Monday, 14 April 2014

Extensor Digitorum: a wrist extensor muscle

Today we'll be discussing the forearm muscle EXTENSOR DIGITORUM.

(If you've been following along with us on Monday's, you may have made the connection that many muscle NAMES often refer to to the Action that the muscle performs, or the bony area where a muscles' tendon attaches.

-EXTENSOR meaning that this muscle does the action of Extension.
-DIGITORUM refers to the the fingers (aka - digits!)
So just by breaking it down we already know that Extensor Digitorum extends the fingers!

Attachment points of EXTENSOR DIGITORUM:

-Originates just the above the elbow onto the humerus (upper arm bone) , in the same area as many of the forearm extensor muscles originate. (aka  "the common extensor tendon" )
-Extensor Digitorum muscle belly (the bulk of the muscle) extends down the forearm until just above the wrist > turns into thinner tendons > splitting off into FOUR separate tendons, each inserting towards the tips of fingers 2-5*
*not including the thumb (aka - #1)

Textbook attachment points:

ORIGIN:  common extensor tendon from the lateral epicondyle of the humerus
INSERTION:  middle and distal phalanges of  second through fifth fingers!
Let's talk about "phalanges" for a moment:  Look at one of your fingers. See how it can be separated into 3 sections just after the knuckle? ( If that doesn't make sense - play with bending the finger and you may see the division better!)  Each "section" is divided by a joint and are referred to as: PROXIMAL, MIDDLE, AND DISTAL PHALANGES. Proximal is closest to your knuckle, (middle speaks for itself), and Distal is furthest away (the tip of the finger)
More Terminology:
Tendons: the end of a muscle > attaching muscle to bone ((can be really long, or short, cord-like or flatter))
Lateral: "towards the outside of the body" > opposite is "medial" meaning closer to the mid-line of the body.
Epicondyle: think bony bump
Humerus: thing hilarious upper arm bone (from elbow to shoulder)
Phalanges: think fingers
- radio-carpal joint: where the radius (1 of 2 forearm bones - other one is Ulna) and the carpal (wrist) bones meet.
- MCP (meta-carpo-phalangeal) joint : where the metacarpals meet the phalanges (like where hand meets finger)
- IP (inter-phalangeal) joint : the joints within each finger > each finger had a proximal and a distal interphalangeal joint.


Not only does EXTENSOR DIGITORUM extend fingers 2-5 (see above!) at the MCP and IP joints* but this muscle also helps to EXTEND THE WRIST at the radio-carpal joint.
See video of the two muscle actions mentioned above!:

Wanna feel your Extensor Digitorum muscle contract?

starting position: seated or standing with arms crossed > bring your left thumb to your right elbow > then slide your thumb off the elbow (up towards your face) > there will be a Dip and before you know it you're on another bony bump! It's called the LATERAL EPICONDYLE (bony bump) of the HUMERUS.  So this BUMP you're on right now is on the distal end of the Humerus (upper arm) bone.
And this is where the 'common extensor tendon' is located > the spot where many of the wrist (and finger!) extensor muscles attach. NOW slide your thumb LEFT > JUST Off this bump > KEEP YOUR THUMB just off the bump AND SPREAD THE FINGERS OF YOUR RIGHT HAND WIDE > relax > and repeat! can you feel the muscle contracting under your Left thumb? You are extending your digitorum!
confusion? here's a visual! :