Muscular System Part 3: Muscle Metabolism Flashcards by Nathan McGuffey

What is involved in Substrate level Phosphorylation?

A substrate gives one phosphate to Adenosene Diphosphate and it becomes Adenosine Triphosphate

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What is Substrate level phosphorylation best for?

immediate energy source, made by borrowing from phosphate groups or other molecules to turn ADP into ATP

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Transfers P from one ADP to another, converting the latter to ATO

Myokinase

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Obtains P from a phosphate storage molecule creating creatine phosphate and gives it to ADP

Creatine Kinase

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What is used to make creatine phosphate and how long does it provide energy for contraction in conjunction with ATP?

Excess ATP is used to synthesize creatine phosphate which is a more stable energy storage
energy for 3-15 seconds of muscle contraction depending on intensity

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What are the times when each different form of ATP production takes over during exertion

Aerobic respiration from 0-8 seconds
Phosphagen system from 8-25 seconds
Glycogen lactate system 30 seconds until heart rate stabilizes and is able to support Aerobic respiration once more.

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point at which lactate becomes detectable in the blood

Anaerobic threshold or lactate threshold

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the pathway from glycogen to lactate

Glycogen-lactate system

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In the absence of oxygen, glycolysis can generate a net gain of _____ for every glucose molecule consumed

2 ATP

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Muscles obtain glucose from____ and __________

blood and their own stored glycogen

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How long does Anaerobic fermentation provide energy?

30-40 seconds of maximum activity

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Activity that lasts longer than half a minute depends on aerobic respiration
Pyruvic acid entering the mitochondria is completely oxidized generating
ATP
carbon dioxide
Water
Heat

Aerobic respiration

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How much ATP does a glucose molecule provide during AR

36 ATP

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What are the two sources of oxygen for muscle tissue

Oxygen from hemoglobin in the blood
Oxygen released by myoglobin in the muscle cell

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oxygen-binding proteins

Myoglobin and hemoglobin

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Progressive weakness from prolonged use of muscles

Muscle fatigue

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What does fatigue in high intensity exercise result from?

potassium accumulation in the T tubules reduces excitability
Excess ADP and phosphate slow cross-bridge movements, inhibit calcium release and decrease force production in myofibrils

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What does fatigue from low-intensity long duration workouts come from?

Fuel depletion as glycogen and glucose levels decline
electrolyte loss through sweat can decrease muscle excitability
Central fatigue when less motor signals are issued from the brain.

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Major determinant of one’s ability to maintain high-intensity exercise for more than 4-5 minutes

Maximum oxygen uptake or VO2 max

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What is VO2 max proportional to and when does it peak

Body size
peaks at 20 years of age
greater in males and can be twice as high in a trained athlete

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what is Excess Post exercise Oxygen Consumption (EPOC)

EPOC meets a metabolic demand also known as oxygen debt
It is the difference between the elevated rate of oxygen consumption following exercise and the usual resting rate

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What is EPOC needed for?

To aerobically replenish ATP (some of which helps regenerate CP stores)
To replace oxygen reserves on myoglobin
To provide oxygen to liver that is busy disposing of lactate
To provide oxygen to many cells that have elevated metabolic rates after exercise

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Have a high myoglobin content
Darker (dark meat in chicken legs and thighs)
Contain more mitochondria
Supplied by more blood capillaries

Red Muscle fibers

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Have a low content of myoglobin
Lighter (white meat in chicken breasts)

White muscle fibers

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Muscle fibers contract at different speeds, and vary in how quickly they fatigue What are the three types

1) Slow oxidative fibers/slow twitch 2) Fast oxidative-glycolytic fibers/intermediate fibers 3) Fast glycolytic fibers/fast twitch

Smallest in diameter Least powerful type of muscle fibers Appear dark red (more myoglobin) Generate ATP mainly by aerobic cellular respiration Have a slow speed of contraction Twitch contractions last from 100 to 200 msec Very resistant to fatigue Capable of prolonged, sustained contractions for many hours Adapted for maintaining posture and for aerobic, endurance-type activities

Slow Oxidative muscle fibers

Intermediate in diameter Large amounts of myoglobin, many blood capillaries Have a dark red appearance Generate considerable ATP by aerobic cellular respiration Moderately high resistance to fatigue Generate some ATP by anaerobic glycolysis Speed of contraction faster Twitch contractions last less than 100 msec Contribute to activities such as walking and sprinting

