The Skeletal and Muscular Systems, Third Edition

Gregory Stewart, Diana Gitig

Description

The skeletal and muscular systems not only allow us to move and stand tall, but they are also involved in protecting the body, allowing it to grow, and performing subconscious activities such as breathing and the beating of the heart. The heart, an organ made of muscle, distributes blood that lets other systems of the body function. These complex systems work together to achieve many essential bodily functions. In The Skeletal and Muscular Systems, Third Edition, learn how these two systems interact to keep the human body alive and in motion. Packed with full-color photographs and illustrations, this absorbing book provides students with sufficient background information through references, websites, and a bibliography.

Sujets

• Life Sciences
• Diseases
• Medical
• Sciences et techniques
• Biology
• Treatment
• Medicine
• Disease
• Science

Informations

• Publié par: Infobase Publishing
• Date de parution: 01 octobre 2021
• Nombre de lectures: 0
• EAN13: 9781646937264
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

The Skeletal and Muscular Systems, Third Edition
Copyright © 2021 by Infobase
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For more information, contact:
Chelsea House An imprint of Infobase 132 West 31st Street New York NY 10001
ISBN 978-1-64693-726-4
You can find Chelsea House on the World Wide Web at http://www.infobase.com
Contents Chapters The Skeletal and Muscular Systems Bones and Other Skeletal Components The Axial Skeleton The Appendicular Skeleton Joints and Soft Tissues of the Skeleton Bone Growth and Repair Muscles, Muscle Cells, and Muscle Tissues Skeletal Muscles Support Materials Glossary Bibliography Further Resources About the Authors Index
Chapters
The Skeletal and Muscular Systems
Anyone who has ever observed a "strongman" competition in which the competitors perform feats of strength such as balancing a metal beam across their knees and supporting thousands of pounds of weight on their lower legs has probably marveled at what seems like an impossible feat. Similarly, anyone who has been to the ballet might watch in awe as dancers appear to defy gravity as they leap and spin. Our skeletomuscular system—all of our body's bones and muscles—is responsible for these acts of strength, power, and grace.
The secret to the heavy weight-balancing act is not extra muscle in the competitors' bodies, but the incredible strength of the bones of the legs. By balancing the weight directly over the long line of the lower leg bones and not moving it once it's in place, the "strongman" or "strongwoman" can support weights many times greater than his or her own weight. This ability to support extraordinary weight is an important feature of many of the bones of the body. The secret to the dancers who appear to defy gravity lies in the incredible strength of their leg muscles. The dancers have strengthened and trained their leg muscles to propel themselves high off the stage and to complete graceful turns and twists before landing. These are dramatic examples of the power and precision of the skeletomuscular system; but the everyday movements that our bones and muscles allow each of us to perform are no less amazing. As you read through this book, you will discover the importance of our skeleton and muscles and how these combined systems contribute to our daily function.
The Skeletal and Muscular Systems Work Together
Although bones and muscles each have other important functions, their main job is to work together to move the parts of the body. Muscle is the only tissue that has the ability to contract, or shorten, so all body movements involve muscle of some kind. The kind of muscle that works with the bones of the skeletal system is called skeletal muscle, and unlike the other kinds of muscle—cardiac muscle, in the heart, and smooth muscle, which lines our blood vessels and digestive tract—it is under voluntary control: we can make it contract at will.
Muscle can contract, but unless it has something to pull against, it cannot move a body part. Both ends of skeletal muscles are attached to bones. By contracting between two bones, the muscles change the position of those bones relative to each other and thereby cause the body to move. Generally, one bone remains basically stationary while the other moves. In the figure below, when the biceps muscle contracts, the lower arm is pulled upward while the upper arm remains stationary.
Skeletal muscles must work in opposing pairs for normal body function. As you will see in later chapters, skeletal muscles work only by pulling on bones. They cannot push on bones. As a result, skeletal muscles must work in pairs to provide a full range of motion for a particular bone or joint, a point where two bones come together. So while contraction of the biceps moves the lower arm up, when the biceps relaxes, another muscle must contract to pull the lower arm down (Try it!). Together the two muscles are an opposing pair, moving the lower arm in two directions.

