Question

Read the following statements carefully and select the correct ones. (i) Cardiac fibres are branched with one or more nuclei (ii) Smooth muscles are unbranched and cylindrical (iii) Skeletal muscles can be branched or unbranched (iv) Smooth muscles are non-striated (a) only (iv) (b) (ii) and (iii) (c) (iii) and (iv) (d) only (iii)

Short answer

(i) and (iv) are true, but there is no option matching these. The closest correct option would be (a) only (iv).

Step-by-step solution

Analyze Statement (i)

Cardiac muscle fibers are indeed branched and typically contain one nucleus per cell, though occasionally they may have two nuclei. Therefore, this statement is correct.

Analyze Statement (ii)

Smooth muscles are unbranched, spindle-shaped and contain a single, central nucleus. They are not cylindrical as well, so this statement is incorrect.

Analyze Statement (iii)

Skeletal muscles are generally unbranched and multinucleated. They attach to bones and cause movements. The usual structure is a long cylindrical shape. Hence statement (iii) is incorrect because skeletal muscles are not branched.

Analyze Statement (iv)

Smooth muscles are indeed non-striated. Unlike skeletal and cardiac muscles, they do not have the banded appearance of striated muscle. Therefore, this statement is correct.

Select the Correct Statements

From the analysis of statements (i) through (iv), it is clear that the correct statements are (i) and (iv). There is no such option offering these two correct statements, thus indicating a possible error in the options provided. In the given options, the closest one that incorporates a correct statement is (a), which has only (iv).

Key concepts

Cardiac Muscle Properties

Understanding the properties of cardiac muscle tissue is essential, as these unique characteristics support its role in continuously pumping blood throughout the body. Unlike other muscle tissues, cardiac muscle cells are interconnected by specialized junctions called intercalated discs. These discs contain gap junctions that allow for the rapid spread of electrical impulses, enabling the muscle cells to contract in unison.

Cardiac muscle displays a distinctive branched structure, with generally one central nucleus per cell, though variations with two nuclei can occur. These branches enable the tissues to form a strong, interconnected network, enhancing the tissue's ability to withstand high pressures within the heart chambers. Another key property is its striation pattern, caused by the organized alignment of contractile proteins, which are indicative of its excellent contracting abilities.

Moreover, cardiac muscle tissue displays automaticity — the ability to initiate its contractions without external nervous stimulus. This is due to the presence of pacemaker cells that regulate the heart's rhythm. Cardiac muscle is also incredibly fatigue resistant; it doesn't tire out despite constant work, thanks to a rich supply of mitochondria that provide ample energy through aerobic respiration.

Smooth Muscle Characteristics

Smooth muscle tissue is known for its fundamental role in various involuntary movements within the body — from propelling food through the digestive system to controlling blood flow in the arteries. The key characteristics of smooth muscle precisely facilitate these functions. Smooth muscles are composed of spindle-shaped cells, each with a single central nucleus. These unbranched cells confer the smooth, uniform appearance that distinguishes them from the banded look of striated muscles.

The lack of striation in smooth muscle is due to the different organization of the contractile fibers within the cells. They contract slower than skeletal muscles but can maintain the contraction longer, which is crucial for processes like peristalsis in the gastrointestinal tract.

Smooth muscle can also stretch and maintain tension over a wider length range, making them highly adaptable to the changing volume of organs such as the bladder and stomach. This elasticity is a defining property of smooth muscle, coupled with its ability to be controlled involuntarily by the autonomic nervous system, which responds to stimuli such as stress, hormones, and changes in pH.

Skeletal Muscle Structure

Skeletal muscle tissue is specialized for voluntary movement, enabling us to perform a wide array of activities from walking to typing. The cells of skeletal muscle — also known as muscle fibers — are long, cylindrical, and multinucleated. They run parallel to each other and are bound together by connective tissue, forming what we recognize as a muscle.

The internal structure of a skeletal muscle fiber features a highly organized arrangement of myofibrils containing the actin and myosin filaments responsible for muscle contraction. It is this organized pattern that causes the striated appearance of skeletal muscle when viewed under a microscope. A hallmark of skeletal muscle structure is the abundance of mitochondria, which supply the energy for muscle contractions.

Moreover, the points where skeletal muscles attach to bones are called tendon insertions, and the bulk of these muscles can span across joints to facilitate movement. Due to their structure, skeletal muscles tend to be fast and powerful in their action but are limited by their susceptibility to fatigue over prolonged periods of use. These intricate structural elements of skeletal muscles are crucial for understanding how they function in tandem with the skeletal system to execute movement.