BONE & MUSCLES

Dr. LUBNA NAZLIASST. PROF. ANATOMY

RAK MHSUDt: 13/ 10/08

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Objectives

• Features of bone

• Cells of bone

• Functions

• Classification of bone: Compact bone and Spongy bone

• Muscle

• Types of muscles.

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Features of bone

• Widely separated cells surrounded by large amounts of matrix containing collagen fibers and mineral salts (mainly calcium and phosphorus).

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Functions of bone

• support - for muscles, organs, and soft tissues

• leverage and movement - the synovial joints

• protection - for critical organs

• calcium phosphate storage - mineral balance

• hemopoiesis - formation of blood cells

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Bone cells

• Osteoblasts - bone forming cells - produce matrix

• Osteocytes - mature bone cells• Osteoclasts – phagocytic cells.

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Osteoblasts

• osteoblasts - these are the "bone forming cells" which secrete the collagen and ground substance that constitutes unmineralized bone (osteoid), and is responsible for calcification of the matrix.

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• Osteocytes are mature bone cells. Each osteocyte occupies a space, the lacuna, and is surrounded by matrix.

• Osteocytes extend processes through canaliculi to connect to neighboring cells.

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Osteoclasts

• Osteoclasts are large multinucleated cells whose function is to resorb (reabsorb) bone.

• Osteoclasts dissolve the matrix and osteoid with acids and hydrolytic enzymes.

• Osteoclasts are phagocytic and are derived from monocytes.

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Osteons or Haversian system

• Osteons, or Haversian systems, are the units of structure in mature bone.

• They are tightly arranged running generally parallel to the long axis of the bone.

• At the center of each is an Haversian canal which carries blood vessels and nerves.

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• Canaliculi (small canals) connect the Haversian canals with lacunae containing the osteocytes.

• Osteocytes extend processes into the canaliculi and receive nutrients and get rid of wastes through the canaliculi.

• The lacunae and canaliculi form lamellae or layers of two types: concentric lamellae form circular rings around each Haversian canal, and interstitial lamellae, fill in the spaces between existing osteons.

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• Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

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Bone or osseous tissue is found in two different forms:

• compact bone

• cancellous or spongy bone

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Compact Bone

• Compact bone is a very dense tissue forming the outer layer of all bones and the thickened shafts or diaphyses of long bones.

• In a microscopic view, compact bone always contains numerous osteons or Haversian Systems. Each consists of a central canal through which blood vessels and nerves pass.  Surrounding this canal are multiple concentric lamellae or layers of bone.  

• Haversian systems are only found in compact bone.   

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Cancellous (Spongy) Bone

• One of the most obvious features of cancellous or spongy bone is the absence of Haversian Systems or Osteons.  

• During bone formation, the first bone to form is always cancellous.  Where compact bone is needed, cancellous bone forms first and later is remodeled into the denser, compact type.

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• Bones of the skeleton contain a combination of both types of bone tissue organization.

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MUSCLE TISSUE

• Made of elongated cells

• Found in muscles, heart and glands that contract

• Functions to produce movement.

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• There are three structurally and functionally distinct types of muscles.

• smooth muscle (involuntary, unstriated)

• skeletal muscle (voluntary, striated)

• cardiac muscle. (involuntary, striated)

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Smooth Muscle

• Smooth muscle consists of spindle shaped cells of variable size.

• Smooth muscle cells contain one centrally placed nucleus.The innervation of smooth muscle is provided by the autonomic nervous system.

• Smooth muscle makes up the visceral or involuntary muscle.

• Eg: walls of hollow organs.

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Skeletal Muscle

• Skeletal muscle consists of very long tubular cells (also called muscle fibres).

• Skeletal muscle fibres contain many peripherally placed nuclei.

• Skeletal muscle fibres show cross-striations. It is therefore also called striated muscle.

• Skeletal muscle is innervated by the somatic nervous system.

• Skeletal muscle makes up the voluntary muscle. • Eg: muscles that move the skeleton

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Cardiac Muscle

• Cardiac muscle consists of muscle cells with one centrally placed nucleus.

• Cardiac muscle is innervated by the autonomic nervous system.

• Cardiac muscle exhibits cross-striations. • Cells branch & joined by intercalated discs.• Cardiac muscle is for these reasons also called

involuntary striated muscle. • Eg: walls of the heart

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