Class 18 - Muscle Tissue pt. 3

Question 1

Anaerobic fermentation

Answer 1

Enables cells to produce ATP in the absence of oxygen

Inefficient - Yields little ATP per glucose

Produces lactate - must be disposed of by liver

Question 2

Aerobic fermentation

Answer 2

Produces much ATP. Does not generate lactate. Requires continual oxygen supply

Question 3

Modes of ATP synthesis during exercise (4)

Answer 3

1. Aerobic respiration - uses oxygen reserve from myoglobin, gone in ~4 secs
2. Phosphagen system - combination of ADP and CP; nearly all oxygen storage for short bursts of activity
3. Anaerobic fermentation
4. Aerobic respiration - oxygen from cardiopulmonary function

Question 4

ATP sources for immediate energy (short, intense exercise) + 2 enzymes

Answer 4

1. Oxygen briefly supplied by myoglobin
2. Make ATP by borrowing phosphate groups from other molecules and transferring them to ADP

—myokinase
—creatine kinase

Question 5

Myokinase

Answer 5

In immediate energy (phosphagen system), transfers P from one ADP to another to make ATP

Question 6

Creatine kinase

Answer 6

For immediate energy (phosphagen system), obtains P from phosphate-storage molecule creatine phosphate (CP) and gives it to ADP to make ATP

Question 7

Short-term energy ATP sources (1)

Answer 7

1. Anaerobic fermentation - muscles obtain glucose from blood/their own storage.
   30-40s of maximum activity

Anaerobic threshold - point at which lactate becomes detectable in blood

Glycogen-lactate system - pathway from glycogen to lactate

Question 8

Long-term energy ATP sources (1)

Answer 8

1. Aerobic respiration - after 40s, cardiorespiratory system delivers oxygen fast enough to meet muscles’ ATP demands

Reaches steady state at 3-4 min, where aerobic ATP production keeps pace with demand

For 30 min: energy equally from glucose and fatty acids

After 30 min: fatty acids more significant fuel

Question 9

Causes of fatigue in high-intensity exercise (2)

Answer 9

1. Potassium accumulation - In T-tubules, reduces excitability
2. ADP and P accumulation - slows cross-bridge movements, inhibits calcium release, decreases force production in myofibrils

Question 10

Causes in fatigue in low-intensity (long duration) exercise (3)

Answer 10

1. Fuel depletion - glycogen and glucose levels decline
2. Electrolyte loss - Na+ and K+ loss through sweat decreases muscle excitability
3. Central fatigue - When less motor signals issued from brain; brain cells inhibited by muscles’ released ammonia

Question 11

Maximum oxygen uptake (VO2 max)

Answer 11

The point at which the rate of oxygen consumption plateaus and does not increase further with added workloads

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

Question 12

Excess post-exercise oxygen consumption (EPOC) (4)

Answer 12

Elevated rate of oxygen consumption following exercise

1. Aerobically replenish ATP (and CP stores)
2. Replace oxygen reserves on myoglobin
3. Provide oxygen to liver which is disposing of lactate
4. Provide oxygen to many cells that have elevated metabolic rates after exercise

Can last an hour

Question 13

Slow oxidative fibers (4)

Answer 13

1. Adapted for endurance (aerobic respiration)
2. Important for muscles that maintain posture (contract constantly)
3. Thin cells with abundant mitochondria, capillaries, myoglobin, myosin with slow ATPase, and SR slowly releasing calcium
4. Grouped in small motor units controlled by small, easily excited motor neurons (precise movements)

Question 14

Fast glycolytic fibers

Answer 14

1. Adapted for quick responses; anaerobic fermentation
2. Abundant in quick, powerful muscles (eye, hand muscles, gastrocnemius, biceps brachii)
3. Myosin with fast ATPase, large SR with quick Ca2+ release
4. Strong, thick fibers; low myoglobin
5. Large motor units controlled by larger, less excitable neurons (powerful movements)

Question 15

Factors affecting muscular strength (7)

