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The Skeletal and Muscular System
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For humans and most other animals, movement is important for survival.
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Being able to move makes it possible to escape danger, get food, and to find a mate.
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Movement is made possible by the skeletal and muscular system.
The Skeletal System
Purpose:
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Supports the body and allows movement.
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It also protects internal organs, stores some materials, and makes blood cells.
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2 Parts:
1. Axial: Skull & vertebral column
2. Appendicular: appendages (arms, legs, hips & shoulders)
Major Organs:
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206 bones (in humans)
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cartilage
Bones:
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Bones are living tissues that make up the skeleton.
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Bones support the body.
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They are made up of bone cells surrounded by deposits of calcium and other minerals.
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A typical bone is surrounded by a tough layer of connective tissue.
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As blood passes through this layer, it supplies oxygen and nutrients to the bone.
Blood Marrow:
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Inside bones are cavities that contain a soft tissue called bone marrow.
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Yellow marrow is made up mostly of fat cells.
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Red marrow produces red blood cells, some kinds of white blood cells, and
platelets.
Cartilage:
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The skeleton of a developing fetus begins as cartilage.
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Cartilage is a flexible connective tissue.
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As the body develops, most of the cartilage in the body is replaced by bone.
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Some parts of the body where cartilage is not replaced by bone include the lower part of
the nose and the connective tissue that forms your ears.
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Cartilage also remains at joints, the places where two bones meet.
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This cartilage helps cushion the joints.
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Many long bones, such as those in the arms and legs, have growth plates at their ends. At
these plates, cartilage grows, making the bones longer.
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After a while, the new cartilage is replaced by bone. By early adulthood, the cartilage in
the growth plates is replaced by bone. When this happens, the person stops growing.
Joints:
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A joint is a place where one bone attaches to another.
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Tough fibers called ligaments connect bones to each other at joints.
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There are three main types of joints:
1. Immovable or fixed joint
2. Slightly movable joint
3. Freely moveable joints
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Each type of joint is described by the type of movement it allows.
Immovable Joints:
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An immovable joint, or fixed joint, does not allow movement.
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At this type of joint, the bones are locked together by connective tissue or fused together.
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The bones in the skull meet at immovable joints.
Slightly Movable Joints:
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Slightly movable joints allow restricted movement.
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The joints between adjacent vertebrae that protect the spinal cord are examples of
slightly movable joints.
Freely Movable Joints:
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Freely movable joints allow movement in one or more directions.
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The four common types of freely movable joints are:
1. Ball and Socket Joint
2. Hinge Joint
3. Pivot Joint
4. Saddle Joint
The Muscular System
Purpose:
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The muscular system consists of the body’s muscles.
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One job of the muscular system is to work with the skeletal system to move the body.
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It also helps to:
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keep the body warm
 give the body shape
 Provides the force needed to move blood throughout the body.
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There are about 600 muscles in the human body!!
Two Main types:
1. Involuntary: you cannot control them
2. Voluntary: you can control them
Types of Muscle:
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There are three basic types of muscle tissue in the human body:
1. skeletal muscle
2. smooth muscle
3. cardiac muscle
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Each type of muscle tissue plays a different role.
Skeletal Muscle:
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Muscle tissue that connects to the bones.
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Most skeletal muscles are consciously controlled by the central nervous system.
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These muscles are used for such movements as kicking a ball, lifting a fork, or turning the
pages of a book.
Smooth Muscle:
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A type of muscle that is usually not under your conscious, voluntary control.
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The stomach and the walls of veins are made up mostly of smooth muscle tissue.
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Smooth muscles do such things as moving food through the digestive tract.
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Smooth muscle cells are not striated.
Cardiac Muscle:
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Cardiac muscle tissue makes up the heart.
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Only in the heart.
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Recall that the heart is a muscular organ that pumps blood through the circulatory
system.
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Cardiac muscle is striated, like skeletal muscle.
However, cardiac muscle is not under your conscious or voluntary control. In this way,
cardiac muscle is more like smooth muscle.
Working Together:
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Skeletal muscles are attached to the bones of the skeleton by strips of connective tissue
called tendons.
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The muscles are attached to bones in opposing pairs.
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When one muscle contracts, or tightens, it pulls the bone in one direction.
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The other muscle in the pair relaxes.
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To return the bone it its original position, the second muscle contracts, pulling the
bone in the opposite direction, as the first muscle relaxes.
Skin
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Skin is the largest organ in the human body.
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Spread out, it covers 1.5 meters squared!
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Functions:
1. Protection
2. Maintain temperature
3. Eliminate wastes
4. Gather information
5. Produce vitamin D
Epidermis:
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Top layer
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Mostly dead skin cells
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Protects the under layers
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Thinner than the dermis
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No nerves or blood vessels
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Does contain melanin-pigment that gives skin it’s color
Dermis:
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Thicker, underneath layer
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Contains:
– Blood vessels
– Nerves
– Sweat glands
– Oil glands
– Hair follicles