16.5 Musculoskeletal System
3 min read•june 18, 2024
The skeletal system forms the body's framework, providing support, protection, and movement. It's divided into the , which includes the and spine, and the , comprising limbs and their attachments.
Joints connect bones, allowing for flexibility and movement. The muscular system works in tandem with the skeleton, using muscles attached to bones via to create motion. This interaction enables our bodies to perform a wide range of movements.
Skeletal System
Axial vs appendicular skeleton
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- forms the central axis of the body
- Consists of the skull, , and rib cage
- Skull protects the brain and sensory organs (eyes, ears, nose)
- Vertebral column provides support and flexibility to the trunk (cervical, thoracic, lumbar, sacral, and )
- Rib cage protects vital organs in the chest cavity (heart, lungs)
- Appendicular skeleton consists of the bones of the limbs and their attachments to the axial skeleton
- attaches the upper limbs to the axial skeleton (, )
- Upper limbs include the , , , , , and (arms, wrists, hands)
- attaches the lower limbs to the axial skeleton (hip bones: , , and )
- Lower limbs include the , , , , , , and phalanges (legs, ankles, feet)
Joints for skeletal flexibility
- Joints are points where two or more bones meet, allowing for movement and flexibility in the skeleton
- Types of joints:
- connected by fibrous connective tissue permit little to no movement (sutures between cranial bones)
- connected by cartilage allow limited movement (intervertebral discs)
- are the most common and movable type, containing a synovial cavity filled with lubricating fluid
- Examples: ball-and-socket (hip, shoulder), hinge (elbow, knee), pivot (atlantoaxial ), and gliding (wrist, ankle) joints
- Joint structure includes:
- surrounds the joint and contains
- covers the ends of bones, reducing friction and absorbing shock
- are fibrous connective tissue that connects bones and stabilizes joints
- are fluid-filled sacs that reduce friction between bones, tendons, and muscles (knee, shoulder)
Bone remodeling and calcium homeostasis
- is the continuous process of bone formation and resorption
- are cells responsible for bone formation, depositing new bone matrix
- are cells that break down and resorb old bone tissue
- This process helps maintain in the body, regulating calcium levels in the blood
- Bone acts as a reservoir for calcium, releasing or storing it as needed to maintain proper levels
Muscular System
Muscle-bone interaction for movement
- Muscles are attached to bones via tendons
- Origin is the fixed attachment point of a muscle, typically proximal
- Insertion is the movable attachment point of a muscle, typically distal
- Muscle contraction occurs through the
- filaments pull on filaments, causing the to shorten
- Requires calcium ions () and ATP for cross-bridge cycling
- Types of muscle contraction:
- Concentric: muscle shortens, generating force (lifting a weight)
- Eccentric: muscle lengthens under tension (lowering a weight)
- Isometric: muscle generates force without changing length (holding a weight)
- Bones act as levers, with joints serving as fulcrums and muscles providing the force to move the levers
- Three classes of levers:
- First-class: fulcrum between effort and resistance (nodding the head)
- Second-class: resistance between effort and fulcrum (standing on tiptoes)
- Third-class: effort between fulcrum and resistance (lifting a weight with the elbow)
- Three classes of levers:
- work in opposition to each other, allowing for precise control and smooth movement
- Examples: biceps (flexor) and triceps (extensor) in the upper arm, quadriceps (extensor) and hamstrings (flexor) in the thigh
- is composed of muscle fibers, which are long, cylindrical cells containing multiple nuclei and contractile proteins
Key Terms to Review (70)
Actin: Actin is a globular protein that forms microfilaments, which are essential components of the cytoskeleton in eukaryotic cells. It plays a critical role in muscle contraction, cell movement, and maintaining the cell's shape by providing structural support. Actin exists in two forms: G-actin (globular actin) and F-actin (filamentous actin), which polymerizes to form the filaments that are crucial for various cellular processes.
