Concept: Learning Muscles

If you are just now getting your feet wet, you may want to start with the anatomy intro.
Muscles are well-known to all of us. Even if we don't know their names or which bony landmarks anchor them, we know they are what give us motion and help pick up the ladies (figuratively, although I guess literally, too). Trying to memorize a bunch of facts about a bunch of muscles that all look the same can be a daunting task if done by rote, so let's break it down into a checklist. For each muscle, you'll want to know at least these basics:

• Proximal attachment
• Distal attachment
• Action
• Innervation

A handy way to keep track of these is to use a note card per muscle and quiz yourself with them. Also, drawing schematic muscle diagrams or even using an anatomy coloring book forces your brain to spend time thinking about the structures and figure out their functions. You'll see that the attachment points and the action are related: if you know the attachments, you can figure out the basic actions.  It's a good bet that if a muscle crosses a joint, it will cause that joint to move. Also, if you know the action, you can get a rough idea of where the attachments might be. Muscle innervation is important because a muscle needs input from a nerve. From a clinical standpoint, if someone has muscle weakness or paralysis, you can figure out which nerve may be injured and where. You'll also start noticing that nerves often innervate muscles that are clustered together or that perform a similar action, which can help you learn the nerves conceptually.

If you need to know more advanced information, usually these extra details are included:

• Specific sites or bony landmarks of attachment
• Origin (more stationary attachment, usually proximal)
• Insertion (more mobile attachment, usually distal)
• All major and minor actions
• Main spinal cord levels that innervate muscle
• Main arterial supply

I include most of these advanced details, but if you're doing graduate-level work, you may need to know other information, like motor point, fiber arrangement (flat, unipennate, etc.), minor arterial supplies, etc. If you're at that level, you're probably well beyond my knowledge already.

Structure: Fibularis Tertius Muscle (aka Peroneus Tertius)

The peroneus tertius is a fun muscle. First of all, it is less of a distinct muscle and more of an accessory tendon of the extensor digitorum longus. When present, the peroneus tertius tendon arises from the extensor digitorum longus, and the muscle fibers it's attached to are considered its muscle belly. Secondly, not everyone has one. Third, and most important, my GTA in undergrad made us say "peroneus tertius" in a British accent, and I would advise you do the same.

Before you try memorizing the info below by rote, let's break down the name to make the structure more conceptual. "Peroneus" refers to the lateral aspect of the leg. "Fibularis" has the same meaning, and is the more preferred term since it avoids confusion with "perineum" and "peritoneum," which are completely unrelated terms. Also, "fibularis" makes more intuitive sense because that's the region where the fibula bone is. Keep in mind, though, that many clinicians and anatomists are old-school and still use "peroneus."

"Tertius" means "third." This is in reference to the fact that there are two other fibularis muscles (fibularis longus and fibularis brevis), making this the third fibularis muscle. It makes sense that this inconsistent, minor muscle would take third place to the other two fibularis muscles. The tricky part is that the fibularis tertius is not really related to the other two. By that I mean it is innervated by a different nerve and is in a different fascial compartment than the other two. The similarities are that it everts the foot and its tendon attaches near the fibularis brevis.

Basic muscle info:
Proximal attachment: Distal fibula.
Distal attachment: Base of fifth metatarsal.
Action: Assists eversion and dorsiflexion.
Innervation: Deep fibular nerve.

Advanced muscle info:
Origin: Distal third of anteromedial fibula, interosseus membrane
Insertion: Dorsomedial aspect of base of 5th metatarsal.
Action: Weak eversion of subtalar (talocalcaneal) joint. Weak dorsiflexion of ankle (talocrural) joint.
Innervation: Deep fibular nerve (L5, S1).
Arterial supply: Anterior tibial artery


References 1,2