Muscles

These learning outcomes are quite broad, so this post will probably end up being a bit vague. Oh well...

Understand the key concepts of muscle action.

The main thing to understand is that muscles never push- they always pull. So, wherever you have a prime mover muscle to perform one action, you will need an antagonist muscle pulling in the other direction to perform the opposite action. Prime movers and antagonists are usually located on opposite side of a joint. Sometimes, other muscles might be needed to help out by stabilising joints or adding force. Muscles that help out are called synergists, and synergists that immobilise bones to provide stability are called fixators.

Another thing to understand is that muscles attach to things (e.g. bones) and they produce movement by contracting and pulling those attachment points closer to each other. Muscles can be attached directly (the layer of connective tissue surrounding muscle can become fused to the layer of connective tissue surrounding bone) or indirectly (the connective tissue of the muscle can extend past the muscle as a rope-like tendon or sheet-like aponeurosis).

Yet another thing to understand is that skeletal muscles generally attach to two bones, and only one of those bones moves. The attachment that remains fixed is called the origin, whereas the attachment that moves is the insertion. When the muscle contracts, the insertion is pulled towards the origin.

Identify superficial muscles of the human body.

I'm not really sure why this is listed as a learning outcome, given that I'm fairly sure that at this stage we're still at the "learn the broad concepts of what muscles are made of" stage and not the "learn every single muscle and what it does" stage. If you want to learn more about muscles, head on over to TeachMeAnatomy.info- never used it myself, but I've heard good things about it.

Describe the actions of muscles.

Muscles have lots of useful actions within the body. As well as being able to help us move, they also help us maintain our posture. They also have many other functions within the body, such as heat generation, pumping blood, moving food through the intestines, and so on.

Understand the naming conventions of skeletal muscle.

Skeletal muscle is what we often think of when someone says the word "muscle." Simply put, it is muscle that is associated with moving the skeleton. It is striated, that is, it has a stripy appearance under the microscope due to the arrangement of its contractile proteins. Each muscle fibre is surrounded by a thin sheet of connective tissue called endomysium. Multiple muscle fibres are grouped together into fascicles, which are surrounded by another layer of connective tissue called perimysium. Finally, dense regular connective tissue surrounding the whole muscle is called epimysium.

Skeletal muscle is often named after various characteristics including location, shape, size, number of origins, action, and so on. For instance, the gluteus maximus is named after location (gluteal region) and size (maximus = large). Understanding what the different parts of a muscle name mean might help you to remember the muscles more easily.

Arrangement of fascicles

This wasn't listed as a learning outcome, but since so many slides are devoted to this, I thought I'd write about it here.

Fascicles can be arranged in many different ways, and there are names for the different arrangements:

• Circular- Fascicles are arranged in concentric rings, forming sphincters. Examples include orbicularis oris and orbicularis oculi.
• Convergent- Fascicles converge towards a single tendon, allowing for the generation of a lot of force at a single point. An example is pectoralis major.
• Parallel- Fascicles are arranged parallel to the long axis of the muscle. Examples include sartorius and rectus abdominis.
• Pennate- Fascicles are short and oblique and attach to a central tendon. In unipennate muscles, fascicles insert on one side of the tendon. In bipennate muscles, fascicles insert on opposite sides of the tendon. Finally, in multipennate muscles, there are many fascicles inserting onto different tendons. Examples include extensor digitorum longus (unipennate), rectus femoris (bipennate), and deltoid (multipennate).