The skull is a bony structure that forms the head in vertebrates. It provides a protective cavity for the brain; the skull is composed of two parts: the mandible. In the human, these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone; the skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, several sensory structures such as the eyes, ears and mouth. In humans these sensory structures are part of the facial skeleton. Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, fixing the position of the ears to enable sound localisation of the direction and distance of sounds. In some animals such as horned ungulates, the skull has a defensive function by providing the mount for the horns; the English word "skull" is derived from Old Norse "skulle", while the Latin word cranium comes from the Greek root κρανίον.
The skull is made up of a number of fused flat bones, contains many foramina, fossae and several cavities or sinuses. In zoology there are openings in the skull called fenestrae. For details and the constituent bones, see Neurocranium and Facial skeleton The human skull is the bony structure that forms the head in the human skeleton, it forms a cavity for the brain. Like the skulls of other vertebrates, it protects the brain from injury; the skull consists of two parts, of different embryological origin—the neurocranium and the facial skeleton. The neurocranium forms the protective cranial cavity that surrounds and houses the brain and brainstem; the upper areas of the cranial bones form the calvaria. The membranous viscerocranium includes the mandible; the facial skeleton is formed by the bones supporting the face Except for the mandible, all of the bones of the skull are joined together by sutures—synarthrodial joints formed by bony ossification, with Sharpey's fibres permitting some flexibility.
Sometimes there can be extra bone pieces within the suture known as sutural bones. Most these are found in the course of the lambdoid suture; the human skull is considered to consist of twenty-two bones—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the occipital bone, two temporal bones, two parietal bones, the sphenoid and frontal bones; the bones of the facial skeleton are the vomer, two inferior nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, two lacrimal bones. Some sources count the maxilla as having two bones; some of these bones—the occipital, frontal, in the neurocranium, the nasal and vomer, in the facial skeleton are flat bones. The skull contains sinuses, air-filled cavities known as paranasal sinuses, numerous foramina; the sinuses are lined with respiratory epithelium. Their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn into the nasal cavity.
The foramina are openings in the skull. The largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels; the many processes of the skull include the zygomatic processes. The skull is a complex structure; the skull roof bones, comprising the bones of the facial skeleton and the sides and roof of the neurocranium, are dermal bones formed by intramembranous ossification, though the temporal bones are formed by endochondral ossification. The endocranium, the bones supporting the brain are formed by endochondral ossification, thus frontal and parietal bones are purely membranous. The geometry of the skull base and its fossae, the anterior and posterior cranial fossae changes rapidly; the anterior cranial fossa changes during the first trimester of pregnancy and skull defects can develop during this time. At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements fuse together into solid bone.
The bones of the roof of the skull are separated by regions of dense connective tissue called fontanelles. There are six fontanelles: one anterior, one posterior, two sphenoid, two mastoid. At birth these regions are fibrous and moveable, necessary for birth and growth; this growth can put a large amount of tension on the "obstetrical hinge", where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein; as growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating sutures. The five sutures are the two squamous sutures, one coronal, one lambdoid, one sagittal suture; the posterior fontanelle closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanelle is located at the junction of the parietal bones. Careful observation will show that you can count a baby's heart
The palpebral fissure is the elliptic space between the medial and lateral canthi of the two open lids. In simple terms, it refers to the opening between the eye lids. In adults, this measures 30 mm horizontally, it can be reduced in horizontal size in Williams syndrome. The chromosomal conditions trisomy 9 and trisomy 21 can cause the palpebral fissures to be upslanted, while Marfan syndrome can cause a downslant. An increase in vertical height can be seen in genetic disorders like cri-du-chat; the fissure may be increased in vertical height in Graves' disease, manifested as Dalrymple's sign. Seen in disorders like cri-du-chat. Narrowing of the fissure can be a prominent indicator of myofascial trigger points in the ipsilateral sternocleidomastoid muscle's sternal division, a common cause of tension headaches those felt around the eyes and sinuses. In animal studies, using four times the therapeutic concentration of the ophthalmic solution Latanoprost, the size of the palpebral fissure can be increased.