Fast Oxidative-Glycolytic fibers

Largest in diameter Generate the most powerful contractions Have low myoglobin content Relatively few blood capillaries Few mitochondria Appear white in color Generate ATP mainly by glycolysis Fibers contract strongly and quickly Fatigue quickly Adapted for intense anaerobic movements of short duration

Fast glycolytic fibers

Muscles that have a high proportion of SO fibers

Postural muscles of the neck, back, and legs

Muscles that have a high proportion of FG fibers

Muscles of the shoulders and arms

Muscles that have a high proportion of FOG and SO fibers

Leg muscles

What are ratios of FG and SO fibers determined by

genetics

Individuals with a higher proportion of ______ excel in intense activity (weight lifting, sprinting)

FG fibers

Individuals with higher percentages of _______ excel in endurance activities (long-distance running)

SO fibers

_______ transforms some FG fibers into FOG fibers

Aerobic exercise Endurance exercises do not increase muscle mass

Exercises that require short bursts of strength produce an increase in the ______

size of the FG fibers Muscle enlargement (hypertrophy) due to increased synthesis of thick and thin filaments

Contraction of a muscle against a load that resists movement A few minutes of resistance exercise a few times a week is enough to stimulate muscle growth Growth is from cellular enlargement Muscle fibers synthesize more myofilaments and myofibrils and grow thicker

Resistance training (example: weightlifting)

Improves fatigue-resistant muscles Slow twitch fibers produce more mitochondria, glycogen, and acquire a greater density of blood capillaries Improves skeletal strength Increases the red blood cell count and oxygen transport capacity of the blood Enhances the function of the cardiovascular, respiratory, and nervous systems

Endurance training (aerobic exercise)

_____ produce(s) a single muscle action potential.

Single nerve impulses

Action potentials are _____ size(s)

the same only the force of contraction varies

Maximum Tension (force) is dependent on

The rate at which nerve impulses arrive The amount of stretch before contraction The nutrient and oxygen availability The size of the motor unit

A motor neuron and the muscle fibers it stimulates The axon of a motor neuron branches out forming neuromuscular junctions with different muscle fibers

Motor Units

2 - 3 muscle fibers/motor unit

Voice production

10 - 20 muscle fibers/unit

Eye movements

200 - 1000 muscle fibers/ unit

Leg muscles

depends on the size of the motor units and the number that are activated

Total strength of contraction depends on

The brief contraction of the muscle fibers in a motor unit in response to an action potential

Twitch contraction

How long do twitch contractions last?

20-200 miliseconds

A brief delay between the stimulus and muscular contraction The action potential sweeps over the sarcolemma and Ca++ is released from the SR

Latent period 2ms

Ca++ binds to troponin Myosin-binding sites on actin are exposed Cross-bridges form

Contraction Period 10-100ms

Ca++ is transported into the SR Myosin-binding sites are covered by tropomyosin Myosin heads detach from actin Muscle fibers that move the eyes have contraction periods lasting 10 msec Muscle fibers that move the legs have contraction periods lasting 100 msec

Relaxation period 10-100ms

keeps skeletal muscles firm Maintains posture Loss of nerve input results in flaccidity

Muscle Tone

The tension developed remains constant while the muscle changes its length Used for body movements and for moving objects Picking a book up off a table

Isotonic Contractions

Muscle shortens

Concentric

muscle lengthens

eccentric

The tension generated is not enough for the object to be moved and the muscle does not change its length Holding a book steady using an outstretched arm

Isometric Contraction

refers to problems at somatic neurons, neuromuscular junctions, or muscle fibers.

Neuromuscular disease

disease of the skeletal muscle

Myopathy

Chronic progressive degeneration of neuromuscular junction Autoimmune, antibodies block some acetylcholine receptors - muscles become increasingly weaker. Affects ~1/10,000 people in US Initially affects eye, throat muscles, may extend to limbs, in severe cases respiratory paralysis. Associated with thyroid dysfunction More common in women, onset 20-40 (males 50-60).

Myasthenia gravis

technique to remove harmful antibodies from blood plasma

Plasmapheresis (Myasthenia Gravis treatment option)

retard breakdown of ACh allowing it to stimulate the muscle longer

cholinesterase inhibitors (Myasthenia Gravis treatment option)

helps to dampen the overactive immune response that causes myasthenia gravis

Thymus removal or thymectomy (Myasthenia Gravis treatment option)

Group of genetic muscle-destroying diseases (many versions)

Muscular dystrophy

most common form. X-linked, 1/3,500 male births Mutation in dystrophin gene - sarcolemma tears easily when muscles contract Most die from respiratory or cardiac failure prior to age 20.

