|
Neuraxis
The neuraxis, also known as the neuroaxis is the axis of the central nervous system. It extends from the brain to the spinal cord and denotes the direction in which the central nervous system lies in both development and in mature organisms. Early on in embryological development, the neuraxis begins as a distinctly straight axis, but quickly develops bends by various flexures, most notably the cephalic flexure, which contributes most to the complex mature structure of the spinal cord and brain. Embryonic development can help in understanding how complex structures form around the neuraxis The embryonic nervous system in vertebrates is highly conserved, meaning its structure and function have stayed the same across species, and generally appear the same. During development, the formation of the neural tube-and later the brain and spinal cord- define the layout of the neuraxis. This establishes the anterior-posterior dimension of the nervous system. The anterior-posterior dimensio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pontine Flexure
Three flexures form in the part of the embryonic neural tube that develops into the brain. At four weeks gestational age in the human embryo, the neural tube has developed at the cranial end into three swellings – the primary brain vesicles. The space into which the cranial part of the neural tube is developing is limited. This limitation causes the neural tube to bend, or flex, at two ventral flexures – the rostral cephalic flexure, and the caudal cervical flexure. It also bends dorsally into the pontine flexure. These flexures have formed by the time that the primary brain vesicles have developed into five secondary brain vesicles in the fifth week. Flexure development The neural tube has a longitudinal axis called the neuraxis, from the future brain area at the cranial end, to the conus medullaris of the spinal cord at the caudal end. By the fourth week in the human embryo, at its cranial end, three swellings have formed as primary brain vesicles. These vesicles form the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flexure (embryology)
Three flexures form in the part of the embryonic neural tube that develops into the brain. At four weeks gestational age in the human embryo, the neural tube has developed at the cranial end into three swellings – the primary brain vesicles. The space into which the cranial part of the neural tube is developing is limited. This limitation causes the neural tube to bend, or flex, at two ventral flexures – the rostral cephalic flexure, and the caudal cervical flexure. It also bends dorsally into the pontine flexure. These flexures have formed by the time that the primary brain vesicles have developed into five secondary brain vesicles in the fifth week. Flexure development The neural tube has a longitudinal axis called the neuraxis, from the future brain area at the cranial end, to the conus medullaris of the spinal cord at the caudal end. By the fourth week in the human embryo, at its cranial end, three swellings have formed as primary brain vesicles. These vesicles form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalic Flexure
Three flexures form in the part of the embryonic neural tube that develops into the brain. At four weeks gestational age in the human embryo, the neural tube has developed at the cranial end into three swellings – the primary brain vesicles. The space into which the cranial part of the neural tube is developing is limited. This limitation causes the neural tube to bend, or flex, at two ventral flexures – the rostral cephalic flexure, and the caudal cervical flexure. It also bends dorsally into the pontine flexure. These flexures have formed by the time that the primary brain vesicles have developed into five secondary brain vesicles in the fifth week. Flexure development The neural tube has a longitudinal axis called the neuraxis, from the future brain area at the cranial end, to the conus medullaris of the spinal cord at the caudal end. By the fourth week in the human embryo, at its cranial end, three swellings have formed as primary brain vesicles. These vesicles form the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three Evolution of mammalian auditory ossicles, middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors Genetic divergence, diverged in the Carboniferous Period over 300 million years ago. Around 6,640 Neontology#Extant taxon, extant species of mammals have been described and divided into 27 Order (biology), orders. The study of mammals is called mammalogy. The largest orders of mammals, by number of species, are the rodents, bats, and eulipotyphlans (including hedgehogs, Mole (animal), moles and shrews). The next three are the primates (including humans, monkeys and lemurs), the Artiodactyl, even-toed ungulates (including pigs, camels, and whales), and the Carnivora (including Felidae, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primitive Streak
The primitive streak is a structure that forms in the early embryo in amniotes. In amphibians, the equivalent structure is the blastopore. During early embryonic development, the embryonic disc becomes oval shaped, and then pear-shaped with the broad end towards the anterior, and the narrower region projected to the posterior. The primitive streak forms a longitudinal midline structure in the narrower posterior (caudal) region of the developing embryo on its dorsal side. At first formation, the primitive streak extends for half the length of the embryo. In the human embryo, this appears by stage 6, about 17 days. The primitive streak establishes bilateral symmetry, determines the site of gastrulation, and initiates germ layer formation. To form the primitive streak, mesenchymal stem cells are arranged along the prospective midline, establishing the second embryonic axis, and the site where cells will ingress and migrate during the process of gastrulation and germ layer formatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neural Tube
