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MSK > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

What are the three types of muscle

A

Skeletal
Smooth
Cardiac

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2
Q

What are the two types of muscles when classified functionally

A

Slow
Fast

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3
Q

What are the two types of muscles when classified biochemically

A

Red
White

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4
Q

What are the features of skeletal muscle

A

Multinucleated
Long, unbranched fibres
Voluntary contraction
Striated (TS only)
Transverse tubules (t-tubules)
Sarcoplasmic reticulum

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5
Q

What are the features of smooth muscle

A

Uninucleate
Unbranched fibres
Involuntary contraction
Unstriated

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6
Q

What are the features of cardiac muscle

A

Branched fibres
Intercalated discs
Purkinje fibres (glycogen)
Faintly striated
Inherent rhythm

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7
Q

What are the features of myosin

A

A-band
Thick filaments
1.6um long
15nm diameter
approx. 300 myosin molecules per filament
approx. 6x10^10 filaments per cm2 muscle

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8
Q

What are the features of actin

A

I-band
Thin filaments
1.0um long
8nm diameter
approx. 380 actin molecules per filament
approx. 6x10^10 filaments

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9
Q

What are the three biological activities of myosin

A

Spontaneously assembles into filaments

Enzyme (ATPase)

Binds polymerised actin

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10
Q

What are the chains of myosin

A

2 major chains - 200,000 MW each

4 light chains
- 1 pair 16,000 MW
- 1 pair 20,000 MW

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11
Q

What are the types of actin

A

Filaments (F-actin) made up of monomers of Globular protein G-actin

G-actin 41,800 MW

G-actin to F-actin (polymerised from an ATPase)

F-actin makes a chain of two alpha helices

Wrapped around these chains is tropomyosin

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12
Q

Describe tropomyosin

A

Double alpha helix approx. 35,000 MW

About every 38.5nm lies a troponin complex

Three troponins (Tn)
1. Tn I - inhibitory
2. Tn T - binds to tropomyosin
3. Tn C - binds to calcium

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13
Q

Define contractility

A

Shortens when stimulated

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14
Q

Define extensibility

A

Capable of being stretched

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15
Q

Define elasticity

A

Returns to its original resting length after being stretched

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16
Q

Define responsiveness

A

(Excitability)

Capable of response to chemical signals, stretch or other signals and responding with electrical changes across the plasma membrane

17
Q

Define conductivity

A

Local electrical change triggers a wave of excitation that travels along the muscle fibre

18
Q

What is the average myofiber size

A

5cm length

100um diameter

19
Q

How many sacromeres are there per myofiber

A

10000

20
Q

Describe sarcoplasm

A

Cytoplasm rich in glycogen to fuel contractions

21
Q

What is the structure of myosin

A

Globular head - neck - tail

Attached/maintained by titin (protein) - creates the spring like structure, ability to stretch out an then spring back into original position

22
Q

How many myosin heads does each thick filament contain

A

Approx. 300

Each head cycles 5 times per second

Sliding mechanism triggered by the myosin head - movement is not coordinated but due to speed can do contraction (think tug of war)

23
Q

What is the movement where the head moves and triggers contraction

A

Power stroke

24
Q

What chemical releases the initiation of muscle contraction

A

Ca2+

25
Q

What is the role of tropomyosin

A

Masks myosin binding sites on thin filaments

Linked to troponin

When Calcium released in sarcoplasm binds to troponin which triggers change of conformation and displaces tropomyosin from the binding site

26
Q

Describe the activation of a muscle contraction

A
  1. Nerve impulse
    - Reaches the nerve terminal, the neuromuscular junction. Ca2+ is released and causes release of ACh by exocytosis
  2. Binding of Ach
    - to its receptor causes entry of Na+ into the sarcoplasm = produces an action potential
  3. Ca2+ is released
    - and binds to troponin, provoking a conformational change that unmasks the binding sites
  4. Myosin heads slide
    - along the actin filament, a process that requires energy (ATP)
  5. Process terminates
    - when nerve impulses stops. Ach is then degraded by Acetylcholinesterase, and C2+ is reabsorbed by the sarcoplasmic reticulum. Ca2+ detached from troponin, which returns to its initial position, masking myosin binding sites
27
Q

Describe type 1

A

Slow oxidative

Fatigue - resistant
Colour - red
Metabolism - oxidative
Glycogen content - low
ATP synthesis - aerobic
Mitochondria - high
Muscles - soleus

28
Q

Describe type 2a

A

Fast oxidative

Fatigue - resistant
Colour - red
Metabolism - oxidative
Glycogen content - abundant
ATP synthesis - aerobic
Mitochondria - higher
Muscles - gastrocnemius

29
Q

Describe type 2b

A

Fatigue - fatigue able
Colour - white
Metabolism - glycolytic
Glycogen content - high
ATP synthesis - anaerobic
Mitochondria - fewer
Muscles - biceps brachii

MSK (13 decks)

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