Muscles Questions in English

(B) Proteins are classified based on their functions and structures.
$Myosin$ is a motor protein found in muscle fibers.
It acts as a structural protein because it forms the thick filaments of the sarcomere,which provide the structural framework for muscle contraction.
It also acts as a functional protein because it possesses ATPase activity and interacts with actin to facilitate muscle contraction,thereby performing a mechanical function.
Hexokinase is an enzyme (functional),Ribozyme is an $RNA$ molecule (not a protein),and Acetyl $Co-A$ is a coenzyme derivative,not a protein.

(A) Contractile proteins are proteins that mediate the sliding of filaments in muscle cells,which results in muscle contraction.
Actin and Myosin are the primary contractile proteins found in muscle fibers.
Troponin and Tropomyosin are regulatory proteins,not contractile proteins.
Collagen is a structural protein found in connective tissues.
Among the given options,Actin is a contractile protein. Therefore,option $A$ is the correct answer.

(A) Cardiac muscle fibers are structurally similar to skeletal muscle fibers because they both exhibit striations due to the arrangement of actin and myosin filaments. However,they differ functionally because cardiac muscles are involuntary (controlled by the autonomic nervous system),whereas skeletal muscles are voluntary (controlled by the somatic nervous system). Therefore,cardiac muscle fibers are striated and involuntary.

(D) Skeletal muscles are closely associated with the skeletal components of the body.
$1$. They have a striped appearance under the microscope and are hence called striated muscles.
$2$. Their activities are under the voluntary control of the nervous system.
$3$. They are primarily involved in locomotory actions and changes in body postures.
$4$. They are not found in the walls of visceral organs (smooth muscles are found there).
Therefore,statements $A$ and $C$ are correct.

(B) Short duration contractions are characteristic of muscles that require rapid,reflexive,or quick movements.
Eyelids contain skeletal muscles that are capable of very rapid,short-duration contractions (blinking).
In contrast,the heart (cardiac muscle) undergoes rhythmic,sustained contractions.
Arm and jaw muscles are also skeletal,but the eyelid muscles are specifically noted for their extremely short contraction duration compared to other skeletal muscles.

(C) Muscle contraction requires energy in the form of $ATP$ (Adenosine Triphosphate).
When a muscle fiber is stimulated,$ATP$ binds to the myosin head,which is then hydrolyzed to $ADP$ and inorganic phosphate $(Pi)$ to provide the energy required for the power stroke.
While creatine phosphate acts as a storage form of high-energy phosphate to rapidly regenerate $ATP$,$ATP$ itself is the direct and immediate molecule used by the myosin heads to facilitate the sliding filament mechanism.

(D) The $Masseter$ muscle,located in the jaw,is considered the strongest muscle in the human body based on its weight. It is capable of exerting a force of up to $890 \ N$ $(200 \ pounds)$ on the molars.

(A) The $Gluteus \ maximus$ is the largest and most superficial muscle in the human gluteal region.
It is primarily responsible for the movement of the hip and thigh,specifically in extending the hip joint.
$Sartorius$ is the longest muscle,while $Stapedius$ is the smallest muscle in the human body.

(C) According to the $Sliding$ $Filament$ $Theory$,muscle contraction occurs when thin filaments $(Actin)$ slide over thick filaments $(Myosin)$.
This process is driven by the formation of cross-bridges between the myosin heads and the active sites on the actin filaments.
As the myosin heads pull the actin filaments toward the center of the $Sarcomere$ $(M-line)$,the length of the $Sarcomere$ decreases,resulting in muscle contraction.
Therefore,the correct statement is that actin filaments slide over myosin.

(C) Skeletal muscles are also known as voluntary muscles.
These muscle fibers are syncytial,meaning they contain multiple nuclei (multinucleated) because they are formed by the fusion of many myoblasts during development.
Cardiac muscles are typically uninucleated or binucleated,and smooth muscles are uninucleated.

