Anatomy and Physiology 1 - The Skeletal System

Introduction to the Skeletal System The skeletal system is a complex system that provides support, protection, and movement for the body. It is composed of bones, cartilage, and ligaments that work together to maintain the body's structure and function. Functions of the Skeletal System The skeletal system has several important functions, including: Supporting and giving shape to the body Protecting internal organs Helping to make movements possible when bones at moveable joints are pulled by muscles Storing calcium Regulating calcium storage through hormones such as calcitonin and parathyroid hormone “The skeletal system is a dynamic system that is constantly being remodeled and repaired to maintain its function and structure.” Classification of Bones There are five types of bones in the human body: Long bones: have a greater length than width and are slightly curved for strength Short bones: are cube-shaped and almost equal in length and width Flat bones: are thin and have two almost parallel plates of compact bone Irregular bones: have complex shapes and cannot be put into any other category Sesamoid bones: are small, rounded bones found in joints that develop in certain tendons where there is friction, tension, and stress Structure of Long Bones The structure of long bones includes: Component Description Diaphysis the shaft of the bone, a hollow tube of hard compact bone Medullary cavity the hollow area inside the diaphysis that contains yellow bone marrow Epiphyses the ends of the bone, made of spongy bone that contains red bone marrow Articular cartilage covers the epiphyses and functions as a cushion Periosteum a strong membrane covering the bone everywhere except at joint surfaces Endosteum a membrane lining the medullary cavity Microscopic Structure of Bones The microscopic structure of bones includes: Compact bone: has a dense, compact structure with a calcified matrix arranged in multiple layers or rings called concentric lamellae Spongy bone: has a spongy, porous structure with a network of open spaces and trabeculae Osteons: the structural unit of compact bone, consisting of a central canal surrounded by concentric layers of calcified bone matrix Haversian canals: allow the passage of blood vessels, lymphatic vessels, and nerve fibers Bone Development Bone development occurs through two main processes: Intramembranous ossification: the development of bone from a fibrous membrane Endochondral ossification: the replacement of hyaline cartilage with bone Factors Regulating Bone Growth Bone growth is regulated by several factors, including: Parathyroid hormone: acts to increase the overall availability of calcium ions in the blood Calcitonin: inhibits osteoclasts and increases the rate of calcium loss in urine Growth hormone: increases osteoblast activity leading to bone growth Sex hormones: increase bone growth dramatically during puberty Vitamins: such as vitamin D, vitamin C, vitamin A, vitamin K, and vitamin B are necessary for bone growth Composition of the Human Skeleton The human skeleton is composed of two main branches: Axial skeleton: includes 80 bones and consists of the skull, spine, thorax, and hyoid bone Appendicular skeleton: includes 126 bones and consists of the upper and lower extremities, including the shoulder and hip girdles Axial Skeleton The axial skeleton includes: Component Description Skull consists of 8 bones that form the cranium, 14 bones that form the face, and 6 tiny bones in the middle ear Vertebral column consists of 33 vertebrae that provide support and protection for the spinal cord Ribcage consists of 24 ribs that provide protection for the heart and lungs Sternum a long, flat bone that connects the ribs and provides attachment for the diaphragm Hyoid bone a small, U-shaped bone that supports the tongue and provides attachment for muscles The thoracic cage is the skeletal part of the thorax, which refers to the entire chest cavity. It is a bony enclosure made up of the sternum, costal cartilage, ribs, and bodies of the thoracic vertebrae. The thoracic cage protects the thoracic and superior abdominal cavities and supports the bones of the shoulder girdle and upper limbs. Bones of the Thorax The bones of the thorax include: 12 pairs of ribs The sternum (breastbone) The thoracic vertebrae The ribs are classified into three types: True ribs (pairs 1-7): attached to the sternum by costal cartilage False ribs (pairs 8-10): attached to the cartilage of the seventh pair Floating ribs (pairs 11-12): not attached to any costal cartilage Vertebrae “The vertebrae are bones that protect the spinal cord. The nerves radiate out from the spinal cord and are named for the vertebrae they radiate from.” The vertebral column is divided into five regions: Region Description Cervical Neck region Thoracic Chest region Lumbar Lower back region Sacrum Five fused vertebrae Coccyx Tailbone Appendicular Skeleton The