Muscular tissue is a specialised group of cells (muscle fibres) that helps different parts of the body to move by contracting and relaxing. It is mainly made up of proteins such as actin and myosin. In this article, we will discuss what muscular tissue is, its properties, and structure, the three major muscular tissue types, and their roles in our body. We will also look at a few additional insights to help you understand the topic better.

What is Muscular Tissue?

Muscular tissue is one of the four major tissues found in the human body (the others being epithelial, connective, and nervous tissues). It is responsible for generating force and producing motion, whether that motion is related to body movement, organ function, or the pumping action of the heart.

Muscular Tissue Location

Skeletal muscles are found attached to bones through tendons.
Smooth muscles are present in the walls of internal organs (e.g., stomach, intestine, blood vessels).
Cardiac muscles are located exclusively in the heart.

Properties of Muscular Tissue

Contractility – Muscles can shorten or contract when stimulated.
Extensibility – Muscles can be stretched without damage.
Elasticity – Muscles can return to their original shape after stretching.
Excitability – Muscles can respond to nerve impulses or chemical signals.

These properties enable muscles to perform diverse functions, from voluntary movements such as walking to involuntary functions like the beating of the heart.

Structure of Muscular Tissue

Muscular tissues are organised into bundles and supported by connective tissues:

Epimysium: A tough outer layer of connective tissue that surrounds the entire muscle. It connects to tendons, which in turn attach to bones.
Fascicles: Long bundles of muscle fibres grouped together. Each fascicle is surrounded by another connective tissue layer called the perimysium.
Endomysium: A thin layer of connective tissue that surrounds each individual muscle fibre.

Inside each muscle fibre:

Sarcolemma is the membrane that encloses the muscle fibre.
Sarcoplasm is the cytoplasm of the muscle cell, containing proteins and organelles.
Sarcoplasmic reticulum is a network of membranes involved in storing and releasing calcium ions essential for muscle contraction.
Myofibrils are thread-like structures within the muscle fibre that contain the contractile proteins (actin and myosin).

When the muscle receives a signal (nerve impulse), actin and myosin filaments slide past each other, causing the muscle to contract. This is explained by the Sliding Filament Theory. Explore more about this concept in [Sliding Filament Theory].

Types of Muscular Tissue

1. Skeletal Muscle Tissue

Location: Attached to bones of the skeleton.
Features:

Also called striated muscular tissue because of its light and dark band pattern.
Multinucleated cells with elongated mitochondria for energy.
Voluntary control (movement is consciously controlled).
Helps in locomotion, posture, and overall movement of the body.
Comprises about 40% of body mass in humans.

Function: Enables movement of bones, supports posture, and generates heat through contractions.

Explore more about Skeletal Muscles to understand how these muscles bring about movement.

2. Smooth Muscle Tissue

Location: Walls of internal organs such as the stomach, intestines, blood vessels, and other hollow structures.
Features:

Non-striated and spindle-shaped cells with a single nucleus.
Involuntary control is governed by the autonomic nervous system.
Actin and myosin are arranged in a random pattern (hence no striations).

Function: Regulates the movement of internal organs (e.g., peristalsis in the digestive tract) and controls the diameter of blood vessels and airways.

3. Cardiac Muscle Tissue

Location: Found exclusively in the heart.
Features:

Striated like skeletal muscle but operates involuntarily.
Cells are uninucleated and branched, joined by special junctions called intercalated discs.
Intercalated discs contain desmosomes for structural support and gap junctions for electrical coupling.

Function: Pumps blood throughout the body via rhythmic contractions. The coordinated heartbeat is driven by electrical signals.

Learn more about the structure and function of the heart in Human Heart.

Muscular Tissue Function

Movement: Muscular tissue helps in moving our body parts (skeletal muscles), pushing food through the digestive system (smooth muscle tissue), and circulating blood (cardiac muscle tissue).
Maintaining posture: Skeletal muscles contract slightly to hold the body upright and stable.
Generating heat: Muscle contractions produce heat that helps maintain body temperature.
Supporting organ function: Smooth muscles help in blood flow regulation, air passage regulation, and movement of substances within organs.

Quick Quiz on Muscular Tissue

1. Which muscular tissue is found in the heart?
A. Smooth
B. Cardiac
C. Skeletal
D. Striated
Answer: B. Cardiac

2. Which property allows muscles to return to their original shape after being stretched?
A. Contractility
B. Extensibility
C. Elasticity
D. Excitability
Answer: C. Elasticity

3. What is the membrane enclosing a muscle fibre called?
A. Endomysium
B. Sarcolemma
C. Sarcoplasm
D. Epimysium
Answer: B. Sarcolemma

4. Which type of muscle is voluntarily controlled?
A. Smooth
B. Cardiac
C. Skeletal
D. All of these
Answer: C. Skeletal

FAQs on Muscular Tissue

1. What is the difference between striated muscular tissue and smooth muscle tissue?

Striated muscular tissue has a banded appearance (as seen in skeletal and cardiac muscles), whereas smooth muscle tissue does not have visible bands. Striated muscles are usually under voluntary or involuntary control (skeletal is voluntary, cardiac is involuntary), while smooth muscles are exclusively involuntary.

2. Why do skeletal muscle fibres have multiple nuclei?

Skeletal muscle fibres form by the fusion of many embryonic cells (myoblasts). This fusion creates long fibres containing multiple nuclei to meet the high protein synthesis demands required for muscle contraction and repair.

3. How does cardiac muscle continue to function without fatigue?

Cardiac muscle cells (cardiomyocytes) contain numerous mitochondria that produce a constant supply of energy. The heart also has specialised conduction tissues and an intrinsic pacemaker (the sinoatrial node) that ensures rhythmic contractions without tiring under normal conditions.

4. What causes muscle contraction at the cellular level?

Muscle contraction is caused by the sliding of actin and myosin filaments past each other, triggered by electrical impulses and the release of calcium ions from the sarcoplasmic reticulum.

5. Can smooth muscle tissue regenerate?

Smooth muscle tissue has a relatively higher capacity to regenerate compared to skeletal and cardiac muscles. Smooth muscle cells can divide to some extent and repair the tissue when needed.

Muscular Tissue

Muscular Tissue – Definition, Types, Structure, and Function