Lecture 22: Muscles

What are the three major types of muscle?

cardiac, smooth, and muscle

What is cardiac muscle?

found in the heart, uni or multi nucleated, striated, and is under involuntary control

What is skeletal muscle?

attaches to bones, multinucleated, striated, and is under voluntary control

What is smooth muscle?

found in organs and vessels, unnucleated, and under involuntary control

What is the organization of muscle fibers?

muscle —> bundle of muscle fibers —> muscle fibers (muscle cells) —> myofibrils —> myofilament (threads of proteins; thick & thin filaments)

What is a sarcomere?

the thin and thick filaments in a myofibril are arranged into repeating units

What is thick filament composed of?

made up to myosin and A bands

What is thin filament composed of?

made up of actin and I band

What is the organization of sarcomere?

Thick filaments are towards the middle of the sarcomere and Thin filaments are towards the edge of the sarcomere; They both overlap partially

What occurs during muscle contraction of the sarcomere

sarcomeres shorten but individual filaments do not change in length but the thin filament slides over the thick filaments (sliding filament model).

What is the function of tropomyosin?

blocks myosin binding sites when the muscle is in a relax state

What is the function of tropomin complex?

made up set of proteins with calcium binding sites; when Calcium is present it binds to the binding sites on the troponin complex and moves the tropomyosin revealing the myosin binding site

What is the role of calcium ions in muscle contraction?

calcium ions are released from the sarcoplasmic reticulum from the response of a action potential which originates from the axon of a motor neurons. Occurs when muscle contraction occurs.

How is muscle contraction regulated?

acetylcholine released by motor neuron and binds to receptors on muscle fibers plasma membrane which triggers an action potential —> action potential moves down to the T tubules —> triggers release of Ca²⁺ from sarcoplasmic reticulum —> Ca²⁺ bind to troponin complex —> myosin head can form a cross bridge and move thin filament toward the middle of sarcomere (muscle contraction) —> tropomyosin covers myosin binding sites, myosin heads cannot bind to think filament and it goes back to resting state