Human Skeletal Joints are Mostly Freely-Moving

Humans Have Synovial, Semi-movable, and Fixed Joints

Apr 14, 2009

Joints in the human body are categorized by their structure or the way they move.

There are two major types of joints including freely movable joints which slide over each other easily and semi-movable joints, such as those in the spine, that are more stable but far less flexible. A few joints, such as those that make up the skull have no mobility at all. The human body has an astounding 300 different joints.

Freely Movable Joints

The majority of joints in the human body are synovial joints, ones that can move freely. These joints have synovial fluid, which is secreted by the joint lining, that provides lubrication so the joint can move with minimal friction.

There are several types of freely moving joints. In pivot joints, the bone rotates with a collar formed by another bone. This type of joint is seen between the upper bones of the neck and skull, allowing the head to turn. Ball and socket joints have a bone with a ball shaped end that fits into the cupped end of the other. This type is seen in the shoulder. Saddle joints are seen at the base of thumbs and are shaped like saddles so that they can move back and forth.

Semi-movable and Fixed Joints

A semi-movable joint is one where the articular surfaces are fused to a pad of cartilage that only allows for a little bit of movement. The joints that make up the spine and the joint at the base of the pelvis are both examples of semi-movable joints. Other joints in the human body are fixed and unable to move.

The human skull is made up of plates that allow the head and skull to grow during childhood. Once the body has reached adulthood the skull fuses together, making a complete skull with completely fixed joints.

Stabilizing the Joints

The body’s semi-movable joints need to be kept stable, but to still allow for as much movement as possible. These joints are stabilized by ligaments. External ligaments attach to the bones on either side of the joint, forming a capsule that protects the joint from damage. A few joints in the body, such as the ankle joints, have a thick sheet of connective tissue, called the retinacula, which helps to hold the tendons in and keep them from bowing.

Shock Absorption

The knee, wrist and spinal joints all have shock-absorbing fibrous disks that are positioned between the bones to prevent them from damage. In the wrist and knee the disk is called the meniscus, and intervertebral disks in the spine. The structure of these disks is comparable to a jelly-filled donut, the inside a jellylike material made up of water and collagen and the outer part a tough fibrous cartilage.

The human body is full of joints, which are necessary for the myriad of movements that it is capable of. These joints, whether movable or fixed, are essential for the functioning of the human body.

Tortora, Gerard and Sandra Grabowski. Principles of Anatomy and Physiology, 10th Edition. Wiley, New York. 15 June 2002.

The copyright of the article Human Skeletal Joints are Mostly Freely-Moving in Skeletal/Muscular System is owned by Megan Worley. Permission to republish Human Skeletal Joints are Mostly Freely-Moving in print or online must be granted by the author in writing.