Muscle tissue - class-XII

A muscle is rich in protein. The muscle cells contain protein filaments of actin and myosin. Actin is a thin filament and myosin is a thick filament. These protein filaments slide past one another to produce contraction. This results in change in length and shape of the cell.

The main function of the muscular system is movement. Muscles are the only tissue in the body that has the ability to contract and therefore move the other parts of the body & the maintenance of the body posture & body position.

From all the above options, only muscle has a property of contraction. Muscle possess contractile proteins named, acitn and myosin on myofibrils. Hence, option C is correct. 

Plasmodesmata are channels that traverse the cell walls of plant cells and some algal cells, allowing transport and communication between them. They are not made of connexon proteins; connexons are found in gap junctions in animal cells.

Sphincter muscles are typically smooth muscles (mesodermal), contain stretch receptors to regulate tone, and exhibit rhythmicity in some cases (like the pyloric sphincter). They are generally not indefatigable; like other muscles, they can fatigue.

Muscles of iris and ciliary body are "smooth muscles". Smooth muscle cells arise from undifferentiated mesenchymal cells (embryonic mesoderm). These cells differentiate first into mitotically active cells, myoblasts, which contain a few myofilaments. Myoblasts give rise to the cells which will differentiate into mature smooth muscle cells. Iris is derived from neuroectoderm but the muscles of iris is derived from mesoderm. Thus, the correct option is B.

Since the 1850s cytologists observed some granular structures in the cytoplasm of the living cells. These structures were originally named as sarcomas. The term mitochondrion was introduced by Carl Benda in 1898. The term mitochondrion became the widely used name for this organelle but still the term sarcosome is accepted to denote this organelle present in the muscle. Sarcosome is a large specialized mitochondrion found in a striated muscle fiber.
Thus, the correct answer is the option (A), 'Mitochondria'.

Involuntary muscles are those, which are not under our control. Diaphragm muscles are internal muscle, that divides the thorax and the abdomen and are involuntary. The walls of large organs like stomach, intestines, uterus and urinary bladder are involuntary.
Thus, the correct answer is option (C), 'Both (A) and (B)'.

Cardiac muscles are the muscles of the heart. They are self-contracting, autonomically regulated (meaning involuntary and must continue to contract in a rhythmic fashion for the whole life of the organism.
Thus, the correct answer is option (B), 'Cardiac muscles'.

Skeletal muscle fiber or striated muscles are characterized as fast or slow based on their activity patterns. Fast, also called white muscle fibers, contract rapidly, have poor blood supply, operate without oxygen and tire quickly.
Thus, the correct answer is option (C), 'Striated'.

Red muscle gives a fused contraction at a slower frequency of stimulation. The red color of muscles is due partly to myoglobin, which is probably freely dissolved in the sarcoplasm and partly to the cytochrome, which are mainly associated with the particulate components of the cytoplasm.
Thus, the correct answer is option (A), 'Red muscles'.

Non-striated muscles are called as smooth muscles. Their activities are not under the voluntary control of the nervous system and are therefore known as involuntary muscles. They are called as visceral muscles because they line the blood vessels, stomach, digestive tract and other internal organs. So, the correct answer is option D. 

Calcium ions play a significant role in the muscle contraction. These activate the interaction of myosin and actin, through the intervention of tropomyosin and troponin.
Magnesium, in muscle contraction, stimulates calcium re-uptake by the calcium-activated ATPase of the sarcoplasmic reticulum. It also affects the translocation of calcium ions through the smooth muscle cell membrane.

Multi unit smooth cells, however, are not electrically coupled and hence, the cells must be stimulated separately. These smooth muscles contain few gap junctions, and therefore contractions do not spread from cell-to-cell as in single-unit smooth muscle. Each cell is therefore situated close to an axon terminal where it can easily make contact with a neurotransmitter. As the cells are not electrically coupled the force of contraction can be controlled by the number of contractile muscle fibres. Multi-unit smooth cells can be found in the in the trachea, the large elastic arteries, the iris of the eye, in the lungs, erectile tissues of hair follicles ( Arrector pili of the dermis) and the vas deferens in the male genital tract.
The response of the whole muscle depends on upon the number of motor units active, the frequency of discharge in the fibers and the relative amount of excitatory and inhibitory input. Multi-unit smooth muscle activity can be initiated by hormones, but it is not much affected by rapidly stretching the muscle.

Most of the skeletal muscles are attached to the bone on their ends by tendons. As the muscles contract, a force is exerted on the bones, which helps to support and move our body along with its appendages. Usually, one end of the muscle is fixed in its position, while the other end moves during contraction.
The "origin" is the attachment site that doesn't move during contraction, while the "insertion" is the attachment site that does move when the muscle contracts. The insertion is usually distal, or further away, while the origin is proximal, or closer to the body, relative to the insertion. "Belly" of muscle is between origin and insertion.

