Name: human skeleton: bones, cells, and disease
Uploaded: 2019-03-11T09:21:29.000Z
Duration: 1 min 2 s
Channel: JoVE

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Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-2

What is the Skeletal System?

The human skeleton is composed of bones that not only come together to provide a rigid framework, giving form to the body, but also allow movement, as they are attached to muscles through tendons.

One of the main divisions, the axial skeleton, is arranged around the central axis of the body. While there are a number of bones in this section of the upper body, including the ossicles of the middle ear, most protect vital organs from damage.

For example, the skull surrounds the brain, and the vertebral column arches around the spinal cord, shielding the central nervous system. Other organs, such as the heart and lungs, are safeguarded by the sternum and rib cage.

The other division, the appendicular skeleton, consists of bones that support and move the appendages, the hands and arms, as well as the feet and legs, and the pectoral and pelvic girdles.

what is the skeletal system?

<h4>Overview</h4>

The adult human skeleton comprises 206 bones that are connected through cartilage, tendons, and ligaments. The skeleton provides a rigid framework for the human body, protects internal organs, and enables movement and locomotion. The human skeletal system consists of the axial and appendicular skeletons. Bone tissue is continuously built up and chewed away by specialized bone cells which are essential to overall health. Dysregulated bone cells and incorrect levels of chemical compounds in the blood lead to bone diseases.

<h4>Axial Skeleton</h4>

The axial skeleton consists of 80 bones and is divided into three regions: the skull, the vertebral column, and the rib cage. The upper portion of the skull&mdash;the cranium&mdash;consists of eight bones that enclose the brain, while the lower part consists of 14 bones. The vertebral column consists of 33 vertebrae: seven cervical, 12 thoracic, five lumbar, five fused sacral vertebrae, and four fused coccygeal vertebrae.

The rib cage adds stability to the vertebral column and also protects the lungs and heart. It consists of 12 pairs of ribs, which attach to the thoracic vertebra via the costovertebral joint. The anterior portion of the rib cage attaches to the sternum&mdash;the flat bone at the center of the front of the chest&mdash;via the costal cartilages. The first seven ribs on each side are known as true ribs, as their cartilages attach directly to the sternum. Ribs eight through 12 are called false ribs because they do not directly attach to the sternum. However, ribs eight through 10 join with the sternum via the costal cartilages of the ribs above. Contrarily, ribs 11 and 12 are referred to as floating ribs since they are only attached to the vertebral column in the back but have no connection to the sternum at all.

<h4>Appendicular Skeleton</h4>

The appendicular skeletal system consists of the 126 bones of the limbs and girdles as they are appended to the axial skeleton. The appendicular skeletal system is made up of several different types of bones.

<h4>Bone Tissue and Cells</h4>

Bone is known as osseous tissue. The cells of osseous tissue are dispersed in the matrix&mdash;the substance that provides strength and hardness to bones. The matrix consists of organic components&mdash;mainly collagen&mdash;and inorganic components consisting of crystallized mineral salts such as calcium phosphate, calcium hydroxide, and magnesium fluoride.

There are three major types of bone cells&mdash;osteoblasts, osteoclasts, and osteocytes. The osteoblasts and osteoclasts have opposite functions. Osteoblasts build up the bone matrix, whereas osteoclasts chew it up. Both functions continue throughout life, and both are essential for good health. Building up bone is important to keep bones strong; chewing up bone allows maintenance of calcium levels in the bloodstream (which is vital for the health of other organs, such as the heart).

Osteocytes are cells which have matured from osteoblasts and are now surrounded by matrix. Osteocytes communicate with the blood through microscopic channels in the bone, sensing the levels of calcium and other minerals in the blood. They then control the functions of the osteoblasts and osteoclasts by secreting substances that affect the activity of these cells.

<h4>Bone Diseases</h4>

Many diseases of the skeletal system have a common feature: weak bones due to poor mineral content. Osteoporosis, for example, is characterized by decreased bone mineral density. It occurs most commonly in postmenopausal women but can occur in men and premenopausal women as well. In this disease, there is more osteoclast than osteoblast activity. Patients with osteoporosis have greatly increased risk of fractures, especially of the spinal column, hip, and wrist.

