PCB 3703 lec 13

How is mechanical work (W) calculated in skeletal muscle?

Work (W) equals load (L) multiplied by distance (D).

How much ATP do muscle cells keep in storage?

Only a little ATP.

How long does stored ATP last during intense exertion?

About 5 seconds.

What enzyme catalyzes the rapid production of ATP via myokinase by transferring a phosphate between ADPs?

Myokinase.

How many seconds of additional energy does myokinase production provide?

Another 5-6 seconds.

What are the three main ways to generate additional ATP in a skeletal muscle fiber?

Creatine phosphate, glycolysis, and aerobic cellular respiration.

What type of bond is contained within creatine phosphate?

A high-energy bond between creatine and phosphate.

What enzyme catalyzes the transfer of phosphate from creatine phosphate to ADP?

Creatine kinase.

How many seconds of additional energy does creatine phosphate provide?

10-15 seconds.

Does glycolysis require oxygen?

No.

What molecule is converted into two pyruvate molecules during glycolysis?

Glucose (from muscle glycogen or blood).

How many ATP molecules are released per glucose molecule during glycolysis?

2 ATP molecules.

In which cellular compartment does glycolysis occur?

The cytosol.

Does aerobic cellular respiration require oxygen?

Yes.

What is pyruvate oxidized into during aerobic cellular respiration?

Carbon dioxide.

Through what cellular process is energy generated during aerobic cellular respiration?

Oxidative phosphorylation.

Besides pyruvate, what other fuel molecules can be used in aerobic cellular respiration?

Fatty acids and amino acids.

Which fuel source yields more ATP: short or long fatty acid chains?

Triglycerides with longer fatty acid chains.

Aerobic cellular respiration is essential for what type of activity level?

Longer, moderate levels of activity.

What are the three primary types of skeletal muscle fibers?

Slow oxidative (SO), fast oxidative (FO), and fast glycolytic (FG) fibers.

What is another name for slow oxidative (SO) fibers?

Type I fibers.

How do contractions of slow oxidative fibers compare in speed and power?

Contractions are slower and less powerful.

Why do slow oxidative fibers have high endurance?

Because ATP is supplied aerobically.

What is the relative diameter and color of slow oxidative fibers?

About half the diameter of other fibers and red in color due to myoglobin.

What is another name for fast oxidative (FO) fibers?

Type IIa or intermediate fibers.

How do contractions of fast oxidative fibers compare in speed and power?

Contractions are fast and powerful.

What primary respiration method do fast oxidative fibers use?

Primarily aerobic respiration, though oxygen delivery is lower.

What is the size and color of fast oxidative fibers?

Intermediate size and light red in color.

What is another name for fast glycolytic (FG) fibers?

Type IIx or fast anaerobic fibers.

Why are contractions of fast glycolytic fibers brief?

Because ATP production is primarily anaerobic.

What is the relative size and color of fast glycolytic fibers?

Largest size and white in color due to lack of myoglobin.

What does a single skeletal muscle typically contain regarding fiber types?

A mixture of fiber types.

Why do hand muscles have a higher proportion of fast glycolytic fibers?

For quickness.

Why do back muscles have a higher proportion of slow oxidative fibers?

To continually maintain postural support.

What type of muscle fibers do long-distance runners typically have in higher proportions?

Slow-oxidative fibers in the legs.

What type of muscle fiber do sprinters typically have in higher percentages?

Fast glycolytic fibers.

Is muscle fiber proportion determined primarily by training or genetics?

Determined primarily by genes, and partially by training.

What characterizes an isotonic contraction?

Same (constant) tension while monitoring change in length over time.

What characterizes an isometric contraction?

Same (constant) length while monitoring change in tension over time.

What is a muscle twitch?

A brief contraction to a single stimulus.

What is the minimum voltage that triggers a twitch called?

The threshold.

What are the three sequential periods of a muscle twitch?

Latent period, contraction period, and relaxation period.

What occurs during the latent period of a muscle twitch?

Time after stimulus but before contraction begins, with no change in tension.

When does the contraction period begin and what happens during it?

Tension increases as power strokes pull thin filaments.

What happens during the relaxation period of a muscle twitch?

Tension decreases to baseline as crossbridges are released.

Which period generally lasts a little longer: contraction or relaxation?

The relaxation period.

How is a motor unit defined?

A motor neuron plus all the muscle fibers it connects to.

Can a single motor neuron connect to multiple muscle fibers?

Yes.

Where are small motor units typically found?

In areas requiring fine control, such as the larynx and eye.

Where are large motor units typically found?

In areas requiring powerful contractions, such as the soleus.

What is multiple fiber summation?

The recruitment of more motor units to increase force.

