internal muscle anatomy and physiology powerpoint

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Muscle Physiology Don't think about how weak you are — think of how strong you're going to be. — Michelle Dougherty

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A Powerpoint lecture examining the inner anatomy of muscles and the physiology of how they contract.

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Muscle Physiology

Don't think about how weak you are think of how strong you're going to be. Michelle Dougherty

Muscle Tissue

There are three types of muscle tissue. Smooth muscle:Lines the walls of hollow organs. Involuntary. No striations, single nucleus.

Muscle Tissue

Cardiac muscle:Forms the walls of the heart. Cells are branching and striated. Single nucleus per cell. Intercalated discs divide each cell.

Muscle Tissue

Skeletal muscle:Attached to bones. Voluntary. Long, striated, with multiple nuclei. The muscular system covers only skeletal muscles. Smooth and cardiac are covered as part of other systems.

Functions of Skeletal Muscles

Produce movement of the skeleton.Maintain body position. Support soft tissues. Guard body openings. Maintain body temperature. Store nutrient reserves.

Muscle Fibers (cells)

Each muscle is made of bundles of muscle cells, which are also referred to as muscle fibers. Skeletal muscle fibers are very long, stretching the entire length of a muscle. Each may contain hundreds of nuclei.These nuclei are needed to maintain control across the entire cell. This arrangement makes mitosis impossible.

Within each muscle cell are hundreds of smaller protein fibers that allow the cell to contract and relax,

Muscle Anatomy Connective Tissue

The epimysium is a layer of collagen fibers that covers the entire muscle, seperating it from surrounding organs. Each muscle is divided into bundles of muscle fibers, called a fascicle.

Each fascicle is divided by the perimysium, which also contains blood vessels and nerves for the muscle.

The endomysium surrounds and separates each individual muscle fiber (cell).

Epimysium Nerves and Blood Vessels

Tendon

Endomysium Permysium

Muscle

Fascicle

Fiber

Epimysium

Perimysium

Endomysium

Nerve

Muscle Fascicle

Muscle Fibers

Blood Vessels

Perimysium Muscle Fiber

Endomysium

Nucleus

Capillary

Myofibril

Endomysium Sarcoplasm

Mitochondria Stem Cell Sarcolemma Nucleus

Important Structures of the Muscle Fiber

The sarcolemma The cell membrane of the muscle fiber. Sarcoplasm The cytoplasm of a muscle fiber. T-Tubules Tubes that travel through the sarcolemma to transmit signals to contract or relax. Myofibrils Bundles of protein filaments within the muscle fiber.

Thin, light filaments, made of the protein actin Thick, dark filaments, made of the protein myosin. The alternation of these filaments creates the striated pattern of skeletal muscle tissue.

Sarcoplasmic reticulum A special type of smooth ER found in muscle cells. Contains calcium needed for contraction.

T-tubules

Sarcoplasmic Reticulum Mitochondria Myosin Filament

Actin Filament

Muscle Contraction

Muscle contraction begins with a nerve signal that is transmitted through the motor neuron.

The neurotransmitter used as a signal is acetylcholine. Contraction ends when the neurotransmitter is broken down by an enzyme (acetylcholinesterase).

This signal is sent to every fiber in the muscle simultaneously through the t-tubules. The sarcoplasmic reticulum releases calcium ions (Ca2+), initiating muscle contraction.

Muscle Contraction

The calcium influx stimulates the myosin filaments to form connections to the actin filaments. The myosin filaments pull the actin filaments inward, causing the muscle to contract.

Muscle Fibers Before Contraction

Muscle Fibers After Contraction

Muscle Contraction

When a muscle contracts, it pulls bones closer together, creating movement.

Example: The biceps, the scapula, radius, and ulna.

Contracted muscles become more visible because all of the volume (cytoplasm) is forced outward.

Twitch

A twitch is a single sequence of a muscle fiber that includes:

Stimulus by a motor neuron. Contraction of the muscle. Relaxation of the muscle.

