Chapter 10: The Muscular Tissue

Functions of the Muscular Tissue

1. Producing body movements. 2. Stabilizing body positions. 3. Storing and moving substances within the body. 4. Generating heat.

The Neuromuscular Junction

1. Release of Acetylcholine. 2. Activation of ACh receptors. 3. Production of muscle action potential. 4. Termination of ACh activity.

3 Main Types of Skeletal Muscle Fibers

1. Slow Oxidative Fibers 2. Fast Oxidative-Glycolytic Fibers 3. Fast Glycolytic Fibers

Between the ages of 30 and 50, there is a ______% reduction in muscle fiber mass.

10%

Between the ages of 50 and 80, there is a _____% reduction in muscle fiber mass.

40%

Latent Period

A brief delay occurs between application of the stimulus (time zero on the time graph) and the beginning of contraction. Action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum. Lasts about 2 milliseconds.

Neurotransmitter

A chemical messenger that allows the first cell to communicate with the second.

H Band

A narrow zone in the center of each A band. Contains thick but not thin filaments.

Acetylcholine (ACh)

A neurotransmitter released at the NMJ

Synapse

A region where communication occurs between two neurons, or between a neuron and a target cell.

Muscle Tone

A small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units.

Motor Unit

A somatic motor neuron plus all the skeletal muscle fibers it stimulates. A singular somatic motor neuron makes contact with an average of 150 skeletal muscle fibers, and all of the muscle fibers in one motor unit contract in unison.

Flaccid

A state of limpness in which the muscle tone is lost due to the damage or cut of the motor neurons serving a skeletal muscle. To sustain muscle tone, small groups of motor units are alternatively active and inactive in a constantly shifting pattern.

Muscle Mass and Aging

Accompanying the loss of muscle mass is a decrease in maximal strength, a slowing muscle reflexes, and a loss of flexibility. With aging, the relative number of slow oxidative (SO) fibers appears to increase.

Creatine Phosphate

An energy-rich molecule that is found in muscle fibers. Together, store of ___ and ATP provide enough energy for muscles to contract maximally for about 15 seconds.

Fascicles

Bundles of muscle fibers wrapped in perimysium.

Contraction Period

Calcium binds to troponin, myosin binding sites on actin are exposed and cross bridges form. Lasts 10-100 milliseconds.

Relaxation Period

Calcium is actively transported back into the sarcoplasmic reticulum, myosin-binding sites are covered by tropomyosin, myosin heads detach form actin, and tension in the muscle fiber decreases. Lasts 10-100 milliseconds.

Slow Oxidative Fibers

Cellular Respiration - Marathon Appear dark red because they contain large amounts of myoglobin and many blood capillaries. Have many large mitochondria. Generate ATP mainly by aerobic respiration. Slow because the APTase in the myosin heads hydrolyzes ATP relatively slowly. Resist to fatigue and capable of prolonged, sustained contractions for many hours.

Fast Glycolytic Fibers

Cellular Respiration and Glycolysis - Weight Lifting White appearance because myoglobin content, few blood capillaries, and few mitochondria. Contains large amount of glycogen and generate ATP mainly by glycolysis. Fibers contract strongly and quickly.

Endomysium

Connective tissue that penetrates the interior of each fascicle and separates individual muscle fibers from one another.

Multi-Unit Smooth Muscle Tissue

Consists of individual fibers each with its own motor neuron terminals and with few gap junctions between neighboring fibers. Found in the walls of the large arteries, airways to the lungs, and arrector pili muscles. Stimulation of one multi-unit fiber causes contraction of that fiber only (Rubber Band)

Sarcoplasm

Cytoplasm of a muscle fiber.

Perimysium

Dense irregular connective tissue that surrounds fascicles.

Sarcoplasmic Reticulum (SR)

Endoplasmic reticulum of a muscle fiber. Stores and releases Calcium.

Fast Oxidative-Glycolytic Fibers

Glycolytic - Walking or Sprinting Appears pink because they contain myoglobin and blood capillaries. Largest fibers. Generate ATP by anaerobic glycolysis. Fast because the ATPase in their myosin head hydrolyzes ATP 3-5 times faster than the myosin ATPase in SO fibers.

Acetylcholine Receptors

Integral transmembrane proteins to which ACh specifically binds.

Smooth Muscle Tissue

Involuntary Two Types: visceral smooth muscle tissue and multi-unit smooth muscle tissue.

I Band

Lighter, less dense area that contains the rest of the thin filaments but no thick filaments.

Synaptic Vesicles

Membrane enclosed sac in a synaptic end bulb that stores neurotransmitters.

M Line

Middle of the sarcomere.

Visceral Smooth Muscle Tissue

More common type of smooth muscle. Found in the skin and tubular arrangements that form part of the walls of small arteries and veins and of hollow organs. The muscle action potential is transmitted to neighboring fibers, which then contract in unison, as a single unit.

Anaerobic Glycolysis

Most of the lactic acid produced by this process diffuses out of the skeletal muscle fiber into the blood. Liver cells can take up some of the lactic acid molecules form the bloodstream and convert them back to glucose.

