The iliolumbar ligament is a strong ligament passing from the tip of the transverse process of the fifth lumbar vertebra to the posterior part of the inner lip of the iliac crest. It forms the thickened lower border of two of the layers of the thoracolumbar fascia. A small ligamentous band stretches from the tip of the transverse process of the fourth vertebra down to the iliac crest behind the main ligament. Fibrous strands are found between this latter process and the iliac crest, but these are only considered a true ligament when dense enough, it radiates as it is attached by two main bands to the pelvis. The lower bands run to the base of the sacrum. In front, it is in relation with the Psoas major; the ililumbar ligament strengthens the lumbosacral joint assisted by the lateral lumbosacral ligament, like all other vertebral joints, by the posterior and anterior longitudinal ligaments, the ligamenta flava, the interspinous and supraspinous ligaments. This article incorporates text in the public domain from page 306 of the 20th edition of Gray's Anatomy pelvis at The Anatomy Lesson by Wesley Norman
The lumbar arteries are arteries located in the lower back or lumbar region. The lumbar arteries are in parallel with the intercostals, they are four in number on either side, arise from the back of the aorta, opposite the bodies of the upper four lumbar vertebrae. A fifth pair, small in size, is present: they arise from the middle sacral artery, they run lateralward and backward on the bodies of the lumbar vertebrae, behind the sympathetic trunk, to the intervals between the adjacent transverse processes, are continued into the abdominal wall. The arteries of the right side pass behind the inferior vena cava, the upper two on each side run behind the corresponding crus of the diaphragm; the arteries of both sides pass beneath the tendinous arches which give origin to the psoas major, are continued behind this muscle and the lumbar plexus. They now cross the quadratus lumborum, the upper three arteries running behind, the last in front of the muscle. At the lateral border of the quadratus lumborum they pierce the posterior aponeurosis of the transversus abdominis and are carried forward between this muscle and the obliquus internus.
They anastomose with the lower intercostal, the subcostal, the iliolumbar, the deep iliac circumflex, the inferior epigastric arteries. Lumbar veins This article incorporates text in the public domain from page 612 of the 20th edition of Gray's Anatomy Anatomy photo:40:11-0201 at the SUNY Downstate Medical Center - "Branches of the Abdominal Aorta" Atlas image: abdo_wall75 at the University of Michigan Health System - "The Abdominal Aorta" Anatomy figure: 40:05-07 at Human Anatomy Online, SUNY Downstate Medical Center - "Parietal and visceral branches of the abdominal aorta."
Muscle contraction is the activation of tension-generating sites within muscle fibers. In physiology, muscle contraction does not mean muscle shortening because muscle tension can be produced without changes in muscle length such as holding a heavy book or a dumbbell at the same position; the termination of muscle contraction is followed by muscle relaxation, a return of the muscle fibers to their low tension-generating state. Muscle contractions can be described based on two variables: tension. A muscle contraction is described as isometric if the muscle tension changes but the muscle length remains the same. In contrast, a muscle contraction is isotonic if muscle tension remains the same throughout the contraction. If the muscle length shortens, the contraction is concentric. In natural movements that underlie locomotor activity, muscle contractions are multifaceted as they are able to produce changes in length and tension in a time-varying manner. Therefore, neither length nor tension is to remain the same in muscles that contract during locomotor activity.
In vertebrates, skeletal muscle contractions are neurogenic as they require synaptic input from motor neurons to produce muscle contractions. A single motor neuron is able to innervate multiple muscle fibers, thereby causing the fibers to contract at the same time. Once innervated, the protein filaments within each skeletal muscle fiber slide past each other to produce a contraction, explained by the sliding filament theory; the contraction produced can be described as a twitch, summation, or tetanus, depending on the frequency of action potentials. In skeletal muscles, muscle tension is at its greatest when the muscle is stretched to an intermediate length as described by the length-tension relationship. Unlike skeletal muscle, the contractions of smooth and cardiac muscles are myogenic, although they can be modulated by stimuli from the autonomic nervous system; the mechanisms of contraction in these muscle tissues are similar to those in skeletal muscle tissues. Muscle contractions can be described based on two variables: length.
Force itself can be differentiated as either load. Muscle tension is the force exerted by the muscle on an object whereas a load is the force exerted by an object on the muscle; when muscle tension changes without any corresponding changes in muscle length, the muscle contraction is described as isometric. If the muscle length changes while muscle tension remains the same the muscle contraction is isotonic. In an isotonic contraction, the muscle length can either shorten to produce a concentric contraction or lengthen to produce an eccentric contraction. In natural movements that underlie locomotor activity, muscle contractions are multifaceted as they are able to produce changes in length and tension in a time-varying manner. Therefore, neither length nor tension is to remain constant when the muscle is active during locomotor activity. An isometric contraction of a muscle generates tension without changing length. An example can be found when the muscles of the forearm grip an object. In isotonic contraction, the tension in the muscle remains constant despite a change in muscle length.
