6.2 Bone Classification
3 min read•june 18, 2024
Bones come in various shapes, each designed for specific functions in the body. provide leverage for movement, while protect organs. Short and offer stability and specialized roles, respectively. , embedded in tendons, act as pulleys.
Bone structure is complex, with a protective covering and internal for strength. and work together in bone remodeling, constantly reshaping our skeleton throughout life. This dynamic process ensures our bones remain strong and adaptable.
Bone Classification and Function
Types of bone shapes
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Top images from around the web for Types of bone shapes
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- Long bones extend lengthwise and are longer than they are wide (, , , , , , )
- Consist of a or shaft and two epiphyses or ends
- Contains a in the center of the diaphysis, which houses bone marrow
- are roughly cube-shaped ( in the wrist, in the ankle)
- Flat bones are thin and flat in shape (skull bones, , , )
- Composed of two layers of with a layer of in between
- Irregular bones have complex shapes that do not fit into other categories (, , , , )
- Sesamoid bones are small, round bones embedded within tendons ( or kneecap, in the wrist, two sesamoid bones in the ball of the foot)
Relationship of shape to function
- Long bones provide leverage and allow for movement
- Diaphysis is hollow, reducing weight while maintaining strength
- Epiphyses provide attachment points for muscles and articulate with other bones
- Short bones have a compact shape that provides stability and strength and allows for limited movement (wrist and ankle)
- Flat bones provide protection for underlying organs and attachment points for muscles
- Two layers of offer strength, while layer reduces weight
- Irregular bones have unique shapes that allow for specific functions
- Vertebrae support and protect the spinal cord while allowing for flexibility
- Sesamoid bones embedded within tendons protect them from wear and tear and act as pulleys, reducing friction and increasing mechanical advantage of muscles
Sesamoid bones in the skeleton
- Patella or kneecap anterior to the knee joint protects the joint and increases the mechanical advantage of the quadriceps muscle
- anterior to the in the wrist increases the mechanical advantage of the muscle
- Two sesamoid bones in the first metatarsal or ball of the foot
- Embedded within the tendons of the muscle
- Increase the mechanical advantage of the muscle and protect the tendons from wear and tear during walking and running
Bone structure and cellular components
- Bones are covered by a tough connective tissue layer called the , which contains blood vessels and nerves
- Bone tissue is composed of structural units called osteons, which are cylindrical structures that run parallel to the long axis of the bone
- Bone remodeling involves two main types of cells:
- Osteoblasts: cells responsible for bone formation and deposition of new bone matrix
- Osteoclasts: cells that break down and resorb old bone tissue
- is the process of bone formation, which occurs throughout life for bone growth, repair, and remodeling
Key Terms to Review (59)
Carpals: The carpals are a group of eight small bones located in the wrist region, forming the connection between the forearm and the hand. These bones play a crucial role in the overall structure and function of the upper limb, as they facilitate the intricate movements and flexibility required for various manual tasks.
Coccyx: The coccyx, often referred to as the tailbone, is a small bone located at the base of the vertebral column. It is composed of three to five fused vertebrae and serves as an attachment site for ligaments and muscles of the pelvic floor.
Coccyx: The coccyx is the small, triangular bone located at the bottom of the vertebral column, formed by the fusion of 3-5 small vertebrae. It serves as an attachment point for several muscles and ligaments, and plays a role in various bodily functions and anatomical structures covered in the topics of bone classification, the skeletal system, the vertebral column, the pelvic girdle and pelvis, and the appendicular muscles of the pelvic girdle and lower limbs.
Compact bone: Compact bone is the dense, hard outer layer of bone that provides strength and structure. It consists of tightly packed cells, blood vessels, and nerves which support the overall function of the skeletal system.
Compact Bone: Compact bone, also known as cortical bone, is the dense, solid outer layer of bone that provides strength and protection. It is the primary component of the skeletal system and plays a crucial role in supporting and protecting the body.
