Muscular System: Anatomy, Function, and Contraction
Muscular System Functions
- Movement: Contraction of skeletal muscles.
- Posture: Maintenance by skeletal muscles.
- Respiration: Movements of thoracic muscles.
- Heat Production: Body heat generation.
- Communication: Muscle actions facilitate communication.
- Organ Constriction: Smooth muscles move substances.
- Heartbeat: Cardiac muscle propels blood.
- Organ Protection: Muscles provide support.
Muscle Connective Tissues
Epimysium
The epimysium is the outermost layer of dense, irregular connective tissue surrounding the entire muscle. It combines with other connective tissues to form tendons. The fascia forms a layer around the muscle.
Perimysium
The perimysium is a membrane that protects and supports groups of muscle fibers (fascicles). It shapes and organizes muscle fibers and transmits forces. Blood vessels and nerves are present within the perimysium.
Endomysium
The endomysium is a thin layer of connective tissue surrounding individual muscle fibers. It consists of reticular fibers made of collagen and separates muscle fibers within a fascicle.
Muscle Contraction Mechanism
T-Tubules
T-Tubules transport calcium ions, essential for muscle contraction.
Myosin and Actin Binding
Tropomyosin covers myosin binding sites on actin. Calcium ions bind with troponin-C, altering tropomyosin and exposing binding sites. The sarcoplasmic reticulum controls calcium concentration. Muscle contraction ends when calcium is pumped back, initiating relaxation.
Filaments
Thick filaments are made of myosin, which has elasticity and contractibility. Thin filaments are primarily made of actin, along with troponin and tropomyosin. These molecules cover myosin-binding sites when the muscle is relaxed.
Sarcomere
The sarcomere is the basic functional unit of striated muscle. Muscles are composed of bundles of muscle fibers, which are made of myofibrils.
Energy and Muscle Function
ATP
ATP provides energy for muscle contraction, derived from glucose and fatty acid metabolism. Creatine phosphate allows for strong contractions before glycolysis and cellular respiration produce more ATP.
Action Potential and Neurotransmitters
An action potential initiates muscle contraction. Acetylcholine, synthesized by choline acetyltransferase, is converted into inactive metabolites by acetylcholinesterase.
Mitochondria and Sarcoplasm
Mitochondria generate ATP and store calcium. The sarcoplasm contains glycosomes (stored glycogen), myoglobin (oxygen-binding protein), and calcium ions.