Muscles Questions in English

(B) The bone is surrounded by a dense,white fibrous connective tissue sheath known as the periosteum.
- Perichondrium is the connective tissue covering cartilage.
- Endosteum is the thin vascular membrane of connective tissue that lines the inner surface of the bony tissue that forms the medullary cavity of long bones.

(B) The correct answer is $B$.
$Tendon$ is a dense,strong fibrous connective tissue composed primarily of collagen fibers.
Its primary function is to attach skeletal muscles to bones,allowing for the transmission of force and movement of the skeleton.

(A) An osteon,also known as a Haversian system,is the fundamental functional unit of compact bone.
Each osteon consists of a central Haversian canal,which contains blood vessels and nerve fibers,surrounded by concentric layers of bone matrix called Haversian lamellae.
Therefore,the correct composition is one Haversian canal and its associated Haversian lamellae.

(C) $Ca^{2+}$ ions are essential for muscle contraction because their release from the sarcoplasmic reticulum triggers the binding of myosin heads to actin filaments. Additionally,$Ca^{2+}$ ions play a crucial role in the release of neurotransmitters at the synaptic knob,which is necessary for nerve impulse transmission.

(A) Skeletal muscles are voluntary muscles that are attached to the skeleton. They undergo rapid contraction and relaxation,leading to the accumulation of lactic acid due to anaerobic respiration during strenuous activity. This accumulation of lactic acid causes muscle fatigue. In contrast,cardiac muscles are fatigue-resistant due to their long refractory period and abundant mitochondria,and smooth muscles are slow-acting and fatigue-resistant.

(B) Unstriped muscles,also known as smooth muscles,are involuntary muscles found in the walls of hollow visceral organs.
They are widely distributed in the body,for example,in the gastrointestinal tract,uterus,urinary bladder,iris,ciliary body,and blood vessels.

(C) Smooth muscles,also known as unstriped or involuntary muscles,are found in the walls of hollow internal organs such as the stomach,intestines,blood vessels,and the iris of the eye.
$A$ (Thigh) contains skeletal muscles.
$B$ (Eye muscles) generally refers to extrinsic muscles which are skeletal.
$C$ (Iris) contains smooth muscles that control the size of the pupil.
$D$ (Tongue) contains skeletal muscles.

(B) The plasma membrane that encloses a muscle fibre is known as the sarcolemma. It acts as a protective barrier and is essential for the conduction of action potentials along the muscle fibre,which triggers muscle contraction.

(B) $Myosin$ is a protein that serves both structural and enzymatic functions.
$1$. Structural role: $Myosin$ filaments form the anisotropic $(A)$ band in muscle fibers and are essential components of the sarcomere structure.
$2$. Enzymatic role: The head of the $Myosin$ molecule possesses $ATPase$ activity,which hydrolyzes $ATP$ to provide the energy required for muscle contraction. The cross-bridges formed by $Myosin$ heads interact with actin filaments to facilitate the sliding filament mechanism.

(D) The "Sliding filament theory" of muscle contraction was proposed by $H.E. Huxley$ and $A.F. Huxley$ in $1954$.
This theory explains that muscle contraction occurs due to the sliding of thin actin filaments over thick myosin filaments, which shortens the sarcomere without the filaments themselves changing in length.

(D) Myofibrils are the contractile elements of muscle fibres. They are composed of repeating units called sarcomeres,which contain thick filaments made of the protein myosin and thin filaments made of the protein actin. Additionally,$ATP$ is essential for the contraction and relaxation cycles of these filaments. Therefore,all the mentioned components are present in the myofibrils.

(B) Single-unit smooth muscles (also known as visceral smooth muscles) are characterized by the presence of gap junctions that allow them to contract as a single unit.
These muscles are myogenic,meaning they can initiate their own contraction without requiring direct neural stimulation for every individual cell.
Therefore,they are capable of spontaneous rhythmic activity.

(A) motor unit consists of a single motor neuron and all the muscle fibers it innervates.
In physiological terms,this functional unit of the neuromuscular system is often referred to as a 'myone'.
$A$ sarcomere,on the other hand,is the basic contractile unit of a muscle fiber,not a motor unit.
Therefore,the correct term for a motor unit is a myone.

