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Question 1
Incorrect
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You've been asked to give a discussion to a group of medical students about skeletal muscle physiology and its use in clinical medicine. They pose a series of difficult questions to you.
Which of the following definitions for the A-band of the sarcomere is correct?
Your Answer: Zones of thin filaments extending from either side of the Z-lines
Correct Answer: A band that contains the entire length of a single thick filament (myosin)
Explanation:Myofibrils, which are around 1 m in diameter, make up each myofiber. The cytoplasm separates them and arranges them in a parallel pattern along the cell’s long axis. These myofibrils are made up of actin and myosin filaments that are repeated in sarcomeres, which are the myofiber’s basic functional units.
Myofilaments are the filaments that make up myofibrils, and they’re made mostly of proteins. Myofilaments are divided into three categories:
Myosin filaments are thick filaments made up mostly of the protein myosin.
Actin filaments are thin filaments made up mostly of the protein actin.
Elastic filaments are mostly made up of the protein titin.
The sarcomere is a Z-line segment that connects two adjacent Z-lines.
The I-bands are thin filament zones that run from either side of the Z-lines to the thick filament’s beginning.
Between the I-bands is the A-band, which spans the length of a single thick filament.
The H-zone is a zone of thick filaments that is not overlaid by thin filaments in the sarcomere’s centre. The H-zone keeps the myosin filaments in place by surrounding them with six actin filaments each.
The M-band (or M-line) is a disc of cross-connecting cytoskeleton elements in the centre of the H-zone.
The thick filament is primarily made up of myosin. The thin filament is primarily made up of actin. Actin, tropomyosin, and troponin are found in a 7:1:1 ratio in thin filaments. -
This question is part of the following fields:
- Basic Cellular Physiology
- Physiology
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Question 2
Incorrect
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Which of the following statements is correct about the extensor digitorum muscle?
Your Answer: It receives its blood supply from the radial artery
Correct Answer: It extends the medial four digits at the metacarpophalangeal joints
Explanation:Extensor digitorum is a long muscle located in the posterior compartment of the forearm. Together with the extensor carpi ulnaris and extensor digiti minimi, extensor carpi radialis longus and brevis as well as the brachioradialis, it belongs to the group of superficial extensors of the forearm. These muscles can be easily palpated in the lateral aspect of the posterior forearm, especially during the extension of hand when they are contracted.
Extensor digitorum runs from the lateral epicondyle of humerus to the medial four phalanges of the hand. In this way, it generates the pull for the extension of the four medial fingers in their metacarpophalangeal and both interphalangeal joints. Extensor digitorum also participates in the extension of the wrist.
Extensor digitorum is innervated by posterior interosseous nerve which is a continuation of a deep branch of radial nerve (root value C7 and C8).
Extensor digitorum is vascularized by the branches of three different arteries: (1) posterior interosseous artery, (2) radial recurrent artery, and (3) anterior interosseous artery. Anterior and posterior interosseous arteries are the branches of the common interosseous artery that arises from the ulnar artery. The radial recurrent artery is a branch of the radial artery.
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This question is part of the following fields:
- Anatomy
- Upper Limb
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Question 3
Incorrect
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Regarding drug interactions with erythromycin, which of the following statements is INCORRECT:
Your Answer: There is an increased risk of myopathy if erythromycin is taken with simvastatin.
Correct Answer: Erythromycin decreases plasma levels of warfarin.
Explanation:Erythromycin and clarithromycin inhibit cytochrome P450-mediated metabolism of warfarin, phenytoin and carbamazepine and may lead to accumulation of these drugs. There is an increased risk of myopathy (due to cytochrome P450 enzyme CYP3A4 inhibition) if erythromycin or clarithromycin is taken with atorvastatin or simvastatin. Erythromycin increases plasma concentrations of theophylline, and theophylline may also reduce absorption of oral erythromycin. All macrolides can prolong the QT-interval and concomitant use of drugs that prolong the QT interval is not recommended.
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This question is part of the following fields:
- Infections
- Pharmacology
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Question 4
Incorrect
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If the null hypothesis is wrongly rejected when it is actually true, this is an example of:
Your Answer: A test with a type II error
Correct Answer: A test with a type I error
Explanation:A type I error occurs when the null hypothesis is wrongly rejected when it is actually true and we conclude that there is a difference of effect when in reality there is none (a false positive result).
