Sistema Muscular Humano

Introduction

• The muscular system is a vital component of the human body, responsible for movement, posture, and heat production.
• It comprises three main types of muscles: skeletal, smooth, and cardiac.

Skeletal Muscle

• Skeletal muscles are attached to bones and are responsible for voluntary movements.
• They are striated, exhibiting a striped appearance under a microscope.
• Functions include locomotion, facial expressions, posture, and speech.
• Skeletal muscle fibers are multinucleated, containing multiple nuclei per cell, distinguishing them from other muscle types.
• Muscle fibers are composed of myofibrils, which are further composed of sarcomeres, the fundamental units of muscle contraction.
• The sliding filament theory describes how muscle contraction occurs. Myosin filaments bind to actin filaments, drawing them closer, thus shortening the sarcomere and generating force.

Smooth Muscle

• Smooth muscle is present in the walls of internal organs and blood vessels.
• It is responsible for involuntary movements, such as digestion, blood flow regulation, and pupil dilation.
• Unlike skeletal muscle, smooth muscle is non-striated and mononucleated.
• Its contraction is slower and more sustained compared to skeletal muscle contractions.
• Smooth muscle plays a key role in maintaining homeostasis within the body.

Cardiac Muscle

• Cardiac muscle is found exclusively in the heart.
• It is responsible for pumping blood throughout the body.
• Cardiac muscle is also striated, similar to skeletal muscle.
• It is branched and involuntary, coordinating contractions for effective heart function.
• Cells are interconnected by intercalated discs, specialized junctions enabling rapid transmission of electrical signals for synchronized contractions.
• This ensures a consistent heartbeat.

Muscle Tissue Properties

• Excitability: Muscles respond to stimuli, like nerve impulses.
• Contractility: Muscles can shorten and generate force.
• Extensibility: Muscles can be stretched beyond their resting length.
• Elasticity: Muscles return to their original length after stretching.

Muscle Fiber Structure and Function

• Muscle fibers consist of myofibrils arranged in parallel.
• Myofibrils are composed of repeating units called sarcomeres.
• Sarcomeres contain actin and myosin filaments that slide past each other during contraction.
• The neuromuscular junction is where a motor neuron connects to a muscle fiber, allowing nerve impulses to trigger muscle contractions.

Muscle Metabolism

• Muscles require energy (ATP) for contraction.
• ATP is produced through cellular respiration.
• Muscles can also use anaerobic respiration for brief bursts of high-intensity activity.
• Muscle fatigue is a decrease in the muscle's ability to contract due to depleted energy stores or accumulated metabolic byproducts.

Muscle Types Summary

Muscle Disorders

• Muscle disorders vary in severity, affecting any muscle type.
• Common examples include muscular dystrophy, myasthenia gravis, and various inflammatory conditions.
• These conditions often lead to impaired muscle function, causing weakness, pain, and potential complications.