BIO 156 Chapter 12 Power Point

8/14/2019 BIO 156 Chapter 12 Power Point

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BIO 156

Chapter 12



The Skeleton and Muscles



Structure and Function of the Human Skeleton

• Bones serve many functions and play an important role inhomeostasis. Bones provide the following:

– Provide internal support.

– Allow for movement.

– Help protect internal body parts. – Produce blood cells and platelets.

– Store fat.

– Help regulate blood calcium levels.



• The human skeleton

consists of two parts:

– The axial skeleton

– The appendicular skeleton



• All bones have a hard,

dense outer layer that

surrounds a less

compact central region. – Inside the bone is the

marrow cavity, filled witheither fat cells (yellow

marrow) or blood cells

and blood-producing

cells (red marrow) or

with combinations of the

two.



• Bones are constantly remodeled in

adults to meet changing stresses

placed on them.

– Two cells are responsible for bone

remodeling:

• Osteoclasts—destroy bone• Osteoblasts—form bone

• Bone is a homeostatic organ that helpsmaintain proper levels of calcium in the

body.



The joints permit varying degrees of mobility.

1. Immovable

2. Slightly movable3. Freely movable

Immovable Joint



Slightly Movable Joints



Freely Movable Joints



Most of the bones of the human skeleton start out as

hyaline cartilage.



• Bone fractures are repaired by fibroblasts and

osteoblasts.

• Osteoporosis involves a loss of calcium, which results

in brittle, easy-to-break bones.



The Skeletal Muscles



1. Bodymovements2. Maintenance of posture3. Production of body heat

Skeletalmuscles areinvolved in:



• Skeletal muscle cells are known as muscle fibers

and are both excitable and contractile.

• Muscle fibers contain many small bundles of

contractile filaments known as myofibrils.



• During muscle contraction, the actin filaments slide inward,

causing the sarcomeres to shorten.

– The energy for muscle contraction comes from ATP.

– ATP is replenished by creatine phosphate, glycolysis, andcellular respiration.



• Individual skeletal muscle fibers contract after being stimulated

by an action potential.

– The strength of muscle contraction can be increased by

stimulating (recruiting) additional muscle fibers to contract. – Additional tension may be created in a muscle fiber if a

nerve impulse arrives while the muscle fiber is still

contracted.



• Muscle tone results from the contraction of a

small number of muscle fibers that keepmuscles slightly tense.

• Two types of muscle fibers are found inskeletal muscle, slow- and fast-twitch.

– Fast-twitch fibers are found in greatest number

in muscles that perform rapid movement.

– Slow-twitch fibers are found in muscles that

perform slower motions or are involved in

maintaining posture.



End of Chapter 12

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BIO 156 Chapter 12 Power Point