appendicular skeleton consists of: Limb girdles (hip and shoulder bones): attach the legs and arms to the axial skeleton Limbs (legs and arms) Hands and feet Girdle Limbs The girdle bones connect the upper and lower extremities to the axial skeleton. There are two types of girdles: Pectoral girdle: attaches arm bones to the axial skeleton Pelvic girdle: attaches leg bones to the axial skeleton Upper Limbs - Arms The main function of the upper limbs is movement. The bones of the upper limb include: Humerus Radius and ulna Carpals Metacarpals Phalanges Lower Limbs - Legs The main function of the lower limbs is movement. The bones of the lower limb include: Femur Patella Tibia and fibula Tarsals Metatarsals Phalanges Joints “A joint is the place where two or more bones attach to each other.” The types of joints are: Diarthroses (free movement) Synarthroses (no movement) Amphiarthroses (slight movement) Types of Joints The joints can be classified into three types: Type Description Example Fibrous Bones held by fibrous tissue Skull and pelvis bones Cartilaginous Bones held by cartilage Vertebrae and ribs Synovial Bones held by dense irregular connective tissue Knee, fingers, and elbow Types of Diarthrosis Joints The types of diarthrosis joints are: Ball-and-socket joints (rotation): shoulder and hip joints Hinge joints (angular): fingers, knees, elbows, and toes Pivot joints (rotation): elbow Saddle joints (gliding): wrist joints Condyloid joints (angular): between the radius and carpals Planar joints (gliding): between the carpals or tarsals Joint Movements The types of joint movements are: Flexion: reduces the angle, as in bending the elbow Extension: increases the angle, as in straightening the elbow Abduction: moves a part away from the midline Adduction: moves a part toward the midline Rotation: spins one bone relative to another Circumduction: moves the distal end of a bone in a circle, proximal end relatively stable Tendons and Ligaments A tendon is a fibrous connective tissue that attaches muscle to bone. A ligament is a fibrous connective tissue that attaches bone to bone, and usually serves to hold structures together and keep them stable. Introduction to Bones and Cartilage Bones can be classified into two main categories: axial bones and appendicular bones. Axial bones are found in the head and torso, making up the spine, rib cage, and skull. Appendicular bones make up our appendages or limbs, including the arms and legs, as well as the pelvis and shoulders. Types of Bones Bones can also be classified by shape, being either: Long bones: longer than they are wide, like the ones in our limbs Short bones: cube-like, found in the ankles and wrists Flat bones: thin and often curved, like the sternum and shoulder blades Irregular bones: complicated shapes that don't fit into the other three categories, like vertebrae and hip bones Functions of Bones The main functions of bones are: Support: the rest of the body hangs on the skeleton, supported by the bones Protection: organs are protected by bones, like the heart within the ribcage Movement: bones act as levers that allow us to perform physical tasks Mineral storage: bones store minerals like calcium and phosphate, which can be released into the bloodstream as necessary Fat storage: bones store fat, which can be used for energy Hormone production: bones produce hormones, which regulate various bodily functions Blood cell formation: bones produce blood cells, which are essential for carrying oxygen and fighting infections Composition of Bones Bones are made up of several types of tissue, including: Bone tissue: the main component of bones Nervous tissue: found in the nerves that pass through the bones Connective tissue: found in the periosteum and endosteum Cartilage: found in the joints and at the ends of bones Blood vessels: found in the medullary cavity and periosteum The composition of bones can be broken down into: Component Description Compact bone dense, smooth outer layer of bone Spongy bone inner layer of bone, filled with open spaces and bone marrow Bone marrow tissue found in the medullary cavity, responsible for producing blood cells Periosteum outer membrane that covers the bone, made up of an outer fibrous layer and an inner osteogenic layer Endosteum inner membrane that lines the medullary cavity and covers the spongy bone Microscopic Anatomy of Bones At the microscopic level, bones are made up of several types of cells, including: Osteogenic cells: stem cells that actively divide and differentiate into other types of cells Osteoblasts: cells that secrete the bone matrix, responsible for bone growth Osteocytes: mature bone cells that monitor and maintain the bone matrix Bone lining cells: flat cells found on the surface of the bone, which help maintain the matrix Osteoclasts: large cells with multiple nuclei that break down bone, releasing minerals into the bloodstream “The process of bone breakdown and rebuilding is called