(A) Myoglobin is a red-colored,iron-containing protein pigment found in the sarcoplasm of muscle fibers.
It acts as an oxygen-binding protein that stores oxygen within the muscle cells,ensuring a ready supply for muscle contraction during activity.

(B) In a muscle twitch,the electrical response (action potential) initiates the process of muscle contraction.
The time interval between the application of the stimulus (beginning of the electrical response) and the development of peak tension in the muscle fiber is defined as the contraction time.
The latent period is the short delay between the stimulus and the start of the tension development,while the relaxation time is the period after peak tension during which the muscle returns to its original length.

(C) $Actin$ and $myosin$ are the contractile proteins found in all muscle types. They are present in both skeletal and visceral (smooth) muscles,which allows them to perform the function of contraction. While skeletal muscles are cylindrical and striated (having light and dark bands),visceral muscles are spindle-shaped and non-striated. Therefore,the presence of $actin$ and $myosin$ filaments is the common feature.

(C) is the correct answer. Striated muscles,also known as voluntary muscles,are under the conscious control of the nervous system. These muscles are primarily attached to the skeletal system via tendons and are most abundant in the limbs,such as the hind limb,to facilitate movement.

(C) . Cardiac muscles are immune to fatigue because they possess a long refractory period,which prevents them from undergoing tetanic contractions and allows them to relax between beats.

(B) The muscles involved in the movement of the arm are skeletal muscles.
Skeletal muscles are also known as striped or striated muscles because they exhibit alternating light and dark bands under a microscope.
These muscles are attached to the bones of the skeleton and are under voluntary control,allowing for the movement of limbs like the arm.

(B) The correct answer is $B$. Skeletal muscles are attached to the bones of the skeleton and are responsible for voluntary movements. Under a microscope,these muscles exhibit alternating light and dark bands,which give them a striated appearance. Therefore,leg muscles,which are skeletal muscles,are both striated and voluntary.

(C) The correct answer is $C$.
During intense physical activity,the rate of oxygen supply by the lungs falls short of the metabolic requirements of the muscles.
As a result,the muscles switch to anaerobic respiration,leading to the accumulation of lactic acid.
After the exercise,the body requires extra oxygen to oxidize this accumulated lactic acid and restore energy reserves ($ATP$ and phosphocreatine) in the muscles.
This extra amount of oxygen consumed after exercise to restore the body to its resting state is known as 'oxygen debt' or 'muscle recovery' phase.

(C) Thigh muscles are composed of skeletal muscle fibers,which are voluntary and prone to fatigue due to the accumulation of lactic acid during prolonged contraction.
In contrast,the heart is composed of cardiac muscle fibers,which are involuntary and specialized for continuous,rhythmic contraction throughout life without fatigue.
Cardiac muscles possess a high density of mitochondria and a rich blood supply,allowing them to sustain aerobic respiration and prevent the buildup of fatigue-inducing metabolites.
Therefore,the primary reason for the difference in fatigue resistance is the structural and functional specialization of cardiac muscle tissue compared to skeletal muscle tissue.

(D) The correct answer is $(d)$.
In living muscle fibres,$ATP$ performs a dual role.
Firstly,at rest,when myosin is not acting as an enzyme,$ATP$ binds to the myosin head,which keeps the muscles supple and extensible.
Secondly,when the muscle is stimulated,$ATP$ hydrolysis provides the necessary energy for the cross-bridge cycle,which leads to muscle contraction.

(C) At $0^\circ C$ and below, the metabolic activities and the physiological processes of the muscle are severely inhibited.
Specifically, the irritability (excitability) of the muscle is lost because the ion channels and enzymatic reactions required for nerve impulse transmission and muscle contraction cannot function at these low temperatures.
Therefore, the correct observation is the loss of irritability.