The condition is reversible. Latanoprost is a prostaglandin F receptor agonist. Blepharophimosis Facial Neurological Examination from University of Toronto
A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. The term is used for the complete set of chromosomes in a species or in an individual organism and for a test that detects this complement or measures the number. Karyotypes describe the chromosome count of an organism and what these chromosomes look like under a light microscope. Attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, any other physical characteristics; the preparation and study of karyotypes is part of cytogenetics. The study of whole sets of chromosomes is sometimes known as karyology; the chromosomes are depicted in a standard format known as a karyogram or idiogram: in pairs, ordered by size and position of centromere for chromosomes of the same size. The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line the chromosome number is n.p28 Thus, in humans 2n = 46.
So, in normal diploid organisms, autosomal chromosomes are present in two copies. There may, or may not, be sex chromosomes. Polyploid cells haploid cells have single copies; the study of karyotypes is important for cell biology and genetics, the results may be used in evolutionary biology and medicine. Karyotypes can be used for many purposes. Chromosomes were first observed in plant cells by Carl Wilhelm von Nägeli in 1842, their behavior in animal cells was described by Walther Flemming, the discoverer of mitosis, in 1882. The name was coined by another German anatomist, Heinrich von Waldeyer in 1888, it is New Latin from Ancient Greek κάρυον karyon, "kernel", "seed", or "nucleus", τύπος typos, "general form"). The next stage took place after the development of genetics in the early 20th century, when it was appreciated that chromosomes were the carrier of genes. Lev Delaunay in 1922 seems to have been the first person to define the karyotype as the phenotypic appearance of the somatic chromosomes, in contrast to their genic contents.
The subsequent history of the concept can be followed in the works of C. D. Darlington and Michael JD White. Investigation into the human karyotype took many years to settle the most basic question: how many chromosomes does a normal diploid human cell contain? In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia, concluding an XX/XO sex determination mechanism. Painter in 1922 was not certain whether the diploid of humans was 46 or 48, at first favoring 46, but revised his opinion from 46 to 48, he insisted on humans having an XX/XY system. Considering the techniques of the time, these results were remarkable. In textbooks, the number of human chromosomes remained at 48 for over thirty years. New techniques were needed to correct this error. Joe Hin Tjio working in Albert Levan's lab was responsible for finding the approach: Using cells in tissue culture Pretreating cells in a hypotonic solution, which swells them and spreads the chromosomes Arresting mitosis in metaphase by a solution of colchicine Squashing the preparation on the slide forcing the chromosomes into a single plane Cutting up a photomicrograph and arranging the result into an indisputable karyogram.
The work took place in 1955, was published in 1956. The karyotype of humans includes only 46 chromosomes; the great apes have 48 chromosomes. Human chromosome 2 is now known to be a result of an end-to-end fusion of two ancestral ape chromosomes; the study of karyotypes is made possible by staining. A suitable dye, such as Giemsa, is applied after cells have been arrested during cell division by a solution of colchicine in metaphase or prometaphase when most condensed. In order for the Giemsa stain to adhere all chromosomal proteins must be digested and removed. For humans, white blood cells are used most because they are induced to divide and grow in tissue culture. Sometimes observations may be made on non-dividing cells; the sex of an unborn fetus can be determined by observation of interphase cells. Six different characteristics of karyotypes are observed and compared: Differences in absolute sizes of chromosomes. Chromosomes can vary in absolute size by as much as twenty-fold between genera of the same family.
For example, the legumes Lotus tenuis and Vicia faba each have six pairs of chromosomes, yet V. faba chromosomes are many times larger. These differences reflect different amounts of DNA duplication. Differences in the position of centromeres; these differences came about through translocations. Differences in relative size of chromosomes; these differences arose from segmental interchange of unequal lengths. Differences in basic number of chromosomes; these differences could have resulted from successive unequal translocations which removed all the essential genetic material from a chromosome, permitting its loss without penalty to the organism or through fusion. Humans have one pair fewer chromosomes than the great apes. Human chromosome 2 appears to have resulted from the fusion of two ancestral chromosomes, many of the genes of those two original chromosomes have been translocated to other chromosomes. Differences in number and position of satellites. Satellites are small bodies attached to a chromosome by a thin thread.
