Physiology: Muscles

Question 1

What are the 3 Muscle Metabolism Types?

Answer 1

1. Direct Phosphorylation
2. Aerobic Respiration
3. Anaerobic Glycolysis

Question 2

Explain Aerobic Respiration (include precursors, location, activity type etc)

Answer 2

• Predominate during
• Moderate Activity
• Precursors: Glucose, O2
• occurs in Mitochondria
• requires continuous O2, thus much slower than direct phosphorylation and Anaerobic Glycolysis (most commonly used in slow-twitch muscles)
• Glucose -> CO2 and H20
• high energy released
  
  • via mobilization of acetyl-coA step followed by TCA cycle (citric acid cycle/Krebs Cycle) followed by electron transport and oxidative phosphorylation step
• Fatty acids and amino acids can also be used to generate energy
• Glucose and fatty acids are catabolized
• ATP produced used to power contraction
• Most common in Slow twitch (Slower muscles)

Question 3

Explain Direct Phosphorylation (include precursors, location, activity type etc)

Answer 3

• immediate reaction but short-lived
  
  • lasts 20 seconds
  • CP depletion
• dependent on Creatine Phosphate (CP)
  
  • high energy molecule
  • contained in muscles
  • ATP stores
• after ATP depleted, CP transfers energy to ADP to regenerate ATP
• No O2 used
• Resting Muscle
• Fatty Acids are catabolized
• ATP produced used to build energy reserves of ATP, CP and glycogen

Question 4

Explain Anaerobic Glycolysis (include precursors, location, activity type)

Answer 4

• Peak activity (High Intensity)
  
  • most ATP produced via glycolysis
    
    • Lactic Acid (LA) byproduct
    • only 1/3 of ATP consumption from Mitochondrial Activity
• fast process
  
  • replenishes ATP within short time period
  • not efficient ATP producer
• breaks down glucose without O2
• Glc->pyruvic acid
  
  • produces minimal ATP
  • pyruvic acid->lactic acid
• requires larger amount of glucose
• Causes Muscle Fatigue and prevents muscle contraction
  
  • due to O2 debt and LA accumulation

Question 5

Explain Rigor Mortis

Answer 5

• No aerobic respiration
  
  • circulation system stopped
• limited pool of ATP
  
  • generated from Phosphagen and Anaerobic Metabolism (around after death)
• Muscle Contraction caused by
  
  • Ca2+ leaking from extracell fluid and SR into muscle fiber
  • lack of ATP prevents relaxation
    
    • myosin head cannot detach from actin
• All M. of body remain contracted
  
  • body becomes rigid
• eventually after days, degeneration of body
• muscle breaks down and appears to relax again

Question 6

Describe Isotonic Contractions

Answer 6

• contractions generate force by changing the length of the M. and can be concentric or eccentric contractions
  • Myofilaments are able to slide past each other during contractions​
  • Muscle Shortens

Question 7

Describe Isometric Contraction

Answer 7

• generate force without changing the length of the m.
  
  • Tension in Muscle increases
  • Muscle unable to shorten

Question 8

What is Muscle Tone

Answer 8

• total tension maintained in muscular structure under relaxed condition
  
  • some fibers are contracted even in a relaxed muscle
  • different fibers contract at different times to providemuscle tone
  • muscle tone stabilizes bones and joints

Question 9

breakdown of muscle tissue causes

Answer 9

non-movement, physical tearing, diseases

Question 10

• higher Mitochondrial Content
• rely more heavily on O2 and aerobic metabolism
  
  • oxidative enzymes and mitochondria

Answer 10

Slow Twitch Muscle Fibers

Question 11

• rely more on glucose stores than O2
• most ATP derived from glycolosis
• recruited as intensity of activity increases/ reaches peak

Answer 11

Fast Fatigable Fibers

Question 12

Describe Muscle Hypertrophy

Answer 12

• muscle regeneration and rebuilt of existing muscle cells
• Net Result: muscle protein syth exceeds degradation leading to increased muscle mass
• mainly a result of muscle fibers increasing in size not in quantity
• strength gained from adding more myosin/actin chains per M. fiber
• increase number of cross-bridges -> more force

Question 13

Describe Muscle Atrophy

Answer 13

• breakdown of muscle tissue
• Net Result: muscle protein degradation exceeds synthesis leading to degeneration
• use it or lose it (caused by disuse)

Question 14

Describe a “motor unit”

Answer 14

• 1 motor neuron and 1+ muscle fibers innervated by same motor neuron
• each motor neuron innervates different group of skeletal m. fibers.
• each motor unit separate from others
• some MU are small
  
  • ex: motor neuron innervates only small # of M. fibers 1 motor neuron -> 3 M. fibers

Question 15

Describe Innervation Ratio (IR)

Answer 15

• number of M fibers innervated by a single MU
• small motor unit = small IR
• produces less force than large motor units
• mostly because of number of fibers innervated

Question 16

Describe “Recruitment” in Muscles

Answer 16

• Force is Additive
• start with the smaller motor units and then turn on larger motor units to produce more force
• Recruit Slow-twitch (small oxidative) -> Fast-twitch fatigue- resistent -> Fast-twitch fatigable fibers
• as increase need for greater force (increase activity level)
• recruiting more fast-twitch m. fibers:
  
  • oxidative capacity of those muscles decreases as increase speed of activity
    
    • need stronger contractions: so use non-oxidative pathways

Question 17

Describe Single Muscle Twitch

Answer 17

• Stimulate Muscle at low frequency
  
  • one muscle contracts
  • results in small amount of force exerted

Question 18

Describe Temporal Summation

Answer 18

• as increase number of motor units in muscle -> add forces together
• stimulate muscle at higher frequency and does’t allow the force to decay

Question 19

Describe Slow-Twitch Muscles

Answer 19

• small cell body and smaller axon diameter
  
  • lower conduction velocity axon
  • lower innervation ratio
• recruited early
• long twitch contraction time
• low twitch contraction force
• low tetanic contraction force
• high fatigue resistance
  
  • high oxidative capacity
  • high mitochondrial content

Question 20

Describe the length of the sarcomere when a muscle obtains the max force

Answer 20

Optimal Length

• maximum overlap between myosin and actin = max cross bridge formation and max force produced
  
  • overly shortened = less cross bridge formation
  • overly stretched = less cross bridge formation

Question 21

What is conduction velocity?

Question 23

• the neurons that innervate muscle
• located in the ventral horn

Answer 23

lower motor neurons

(not relegated to lower part of body, just called that)

Question 24

muscle fibers innervated by single neuron spread out within a muscle

Answer 24

Question 25

How is energy obtained for muscle contraction during rest, mild activity and peak activity?

Answer 25

• Resting Muscle: Creatine Phosphate releases stored energy to convert ADP to ATP
• Aerobic metabolism provides most ATP needed for contraction
• At peak activity, anaerobic glycolysis needed to generate ATP