Antagonistic muscle pairs: Antagonistic muscle pairs refer to pairs of muscles that work in opposition to each other to create movement at a joint. When one muscle in the pair contracts (the agonist), the other muscle relaxes (the antagonist), allowing for controlled movement and stabilization. This mechanism is essential for proper functioning of the musculoskeletal system, as it enables a range of motion and helps maintain posture.
Appendicular skeleton: The appendicular skeleton is the portion of the skeleton that includes the bones of the limbs and the supporting bones, such as the pelvis and shoulder girdles. This part of the skeleton is crucial for movement and interaction with the environment, as it supports the arms and legs that enable a wide range of motions and activities.
Articular capsule: An articular capsule is a fibrous structure that surrounds a synovial joint, providing stability and protection to the joint while allowing for a wide range of movement. This capsule is composed of two layers: an outer fibrous layer, which strengthens the joint, and an inner synovial membrane that secretes synovial fluid, nourishing the cartilage and lubricating the joint surfaces.
Articular cartilage: Articular cartilage is a smooth, white tissue that covers the ends of bones where they come together to form joints. This specialized connective tissue reduces friction between bones in a joint during movement and acts as a shock absorber, helping to distribute loads and protect the underlying bone from wear and tear. Its unique composition allows for flexibility and resilience, playing a crucial role in joint health and function.
Auditory ossicles: Auditory ossicles are the three small bones located in the middle ear that transmit sound vibrations from the eardrum to the inner ear. These bones are known as the malleus, incus, and stapes.
Axial skeleton: The axial skeleton is the central core of the human skeleton, consisting of 80 bones. It includes the skull, vertebral column, and thoracic cage, providing support and protection for the brain, spinal cord, and vital organs.
Axial Skeleton: The axial skeleton is the central part of the skeleton that supports the head, neck, and trunk, consisting of 80 bones in total. It includes the skull, vertebral column, and rib cage, forming a protective structure for vital organs like the brain, heart, and lungs. This skeletal system plays a critical role in maintaining posture and facilitating movement.
Ball-and-socket joint: A ball-and-socket joint is a type of synovial joint that allows for rotational movement in multiple directions, where a spherical head of one bone fits into a cup-like socket of another bone. This structure enables a wide range of motion, making it crucial for various movements in the musculoskeletal system, particularly in the limbs.
Bone remodeling: Bone remodeling is the continuous process of bone resorption and formation, allowing bones to adapt to stress, repair micro-damage, and maintain mineral homeostasis. This dynamic cycle involves the coordinated activity of osteoclasts, which break down bone tissue, and osteoblasts, which build new bone, ensuring that bones remain strong and healthy throughout a person's life.
Bursae: Bursae are small, fluid-filled sacs located throughout the body that act as cushions between bones and tendons or muscles around joints. These structures help reduce friction and allow for smoother movement of muscles and tendons over bones, playing a crucial role in the overall function of the musculoskeletal system.
Calcium homeostasis: Calcium homeostasis refers to the processes that maintain a stable level of calcium ions in the body, crucial for various physiological functions. This regulation is vital in the musculoskeletal system, where calcium plays a key role in bone formation, muscle contraction, and nerve signaling. Achieving balance involves the interplay of hormones and organs, ensuring that calcium levels neither rise too high nor drop too low.
Cardiac muscle tissue: Cardiac muscle tissue is a specialized type of muscle found only in the walls of the heart. It is responsible for the involuntary contractions that pump blood throughout the body.
Carpals: Carpals are a set of eight small bones that make up the wrist joint, connecting the hand to the forearm. These bones play a crucial role in providing stability and flexibility to the wrist, allowing for a wide range of motion in the hand. The carpals are arranged in two rows, each with four bones, and their unique structure helps facilitate the complex movements required for various hand functions.
Cartilaginous joints: Cartilaginous joints are connections between bones held together by cartilage. They allow more movement than fibrous joints but less than synovial joints.