Visceral muscles are located in the inner walls of hollow visceral organs of the body like the alimentary canal, reproductive tract, etc. Each spindle-shaped smooth muscle fiber contains a single, central nucleus. They do not exhibit any striation and are smooth in appearance. Hence, they are called smooth muscles (non-striated muscle). Their activities are not under the voluntary control of the nervous system and are therefore known as involuntary muscles. They assist, for example, in the transportation of food through the digestive tract and gametes through the genital tract.

Muscular strength usually refers to the "ability to exert a force on an external object". The strongest muscle in humans, based on its weight is the masseter muscle or the jaw muscle. It is the muscle that can generate the largest externally measurable force attributable to the action of a specific, single muscle. Its strength is the result of incredibly densely packed muscle fibers combined with being attached to a short-armed lever. With all muscles of the jaw working together it can close the teeth with a force as great as 55 pounds (25 kilograms) on the incisors or 200 pounds (90.7 kilograms) on the molars.

Striated and unstriated are the types of muscles. Skeletal muscles are closely associated with the skeletal components of the body like limbs. They have a striped appearance under the microscope and hence, are called striated muscles. As their activities are under the voluntary control of the nervous system, they are known as voluntary muscles too. They are primarily involved in locomotory actions and changes of body postures. 

Epimysium is the outermost white fibrous connective tissue that completely surrounds and encases skeletal muscle. It is composed of dense irregular connective tissue. The most important biological purposes of this layer are protection from strain and friction. The smoothness of the tissues promotes seamless gliding, and also protect joints and other high-impact areas from rips or tears and promotes smooth movement of the limbs and joints.

The gluteus maximus (also known as glutus maximus or, collectively with the gluteus medius and minimus, the glutes) is the largest and most superficial of the three gluteal muscles. It makes up a large portion of the shape and appearance of the hips. It permits a variety of motion and allows us to sit upright.

myosin filament is a polymerised protein. Many monomeric proteins, called meromyosin constitute one thick filament. Each meromyosin has two important parts, a globular head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter, the light meromyosin (LMM). The HMM component, i.e., the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerised myosin filament and are known as the cross arm. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.

Muscles cannot expand. They can only contract. Hence, muscles responsible for body movements frequently occur in pairs called agonist-antagonist pairs, for example, biceps and triceps. The biceps cause movement towards the body or central axis and triceps cause movement away from the body or away from the central axis.

There are two types of muscles, voluntary and involuntary. Voluntary muscles are under our own control while involuntary muscles are not. The arrector pili muscles are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end. Each arrector pili is composed of a bundle of smooth muscle fibres, which attach to several follicles (a follicular unit) and is innervated by the sympathetic branch of the autonomic nervous system. The contraction of the muscle is, therefore, involuntary stresses such as cold, fear etc., may stimulate the sympathetic nervous system and thus, cause contraction, but the muscle is not under conscious control.

Shivering is an involuntary action of striated muscles ( skeletal muscles). Shivering is also called as rigors or shuddering. It is a bodily function in response to early hypothermia or just feeling cold in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Skeletal muscles around begin to shake in small movements, creating warmth by expending energy. 

Myosin is found in muscle filaments. The head portion of myosin forms cross linkage with actin filaments during muscular contraction. The cross bridges between actin and myosin are very important for muscular contraction activity. Thus, myosin fulfills both structural and functional roles.

Autorhythmicity is a property of electrically active cells, that show rhythmic activity without being driven by the rhythmic external stimulation, e.g., heart muscle cells or neurons.
Thus, the correct answer is option (C), 'Heart'.

The shape of the skeletal muscle is cylindrical, while that of visceral muscle is pear-shaped or spindle-shaped. Actin filaments which are thin filaments and myosin which are thick filaments are contractile proteins in the skeletal muscle as well as in the visceral muscle.
Thus, the correct answer is the option (D), 'Presence of actin and myosin filaments'.

• Cardiac muscles have the property of both the striated muscles (or skeletal muscle) and unstriated muscle or smooth muscle.
• Cardiac muscle is involuntary, which is the property of smooth muscle.
• Cardiac muscles also have features of skeletal muscles. Like skeletal muscle, cardiac muscle cross striations formed by rotating segments of thick and thin protein filaments and the primary structural proteins of cardiac muscle are myosin and actin. 
• However, skeletal muscles are voluntary as they are supplied with the somatic nerve.

The muscles in the upper arm and shoulder are striated muscles. So, option B is incorrect.
Heart possesses unique muscles, called cardiac muscles, which are involuntary striated muscles. So, option C is incorrect.
The intestinal muscles are involuntary and are smooth muscle. So, option D is incorrect.

