Extensor: this muscle extends something ! (in this case : thumb)
Pollicis: referring to the thumb
Brevis : means short in Latin. When a muscle is referred to as brevis there is a good chance there is a very similar, longer version (longus) of this muscle.
Remember our last post: Extensor Pollicis Longus ? Let's refer to Extensor Pollicis Brevis as their little brother (brother/brevis?)
Muscle Attachment Points:
Origin: Posterior surface of the Radius (forearm bone on thumb side ) and the interosseus membrane
(connective tissue between the radius and the other forearm bone - the Ulna)
Insertion: Proximal Phalange of the thumb (proximal meaning closer - while last week's Longus tendon went all the way to the tip (distal end) of the thumb because is longer.
Like a little brother, Brevis
Helps Extensor Pollicis Longus to
Extend the Thumb at the carpo-metacarpal joint* (where wrist meets base of thumb)
and at the metacarpo-phalangeal joint* (the joint towards the tip of your thumb - helping it to 'wiggle')
Basically this means the Longus does most of the work of thumb extension
(*thumb joint images at end of this post)
That's it for the 4 long muscles of the thumb! Fun Fact:
The skinny tendons (where the muscle meets bone) of Abductor Pollicis Longus and both Extensor Pollicis Longus and Brevis (this post!) are visible on the hand and form what is called:
The Anatomical Snuff box . Say what you say? Look at your right hand - fingers spread and thumb extended. The above tendons form the walls of a cavity right around where your thumb meets wrist (the floor of this cavity being your carpal (wrist)bones.
This cavity was used historically to inhale powdered tobacco or "snuff'.
Stay tuned next week where we explore the 4 SHORT muscles of the thumb!