(A) The iris of the eye contains involuntary smooth muscles that control the size of the pupil.
$A$ is correct because the iris is composed of smooth muscles which are involuntary.
$B$ is incorrect because the heart wall is composed of cardiac muscles,which are striated and involuntary.
$C$ is incorrect because the upper arm (biceps/triceps) is composed of skeletal muscles,which are voluntary and striated.
$D$ is incorrect because the abdominal wall is primarily composed of skeletal muscles,which are voluntary.

(C) White muscle fibers are characterized by a low content of myoglobin,which gives them a pale or whitish appearance.
They contain a fewer number of mitochondria,which limits their aerobic capacity.
They rely heavily on anaerobic processes (glycolysis) for energy production.
However,they possess a high amount of sarcoplasmic reticulum,which facilitates rapid calcium release and uptake,allowing for quick and powerful contractions. Therefore,the statement that they have a low sarcoplasmic reticulum content is incorrect.

(D) Cardiac muscle fibers exhibit the following characteristics:
$1$. They are $Involuntary$ in nature,meaning they are not under conscious control.
$2$. They are $Striated$ due to the presence of alternating light and dark bands (sarcomeres).
$3$. They are $Fatigue-resistant$ because they contain a high density of mitochondria and myoglobin to support continuous,rhythmic contraction throughout life.
Therefore,all the given options are correct.

(B) The functional and contractile unit of a striated muscle fiber is called a $Sarcomere$.
It is the segment of a myofibril located between two successive $Z$-lines (or $Z$-discs).
It contains the arrangement of actin (thin) and myosin (thick) filaments that slide past each other during muscle contraction,as explained by the Sliding Filament Theory.

(B) Muscle fatigue is the decline in the ability of a muscle to generate force. During intense or prolonged physical activity,the muscle cells undergo anaerobic respiration because the oxygen supply is insufficient to meet the energy demand. This process leads to the accumulation of lactic acid in the muscle fibers. The buildup of lactic acid lowers the $pH$ within the muscle,which interferes with the contractile mechanism and leads to muscle fatigue.

(A) The $ATP_{ase}$ enzyme activity is located in the head of the myosin molecule.
During muscle contraction,the myosin head binds to the active sites on actin to form a cross-bridge.
This process requires energy,which is provided by the hydrolysis of $ATP$ catalyzed by the $ATP_{ase}$ activity of the myosin head.

(C) Striated muscles,also known as skeletal muscles,are attached to the bones of the skeleton by tendons. They are responsible for voluntary movements of the body. Since the muscles in the legs are skeletal muscles,they exhibit striations under a microscope. Trachea,lungs,and gallbladder contain smooth muscles,which are non-striated and involuntary.

(C) In the structure of a myofibril, the $I$-band (isotropic band) contains actin filaments.
Each $I$-band is bisected by an elastic fiber called the $Z$-line (or $Z$-disc).
The $Z$-line serves as the attachment point for the thin actin filaments.
Therefore, the correct option is $C$.

(A) In muscle fibers,the sarcoplasmic reticulum is a specialized type of smooth endoplasmic reticulum that regulates the calcium ion concentration in the cytoplasm of striated muscle cells.
It acts as a storage site for $Ca^{++}$ ions.
When a muscle fiber is stimulated by an action potential,$Ca^{++}$ is released from the sarcoplasmic reticulum into the sarcoplasm,which triggers muscle contraction.
Therefore,the correct option is $A$.

(C) In the structure of a sarcomere,the thick filaments (myosin) are located in the center of the $A$-band.
During the resting state,the central portion of the thick filaments is not overlapped by the thin filaments (actin).
This specific central region is known as the $H$-zone.
As the muscle contracts,the thin filaments slide over the thick filaments,causing the $H$-zone to narrow or disappear.