bone remodeling, and it is essential for maintaining the health and strength of bones.” Structure of Compact Bone Compact bone is made up of osteons, which are cylindrical units with open canals at the center. Each osteon is made up of: Lamellae: hollow tubes that are arranged like the rings of a tree trunk Collagen fibers: fibers that run in a specific direction, with crystals of bone salts in between Central canal: the open region at the center of the osteon, which contains blood vessels and nerve fibers Lacunae: tiny gaps that are filled with osteocytes Canaliculi: tiny canals that connect the lacunae and allow for the exchange of nutrients and waste products The structure of compact bone can be broken down into: Component Description Osteon cylindrical unit with open canal at the center Lamella hollow tube that is arranged like the rings of a tree trunk Collagen fiber fiber that runs in a specific direction, with crystals of bone salts in between Central canal open region at the center of the osteon, which contains blood vessels and nerve fibers Lacuna tiny gap that is filled with osteocytes Canaliculus tiny canal that connects the lacunae and allows for the exchange of nutrients and waste products The bone matrix is composed of two main components: organic and inorganic parts. The organic part, also known as osteoid, is made up of ground substance and collagen fibers. These materials are secreted by osteoblasts and contribute to the structure, flexibility, and tensile strength of the bone. “The ground substance is a gel-like material that fills the space between cells and fibers, providing a medium for the exchange of nutrients and waste products. The collagen fibers are long, thin fibers that provide strength and flexibility to the bone.” The inorganic components of the bone matrix include hydroxyapatites, which are needle-like crystals of calcium phosphate that surround the collagen fibers. These crystals are responsible for the hardness of the bone. Bone Strength and Durability The combination of organic and inorganic components in the bone matrix allows bones to be durable and strong without being brittle. The following table summarizes the key properties of bones: Property Description Tensile strength The ability of the bone to resist stretching or pulling forces Compression strength The ability of the bone to resist squeezing or compressing forces Flexibility The ability of the bone to bend or flex without breaking Hardness The ability of the bone to resist scratching or abrasion Some key features of bones include: High tensile strength: bones are able to resist tension and compression forces, making them almost as strong as steel Flexibility: bones are able to bend and flex without breaking, allowing for a range of motion and movement Durability: bones are able to withstand the stresses and strains of daily life, making them a vital component of the human skeleton Bone Formation The process of bone formation involves the combination of organic and inorganic components to create a strong and durable bone matrix. This process is mediated by osteoblasts, which secrete the ground substance and collagen fibers that make up the osteoid. The hydroxyapatites are then deposited into the osteoid, creating a hard and rigid bone matrix. Introduction to the Skeletal System The skeletal system is comprised mainly of bones, around 206 of them in an adult, as well as cartilage, joints, and ligaments, which altogether make up around 20% of a person's body mass. Axial Skeleton The axial skeleton is made up of the skull, vertebral column, and thoracic cage. Skull The skull is a fascinating structure made of 22 different bones. “The cranial bones are the ones that protect the brain, while the facial bones give structure to the face. The cranial bones are connected at serrated lines called sutures. The main cranial bones are:” Frontal bone Parietal bones (2) Occipital bone Temporal bones (2) Sphenoid bone Ethmoid bone The sutures that connect the cranial bones have specific names: Coronal suture Sagittal suture Lamboid suture Squamous suture Occipitomastoid suture Vertebral Column The vertebral column, also called the spinal column or simply the spine, is comprised of 26 irregular bones that come together to form a flexible structure in a curvy S shape. The vertebral column can be divided into five sections: Cervical vertebrae (7) Thoracic vertebrae (12) Lumbar vertebrae (5) Sacrum (5 fused vertebrae) Coccyx (4 fused vertebrae) The main ligaments that keep the vertebral column together are: Anterior longitudinal ligament Posterior longitudinal ligament There are also intervertebral discs that act as shock absorbers between each vertebra. Vertebral Structure Each vertebra has a body and a vertebral arch, with a hole called the vertebral foramen. The vertebral arch is made of two pedicles and two laminae, with various processes that project from them, including: Spinous process Transverse processes (2) Superior and inferior articular processes Thoracic Cage The thoracic cage is essentially comprised of the sternum and the ribs, as well as costal cartilage. The sternum is a flat bone made from three smaller bones that have fused together: Manubrium Body Xiphoid process There are 12 pairs of ribs that project from the vertebrae, with the first 7 pairs attaching directly to the sternum via costal cartilage. Appendicular Skeleton The appendicular skeleton is mainly made up of the limbs, but also includes other components such as the pectoral girdle and pelvic girdle. Pectoral Girdle The pectoral girdle is comprised of the clavicle and the scapula, which together give structure to the shoulder and attach the upper limbs to the axial skeleton. The clavicle has a sternal end and an acromial end, while the scapula is a thin, flat bone with three borders: Superior border Medial border (or vertebral border) Lateral border (or axillary border) Upper Limb The upper limb consists of the arm, forearm, and hand. The arm contains the humerus, a typical long bone with various tubercles and grooves. The forearm contains two bones: the radius and the ulna. The hand contains many separate bones, including: Carpals (8 short bones in the wrist) Metacarpals (5 bones in the palm) Phalanges (14 bones in the fingers, with 3 phalanges per finger except for the thumb, which has 2)## The Pelvis and Lower Limb The pelvis is a girdle that provides far less mobility and far more stability than other parts of the skeleton. It starts at the sacrum and continues with two hip bones, which are made of three separate bones at birth: the ilium, isum, and pubis. These bones fuse to become one by adulthood. The Lower Limb The lower limb contains very thick bones, allowing us to run and jump effectively. The thigh is made of a single bone called the femur, which is the largest bone in the body. The femur has several distinct features, including: The head with a small pit called the fobia capitus The greater and lesser trochanter The intertrochanteric crest The gluteal tuberosity The linea aspera The medial and lateral condyle The epicondyle The lateral condyle The intercondylar eminence The tibial tuberosity The anterior border The medial malleolus The fibular notch The fibula is much thinner, with its head and lateral malleolus. The Foot The foot is similar to the hand, with the following components: The tarsus, made of seven bones called tarsals The talus and calcaneus make up the ankle The cuboid, navicular, and medial, intermediate, and lateral cuneiform bones The metatarsus, with five long metatarsals (numbered 1 through 5) The phalanges, with 14 phalanges (three per toe, except two for the big toe, also known as the hallux) Definition of Joints “A joint is a structure that connects two or more bones and allows for movement and mobility of the skeleton.” The following table summarizes the bones of the lower limb: Bone Description Femur The largest bone in the body, making up the thigh Fibula A thinner bone, with its head and lateral malleolus Tarsals Seven bones making up the tarsus, including the talus and calcaneus Metatarsals Five long bones making up the metatarsus Phalanges 14 bones making up the toes, with three per toe except two for the big toe Introduction to Joints Joints are found where bones meet, and they allow for a variety of motion in the human body. There are two ways to classify joints: by their structure or by their function. Classification by Function If classified by function, joints can be categorized into three types based on their mobility: Synarthrosis: immovable joints Amphiarthrosis: slightly movable joints Diarthrosis: freely movable joints Classification by Structure If classified by structure, joints can be categorized into three types: Fibrous joints: tend to be immovable Synovial joints: tend to be freely movable Cartilaginous joints: exhibit a range of mobilities Fibrous Joints Fibrous joints are characterized by a lack of joint cavity and are connected by dense fibrous connective tissue. There are three types of fibrous joints: Sutures: found in the skull, contain interlocking fibers of connective tissue Syndesmosis: bones are connected only by ligaments, which are bands of fibrous tissue Gomphosis: a peg-in-socket type of joint, found between a tooth and its alveolar socket “A suture is a type of fibrous joint that is found in the skull, where interlocking fibers of connective tissue connect the bones.” Cartilaginous Joints Cartilaginous joints are connected by cartilage and lack a joint cavity. There are two types of cartilaginous joints: Synchondrosis: contain hyaline cartilage, found in the epiphyseal plate of long bones in children Symphysis: made of fibrocartilage, found between vertebrae and in the pelvis Synovial Joints Synovial joints are characterized by a joint cavity filled with synovial fluid, which allows for substantial mobility. The structure of synovial joints