DENTAL GROSS ANATOMY: Answers to Sample Questions

WEEK 2 -- September 12, 2005

1. Fertilization normally takes place in the:
   • A. Ovary
   • B. Isthmus
   • C. Ampulla
   • D. Uterus
   • E. Vagina
   
   
2. The follicular phase of ovarian development which precedes ovulation is influenced by secretion of the ovarian hormone:
   • A. Estradiol
   • B. Progesterone
   • C. Luteinizing hormone (LH)l
   • D. Follicle stimulating hormone (FSH)
   • E. Human chorionic gonadotropin (hCG)
   
   
3. The brain and spinal cord are derived from:
   • A. Hypoblast
   • B. Ectoderm
   • C. Neural crest cells
   • D. Lateral plate mesoderm
   • E. Endoderm
   
   

Answers Clinical Case :
1. The knife has penetrated the lateral aspect of the arm and appears to track posteriorly. The posterior aspect of the arm is also known as the extensor arm. The triceps muscle is at risk for injury, making it difficult for the patient to extend his elbow. More importantly, however, are the structures that pass within the Radial Groove between the lateral and medial heads of the triceps muscle . These include the Deep Brachial Artery, (Profunda Brachii), and the Radial Nerve, (see figure 4).

2. Damage to the Deep Brachial Artery may produce significant bleeding from the wound but is less likely to prevent blood supply to the posterior arm. This is due to the collateral flow that exists between the Radial and Deep Brachial Arteries, (see figure5). Every major joint of the extremities has a similar 'backup plan' of collateral anastamosis to provide the joint and its^M distal tissues with adequate blood flow in the event of stenosis or occlusion of the main arterial supply. Recall that the arterial system is valveless, enabling blood to flow in the direction of highest to least pressure at all times.

3. The Radial Nerve is known as the extension nerve: all extensor muscles (plus brachioradialis, abductor pollcis, supinator) are supplied by this nerve. Given the location of the stab wound, the Radial Nerve may be damaged as it passes through the radial groove. Therefore, all muscles and sensory innervation beyond the point of damage will be affected. The nerve is damaged before it innervates the 'extensor wad' of muscles in the dorsal forearm that originate on the lateral epicondyle of the humerus and hence all muscles and sensory distributions below the elbow. This would include the brachioradialis muscle, (elbow flexion when the forearm is pronated), extensor carpi muscles, (wrist extension), the extensor pollicis and digitorum muscles, (thumb and digital extension), the supinator muscle, (forearm/wrist supination), and the abductor pollicis, (thumb abduction). The patient will experience numbness along the dorsal forearm and hand for damage to the superficial branch of the Radial Nerve, (see figure 6).

4. Sir Issac Newton noted that for every action there is an equal and opposite reaction. The extremity musculature is no exception. There are joint extensor muscles that act equal and opposite to joint flexors. This allows the limb to perform a myriad of different positions. However, when the Radial Nerve supply to the extensor muscles in the forearm is damaged, the extensors cannot contract, leaving the flexor forearm muscles to contact unopposed. Thus the patient's wrist assumes a 'flexed' position at rest instead of the 'neutral' position