Diaphysis: The diaphysis is the elongated, tubular shaft of a long bone, primarily composed of compact bone and surrounding the medullary cavity, which contains bone marrow. This structure is crucial for providing strength and support to the bone while also facilitating the storage of bone marrow, where blood cell production occurs. The diaphysis is essential for bone classification, structure, formation, and development throughout the skeletal system.
Epiphysis: The epiphysis is the end part of a long bone, initially growing separately from the shaft. It is made up primarily of spongy bone covered by a thin layer of compact bone.
Epiphysis: The epiphysis is the expanded end of a long bone, separated from the main bone shaft (diaphysis) by a cartilaginous growth plate known as the epiphyseal plate. It plays a crucial role in the growth and development of bones.
Femoropatellar joint: The femoropatellar joint is the point of articulation between the patella (kneecap) and the femur (thigh bone), functioning within the knee as a type of synovial joint. It facilitates movements such as bending and straightening of the knee, playing a critical role in walking, running, and jumping.
Femur: The femur is the longest and strongest bone in the human body, located in the thigh, and plays a crucial role in supporting weight and facilitating movement. Its unique structure allows it to bear significant loads, connecting the pelvis to the knee and serving as an essential component of the lower limb's anatomy and function.
Flat bone: Flat bones are bones that have a thin, flattened shape and provide protection for internal organs while also serving as sites for muscle attachment. They are characterized by a layer of spongy bone between two layers of compact bone.
Flat Bones: Flat bones are a type of bone that are thin, flattened, and typically found in areas that provide protection or serve as attachment points for muscles and tendons. They are characterized by their broad, thin shape and are composed of two layers of compact bone with a layer of spongy bone in between.
Flexor Carpi Ulnaris: The flexor carpi ulnaris is a muscle located in the forearm that is responsible for flexing and adducting the wrist. It is one of the key muscles involved in the classification of bones based on their movements.
Flexor Hallucis Brevis: The flexor hallucis brevis is a small muscle located in the sole of the foot that is responsible for flexing the big toe. It is classified as a short intrinsic muscle of the foot and plays a crucial role in the biomechanics of gait and balance.
Humerus: The humerus is the long bone in the upper arm that runs from the shoulder to the elbow, connecting with both the scapula at the shoulder joint and the radius and ulna at the elbow joint. It plays a critical role in both the mobility and stability of the upper limb.
Humerus: The humerus is the upper arm bone, connecting the shoulder to the elbow. It is the longest, largest, and strongest bone in the upper limb and plays a crucial role in the structure and function of the arm and shoulder.
Hyoid bone: The hyoid bone is a U-shaped bone located in the anterior neck, between the lower jaw and the larynx. It serves as an attachment site for muscles associated with swallowing and speech.
Hyoid Bone: The hyoid bone is a small, U-shaped bone located in the neck, just above the thyroid cartilage. It serves as an attachment point for several muscles involved in swallowing, speech, and other functions of the head and neck.
Irregular bone: Irregular bones are bones in the human body that do not fit into any other category of bone due to their complex shapes. They primarily serve to protect internal organs and provide attachment sites for muscles.
Irregular Bones: Irregular bones are a classification of bones that have complex, asymmetrical shapes and do not fit neatly into the categories of long, short, flat, or sesamoid bones. They are found in various regions of the body and serve specialized functions, often providing structural support and protection for vital organs and structures.
Long bone: Long bones are characterized by a greater length than width and consist of a shaft with two ends, which are often expanded. They play crucial roles in support, movement, and the storage of minerals such as calcium.
Long Bones: Long bones are a type of bone classified by their elongated, cylindrical shape. They are the primary bones found in the appendicular skeleton, specifically in the upper and lower limbs, and are responsible for providing structure, support, and facilitating movement.
Medullary cavity: The medullary cavity is a hollow region within the diaphysis (shaft) of long bones, filled with yellow bone marrow. It plays a crucial role in the storage of adipose tissue (fat) and serves as the main site of red blood cell production in adults.
