A&P: Muscular System

What is an anaerobic process (in terms of exercise)?

the production of ATP to power muscle contraction without the immediate use of oxygen, producing lactic acid through glycolysis

When do anaerobic processes in muscle contraction occur?

during short duration, high-intensity activities (ex. sprinting, weight lifting)

What is the reaction of anaerobic process in muscle contraction?

creatine phosphate + ADP <-> creatine + ATP

What is creatine phosphate?

a high-energy compound that is the fastest way to make ATP available for muscles, used in activities lasting <15 seconds

When is creatine phosphate made?

when muscle is at rest

What happens to muscles during anaerobic exercise?

muscles break down glucose for energy w/o oxygen, causing rapid fatigue & burning sensation

How is oxygen debt related to anaerobic exercise?

during high intensity exercise, muscles consume more energy than oxygen can supply

What is oxygen debt/excess post-exercise oxygen consumption (EPOC)?

the additional oxygen required by the body to recover after intense exercise (after anaerobic respiration has produced lactic acid), ensuring toxins are removed from muscles

What causes muscles to go into anaerobic respiration?

high intensity activity, insufficient oxygen delivery, extremely cold conditions

What is a motor unit?

a motor neuron and all the muscle fibers it controls

What is motor unit recruitment?

an increase in the number of activated motor units within a muscle at higher intensities of stimulation

What is maximum tension?

when all motor units have been recruited

What is threshold stimulus?

the minimum strength of stimulus required to generate an impulse through the muscle fiber, release calcium ions, activate cross-bridges, and contract the muscle

Why is ATP needed for the muscle?

ATP detatches myosin heads from actin, ending contractions, "cocking" the myosin head for the next stroke and power the calcium pumps in sarcoplasmic reticulum

What enzyme powers the cross-bridges that convert ATP to ADP?

ATPase

Where is Acetylcholine (ACh) produced and stored?

produced in the motor neuron, stored in the synaptic vesicles at the distal end of the neuron

How does a motor neuron bring a muscle fiber to its threshold/stimulate muscle fibers?

the motor neuron releases sufficient ACh in the neuromuscular junction

What is ATPase?

a diverse group of enzymes that catalyze the breakdown of ATP into ADP by freeing a phosphate ion and releasing stored chemical energy

Where is ATPase located?

inner mitochondrial membrane

What is the tropenine complex?

a group of regulatory proteins that are cruical for muscle contraction in cardiac and skeletal muscles

What does the tropenine complex do?

acts as a calcium dependent switch, enabling muscle contraction when Ca+ binds to the tropenine complex, exposing myosin-binding sites on actin

What is tropomyosin?

regulatory, rope-shaped protein that wraps around actin filaments in muscle cells to control contraction by preventing myosin from attaching

What is a motor unit?

the basic functional unit of skeletal muscle contraction

What is a motor unit made up of?

motor neuron and skeletal muscle fibers

Put the sequence of events of a muscle contraction.

1. an impulse travels down a motor neuron axon

2. The motor neuron releases the neurotransmitter acetylcholine (ACh)

3. ACh binds to ACh receptors in the muscle fiber membranes

4. The sacrolemma is stimulated. An impulse travels over the surface of the muscle fiber and deep into the fiber through the transverse tubules

5. The impulse reaches the sarcoplasmic reticulum, and calcium channels open

6. Calcium ions diffuse from the sarcoplasmic reticulum into the cytosol and bind to troponin molecules

7. Tropomyosin molecules move and expose specific sites on actin where myosin heads can bind

8. Cross-bridges form, linking thin and thick filaments

9. Thin filaments are pulled toward the center of the sacromere by pulling of the cross-bridges

10. The muscle fiber exerts a pulling force on its attachments as a contraction occurs

Put the sequence of events of muscle relaxation.