(D) Involuntary muscles are those muscles whose activity is not under the conscious control of the individual.
These muscles are regulated by the autonomic nervous system,which manages involuntary bodily functions such as digestion,heart rate,and blood vessel constriction.
Therefore,both statements $(b)$ and $(c)$ are correct descriptions of involuntary muscles.

(B) The cytoplasm of a muscle fibre is known as sarcoplasm.
It contains various organelles,including the sarcoplasmic reticulum,which acts as a storehouse of calcium ions essential for muscle contraction.

(B) The refractory period is defined as the interval of time during which a muscle fibre remains unresponsive to a new stimulus after having been stimulated once.
In mammalian skeletal muscle fibres, this period is extremely short, lasting approximately $0.002$ seconds.
Therefore, the correct option is $B$.

(A) The strongest muscle in the human body,based on its weight,is the masseter muscle,which is located in the jaw. It is responsible for closing the jaw and is capable of exerting a force of up to $890 \ N$ $(200 \ lbs)$ on the molars.

(C) The human body contains a total of $639$ muscles.
Out of these,$317$ are paired muscles and $5$ are unpaired muscles.

(B) The portion of the myofibril between two successive $Z$-lines is considered as the functional unit of contraction and is called a sarcomere.
Each sarcomere consists of one complete $A$-band and two halves of $I$-bands on either side,represented as $(I/2 + A + I/2)$.

(B) $Hypertrophy$ is defined as an increase in the size of an organ or tissue due to the enlargement of its constituent cells. In the context of muscle tissue,excessive work or resistance training leads to an increase in the size of muscle fibers,making the muscles thicker and stronger. Therefore,option $B$ is the correct answer.

(B) $Myofibrils$ are the characteristic contractile structures found within muscle cells.
They are embedded in the sarcoplasm of the muscle fibre.
$Myofibrils$ contain alternating light and dark bands,which give the muscle its characteristic striated appearance due to the arrangement of actin and myosin filaments.

(B) The correct answer is $B$. Cardiac muscles form the wall of the heart. These muscles are characterized by being striped (striated),branched,and involuntary in nature. They contain a single nucleus per cell and are connected by intercalated discs.

(A) During muscle contraction,the myosin head acts as an $ATPase$ enzyme.
It hydrolyzes $ATP$ into $ADP$ and inorganic phosphate $(Pi)$ in the presence of water.
This reaction releases the energy required for the cross-bridge cycle,which allows the actin filaments to slide over the myosin filaments,resulting in muscle contraction.

(B) During muscle contraction,the sliding filament theory explains that actin filaments slide over myosin filaments towards the center of the sarcomere.
As the actin filaments move inward,they overlap more with the myosin filaments.
This process causes the $H$-zone (the central region of the $A$-band containing only myosin) to narrow and eventually disappear or become obliterated when the muscle is fully contracted.
The length of the $A$-band remains constant,and the $Z$-lines move closer to each other.

(A) Myoglobin is an iron-containing oxygen-binding protein found in the muscle tissue of vertebrates.
It acts as an oxygen reservoir,providing oxygen to muscle cells during periods of intense activity.
Therefore,the correct answer is $A$ (Muscles).

(B) In animals,the primary form of stored carbohydrate is $Glycogen$.
Muscles store $Glycogen$ to provide a quick source of glucose for energy production during muscle contraction.
When the body requires energy,$Glycogen$ is broken down into glucose through the process of glycogenolysis.

(A) Muscles are classified based on their action on the body parts.
$1$. $A$ $Retractor$ muscle is a muscle that moves a part of the body away from the extended position or pulls it back towards the body.
$2$. $A$ $Protractor$ muscle moves a part of the body forward or away from the body.
$3$. $An$ $Abductor$ muscle moves a limb or other part away from the midline of the body.
Therefore,the muscles that can retract are specifically called $Retractor$ muscles.

(A) Each thin filament (actin filament) is made of two $F$-actins helically wound to each other. Each $F$-actin is a polymer of monomeric $G$-actins.
Two filaments of another protein,tropomyosin,also run close to the $F$-actins throughout its length.
$A$ complex protein troponin is distributed at regular intervals on the tropomyosin.
Thus,the actin filament is composed of actin,troponin,and tropomyosin.

