Muscles and Muscle Tissue Anatomy and Physiology Mr. Cengel.

Muscles and Muscle TissueAnatomy and Physiology

Mr. Cengel

Muscle Types

• Skeletal - voluntary, striated

(fast, short contractibility)

• Cardiac - involuntary, striated

(fast, rapid recovery)

• Smooth- involuntary, nonstriated, visceral

(slow, sustained contractibility)

Muscle Functions

• Producing movement

• Maintaining posture

• Stabilizing joints

• Generating heat

Functional properties of Muscle

• Excitable (irritable)

• Contractible

• Extensible

• Elastic

Anatomy of Skeletal Muscle

• A single skeletal muscle, such as the triceps muscle, is attached at its origin to a large area of bone; in this case, the humerus

At its other end, the insertion, it tapers into a glistening white tendon which, in this case, is attached to the ulna, one of the bones of the lower arm.

• Each skeletal muscle is an organ.

• Each muscle fiber is a cell.

• Each muscle is surrounded by Connective tissue

• Muscles contain nerve fibers and blood vessels.

• Tendons are extensions of connective tissue beyond muscle cells that attaches muscle to bone.

Other muscle injuries

• Muscle strain = pull = tear

• Charlie horse (muscle tear and/or contusion usually due to impact I.e. helmet to quadracep)

• Each muscle fiber – long cell with many nuclei just below the cell membrane (sarcolemma)

• Sarcolemma- wraps each muscle fiber.

Microscopic Anatomy

Microscopic Anatomy

• The sarcoplasm of the muscle fiber is similar to the cytoplasm of other cells.

It also has a higher content of myoglobin-

an oxygen-binding pigment.

• Myofibrils- the contractile proteins (actin and myosin) that make up muscle fibers.

• Sarcoplasmic reticulum- surrounds each myofibril. It regulates intracellular levels of ionic calcium.

• T-tubules- where the interior of the cell meets with the sarcolemma. It conducts impulses to every sarcomere.

A. Sarcomere- region between two successive Z lines.

B. A bands- thick (myosin) filaments

C. I bands- thin (actin) filaments

D. Z line- intersection between sarcomeres.

Two types of proteins involved:

A. Contractile proteins – actin and myosin do the contracting.

Myosin – Thick. Shaped like golf clubs twisted together.

Actin – Thin. Looks like a twisted helix. Has a myosin binding site.

B. Regulatory proteins – troponin and tropomyosin.

Found on the actin myofiber. Help switch contractions on and off.

Contraction of a Skeletal Muscle Fiber

Sarcomeres shorten because filaments in each sarcomere slide together.

This makes the myofibrils shorten, making the fiber shorten, and finally the whole muscle shortens.

Sliding Filament Theory of Contraction – what happens when a muscle contracts

A. Troponin blocks the binding site for the myosin head.B. A nerve impulse causes Ca++ to enter the cytoplasm.C. Ca++ moves troponin aside. D. The myosin head can attach to the binding site.E. The myosin head bends and pulls the actin – this is the

power stroke.F. ATP provides energy to release the myosin head from the

binding site.G. This re-cocks the myosin head, making it ready for its next

attachment and power stroke sequencehttp://entochem.tamu.edu/musclestruccontractswf/index.html

Energy for contraction• Movement of myosin requires ATP.

• Each stroke shortens muscle 1%

• When a muscle contracts, it shortens about 35%

• Therefore, many attachments form and break with each contraction.

• Takes lots of ATP.

Neuromuscular Junction – nerve impulse triggers muscle contraction

A. Where the axon terminal (end of nerve) and the sarcolemma meet. Called a motor end plate.

B. When a nerve impulse reaches the axon terminal, the muscle cell allow the entry of calcium.

C. The calcium causes acetylcholine to diffuse across the membrane and attach to the ACh receptors on the sarcolemma.

Generation of an Action Potential

A. The outside of the sarcolemma has Na+ ions.

B. The inside of the sarcolemma has K+ ions.

C. When ACh attaches to the sarcolemma, it causes Na+ ions to rush in.

D. If the effect is great enough, than an action potential will occur across the sarcolemma. If not, then is will stop right there. This is called the all-or-none response.

E. After the action potential propagates across the entire membrane, the membrane repolarizes to its original state.

Muscle Responses- Terms To Learn

A. Tetanus- smooth, continuous contraction without relaxation.

B. Muscle Tone- muscles are in a slightly contracted state.

Isotonic and Isometric Contractions

IsotonicChanges in length to

move the load.

