Functions of the Muscular System Muscles are organs composed of specialized cells that use chemical energy stored in nutrients to contract

Functions of the Muscular System The main function of the muscular system is movement Muscular action also: Propels body fluids and foods Generates heartbeat

Skeletal Muscle -Composed of -Muscle tissue -Nervous tissue -Blood -Other Connective Tissues

Connective Tissue Coverings -Fascia is a connective tissue that separates an individual skeletal muscle from adjacent muscles -It also holds the muscle in position -Like plastic wrap around muscles

Connective Tissue Coverings -Aponeuroses are broad fibrous sheets of connective tissue -These can attach to bone or to the coverings of adjacent muscles

Skeletal Muscle Anatomy -Tendons attach muscle to bone -The main part of the muscle is called the belly of the muscle

Skeletal Muscle Anatomy -Muscles are made up of bundles of muscle fibers which are called fascicles -These fascicles are separated by connective tissue

Skeletal Muscle Anatomy -Fascicles are made of individual muscle fibers, which are the muscle cells

Skeletal Muscle Anatomy -Muscle cells are called fibers because they are much longer than they are wide -These cells are usually as long as the whole muscle

Skeletal Muscle Fibers -Skeletal muscle fiber is a single cell that contracts in response to a stimuli -The cytoplasm of the skeletal muscle fiber is called sarcoplasm

Skeletal Muscle Fibers -The muscle fiber has many nuclei, because it is so long -The endoplasmic reticulum of the muscle fiber is called sarcoplasmic reticulum

Skeletal Muscle Fibers -The muscle cell contains many myofibrils which are composed of thick and thin elements

-The thin filaments in myofibrils are actin, the thick ones are called myosin -The organization of these filaments make up the striations you see in skeletal muscle fibers

-The cytoplasm within the muscle fiber is called sarcoplasm -The endoplasmic reticulum inside the muscle fiber is called sarcoplasmic reticulum

-The repeating units on the myofibrils are called sarcomeres -Myofibrils can be thought of a chain of sarcomeres.

-Sarcomeres run from Z-line to Z-line, which the actin filaments are attached directly to

-I bands are the part of the sarcomere which is only actin filaments

-A bands are composed of thick myosin filaments -In parts of the A band, the myosin and actin overlap

-I bands are the lighter colored bands -A bands are the darker colored bands

-The brain sends signals to muscle fibers to cause a contraction -Motor neurons are the nerves that bring the signal from the brain to the muscle

-Skeletal muscle fibers are functionally but not physically connected to the neuron -Think of how your voice travels from your mouth to your cell phone

-This functional connection is called a synapse -Neurons communicate with the cell through neurotransmitters, which are a chemical signal

-A neuromuscular junction is the entire connection between the motor neuron and the muscle fiber (what this picture is showing)

-The brain sends a signal through the neuron -When the signal reaches the end of the neuron, neurotransmitters are released from the synaptic vesicles

-The neurotransmitter travels through the synaptic cleft and is picked up by receptors on the muscle fiber

-When the receptors sense the neurotransmitter, they cause calcium to enter the muscle fiber -This increase in calcium is what causes a muscle contraction

-The functional unit of a muscle contraction is the sarcomere

-Let’s start off when the neurotransmitter is picked by the receptors on the outside of the muscle cell -This causes a flood of calcium into sarcoplasm

Where did the calcium come from? - The sarcoplasmic reticulum has a storage of calcium - When the cell senses the neurotransmitter, calcium is released from the SR into the sarcoplasm

-Calcium floods over the myofibrils -The calcium binds to troponin -This causes the troponin to move tropomyosin off of the myosin binding sites of the actin

-Now, the myosin cross bridges can bind to myosin to actin -Cross bridge pulls the actin filament, and then releases -If calcium is still present, this happens again -This is how the myosin “walks” across the actin

-When the signal to the muscle stops, myosin cross bridges release -The muscle contraction stops