Muscle tissue pt 3

Question 1

Muscle fiber type

Answer 1

3 types
- slow oxidative fibers, fast oxidative fibers, fast glycolytic fibers

• most muscles contain mixture of fiber types
• all fibers in 1 motor unit same type
• genetics dictate individual’s % of each

Question 1

Fast + slow fibers

Answer 1

Fast fibers
large diameters, densely packed myofibrils, large glycogen reserves and few mitochondria
- produce powerful contractions
- use massive amts of ATP + fatigue quickly
- use anaerobic glycolysis

Slow fibers
- half diameter as fast fibers
- specialized for long periods of contraction
-large capillary network supports oxygen demand
- myoglobin: red pigment that binds oxygen oxidative fibers (slow) use aerobic pathways

Question 2

Membrane potential

Answer 2

1. Na+ channels open
2. Depolarization: due to entry of Na+
3. Na+ channels close, K+ opens
4. Repolarization: K+ exit
5. K+ channels close

Question 3

Influence of load

Answer 3

• muscles contract fastest when no load added
• increase load leads to increase latent period, slower contraction, and decrease duration of contraction
• if load exceeds muscle maximal tension speed of contractions i 0 (isometric)

Question 4

Adaptations to exercise (2)

Answer 4

1. Aerobic endurance exercise
   - leads to increased muscle capillaries, number of mitochondria, myoglobin synthesis
   - results in greater endurance, strength, and resistance to fatigue
   - may convert fast glycolytic fibers into fast oxidative fibers
2. Resistance exercise typically anerobic
   - muscle hypertrophy: due primarily to increase in fiber size
   - increased myofilaments, glycogen stores, and CT
   - increase muscle strength + size

Question 5

Homeostatic imbalance

Answer 5

• disuse atrophy: result of immobilization, muscle strength declines 5% per day

neurogenic atrophy: w/o neural stimulation muscles atrophy to 1/4 initial size
- fibrous CT replaces lost muscle tissue –> rehabilitation impossible

Question 6

Smooth muscle

Answer 6

• found in walls of most hollow organs (except heart)
• usually in 2 layers (longitudinal + circular)
• allows peristalsis: alternating contractions + relaxations of smooth muscle layers that mix + squeeze substances through lumen of hollow organs
• 2 types: unitary + multi unit

Question 7

microscopic structure

Answer 7

• spindle-shaped fibers: only one nucleus, no striations
• lacks CT sheaths; endomysium only
• SR: less developed than skeletal muscle
• pouchlike infoldings (caveolae) of sarcolemma store Ca2+ - most calcium influx from outside cell; rapid
• no sarcomeres, myofibrils, or t tubules

Question 8

innervation of smooth muscle

Answer 8

• no NMJ as in skeletal muscle
• autonomic nerve fibers innervate smooth muscle at diffuse junctions
• varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters into diffuse junctions
• slow synchronized contractions
• may be initiated by pacemaker cells, hormones/local chemicals

Question 9

2 types of smooth muscle

Answer 9

1. Unitary visceral smooth muscle
   - in all hollow organs except heart
   - electrically coupled by gap junctions
   - contract synchronously
2. Multi unit smooth muscle
   - located in large airways, large arteries, arrector pili muscles, and iris of eye
   - contractions are rarely synchronously

Question 10

Developmental aspects

Answer 10

• w/ age, CT increases and muscle fibers decrease
• by 30, loss of muscle mass (sarcopenia) begins
• regular exercise reverses sarcopenia
• atherosclerosis may block distal arteries, leading to intermittent claudication and severe pain in leg muscles