1) A friend has pain in his back, and wants to know why, whe he presses on a cer
ID: 3517652 • Letter: 1
Question
1) A friend has pain in his back, and wants to know why, whe he presses on a certain spot, his knee gives out under him. The most lkely reason is that he is pressing on the:
a) tibial portion of the sciatic nerve
b) common peroneal portion of the sciatic nerve
c) femoral nerve
d) phrenic nerve
e) blood vessels supplying the lower extreminity
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2) In order for a positive Achilles reflex to occur, the effectors must receive stimulation from the:
a) femoral nerve
b) tibial nerve
c) pudendal nerve
d) common peroneal nerve
e) obturator nerve
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3) The virus that causes shingles stays latent in the:
a) plexuses
b) anterior gray horns of the spinal cord
c) ascending spinal tracts
d) central canal of the spinal cord
e) dorsal root ganglia
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4) A misplaced intramuscular injection has rendered a patient unable to extend the wrist. This patient most likely has damange to the:
a) sciatic nerve
b) ulnar nerve
c) radial nerve
d) phrenic nerve
e) third intercostal nerve
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5) Sensations of proprioception and discriminative touch are conveyed by the:
a) spinothalamic tracts
b) posterior column tracts
c) corticospinal tracts
d) rubrospinal tract
e) vestibulospinal tract
Explanation / Answer
1. We can approach this question by eliminating the most obvious wrong choices first.
Option d is not a choice as it supplies the diaphragm.
Option e is also excluded as other signs and symptoms are more prominent if blood supply is occluded.
That leaves us with options a, b and c. The question has 2 portions. It mentions pain in the back and giving away of the knee joint.
The Anterior and Posterior Cruciate ligaments are powerful cord-like structures that are part of the knee joint. These powerful ligaments prevent movement of the tibia and fibula on each other in an anteroposterior direction and provide stability to the joint.
These ligaments are supplied by the posterior articular branches of the tibial nerve. Any injury to the nerve will result in weakness of the Cruciate ligaments and hence, a sense of giving away of the knee joint. Also, since it is an extension of the sciatic nerve, its damage may result in back pain too.
Though the common peroneal and femoral nerves supply muscles of the leg too, they have no role in the functioning of the knee.
Hence, Option a seems to be the most logical answer here.
2. The Achilles reflex or the Ankle Jerk reflex is a monosynaptic stretch reflex which tests the integrity of nerve roots S1 and S2. A positive response is a jerking of the foot towards the plantar surface, also known as plantar flexion. The effector muscle which produces this response is the Gastrocnemius muscle which is supplied by the tibial nerve.
Hence, Option b is the correct answer.
3. The virus that causes Shingles is Herpes Simplex Virus(HSV). It is of 2 types: HSV-1 and HSV-2. After initial infection, both these viruses remain dormant in the dorsal root ganglia until reactivated. HSV-1 remains latent in the trigeminal ganglion while HSV-2 remains latent in the sacral ganglia.
Options a, b, c and d are all parts of the spinal cord and nerves structures adjacent to it which are not involved in Herpes Simplex Viral infections.
Hence, Option e is the correct choice.
4. Extension of the wrist is brought about by Extensor carpi radialis longus, Extensor carpi radialis brevis and Extensor carpi ulnaris. These are the primary extensors. Various other muscles form the secondary extensors. All these muscles are innervated by the Radial nerve which has nerve roots in C6, C7 and C8. Any injury to the Radial nerve will result in weakness or loss of extension action of the wrist.
It is also worthwhile to remember that the radial nerve is the most commonly affected upper extremity nerve during inadvertent intramuscular injections!
Hence, the answer is Option c.
5. Options c, d and e can be excluded as they are all descending tracts of the spinal cord.
Options a and b are the ascending spinal tracts. Lets see the function of each.
The Spinothalamic tracts carry sensations of pain, temperature and crude touch.
he Posterior column tract also known as Posterior Column Medial Lemniscus (PCML) pathway or the Dorsal Column Medial Lemniscus (DCML) pathway carry sensations of fine touch, proprioception, vibration and two-point discrimination.
Hence, Option b is the right choice.
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