Medullary Cavity: The medullary cavity, also known as the marrow cavity, is the hollow, central region within the diaphysis (shaft) of long bones. This space is filled with bone marrow, which plays a crucial role in the production of blood cells and the storage of fat.
Metacarpals: The metacarpals are a group of five bones located in the palm of the hand, connecting the wrist to the fingers. These bones play a crucial role in the structure and function of the hand, providing a stable foundation for the fingers and enabling various hand movements.
Metatarsals: The metatarsals are a group of five bones located in the middle part of the foot, between the tarsal bones and the phalanges of the toes. These bones play a crucial role in the structure and function of the foot, providing a stable platform for weight-bearing and facilitating movement during activities such as walking and running.
Ossification: Ossification is the process by which bone tissue forms, either through the transformation of connective tissue or the laying down of new bone material. It is a critical aspect of bone formation and development, and it also plays a role in the repair of bone fractures.
Osteoblasts: Osteoblasts are specialized bone cells responsible for the formation and mineralization of bone tissue. They play a crucial role in the growth, maintenance, and repair of the skeletal system, as well as in calcium homeostasis throughout the body.
Osteoclasts: Osteoclasts are large, multinucleated cells responsible for the resorption and breakdown of bone tissue. They play a crucial role in the remodeling and maintenance of the skeletal system, as well as in the regulation of calcium homeostasis within the body.
Osteons: Osteons are the fundamental structural units of compact bone tissue. They are cylindrical structures that run parallel to the long axis of the bone and contain a central canal, known as the Haversian canal, which houses blood vessels and nerves to nourish the bone.
Patella: The patella, commonly known as the kneecap, is a small, flat, and triangular bone located at the front of the knee joint. It is the largest sesamoid bone in the human body and plays a crucial role in the mechanics and function of the knee joint.
Periosteum: The periosteum is a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints. It serves as a protective layer for bones and provides a channel for the blood supply and nutrients needed for bone health and repair.
Periosteum: The periosteum is a specialized layer of connective tissue that covers the outer surface of all bones, except at the joints where the bone is covered by articular cartilage. It plays a crucial role in the functions, classification, structure, formation, development, repair, and joints of the skeletal system.
Phalanges: The phalanges are the bones that make up the fingers and toes. They are the distal bones of the upper and lower limbs, responsible for the fine motor movements and dexterity of the hands and feet.
Pisiform: The pisiform is a small, pea-shaped carpal bone located in the proximal row of the carpus, on the ulnar side of the hand. It articulates only with the triquetrum and acts as a sesamoid bone, embedded within the tendon of the flexor carpi ulnaris muscle.
Pisiform: The pisiform is a small, pea-shaped bone located on the medial side of the wrist, forming part of the proximal row of carpal bones. It is one of the eight carpal bones that make up the wrist joint, connecting the forearm to the hand.
Radius: The radius is one of the two bones that make up the forearm, located on the lateral (thumb) side. It is responsible for rotating the forearm and wrist, allowing for a wide range of motion in the upper limb.
Ribs: Ribs are curved, bony structures that form the thoracic cage, which protects the vital organs in the chest cavity. They are an essential component of the axial skeleton and play a crucial role in various functions of the skeletal system.
Sacrum: The sacrum is a large, triangular bone located at the base of the vertebral column. It is formed by the fusion of five sacral vertebrae and serves as the connection between the spine and the pelvic girdle, playing a crucial role in the structure and function of the skeletal system.
Scapula: The scapula, also known as the shoulder blade, is a flat, triangular bone that forms the posterior part of the pectoral girdle. It is a key component of the skeletal system, playing a crucial role in the structure and function of the upper limb.
Secondary ossification center: A secondary ossification center is the region in the epiphyses (ends) of long bones where bone tissue begins to form during fetal development and continues through adolescence. Unlike the primary ossification center in the diaphysis (shaft), these centers contribute to bone growth in length and commence after the primary centers are established.
