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

What Are Muscles?

Muscles are specialised tissues in the human body whose major function is to move by their ability to contract. They are essential for a wide range of operations or activities that occur or take place 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.

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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

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

Skeletal Muscles

• They 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

• 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.

Diagram: Types Of Muscles

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: The Functional Unit

• Repeating units of myofibrils

• Units responsible for muscle contraction

Myofibrils, Actin And Myosin Filaments

• Myofibrils: Contractile threads within muscle fibers

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

Connective Tissue Components

• Endomysium: surrounds individual muscle fibres

• Perimysium: encases bundles of fibres (fascicles)

• Epimysium: encloses the entire muscle

Tendons And Their Role In Muscle Attachment:

• Connect muscles to bones

• Transmit force from muscle contraction to the skeleton.

Muscle Function

The mechanism of muscle function centres on the process of contraction and how muscles contract.

Sliding Filament Theory:

• Actin and myosin filaments slide past each other

• Shortens the sarcomere, producing contraction.

Role Of ATP And Calcium Ions:

• ATP provides energy for contraction

• Calcium ions control the interaction of actin and myosin.

Neuromuscular Junction And Action Potential:

• Synapse between a motor neuron and muscle fibre.

• Action potential leads to muscle contraction.

Isotonic And Isometric Contractions:

• Isotonic: length of the muscle changes (e.g. lifting a weight)

• Isometric: muscle does not change in length (e.g. holding a position)

Concentric And Eccentric Contractions:

• Concentric: Muscle shortens when contracting

• Eccentric: Muscle lengthens when contracting

Energy Sources For Muscle Activity

Body gets energy for muscle activity through:

ATP And Creatine Phosphate:

• Immediate sources of energy

• Give rapid flashes of power

Glycolysis And Oxidative Phosphorylation:

• Glycolysis: Glucose breakdown for short-term energy.

• Oxidative phosphorylation: Sustained production of energy through aerobic respiration.

Muscle Growth And Repair

This is important for good health and function within the muscles.

Factors Influencing Muscle Growth:

• Resistance exercise

• Proper nutrition

Effects Of Exercise And Nutrition:

• Resistance exercise induces hypertrophy of the muscle.

• Poor nutrition or failure to exercise leads to atrophy of the muscles.

Role Of Satellite Cells:

• Stem cells that help to repair the muscles.

• Activate and proliferate in response to muscle injury.

Inflammation And Healing Process:

• Early inflammation removes damaged tissue.

• Healing requires tissue regeneration and remodelling.

Common Muscle Disorders And Diseases

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

Muscular Dystrophy

• Duchenne muscular dystrophy: Progressive muscle weakness

• Becker muscular dystrophy: Similar but milder

Genetic Basis And Treatment Options:

• Genetic mutations that alter muscle proteins.

• Treatment is symptomatic and aims to retard the progression.

Myasthenia Gravis

• Muscle weakness, fatigue

• Autoimmune disorder at the neuromuscular junction.

Treatment And Management:

• Medications aimed at improving nerve-muscle communication.

• Immunosuppressive therapies.

Muscle Cramps And Strains

• Caused by dehydration, over-use, electrolyte imbalance.

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

Treatment And First Aid:

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

• Gentle stretch and rehydrate

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