The Muscular System

The Muscular System

• Muscles are soft tissues composed of many stretchy fibers, with over 600 muscles in the human body.
• The main function of the muscular system is to move the skeleton.
• Organs, including muscles and tendons, are part of the muscular system.

Types of Muscle Tissue

• There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle.
• Skeletal muscle is voluntary, attached to bone, and dependent on signaling from the nervous system.
• Smooth muscle is involuntary, found in internal organs, and can respond to hormones and local stimuli.
• Cardiac muscle is found in the heart and is striated, with highly coordinated contractions pumping blood into the circulatory system.

Skeletal Muscles

• Skeletal muscles contract to cause movement and maintain posture, stability, and skeletal structure.
• They contribute to the maintenance of homeostasis by generating heat, noticeable during exercise or in extreme cold.
• Skeletal muscle cells are long and cylindrical, with the functional unit being the sarcomere, a highly organized arrangement of contractile myofilaments.

How Muscles Move

• For a skeletal muscle fiber to contract, its membrane must be stimulated to fire an action potential.
• The muscle fiber action potential releases calcium ions, which interact with shielding proteins, allowing myosin to pull actin filaments and shorten the muscle fiber.

Smooth Muscle

• Smooth muscle is present in the walls of hollow organs and passageways, such as the urinary bladder, uterus, stomach, intestines, and arteries and veins.

Cardiac Muscle

• Cardiac muscle tissue is only found in the heart, with highly coordinated contractions pumping blood into the circulatory system.
• Cardiac muscle fibers are shorter than skeletal muscle fibers, with a single nucleus and many mitochondria and myoglobin.

Voluntary and Involuntary Muscles

• Voluntary muscles are skeletal muscles under conscious control, while involuntary muscles are smooth and cardiac muscles not under conscious control.

Muscle Functions

• The main functions of the muscular system are mobility, stability, posture, circulation, respiration, digestion, urination, childbirth, vision, organ protection, and temperature regulation.
• Mobility involves the contraction of muscles to contribute to gross and fine movement.
• Stability involves muscle tendons and core muscles stabilizing the body and assisting in tasks.
• Posture involves skeletal muscles helping to maintain the correct position when sitting or standing.

Circulation and Respiration

• The heart is a muscle that pumps blood throughout the body, with smooth muscle in the arteries and veins maintaining blood pressure and circulation.
• Breathing involves the use of the diaphragm muscle, which contracts and relaxes to expand and deflate the lungs.

Digestion and Urination

• The muscular system allows for movement within the body, such as during digestion and urination.
• Smooth muscles in the gastrointestinal tract control digestion, with peristalsis moving food through the digestive system.
• The urinary system involves both smooth and skeletal muscles working together to hold and release urine from the bladder.

Vision and Organ Protection

• Six skeletal muscles around the eye control its movements, allowing for quick and precise movements.
• Muscles in the torso protect internal organs at the front, sides, and back of the body, absorbing shock and reducing friction in the joints.

Temperature Regulation

• The muscular system generates heat through muscle contractions, with shivering being an example of this mechanism.
• Muscles in the blood vessels contract to maintain body heat, and relax to increase blood flow and release excess heat through the skin.

Terminology Related to Muscle Movement

• Abduction: moving away from the center
• Adduction: moving towards the center
• Flexing: bending of a joint
• Extension: straightening out of a limb
• Hyperextension: straightening of a limb beyond its capability
• Pronation: face down or hands palm down
• Supination: face up or hands palm up
• Internal rotation: turning a limb towards the body
• External rotation: turning a limb away from the body
• Atrophy: shrinkage of muscle due to lack of use

Disorders of the Muscular System

• Atrophy: shrinkage of muscle due to lack of use
• Muscular dystrophy: a genetic disease causing damage to muscle fibers
• Myalgia: muscle pain
• Polio: caused by a virus
• Tendonitis: inflammation of the tendons