Sesamoid bone: A sesamoid bone is a small, round bone that is embedded within a tendon, where the tendon passes over a joint. These bones serve to protect the tendon and increase its mechanical advantage by modifying pressure, reducing friction, and altering the direction of muscle forces.
Sesamoid Bones: Sesamoid bones are small, rounded bones that are embedded within certain tendons, usually near joints. They act as pulleys, reducing friction and increasing the mechanical advantage of the tendons they are associated with.
Shaft of the radius: The shaft of the radius is the long, central part of the radius bone in the forearm, extending from below the head near the elbow to just above the wrist where it widens to form part of the wrist joint. It serves as a major structural component of the forearm, providing attachment sites for muscles and supporting movements of the wrist and hand.
Short bone: Short bones are approximately cube-shaped and provide support and stability with little to no movement. They are primarily found in the wrist (carpals) and ankle (tarsals).
Short Bones: Short bones are a type of bone classification characterized by their cube-like shape and relatively equal dimensions in length, width, and thickness. They are found in the wrist, ankle, and other areas of the body where compact, stable joints are required for limited range of motion.
Spongy bone: Spongy bone, also known as cancellous or trabecular bone, is a type of bone tissue characterized by a porous, honeycomb structure. It is found at the ends of long bones and in the inner layers of other bones, providing structural support and aiding in the production of red blood cells.
Spongy Bone: Spongy bone, also known as cancellous or trabecular bone, is a type of osseous tissue that is porous and lightweight, with a honeycomb-like structure. It is found in the interior of bones and plays a crucial role in supporting and protecting the body, as well as in the formation and development of bone.
Sternum: The sternum, or breastbone, is a long, flat bone located in the center of the chest. It connects to the rib bones via cartilage, forming the front part of the rib cage which protects vital organs such as the heart and lungs.
Sternum: The sternum is a flat, elongated bone located in the center of the chest that serves as the anterior portion of the thoracic cage. It plays a crucial role in the structure and function of the skeletal system.
Subscapular fossa: The subscapular fossa is a concave depression located on the anterior (frontal) surface of the scapula bone, serving as the attachment site for the subscapularis muscle. It plays a critical role in arm and shoulder movement by allowing for muscle attachment and facilitating upper limb mobility.
Superior articular process of the sacrum: The superior articular process of the sacrum is a paired anatomical structure located at the top part of the sacrum, which articulates (forms a joint) with the inferior articular processes of the lumbar vertebra above it. It plays a critical role in connecting the spine to the pelvis and contributes to the flexibility and movement of the lower back.
Tarsals: Tarsals are a group of seven bones located in the posterior part of the foot, forming the ankle and heel. These bones are an important component of the skeletal system, playing a crucial role in the classification, division, and development of the appendicular skeleton.
Triquetrum: The triquetrum is one of the eight small carpal bones located in the wrist, specifically on the ulnar side where it articulates with the pisiform, lunate, and hamate bones. It plays a crucial role in the complex movements and stability of the wrist.
Triquetrum: The triquetrum is one of the carpal bones located in the wrist, specifically in the proximal row of the carpals. It is a small, pyramidal-shaped bone that plays an important role in the structure and function of the hand and wrist.
Turbinate Bones: Turbinate bones are small, scroll-shaped bones located within the nasal cavity. They play a crucial role in the respiratory system by regulating airflow and humidifying inhaled air.
Ulna: The ulna is one of the two bones that make up the forearm, located on the little finger side. It is responsible for several important functions related to the skeletal system, joint anatomy, and upper limb movement.
Ulnar nerve: The ulnar nerve is one of the major nerves of the arm, responsible for innervating (supplying with nerves) parts of the hand and facilitating muscle movement and sensation in the forearm and hand. It runs from the shoulder to the hand, passing through areas such as the inner elbow (often referred to when talking about hitting your "funny bone").
Vertebrae: Vertebrae are the individual bones that make up the vertebral column, also known as the spine or backbone. They are the central structural components of the axial skeleton and play a crucial role in the functions of the skeletal system.