An elbow joint is depicted in this figure. When the biceps muscle contracts, or shortens, it pulls on the radius of the forearm, which flexes the arm at the elbow.
Source: Infobase Learning.
Bones and Other Skeletal Components
The human skeleton is located inside of our bodies, and is called an endoskeleton. Other animals, such as insects and crustaceans (shellfish), have an exoskeleton—a rigid, tough, outer protective layer that covers their soft tissues. Exoskeletons are only found in some invertebrates, and they provide strength and a degree of movement, but they have their limitations. For one thing, the growth of the animal is restricted and happens in phases. After a certain amount of growth, the exoskeleton becomes constrictive and the organism must molt, or shed, its exoskeleton in order to become larger (see figure below). During the molting phase, these animals are particularly vulnerable to damage and to predators. Ultimately, animals with exoskeletons are limited in size, so there are no animals with exoskeletons among the largest animals on Earth or in its waters. However, not all organisms even have skeletons. Bacteria, protozoa, and fungi are mostly microscopic single-celled organisms. Although there are structures within their cells that serve some of the functions of skeletons, these organisms do not have skeletons in the same sense as animals. As organisms become more complex and increase in size, they develop the need for a skeleton of some type.

Insects including cicadas are encased in a hard shell, or exoskeleton. As the insect grows, this exoskeleton becomes so confining that it must be shed. A new, larger exoskeleton forms after the old one is completely shed.
Source: Basile Morin. CC BY-SA 4.0Wikimedia. 2020.
Composition of Bone Tissue
Bone contains both organic and inorganic substances. The organic parts of bone include living cells calledosteoblasts and osteoclasts; ground substance, which consists of glycoproteins (proteins modified with sugars) and proteoglycans (sugars modified with amino acids); and collagen. The remainder of bone is composed of inorganic salts, mainly calcium phosphate. The organic components, particularly the collagen, account for the resilience of bone, specifically its ability to resist breaking when stressed. The inorganic components account for its hardness.
Bone is a dynamic structure that is constantly changing. Osteoblasts are cells that build new bone tissue, while osteoclasts are cells that break down bone. This allows bone to grow, heal, and adapt to changing conditions.
Structure of Bones
At first glance, a bone appears to be a solid structure, like a rock. However, living bone is actually a complex network of channels and solid sections (see figure below). A thin section of bone examined under the microscope shows these channels. Each channel has two parts. The outer portion is a series of concentric rings that form the osteon. The osteon is shaped like a cylinder and runs parallel to the long axis of the bone. The opening in the center of the osteon is called the Haversian canal. Blood vessels and nerves pass through the Haversian canals.

Although bones are extremely sturdy structures, they are not completely solid. There are small openings containing cells, small canals running between the trapped cells, and larger channels through the bone that contain blood vessels and nerves.
Source: Infobase Learning.
The structure of the osteon makes bone strong. The layers of the concentric rings consist of long collagen fibers composed of tough connective tissue. These fibers are arranged in a helix, or spiral, rather than in a straight line. They curve around the central axis of the canal like a spring. This spiral structure contributes to the strength of the osteon, and is further strengthened by the fact that each individual layer of the concentric rings spirals in the direction opposite the layers on either side of it. A closer look at the bone section under the microscope reveals another group of channels that moves away from the Haversian canals at right angles. These are the Volkmann's (perforating) canals, which contain blood vessels and nerves that enter the bone from the periosteum.
The Periosteum
The periosteum is a double membrane that surrounds the outside of a bone (from the Greek;  peri means "around" and osteum means "bone"). The tough, fibrous outermost layer serves as a protective coating. The inner layer, called the osteogenic layer, is responsible for the growth and reshaping of bones. ( Osteo  for "bone," and genic means "to make or create.") Two basic types of cells are found within this layer: osteoblasts, or bone-building cells, and osteoclasts, or bone-destroying cells. An easy way to remember these cells is that "osteoBlasts Build," bones while "osteoClasts Crunch" (destroy) bones. The periosteum is anchored to the bone itself by bits of collagen called Sharpey's perforating fibers.
The Endosteum
Long bones have a hollow core. This core is lined by another membrane, called the endosteum ( endo means "inside" and osteum  for "bone"). This membrane also lines the canals of the bone. Like the periosteum, the endosteum contains osteoblasts and osteoclasts. This allows bone to grow from the inside as well as the outside.
Functions of Bones
Bones are the foundation on which the rest of the body is built. They are the first components that define our shape and form. Bones also serve a number of specific functions that may not be obvious. It is important to remember that not all bones serve the same functions. Each bone is specialized for its location and the job it must perform. For example, bones on the right side of the body are slightly different from the same bones on the left side of the