(C) In the structure of a skeletal muscle myofibril,the arrangement of filaments is highly organized. Each myosin filament (thick filament) is surrounded by $6$ actin filaments (thin filaments) in a hexagonal pattern. This arrangement is crucial for the sliding filament theory of muscle contraction,where the myosin heads interact with the surrounding actin filaments to generate force.

(C) sub-threshold stimulus is a stimulus that is too weak to elicit an action potential in a muscle fiber or a nerve cell. According to the 'All-or-None' law,a muscle fiber will only contract if the stimulus reaches or exceeds the threshold level. If the stimulus is below this threshold,the muscle fiber will not contract at all. Therefore,the correct answer is that the muscle will not contract.

(D) $1$. Muscles in the human body are classified as skeletal,smooth,and cardiac muscles.
$2$. Skeletal muscles are striated and voluntary; they are attached to bones,such as those in the thigh (femur region),allowing for voluntary movement.
$3$. Smooth muscles are non-striated and involuntary; they are found in the walls of internal organs like the intestine.
$4$. Cardiac muscles are striated and involuntary; they are found exclusively in the heart.
$5$. Therefore,option $D$ is correct because thigh muscles are skeletal muscles,which are striated and voluntary.

(A) Cardiac muscles are structurally similar to striated muscles because they possess striations due to the regular arrangement of actin and myosin filaments. However,they are functionally similar to smooth muscles because they are involuntary in nature,meaning they are not under conscious control.

(B) skeletal muscle consists of a central,thick,contractile portion known as the belly (or gaster). The ends of the muscle are usually attached to bones via tendons. Therefore,the belly is the middle,fleshy,and contractile part of the muscle.

(C) Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates. It acts as an oxygen storage unit in muscle cells,providing oxygen to the mitochondria during muscle contraction. Therefore,it is specifically located in the muscles.

(B) Cardiac muscles are involuntary,striated muscles found exclusively in the heart.
They are specialized to contract rhythmically and continuously throughout an individual's life without getting fatigued.
This is due to the presence of a large number of mitochondria and a rich blood supply,which ensures a constant supply of oxygen and nutrients for aerobic respiration.
Therefore,they contract rapidly and do not get fatigued.

(A) Ligaments are specialized connective tissues that are highly elastic.
They are responsible for connecting one bone to another bone.
In contrast,tendons connect skeletal muscles to bones.
Therefore,the correct option is $(A)$.

(C) The cells responsible for bone resorption or bone dissolution are called $Osteoclasts$.
$Osteoblasts$ are cells that form new bone tissue.
$Osteocytes$ are mature bone cells trapped within the bone matrix.
$Fibroblasts$ are cells found in connective tissue that produce collagen and other fibers.

(C) Tendons are specialized dense regular connective tissues that connect skeletal muscles to bones.
Ligaments connect bone to bone.
Cartilage is a type of skeletal connective tissue.
Adipose tissue is a type of loose connective tissue that stores fat.
Therefore,the correct answer is $C$ (Tendons).

(A) Skeletal muscles are attached to bones by tendons. When muscles contract,they pull on the bones,which act as levers,resulting in movement at the joints. Therefore,bones are the primary structures that interact with skeletal muscles to produce movement.

(A) Body movement and contraction are primarily caused by the contraction of muscles. Muscles are attached to bones via tendons. When muscles contract,they pull on the bones to which they are attached,resulting in movement. Therefore,the pulling force that leads to contraction and movement is generated by the muscles.

(B) In humans,the muscles responsible for the movement of the pinna (auricle) are present but are considered $vestigial$ muscles. These muscles,known as the auricular muscles,are functional in many mammals (like dogs or cats) to rotate the ears toward sound,but in humans,they have lost their primary function due to evolutionary changes. Therefore,they are classified as vestigial structures.

(D) In rabbits,the pinna (external ear) is large and highly mobile,allowing the animal to detect sounds from various directions. This movement is controlled by well-developed,functional muscles. In contrast,in humans,these muscles are present but are vestigial and non-functional,which is why most humans cannot move their ears voluntarily.

