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.

 MUSCLE ACTION:

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!: https://vine.co/v/MAqJgzrHng2

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! : https://vine.co/v/MAq5PjtjPAh

Extensor Capri Ulnaris: a wrist extensor muscle

We're BACK in the forearm with EXTENSOR CARPI ULNARIS muscle!

Extensor: tells us that this muscle "extends something" as far as muscle actions go!
Carpi: refers to the WRIST Ulnaris: referring the the forearm bone: the ULNA (between the Radius & the Ulna - the ulna is on the 'pinky finger' side of the forearm.)

Attachment points:

This muscle originates at the "common extensor tendon" from the lateral epicondyle of the humerus. This area is just above the elbow and 'common extensor'  refers to the area where many of the wrist extensor muscle muscles come from.

Insertion point: Base of the 5th metacarpal (the pinky side of the wrist - the pinky is the 5th digit)

 TWO MUSCLE ACTIONS:

By breaking down its name,  we know that this muscle EXTENDS THE WRIST (aka - holding your hand out (palm down) and extending fingers towards ceiling - as if to say Hello!)

This muscle also helps to ADDUCT the wrist as well!

See video link for demo of muscle actions:
https://vine.co/v/MqUYwXheiKT

 Both of these actions happen at the RADIO-CARPAL joint - where the radius (other forearm bone that isn't the Ulna) and carpal (wrist) bones meet :)

Extensor Carpi Radialis LONGUS & BREVIS: wrist-extensor muscles

Our wrist EXTENSOR muscles live in our forearms, more specifically, they all hang out on the side of our arm that turns into the top/back of our hands. Wrist EXTENSOR muscles help to lift your hand up as if to say 'hello' !  Today we're going to talk about TWO wrist extensor muscles :

1) Extensor Carpi Radialis BREVIS &
2) Extensor Carpi Radialis LONGUS

Let's break down each word so it makes a bit more sense!

- EXTENSOR meaning that they extend

- CARPI meaning the carpal bones of the WRIST

(these muscles extend the wrist!)

- RADIALIS referring to the radius bone in the arm. The radius is in line with our thumb* - therefore these muscles extend down the thumb side of our arm.

- BREVIS meaning SHORT & LONGUS meaning LONG ;)

 Extensor Carpi Radialis Longus & Brevis ATTACHMENT POINTS:

Origin: BOTH Extensor Carpi Radialis Longus AND Brevis attach at the same point just above the elbow > onto the upper arm bone (the Humerus bone)

(officially "the lateral supracondylar ridge of the humerus)

(then they both extend down the radius bone...)

Insertion points:

1) Extensor Carpi Radialis BREVIS attaches at the base of the THIRD metacarpal

2) Extensor Carpi Radialis LONGUS attaches at the base of the SECOND metacarpal

METACARPAL aka "where your knuckle meets your finger"

(our thumb is considered the "first metacarpal" and so on...

*to help remember which of the two forearm bones (RADIUS or ULNA) is on which side I think "RAD dude - thumbs up!" Because the RADius is the bone that extends to the thumb (up!) side! 

MUSCLE ACTIONS:

Both BREVIS and LONGUS perform the SAME THREE actions so that easy!

1) no surprise here that these two wrist extensors EXTEND THE WRIST at the radio-carpal joint > (where radius bone meets the Carpal bones of the wrist - on the Thumb side!)

2) they also ABDUCT the wrist at the radio-carpal joint
> tipping the wrist towards the Radial (thumb) side ((like if you were giving someone a "thumbs up" and then you pointed your thumb towards your face))

that was really hard to describe so if it doesn't make sense be sure to check out the video version!

3) Surprise! These two muscles also assist in FOREARM FLEXION (aka - bending your arm at the elbow!) Can you guess why? Remember how both muscles CROSS the elbow joint and attach onto the Humerus (the upper arm bone) ? 

https://vine.co/v/MmImJwOi9Du

 In that order : wrist extension & abduction (aka radial deviation) and forearm (elbow) flexion ! 

Whenever a muscle Crosses a JOINT it WILL create an action of some sort. Extensor Carpi Radialis Brevis and Longus BOTH cross the elbow joint and the wrist joint - creating actions of both joints!