Question

Which of these muscle types is striated and contains gap junctions? a. Single-unit smooth muscle b. Multiunit smooth muscle c. Cardiac muscle d. Skeletal muscle

Short answer

The correct answer is c. Cardiac muscle, as it is both striated and contains gap junctions.

Step-by-step solution

Understand the Characteristics of Each Muscle Type

Before we can find the answer, let's become familiar with each muscle type: a. Single-unit smooth muscle: These muscles are found in the walls of internal organs like the stomach, intestines, and blood vessels. They are non-striated and contain gap junctions. b. Multiunit smooth muscle: These muscles are found in places like the iris of the eye and the walls of airways in the lungs. They are also non-striated but do not contain gap junctions. c. Cardiac muscle: This type of muscle is found in the walls of the heart and is responsible for the heartbeat. It is striated and contains gap junctions. d. Skeletal muscle: These muscles are attached to the bones and are responsible for body movement. They are striated but do not contain gap junctions.

Finding the Answer

Now that we understand the characteristics of each muscle type listed, we can find the answer to the question: Which of these muscle types is striated and contains gap junctions? Based on the descriptions given, the correct answer is: c. Cardiac muscle This muscle type is both striated and contains gap junctions.

Key concepts

Striated Muscle

Striated muscle refers to the type of muscle tissue that has a striped appearance under the microscope due to the presence of repetitive structural units called sarcomeres. These sarcomeres are composed of long, fibrous proteins such as actin and myosin, which slide past each other when the muscle contracts and relaxes, causing the striation pattern.

There are two types of striated muscles: skeletal and cardiac. Skeletal muscles primarily connect to bones and are under voluntary control, allowing us to carry out daily activities like walking and writing. Cardiac muscle, on the other hand, is found only in the heart and is the powerhouse behind the pumping action required to circulate blood throughout the body.

Gap Junctions

Gap junctions are specialized intercellular connections between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells.

One of the key roles of gap junctions is to enable cells to communicate quickly and synchronize their activities, which is crucial in muscle physiology, particularly for the heart. For example, gap junctions in cardiac muscle cells support the synchronous contraction of the heart by allowing the rapid spread of excitation from one cell to another.

Cardiac Muscle

Cardiac muscle is one of the three main types of muscle tissue and it possesses unique structural and functional qualities. As part of the myocardium, or the middle layer of the heart wall, it has the responsibility of contracting to pump blood from the heart chambers. Unlike other muscles, cardiac muscle contracts involuntarily and does so in a rhythmic and coordinated fashion.

This coordination is made possible partly due to the presence of gap junctions within the intercalated discs that join cardiac muscle cells (cardiomyocytes) together. These features enable the cells to act as a unit, even though each one beats in response to its own inherent rhythm.

Smooth Muscle

Smooth muscle, named for its non-striated appearance, makes up the muscular tissue found within the walls of internal hollow organs like the stomach, intestines, and blood vessels. Unlike skeletal muscle, smooth muscle is under involuntary control, which means it is regulated by the autonomic nervous system and doesn't require conscious thought to function.

Smooth muscle can be further categorized into two types based on how the cells are organized and function: single-unit smooth muscle, which contracts as a single entity due to the presence of gap junctions, and multi-unit smooth muscle, where each cell operates independently without gap junctions. Single-unit smooth muscle is commonly found in the walls of blood vessels and the digestive tract, whereas multi-unit smooth muscle is present in the iris of the eye and around airways in the lungs.