The musculoskeletal system is an organ system that enables an organism to move, support itself, and maintain stability during locomotion.
The skeletal system is divided into two distinct divisions: the axial skeleton and the appendicular system.
The axial skeleton consists of the 80 bones along the central axis of the human body.
The axial skeleton functions to support and protect the organs of
the dorsal and ventral cavities and serves as a surface for the attachment
of muscles and parts of the appendicular skeleton.
The human skull is the part of the skeleton that supports the structures of the face and forms a cavity for the brain.
The neurocranium is comprised of eight bones: occipital, two temporal bones, two parietal bones, sphenoid, ethmoid, and the frontal bone.
The viscerocranium (face) includes these bones: vomer, 2 inferior nasal conchae, 2 nasals, maxilla, mandible, palatine, 2 zygomatics, and 2 lacrimals.
The orbit is the cavity or socket of the skull in which the eye and its appendages are situated.
The human skull has numerous holes known as foramina through which cranial nerves, arteries, veins, and other structures pass.
A suture is a type of fibrous joint (or synarthrosis) that only occurs in the skull (or cranium).
The paranasal sinuses (four, paired, air-filled spaces) surround the nasal cavity, and are located above and between the eyes, and behind the ethmoids.
A fontanelle is an anatomical feature on an infant's skull that allows its plates to be flexible to pass through the birth canal.
The hyoid, a horseshoe-shaped bone situated in the anterior of the neck, between chin and thyroid, aids tongue movement and swallowing.
The spine is made of vertebrae that link together to protect the spinal cord.
A vertebra consists of two parts: an anterior segment, or the vertebral body; and a posterior part, or the vertebral (neural) arch.
The vertebrae of the spinal column are divided into five regions: cervical, thoracic, lumbar, sacral, and coccyx.
The sternum or breastbone is a long, flat, bony plate connected to the rib bones via cartilage that forms the anterior section of the rib cage.
The ribs are long, curved bones that protect the lungs, heart, and other organs of the thoracic cavity.
A black eye (periorbital hematoma) is a generally mild injury caused by bruising around the eye commonly due to an injury to the face.
Cleft lip and cleft palate are variations of a type of clefting congenital deformity caused by abnormal facial development during gestation.
Nasal septum deviation (displacement) is a common physical disorder of the nose that may require corrective surgery.
TMJ syndrome is a common disorder that spans both neurology and dentistry, which manifests as acute or chronic pain in the jaw area.
Sinusitis, the inflammation of the paranasal sinuses, is a very common condition in the US with potentially dangerous complications.
An epidural, or epidural anesthesia, is a form of regional anesthesia involving injection of drugs into the epidural space.
Joint dislocations and rib cage fractures are painful but treatable injuries involving the axial skeleton.
Spina bifida is a developmental congenital disorder caused by the incomplete closing of the embryonic neural tube.
A disc herniation is a common injury caused by a tear in the fibrous ring of an intervertebral disc, allowing the central portion to bulge.
Abnormal curvatures of the spine include kyphosis, lordosis, retrolisthesis, and scoliosis.
A spinal fracture (or vertebral fracture) is a fracture affecting the bones of the spinal column.
The unfused appendicular skeleton is composed of the appendages (legs and arms) and their supporting girdles, totaling 126 bones.
The clavicle or collar bone is a long, curved bone on the upper portion of the shoulder that connects with the scapula and the sternum.
The scapula, or shoulder bone, is a flat, triangular bone that connects to the humerus and the clavicle.
The bone forming the upper arm is the humerus.
The forearm contains two bones, the radius and the ulna.
Each hand consists of 27 bones, divided between the wrist bones (carpals), the palm bones (metacarpals), and the finger bones (phalanges).
The ilium is the uppermost and largest bone of the pelvis.
The ischium forms the lower and posterior portion of the hip bones of the pelvis.
The pubis is the lowest and most anterior portion of the hip bones of the pelvis.
The false (greater) pelvis is larger and superior to the true (lesser) pelvis where the pelvic inlet is located.
The female pelvis has evolved to its maximum width for childbirth and the male pelvis has been optimized for bipedal locomotion.
The human pelvis has evolved to be narrow enough for efficient upright locomotion, while still being wide enough to facilitate childbirth.
The femur—the bone of the upper leg—is the longest bone in the human body and one of the strongest.
The patella (knee cap) is the bone between the fibula and femur.
The tibia and the smaller fibula bones comprise the lower leg and articulate at the knee and ankle.
The human ankle and foot bones include tarsals (ankle), metatarsals (middle bones), and phalanges (toes).
The arches of the foot are formed by the tarsal and metatarsal bones; they dissipate impact forces and store energy for the subsequent step.
Early in gestation, a fetus has a cartilaginous skeleton that becomes bone in the gradual process of endochondral ossification.
In osteoporosis, bone mineral density (BMD) is reduced and the integrity of bone proteins is altered, increasing the risk of fracture.
A clavicle fracture is a bone fracture in the clavicle or collarbone.
Though less common now, pelvimetry was once common as the assessment of the female pelvis for the successful delivery of a baby.