Answer 15

1. Muscle size - thicker muscles form more cross-bridges
2. Fascicles arrangement - pennate stronger than parallel, parallel than circular
3. Size of active motor units - larger the motor unit, stronger the contraction
4. Multiple motor unit summation - simultaneous activation of more units increases tension
5. Temporal summation - The greater the frequency of stimulation, the stronger the muscle contraction
6. Length-tension relationship
7. Fatigue

Question 16

Resistance exercise vs. endurance exercise

Answer 16

Resistance - Growth from cellular enlargement, muscle fibers synthesize more myofilaments and myofibrils grow thicker

Endurance - Improves fatigue resistance of muscle. Increases skeletal strength, red blood cell count, and oxygen carrying capacity of blood. Enhances cardiovascular, respiratory, and nervous system function

Question 17

Unique features of cardiac muscle cells (5)

Answer 17

1. Receive innervation from automatic nervous system
2. Cells contract in unison
3. Endomysium (NO peri- or epimysium)
4. Limited mitosis, heal by fibrosis
5. Autorhythmic - contract rhythmically and independently

Question 18

Features of smooth muscle cells (4)

Answer 18

1. Varying innervation; some none and others from autonomic nervous system
2. Capable of mitosis and hyperplasia - regenerate well
3. Slower contractions but can maintain for long period of time
4. Forms layers within walls of all hollow organs - propel contents, modify pressure/blood or airflow, allow fine control

Question 19

Smooth muscle myocyte structure

Answer 19

1. Fusiform shape
2. Single central nucleus
3. Thick and thin filaments, not aligned (no striations)
4. Z discs absent, replaced by dense bodies

Question 20

2 types of smooth muscle

Answer 20

1. Multiunit - Individual myocytes respond independently of all others. Occurs in largest arteries and air passages.
2. Unitary (single-unit) - myocytes coupled by gap junctions, contract as a unit. Most common type

Question 21

Stimuli which can excite smooth muscle (5)

Answer 21

1. Autonomic nerve fibers and neurotransmitters
2. Chemicals - hormones, oxygen, low pH
3. Temperature
4. Stretch (stomach)
5. Autorhythmicity - some single unit smooth muscle cells in digestive tract depolarize at regular intervals

Question 22

Features of contraction and relaxation in smooth muscle (5)

Answer 22

1. Always triggered by Ca2+, energized by ATP, and achieved by sliding filaments
2. Gets most calcium from ECF via gated Ca2+ channels
3. No troponin, calmodulin instead
4. Contraction SLOW compared to skeletal muscle
5. Latch-bridge mechanism resistant to fatigue - myosin heads don’t detach from actin immediately, maintains continual tonic contraction (smooth muscle tone)

Question 23

Smooth muscle response to stretch

Answer 23

1. Can open mechanically gated calcium channels in sarcolemma, causing contraction (peristalis=contraction in response to food/feces)
2. Stress-relaxation response - Helps hollow organs gradually fill. When stretched, tissue briefly contracts then relaxes
3. Contracts forcefully even when greatly stretched - allow hollow organs to fill and dispel contents
4. Exhibits plasticity - adjusts tension to degree of stretch

Question 24

Reasons smooth muscle can contract when stretched

Answer 24

1. No Z-discs for thick filaments to butt against
2. Thick/think filaments not arranged in sarcomeres, so no issue with too little cross-bridge overlap
3. Thick filaments of smooth muscle have myosin heads along entire length, so cross-bridges can form everywhere

Question 25

Muscular dystrophy

Answer 25

Group of hereditary diseases in which skeletal muscles degenerate and weaken, and are replaced with fat and fibrous scar tissue

Mutation in dystrophin, so actin not linked to sarcolemma and cell membranes are damaged during contraction

Question 26

Myasthenia gravis

Answer 26

Autoimmune disease in which antibodies attach neuromuscular junctions and bind ACh receptors together in clusters.

Effects usually first appear in facial muscles; drooping eyelids and double vision.