TBL4 - Muscles of Posterior Arm

Question 1

Where are the infraglenoid tubercle, radial groove, & olecranon located?

Answer 1

1) Infraglenoid tubercle is a crevice located directly below the glenoid cavity
2) The radial groove is found on the posterior side of the humeral shaft (elbow joint)
3) The olecranon is found on the posterior aspect of the proximal ulna

Question 2

Where is the triceps brachii muscle located? Where does the long head attach proximally? What is its function?

Answer 2

1) The triceps brachii muscle covers the posterior side of the humerus
2) The long head of the muscle attaches proximally to the infraglenoid tubercle
3) The long head of the triceps brachii muscle helps resist inferior displacement of the humeral head

Question 3

Where do the lateral and medial heads of the triceps brachii muscle attach proximally? Where does the common tendon of the triceps attach distally? What are their functions?

Answer 3

1) The lateral head of the muscle attaches proximally to the posterior humerus
2) The medial head of the muscle attaches proximally below the radial groove
3) The common tendon of the triceps attaches distally to the olecranon of the ulna; thus, the muscle is positioned to extend the forearm at the elbow joint
4) The triceps brachii is the chief extensor of forearm & is especially important during adduction
5) The medial head of the triceps is the workhorse of forearm extension while the stronger lateral head is recruited only to counter resistance against the extension

Question 4

Which nerve innervates the three heads of the triceps muscle? Where does this nerve travel?

Answer 4

1) The radial nerve innervates the three heads of the triceps
2) The nerve courses along the radial groove on the posterior surface of the humerus

Question 5

Why is forearm extension weakened but not lost after fracture along the radial groove of the humerus? (Please explain)

Answer 5

1) A midhumeral fracture may injure the radial nerve in the radial groove in the humeral shaft
2) When this nerve is damaged, the fracture is not likely to paralyze the triceps because the low origin of the medial head allows it to be unaffected