In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord. The neural groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into the closed neural tube. In humans, neural tube closure usually occurs by the fourth week of pregnancy (the 28th day after conception). Development The neural tube develops in two ways: primary neurulation and secondary neurulation. Primary neurulation divides the ectoderm into three cell types: * The internally located neural tube * The externally located epidermis * The neural crest cells, which develop in the region between the neural tube and epidermis but then migrate to new locations # Primary neurulation begins after the neural plate forms. The edges of the neural plate start to thicken and lift upward, forming the neural folds. The center ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embryology
Embryology (from Ancient Greek, Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, ''-logy, -logia'') is the branch of animal biology that studies the Prenatal development (biology), prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology. Early embryology was proposed by Marcello Malpighi, and known as preformationism, the theory that organisms develop from pre-existing miniature versions of themselves. Aristotle proposed the theory that is now accepted, Epigenesis (biology), epigenesis. Epigenesis (biology), Epigenesis is the idea that organisms develop from seed or egg in a sequence of steps. Modern embryology developed from the work of Karl Ernst von Baer, though accurate observations had been made in Italy by anatomists such as Aldrovandi and Leonardo da Vinci in the Renaissance. Comparative ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Androgen Insensitivity Syndrome
Androgen insensitivity syndrome (AIS) is a condition involving the inability to respond to androgens, typically due to androgen receptor dysfunction. It affects 1 in 20,000 to 64,000 XY (karyotype, karyotypically male) births. The condition results in the partial or complete inability of Animal cell, cells to respond to androgens. This unresponsiveness can impair or prevent the Development of the reproductive system, development of male genitals, as well as impairing or preventing the development of male Secondary sex characteristics, secondary sexual characteristics at puberty. It does not significantly impair female genital or sexual development. The insensitivity to androgens is therefore clinically significant only when it occurs in genetic males, (i.e. individuals with a Y chromosome, Y-chromosome, or more specifically, an SRY, SRY gene). Clinical phenotypes in these individuals range from a typical body shape, male habitus with mild spermatogenesis, spermatogenic defect or re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ehlers–Danlos Syndrome
Ehlers–Danlos syndromes (EDS) is a group of 14 genetic connective-tissue disorders. Symptoms often include loose joints, joint pain, stretchy velvety skin, and abnormal scar formation. These may be noticed at birth or in early childhood. Complications may include aortic dissection, joint dislocations, scoliosis, chronic pain, or early osteoarthritis. The existing classification was last updated in 2017, when a number of rarer forms of EDS were added. EDS occurs due to mutations in one or more particular genes—there are 19 genes that can contribute to the condition. The specific gene affected determines the type of EDS, though the genetic causes of hypermobile Ehlers–Danlos syndrome are still unknown. Some cases result from a new variation occurring during early development, while others are inherited in an autosomal dominant or recessive manner. Typically, these variations result in defects in the structure or processing of the protein collagen or tenascin. Diagnos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arnold-Chiari Malformation
In neurology, the Chiari malformation ( ; CM) is a structural defect in the cerebellum, characterized by a downward displacement of one or both cerebellar tonsils through the foramen magnum (the opening at the Base of skull, base of the skull). CMs can cause headaches, Dysphagia, difficulty swallowing, vomiting, dizziness, neck pain, unsteady gait, poor hand coordination, Hypoesthesia, numbness and Paresthesia, tingling of the hands and feet, and speech problems. Less often, people may experience tinnitus, ringing or buzzing in the ears, weakness, Bradycardia, slow heart rhythm, Tachycardia, fast heart rhythm, curvature of the spine (scoliosis) related to spinal cord impairment, abnormal breathing such as in central sleep apnea, and, in severe cases, paralysis. CM can sometimes lead to non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow. The CSF outflow is caused by phase difference in outflow and influx of blood in the vasculature of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scoliosis
Scoliosis (: scolioses) is a condition in which a person's Vertebral column, spine has an irregular curve in the coronal plane. The curve is usually S- or C-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not typically cause problems, but more severe cases can affect breathing and movement. Pain is usually present in adults, and can worsen with age. As the condition progresses, it may alter a person's life, and hence can also be considered a disability. It can be compared to kyphosis and lordosis, other abnormal curvatures of the spine which are in the sagittal plane (front-back) rather than the coronal (left-right). The cause of most cases is unknown, but it is believed to involve a combination of Genetics, genetic and environmental factors. Scoliosis most often occurs during growth spurts right before puberty. Risk factors include other affected family members. It can also occur due to anoth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embryogenesis
An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres (4-cell stage) are arranged as a solid ball that when reaching a certain size, called a morula, (16-cell stage) takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals. The mammalian blastocyst hatches before implantating into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of gastrulation, neurulation, and organogenesis. Gastrulation is the formation of the three germ layers that will form all of the different parts o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