Another widespread bone disease is renal osteodystrophy. This disease is a part of a larger condition known as mineral and bone disorder in chronic kidney disease. The kidneys perform many functions, including regulation of calcium, phosphorus, and vitamin D, which are all critical to bone health. When the kidneys are not functioning correctly, such as in diabetic kidney disease, the bones may become weakened and painful, and the joints may become painful as well.

Overview

The adult human skeleton comprises 206 bones that are connected through cartilage, tendons, and ligaments. The skeleton provides a rigid ...

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KEY TERMS AND CONCEPTS

human skeleton: bones, cells, and disease

The human skeleton is a living framework made of 206 bones in adults. Bones connect with cartilage, tendons, and ligaments. This system gives the body support, protects organs, and helps with movement and locomotion.

The skeleton has two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton has 80 bones and includes the skull, the vertebral column, and the rib cage. The cranium, or upper skull, has eight bones that enclose the brain, while the lower part of the skull has 14 bones. The vertebral column has 33 vertebrae. These include seven cervical, 12 thoracic, five lumbar, five fused sacral, and four fused coccygeal vertebrae.

The rib cage adds stability to the vertebral column and protects the lungs and heart. It has 12 pairs of ribs that attach to the thoracic vertebrae at the costovertebral joint. The front of the rib cage connects to the sternum, the flat bone in the center of the chest, through costal cartilages. The first seven ribs are true ribs because their cartilages attach directly to the sternum. Ribs eight through 12 are false ribs. Ribs eight through 10 connect to the sternum through the cartilages of the ribs above them, while ribs 11 and 12 are floating ribs because they do not connect to the sternum at all.

The appendicular skeleton has 126 bones. It includes the bones of the limbs and the girdles that attach them to the axial skeleton. Bone tissue is also called osseous tissue. Its cells sit in a matrix, which is the material that gives bone strength and hardness. The matrix contains organic material, mainly collagen, and inorganic mineral salts such as calcium phosphate, calcium hydroxide, and magnesium fluoride.

Bone cells have different jobs. Osteoblasts build bone matrix, while osteoclasts break it down. Both actions continue throughout life and are important for health. Building bone helps keep bones strong. Breaking down bone helps maintain calcium levels in the bloodstream, which is important for organs such as the heart. Osteocytes are mature bone cells that come from osteoblasts. They sit inside the matrix and communicate with the blood through tiny channels in bone. They sense calcium and other mineral levels and help control osteoblast and osteoclast activity by releasing substances that affect these cells.

Problems in bone cell balance or mineral levels can lead to bone disease. Osteoporosis is a common example. It is marked by low bone mineral density and more osteoclast activity than osteoblast activity. It occurs most often in postmenopausal women, but it can also occur in men and premenopausal women. People with osteoporosis have a much higher risk of fractures, especially in the spine, hip, and wrist.

Renal osteodystrophy is another widespread bone disease. It is part of mineral and bone disorder in chronic kidney disease. The kidneys help regulate calcium, phosphorus, and vitamin D, and these are all needed for bone health. When the kidneys do not work properly, such as in diabetic kidney disease, bones may become weak and painful, and the joints may hurt as well.

Human Skeleton: Bones, Cells, and Disease

The human skeleton is a living framework made of 206 bones in adults. Bones connect with cartilage, tendons, and ligaments. This system gives the body support, protects organs, and helps with movement and locomotion. The skeleton has two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton has 80 bones and includes the skull, the vertebral column, and the rib cage. The cranium, or upper skull, has eight bones that enclose the brain, while the lower part of the skull...

bone structure

Inside a Long Bone

Inside a long bone, osseous tissue is organized into two main types: cortical bone and cancellous bone. A femur is a clear example of this structure. The bone also includes outer coverings and inner spaces that support growth, repair, and blood cell production. Cortical bone, also called compact bone, forms the dense outer layer along the diaphysis, or shaft. It is covered by the periosteum, a membrane with connective tissue, capillaries, and nerves. Beneath the cortical layer is the medullary...

joints

Types of Joints in the Human Body

Joints are the places where adjacent bones connect. They are also called articulations or articular surfaces. Joints help the body move and stay stable. Joints can be classified by structure or by function. Structural classification depends on the material that forms the joint and whether there is a space between the bones. By structure, joints are fibrous, cartilaginous, or synovial. Fibrous joints are connected by fibrous tissue and have no cavity between the bones. Because of this, they do...