Twitch

A twitch begins with a stimulus, or signal by a motor neuron. During the latent period, the signal is spreading across the muscle. No actual tension occurs.

Resting Phase

Latent Period

Twitch

In the contraction phase, the myosin filaments pull on the actin, creating increasing amounts of tension.Resting Latent Phase Period Contraction Phase

Twitch

Calcium levels drop during the relaxation phase, and linkages between actin and myosin decline.

Resting Latent Phase Period

Contraction Phase

Relaxation Phase

Summation

A single twitch is short (milliseconds) and doesnt really produce a useful movement. If a second stimulus arrives before the relaxation phase completes, a more powerful contraction occurs. This is summation.

Summation

Eventually this builds into the maximum tension possible with the muscle. This is called incomplete tetanus.

Relaxation phases still occur, just not completely.

Summation

Complete tetanus occurs if the stimulus frequency is so high that the relaxation phase is completely eliminated.

How long can muscles contract?

The duration of muscle contraction depends on three factors:How long the stimulus from the neuron lasts. How many electrolytes needed for contraction (K+, Na+, Ca2+) are available within the muscle. How much ATP energy is available within the muscle.

ATP is the direct unit of energy used by muscle fibers. If the supply of ATP is exhausted, the muscle becomes fatigued and will not contract.

ATP + ATPase enzyme ADP + P + Energy

An active skeletal muscle fiber may use 600 trillion molecules of ATP per second.

ATP while Resting

While at rest, muscles build up their energy reserves.

Energy in the form of fatty acids or glucose is brought in by the blood.

Mitochondria convert the fatty acids and glucose into ATP by cell respiration.

Cell Respiration

There are two main parts of cell respiration: Glycolysis, which occurs in the cytoplasm.

Breaks down glucose (6-carbon sugar) into two molecules of pyruvate (3-carbon) Produces 2 molecules of ATP. Occurs quickly, does not require oxygen. Metabolizes the pyruvate into 3 molecules of CO2. Produces 34 molecules of ATP. Requires oxygen.

The rest occurs in the mitochondria.

Fatty Acids

Blood Vessel

Glucose

Glycogen

Mitochondria

Creatine

Cell Respiration: C6H12O6 + 6O2 6CO2 + 6H2O + 36ATP ATP is stored in creatine-phosphate or glycogen.

Energy Storage in Muscles

Creatine (C4H9N3O2) is an organic acid that can store energy in muscles as creatinephosphate. Glycogen is a polysaccharide similar in structure to starch.

Made of multiple glucose molecules bonded together.Some atheletes take supplements to increase creatine levels in muscle.

ATP During Moderate Activity

During moderate activity (e.g. jogging), the stored creatine phosphate and glycogen in the muscle is metabolized.

CP can be directly used to generate ATP. Glycogen can be broken down into glucose, which the mitochondria can use to generate ATP. Oxygen levels are sufficient ( breathing rate) Glycogen is not used up. Hitting the wall

Moderate activity can continue as long as:

Fatty Acids

Blood Vessel

Glucose

Glycogen

Pyruvate

MitochondriaATP used as energy for contraction.

ATP During Intense Activity

During intense activity (e.g. sprinting), oxygen is unable to diffuse into the muscle fast enough to provide the needed ATP by cell respiration. The muscle begins relying on glycolysis to make up for this deficiency.

This creates an excess of pyruvate, which is converted to lactic acid. Lactic acid lowers the pH of the muscle and interferes with normal function. Soreness.

Lactic Acid

Glucose

Glycogen

Pyruvate Lactic Acid ATP used as energy for contraction.

Fatigue

Fatigue occurs when the muscle can no longer contract, despite stimulus from the brain. Caused by rapid and repeated contractions.ATP levels are too low. Lactic acid levels are too high.

The muscles will not regain their normal ability to contract until pH, oxygen, and ATP levels have been restored.