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 5
Incorrect
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Pressure across the wall of a flexible tube (the transmural pressure) increases wall tension and extends it.
Which law best describes transmural pressure?
Your Answer: Darcy’s law
Correct Answer: Laplace’s law
Explanation:The transmural pressure (pressure across the wall of a flexible tube) can be described by Laplace’s law which states that:
Transmural pressure = (Tw) / r
Where:
T = Wall tension
w = Wall thickness
r = The radius
A small bubble with the same wall tension as a larger bubble will contain higher pressure and will collapse into the larger bubble if the two meet and join.Fick’s law describes the rate of diffusion in a solution
Poiseuille’s law is used to calculate volume of flow rate in laminar flow
Darcy’s law describes the flow of a fluid through a porous medium.
Starling’s law describes cardiac haemodynamics as it relates to myocyte contractility and stretch.
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This question is part of the following fields:
- Basic Cellular Physiology
- Physiology
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Question 6
Incorrect
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Depression of the eyeball is primarily produced by which of the following muscles:
Your Answer: Inferior rectus and inferior oblique
Correct Answer: Inferior rectus and superior oblique
Explanation:Depression of the eyeball is produced by the inferior rectus and the superior oblique muscles.
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This question is part of the following fields:
- Anatomy
- Head And Neck
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Question 7
Correct
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A type II error occurs when:
Your Answer: The null hypothesis is accepted when it is false.
Explanation:A type II error occurs when the null hypothesis is wrongly accepted when it is actually false and we conclude that there is no evidence of a difference in effect when one really exists (a false negative result).
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This question is part of the following fields:
- Evidence Based Medicine
- Statistics
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Question 8
Incorrect
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Which of the following statements accurately describes the flexor digitorum superficialis muscle?
Your Answer: It has a point of origin on the lateral epicondyle of the humerus
Correct Answer: It flexes the middle phalanges of the medial four fingers at the proximal interphalangeal joints
Explanation:Flexor digitorum superficialis is the largest muscle of the anterior compartment of the forearm. It belongs to the superficial flexors of the forearm, together with pronator teres, flexor carpi radialis, flexor carpi ulnaris and palmaris longus. Some sources alternatively classify this muscle as an independent middle/intermediate layer of the anterior forearm, found between the superficial and deep groups.
Flexor digitorum superficialis is innervated by muscular branches of the median nerve, derived from roots C8 and T1 that arises from the medial and lateral cords of the brachial plexus. The skin that overlies the muscle is supplied by roots C6-8 and T1.
The primary arterial blood supply to the flexor digitorum superficialis is derived from the ulnar artery and its anterior recurrent branch. In addition to branches of the ulnar artery, the anterior and lateral surfaces of the muscle are supplied by branches of the radial artery; and its posterior surface also receives branches from the median artery.
The main function of flexor digitorum superficialis is flexion of the digits 2-5 at the proximal interphalangeal and metacarpophalangeal joints. Unlike the flexor digitorum profundus, flexor digitorum superficialis has independent muscle slips for all four digits. This allows it to flex the digits individually at their proximal interphalangeal joints. In addition, flexor digitorum superficialis aids the aids flexion of the wrist.
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This question is part of the following fields:
- Anatomy
- Upper Limb
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Question 9
Incorrect
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Glomerular filtration rate can be calculated using any substance that:
Your Answer: is freely filtered and secreted by the nephron
Correct Answer: is freely filtered and neither reabsorbed nor secreted by the nephron
Explanation:Clearance of a substance can provide an accurate estimate of the glomerular filtration rate (GFR) provided that the substance is:freely filterednot reabsorbed in the nephronnot secreted in the nephronnot synthesised or metabolised by the kidney
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This question is part of the following fields:
- Physiology
- Renal
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Question 10
Incorrect
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You are reviewing a patient complaining of loss of vision. Previous images shows a lesion at the optic chiasm. What type of visual field defect are you most likely to see in a lesion at the optic chiasm:
Your Answer: Contralateral homonymous hemianopia
Correct Answer: Bitemporal hemianopia
Explanation:A lesion at the optic chiasm will result in a bitemporal hemianopia.
A lesion of the optic nerve will result in ipsilateral monocular visual loss.
A lesion of the optic tract will result in a contralateral homonymous hemianopia. -
This question is part of the following fields:
- Anatomy
- Central Nervous System
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SESSION STATS - PERFORMANCE PER SPECIALTY