bone remodeling

How Hormones Control Bone Turnover

Bone turnover is a continuous process in which old bone is broken down and new bone is built. Osteoclasts carry out bone resorption, and osteoblasts carry out bone formation. In adults, this balanced cycle helps maintain bone mass and calcium homeostasis. Mechanical stress can also stimulate turnover as part of normal maintenance and repair. Parathyroid hormone, or PTH, helps control blood calcium levels by increasing bone resorption when calcium is low. It is released from the parathyroid...

skeletal muscle anatomy

Muscle Fibers, Tendons, and Contraction

Skeletal muscle moves the body by pulling on bones through tendons. Tendons are the connective tissue that attaches skeletal muscle to bones. When skeletal muscles contract, they create voluntary movement. Skeletal muscle is wrapped in layers of connective tissue. The outer layer is the epimysium, which helps protect the muscle. Beneath it, the perimysium surrounds and groups fasciculi, which are bundles of skeletal muscle cells called myocytes. These cells are also called skeletal muscle...

classification of skeletal muscle fibers

Skeletal Muscle Fiber Speed and Energy

Skeletal muscle fibers can be grouped by how fast they contract and how they make ATP, the energy cells use for movement. These differences also shape their physical features. Most human muscles contain all three fiber types, but in different amounts. Slow oxidative fibers, also called slow-twitch fibers, appear red because they have many capillaries and high levels of myoglobin, an oxygen-storing protein. They also contain more mitochondria, which make ATP through oxidative phosphorylation,...

muscle contraction

Nerve Signals That Trigger Muscle Contraction

Nerve signals trigger muscle contraction in both skeletal and smooth muscle, but the two muscle types use different control systems. In skeletal muscle, the signal begins at the motor end plate, which is the synapse between a motor neuron and a muscle fiber. In smooth muscle, contraction is controlled by the autonomic nervous system and happens without conscious control. In skeletal muscle, motor nerve terminals release acetylcholine. This neurotransmitter binds to receptors on the sarcolemma,...

cross-bridge cycle

Calcium Control in Muscle Contraction

Calcium control in muscle contraction depends on ATP, motor neurons, and the sliding action of actin and myosin. As a muscle contracts, the thin and thick filaments overlap more, and the sarcomere, which is the contractile unit of the muscle, becomes shorter. This process uses energy from ATP and happens in a repeating cycle at the molecular level. Myosin drives the movement of actin through a cross-bridge cycle. When ATP attached to the myosin head is hydrolyzed to ADP, myosin shifts into a...

motor units

How Motor Units Control Muscle Movement

Motor units control skeletal muscle movement. A motor unit includes one efferent motor neuron, which carries signals away from the central nervous system, and all of the muscle fibers it innervates. A single motor neuron can connect with multiple muscle fibers, but each muscle fiber is innervated by only one motor neuron. Lower motor neurons are the efferent neurons that control skeletal muscle, the most abundant type of muscle in the body. Their cell bodies are found in the spinal cord or...

the spinal cord

Spinal Cord Structure and Dermatomes

The spinal cord is the main nerve pathway of the central nervous system. It carries sensory signals from the body to the brain and motor signals from the brain to the body. It begins at the foramen magnum, the opening at the base of the skull, and extends to the level of the first or second lumbar vertebra. In cross-section, the spinal cord is cylindrical and contains both gray matter and white matter. The central canal lies in the middle and is a remnant of the lumen of the primitive neural...

nociception

Pain Signaling and Inflammation

Pain signaling begins when the body detects a harmful stimulus. Sharp objects, open flames, and corrosive chemicals can trigger this response. Sensory receptors called nociceptors, which sit on nerve endings, detect these noxious stimuli and use ion channels to turn them into electrical signals. Those electrical signals travel through sensory neurons to the brain, where they are experienced as pain. This warning system helps an organism avoid damage and stay safe. Pain is therefore an...

key terms and concepts

Explore the human skeleton, including axial and appendicular bones, bone cells, and common bone diseases like osteoporosis and renal osteodystrophy.

Human Skeleton: Bones, Cells, and Disease | JoVE K12

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Human Skeleton: Bones, Cells, and Disease

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