1. Acetylcholinsterase decomposes acetylcholine, and the muscle fiber membrane is no longer stimulated

2. Calcium ions are actively transported into the sarcoplasmic reticulum

3. ATP breaks cross-bridge linkages between actin and myosin filaments without breakdown of the ATP itself

4. Breakdown of ATP "cocks" myosin heads

5. Troponin and tropomyosin molecules block the interaction between myosin and actin filaments

6. The muscle fiber remains relaxed, yet ready, until sitimulated again

What is a sarcolemma?

the fine transparent tubular sheath which envelops the fibers of skeletal muscles

What is the function of skeletal muscles?

movement of bones at joints, maintenance of posture

What is the function of smooth muscles?

movement of viscera, peristalsis, vasoconstriction

What is the function of cardiac muscles?

pumping action of the heart

What is hypertrophy?

enlargement of a muscle due to repeated exercise

What is atrophy?

decrease in muscle size and strength, due to disuse

What does low intensity exercise (ex. walking, casual cycling, swimming, yoga, pilates) do to muscles?

causes slow fibers to increase mitochondria and capillaries, becoming more fatigue resistant

What does forceful exercise (ex. high-intensity movements, olympic lifts, sprints) do to muscles?

causes fast fibers to increase numbers of actin and myosin filaments, enlarging fiber and entire muscles, allowing strong contractions

What are the characteristics of slow twitch fibers (type I)?

small diameter, takes longer to reach peak tension but resistant to fatigue, provide prolonged contraction, many mitochondria and capillaries, aerobic metabolism

What are the characteristics of fast twitch fibers (type II)?

make up majority of muscle fibers, rapid movements, reach maximum force quickly, fatigue quickly, large diameter, few mitochondria, store glycogen, anaerobic metabolism, powerful contractions best for short-term activites

What is rigor mortis?

the temporary stiffening of a body's muscles after death

What causes rigor mortis?

the depletion of ATP in muscle fibers prevents actin-myosin filaments within muscle fibers to separate

What causes muscle cramps?

thought to occur due to changes in the extracellular fluid around the muscle fibers, leading to uncontrolled muscle fiber stimulation by its motor neurons

What is the name for the binding sites on the surface of actin?

myosin binding sites

What is AChE/acetylcholinesterase?

enzyme that decomposes acetylcholine, preventing continuous involuntary muscle contraction

Where are AChE/acetylcholinesterase and other neurotransmitter moleules stored?

stored in the synaptic vesicles within the presynaptic terminal of neurons

What are transverse tubules?

deep folds of the sacrolemma found in skeletal and cardiac muscle cells that carry electrical impulses from the cell surface to the interior

What do transverse tubules allow for?

electrical impulse to travel into the skeletal muscle/transverse impulse

What are myofibrils made up of?

thick and thin filaments

What are thick filaents in myofibrils made up of?

the protein myosin

What are the thin filaments in myofibrils made up of?

mostly actin, also contains troponin, tropomyosin

What is a sacromere?

the basic, repeating contractile unit of striated muscle fibers (skeletal and cardiac) spanning from one Z-line to the next

What are I bands/light bands in sacromeres?

bands made up of actin filaments anchored to Z lines

What are A bands/dark bands in sacromeres?

bands made up of overlapping thick and thin filaments

What is the H zone in sacromeres?

zone in the center of A bands, consisting of myosin filaments only

What is the M line in sacromeres?

zone in the center of the H zone, consisting of proteins that hold the myosin filaments in place

What is threshold stimulus?

the minimum strength of stimulus required to generate an impulse through the muscle fiber, relase calcium ions, activate cross-bridges, and acontract the muscle

What is a twitch?

the response of a single muscle fiber to a single impulse, consisting of a cycle of contraction and relaxation

What is a myogram?

the recording of an electrically-stimulated muscle contraction

What is the latent period?

a breif delay between the stimulation and beginning of the contraction, followed by a period of contraction and a period of relaxation

What is the all-or-none response?

when a muscle fiber contracts, it contracts to its full extent, with each twitch generating the same force

What is summation?

the process where the froce of individual twitches combine after a muscle fiber recieves a series of stimuli of increasing frequency, reachinga point where it is unable to relax completely

What is partial tetany?

when relaxation time becomes very short after being exposed to high frequency stimulation

What is complete tetanic contraction?

when the sustained contraction lacks any relaxation due to the frequency of stimulation being very high (can only be accomplished in a lab)