Duchenne Muscular dystrophy

Major signs of Duchenne's muscular dystrophy

Progressive muscular wasting Poor balance/Frequent falls Walking difficulty/Waddling gait Limited range of motion Calf deformation Scoliosis Respiratory difficulty Droopy eyelids Loss of bladder control

Result from inadequate blood flow, low electrolytes, overuse, dehydration

Cramps

Involuntary spasmodic contractions of normally voluntary muscles

tics

Brief twitch of an entire motor unit - often associated with multiple sclerosis or amyotrophic lateral sclerosis

Fasciculation

Spontaneous contraction of a single muscle fiber - may signal destruction of motor neurons.

Fibrilation

Pain associated with fibrous connective tissue components of muscles, tendons, ligaments Pain, tenderness, stiffness,General fatigue, headaches, depression Affects ~ 3 million in US Onset ages 25-50 15 X more common in women

Fibromyalgia

Contracts with regular rhythm Contract in unison Contraction lasts long enough to expel blood Must function during wake and sleep (autonomic) Must be resistant to fatigue (uses aerobic cellular respiration)

Features of cardiac muscle

Visceral layer of serous pericardium Smooth, slippery texture to outermost surface

Epicardium (single layer)

95% of heart is cardiac muscle

Myocardium

Smooth lining for chambers of heart, valves and continuous with lining of large blood vessels

Endocardium (inner layer)

Same arrangement of actin and myosin Shorter fibers 50-100µ long, branched Usually one centrally located nucleus Numerous large mitochondria (~25% cell volume) Very aerobic, can use lactate Ends of fibers connected by intercalated discs Discs contain gap junctions (allow action potential conduction between fibers) - act as a unit.

Cardiac muscle tissue

Specialized cardiac muscle fibers Self-excitable Repeatedly generate action potentials that trigger heart contractions 100 beats/min, modified by autonomic nervous system -Autonomic nervous system can increase or decrease heart rate and contraction strength Very slow twitches; does not exhibit quick twitches like skeletal muscle - Maintains tension for about 200 to 250 ms- Gives the heart time to expel blood

Autorhythmic fibers

2 Important functions of Autorhythmic fibera

Acts as a pacemaker Forms a conduction system

_______ is named for its lack of striations Some _______ lack nerve supply; others receive input from autonomic fibers with many varicosities containing synaptic vesicles Capable of mitosis and hyperplasia Injured _________ regenerates well ________ is slower than skeletal and cardiac muscle Takes longer to contract but can remain contracted for a long time without fatigue

Smooth muscle

It can propel contents of an organ (e.g., food in GI tract) It can modify pressure and flow of blood in the circulatory system and air in the respiratory system

Smooth muscle

Provides fine control in areas like iris and piloerectors in hair

smooth muscle

One nucleus near the middle of the cell thick and thin filaments are present but not aligned with each other, smooth not striated

Myocytes of smooth muscle cells

Occurs in some of the largest arteries and pulmonary air passages, in piloerector muscles of hair follicle, and in the iris of the eye

Multiunit smooth muscle

Autonomic innervation similar to skeletal muscle Terminal branches of a nerve fiber synapse with individual myocytes and form a motor unit Each motor unit contracts independently of the others

Multiunit smooth muscle

More widespread Occurs in most blood vessels, in the digestive, respiratory, urinary, and reproductive tracts Often in two layers: inner circular and outer longitudinal Myocytes of this cell type are electrically coupled to each other by gap junctions They directly stimulate each other and a large number of cells contract as a single unit

Single-unit smooth muscle or Visceral muscle

Smooth muscles can contract or relax due to a variety of stimuli, what are those stimuli?

Autonomic activity Parasympathetic nerves secrete acetylcholine stimulating GI tract smooth muscle Sympathetic nerves secrete norepinephrine relaxing smooth muscle in bronchioles (dilating them) Hormones, carbon dioxide, oxygen, and pH Hormone oxytocin stimulates uterine contractions Temperature Cold excites piloerector muscles Warmth relaxes muscle in skin blood vessels Stretch Stomach contracts when stretched by food Autorhythmicity Some single-unit smooth muscle cells in GI tract depolarize at regular intervals

Smooth muscles get most of their C++ from ____

ECF or extracellular fluid

Pockets on teh sarcolemma that concentrate calcium channels

caveolae

Calcium binds to ________ on thick filaments

calmodulin