Differences in degree and distribution of heterochromatic regions. Het
Chromosome 9 is one of the 23 pairs of chromosomes in humans. Humans have two copies of this chromosome, as they do with all chromosomes. Chromosome 9 spans about 138 million base pairs of nucleic acids and represents between 4 and 4.5 percent of the total DNA in cells. The following are some of the gene count estimates of human chromosome 9; because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies. Among various projects, the collaborative consensus coding sequence project takes an conservative strategy. So CCDS's gene number prediction represents a lower bound on the total number of human protein-coding genes; the following is a partial list of genes on human chromosome 9. For complete list, see the link in the infobox on the right; the following diseases are some of those related to genes on chromosome 9: National Institutes of Health. "Chromosome 9". Genetics Home Reference. Retrieved 2017-05-06. "Chromosome 9". Human Genome Project Information Archive 1990–2003.
The occipital bone is a cranial dermal bone and the main bone of the occiput. It is trapezoidal in shape and curved on itself like a shallow dish; the occipital bone overlies the occipital lobes of the cerebrum. At the base of skull in the occipital bone, there is a large oval opening called the foramen magnum, which allows the passage of the spinal cord. Like the other cranial bones, it is classed as a flat bone. Due to its many attachments and features, the occipital bone is described in terms of separate parts. From its front to the back is the basilar part called the basioccipital, at the sides of the foramen magnum are the lateral parts called the exoccipitals, the back is named as the squamous part; the basilar part is a thick, somewhat quadrilateral piece in front of the foramen magnum and directed towards the pharynx. The squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone; the occipital bone, like the other seven cranial bones, has outer and inner layers of cortical bone tissue between, the cancellous bone tissue known in the cranial bones as diploë.
The bone is thick at the ridges, protuberances and anterior part of the basilar part. Near the middle of the outer surface of the squamous part of the occipital there is a prominence – the external occipital protuberance; the highest point of this is called the inion. From the inion, along the midline of the squamous part until the foramen magnum, runs a ridge – the external occipital crest and this gives attachment to the nuchal ligament. Running across the outside of the occipital bone are three curved lines and one line that runs down to the foramen magnum; these are known as the nuchal lines which give attachment to various muscles. They are named as the highest and inferior nuchal lines; the inferior nuchal line runs across the midpoint of the medial nuchal line. The area above the highest nuchal line is termed the occipital plane and the area below this line is termed the nuchal plane; the inner surface of the occipital bone forms the base of the posterior cranial fossa. The foramen magnum is a large hole situated in the middle, with the clivus, a smooth part of the occipital bone travelling upwards in front of it.
The median internal occipital crest travels behind it to the internal occipital protuberance, serves as a point of attachment to the falx cerebri. To the sides of the foramen sitting at the junction between the lateral and base of the occipital bone are the hypoglossal canals. Further out, at each junction between the occipital and petrous portion of the temporal bone lies a jugular foramen; the inner surface of the occipital bone is marked by dividing lines as shallow ridges, that form four fossae or depressions. The lines are called the cruciform eminence. At the midpoint where the lines intersect a raised part is formed called the internal occipital protuberance. From each side of this eminence runs a groove for the transverse sinuses. There are two midline skull landmarks at the foramen magnum; the basion is the most anterior point of the opening and the opisthion is the point on the opposite posterior part. The basion lines up with the dens; the foramen magnum is a large oval foramen longest front to back.
The clivus, a smooth bony section, travels upwards on the front surface of the foramen, the median internal occipital crest travels behind it. Through the foramen passes the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membrane and alar ligaments; the superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle. The lateral angles are situated at the extremities of the groove for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal bone, the mastoid portion of the temporal bone; the inferior angle is fused with the body of the sphenoid bone. The superior borders extend from the superior to the lateral angles: they are serrated for articulation with the occipital borders of the parietals, form by this union the lambdoidal suture; the inferior borders extend from the lateral angles to the inferior angle.
These two portions of the inferior border are separated from one another by the jugular process, the notch on the anterior surface of which forms the posterior part of the jugular foramen. The lambdoid suture joins the occipital bone to the parietal bones; the occipitomastoid suture joins the occipital mastoid portion of the temporal bone. The sphenobasilar suture joins the basilar part of the occipital bone and the back of the sphenoid bone body; the petrous-basilar suture joins the side edge of the basilar part of the occipital bone to the petrous-part of the temporal bone. The occipital plane of the squamous part of the occipital bone is developed in membrane, may remain separate throughout life when it constitutes the interparietal bone; the number of nuclei for the occipital plane is given as four, two appearing near the middle line about the second month, two some little distance from the middle line about the third month of
Medical genetics is the branch of medicine that involves the diagnosis and management of hereditary disorders. Medical genetics differs from human genetics in that human genetics is a field of scientific research that may or may not apply to medicine, while medical genetics refers to the application of genetics to medical care. For example, research on the causes and inheritance of genetic disorders would be considered within both human genetics and medical genetics, while the diagnosis and counselling people with genetic disorders would be considered part of medical genetics. In contrast, the study of non-medical phenotypes such as the genetics of eye color would be considered part of human genetics, but not relevant to medical genetics. Genetic medicine is a newer term for medical genetics and incorporates areas such as gene therapy, personalized medicine, the emerging new medical specialty, predictive medicine. Medical genetics encompasses many different areas, including clinical practice of physicians, genetic counselors, nutritionists, clinical diagnostic laboratory activities, research into the causes and inheritance of genetic disorders.