Smooth Muscle Tissue

Muscle Tissue in the walls of hollow internal structures: blood vessels, airways, organs in the abdominopelvic cavity. One nucleus Non-striated Involuntary

Cardiac Muscle Tissue

Muscle tissue that forms most of the heart wall. Pumps blood in body. Gap Junctions --> intercalated discs One nucleus Striated Involuntary

Skeletal Muscle Tissue

Muscle tissue that moves the bone of the skeleton. Multi-nucleus Striated Voluntary

Muscle Fibers

Myocytes Muscle cells

Z Discs

Narrow, plate-shaped regions of dense protein material that separate one sarcomere form the next (boundaries).

Sarcolemma

Plasma membrane of a muscle cell.

Troponin

Regulatory protein that binds to actin, tropomyosin, and calcium.

Tropomyosin

Smaller amounts of two regulatory proteins.

The Contraction Cycle

The Cross-Bridge Cycle The repeating sequence of events that causes the filaments to slide.

Contractibility

The ability of muscular tissue to contract forcefully when stimulated by an action potential. Generated tension great enough to overcome the resistance of the object to be moved.

Elasticity

The ability of muscular tissue to return to its original length and shape after contraction or extension. Rubber Band.

Extensibility

The ability of muscular tissue to stretch, within limits, without being damaged.

Electrical Excitability

The ability to respond to stimuli by producing electrical signals (action potentials - impulses)

Oxygen Debt

The added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise.

Sarcomeres

The basic functional units of a myofibril.

Twitch Contraction

The brief contraction of all muscle fibers in a motor unit in response to a single action potential in its motor neuron.

Myofibrils

The contractile organelles of skeletal muscle. Appear striped (striated)

A Band

The darker middle part of the sarcomere that extends the entire length of the thick filaments.

Axon Terminal

The end of a motor neuron.

Creatine Kinase (CK)

The enzyme that catalyzes the transfer of one of the high-energy phosphate groups from ATP to creatine, forming creatine phosphate and ADP.

Muscle Fatigue

The inability of a muscle to maintain force of contraction after prolonged activity.

Actin

The main component of the thin filament.

Myosin

The main component of thick filaments.

Somatic Motor Neurons

The neurons that stimulate skeletal muscle fibers to contract.

Epimysium

The outer connective tissue layer, encircling the entire muscle.

Cardiac Muscle Tissue

The principle tissue in the heart wall. Striated Involuntary Intercalated Discs Unique to cardiac muscle fibers Gap Junctions - allow muscle action potentials to spread from one cardiac muscle fiber to another (communicate when the "lub dub" of the heart contracts)

Anaerobic Glycolysis

The process by which the breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration. 2 molecules of lactic acid = 2 molecules of ATP (2 minutes of muscle activity)

Motor Unit Recruitment

The process in which the number of active motor units increases. The weakest motor units are recruited first, with progressively stronger motor units added if the task requires more force.

Myology

The scientific study of muscles.

The Neuromuscular Junction

The synapse between a somatic motor neuron and a skeletal muscle fiber.

Isotonic Contraction

The tension developed in the muscle remains almost constant while the muscle changes its length. Two types: concentric and eccentric.

Isometric Contraction

The tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length.

Concentric Isotonic Contraction

The tension great enough to overcome the resistance of the object to be moved, the muscle shortens and pulls on another structure (tendons) to produce movement and to reduce the angle at a joint.

Unfused Tetanus

Type of wave summation with partial relaxation observed between twitches. Muscle fiber is stimulated 20-30 times per second.

Refractory Period

When a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a time. Loss of excitability Skeletal Muscle = 1 millisecond Cardiac Muscle = 250 millisecond

Aerobic Respiration

When oxygen is present, glycolysis, the Krebs cycle, and the electron transport chain occur. 1 molecule of glucose = 30 or 32 molecules of ATP (hours of muscle activity)

Wave Summation

When stimuli arriving at different times cause larger contractions.

Fused Tetanus

When stimulus frequency is so high that no muscle relaxation takes place between stimuli. Muscle fiber is stimulated 80-100 times per second.

Eccentric Isotonic Contraction

When the length of a muscle increase during a contraction.

The Contraction Cycle

1. ATP Hydrolysis. 2. Attachment of myosin to actin. 3. Power stroke. 4. Detachment of myosin from actin.

Extra Oxygen is Used to Restore Metabolism in 3 Ways

1. Convert lactic acid back into glycogen stores in the liver. 2. Resynthesize creatine phosphate and ATP in muscle fibers. 3. Replace the oxygen removed from myoglobin.

3 Ways Muscle Fibers Produce ATP

1. Creatine Phosphate 2. Anaerobic Glycolysis 3. Aerobic Respiration

Properties of Muscular Tissue

1. Electrical Excitability. 2. Contractility. 3. Extensibility. 4. Elasticity.

Three Layers of Connective Tissue

1. Epimysium 2. Perimysium 3. Endomysium

Factors That Contribute to Muscle Fatigue

1. Insufficient oxygen 2. Depletion of glycogen and other nutrients 3. Buildup of lactic acid and ADP 4. Failure of action potentials in the motor neuron to release enough acetylcholine.

Excitation-Contraction Coupling

Sequence of events that links excitation (a muscle action potential) to contraction (sliding of the filaments)