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Chapter 18
The Musculoskeletal System
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The Skeleton
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The Skeleton
• Functions
– Support
– Protection
– Movement
– Hematopoiesis
– Storage
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Bones
• The adult human body has 206 bones.
• Classification
– Long
– Short
– Flat
– Irregular
• Sesamoid bones: Bones in the middle ear
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Structure of Bones
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Bone Marrow
• Marrow
– Yellow marrow
• Found in the medullary cavity of long bones
– Red marrow
• Found in the ends of long bones, in the bodies of
vertebrae, and in flat bones
• Manufactures red blood cells, white blood cells,
and platelets—hematopoiesis
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Joints
• Synarthroses (synarthrodial, fibrous, or fixed joints)
• Amphiarthroses (amphiarthrodial or cartilaginous joints)
• Diarthroses (synovial joints)
– Hinge (ginglymus) joints
– Ball-and-socket (spheroidal) joints
– Pivot joints; gliding (arthrodial, plane) joints
– Condyloid joints; saddle joints
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Hinge Joints
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Ball-and-Socket Joints
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Pivot Joints
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Ligaments
• Strong fibrous bands that hold bones together
– Strengthen or support other ligaments
– Produce stability in a joint
– Connect bones to muscles or cartilage
– Allow for great flexibility, stretching, and movement
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Cartilage
• Soft and flexible connective tissue organized into a
system of fibers
– Helps reduce friction in joints and distribute weight
evenly
– Provides a slick surface for rotation
– Absorbs shocks and jars to the body
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Divisions of the Skeleton
• Axial Skeleton
– Skull
– Hyoid
– Auditory ossicles
– Vertebral column
– Thorax
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Divisions of the Skeleton (cont’d)
• Appendicular Skeleton
– Pectoral (shoulder) girdles
– Upper limbs (extremities)
– Pelvic (hip) girdle
– Lower limbs (extremities)
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Skull
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Fontanels of the Skull at Birth
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Vertebral Column
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Thoracic (Rib) Cage
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Question
Is the following statement true or false?
All adults have 26 vertebrae.
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Answer
False
Most people have 26 vertebrae. Individuals from certain
ethnic groups may have fewer—11% of African American
women have 23 vertebrae, and 12% of Alaska Natives and
Native Americans have 25.
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Muscles
• Types of muscle tissue
– Skeletal muscles, smooth muscles, cardiac muscle
• Functions
– Voluntary movement
– Involuntary muscle action
– Protection
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Skeletal Muscles and Tendons
• Skeletal muscles are considered organs.
– Muscle fibers are made up of many thin threads
called myofilaments or myofibrils.
• Tendons
– The ends of muscle fascia lengthen into tough cords
called tendons, which attach muscle to bones.
• Permits a smooth, gliding movement
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Question
Is the following statement true or false?
Skeletal muscles are under involuntary control, and the
cardiac muscle is under involuntary control.
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Answer
False
Skeletal muscles, which are responsible for locomotion,
facial expression, and posture, are under voluntary
control. Smooth muscle controls involuntary motion
inside body organs and structures. Cardiac muscle, which
is involuntary, is responsible for propelling blood through
blood vessels. The heart muscle is the muscle that works
the longest; it pumps continually for a lifetime.
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Major Muscles of the Body
• Diaphragm and intercostals
– Primary muscles of respiration
• Muscles of the hands and feet
– Provide movement
– Permits accuracy and a variety of movements without
great bulk
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Question
Is the following statement true or false?
The jaw muscle is believed to be the strongest muscle in
the body.
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Answer
True
The masseter (jaw) muscle is considered to be the
strongest muscle in the body by volume, because it is able
to exert great bite strength. The tongue is also a strong
muscle, actually being made up of 16 muscles.
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Formation of Bone Tissue
• Osteoblasts: Bone-building cells
• Ossification: Formation of bone by osteoblasts
• Factors that affect bone growth and maintenance
– Heredity
– Nutrition
– Exercise
– Hormones
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Muscle: Specific Characteristics
• Contractility
• Extensibility
• Elasticity
• Irritability
• Contraction and relaxation
• Power source
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Muscle
• Exercise
– Isometric and isotonic contractions
– Aerobic and anaerobic exercise
– Rehabilitation
• Mobility
– Range of motion
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Effects of Aging
• Bone mass and strength are lost.
• Calcium is lost.
• Vertebral column shortens.
• Degeneration occurs in joints.
• Muscle cells are lost.
• Muscle cells are replaced by fat.
• Elasticity of fibers is lost.
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End of Presentation
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