Skeletal Muscle Physiology – Structure & Types Of Muscle Fibers

SKELETAL MUSCLE PHYSIOLOGY – STRUCTURE & TYPES OF MUSCLE FIBERS

Q. 1 Receptor responsible for malignant hyperthermia is?
 A Nicotinic receptor
 B

Ryanodine receptor

 C Muscarinic receptor 
 D

None

Q. 1 Receptor responsible for malignant hyperthermia is?
 A Nicotinic receptor
 B

Ryanodine receptor

 C Muscarinic receptor 
 D

None

Ans. B

Explanation:

 

Ryanodine receptor

REF: Morgan 3rde p. 869

This condition is known by a number of names, including malignant hyperthermia (MH), malignant hyperthermia

syndrome (MHS), and malignant hyperpyrexia.

Signs and symptoms:

The typical symptoms of malignant hyperthermia are due to a hypercatabolic state, which presents as a very

high temperature, an increased heart rate and breathing rate, increased carbon dioxide production, increased

oxygen consumption, acidosis, rigid muscles, and rhabdomyolysis.

The symptoms usually develop within one hour after exposure to trigger substances, but may even occur several

hours later in rare instances.

Causes:

Volatile anesthetic gases halothane, sevoflurane, desflurane

Local anesthetics                  lidocaine, bupivicaine, mepivacaine

Depolarizing muscle             succinylcholine

relaxants

Other                                      Opiates (morphine, fentanyl), ketamine, barbiturates, nitrous

                                                oxide, propofol, etomidate, benzodiazepines

Genetics:

Malignant hyperthermia’s inheritance is autosomal dominant. The defect is typically located on the long arm of the nineteenth

chromosome (19q13.1) involving the ryanodine receptor.


Q. 2

Actin filament is not present in which of the band zones?

 A

H band

 B

I band

 C

M band

 D

Z band

Q. 2

Actin filament is not present in which of the band zones?

 A

H band

 B

I band

 C

M band

 D

Z band

Ans. A

Explanation:

The myosin and actin filaments overlap in peripheral regions of the A band, whereas a middle region (called the H zone) contains only myosin. H-band is the zone of the thick filaments that is not superimposed by the thin filaments.


Q. 3

Which among the following is the contractile unit of muscle?

 A

Sarcomere

 B

Sarcolemma

 C

Myofibril

 D

Sarcotubular System

Q. 3

Which among the following is the contractile unit of muscle?

 A

Sarcomere

 B

Sarcolemma

 C

Myofibril

 D

Sarcotubular System

Ans. A

Explanation:

The basic contractile unit of skeletal muscle is the sarcomere. Sarcomeres are connected to each other by their Z lines. Each sarcomere contains an array of filaments that consist of actin and myosin molecules, which interact to produce contractile force.

Ref: Medical Physiology: Principles for Clinical Medicine By Rodney A. Rhoades, Ph.D., David R. Bell, Ph.D., 2012, Page 141; Guyton’s physiology 22nd edition, Page 73.


Q. 4

Sarcolemma is the cell wall surrounding:

 A

Neurons

 B

Muscle cells

 C

Red blood cells

 D

None of the above

Q. 4

Sarcolemma is the cell wall surrounding:

 A

Neurons

 B

Muscle cells

 C

Red blood cells

 D

None of the above

Ans. B

Explanation:

Each muscle fiber is a single cell that is multinucleated, long, cylindrical, and surrounded by a cell membrane, the sarcolemma.
Ref: Ganong’s Review of Medical Physiology 23rd edition, Chapter 45.

 


Q. 5

The function of the transverse tubule of the skeletal muscle is to?

 A

Transmit the action potential to the sarcoplasmic reticulum

 B

Carry ATP from the mitochondria

 C

Conduct impulses from the muscle spindle

 D

Provide energy for the actin molecule

Q. 5

The function of the transverse tubule of the skeletal muscle is to?

 A

Transmit the action potential to the sarcoplasmic reticulum

 B

Carry ATP from the mitochondria

 C

Conduct impulses from the muscle spindle

 D

Provide energy for the actin molecule

Ans. A

Explanation:

The function of the transverse tubule (T-tubule) is to transmit the action potential to the sarcoplasmic reticulum. This signal is relayed through the cisternae and to the sarcoplasmic reticulum which releases Ca++. Myosin heads contain ATP and provide energy to form and release crossbridges with the actin filaments. Impulses from the muscle spindles are conducted by groups I and II sensory fibers.
 
Ref: Mescher A.L. (2013). Chapter 10. Muscle Tissue. In A.L. Mescher (Ed),Junqueira’s Basic Histology, 13e.

Q. 6

Which of the following is not a Sarcolemmal Proteins?

 A

Sarcoglycan

 B

Dystrophin

 C

Dystroglycan

 D

Perlecan

Q. 6

Which of the following is not a Sarcolemmal Proteins?

 A

Sarcoglycan

 B

Dystrophin

 C

Dystroglycan

 D

Perlecan

Ans. D

Explanation:

D i.e. Perlecan

Caplin, dystrophin, dysferlin, dystroglycan, sacroglycan, caveoli & integrins are sacrolemmal proteinsQ. Where as perlecan is a large multidomain proteoglycan, which is synthesized by both vascular endothelium and smooth muscle cells and deposited in extra cellular matrixQ.


Q. 7

There is mutation of gene coding for the ryanodine receptors in malignant hyperthermia. Which of the following statements best explains the increased heat production in malignant hyperthermia?

 A

Increased muscle metabolism by excess of calcium ions

 B

Thermic effect of blood

 C

Increased sympathetic discharge

 D

Mitochondria thermogenesis

Q. 7

There is mutation of gene coding for the ryanodine receptors in malignant hyperthermia. Which of the following statements best explains the increased heat production in malignant hyperthermia?

 A

Increased muscle metabolism by excess of calcium ions

 B

Thermic effect of blood

 C

Increased sympathetic discharge

 D

Mitochondria thermogenesis

Ans. A

Explanation:

A i.e. Increased muscle metabolism by excess of Ca2+ ions


Q. 8

Calcium channel ryanodine receptor:disorder is seen in:

 A

Malignant hyperthermia

 B

Duchene Muscular Dystrophy

 C

Tibial muscular dystrophy

 D

Limb girdle muscle dystrophy

Q. 8

Calcium channel ryanodine receptor:disorder is seen in:

 A

Malignant hyperthermia

 B

Duchene Muscular Dystrophy

 C

Tibial muscular dystrophy

 D

Limb girdle muscle dystrophy

Ans. A

Explanation:

Answer is A (Malignant Hyperthermia):

Malignant hyperthermia is associated with mutations within the gene encoding the skeletal muscle ryanodine receptor, the calcium channel that releases calcium from sarcoplasmic reticulum. Disordered muscle calcium regulation is recognized as the underlying disorder in malignant hyperthermia.

Ryanodine receptor is the calcium channel on the sarcoplasmic reticulum which controls the flux of calcium from the sarcoplasmic reticulum into the cytoplasm. It plays an important role in the activation of the contractile mechanism, and its malfunction causes malignant hyperthermia. RYR1 is the receptor type in muscle. The ryanodine receptor interacts with an L-tvpe calcium channel.

Mutations in the ryanodine receptor are associated with central core myopathy and malignant hyperthermia.




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