Patellofemoral pain syndrome is discomfort originating from the contact of the posterior of the patella (kneecap) with the femur.
Bone grafting is a surgical procedure that replaces missing bone in order to repair bone fractures.
Fractures commonly include the 5th metatarsal (a Jones fracture) or fractures of the distal third of one of the metatarsal (March fracture).
Flatfoot and crowfoot are medical conditions that appear as flat and high arches, respectively.
A hip fracture is a femoral fracture that occurs in the proximal end of the femur (the long bone running through the thigh) near the hip.
Cartilage is an avascular, flexible connective tissue located throughout the body that provides support and cushioning for adjacent tissues.
Chondrification is the process by which cartilage is formed from condensed mesenchyme tissue.
All the bones in the body can be described as long bones or flat bones.
The blood and nerve supply to bones are carried in Haversian canals that run along the long axis of bones.
The basic microscopic unit of bone is an osteon, which can be arranged into woven bone or lamellar bone.
Acid-base imbalances, including metabolic acidosis and alkalosis, can produce severe, even life-threatening medical conditions.
During fetal development, bone tissue is created through intramembranous ossification and endochondral ossification.
Secondary ossification occurs after birth at the epiphyses of long bones and continues until skeletal maturity.
Bone remodeling or bone turnover is the process of resorption followed by replacement of bone and occurs throughout a person's life.
Bone fractures are repaired through physiological processes in the periosteum via chrondroblasts and osteoblasts.
Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels.
Although bone initially forms during fetal development, it undergoes secondary ossification after birth and is remodeled throughout life.
Bones adapt to the muscle force loads placed on them, becoming thicker and stronger under stress and use and weaker and thinner when unused.
As individuals age, bone resorption can outpace bone replacement, which can lead to osteoporosis and fractures.
Osteomalacia (in adults) and rickets (in infants and children) are bone mineralization disorders caused by vitamin D deprivation.
Osteoporosis, the result of reduced bone mineral density, can lead to an increased risk for fractures.
Paget's disease is a chronic bone disorder that causes affected bones to become large and misshapen.
Advances in bone repair include osseointegration: the direct structural and functional connection between bone and an artificial implant.
Orthodontics is a dental specialty concerned with malocclusions caused by improperly sited teeth and/or problems with the mandible.
Bone scans are a special type of nuclear scanning test that is often used to find bone cancer or bone inflammation.
Abnormal production of growth hormone due to tumors on the pituitary or other genetic causes can cause pathological changes in growth.
Fibrous joints are also called fixed or immovable joints because they do not move.
A suture is a type of fibrous joint (synarthrosis) bound by Sharpey's fibers that only occurs in the skull (cranium).
Syndesmoses are slightly movable joints formed where an interosseous ligament joins two bones.
An interosseous membrane is a broad and thin plane of fibrous tissue that separates many of the bones of the body.
A gomphosis is a fibrous joint that binds the teeth to bony sockets in the bones of the maxilla mandible.
Cartilaginous joints connected by hyaline cartilage are termed synchondroses.
A symphysis is a secondary cartilaginous joint that is permanent and slightly movable.
A synovial joint or diarthrosis occurs at articulating bones to allow movement. It is distinguished by a surrounding synovial capsule.
Synovial joints are highly innervated but vascularized indirectly by nearby tissues.
Joints are cushioned by small fluid-filled sacs called bursae and stabilized by tough bands of fibrous connective tissue called tendons.
Tendons provide stability at joints.
Synovial joints allow an individual to achieve a wide range of movements.
There are six different types of synovial joint based on their shapes, each allowing a different kind of movement.
Movable joints are formed at the intersection of bones and are covered by cartilage, which allows them to move freely.
Aging is a common cause of chronic joint pain, as wear and tear from years of use results in inflammation and osteoarthritis.
Arthroplasty is a surgical procedure in which an arthritic or dysfunctional joint surface is replaced or repaired.
Arthroscopy is a minimally-invasive surgical procedure used in treating damage to the interior of a joint using a small incision and scope.
A strain is a tear in tendon fibers resulting from overstretching, while a sprain is an equivalent injury to a ligament.
Bursitis, the inflammation of bursae (small sacs) of synovial fluid, impedes the movement of muscles and tendons over joint bones.
A dislocated mandible or jaw occurs at the temporomandibular joint: the mandibular condyles and the temporal bone fail to align correctly.
Injuries to the rotator cuff, or a dislocated or separated shoulder are painful events that severely limit arm movements.
The elbow joint is subject to a number of injuries including tennis elbow, Little League elbow, and nursemaid's elbow.
The knee is particularly vulnerable to injury due to enormous twisting forces that it is subjected to especially during sports.
Rheumatoid arthritis is a chronic, systemic inflammatory disorder that affects many tissues and organs, but mainly attacks flexible joints.
Lyme disease, a tick-borne bacterial disorder, causes fever, headache, fatigue, joint pain, and a characteristic bull's-eye skin rash.
Ankylosing spondylitis is a chronic inflammatory, autoimmune disease that results in joint fusion in the vertebrae and the sacroiliac joint.