This occurs. In concentric contraction, muscle tension is sufficient to overcome the load, the muscle shortens as it contracts; this occurs. During a concentric contraction, a muscle is stimulated to contract according to the sliding filament theory; this occurs throughout the length of the muscle, generating a force at the origin and insertion, causing the muscle to shorten and changing the angle of the joint. In relation to the elbow, a concentric contraction of the biceps would cause the arm to bend at the elbow as the hand moved from the leg to the shoulder. A concentric contraction of the triceps would change the angle of the joint in the opposite direction, straightening the arm and moving the hand towards the leg. In eccentric contraction, the tension generated while isometric is insufficient to overcome the external load on the muscle and the muscle fibers lengthen as they contract. Rather than working to pull a joint in the direction of the muscle contraction, the muscle acts to decelerate the joint at the end of a movement or otherwise control the repositioning of a load.
This can occur voluntarily. Over the short-term, strength training involving both eccentric and concentric contractions appear to increase muscular strength more than training with concentric contractions alone. However, exercise-induced muscle damage is greater during lengthening contractions. During an eccentric contraction of the biceps muscle, the elbow starts the movement while bent and straightens as the hand moves away from the shoulder. During an eccentric contraction of the triceps muscle, the elbow starts the movement straight and bends as the hand moves towards the shoulder. Desmin and other z-line proteins are involved in eccentric contractions, but their mechanism is poorly understood in comparison to crossbridge cycling in concentric contractions. Though the muscle is doing a negative amount of mechanical work, (work is being d
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.
The rib cage is the arrangement of ribs attached to the vertebral column and sternum in the thorax of most vertebrates, that encloses and protects the heart and lungs. In humans, the rib cage known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic cavity and supports the shoulder girdle to form the core part of the human skeleton. A typical human rib cage consists of 24 ribs in 12 pairs, the sternum and xiphoid process, the costal cartilages, the 12 thoracic vertebrae. Together with the skin and associated fascia and muscles, the rib cage makes up the thoracic wall and provides attachments for the muscles of the neck, upper abdomen, back; the rib cage has a major function in the respiratory system. Ribs are described based on their connection with the sternum. All ribs are numbered accordingly one to twelve. Ribs that articulate directly with the sternum are called true ribs, whereas those that connect indirectly via cartilage are termed false ribs. Floating ribs are not attached to the sternum at all.
The terms true ribs and false ribs describe rib pairs that are directly or indirectly attached to the sternum. The first seven rib pairs known as the fixed or vertebrosternal ribs are the true ribs as they connect directly to the sternum, their elasticity allows rib cage movement for respiratory activity. The phrase floating rib refers to the eleventh and twelfth rib pairs; these ribs are small and delicate, include a cartilaginous tip. The spaces between the ribs are known as intercostal spaces; each rib consists of a head, a shaft. All ribs are attached posteriorly to the thoracic vertebrae, they are numbered to match the vertebra -- one to twelve, from top to bottom. The head of the rib is the end part closest to the vertebrae, it is marked by a kidney-shaped articular surface, divided by a horizontal crest into two articulating regions. The upper region articulates with the inferior costal facet on the vertebra above, the larger region articulates with the superior costal facet on the vertebra with the same number.
The transverse process of a thoracic vertebra articulates at the transverse costal facet with the tubercle of the rib of the same number. The crest gives attachment to the intra-articular ligament; the neck of the rib is the flattened part. The neck is about 3 cm long, its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck. Its upper border presents a rough crest for the attachment of the anterior costotransverse ligament. On the posterior surface at the neck, is an eminence—the tubercle that consists of an articular and a non-articular portion; the articular portion is the lower and more medial of the two and presents a small, oval surface for articulation with the transverse costal facet on the end of the transverse process of the lower of the two vertebrae to which the head is connected. The non-articular portion is a rough elevation and affords attachment to the ligament of the tubercle.
The tubercle is much more prominent in the upper ribs than in the lower ribs. The angle of a rib may both refer to the bending part of it, a prominent line in this area, a little in front of the tubercle; this line is directed laterally. At this point, the rib is bent in two directions, at the same time twisted on its long axis; the distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The area between the angle and the tubercle is rounded and irregular, serves for the attachment of the longissimus dorsi muscle; the first rib is the most curved and the shortest of all the ribs. The head is small and rounded, possesses only a single articular facet, for articulation with the body of the first thoracic vertebra; the neck is rounded. The tubercle and prominent, is placed on the outer border, it bears a small facet for articulation with the transverse costal facet on the transverse process of T1. There is no angle, but at the tubercle, the rib is bent, with the convexity upward, so that the head of the bone is directed downward.
