía & histología , Arteria Carótida Interna/anatomía & histología , Primates/anatomía & histología , Escandentios/anatomía & histología , Arteria Vertebral/anatomía & histología , Anatomía Comparada , Animales , Metabolismo Basal , Encéfalo/irrigación sanguínea , Encéfalo/metabolismo , Arteria Carótida Interna/fisiología , Filogenia , Primates/sangre , Primates/fisiología , Escandentios/sangre , Escandentios/fisiología , Arteria Vertebral/fisiologíaRESUMEN
The crouched limb posture of small mammals enables them to react to unexpected irregularities in the support. Small arboreal primates would benefit from these kinematics in their arboreal habitat but it has been demonstrated that primates display certain differences in forelimb kinematics to other mammals. The objective of this paper is to find out whether these changes in forelimb kinematics are related to changes in body size and limb proportions. As primates descended from small ancestors, a comparison between living small primates and other small mammals makes it possible to determine the polarity of character transformations for kinematic and morphometric features proposed to be unique to primates. Walking kinematics of mouse lemurs, brown lemurs, cotton-top tamarins and squirrel monkeys was investigated using cineradiography. Morphometry was conducted on a sample of 110 mammals comprising of primates, marsupials, rodents and carnivores. It has been shown that forelimb kinematics change with increasing body size in such a way that limb protraction increases but retraction decreases. Total forelimb excursion, therefore, is almost independent of body size. Kinematic changes are linked to changes in forelimb proportions towards greater asymmetry between scapula and radius. Due to the spatial restriction inherent in the diagonal footfall sequence of primates, forelimb excursion is influenced by the excursion of the elongated hind limb. Hindlimb geometry, however, is highly conserved, as has been previously shown. The initial changes in forelimb kinematics might, therefore, be explained as solutions to a constraint rather than as adaptations to the particular demands of arboreal locomotion.
Asunto(s)
Brazo/anatomía & histología , Brazo/fisiología , Miembro Anterior/anatomía & histología , Miembro Anterior/fisiología , Primates/anatomía & histología , Primates/fisiología , Animales , Fenómenos Biomecánicos , Tamaño Corporal , Carnívoros/anatomía & histología , Carnívoros/fisiología , Marsupiales/anatomía & histología , Marsupiales/fisiología , Roedores/anatomía & histología , Roedores/fisiología , Escandentios/anatomía & histología , Escandentios/fisiologíaRESUMEN
A comparative study of quantitative kinematic data of fore- and hindlimb movements of eight different mammalian species leads to the recognition of basic principles in the locomotion of small therians. The description of kinematics comprises fore- and hindlimb movements as well as sagittal spine movements including displacement patterns of limb segments, their contribution to step length, and joint movements. The comparison of the contributions of different segments to step length clearly shows the proximal parts (scapula, femur) to produce more than half of the propulsive movement of the whole limb at symmetrical gaits. Basically, a three-segmented limb with zigzag configuration of segments is mainly displaced at the scapular pivot or hip joint, both of which have the same vertical distance to the ground. Two segments operate in matched motion during retraction of the limb. While kinematic parameters of forelimbs are independent of speed and gait (with the scapula as the dominant element), fundamental changes occur in hindlimb kinematics with the change from symmetrical to in-phase gaits. Forward motion of the hindlimbs is now mainly due to sagittal lumbar spine movements contributing to half of the step length. Kinematics of small therian mammals are independent of their systematic position, their natural habitat, and also of specific anatomical dispositions (e.g. reduction of fingers, toes, or clavicle). In contrast, the possession of a tail influences 'pelvic movements'.
Asunto(s)
Extremidades/fisiología , Mamíferos/fisiología , Animales , Evolución Biológica , Fenómenos Biomecánicos , Cheirogaleidae/anatomía & histología , Cheirogaleidae/fisiología , Cinerradiografía , Extremidades/anatomía & histología , Femenino , Miembro Anterior/anatomía & histología , Miembro Anterior/fisiología , Cobayas/anatomía & histología , Cobayas/fisiología , Miembro Posterior/anatomía & histología , Miembro Posterior/fisiología , Lagomorpha/anatomía & histología , Lagomorpha/fisiología , Locomoción/fisiología , Masculino , Mamíferos/anatomía & histología , Marsupiales/anatomía & histología , Marsupiales/fisiología , Zarigüeyas/anatomía & histología , Zarigüeyas/fisiología , Ratas , Escandentios/anatomía & histología , Escandentios/fisiología , Tupaia/anatomía & histología , Tupaia/fisiologíaRESUMEN
In three species of small therian mammals (Scandentia: Tupaia glis, Rodentia: Galea musteloides and Lagomorpha: Ochotona rufescens) the net joint forces and torques acting during stance phase in the four kinematically relevant joints of the forelimbs (scapular pivot, shoulder joint, elbow joint, wrist joint) and the hindlimbs (hip joint, knee joint, ankle joint, intratarsal joint) were determined by inverse dynamic analysis. Kinematics were measured by cineradiography (150 frames s(-1)). Synchronously ground reaction forces were acquired by forceplates. Morphometry of the extremities was performed by a scanning method using structured illumination. The vector sum of ground reaction forces and weight accounts for most of the joint force vector. Inertial effects can be neglected since errors of net joint forces amount at most to 10 %. The general time course of joint torques is comparable for all species in all joints of the forelimb and in the ankle joint. Torques in the intratarsal joints differ between tailed and tail-less species. The torque patterns in the knee and hip joint are unique to each species. For the first time torque patterns are described completely for the forelimb including the scapula as the dominant propulsive segment. The results are compared with the few torque data available for various joints of cats (Felis catus), dogs (Canis lupus f. familiaris), goats (Capra sp.) and horses (Equus przewalskii f. caballus).