includes: Articular cartilage: covers each opposing bone surface, protecting the ends of the bones Joint cavity: contains synovial fluid, which acts as a lubricant and reduces friction between the layers of cartilage Synovial membrane: together with the fibrous layer, comprises the articular capsule Types of Motion Synovial joints allow for various types of motion, including: Nonaxial movement: slipping movements Uniaxial movement: movement in one plane Biaxial movement: movement in two planes Multi-axial movement: movement in all three planes of three-dimensional space The following table summarizes the types of motion: Type of Motion Description Gliding one flat bone surface slips over another Angular the angle between two bones changes Rotation a bone turns around its own axis Special Movements There are also special movements that don't fit into the above categories, including: Supination and pronation: movement of the radius around the ulna in the forearm Dorsiflexion and plantarflexion: movement of the foot Protraction and retraction: movement of the mandible Terminology The following terminology is used to describe the types of motion: Abduction: movement of a limb away from the midline of the body Adduction: movement of a limb towards the midline of the body Circumduction: making circles with a limb Rotation: turning of a bone around its own axis The following table summarizes the terminology: Term Description Abduction movement away from the midline Adduction movement towards the midline Circumduction making circles with a limb Rotation turning around its own axis Introduction to Joints Skeletal joints determine movement of the body and its limitations. As artists, it is essential to learn about synovial joints, such as the shoulder and knee, because they move. Fibrous joints, on the other hand, have limited movement or no movement at all. Types of Synovial Joints There are 6 types of synovial joints, each with different shapes and allowing various movements. The 6 types are: Articular Hub Ball and Socket Elliptical Saddle Plane Definitions “A synovial joint is a type of joint that allows for movement and is characterized by a space between the bones that is filled with synovial fluid. A fibrous joint is a type of joint that has limited or no movement and is characterized by a layer of fibrous tissue that connects the bones.” Hinge Joint The hinge joint is a simple joint that allows movement only on one axis. It is a structure that prevents rotation and allows for flexion and extension. The bone head wraps around the other cylindrical head, allowing for stable rotation. An example of a hinge joint is the elbow. Pivot Joint The pivot joint also allows for rotation on a single axis, but it rotates along a long axis. A cylindrical bone fits into a ring of bones and ligaments, allowing for rotation. An example of a pivot joint is the ulnar radio joint just below the elbow. Ball and Socket Joint The ball and socket joint is the most versatile joint, allowing for movement in all axes, including bending, extending, abduction, adduction, rotation, and circumduction. Two examples of ball and socket joints are the hip and shoulder. Comparison of Joints The following table compares the different types of synovial joints: Joint Type Movement Example Hinge Flexion and extension Elbow Pivot Rotation on a single axis Ulnar radio joint Ball and Socket Movement in all axes Hip and shoulder Elliptical Flexion, extension, abduction, adduction, and rotation Wrist Saddle Flexion, extension, abduction, adduction, and rotation Carpometacarpal joint of the thumb Plane Sliding and rotation Cartels of the hand and foot tarsals Elliptical Joint The elliptical joint is similar to the ball and socket joint, but the ligaments and oval shape prevent rotation. It allows for flexion, extension, abduction, adduction, and rotation. An example of an elliptical joint is the wrist. Saddle Joint The saddle joint has a unique structure, with both bones having a concave and convex surface. The concave plane of one bone fits onto the convex plane of the other, allowing for flexion, extension, abduction, adduction, and rotation. An example of a saddle joint is the carpometacarpal joint of the thumb. Plane Joint The plane joint is a simple joint that allows for sliding and rotation. It is characterized by two flat surfaces that slide or rotate against each other. Examples of plane joints are the cartels of the hand and foot tarsals. Assignments For this lesson, there are two assignments: Find and study the movement of the joints on yourself Draw simple versions of the joints and post them on the Facebook group at facebook.com/groups/anatomy4artists Resources Additional resources for this lesson include: A PDF eBook that visually explains the terms and concepts A 3D Robo-Skilly model that allows for zooming and rotation A premium feature that includes a simplified skeleton model and additional resources for learning anatomy.