Cartilaginous joints: Cartilaginous joints are a type of synarthrosis that allows little to no movement and are connected entirely by cartilage. This type of joint provides stability and support while also allowing for slight flexibility, making it essential in areas like the spine and ribcage where both rigidity and movement are necessary for function.
Cervical vertebrae: Cervical vertebrae are the seven vertebrae in the neck region of the spine, designated C1 to C7, that support the skull, allow for head movement, and protect the spinal cord. These vertebrae are unique in their structure, featuring smaller bodies compared to other vertebrae, along with transverse foramina that allow for the passage of blood vessels to the brain. Their design enables a wide range of motion and flexibility while providing essential support for the head.
Clavicles: Clavicles, commonly known as collarbones, are two elongated bones that connect the arms to the body, specifically linking the sternum (breastbone) to the scapula (shoulder blade). They play a crucial role in maintaining shoulder stability and facilitating arm movement while also serving as a protective barrier for underlying structures such as blood vessels and nerves.
Coccygeal Vertebrae: Coccygeal vertebrae are the small, fused bones that form the tailbone, located at the base of the vertebral column in humans. These vertebrae are a remnant of a tail found in other vertebrates and play a role in supporting pelvic organs and serving as an attachment site for various muscles and ligaments.
Concentric Contraction: A concentric contraction is a type of muscle contraction where the muscle shortens while generating force, allowing for movement against resistance. This kind of contraction is crucial during activities like lifting weights or performing push-ups, as it helps to overcome resistance and perform work. Understanding concentric contractions is essential for analyzing how muscles function during various physical activities and the overall biomechanics involved in movements.
Eccentric contraction: Eccentric contraction is a type of muscle contraction where the muscle lengthens while generating force, often occurring during the lowering phase of movements. This process plays a critical role in controlling movement and absorbing shock, making it essential for various physical activities, from everyday tasks to athletic performance.
Femur: The femur, commonly known as the thigh bone, is the longest and strongest bone in the human body, extending from the hip to the knee. It plays a crucial role in supporting the weight of the body during standing and walking, while also facilitating movement and stability within the musculoskeletal system.
Fibrous joints: Fibrous joints are connections between bones that are held together by dense connective tissue, primarily composed of collagen. These joints do not have a joint cavity and allow for little to no movement.
Fibrous Joints: Fibrous joints are a type of synarthrosis, meaning they are immovable joints where bones are connected by dense connective tissue. These joints play a vital role in providing stability and support to the skeleton, particularly in areas where movement is not necessary, such as the skull. They are categorized into three types: sutures, syndesmoses, and gomphoses, each serving specific functions in the body.
Fibula: The fibula is a long, thin bone located on the lateral side of the tibia in the lower leg. It plays a crucial role in providing stability to the ankle and supports the muscles of the lower leg. Although it is not weight-bearing like the tibia, it serves as an attachment point for various muscles and ligaments.
Gliding Joint: A gliding joint is a type of synovial joint that allows for limited movement in multiple directions, characterized by the sliding of flat or slightly curved bone surfaces over one another. These joints facilitate smooth movements, making them essential for activities that require flexibility and adaptability, like bending and twisting. Gliding joints are found in various areas of the body, contributing to the overall functionality of the musculoskeletal system.
Hinge joint: A hinge joint is a type of synovial joint that allows for movement primarily in one plane, functioning similarly to the hinge of a door. This design permits flexion and extension movements, making it crucial for various everyday activities, such as bending the elbow or knee. Hinge joints play a significant role in providing stability and support to the skeletal system while allowing for essential ranges of motion.
Humerus: The humerus is the long bone in the upper arm or forelimb, extending from the shoulder to the elbow. It plays a crucial role in connecting the shoulder joint to the forearm and is integral to a range of movements such as lifting, throwing, and pushing. The humerus also serves as an attachment point for muscles that facilitate these movements, making it essential for both locomotion and manipulation of objects.