What does the size principle state regarding motor units?

Small stimuli activate small motor units for control; large stimuli activate large motor units for force.

What is frequency summation?

Higher firing rate causing contractions to compound on each other without relaxation.

What accumulates in the sarcoplasm during frequency summation?

Calcium ions.

What is tetanus in muscle physiology?

A sustained contraction at high frequency.

What is muscle tone?

Constant, resting, involuntary contraction alternating fibers to avoid fatigue.

What is the primary cause of muscle fatigue during exercise?

Decreased glycogen stores.

Besides glycogen, what ion deficiency contributes to muscle fatigue?

Low calcium ion concentration.

How does endurance exercise improve muscle performance?

Better ATP production via more mitochondria and enzymes.

How does resistance exercise affect muscle fibers?

Causes hypertrophy and increased contractile protein synthesis.

What is muscle atrophy?

Degradation of muscle filaments and loss of muscle fibers.

What happens to severely damaged muscle in extreme cases of atrophy?

Damage is permanent, and muscle is replaced by connective tissue.

What are the structural features of cardiac muscle cells?

Short, branching fibers, one or two nuclei, and striations.

What type of cellular respiration do cardiac muscle cells heavily rely on?

Aerobic respiration.

What structures join the ends of neighboring cardiac muscle fibers?

Intercalated discs.

What two specialized cell junctions are found in cardiac intercalated discs?

Desmosomes and gap junctions.

What cells initiate contractions in the heart?

Autorhythmic pacemaker cells.

What system influences heart rate and contraction force?

The autonomic nervous system.

How does smooth muscle in cardiovascular blood vessels help the body?

It helps regulate blood pressure and flow.

What role does smooth muscle play in respiratory bronchioles?

It controls airflow to alveoli.

What is smooth muscle's function in the digestive system's intestines?

It mixes and propels materials.

What does smooth muscle do in the urinary system's ureters?

It propels urine from the kidneys to the bladder.

Where is smooth muscle located in the female reproductive system?

In the uterus.

What are the two categories of smooth muscle?

Multiunit and single-unit smooth muscle.

How are multiunit smooth muscle cells stimulated?

They are arranged in units that receive stimulation to contract individually.

Where is multiunit smooth muscle found in the body?

Iris and ciliary muscles of the eye, arrector pili muscles, larger air passageways, and large artery walls.

What is the most common type of smooth muscle?

Single-unit (visceral) smooth muscle.

How do single-unit smooth muscle cells contract?

They contract in unison as cells linked by gap junctions.

How are single-unit smooth muscle cells structured in organ walls?

They form two or three sheets in the wall of a hollow organ.

Through what structures does stimulation of single-unit smooth muscle occur?

Varicosities (swellings of autonomic neurons).

What do varicosities contain in single-unit smooth muscle?

Synaptic vesicles with neurotransmitters (ACh or norepinephrine).

What type of junctions feature scattered receptors across the smooth muscle sarcolemma?

Diffuse junctions.

How is contraction spread rapidly among numerous smooth muscle cells simultaneously?

From cell to cell via gap junctions for synchronous contraction.

Where do axial muscles have both their origins and insertions?

On the axial skeleton.

What are the general functions of axial muscles?

Support/move head and vertebral column, facial expression, breathing, chewing, swallowing, and protecting abdominal/pelvic organs.

What is the primary function of appendicular muscles?

Control movements of upper/lower limbs and pectoral/pelvic girdles.

For axial muscles, which attachment is typically superior and more moveable?

The insertion.

For axial muscles, which attachment is typically inferior and less moveable?

The origin.

For appendicular muscles, which attachment is proximal and usually less moveable?

The origin.

For appendicular muscles, which attachment is distal and usually more moveable?

The insertion.

What are fascicles in skeletal muscle?

Bundles of muscle fibers.

What are circular muscles characterized by, and what is their function?

Concentrically arranged fascicles that form a sphincter to control passage through an opening.

How do parallel muscle fascicles run relative to the muscle's long axis?

Parallel to the muscle's long axis.

What shape do parallel muscles sometimes feature that gives them high endurance?

An expanded central belly.

Towards what do convergent muscles merge their fascicles?

A common attachment site.

How are pennate muscles organized regarding their fascicles?

Organized like a feather, with fibers pulling at an angle to the tendon.

How do pennate muscles compare to parallel muscles in tension and distance?

They generate more tension but don't pull their tendons as far.

What are the three subtypes of pennate muscles?

Unipennate, bipennate, and multipennate.

What characterizes a bipennate muscle?

Fascicles are on both sides of the tendon (the most common subtype).

What does naming a muscle after its action indicate?

The muscle's primary action (e.g., flexor digitorum longus).