Muscles & bone work like a lever machine
As you study human muscles you will hear that they work with bone as levers. But what does that mean? How does a lever machine work?
It can be difficult to connect memorizing the origin, and insertion points of muscles on bones with the concept of leverage. So, let’s try to sort how muscles work as levers now.
3 Types of levers
Muscles pulling on bone work like one of the 3 types of levers displayed below.
A set of levers with a load placed at various positions, Fouad A Saad/Shutterstock.com
Muscle & Bone Levers
In anatomy, muscle and bone levers consist of bone [a rigid bar] that pivots at an anatomical structure that acts as a hinge or a point of support [a fulcrum] and moves a weight [load] at one end or at the midpoint of the bar by applying a muscle contraction [force].
Thinking of muscles and bones as a set of levers helps to clarify how an array of angular movements can be accomplished by cells, skeletal muscle fibers, that work only linearly.
The angle of muscle fibers relative to the muscle’s tendon assists in converting linear to non-linear movement. The arrangement of muscle origins and insertion points on bone is also important for fine-tuning the direction of motion. Lever arrangements, judicious use of insertions and points of origin, and an assortment of muscle sizes and shapes produce precise performance.
Various shapes used by skeletal muscle to convert linear into angular movement, OpenStax College/Wikimedia Commons
Muscle origins and insertions
Each muscle has an origin and an insertion point. Muscle origins and insertions can be described as the anchor end [origin] and the most mobile end [insertion] when the muscle shortens.
A muscle’s origin is usually at the attachment of its tendon to the bone with greater mass and stability. Bones at the origin of a muscle are typically those nearer the axis of the skeleton, proximal. The bone at a muscle’s insertion point is usually lighter and distal.
The illustration below displays the origins and insertions of the anterior hip muscles. Here the origins are the spinal column and hip bone. The insertion points are on the bones of the legs. As the muscles contract the legs move.
But sometimes muscle insertions are on soft tissues. For example, the orbicularis oris muscle, an oval shaped muscle, inserts on the skin around the lips and has its origin on the maxilla and mandible.
Location of the slender right Gracillis muscle, Beth O’Hara/Wikimedia Commons
Learning the origin and insertion points of various muscles is much easier if bones are well-learned first. Bones appear a bit boring without something attached to them, but it is well worth going back and reviewing the size, shape and location of the larger bones before trying to learn muscle origins and insertions.
The best way to study muscle origins and insertions is to keep in mind the shape of the muscle and its tendons. Long thin tendons are likely to attach to lighter, thinner, distal bones as insertions. Thicker broader tendons make much better anchors and are found proximal as muscle origins.
Examples of human muscle and bone levers
This video by Bob Myers describes specific examples of muscle and bone arrangements that work as the 3 types of levers to make the body mobile.
Further reading
Do you have questions?
Dr. Reece is always available to answer your questions at DrReece@MedicalScienceNavigator.com. If you found this discussion of muscles, origins, insertions and levers helpful please share it with your followers on social media by clicking on one of the buttons below.
Margaret Thompson Reece PhD, physiologist, former Senior Scientist and Laboratory Director at academic medical centers in California, New York and Massachusetts is now Manager at Reece Biomedical Consulting LLC.
She taught physiology for over 30 years to undergraduate and graduate students, at two- and four-year colleges, in the classroom and in the research laboratory. Her books “Physiology: Custom-Designed Chemistry”, “Inside the Closed World of the Brain”, and her online course “30-Day Challenge: Craft Your Plan for Learning Physiology”, and “Busy Student’s Anatomy & Physiology Study Journal” are created for those planning a career in healthcare. More about her books is available at https://www.amazon.com/author/margaretreece. You may contact Dr. Reece at DrReece@MedicalScienceNavigator.com, or on LinkedIn
Dr. Reece offers a free 30 minute “how-to-get-started” phone conference to students struggling with human anatomy and physiology. Schedule an appointment by email at DrReece@MedicalScienceNavigator.com.