Hyoid bone: The hyoid bone is a U-shaped bone located in the anterior neck. It supports the tongue and serves as an attachment point for muscles associated with swallowing and speech.
Ilium: The ilium is the largest and uppermost bone of the pelvis, playing a crucial role in supporting the trunk and connecting the spine to the lower limbs. It forms part of the hip bone and contributes to the structure of the pelvic cavity, providing attachment points for muscles and ligaments essential for movement and stability. This bone is significant for its involvement in weight-bearing activities and its protective role for internal organs located within the pelvic region.
Ischium: The ischium is one of the three main bones that make up the pelvis, located in the lower part of the hip bone. It plays a crucial role in supporting the body when sitting and serves as an attachment point for various muscles and ligaments, contributing to movement and stability of the lower body.
Isometric contraction: Isometric contraction is a type of muscle contraction where the muscle generates tension without changing its length. This means that during isometric contractions, the muscle fibers are activated and produce force, but there is no visible movement of the joint. This form of contraction is important for maintaining posture and stabilizing joints during activities.
Joint: A joint is a connection between two or more bones in the body that allows for movement and flexibility. Joints are essential components of the musculoskeletal system, facilitating various types of motion.
Ligaments: Ligaments are strong, flexible bands of connective tissue that connect bones to other bones at joints. They play a crucial role in stabilizing the skeletal structure, supporting the movement of joints, and providing necessary flexibility while preventing excessive movements that could lead to injuries.
Lumbar vertebrae: Lumbar vertebrae are the five large, weight-bearing vertebrae located in the lower back, numbered L1 to L5. They are designed to support the upper body and allow for a wide range of motion, including bending and twisting. Their robust structure helps protect the spinal cord while also providing flexibility and stability to the lumbar region.
Metacarpals: Metacarpals are the five long bones located in the hand, specifically between the carpal bones of the wrist and the proximal phalanges of the fingers. These bones play a vital role in hand structure and function, allowing for various movements such as gripping and manipulating objects. Each metacarpal is associated with a digit and contributes to the overall dexterity and strength of the hand.
Metatarsals: Metatarsals are the five long bones in the midfoot, connecting the ankle to the toes. These bones play a crucial role in providing structure and support to the foot, enabling movement and weight-bearing activities. Each metatarsal is numbered from one to five, starting with the big toe, and they work together with other bones in the foot to allow for balance and mobility during walking and running.
Muscle fiber: Muscle fiber is a specialized cell that makes up the muscle tissue responsible for movement in the body. These elongated cells are packed with myofibrils, which contain the contractile proteins actin and myosin, essential for muscle contraction. Muscle fibers come in different types, each adapted for specific functions such as endurance or power, highlighting their diverse roles in the musculoskeletal system.
Myofibrils: Myofibrils are long, thread-like structures found in muscle cells that are essential for muscle contraction. They are composed of repeating units called sarcomeres, which contain the proteins actin and myosin.
Myofilaments: Myofilaments are the filaments of myofibrils, constructed from proteins, primarily actin and myosin. They play a key role in muscle contraction within muscle fibers.
Myosin: Myosin is a type of motor protein that plays a critical role in muscle contraction and various cellular processes. It interacts with actin filaments to generate force and movement, making it essential for muscle tissue's ability to contract and relax. Myosin not only contributes to skeletal muscle movement but also has important functions in non-muscle cells, including cell division and intracellular transport.
Osteoblasts: Osteoblasts are specialized bone cells responsible for the formation and mineralization of bone tissue. They play a crucial role in the skeletal system by producing the bone matrix and facilitating the deposition of calcium and phosphate, essential for strong bones. Their activity is vital during growth, repair, and remodeling of bones throughout life.
Osteoclasts: Osteoclasts are specialized cells that break down bone tissue, playing a crucial role in the maintenance and remodeling of the skeletal system. They work in tandem with osteoblasts, which are responsible for bone formation, to maintain a balance between bone resorption and formation. This process is vital for regulating calcium levels in the body and ensuring overall bone health.