A syncytium is a multinucleated mass of cytoplasm, that is not separated into individual cells.
Example: Formation of skeletal muscle. Large skeletal muscle fibers formed by the fusion of thousands of individual muscle cells.
Cardiac muscle's syncytium is important because it allows rapid coordinated contraction of muscles along their entire length.
Smooth muscles, however, are not syncytial
So, the correct answer is 'Smooth muscle'

There are three types of muscle tissue such as cardiac, smooth or unstriated and skeletal or striated.
Cardiac muscle cells are located in the walls of the heart, appear striated and are under involuntary control.
Smooth or unstriated muscle fibers are located in the walls of hollow visceral organs, except the heart, appear spindle-shaped and are under involuntary control.
Skeletal or striated muscles fibers occur in muscles, which are attached to the skeleton. They are striated in appearance and are under voluntary control.
Thus, the correct answer is option D.

Myoglobin is a protein found in the muscle cells of animals. It functions as an oxygen-storage unit, providing oxygen to the working muscles.
Thus, the correct answer is option (A), 'Muscles'.

Smooth muscles are the muscle tissues that contracts without conscious control (involuntary), having the form of thin layers or sheets. It is made up of spindle-shaped, unstriated cells with single nuclei and found in the walls of the internal organs such as stomach, uterus, bladder, intestine and blood vessels (veins, arteries) except for heart.
Thus, the correct answer is option D.

Structural proteins are fibrous proteins and form the largest class of proteins measured in terms of their total mass. Structural proteins include myosin, collagen, and keratin. 

The phosphagens are energy storage compounds, also known as high-energy phosphate compounds. They are chiefly found in muscular tissue in animals. ATP molecules can provide energy for only a few seconds of strenuous muscular activity. Thus muscle cells have backup energy storage compound, creatine phosphate, that can be stockpiled. The energy stored in creatine phosphate is transferred to ATP as needed. But during vigorous exercise, the supply of creatine phosphate is quickly depleted. Muscle cells must replenish their supplies of these energy-rich compounds. Chemical energy is stored in muscle fibers in glycogen, a large polysaccharide formed from hundreds of glucose molecules. Glycogen can be degraded, yielding glucose, which is then degraded in cellular respiration. When sufficient oxygen is available, enough energy is captured from glucose to produce needed quantities of ATP and creatine phosphate.

Three major types of skeletal muscle fibers have been identified in vertebrates: slow-oxidative, fast-oxidative, and fast-glycolytic. Slow-oxidative fibers are specialized for endurance activities such as swimming, running long distances like the marathon, or maintaining posture. They contract slowly and fatigue slowly. These fibers require a steady supply of oxygen. They derive most of their energy from aerobic respiration and are rich in mitochondria and capillaries. Slow-oxidative fibers are rich in myoglobin, a red pigment similar to hemoglobin in red blood cells, which stores oxygen. Myoglobin enhances rapid diffusion of oxygen from blood into muscles during strenuous muscle exertion. Because of the myoglobin, slow-oxidative fibers are red. Birds that fly have red breast muscles specialized to support sustained activity. In humans, the proportions of slow-oxidative and fast-oxidative fibers vary among individuals and from muscle to muscle in the same person.

Six actin filaments surround each myosin filament and the active sites of an actin filament are available to three different myosin filaments in the myofibril of skeletal muscle fibre.

Thigh muscles are skeletal muscles, which are striated and under voluntary control.

Cardiac muscles are striated involuntary, Contract quickly and do not get fatigued.

In cardiac muscle cells, adrenaline binds to beta-adrenergic receptors, activating adenylate cyclase to produce cAMP, which acts as a second messenger to increase contraction rate and force.

When oxygen demand increases, heart rate and cardiac output increase, which increases the flow of blood through the lung and the pressure required to force blood through the arterioles and capillaries of the lung. Due to this, the cardiac muscles are most affected due to deficiency of oxygen. So, the correct option is 'Cardiac muscles'.

• The somatic nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The somatic nervous system consists of afferent nerves or sensory nerves, and efferent nerves or motor nerves.
  
• Skeletal muscle is a form of striated muscle tissue, which is under the voluntary control of the somatic nervous system. 
  
• Hence Skeletal muscles are controlled by Somatic nervous system.
• So, the correct answer is 'Somatic nervous system'.

The uterus undergoes significant hypertrophy during pregnancy, making its smooth muscle cells the largest in the body.

The iris of the eye contains involuntary smooth muscle fibers that control the size of the pupil.

Involuntary smooth muscles are those muscles that are not under the control of our will and are without any striations (stripes). Iris has involuntary smooth muscle. Biceps of upper arm have  striated muscle fibres and abdominal wall has involuntary smooth muscles. Heart wall has involuntary striated muscle.

The thin filaments of a myofibril are composed of actin, troponin, and tropomyosin.