Muscular System 1

Question 1

What are the primary functions of the muscular system? What are the 5 things muscular system produces?

Answer 1

Primary function- transform chemical energy into mechanical energy This produces:
- Equilibrium- posture (tension generation under isometric contraction)
- Force- changes in velocity of muscle shortening (F=ma)
- Work- displacement in the direction of force (W=Fs)
- Transport- circulation & digestion
- Heat production- maintain bod temp

Question 2

What are the 3 types of muscle tissue? (Nuclei, twitching, purpose, voluntary or involuntary)

Answer 2

• Skeletal muscle- multinucleated, fastest muscle twitch
  Attached to bone by tendon, made for locomotion and balance (posture)
  Voluntarily controlled and involuntary
  Lacks pace making capability
• Cardiac muscle- uninucleate
  Attached to blood vessels, used for blood circulation with adequate volume and pressure
  Involuntary
• Smooth muscle- uninucleated, slowest muscle twitch
  Attached to wall of organs and blood vessels
  Used for blood pressure control, digestion, bladder control, air flow
  Involuntary.

Question 3

What regulates the action for smooth and cardiac muscle? What regulates action for skeletal muscle.

Answer 3

Cardiac/smooth:
- Involuntarily by Autonomic nervous system and endocrine system

Skeletal:
- Mainly voluntarily by somatic nervous system Can also be subconscious (posture, diaphragm contract/relax)

Question 4

What are the 5 special properties of muscle are tissues?

Answer 4

• Excitability- ability to respond to stimuli by producing action potentials (cardiac/smooth have electrical stimulus, skeletal has chemical)
• Contractibility- ability of muscular tissues to contract forcefully when stimulated by action potentials (greater change in velocity of muscle fibre shortening, greater force of contraction)
• Extensibility- ability of muscular tissues to stretch without being damaged (connective tissues keep stretch in range of physiological contractile range of muscle cells)
• Elasticity- ability of muscular tissues to return to its original length and shape after contraction or extension
• Adaptability- muscular tissues have ability to undergo hypertrophy or atrophy.

Question 5

What are the 4 properties of the skeletal muscle?

Answer 5

• Force of contraction
• Contraction speed
• Endurance
• Oxidative/glycolytic capacity (related to energy production to sustain muscle)

Question 6

What are the 2 phenotypes of muscle fibers in skeletal muscle?

Answer 6

• Slow-twitch oxidative fibers (type I)- rate ATP break is slower than that of other types of muscle fibers (require good supply of oxygen)
• Fast-twitch oxidative/glycolytic fibers (type II)
  Type II divides into two smaller groups:
  Type IIa (fast-twitch oxidative fibers)
  Type IIb/IIx (fast-twitch glycolytic fibers)
• Type IIb express myosin heavy chain (MyHC) gene which is homologous to that of typeIIx gene in rodents.

Question 7

What is a motor unit?

Answer 7

• All the muscle fibers being innervated by a single motor neuron
• Muscle fibers belonging to one motor unit are all of the same MyHC type (muscle type)

Question 8

How is the type II muscle fibers differentiated?

Answer 8

• Type IIa- ATP break is quicker than type I (velocity of shortening is quicker)
  Require good supply of O2 (aerobic respiration)
  Fatigue resistant but less endurance compared to slow-twitch
  Creatine phosphate is reservoir for ATP storage
• Type IIb- ATP break is much quicker than the rest of muscle fibers (velocity much faster)
  Anaerobic respiration
  Easily fatigable and low in endurance

Question 9

What are the 4 main events in excitation-contraction coupling?

Answer 9

1. Ach is released from the somatic motor neuron.
2. Ach initiates an action potential in the muscle fiber.
3. Action potential travels along the sarcolemma into the T-tubules and triggers Ca2+ release from the sarcoplasmic reticulum (SR).
4. Ca2+ binds with TnC and initiates muscle contraction.

Question 10

How do you end a contraction?

Answer 10

Ca2+ must be removed from the cytosol back to SR through sarco-endoplasmic reticulum ATPase (SERCA).

Question 11

What is the DHP?

Answer 11

Dihydropyridine receptor (L-type calcium channel).

Question 12

What is the RyR?

Answer 12

Ryanodine receptor (Ca2+ release channel)

Question 13

How does the skeletal muscle fiber contract?

Answer 13

• ATP binds to myosin. Myosin releases actin.
• Myosin hydrolyzes ATP rotates the myosin head to the cocked position. Myosin binds to actin.
• The releases of Pi enable the myosin head to swivel, generating the power stroke.
• Myosin releases ADP at the end of the power stroke.