Key terms

TermMeaning
Musculoskeletal systemThe body system that provides support, stability, shape, and movement to the body
JointThe point at which two (or more) bones meet.
CartilageSoft connective tissue found between joints
LigamentsConnective tissue that attaches bone to bone at a joint
TendonsConnective tissue that attaches muscle to bone
Voluntary muscleMuscle that can be consciously controlled
Involuntary muscleMuscle that is controlled by the autonomic nervous system (not consciously controlled)
Striated muscleMuscle tissue that has a striped appearance due to its fiber composition

The musculoskeletal system

In the musculoskeletal system, the muscular and skeletal systems work together to support and move the body.
The bones of the skeletal system serve to protect the body's organs, support the weight of the body, and give the body shape. The muscles of the muscular system attach to these bones, pulling on them to allow for movement of the body.

The human skeleton

The human skeleton performs several major functions. It protects the internal organs, supports and gives shape to the body and allows for movement. It also is the site of blood cell production, which occurs in the marrow of some bones.

The skeleton

The human skeleton is divided into two parts: the axial skeleton and the appendicular skeleton.
Diagram labeling the axial and appendicular skeletons of the human body
Image modified from OpenStax, CC BY 4.0
The axial skeleton consists of:
  • the skull, which protects the brain and supports facial structure
  • the vertebral column (spine), which surrounds and protects the spinal cord and support the head
  • the thoracic (rib cage), which surrounds and protects the organs within the chest (including heart and lungs)
The appendicular skeleton consists of:
  • the pectoral girdle (shoulders):
  • upper and lower limbs (arms and legs)
  • the pelvic girdle (hip bones)

Joints, cartilage, ligaments, and tendons

Diagram of a synovial joint, illustrating the various connective tissues (tendons, ligaments, cartilage)
Synovial joint example. Image from Wikimedia, CC BY-SA 3.0.
The musculoskeletal system also contains connective structures and tissues that support the body and allow for its movement.
Cartilage acts as a shock absorber to reduce friction. Ligaments help stabilize the joint, keeping it from moving outside of its intended range of motion. Tendons connect the skeletal system to the muscular system by attaching muscle to bone. When muscle contracts, the tendon acts on the bone, causing movement.
Comparison of three types of joints: suture joints in the skull (fixed), cartilaginous vertebral discs (slightly movable), and a synovial joint (freely movable)
(a) Suture joint - fixed; (b) Vertebral discs - slightly movable; (c) Synovial joint - freely movable. Image from OpenStax, CC BY 4.0
Joints, the point at which two or more bones connect, can be fixed, slightly movable, or freely movable.

Muscles

The body contains three types of muscle tissue: skeletal muscle, smooth muscle, and cardiac muscle.
Comparison of the three types of muscle - skeletal, smooth, and cardiac
(a) Skeletal muscle; (b) Smooth muscle; (c) Cardiac muscle. Image from OpenStax, CC BY 4.0
Skeletal muscle is voluntary and striated. These are the muscles that attach to bones and control conscious movement. Smooth muscle is involuntary and non-striated. It is found in the hollow organs of the body, such as the stomach, intestines, and around blood vessels. Cardiac muscle is involuntary and striated. It is found only in the heart and is specialized to help pump blood throughout the body.

Muscle contraction

When a muscle fiber receives a signal from the nervous system, myosin filaments are stimulated, pulling actin filaments closer together. This shortens sarcomeres within a fiber, causing it to contract.
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