The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the scalene tubercle, for the attachment of the anterior scalene. Behind the posterior groove is a rough area for the attachment of the medial scalene; the under surface is smooth and without a costal groove. The outer border is convex and rounded, at its posterior part gives attachment to the first digitation of the serratus anterior; the inner border is concave and sharp, marked about its center by the scalene tubercle. The anterior extremity is larger and
The pelvis is either the lower part of the trunk of the human body between the abdomen and the thighs or the skeleton embedded in it. The pelvic region of the trunk includes the bony pelvis, the pelvic cavity, the pelvic floor, below the pelvic cavity, the perineum, below the pelvic floor; the pelvic skeleton is formed in the area of the back, by the sacrum and the coccyx and anteriorly and to the left and right sides, by a pair of hip bones. The two hip bones connect the spine with the lower limbs, they are attached to the sacrum posteriorly, connected to each other anteriorly, joined with the two femurs at the hip joints. The gap enclosed by the bony pelvis, called the pelvic cavity, is the section of the body underneath the abdomen and consists of the reproductive organs and the rectum, while the pelvic floor at the base of the cavity assists in supporting the organs of the abdomen. In mammals, the bony pelvis has a gap in the middle larger in females than in males, their young pass through this gap.
The pelvic region of the trunk is the lower part of the trunk, between the thighs. It includes several structures: the bony pelvis, the pelvic cavity, the pelvic floor, the perineum; the bony pelvis is the part of the skeleton embedded in the pelvic region of the trunk. It is subdivided into the pelvic spine; the pelvic girdle is composed of the appendicular hip bones oriented in a ring, connects the pelvic region of the spine to the lower limbs. The pelvic spine consists of the coccyx; the pelvic cavity defined as a small part of the space enclosed by the bony pelvis, delimited by the pelvic brim above and the pelvic floor below. Each hip bone consists of 3 sections, ilium and pubis. During childhood, these sections are separate bones, joined by the triradiate cartilage. During puberty, they fuse together to form a single bone; the pelvic cavity is a body cavity, bounded by the bones of the pelvis and which contains reproductive organs and the rectum. A distinction is made between the lesser or true pelvis inferior to the terminal line, the greater or false pelvis above it.
The pelvic inlet or superior pelvic aperture, which leads into the lesser pelvis, is bordered by the promontory, the arcuate line of ilium, the iliopubic eminence, the pecten of the pubis, the upper part of the pubic symphysis. The pelvic outlet or inferior pelvic aperture is the region between the subpubic angle or pubic arch, the ischial tuberosities and the coccyx. Ligaments: obturator membrane, inguinal ligament Alternatively, the pelvis is divided into three planes: the inlet and outlet; the pelvic floor has two inherently conflicting functions: One is to close the pelvic and abdominal cavities and bear the load of the visceral organs. To achieve both these tasks, the pelvic floor is composed of several overlapping sheets of muscles and connective tissues; the pelvic diaphragm is composed of the coccygeus muscle. These arise between the symphysis and the ischial spine and converge on the coccyx and the anococcygeal ligament which spans between the tip of the coccyx and the anal hiatus; this leaves a slit for the urogenital openings.
Because of the width of the genital aperture, wider in females, a second closing mechanism is required. The urogenital diaphragm consists of the deep transverse perineal which arises from the inferior ischial and pubic rami and extends to the urogential hiatus; the urogenital diaphragm is reinforced posteriorly by the superficial transverse perineal. The external anal and urethral sphincters close the urethra; the former is surrounded by the bulbospongiosus which narrows the vaginal introitus in females and surrounds the corpus spongiosum in males. Ischiocavernosus clitoridis. Modern humans are to a large extent characterized by large brains; because the pelvis is vital to both locomotion and childbirth, natural selection has been confronted by two conflicting demands: a wide birth canal and locomotion efficiency, a conflict referred to as the "obstetrical dilemma". The female pelvis, or gynecoid pelvis, has evolved to its maximum width for childbirth—a wider pelvis would make women unable to walk.
In contrast, human male pelvises are not constrained by the need to give birth and therefore are more optimized for bipedal locomotion. The principal differences between male and female true and false pelvis include: The female pelvis is larger and broader than the male pelvis, taller and more compact; the female inlet is oval in shape, while the male sacral promontory projects further. The sides of the male pelvis converge from the inlet to the outlet, whereas the sides of the female pelvis are wider apart; the angle between
The pyramidalis is a small triangular muscle, anterior to the rectus abdominis muscle, contained in the rectus sheath. Inferiorly, the pyramidalis attaches to the pelvis in two places: the pubic symphysis and pubic crest, arising by tendinous fibers from the anterior part of the pubis and the anterior pubic ligament. Superiorly, the fleshy portion of the pyramidalis passes upward, diminishing in size as it ascends, ends by a pointed extremity, inserted into the linea alba, midway between the umbilicus and pubis; the pyramidalis is innervated by the ventral portion of T12. The inferior and superior epigastric arteries supply blood to this muscle; the pyramidalis muscle is present in 80% of human population. This muscle may be absent on both sides, it is double on one side, the muscles of the two sides are sometimes of unequal size. It may extend higher than the usual level; the pyramidalis, when contracting, tenses the linea alba. While making the longitudinal inscision for a classical caesarean section, the pyramidalis is used to determine midline and location of the linea alba.
Anatomy photo:35:11-0100 at the SUNY Downstate Medical Center - "Anterior Abdominal Wall: The Pyramidalis Muscle" Anatomy image:7283 at the SUNY Downstate Medical Center Cross section image: pelvis/pelvis-female-17—Plastination Laboratory at the Medical University of Vienna