The vertebral column known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs; the vertebral column houses a cavity that encloses and protects the spinal cord. There are about 50,000 species of animals; the human vertebral column is one of the most-studied examples. In a human's vertebral column there are thirty-three vertebrae; the articulating vertebrae are named according to their region of the spine. There are twelve thoracic vertebrae and five lumbar vertebrae; the number of vertebrae in a region overall the number remains the same. The number of those in the cervical region however is only changed. There are ligaments extending the length of the column at the front and the back, in between the vertebrae joining the spinous processes, the transverse processes and the vertebral laminae.
The vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are alike, with minor variation; these regions are called the cervical spine, thoracic spine, lumbar spine and coccyx. There are twelve thoracic vertebrae and five lumbar vertebrae; the number of vertebrae in a region overall the number remains the same. The number of those in the cervical region however is only changed; the vertebrae of the cervical and lumbar spines are independent bones, quite similar. The vertebrae of the sacrum and coccyx are fused and unable to move independently. Two special vertebrae are the axis, on which the head rests. A typical vertebra consists of two parts: the vertebral arch; the vertebral arch is posterior. Together, these enclose the vertebral foramen; because the spinal cord ends in the lumbar spine, the sacrum and coccyx are fused, they do not contain a central foramen.
The vertebral arch is formed by a pair of pedicles and a pair of laminae, supports seven processes, four articular, two transverse, one spinous, the latter being known as the neural spine. Two transverse processes and one spinous process are posterior to the vertebral body; the spinous process comes out the back, one transverse process comes out the left, one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin. Above and below each vertebra are joints called facet joints; these restrict the range of movement possible, are joined by a thin portion of the neural arch called the pars interarticularis. In between each pair of vertebrae are two small holes called intervertebral foramina; the spinal nerves leave the spinal cord through these holes. Individual vertebrae are named according to their position. From top to bottom, the vertebrae are: Cervical spine: 7 vertebrae Thoracic spine: 12 vertebrae Lumbar spine: 5 vertebrae Sacrum: 5 vertebrae Coccyx: 4 vertebrae The upper cervical spine has a curve, convex forward, that begins at the axis at the apex of the odontoid process or dens, ends at the middle of the second thoracic vertebra.
This inward curve is known as a lordotic curve. The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra, its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. This curve is known as a kyphotic curve; the lumbar curve is more marked in the female than in the male. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two; this curve is described as a lordotic curve. The sacral curve begins at the sacrovertebral articulation, ends at the point of the coccyx; the thoracic and sacral kyphotic curves are termed primary curves, because they are present in the fetus. The cervical and lumbar curves are compensatory or secondary, are developed after birth; the cervical curve forms when the infant is able to sit upright. The lumbar curve forms from twelve to eighteen months, when the child begins to walk. Anterior surfaceWhen viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic.
From this point there is a rapid diminution, to the apex of the coccyx. Posterior surfaceFrom behind, the vertebral column presents in the median line the spinous processes. In the cervical region these are short and bifid. In the upper part of the thoracic region they are directed obliquely downward.
Cruciate ligament of atlas
The cruciform ligament of atlas is a cruciate ligament in the neck forming part of the atlanto-axial joint. The ligament is named as such, it consists of the transverse ligament of the atlas, along with additional fibers below. These fibers are known as "longitudinal bands"; this article incorporates text in the public domain from page 293 of the 20th edition of Gray's Anatomy
A synovial joint known as diarthrosis, joins bones with a fibrous joint capsule, continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, surrounds the bones' articulating surfaces. The synovial cavity/joint is filled with synovial fluid; the joint capsule is made up of an outer layer, the articular capsule, which keeps the bones together structurally, an inner layer, the synovial membrane, which seals in the synovial fluid. They are the most movable type of joint in the body of a mammal; as with most other joints, synovial joints achieve movement at the point of contact of the articulating bones. Synovial joints contain the following structures: Synovial cavity: all diarthroses have the characteristic space between the bones, filled with synovial fluid Joint capsule: the fibrous capsule, continuous with the periosteum of articulating bones, surrounds the diarthrosis and unites the articulating bones. Articular cartilage: the bones of a synovial joint are covered by this layer of hyaline cartilage that lines the epiphyses of joint end of bone with a smooth, slippery surface that does not bind them together.