Examples of conditions that fall within the scope of medical genetics include birth defects and dysmorphology, mental retardation, mitochondrial disorders, skeletal dysplasia, connective tissue disorders, cancer genetics and prenatal diagnosis. Medical genetics is becoming relevant to many common diseases. Overlaps with other medical specialties are beginning to emerge, as recent advances in genetics are revealing etiologies for neurologic, cardiovascular, ophthalmologic, renal and dermatologic conditions; the medical genetics community is involved with individuals who have undertaken elective genetic and genomic testing. In some ways, many of the individual fields within medical genetics are hybrids between clinical care and research; this is due in part to recent advances in science and technology that have enabled an unprecedented understanding of genetic disorders. Clinical genetics is the practice of clinical medicine with particular attention to hereditary disorders. Referrals are made to genetics clinics for a variety of reasons, including birth defects, developmental delay, epilepsy, short stature, many others.
Examples of genetic syndromes that are seen in the genetics clinic include chromosomal rearrangements, Down syndrome, DiGeorge syndrome, Fragile X syndrome, Marfan syndrome, Neurofibromatosis, Turner syndrome, Williams syndrome. In the United States, Doctors who practice clinical genetics are accredited by the American Board of Medical Genetics and Genomics. In order to become a board-certified practitioner of Clinical Genetics, a physician must complete a minimum of 24 months of training in a program accredited by the ABMGG. Individuals seeking acceptance into clinical genetics training programs must hold an M. D. or D. O. degree and have completed a minimum of 24 months of training in an ACGME-accredited residency program in internal medicine, pediatrics and gynecology, or other medical specialty. Metabolic genetics involves the diagnosis and management of inborn errors of metabolism in which patients have enzymatic deficiencies that perturb biochemical pathways involved in metabolism of carbohydrates, amino acids, lipids.
Examples of metabolic disorders include galactosemia, glycogen storage disease, lysosomal storage disorders, metabolic acidosis, peroxisomal disorders and urea cycle disorders. Cytogenetics is the study of chromosomes and chromosome abnormalities. While cytogenetics relied on microscopy to analyze chromosomes, new molecular technologies such as array comparative genomic hybridization are now becoming used. Examples of chromosome abnormalities include aneuploidy, chromosomal rearrangements, genomic deletion/duplication disorders. Molecular genetics involves the discovery of and laboratory testing for DNA mutations that underlie many single gene disorders. Examples of single gene disorders include achondroplasia, cystic fibrosis, Duchenne muscular dystrophy, hereditary breast cancer, Huntington disease, Marfan syndrome, Noonan syndrome, Rett syndrome. Molecular tests are used in the diagnosis of syndromes involving epigenetic abnormalities, such as Angelman syndrome, Beckwith-Wiedemann syndrome, Prader-willi syndrome, uniparental disomy.
Mitochondrial genetics concerns the diagnosis and management of mitochondrial disorders, which have a molecular basis but result in biochemical abnormalities due to deficient energy production. There exists some overlap between molecular pathology. Genetic counseling is the process of providing information about genetic conditions, diagnostic testing, risks in other family members, within the framework of nondirective counseling. Genetic counselors are non-physician members of the medical genetics team who specialize in family risk assessment and counseling of patients regarding genetic disorders; the precise role of the genetic counselor varies somewhat depending on the disorder. Although genetics has its roots back in the 19th century with the work of the Bohemian monk Gregor Mendel and other pioneering scientists, human genetics emerged later, it started to develop, albeit during the first half of the 20th century. Mendelian inheritance was studied in a number of important disorders such as albinism and hemophilia.
Mathematical approaches were devised