Closer look into muscular system - class-XII

• Each myofibril(a unit of the muscle cell) has alternate dark and light bands on it.
  
• The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin.
  
•  In the center of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line.
  
• The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. 
  
• The sarcomere is considered as the functional unit of contraction. The portion of the myofibril between two successive ‘Z’ lines is considered as a sarcomere. Hence sarcomere is the distance between two Z lines.
• So, the correct answer is 'Two Z-lines'.

• Each myofibril(a unit of the muscle cell) has alternate dark and light bands on it.
  
• The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin.
  
•  In the center of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line.
  
•  The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. 
  
• The sarcomere is considered as the functional unit of contraction. The portion of the myofibril between two successive ‘Z’ lines is considered as a sarcomere. Hence The functional unit of the contractile system of a striated muscle is sarcomere.
• So, the correct answer is 'Sarcomere'.

Syncytial cell is a cell that is multinucleated. It contains more than one nuclei. It is resulted from multiple cell fusions of uninuclear cells. The muscle fibre is a syncytial cell as it has multiple nuclei, in which each nucleus has originated from single myoblast.

• Aryepiglotticus is a muscle of the larynx running in the aryepiglottic fold from the arytenoid cartilage to the epiglottis.
• Hiltons' muscle is a muscle in which the nerve supplying the muscles extending directly across and acting at a given joint not only supplies the muscle but also innervates the joint and the skin overlying the muscle.
• Aryepiglotticus muscle is a Hiltons' muscle.
• So, the correct answer is 'Aryepiglotticus'.
  

• The 650 muscles in the body support movement  controlling  walking, talking, sitting, standing, eating and other daily functions that people consciously perform .
•  also help to maintain posture and circulate blood and other substances throughout the body.  so , option A is  correct

• 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.
• Latissimus dorsal muscle is a shoulder muscle.
• The latissimus dorsi muscle is responsible for extension, adduction, the transverse extension(horizontal abduction), flexion from an extended position, and (medial) internal rotation of the shoulder joint.
• So, the correct answer is 'Shoulder joint'.

The human body is comprised of about 639 muscles in total. Muscles are found within the muscular system, which is the body's own network of tissues and fibers responsible for both outward and inward movements of the body.

Unstriated muscles consists of muscle fibres which are long flattened and uninucleate because these muscles are smooth muscle fibres. They are present in the form of thin sheets and spindle shaped fibres wth only one nucleus in them.

It helps in adduction, extension and medial rotation of the shoulder as in swimming, rowing, climbing, pulling folding the arm behind back and scratching the opposite scapula. It also helps in violent expiratory efforts as coughing, sneezing, etc.

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'.

Cardiac cells are connected to each other by intercalated discs. Cardiac muscle cells have three distinct types of intercellular junctions, namely gap junctions, desmosomes, and fascia adherens. All these junctions are located in the intercalated disc.  Hence, all these cell junction make up an intercalated disc of cardiac cells. 

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.

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.

For contraction of muscles, a stimulus is required 

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.

The question asks for the WRONG set. Abductor/adductor, pronator/supinator, and elevator/depressor are all valid antagonistic pairs. Flexor and relaxor is not a correct pair - flexor works with extensor, not relaxor. Also, spelling is flexor not fexor.

The sartorius muscle is the longest superficial muscle in the interior compartment of the human body. It is a two joint muscle that moves both hip and knee joint. It forms the lateral boundary of the femoral triangle and covers the abductor canal. It flexes the hip and knees and helps in the lateral rotation and thigh abduction. These all are necessary for the crossed leg position. So, the correct option is C.

• In a normal human adult male, the total weight of muscle is 30 kg.
• Muscle mass is important in determining healthy body composition. A person with a higher % of muscle mass finds it easier to move but needs more energy to do it. 
• The normal muscle mass percentage on the bodyweight lies between 38% and 54% for men and between 28% and 39% for women depending on age and physical activity level.
  
  Hence, option C is the answer.

Skeletal muscle is composed of muscle fibres which have smaller units called myofibrils. There are three types of proteins make up each myofibril; they are contractile, regulatory and structural proteins. By contractile proteins, we mean actin (thin filament) and myosin (thick filament).

When there is oxygen deficiency in the muscle cells, they undergo anaerobic respiration and start producing lactic acid. This lactic acid causes muscle fatigue. The muscle that has been contracted many times short intervals, exhaust its storage of ATP and glycogen and produces lactic acid.