(B) The mineral element required for blood clotting is $Calcium$ $(Ca^{2+})$.
$Calcium$ ions play a crucial role in the blood coagulation cascade by facilitating the activation of clotting factors.
Apart from blood clotting, $Calcium$ ions are also essential for muscle contraction.
During muscle contraction, $Ca^{2+}$ ions bind to troponin, which causes a conformational change in the tropomyosin complex, exposing the active sites on actin filaments for myosin binding.

(C) Muscle contraction is initiated by the release of $Ca^{++}$ ions from the sarcoplasmic reticulum into the sarcoplasm.
These $Ca^{++}$ ions bind to the troponin complex on the actin filaments,which causes a conformational change.
This change exposes the active binding sites on the actin for the myosin heads,allowing the formation of cross-bridges and subsequent muscle contraction.

(D) Muscle contraction is initiated by the release of calcium ions $(Ca^{2+})$ from the sarcoplasmic reticulum into the sarcoplasm.
These $Ca^{2+}$ ions bind to the troponin subunit on the actin filaments.
This binding causes a conformational change in the troponin-tropomyosin complex,exposing the active binding sites on the actin filaments for the myosin heads.
Therefore,$Ca^{2+}$ is the essential mineral element required for the process of muscle contraction.

(D) Muscles are composed of contractile proteins that facilitate movement. The two primary contractile proteins found in muscle fibers are Actin and Myosin. Actin is a thin filament protein,while Myosin is a thick filament protein. Together,they form the structural basis of the sarcomere,the functional unit of muscle contraction. Therefore,both Actin and Myosin are present in muscles.

(A) Contractile proteins are specialized proteins that are responsible for muscle contraction and movement.
$Actin$ and $Myosin$ are the primary contractile proteins found in muscle fibers.
$Hemoglobin$ is a respiratory pigment responsible for oxygen transport in the blood.
$Globular$ is a term describing the shape of proteins (globular proteins) rather than a specific contractile protein.
Therefore,$Hemoglobin$ is not a contractile protein.

(A) Proteins are essential for various biological functions.
$1$. $Actin$ and $Myosin$ are contractile proteins found in muscle fibers,which are primarily responsible for muscle contraction and movement.
$2$. $Tubulin$ is a protein that forms microtubules,which are essential for intracellular transport and the movement of cilia and flagella.
$3$. $Flagellin$ is the protein subunit of bacterial flagella,which facilitates the movement of bacteria.
Since $Actin$,$Myosin$,$Tubulin$,and $Flagellin$ are all involved in various forms of movement,the question implies identifying proteins associated with motility. However,in the context of standard biology,$Actin$ and $Myosin$ are the primary contractile proteins for movement. Given the options,if we consider all proteins that facilitate movement,$Actin$,$Myosin$,$Tubulin$,and $Flagellin$ are all involved. Since the question asks for proteins responsible for movement,and $Actin$ and $Myosin$ are the most prominent,but $Tubulin$ and $Flagellin$ are also correct,the most comprehensive answer in a multiple-choice context often highlights the contractile proteins. However,based on the provided options,$Actin$ and $Myosin$ are the classic examples of proteins responsible for movement.

(A) During muscle contraction,the $Ca^{2+}$ ions play a critical role.
When a signal from the motor neuron reaches the muscle fiber,$Ca^{2+}$ ions are released into the sarcoplasm.
These $Ca^{2+}$ ions bind to the $Troponin$ subunit on the actin filaments.
This binding causes a conformational change in the $Troponin-Tropomyosin$ complex,which shifts the $Tropomyosin$ away from the active sites on the $F-actin$ filaments.
By unmasking these active sites,the $Myosin$ heads can bind to them to form cross-bridges,leading to muscle contraction.

(A) : Tetanus refers to a sustained state of muscle contraction resulting from the summation of a series of rapid muscular contractions (twitches) that are induced by repeated stimulation of the muscle. When the frequency of stimuli is high enough that the muscle cannot relax between them,the contractions fuse into a smooth,sustained contraction.

