Chapter 10

What promotes a power stroke?

A power stroke occurs when ADP + Pi are released from the myosin head.

The main immediate energy is stored as _______ in the muscle fiber and is rapidly consumed during muscle contraction.

ATP

diffuses across the synaptic cleft where it can bind to ligand- gated channels found in the motor end plate of the muscle fiber plasma membrane.

Acetylcholine

the neurotransmitter released from a motor neuron that stimulates a muscle fiber.

Acetylcholine

a contractile protein that has active sites that bind with the myosin heads of the thick filament

Actin

When glucose levels are exhausted, what molecules can be catabolized to generate ATP?

Amino acids and fatty acids.

What is an end-plate potential?

An end-plate potential is a small region of the plasma membrane that has been depolarized.

What do skeletal muscle cells and cardiac muscle cells have in common?

Both skeletal and cardiac muscle cells have striations, giving both cell types a striped appearance

are structurally similar to skeletal fibers with some noticeable major differences.

Cardiac muscle cells

are autorhythmic. Pacemaker cells are found in specific regions of the heart where they spontaneously generate action potentials.

Cardiac pacemaker cell

Compare the number of mitochondria, myoglobin and the blood supply in fast-twitch fibers to slow-twitch fibers.

Compared to slow-twitch fibers, fast-twitch fibers have fewer mitochondria and lower levels of myoglobin and smaller blood supply, giving them their characteristic "white meat" appearance.

Define contractility.

Contractility is the ability to contract where proteins in the cell draw closer together.

of smooth muscle involves influx of extracellular calcium ions that bind to calmodulin, which activates myosin light chain kinase. This in turn activates myosin ATPase.

Contraction

occur when the muscle length remains unchanged because

Isometric contractions

How is an end-plate potential accomplished?

Ligand-gated channels open when they bind acetylcholine which allows Na+ ions to enter the muscle fiber generating an end-plate potential.

a dark line in the middle of the A band made up of structural proteins.

M line

due to an unequal distribution of ions near the plasma membrane resulting in a polarized resting state.

Membrane potentials

found in the uterus, eye, and skin. These are individual cells that contract independently to allow for precision.

Multi-unit smooth muscl

chemicals that trigger changes in a target tissue when released, allowing for cell-to-cell communication (Core Principle).

Neurotransmitters

What does the cocked myosin head bind?

Once cocked the myosin head is able to bind to the active site of actin.

What are some other functions of muscle tissue?

Other functions of muscle tissue are to create movement, maintain posture, stabilize joints, generate heat, and regulate the flow of materials through hollow organs.

occurs when Ca++ is removed from the cytosol, MLCK is deactivated, and the myosin ATPase is deactivated.

Relaxation

Summarize how repolarization occurs

Repolarization occurs as voltage- gated K+ channels open allowing K+ ions to exit the cell returning the cell back to its resting membrane potential.

What makes smooth muscle different from skeletal and cardiac muscle tissues?

Smooth muscle cells do not have striations unlike skeletal and cardiac muscle tissue.

What other features do smooth muscle cells lack?

Smooth muscle cells lack motor end plates, the SR is much less extensive, and there are no T-tubules.

________ and _________ ions move through the sarcolemma using protein channels and carriers.

Sodium and potassium

enlarged sections of SR found flanking each T-tubule.

Terminal cisternae

Describe what happens during the relaxation period

The relaxation period begins as calcium ion levels are reduced in the cytosol by SR pumps and tension diminishes.

What is the function of the pacemaker cells?

These cells coordinate electrical activity and trigger the contraction of surrounding cells.

are deep inward extensions of sarcolemma that are filled with extracellular fluid.

Transverse tubules (T-tubules)

results when fibers are stimulated about 50 times per second and the fiber partially relaxes between stimuli. Tension pulsates and increases to a maximum of 80% of the maximum

Unfused tetanus

How does this change in position return the muscle to a relaxed state?

With troponin and tropomyosin back to their original blocking positions, the active sites on the actin filaments are no longer exposed for the crossbridge cycle to occur.

The ________ is found in the middle of the I band and is composed of structural proteins.

Z disc

The sarcoplasm is the ___________ of the myocyte.

cytoplasm

Myocytes

muscle cells

A _______ is the smallest unit of contraction.

muscle twitch

The______________ is the space between axon terminal and muscle fiber.

synaptic cleft

Define distensibility.

the ability of a cell that allows it to be stretched without being ruptured.

Define elasticity

the ability of a cell that allows it to return to its original length after it has been stretched.

What causes EPOC?

EPOC is caused by changes in body temperature, by imbalances of intracellular and extracellular ion concentrations, and by blood pH imbalances.

are composed of a single massive, spring-like structural protein called titin that stabilizes the myofibril structure and resists excessive stretching force.

Elastic filaments

How is a functional muscle contraction produced?

Multiple end-plate potentials must be generated to produce a functional muscle contraction.

the electrical potential across the sarcolemma of a resting muscle fiber and measures -85 mV.

Resting membrane potential

is found in all hollow organ walls where they are linked electrically by gap junctions.

Single unit smooth muscle

____________fibers are thin cylinders but can be quite long and thick. Skeletal muscle fibers are formed by the fusion of many embryonic myoblasts giving each fiber multiple nuclei.

Skeletal muscle

What is the latch state?