(B) Muscle contraction is primarily driven by the interaction of two key proteins: $Actin$ and $Myosin$.
$Myosin$ is the primary contractile protein that forms the thick filaments in muscle fibers.
$Tropomyosin$ is a regulatory protein that covers the binding sites on $Actin$ filaments,and $Tubulin$ is a structural protein involved in the cytoskeleton and microtubule formation,not muscle contraction.
Therefore,$Myosin$ is the correct contractile protein among the given options.

(A) During muscle contraction,the sliding filament theory explains that the thin filaments slide over the thick filaments.
As a result,the $I$ band and the $H$ zone shorten and may eventually disappear.
The length of the $A$ band remains constant because the thick filaments do not change in length.
The diameter of the muscle fibre does not increase; in fact,the muscle fibre shortens and thickens slightly due to the sliding mechanism,but the statement that the diameter increases is considered false in the context of the sliding filament mechanism compared to the other specific structural changes.

(C) Shivering is a rapid,involuntary contraction and relaxation of skeletal (striated) muscles.
These contractions occur in response to a drop in body temperature detected by the hypothalamus.
Since these muscles are under involuntary control during this process and they generate heat through metabolic activity to warm the body,the correct answer is the involuntary action of striated muscles.

(B) Actin and myosin are contractile proteins found in muscle fibers.
During muscle contraction,the sliding filament theory explains that actin filaments slide over myosin filaments.
This process involves the formation of cross-bridges between actin and myosin molecules,resulting in the formation of an actomyosin complex,which leads to the shortening of the sarcomere and muscle contraction.

(B) Red muscle fibres are specialized for sustained,aerobic activity.
They contain a high concentration of myoglobin,which gives them a reddish appearance.
Because they rely on aerobic respiration for energy,they are rich in mitochondria,which produce the necessary $ATP$ for prolonged and continued muscle contraction.

(A) myofibril is composed of repeating functional units called sarcomeres.
Each sarcomere is defined as the segment of a myofibril between two successive $Z$-lines (also known as Krause's membrane).
These $Z$-lines are dense,dark-colored protein discs that bisect the $I$-bands and anchor the actin filaments.
Therefore,the $Z$-line acts as the boundary that separates two adjacent sarcomeres.

(B) Titin (or Titan) is a giant elastic protein that acts as a molecular spring in muscle cells.
It extends from the $Z$-line to the $M$-line within the sarcomere.
Its primary function is to anchor the thick myosin filaments to the $Z$-line,thereby maintaining the structural integrity of the sarcomere and providing elasticity to the muscle fiber during contraction and relaxation.

(A) Muscle contraction involves the conversion of chemical energy (stored in $ATP$) into mechanical energy.
During this process,the sliding filament mechanism occurs where actin and myosin filaments slide over each other,resulting in the shortening of muscle fibers.
This physical movement of muscles to perform work is defined as mechanical energy.
Therefore,the correct answer is mechanical energy.

(C) The sarcoplasmic reticulum $(SR)$ is a specialized type of smooth endoplasmic reticulum found in smooth and striated muscle fibers.
Its primary function is to store and release calcium ions $(Ca^{++})$.
When a muscle fiber is stimulated,the $SR$ releases $Ca^{++}$ into the sarcoplasm,which triggers the interaction between actin and myosin filaments,leading to muscle contraction.

(D) The $Obturator$ $externus$ is a flat, triangular muscle that covers the outer surface of the anterior wall of the pelvis. Its primary function is to act as a lateral rotator of the thigh at the hip joint. While the $Gluteus$ $medius$ and $Gluteus$ $minimus$ primarily function in abduction and medial rotation of the thigh, the $Obturator$ $externus$ is specifically involved in lateral rotation.

(B) The triceps brachii is a large muscle on the back of the upper arm.
It has three heads (long,lateral,and medial) that originate primarily from the humerus and the scapula.
These three heads converge into a single tendon that inserts onto the olecranon process of the ulna.
Therefore,the triceps muscle connects the ulna to the humerus (and scapula).