Human Anatomy and Physiology : Help with Other Muscle Physiology

Study concepts, example questions & explanations for Human Anatomy and Physiology

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Example Questions

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Example Question #1 : Help With Other Muscle Physiology

Which of the following statements does not describe type 2 muscle fibers?

Possible Answers:

Decreased myoglobin content

Slow twitch

White fibers

Decreased mitochondria 

Fast twitch

Correct answer:

Slow twitch

Explanation:

Type 2 muscle fibers are fast twitch, and grossly appear white due to decreased mitochondria and myoglobin concentration. Because of the decreased number of mitochondria, sustained activity of type 2 muscle fibers results in lactic acid accumulation due to anaerobic glycolysis.

Type 1 muscle fibers are slow twitch, and grossly appear red due to increased mitochondria and myoglobin concentration, which allows for oxidative phosphorylation. Type 1 muscle fibers allow for low, sustained muscle contraction.

Example Question #2 : Help With Other Muscle Physiology

Which ion is quintessential for muscle contraction in skeletal muscle, but not in smooth muscle?

Possible Answers:

Sodium

Potassium

Calcium

Bicarbonate

Chloride

Correct answer:

Calcium

Explanation:

The sarcoplasmic reticulum of the muscle fiber is used to store calcium. When an action potential causes depolarization of the T-tubules, adjacent proteins cause the calcium channels of the sarcoplasmic reticulum to open. The released calcium binds to troponin, influencing a change in tropomyosin and allowing myosin to bind the active sites of actin. Without the presence of calcium, tropomyosin remains in place to block myosin binding and contraction cannot occur.

This process, however, does not occur in smooth muscle. Smooth muscle lacks both troponin and tropomyosin, and is thus not reliant on calcium for contraction.

Example Question #3 : Help With Other Muscle Physiology

A scientist is examining a sample of tissue taken from a skeletal muscle biopsy. Which of the following is most likely true of sample?

Possible Answers:

The cells have well-developed sarcoplasmic reticulum for storing calcium cations

The cells have well-developed sarcoplasmic reticulum for storing potassium cations

The cells have well-developed sarcoplasmic reticulum for storing sodium cations

The cells have well-developed endoplasmic reticulum for storing calcium cations

The cells have well-developed endoplasmic reticulum for storing potassium cations

Correct answer:

The cells have well-developed sarcoplasmic reticulum for storing calcium cations

Explanation:

The sarcoplasmic reticulum is a specialized cell structure, characteristic of skeletal muscle cells, that is used to store calcium ions.

Upon neural stimulation, depolarization of the T-tubules causes a cellular reaction to open ion channels in the membrane of the sarcoplasmic reticulum. Calcium is released into the cell, where it can bind to troponin and allow for muscle contraction.

The endoplasmic reticulum is found in most eukaryotic cells, and is used for lipid synthesis, detoxification, and several other functions. Sodium and potassium play significant role in regulating membrane potential, but are not stored in the muscle cell in large amounts as calcium is.

Example Question #4 : Help With Other Muscle Physiology

During fasting, blood sugar begins to drop as time from the last meal increases. As blood sugar drops and activity level increases, which of the following is most likely to happen in skeletal muscle tissue?

Possible Answers:

Glycogen phosphorylase activity will decrease, secondary to glucagon elevation

Glycogen phosphorylase activity will increase, secondary to glucagon elevation

Glycogen synthase activity will increase, secondary to glucagon elevation

Glycogen synthase activity will increase, secondary to epinephrine elevation

Glycogen phosphorylase activity will increase, secondary to epinephrine elevation

Correct answer:

Glycogen phosphorylase activity will increase, secondary to epinephrine elevation

Explanation:

During fasting, glycogen production is reduced and glycogen catabolism (glycogenolysis) is increased. Glycogen stored within muscle is broken down into glucose by circulating catecholamines (epinephrine, not glucagon) during prolonged fasting.

Prolonged fasting also causes glycogen breakdown in the liver. This process is mediated by glucagon.

Example Question #5 : Help With Other Muscle Physiology

After a heavy meal, which type of glucose transporters are most likely to be found in muscle cells?

Possible Answers:

GLUT3

GLUT4

GLUT5

GLUT2

GLUT1

Correct answer:

GLUT4

Explanation:

GLUT4 glucose transporters are insulin-mediated, and found on the apical membrane of certain cells. Insulin release follows a heavy meal, and thus we would expect to find increased levels of GLUT4 transporters on muscle cells following the meal, with the absorbed glucose being used to produce intra-muscular glycogen.