Many, but not all, synovial joints contain additional structures: Articular discs or menisci - the fibrocartilage pads between opposing surfaces in a joint Articular fat pads - adipose tissue pads that protect the articular cartilage, as seen in the infrapatellar fat pad in the knee Tendons - cords of dense regular connective tissue composed of parallel bundles of collagen fibers Accessory ligaments - the fibers of some fibrous membranes are arranged in parallel bundles of dense regular connective tissue that are adapted for resisting strains to prevent extreme movements that may damage the articulation Bursae - saclike structures that are situated strategically to alleviate friction in some joints that are filled with fluid, similar to synovial fluidThe bone surrounding the joint on the proximal side is sometimes called the plafond in the talocrural joint. A damage to this occurs in a Gosselin fracture; the blood supply of a synovial joint is derived from the arteries sharing in the anastomosis around the joint.
There are six types of synovial joints. Some are immobile, but are more stable. Others at the expense of greater risk of injury. In ascending order of mobility, they are: The movements possible with synovial joints are: abduction: movement away from the mid-line of the body adduction: movement toward the mid-line of the body extension: straightening limbs at a joint flexion: bending the limbs at a joint rotation: a circular movement around a fixed point The joint space equals the distance between the involved bones of the joint. A joint space narrowing is a sign of either inflammatory degeneration; the normal joint space is at least 2 mm in the hip, at least 3 mm in the knee, 4–5 mm in the shoulder joint. For the temporomandibular joint, a joint space of between 1.5 and 4 mm is regarded as normal. Joint space narrowing is therefore a component of several radiographic classifications of osteoarthritis
The torso or trunk is an anatomical term for the central part or core of many animal bodies from which extend the neck and limbs. The torso includes: the thoracic segment of the trunk, the abdominal segment of the trunk, the perineum. Most critical organs are housed within the torso. In the upper chest, the heart and lungs are protected by the rib cage, the abdomen contains most of the organs responsible for digestion: the stomach, which breaks down digested food via gastric acid; the pelvic region houses both the male and female reproductive organs. The torso harbours many of the main groups of muscles in the body, including the: pectoral muscles abdominal muscles lateral muscle epaxial muscles The organs and other contents of the torso are supplied by nerves, which originate as nerve roots from the thoracic and lumbar parts of the spinal cord; some organs receive a nerve supply from the vagus nerve. The sensation to the skin is provided by: Lateral cutaneous branches of torso|Lateral cutaneous branches Dorsal cutaneous branches Belly cast Waist Belvedere Torso
Transverse ligament of atlas
The transverse ligament of the atlas is a thick, strong band, which arches across the ring of the atlas, retains the odontoid process in contact with the atlas. It is concave in front, convex behind and thicker in the middle than at the ends, attached on either side to a small tubercle on the medial surface of the lateral mass of the atlas; as it crosses the odontoid process, a small fasciculus is prolonged upward, another downward, from the superficial or posterior fibers of the ligament. The former is attached to the basilar part of the occipital bone, in close relation with the membrana tectoria; the transverse ligament divides the ring of the atlas into two unequal parts: of these, the posterior and larger serves for the transmission of the medulla spinalis and its membranes and the accessory nerves. The neck of the odontoid process is constricted where it is embraced posteriorly by the transverse ligament, so that this ligament suffices to retain the odontoid process in position after all the other ligaments have been divided.
Excessive laxity of the posterior transverse ligament can lead to atlantoaxial instability, a common complication in patients with Down's Syndrome. Laxity has been hypothesized as the cause of degenerative hypertrophy and mechanical atlantoaxial stress. Degenerative processes can give rise to transverse ligament cysts, resulting in progressive cervical myelopathy; the treatment of choice for transverse ligament cysts with progressive neurological decline is surgical resection and cervical fusion. Conservative treatment with external neck immobilization is less reported, but may be useful in select cases where immediate surgical intervention is not indicated
The obturator membrane is a thin fibrous sheet, which completely closes the obturator foramen. Its fibers are arranged in interlacing bundles transverse in direction; the membrane is attached to the sharp margin of the obturator foramen except at its lower lateral angle, where it is fixed to the pelvic surface of the inferior ramus of the ischium, i. e. within the margin. Both obturator muscles are connected with this membrane; this article incorporates text in the public domain from page 476 of the 20th edition of Gray's Anatomy Anatomy figure: 17:03-11 at Human Anatomy Online, SUNY Downstate Medical Center lljoints at The Anatomy Lesson by Wesley Norman
The sternocostal joints known as sternochondral joints, are synovial plane joints of the costal cartilages of the true ribs with the sternum, with the exception of the first, a synchondrosis since the cartilage is directly united with the sternum. The ligaments connecting them are: Articular capsules Interarticular sternocostal ligament Radiate sternocostal ligaments Costoxiphoid ligaments Costochondritis This article incorporates text in the public domain from page 203 of the 20th edition of Gray's Anatomy