Muscles: Types, Groups, Anatomy, Functions, Composition, Development

What are Muscles?

Muscles are specialised tissues in the human body whose function is to move by the ability to contract. They are essential for a wide range of activities within the body, such as maintaining posture, providing means and enabling locomotion, and assisting in critical functions like breathing and digestion. They contribute to overall health by way of supporting the skeletal system, protecting the internal organs, and offering help in metabolic processes.

Muscles take part in movement but play a crucial role in the overall health of the body. Regular muscle activity improves cardiovascular health, supports metabolic functions, and aids in maintaining a healthy weight. Other than daily movements, muscle strength is also vital for daily acts and the prevention of injuries of any type.

Types of Muscles in the Human Body

The types of muscles in the human body are broadly divided into three categories: skeletal, cardiac, and smooth muscles.

Skeletal Muscles

• Skeletal muscles are striated in appearance.

• Multinucleated fibers

• Voluntary control

• Fixed to bones by tendons

• Extensively in limbs and torso

• Cause movement due to contraction and relaxation abilities

• Examples: Biceps brachii (arm), Quadriceps femoris (thigh)

Cardiac Muscles

• Cardiac muscles are striated with intercalated discs

• One nucleus per cell

• Involuntary

• In the Walls of the heart (myocardium)

• Pump blood throughout the body

• Contraction occurs continually in a rhythmic manner.

Smooth Muscles

• Not striated

• One nucleus per cell

• Autonomic nervous control

• In the Walls of hollow organs (e.g., intestine, blood vessels)

• Move substances along the body

• Examples: Muscles in the digestive tract, blood vessel walls.

Muscle Structure

Muscle structure is complex, comprising different parts that interact to produce contraction and movement.

Muscle Fibers

• Elongated, cylindrical cells

• Several nuclei peripherally located

Sarcomere – Functional Unit

• Repeating units of myofibrils

• Units responsible for muscle contraction

Myofibrils, Actin & Myosin Filaments

• Myofibrils: Contractile threads within muscle fibers

• Actin (thin) and myosin (thick) filaments: Proteins involved in contraction.

Connective Tissue Layers

• Endomysium: surrounds individual muscle fibres

• Perimysium: encases bundles of fibres (fascicles)

• Epimysium: encloses the entire muscle

Tendons

• Connect muscles to bones

• Transmit force from muscle contraction to the skeleton.

Muscle Function: How Muscles Contract

The mechanism of muscle contraction is discussed below:

Sliding Filament Theory

• Actin and myosin filaments slide past each other

• Shortens the sarcomere, producing contraction.

Role of ATP

• Detaches myosin head

• ATP provides energy for contraction

Role of Calcium Ions (Ca²⁺)

• Exposes binding sites on actin

• Triggers contraction cycle

Neuromuscular Junction & Action Potential:

• Synapse between a motor neuron and muscle fibre.

• Action potential leads to muscle contraction.

Types of Muscle Contraction

Types of muscle contraction are:

Isotonic Contractions

• Length of the muscle changes

• E.g., lifting a weight

Isometric Contractions

• Muscle does not change in length

• E.g., holding a position like plank

Concentric Contractions

• Muscle shortens when contracting

Eccentric Contractions

• Muscle lengthens when contracting

Muscle Disorders and Diseases

Several disorders and diseases can compromise muscle and thus function and quality of life.

Muscular Dystrophy

• Genetic mutations that alter muscle proteins.

• Treatment is symptomatic and aims to retard the progression.

• Duchenne muscular dystrophy: Progressive muscle weakness

• Becker muscular dystrophy: Similar but milder

Myasthenia Gravis

• Muscle weakness, fatigue

• Autoimmune disorder at the neuromuscular junction.

• Medications aimed at improving nerve-muscle communication.

• Immunosuppressive therapies.

Muscle Cramps and Strains

• It is caused by dehydration, overuse, and electrolyte imbalance.

• This can be prevented by regular stretching and proper hydration.

• Rest, ice application, compression, elevation (RICE)

• Gentle stretch and rehydrate

Muscles NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Types of muscles

• How muscles contract

• Types of muscle contraction

Practice Questions for NEET

Q1. Which of the following is not a type of muscle?

1. Skeletal muscle

2. Visceral muscle

3. Cardiac muscle

4. Lymphatic muscle

Correct answer: 4) Lymphatic muscle

Explanation:

Muscles have been classified using different criteria, namely location, appearance and nature of regulation of their activities. Based on their location, three types of muscles are identified : (i) Skeletal (ii) Visceral and (iii) Cardiac. Muscles can be classified based on their location, appearance, and regulation of activity. Skeletal muscles are attached to bones and are responsible for voluntary movements. Visceral muscles, found in the walls of internal organs like the stomach and intestines, are typically involuntary and help with processes like digestion. Cardiac muscle, found in the heart, is also involuntary and specialized for rhythmic contractions. Each type of muscle has distinct structural and functional characteristics suited to its role in the body.

Hence, the correct answer is option 4) Lymphatic muscle.

Q2. Which of the following statements is incorrect ?

1. Smooth muscles are found in urinary bladder , alimentary canal and genital tract

2. A striated muscle is a syncytium i.e., a multinucleate structure

3. The cytoplasm of striated muscle is called endoplasm

4. The plasma membrane and ER of striated muscles are called sarcolemma and sarcoplasmic reticulum respectively

Correct answer: 3) The cytoplasm of striated muscle is called endoplasm

Explanation:

Visceral muscles are involuntary muscles, as their activities are not under the conscious control of the nervous system. They play a crucial role in various physiological functions, such as transporting food through the digestive tract and moving gametes through the genital tract. These muscles are primarily found in the walls of internal organs like the stomach, intestines, and blood vessels, facilitating essential bodily processes without conscious effort.

Hence the correct answer is option 3) The cytoplasm of striated muscle is called endoplasm.

Q3. The muscle fibers that contract slowly are

1. Red muscle fibres

2. White muscle fibres

3. Both a and b

4. None of these

Correct answer: 1) Red muscle fibres

Explanation:

Red muscle fibers, also known as slow-twitch fibers, contract slowly but are highly resistant to fatigue. They are rich in myoglobin, mitochondria, and blood supply, which enable sustained aerobic energy production. These fibers are well-suited for endurance activities like walking, running long distances, or maintaining posture, as they rely on oxidative metabolism for energy.

Hence, the correct answer is option 1) Red muscle fibers.

Also Read:

• MCQs on Muscles and their Types

• Vertebral Column

• Pectoral Girdle

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