Anatomy & PhysiologyScience and Technology
The 206 bones that compose the adult skeleton are divided into five categories based on their shapes ([link]). Their shapes and their functions are related such that each categorical shape of bone has a distinct function.
A long bone is one that is cylindrical in shape, being longer than it is wide. Keep in mind, however, that the term describes the shape of a bone, not its size. Long bones are found in the arms (humerus, ulna, radius) and legs (femur, tibia, fibula), as well as in the fingers (metacarpals, phalanges) and toes (metatarsals, phalanges). Long bones function as levers; they move when muscles contract.
A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness. The only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles. Short bones provide stability and support as well as some limited motion.
The term “flat bone” is somewhat of a misnomer because, although a flat bone is typically thin, it is also often curved. Examples include the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone), and the ribs. Flat bones serve as points of attachment for muscles and often protect internal organs.
An irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification. These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Many facial bones, particularly the ones containing sinuses, are classified as irregular bones.
A sesamoid bone is a small, round bone that, as the name suggests, is shaped like a sesame seed. These bones form in tendons (the sheaths of tissue that connect bones to muscles) where a great deal of pressure is generated in a joint. The sesamoid bones protect tendons by helping them overcome compressive forces. Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and knees. The patellae (singular = patella) are the only sesamoid bones found in common with every person. [link] reviews bone classifications with their associated features, functions, and examples.
|Long||Cylinder-like shape, longer than it is wide||Leverage||Femur, tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges|
|Short||Cube-like shape, approximately equal in length, width, and thickness||Provide stability, support, while allowing for some motion||Carpals, tarsals|
|Flat||Thin and curved||Points of attachment for muscles; protectors of internal organs||Sternum, ribs, scapulae, cranial bones|
|Irregular||Complex shape||Protect internal organs||Vertebrae, facial bones|
|Sesamoid||Small and round; embedded in tendons||Protect tendons from compressive forces||Patellae|
Bones can be classified according to their shapes. Long bones, such as the femur, are longer than they are wide. Short bones, such as the carpals, are approximately equal in length, width, and thickness. Flat bones are thin, but are often curved, such as the ribs. Irregular bones such as those of the face have no characteristic shape. Sesamoid bones, such as the patellae, are small and round, and are located in tendons.
Most of the bones of the arms and hands are long bones; however, the bones in the wrist are categorized as ________.
- flat bones
- short bones
- sesamoid bones
- irregular bones
Sesamoid bones are found embedded in ________.
Bones that surround the spinal cord are classified as ________ bones.
Which category of bone is among the most numerous in the skeleton?
- long bone
- sesamoid bone
- short bone
- flat bone
Long bones enable body movement by acting as a ________.
- resistive force
Critical Thinking Questions
What are the structural and functional differences between a tarsal and a metatarsal?
Structurally, a tarsal is a short bone, meaning its length, width, and thickness are about equal, while a metatarsal is a long bone whose length is greater than its width. Functionally, the tarsal provides limited motion, while the metatarsal acts as a lever.
What are the structural and functional differences between the femur and the patella?
Structurally, the femur is a long bone, meaning its length is greater than its width, while the patella, a sesamoid bone, is small and round. Functionally, the femur acts as a lever, while the patella protects the patellar tendon from compressive forces.
- Anatomy & Physiology
- Unit 1: Levels of Organization
- An Introduction to the Human Body
- The Chemical Level of Organization
- The Cellular Level of Organization
- The Tissue Level of Organization
- Unit 2: Support and Movement
- The Integumentary System
- Bone Tissue and the Skeletal System
- Axial Skeleton
- The Appendicular Skeleton
- Muscle Tissue
- The Muscular System
- Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems
- Naming Skeletal Muscles
- Axial Muscles of the Head, Neck, and Back
- Axial Muscles of the Abdominal Wall, and Thorax
- Muscles of the Pectoral Girdle and Upper Limbs
- Appendicular Muscles of the Pelvic Girdle and Lower Limbs
- Unit 3: Regulation, Integration, and Control
- The Nervous System and Nervous Tissue
- Anatomy of the Nervous System
- The Brain and Cranial Nerves
- The Autonomic Nervous System
- The Neurological Exam
- The Endocrine System
- An Overview of the Endocrine System
- The Pituitary Gland and Hypothalamus
- The Thyroid Gland
- The Parathyroid Glands
- The Adrenal Glands
- The Pineal Gland
- Gonadal and Placental Hormones
- The Endocrine Pancreas
- Organs with Secondary Endocrine Functions
- Development and Aging of the Endocrine System
- Unit 4: Fluids and Transport
- The Cardiovascular System: Blood
- The Cardiovascular System: The Heart
- The Cardiovascular System: Blood Vessels and Circulation
- The Lymphatic and Immune System
- Anatomy of the Lymphatic and Immune Systems
- Barrier Defenses and the Innate Immune Response
- The Adaptive Immune Response: T lymphocytes and Their Functional Types
- The Adaptive Immune Response: B-lymphocytes and Antibodies
- The Immune Response against Pathogens
- Diseases Associated with Depressed or Overactive Immune Responses
- Transplantation and Cancer Immunology
- Unit 5: Energy, Maintenance, and Environmental Exchange
- The Respiratory System
- The Digestive System
- Metabolism and Nutrition
- The Urinary System
- Physical Characteristics of Urine
- Gross Anatomy of Urine Transport
- Gross Anatomy of the Kidney
- Microscopic Anatomy of the Kidney
- Physiology of Urine Formation
- Tubular Reabsorption
- Regulation of Renal Blood Flow
- Endocrine Regulation of Kidney Function
- Regulation of Fluid Volume and Composition
- The Urinary System and Homeostasis
- Fluid, Electrolyte, and Acid-Base Balance
- Unit 6: Human Development and the Continuity of Life
- The Reproductive System
- Development and Inheritance