This document discusses the skeletal system, including bones, joints, and muscles. It states that bones provide structure, protect organs, allow movement, store minerals, and produce blood cells. Bones are made of three layers including spongy bone marrow, dense compact bone, and a repairing outer layer. Joints connect bones and allow movement, with ligaments and cartilage between bones. Muscles are attached to bones and work in pairs to control voluntary and involuntary movement. There are three main types of muscles: skeletal, smooth, and cardiac.

1. 7th Grade Science
Weiner High School

2.  Provides a framework for the body that
helps protect the internal organs.
 Works with the muscles to enable the
body to move.
 Has bone marrow that manufactures
blood cells.
 Stores calcium & phosphorus needed for
the body’s chemical processes.

3. Bones…
 Generally have 3
layers:
1. The Core, a spongy
material containing
bone marrow that
makes new blood.
2. Compact bone, a
hard dense layer that
strengthens the
skeleton.
3. The Periosteum, a
thin layer that helps
repair broken bones.
 Are not solid. They
have microscopic
canals that contain tiny
blood vessels & nerve
fibers connecting bone
cells to the main blood
& nerve supply.
Joints…
 Are the points where two
bones connect.
 Are primarily movable;
although there are a few
that are fixed, such as the
adult skull that protects the
brain.
 Are connected by
ligaments, a flexible tissue
made of collagen that
holds the bones together.
 Are covered with cartilage
that allows them to move
smoothly.
 Consist of four basic
types:
1. Ball-and-socket
2. Hinge
3. Pivot (Rotating)
4. Gliding

5.  Is a mixture of bone and cartilage.
 Has ligaments that hold it together.
 Has about 206 bones.
 Is 70% nonliving tissue and about 30%
living tissue. The nonliving part is
made of minerals that make the bones
hard. The living part is made of cells
that maintain healthy bones and help
heal bones when they break.

6.  Works with the skeletal and nervous
system to help move the body.
 Helps control body processes such
as breathing, digestion, and blood
flow.
 Holds the skeleton together and
gives the body its build and general
shape.

7.  Are strong tissue made of long, thin cells called muscle
fiber.
 Are arranged in layers over the skeleton and are
attached to the bones or to other muscles by tendons.
 Number over 600 in the average person’s body.
 Work in pairs. When one muscle contracts, the other
relaxes.
 Are either voluntary or involuntary:
1. Voluntary muscles control all forms of conscious
movement.
2. Involuntary muscles control the movement of
internal organs.

8.  Are categorized as skeletal, smooth, or
cardiac.
1. Skeletal muscles are voluntary muscles
that help hold the bones of the skeleton
together.
2. Smooth muscles are involuntary
muscles that control the movement of
internal organs such as the stomach and
lungs
3. Cardiac muscles are involuntary
muscles that form the walls of the heart.