Case Study: Rigor Mortis

When an organism dies, skeletal muscle is deprived of nutrients and oxygen. Calcium ions will leak out of the sarcoplasmic reticulum, causing one last sustained muscle contraction.

Because no ATP is left in the muscle, the myosin and actin are unable to separate, causing rigor mortis.

Case Study: Rigor Mortis

As the cells of the body die, enzymes are released from the lysosomes. These enzymes break down the actin and myosin filaments, and the muscles permanently go limp.

Endurance

Two factors influence muscle endurance:

The type of fibers within the muscle. Physical conditioning.

Types of Muscle Fibers

Fast-twitch fibers are able to reach peak tension within 0.01 seconds or less of neural stimulation.

Large in diameter. Densely packed with myofibrils (actin and myosin). Large glycogen reserves. Fewer mitochondria.

Fast-twitch fibers produce the most tension, but get fatigued quickly.

Types of Muscle Fibers

Slow-twitch fibers can take three times as long to reach peak tension.Half the diameter of fast-twitch fibers. Increased network of capillaries, allowing for a greater and more reliable oxygen supply. Contain a special protein called myoglobin that reserves additional oxygen within the muscle. Higher numbers of mitochondria.

Chicken meat is a good example of the differences between muscles with lots of slow-twitch or fast-twitch fibers. The breasts are white meat because they have mostly fasttwitch fibers and less myoglobin.

Wings are only used for short intervals to escape predators.

The legs and thighs are dark meat and have mostly slow-twitch fibers and more myoglobin.

Used much more frequently during the day, but not at the same intensity.

Physical Conditioning

The percentage of fast vs. slow-twitch fibers in a muscle is genetically determined. The ability of fast-twitch muscles to resist fatigue can be increased through physical conditioning. Aerobic exercise focuses on improving endurance.

Improved oxygen intake and delivery. Higher glycogen stores within muscle.

Physical Conditioning

Anaerobic exercise focuses on improving strength.

The number of muscle fibers does not change, but their size can. An increase in size is hypertrophy. A decrease in size is atrophy.

Anabolic Steroids

Anabolic steroids are chemical compounds that mimic the effects of testosterone.

Increases protein synthesis, causing muscle buildup.

The change in hormone levels has a lot of other side effects:

Increase in blood cholesterol. Acne High blood pressure Testicular atrophy Increase in male characteristics in women.

Testicular Atrophy?

One of the primary functions of the testes is to produce the hormone testosterone. If anabolic steroids are taken externally, the testes will shrink in size, as the body attempts to compensate.

This is called negative-feedback inhibition.

Synthol

Synthol is a mixture of oil, a pain killer, and alcohol that is injected to mimic the appearance of muscle. Can cause infections, nerve damage, and blood clots.

Gregg Valentino has admitted to using steroids, but denies using synthol or implants.

Polio

Polio is a viral infection that can enter the nervous system, specifically infecting and destroying motor neurons. This causes paralysis. Polio is now considered eradicated due to the use of a vaccine.

Tetanus

Tetanus is a disease caused by a bacteria called Clostridium tetanii. The bacteria releases a toxin that stops the normal motor neuron inhibition process.

Muscles will uncontrollably contract and maintain the contraction. The toxin spreads, causing symptoms such as lockjaw.

Botulism

Botulism occurs when food contaminated with a bacterial toxin are ingested. The toxin prevents the release of acetylcholine by motor neurons, causing paralysis.

Muscular Dystrophy

Muscular dystrophy is a group of degenerative disorders that affect muscle tissue.

Multiple causes, the most common one is the lack of a protein needed to maintain muscle integrity.

Curare

This is a toxin produced by poison dart frogs. Blocks acetylcholine receptors in muscles, causing paralysis. Neostigmine is a drug that prevents acetylcholine from breaking down. This makes it an effective treatment for curare. Discovered when it was observed that animals called peccaries were immune to the poison.