Lecture 5 - SQ

Question 1

1. What muscles that insert on either the scapula or the humerus are innervated by dorsal rami of
   spinal nerves?

Answer 1

1. None. All spinal nerve innervation to the upper limb muscles is from ventral rami.

Question 2

2. What muscle(s) that insert on either the scapula or the humerus are not innervated by any
   spinal nerves?

Answer 2

2. Trapezius is not innervated by segmental spinal nerves but by cranial nerve XI (spinal
   accessory nerve).

Question 3

3. If there are only seven cervical vertebrae, how come there are eight cervical spinal nerves?

Answer 3

3. In the neck, spinal nerves are numbered according to the vertebra below them. However, in
   the thorax and further inferiorly spinal nerves are named according to the vertebra above.
   This leaves an extra spinal nerve, C8, emerging above the T1 vertebra but below the C7.

Question 4

4. What part of the glenohumeral joint is naturally most relaxed?

Answer 4

4. The glenohumeral joint is most relaxed inferiorly. This has implications to where the head of
   the humerus can go, during dislocation. The short tendons of the rotator cuff and the
   proximity of the acromion process prohibit the humerus from dislocating upward.

Question 5

5. According to some anatomy books, the function of the subclavius muscle is to protect the
   subclavian artery when the clavicle breaks. Is this possible?

Answer 5

5. If the clavicle breaks the subclavius muscle can protect the underlying artery. This can happen
   in two ways. First, since the muscle lies between the bone and the artery fragment of the
   broken bone gets imbedded in the muscle rather than in the artery. Secondly, if the muscle
   spastically contracts, as muscles do around broken bones, this can cause the broken ends of
   the clavicle to bow outward, away from the artery. However, neither explanation is
   acceptable as a primary function for the muscle. Clavicles don’t fracture often enough and a
   muscle which is not occasionally active will atrophy.

Question 6

6. What type of joints are: a) the sternoclavicular, b) sternocostal and c) costochondral joints?

Answer 6

6. The sternoclavicular joints are complex synovial joints with interceding fibrocartilage articular
   discs. The sternocostal (sternochondral) joints are most commonly synovial, and the
   costochondral joints are synchondroses.

Question 7

7. What is the action of the pectoralis major muscle?

Answer 7

7. The pectoralis major is a medial rotator and adductor of the arm. Its clavicular portion helps to
   rotate the arm medially and to flex it. The sternocostal part depresses the arm and shoulder.