Patella: The patella, commonly known as the kneecap, is a small, flat, triangular bone located in front of the knee joint. It serves as a protective shield for the knee and plays a crucial role in facilitating the movement of the leg by improving the leverage of the thigh muscles during activities like walking, running, and jumping.
Pectoral girdle: The pectoral girdle, also known as the shoulder girdle, is a bony structure that connects the upper limb to the axial skeleton. It comprises two main bones, the clavicle and the scapula, which provide support and mobility to the shoulder region. This structure is essential for a range of movements and functions, including arm elevation and rotation, making it a critical component of the musculoskeletal system.
Pelvic girdle: The pelvic girdle is a ring-like bony structure located in the lower part of the trunk. It connects the spine to the femurs and supports the weight of the upper body when sitting or standing.
Pelvic Girdle: The pelvic girdle, also known as the hip girdle, is a bony structure that connects the vertebral column to the lower limbs. It consists of two hip bones (also called coxal bones) that meet at the pubic symphysis in the front and articulate with the sacrum at the back. This structure provides support for the weight of the upper body and serves as an attachment point for various muscles and ligaments that facilitate movement and stability of the lower body.
Phalanges: Phalanges are the bones that make up the fingers and toes in the human body. They play a crucial role in providing structural support and facilitating movement, allowing for a wide range of functions such as grasping and balance. Each finger has three phalanges, except for the thumb, which has two, while each toe also consists of three phalanges, except for the big toe that has two.
Pivot joint: A pivot joint is a type of synovial joint that allows for rotational movement around a single axis. This joint enables one bone to rotate around another, providing a limited range of motion primarily in the form of rotation. Key examples of pivot joints include the atlantoaxial joint in the neck, which allows for head rotation, and the proximal radioulnar joint, facilitating the twisting motion of the forearm.
Pubis: The pubis is one of the three bones that make up each half of the pelvis, located in the lower front part of the hip bone. It plays a crucial role in connecting the two sides of the pelvis and provides attachment points for various muscles and ligaments. The pubis also contributes to the structure of the pelvic cavity, which is essential for supporting internal organs and facilitating movement in the musculoskeletal system.
Radius: The radius is a line segment that connects the center of a circle or sphere to any point on its circumference or surface. In the context of the musculoskeletal system, the radius is one of the two long bones in the forearm, situated on the lateral side (thumb side) and plays a critical role in forearm movement, wrist stability, and overall arm function.
Sacral Vertebrae: Sacral vertebrae are a group of five fused vertebrae located at the base of the spine, forming the sacrum. This bony structure plays a vital role in connecting the spine to the pelvis, providing stability and support for the upper body while allowing for weight transfer to the lower limbs.
Sarcolemma: The sarcolemma is the cell membrane that encloses a muscle fiber (muscle cell). It plays a crucial role in the transmission of action potentials, initiating muscle contraction.
Sarcomere: A sarcomere is the basic contractile unit of striated muscle tissue, consisting of repeating units that extend from one Z line to another. It is crucial for muscle contraction and relaxation, as it contains the actin and myosin filaments that slide past each other to create force. Sarcomeres work together in a muscle fiber to facilitate movement and are essential in understanding how muscles function within the musculoskeletal system.
Scapulae: Scapulae, commonly known as shoulder blades, are flat, triangular bones located in the upper back that play a crucial role in the musculoskeletal system. They connect the humerus (the upper arm bone) to the clavicle (collarbone) and provide attachment points for various muscles that facilitate movement of the shoulder and upper limb. Their unique shape and position are essential for shoulder mobility and stability.
Skeletal muscle: Skeletal muscle is a type of striated muscle tissue that is primarily responsible for voluntary movements in the body. It is attached to bones via tendons and allows for the movement of the skeleton, playing a crucial role in locomotion, posture, and overall body movement. Skeletal muscle fibers are multinucleated and can vary in fiber type, which influences their function and metabolism.