The latch state is an alternative to relaxation where the cell remains contracted in an energy-efficient mode.

Describe what happens during the latent period.

The latent period is the time it takes the action potential to propagate across the sarcolemma.

How is the concentration gradient maintained?

The concentration gradient is maintained by the Na+/K+ pump.

Describe what happens during the contraction period

The contraction period begins as repeated crossbridge cycles generate tension.

Summarize how the contraction phase begins.

The contraction phase begins when Ca++ bind troponin, which pulls tropomyosin away from actin's active site.

What is required for the crossbridge cycle to repeat?

The cycle may be repeated as long as the stimulus to contract continues and ATP is available.

Summarize how the excitation phase begins.

The excitation phase begins when an action potential of a motor neuron signals the release of acetylcholine from the axon terminal into the synaptic cleft.

The ____________ of the neuron contains synaptic vesicles filled with acetylcholine.

axon terminal

Describe repolarization.

begins after Na+ channels have closed and voltage-gated K+ channels have opened, allowing K+ to diffuse out of the cell. K+ channels close once the cell returns to its resting membrane potential.

Describe depolarization.

begins when voltage-gated Na+ channels open, allowing Na+ to flow inward. The membrane quickly reaches 0 mV and peaks at approximately +30 mV.

What do voltage-gated channels open and close in response to?

changes in the membrane potential of the plasma membrane.

The _____________ is a specialized region of the muscle fiber plasma membrane that has ligand-gated Na+ channels.

motor end plate

A single ___________ and all the muscle fibers that it innervates define a motor unit.

motor neuron

The sarcolemma is the __________ of the myocyte.

plasma membrane

The ___________ is modified endoplasmic reticulum that forms a web-like network surrounding the myofibrils. It stores and releases calcium ions.

sarcoplasmic reticulum (SR)

Cardiac muscle cells, found only in the heart, are

short and highly branched.

The three types of cells in muscle tissue are

skeletal, cardiac, and smooth muscle

Define conductivity.

the ability of a cell to conduct electrical changes across the entire plasma membrane.

Define excitability.

the ability of a cell to respond to a stimulus or signal.

What do ligand-gated channels (chemically-gated) open in response to?

the presence of a chemical or ligand

The pump moves _________ Na+ ions out of the cell and _______ K+ ions into the cell.

3 and 2

The __________ ("a" in dark, mnemonic) contains the zone of overlap, the region where we find thick and thin filaments and where tension is generated during contraction.

A band

____________ fibers have high myoglobin

Fast-twitch

occurs when the fiber is stimulated at a rate of 80-100 stimuli per second and the fiber does not relax between stimuli. Tension stays constant at nearly 100% of the maximum

Fused tetanus

What function do all three muscle tissue types share in common?

Generating a force called muscle tension is a basic function common to each muscle tissue type.

is a series of reactions that occurs in all cells' cytosol. Glycolysis breaks glucose down into pyruvate and provides energy (ATP) for muscle contraction once immediate sources of energy are depleted.

Glycolysis

In the middle of the A band where only thick filaments exist is the

H zone

What happens to pyruvate if oxygen is abundant

If oxygen is abundant pyruvate formed by glucose catabolism enters the mitochondria for oxidative catabolism.

What happens to pyruvate if oxygen is not abundant?

If oxygen is not abundant the pyruvate is converted to lactic acid. Lactic acid can either be converted back into glucose by the liver or taken up in the mitochondria for oxidative catabolism.

How do the positions of troponin and tropomyosin change in the absence of calcium ions?

In the absence of calcium ions, troponin and tropomyosin shift back to their original blocking positions

link cells together both electrically by gap junctions and physically by desmosomes, permitting the heart to contract as a coordinated unit.

Intercalated discs

maintain constant tension while the muscle shortens.

Isotonic concentric contractions

maintain constant tension, but the muscle lengthens

Isotonic eccentric contractions

___________is a baseline level of involuntary activation of motor units.

Muscle Tone

______________ consists of many fibers and their surrounding endomysium.

Muscle tissue

cylindrical organelles found in each of the three muscle cell types. Myofibrils are made up of bundles of specialized proteins that allow for contraction.

Myofibrils

How is another crossbridge cycle accomplished?

Myosin pulls the actin towards the M line of the sarcomere

An end-plate potential leads to the opening of voltage-gated ______ channels in the sarcolemma surrounding the motor end plate, which triggers an action potential.

Na+

How are the two main types of skeletal muscle fibers classified?

Skeletal muscle fibers are classified mainly on myosin ATPase activity that determines how fast or how slowly a power stroke can occur.

__________ fibers have low myosin ATPase activity.

Slow-twitch

are composed of bundles of myosin.

Thick filaments

are composed of the proteins actin, tropomyosin, and troponin

Thin filaments

Two terminal cisternae and their corresponding T-tubule form a

Triad

a long rope-like regulatory protein that twists around actin, covering up its active sites.

Tropomyosin

a small globular regulatory protein that holds tropomyosin in place and assists with turning contractions on and off.

Troponin

Skeletal muscle cells are known as

fibers due to their length and appearance.

Define fatigue

is the inability to maintain a given level of intensity during activity.

The ______________ states that the optimal length of a sarcomere is about 100-120% of the natural length of the sarcomere.

length-tension relationship