Muscle Biology

Arrector pili muscles are small muscles attached to hair follicles in the skin. They are smooth muscles and are controlled by the autonomic nervous system, making them involuntary.

Cardiac muscle is immune to fatigue because it has more mitochondria than skeletal muscles. It contains up to 35% mitochondria whereas skeletal muscles contain only 1-2%. Mitochondria is necessary for ATP production that provides energy to the cells. Hence even if the heart pumps for a lifetime it resists fatigue due to presence of cardiac muscles. Thus the correct answer is option B.

When the triceps muscle contracts, the biceps muscle relaxes and the arm straightens. As triceps muscles are not as powerful as the biceps it does not have to exert great force to straighten the arm. Thus. the biceps exerts force to straighten the arms and lifting a heavy object.
Therefore, the correct answer is option B.

• Each muscle fibre(muscle cell) is lined by the plasma membrane called sarcolemma enclosing the sarcoplasm(cytoplasm of muscle fibre). 
• Sarcoplasm is a water solution containing ATP and phosphagens, as well as the enzymes and intermediate and product molecules involved in many metabolic reactions. The most abundant metal in the sarcoplasm is potassium.
• Hence The cytoplasm of muscle fibre is known as sarcoplasm.
• So, the correct answer is 'Sarcoplasm'.

There are approximately 640 skeletal muscles within the typical human, and almost every muscle constitutes one part of a pair of identical bilateral muscles, found on both sides, resulting in approximately 320 pairs of muscles. Nevertheless, the exact number is difficult to define because different sources group muscles differently. 

• The smooth muscle fibres(muscle cell) are tapered at both ends (fusiform) and do not show striations.
  
• Smooth muscles are involuntary muscles because their functioning cannot be directly controlled.
  
• The wall of internal organs such as the blood vessels, stomach, intestine and iris contains this type of muscle tissue.
  
• Hence Iris-Involuntary, smooth muscle.
• So, the correct answer is 'Iris-Involuntary, smooth muscle'.

• The stroma and the anterior border layer of the iris are derived from the neural crest, and behind the stroma of the iris, the sphincter pupillae and dilator pupillae muscles, as well as the iris epithelium, develop from optic cup neuroectoderm. Hence, Muscles of iris and ciliary body are not smooth muscles of mesodermal origin.
• Pericytes are multi-functional cells that wrap around the endothelial cells that line the capillaries and venules throughout the body. Pericytes are specialized mural cells located at the abluminal surface of capillary blood vessels, embedded within the basement membrane. Hence,  Quiescent mononucleate myogenic cells of skeletal muscles are not called pericytes.

Muscle is a  bundle of fibrous tissue in a body that has the ability to contract, producing movement in or maintaining the position of parts of the body. The total number of muscles in the human body comes in the range of 640-850. Muscle fibers are incorporated with an oxygen-carrying protein called myoglobin. Myoglobin receives oxygen from the red blood cells and transports it to the mitochondria of muscle cells, where the oxygen is used in cellular respiration to produce energy. Hence myoglobin is incorporated into muscle fibers. So, the correct answer is 'Myoglobin'.

In the marathon runners, the skeletal muscles are of the type of slow twitch. These type of muscles are known for the prolonged activity and so contain a large amount of myoglobin which carries the oxygen to the muscle fibers. They need slow and continuous supply of oxygen which is provided by the slow twitch muscle fibres. 

Muscle activity causes an increase in body temperature. During muscle contraction, the stored energy which is ATP breaks down into ADP and Pi to produce energy that is required for muscle activity. This is an exothermic reaction which causes an increase in body temperature. when skeletal muscles contract the myofibrils slide past each other and this friction generates the heat which also causes an increase in body temperature in fewer levels. So, the correct answer is 'Increase in body temperature'.

The strongest muscle based on its weight is the masseter. With all muscles of the jaw working together it can close the teeth with a force as great as 55 pounds on the incisors on the molars.

Fascia is the connective tissue sheath that surrounds and bundles together groups of muscle fibers (fascicles) to form a whole muscle. Endomysium wraps individual fibers, and perimysium wraps fascicles.

The brachialis is a muscle in the upper arm that flexes the elbow joint.
The Latissimus dorsi is the larger, flat, dorsolateral muscle on the trunk, posterior to the arm.
The dorsal scapular is the nerve that is the right brachial plexus with its short branches, viewed from in front.
Triceps brachii is that large muscle on the back of the upper limb and is principally responsible for extension of the elbow joint (straightening of the arm).
Therefore, the correct answer is option A.