(A) : During muscle contraction,the laterally projecting heads (cross bridges) of the thick myosin myofilaments come in contact with the thin actin myofilaments and rotate on them.
This pulls the thin myofilaments toward the middle of the sarcomere,past the thick myofilaments.
The $Z$ lines come closer together and the sarcomere becomes shorter.
Length of the $A$ band remains constant.
Myofilaments (both actin and myosin) stay the same length.
Free ends of actin myofilaments move closer to the centre of the sarcomere,bringing $Z$ lines closer together.
$I$ bands shorten and $H$ zone narrows.
$A$ similar action in all the sarcomeres results in shortening of the entire myofibril and thereby of the whole fibre and the whole muscle.

(A) The stimulation of a muscle fiber by a motor neuron occurs at the neuromuscular junction.
$1$. $A$ motor neuron is a nerve cell that transmits impulses to muscle tissue.
$2$. $A$ motor unit consists of a single motor neuron and all the muscle fibers it innervates.
$3$. The region where the axon terminal of a motor neuron meets the sarcolemma (muscle plasma membrane) is known as the motor end plate.
$4$. The junction between the axon terminal and the motor end plate is called the neuromuscular junction or motor end plate junction,where neurotransmitters like acetylcholine are released to initiate muscle contraction.

(A) The correct answer is $A$.
Each muscle fibre contains many parallelly arranged myofibrils.
Each myofibril consists of serially arranged functional units called sarcomeres.
Each sarcomere has a central $A$-band composed of thick myosin filaments and two half $I$-bands composed of thin actin filaments on either side,marked by $Z$-lines.
In a resting state,the edges of the thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments.
The central part of the thick filament that is not overlapped by thin filaments is known as the $H$-zone.

(B) : According to the sliding-filament theory of muscle contraction,actin and myosin filaments slide past each other with the help of cross-bridges to reduce the length of the sarcomeres.
The smallest unit of muscle contraction is a sarcomere (which is delineated by $Z$-lines).
As a muscle contracts,the $Z$-lines come closer together (shortening the sarcomere),the width of the $I$-bands decreases,and the width of the $H$-zones decreases,but there is no change in the width of the $A$-band.
During relaxation,cross-bridges disappear and actin filaments slide back from $A$-bands; the width of the $I$-bands and $H$-zones increases,but there is still no change in the width of the $A$-band.

(C) is the correct answer.
Troponin and myosin are essential protein components of striated (skeletal) muscles.
Myosin is a thick filament protein that acts as a motor protein,while troponin is a regulatory protein complex associated with actin filaments that helps in the regulation of muscle contraction.
Option $(a)$ is incorrect because thymosin is a peptide hormone secreted by the thymus,not the thyroid.
Option $(b)$ is incorrect because prolactin is a hormone secreted by the anterior pituitary,not a digestive enzyme.
Option $(d)$ is incorrect because rhodopsin is a light-sensitive pigment found in the retina of the eye,not a hormone.

(C) is the correct answer.
$1$. Cardiac muscles are found in the wall of the heart; they are involuntary and striated.
$2$. Smooth muscles are found in the gastrointestinal tract (like the intestine); they are non-striated and involuntary.
$3$. Striated (or skeletal) muscles are found in the limbs (like the thigh and upper arm) and body walls. These muscles are voluntary (under the control of the animal's will) and show dark and light bands,thus they are striated.

(C) The correct answer is $C$.
Myosin is a motor protein that functions as a contractile protein in skeletal muscle.
It possesses ATPase activity,meaning it can hydrolyze $ATP$ to release energy required for muscle contraction.
The myosin molecule consists of a tail and a globular head; the head contains binding sites for actin and $ATP$.
Troponin and tropomyosin are regulatory proteins associated with the thin filament (actin),while $\alpha$-actinin is a structural protein that anchors actin filaments to the $Z$-line.