Ex. Picking up a book,

Your calf muscle when you walk up a hill.

IsometricThe tension continues to

increase but the muscle neither shortens or lengthens.

Ex. Muscles that hold your posture or hold joints.

Examples of Isotonic and Isometric Contractions

Throwing is a Isotonic Contraction

Squeezing is a Isometric Contraction

Lifting up a heavy object uses both contractions in your leg muscles.

Muscle Metabolism Making ATP for Energy

1. Direct Phosphorylation of ADP by Creatine Phosphate- Uses stored creatine phosphate and ADP to make creatine and ATP. Altogether, they provide max. power for 15-20 seconds.

2. Aerobic Respiration- occurs in the mitochondria. Yields 36 ATP. Glucose+Oxygen>Carbon Dioxide+Water+ATP

3. Anaerobic Glycolysis and Lactic Acid Formation- Glucose>Pyruvic Acid>Lactic Acid

Muscle Fatigue and Oxygen Debt

Muscle FatigueMuscle Fatigue- the state of physiological inability to contract. When you lack ATP, you are in a phase of continuous contractions because the cross bridges cannot detach from the binding site.

Other CausesOther Causes- Excessive accumulation of lactic acid and ionic imbalances.

Oxygen DebtOxygen Debt- Extra amount of oxygen that must be replenished.

Force of muscle contractions

1. # of muscle fibers contracting- the more the greater

2. Size of the muscle- the bulkier the more tension and strength it can produce

3. Degree of muscle stretch- the optimal resting length is when a muscle is slightly stretched and the actin and myosin filaments barely overlap. This allows sliding across the entire length of the action filaments.

Muscle Fiber TypesA. Red slow-twitch fibers

Lots of mitochondria, lots of oxygen, long endurance, low power, reddish color.

B. Intermediate fast-twitch fibers

Contract quickly like fast-twitch fibers but are oxygen dependent like slow-twitch fibers.

C. White fast-twitch fibers

Few mitochondria, contracts quickly, fatigable, high power, and high glycogen reserves.

Pic of different fiber types.

Can you guess this guy’s fiber type?

How about this guy?

Slow-twitch Fibers

Fast- Twitch Fibers

A nice analogy can be used to explain the various actions of these two fiber types. Chickens, like us, have both fast and slow-twitch fibres:

their darker (red) meat is composed of slow-twitch fibers

the white meat of fast-twitch fibers. Chickens use their legs (red meat) for walking and standing for large periods of time, while their wings (white meat) are used for brief bursts of activity.

Human muscles contain a genetically determined mixture of both slow and fast fiber types. On average, we have about 50 percent slow twitch and 50 percent fast twitch fibers in most of the muscles used for movement.

Our muscle fiber type may influence what sports we are naturally good at or whether we are fast or strong. Olympic athletes tend to fall into sports that match their genetic makeup. Olympic sprinters have been shown to possess about 80 percent fast twitch fibers, while those who excel in marathons tend to have 80 percent slow twitch fibers.

Effects of Exercise on Muscles• Regular aerobic exercise

efficiency, endurance, and strength of skeletal muscles.

• Resistance exercises– skeletal muscle hypertrophy.

• Immobilization– muscles weakness and muscle atrophy.

• Cross-training provides the best health program because it alternates between aerobic and anaerobic exercises.

Smooth Muscles

Small spindle-shaped cells, each with one Small spindle-shaped cells, each with one centrally located nucleus.centrally located nucleus.

• Located in the walls of hollow organs.

• Ex. Digestive, urinary, and reproductive tracts.

• Movements slow and synchronized

Smooth Muscle

• Two different types of sheets are usually present– Longitudinal Layer- runs parallel to the long

axis of the organ. Shortens the organ.

– Circular Layer- run around the circumference. Elongates the organ.

• Peristalsis- the alternation between these two opposing layers mix substances in the lumen (cavity) and pushes them through the organ pathway.

Smooth Muscle Examples

The smooth muscles help dilate the eyes                                               

The smooth muscles help line the respiratory tracts

Developmental Aspects of Muscles

• Women’s muscles=36% of total body weight

• Men’s muscles=42% of total body weight.

• Skeletal muscles become fibrous and atrophy as we age.