The Skeletal System Department of Biology Mission Hills High School Department of Biology Mission Hills High School

Bones: The human body is born with over 300 bones but quickly begins to reduce in number as bones fuse. By the time the child becomes an adult, the number of bones is 206 ½ of these bones are in the hands and feet. Age of a young skeleton can be determined by the number of bones fused using x-ray of hands. The human body is born with over 300 bones but quickly begins to reduce in number as bones fuse. By the time the child becomes an adult, the number of bones is 206 ½ of these bones are in the hands and feet. Age of a young skeleton can be determined by the number of bones fused using x-ray of hands.

Functions of bone: Forms the framework for the human body (the skeleton) Bases for attachment of muscles and tendons Provides minerals (calcium and phosphates) Protection for vital organs: –Brain: cranium –Heart and Lungs: ribcage and sternum Produces blood elements (RBC’s and WBC’s): Red bone marrow – center of bone Forms the framework for the human body (the skeleton) Bases for attachment of muscles and tendons Provides minerals (calcium and phosphates) Protection for vital organs: –Brain: cranium –Heart and Lungs: ribcage and sternum Produces blood elements (RBC’s and WBC’s): Red bone marrow – center of bone

Anatomy of The Human Skeleton

The Human skeleton’s 206 bones are divided into two sections: Axial skeleton (74 bones) Appendicular skeleton (126 bones) Ear ossicles are the smallest bones found in the cranium – 6 bones) Total is 206 bones! Axial skeleton (74 bones) Appendicular skeleton (126 bones) Ear ossicles are the smallest bones found in the cranium – 6 bones) Total is 206 bones!

Axial Skeleton Appendicular Skeleton

Axial Skeleton Skull (Cranium and face): 22 bones Vertebral column: 26 bones Ribs:24(12 pairs) bones Sternum: 2 bones Skull (Cranium and face): 22 bones Vertebral column: 26 bones Ribs:24(12 pairs) bones Sternum: 2 bones

Appendicular Skeleton Shoulder girdle: 2 pairs (4 bones) Arms and hands: 62 bones Pelvic Girdle: 2 bones each fused from three bones. Legs and feet: 60 bones Shoulder girdle: 2 pairs (4 bones) Arms and hands: 62 bones Pelvic Girdle: 2 bones each fused from three bones. Legs and feet: 60 bones

Putting it all together: Bones are held together by a connective tissue called ligament. A joint (articulation) is formed where two bones meet. Some joints are immovable, others glide, some pivot, some are hinge and some are ball-socket type. This forms the basis of joint types. Bones are held together by a connective tissue called ligament. A joint (articulation) is formed where two bones meet. Some joints are immovable, others glide, some pivot, some are hinge and some are ball-socket type. This forms the basis of joint types.

Composition of bone: Bone is primarily composed of calcium and phosphate Both give bone a very hard consistency to perform its job as the framework for the body Bone is hard and strong, yet very light. Bone is primarily composed of calcium and phosphate Both give bone a very hard consistency to perform its job as the framework for the body Bone is hard and strong, yet very light.

Classification of bones is by shape: Short bones (wrist and ankles) Long bones (arms, fingers, legs and toes) Flat bones (skull) Irregular bones (hip,vertebrae, sacrum and maxilla ) Sesmoid – no direct articulation with other bones (knee cap) Short bones (wrist and ankles) Long bones (arms, fingers, legs and toes) Flat bones (skull) Irregular bones (hip,vertebrae, sacrum and maxilla ) Sesmoid – no direct articulation with other bones (knee cap)

Short bones Short bones are "short": cubelike. They do not have any cavity similar to the medullary cavity of the long bones. Short bones are made mostly of spongy bone tissue, but their outer parts are made of a thin crust of compact bone tissue. Short bones are "short": cubelike. They do not have any cavity similar to the medullary cavity of the long bones. Short bones are made mostly of spongy bone tissue, but their outer parts are made of a thin crust of compact bone tissue.

Long Bones Long bones are "long": their length is superior to their width. Long bone consist of a shaft (diaphysis) and two expanded ends (epiphysis, plural: epiphyses) Long bones are "long": their length is superior to their width. Long bone consist of a shaft (diaphysis) and two expanded ends (epiphysis, plural: epiphyses)

Flat bones Flat bones are "flat", platelike. They are thin and do not have any cavity similar to the medullary cavity of the long bones. The outer part of a flat bone is made of a layer of spongy bone tissue sandwiched between two layers of compact bone tissue. Flat bones are "flat", platelike. They are thin and do not have any cavity similar to the medullary cavity of the long bones. The outer part of a flat bone is made of a layer of spongy bone tissue sandwiched between two layers of compact bone tissue.

Irregular bones Irregular bones are all the weird-shaped bones that do not belong in any other category. They do not have any cavity similar to the medullary cavity of the long bones. They are made mostly of spongy bone tissue enclosed by a thin crust of compact bone tissue. Irregular bones are all the weird-shaped bones that do not belong in any other category. They do not have any cavity similar to the medullary cavity of the long bones. They are made mostly of spongy bone tissue enclosed by a thin crust of compact bone tissue.

Parts of long bones: Diaphysis (shaft) Epiphysis (ends) Neck (region between diaphysis and epiphysis) Diaphysis (shaft) Epiphysis (ends) Neck (region between diaphysis and epiphysis)

Structure of Bone Tissue Periosteum: Connective tissue which contains nerves, blood vessels, gives rise to new bone and repairs fractures. Compact bone: Hardest part of the bone, contains Haversian systems where bone cells are located. Spongy (Cancellous) bone: Marrow: –Red marrow – forms blood tissue. –Yellow Marrow- With increasing age parts become inactive in blood formation and function as fat storage. It then appears yellow and is called yellow marrow Periosteum: Connective tissue which contains nerves, blood vessels, gives rise to new bone and repairs fractures. Compact bone: Hardest part of the bone, contains Haversian systems where bone cells are located. Spongy (Cancellous) bone: Marrow: –Red marrow – forms blood tissue. –Yellow Marrow- With increasing age parts become inactive in blood formation and function as fat storage. It then appears yellow and is called yellow marrow