The remaining glucose transporters are located as follows:

GLUT1: Erythrocytes, constitutively expressed

GLUT2: Pancreatic islet cells monitoring serum glucose levels, constitutively expressed

GLUT3: Brain tissue, highest glucose affinity & constitutively expressed

GLUT5: Present on the basolateral side of enterocytes to allow movement of absorbed carbohydrate from the enterocyte into the circulation, constitutively expressed

Note that GLUT4, in contrast to other subtypes, is inducible by insulin release.

Example Question #6 : Help With Other Muscle Physiology

Three muscle cells are placed side by side.

In muscle cell 1, striations are clearly visible.

In muscle cell 2, striations are also present, with sharp discs periodically found along muscle fibers. Further examination shows gap junctions between adjacent cells.

In muscle cell 3, no striations are present.

Which of the three cells could have been sampled from the upper third of the esophagus?

Possible Answers:

Muscle cells 1 and 3

Muscle cell 2

Muscle cells 1 and 2

Muscle cell 3

Muscle cell 1

Correct answer:

Muscle cell 1

Explanation:

Of the three primary muscle types, only skeletal muscle is under voluntary control. The upper third of the esophagus is under voluntary control by the cerebral cortex, and thus relies on skeletal muscle to contract. This can be appreciated when one initiates a swallow. The swallow is started deliberately, and then continues down deeper into the esophagus without conscious or voluntary effort.

Striations are characteristic of skeletal muscle, eliminating the option of muscle cell 3. Muscle cell 2 is said to contain gap junctions, which are characteristic of cardiac muscle, but not skeletal muscle. We can conclude that muscle cell 1 corresponds to skeletal muscle, and must be the only answer.

Example Question #7 : Help With Other Muscle Physiology

What process releases the myosin head from actin?

Possible Answers:

The binding of tropomyosin to actin

The attachment of ATP to the myosin head

The expulsion of ADP and a phosphate from the myosin head

The cleavage of ATP to ADP on the myosin head

The attachment of calcium to the myosin head

Correct answer:

The attachment of ATP to the myosin head

Explanation:

In order for the myosin head to perform a power stroke, an ATP must be cleaved to form ADP and a phosphate. This places the head in a cocked, high energy position. When the phosphate and ADP are expelled from the head, the myosin moves to a low energy position and drags the actin, causing the sarcomere to shorten. Once a new ATP is attached to the myosin, it detaches from the actin filament to begin the process again.

Lack of ATP causes myosin to remain attached to actin. This is the cause of rigor mortis.

Example Question #8 : Help With Other Muscle Physiology

What is the action of the masseter muscle?

Possible Answers:

Elevate the eyelid

Elevate the shoulder blade

Smiling

Close the jaw and clench the teeth

Correct answer:

Close the jaw and clench the teeth

Explanation:

The masseter muscle is a facial muscle that plays a major role in the chewing of solid foods (it is one of the muscles of mastication: masseter, temporalis, medial pterygoid, lateral pterygoid). The action of the muscle is to elevate the mandible (raise the lower jaw) which results in closing of the jaws. It connects to the mandible (lower jawbone) and the maxilla/zygomatic arch. 

Example Question #9 : Help With Other Muscle Physiology

What is the function of the levator scapulae?

Possible Answers:

Bend the knee 

Elevate the scapula 

Aid in digestion

Depress the scapula

Correct answer:

Elevate the scapula 

Explanation:

The levator scapulae is a long skeletal muscle of the shoulder girdle. It originates in the transverse processes of the atlas and axis as well the posterior tubercles of the 3rd and 4th cervical vertebrae (or in simple terms: it originates at the first four cervical vertebrae, and runs along the back and side of the neck). Its function is to elevate the scapula. 

Example Question #10 : Help With Other Muscle Physiology

Which function is performed by muscle cells?

Possible Answers:

Protection from infection

Sensory detection

Secretion

Contraction

Absorption

Correct answer:

Contraction

Explanation:

The correct answer is contraction. Muscle cells shorten or contract to move body parts. These contractions can be under voluntary or involuntary control. The primary function of muscle cell contraction is movement, but contraction is responsible for many other important functions like posture, joint stability and heat production. Muscles contract to allow maintenance of postures like sitting and help stabilize joints. Heat is also generated by contraction.

The other answer choices are functions performed by epithelial cells. Epithelial cells contain neuron endings (nerves) that perceive external stimuli and function as sensory receptors. Epithelial cells form coverings over body parts, including the skin, which prevents infection from microbes. They can form taste buds, line the nose and are located in the ear and eye. Epithelial cells serve an absorptive function through active-transport systems to absorb filtered material and transport to the rest of the body. Epithelial cells also secrete fluids necessary for other functions. For example, some epithelial cells secrete mucus, which lubricates body cavities and the passageways they line.

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