Relaxation and Contraction of Muscle Systems

Transverse Tubules (T-Tubes). Tunnel like extensions of the sarcolemma. Sarcoplasm: The cytoplasm of the muscle fiber. It contains large amounts of mitochondria that produce the ATP during contraction.

Muscle Fibers: elongated cylindrical cells that run parallel to each other. Sarcolemma: a plasma membrane that covers each membrane.

Sarcoplasmic Reticulum: A network of fluid filled tubules that contain calcium ions needed for contraction. These tubules run thoughout the sarcoplasm. Myoglobin: Reddish pigment also found in the sarcoplasm that stores oxygen needed in ATP production. Myofribriles: Cylindrical structures that extend along the entire length of the muscle fiber. It consists of two types of protein filaments. Thin filaments : composed of a protein called Actin b. Thick Filaments : Composed of a protein called Myosin

Sacromeres: The basic units of striated muscles and are created when the filaments overlap each other. Z-discs: these separate the Sarcomeres. A-Band: a darker area that extends the length of the thick filament. Found in the sarcomere.

Muscle Cell

Sliding Filaments During muscle contraction the myosin heads of the thick filaments pull on the thin filaments. This causes the thin filament to slide toward the center of the sarcomere. This will cause the I and H bands to become thinner and almost dissapear when the muscle is fully contracted.

H-Zone: a narrow center area of the A-band that contains only thick filaments. I-Band: The lighter area on either side of the A-band that is made up of thin filaments.   The alternating darker A-bands and lighter I-bands give the muscle it striated appearance.

A sarcomere has a distinctive structure that is established by a specific arrangement of zones, bands, and lines

Electron micrograph shows the real relations of the various zones, bands and lines

The lengths of the filaments do not change!! “The Sliding Filament Mechanism” describes the contraction of a sarcomere Thick and Thin filaments slide past each other and shorten the sarcomere The lengths of the filaments do not change!! Animate Me!

Remember that the lengths of the filaments do not change they only slide past each other. The sliding-filament mechanism occurs only when the concentration of Ca+ ions is high and the ATP is available.

Neuromuscular Junction: Muscle action Potential: An electrical signal that Stimulates a skeletal muscle.   Motor Neuron: This is the neuron that delivers the signal to the muscle. Motor Unit: The muscle fibers and the motor unit.

Muscles that control fine precise movements have many motor units Muscles that control fine precise movements have many motor units. (Ten or less) Those muscles that have gross movements have fewer units with many more muscle fibers. (Up to several thousand.)

Axon: The long process of the motor neuron.   Axon Terminals: These are the branches of the axon and form bulbs at the ends. Synaptic end bulbs: These are the swellings at the axon terminals. Synaptic Vesicles: These contain the chemicals called the neutransmitters.

Motor End Plate: Region sacrolemma near the axon terminal. Synaptic Cleft: The space between the axon terminal and the sacrolemma. Neuromuscular Junction: The synapse formed between the axon terminal and the motor end plate.

The Exciting of a Motor Neuron: 1. Release of acetylcholine: Diffuses from the motor neuron to the motor end plate.  2. Activation of Acetylcholine receptors: As ACh binds to the motor end plate channels open that allow positive ions such a sodium ( Na+) to diffuse across a membrane.  3. Generation of Action Potential: As Na+ diffuses this generated the muscle action potential. 4. Breakdown of ACh: Lasts briefly, due to it being broken down by the enzyme Acetylcholinesterase.

Physiological Contraction Ca+ and ATP are needed for the contraction of the muscle fiber.   ATP is produced in the Mitochondria of the cell and the Muscle cells have a high number of Mitochondria.

1.When the Muscle is relaxed there is a Low number of Ca+ in the Sarcroplasm. The Ca+ active transport pumps are contained in the membrane of the Sarcoplasmic reticulum. 2.The Ca+ ions move into the sarcoplasm. 3.The Ca+ will then bind with Troponin. This moves the Tropomyosin, on the thin filament exposing the Actin bonding sites for myosin.

4. Contraction or the Power Stroke : Uses the ATP myosin heads bind to actin filiments are pulled toward center of sarcomere.   5. Troponin-tropomyosin complex slides back into position where it blocks the myosin. 6. Muscle relaxes: as the Ca+ is restored in the sarcoplasm and it uses ATP. Muscles then relax.

Energy For Muscle Contraction Muscles Need ATP for contraction or use, but there is only enough ATP in the muscle fiber to last only a few seconds.   Muscle fibers have 3 sources for the production or synthesis of ATP. 1. Creatine phosphate 2. Glycolysis 3. Aerobic cellular respiration

Creatine phosphate: A high energy molecule that is unique to muscle tissue. When the muscle is at rest each fiber produces more ATP than is needed, some of the excess ATP is used to create Creatine phosphate and ADP. When the muscles are used they then transfer the creatine phosphate back to ADP thus creating more ATP.

ATP and creatine phosphate produce enough energy for about 15 seconds of maximum muscle contraction. After 15 second of exercise the muscle must go to glycolysis to find the energy.

Glycolysis: This is the process of breaking down glucose into pyruvic acid and 2 ATP. Glucose passes easily to the muscle from the blood. Glycolysis occurs in the sarcoplasm and is anerobic.. It provides enough energy for the muscles 30 to 40 seconds, to be the main energy system.   After 40 sec. The muscle performs either lactic acid fermentation or aerobic cellular respiration if oxygen is present. (This will keep working for up to 2 min. Think conditioning.)

Aerobic Cellular Respiration 2 sources of oxygen used 1.) from Blood 2.) from Myoglobin   Used exclusively in activities that last more than 10 min.

If enough Oxygen is present Pyruvic acid enters the Mitochondria and is completely oxidized. This generates 36 ATP, carbon dioxide, water, and heat. Lactic Acid Fermentation: If Oxygen levels are low the pyruvic acid that is made during glycolysis is converted to lactic acid

Review of Main Ideas Skeletal Muscles contract with the aid of nerves and blood vessels. The nerves supply the electrical impulses and the blood delivers the nessessary oxygen and nutrients needed for proper operation.

The oxygen and nutrients are required for the production of ATP, Adenosine Tri-phosphate, that give the muscles the energy needed. The cells of the muscle have a large number of Mitochondria where ATP synthesis takes place.

Each skeletal muscle has an artery and a nerve that delivers the nutrients. They also have a few veins that carry waste products away. The arteries branch out into small capillaries that supply each muscle fiber with the proper amount of materials.

Muscle Contraction and Function: Proper muscle function is required for daily living and most of us have no idea of how a muscle works.   The muscle is made up of different components:

Book Work on Muscle Function page 225-226. Problem #’s 1-7, 10-13, 17, 19, 23, 24, & 25. Due Tuesday.