Skeletal muscle tissue: Skeletal muscle tissue is a type of muscle that attaches to bones and enables voluntary body movements. It is characterized by its striated appearance and multinucleated cells.
Skull: The skull is a bony structure that forms the head in vertebrates, supporting the structures of the face and protecting the brain. It consists of 22 bones joined together by sutures.
Sliding Filament Model: The sliding filament model explains how muscles contract at the molecular level, specifically through the interaction between actin and myosin filaments within muscle fibers. In this process, myosin heads attach to binding sites on actin filaments and pull them inward, leading to muscle shortening and contraction. This model is essential for understanding how muscles produce force and movement in the musculoskeletal system.
Smooth muscle tissue: Smooth muscle tissue is a type of involuntary muscle found in the walls of internal organs such as the stomach, intestines, and blood vessels. Unlike skeletal muscle, it is not striated and contracts without conscious control.
Synovial fluid: Synovial fluid is a viscous, egg white-like substance found in the cavities of synovial joints, which serves to lubricate and cushion the joints during movement. This fluid plays a crucial role in reducing friction between the articular cartilage of synovial joints, thus facilitating smooth motion and maintaining joint health. Additionally, it acts as a shock absorber and provides essential nutrients to the cartilage.
Synovial joints: Synovial joints are freely movable joints found in the human body. They are characterized by a fluid-filled synovial cavity that reduces friction between articulating bones.
Synovial joints: Synovial joints are the most common and movable type of joint in the human body, characterized by a fluid-filled joint cavity that allows for a wide range of motion. These joints are enclosed by a synovial membrane, which secretes synovial fluid to lubricate and nourish the articular cartilage covering the ends of the bones. The structure and function of synovial joints play a crucial role in the overall flexibility and mobility of the musculoskeletal system.
Tarsals: Tarsals are a group of seven bones located in the hindfoot that connect the foot to the ankle. These bones play a crucial role in supporting body weight, facilitating movement, and providing stability during activities such as walking, running, and jumping. The tarsals work in conjunction with other bones in the foot and ankle to form the complex structure necessary for proper locomotion.
Tendons: Tendons are flexible but strong connective tissues that connect muscles to bones, playing a crucial role in the musculoskeletal system. They help transmit the force generated by muscles to bones, enabling movement and stability. Tendons are essential for joint function, allowing for coordinated motion and support during physical activities.
Thoracic cage: The thoracic cage is the bony structure surrounding the chest cavity, composed of the ribs, thoracic vertebrae, and sternum. It serves to protect vital organs such as the heart and lungs and supports respiratory function.
Thoracic vertebrae: Thoracic vertebrae are the twelve individual bones that make up the middle section of the vertebral column, located between the cervical and lumbar vertebrae. They play a crucial role in providing support for the rib cage, protecting the spinal cord, and facilitating movement and flexibility of the upper body.
Tibia: The tibia, commonly known as the shinbone, is the larger and stronger of the two bones in the lower leg, located medially to the fibula. It plays a crucial role in supporting body weight, providing stability to the leg, and facilitating movement at the knee and ankle joints. As part of the musculoskeletal system, the tibia connects with several other bones and serves as an important attachment point for muscles and ligaments that enable walking and running.
Ulna: The ulna is one of the two long bones in the forearm, located opposite the radius and extending from the elbow to the wrist. It plays a crucial role in forming the elbow joint and is essential for the movement and stability of the arm, particularly during activities like lifting and throwing.
Vertebral column: The vertebral column, also known as the spine or backbone, is a bony structure that supports the body and protects the spinal cord in vertebrates. It consists of individual vertebrae stacked on top of each other, allowing for flexibility and movement while maintaining stability. The vertebral column plays a critical role in the musculoskeletal system, connecting various parts of the skeleton and serving as an attachment point for muscles and ligaments.