Muscle Physiology

Question 1

What are the three types of muscle

Answer 1

Skeletal
Smooth
Cardiac

Question 2

What are the two types of muscles when classified functionally

Answer 2

Slow
Fast

Question 3

What are the two types of muscles when classified biochemically

Answer 3

Red
White

Question 4

What are the features of skeletal muscle

Answer 4

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

Question 5

What are the features of smooth muscle

Answer 5

Uninucleate
Unbranched fibres
Involuntary contraction
Unstriated

Question 6

What are the features of cardiac muscle

Answer 6

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

Question 7

What are the features of myosin

Answer 7

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

Question 8

What are the features of actin

Answer 8

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

Question 9

What are the three biological activities of myosin

Answer 9

Spontaneously assembles into filaments

Enzyme (ATPase)

Binds polymerised actin

Question 10

What are the chains of myosin

Answer 10

2 major chains - 200,000 MW each

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

Question 11

What are the types of actin

Answer 11

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

Question 12

Describe tropomyosin

Answer 12

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

Question 13

Define contractility

Answer 13

Shortens when stimulated

Question 14

Define extensibility

Answer 14

Capable of being stretched

Question 15

Define elasticity

Answer 15

Returns to its original resting length after being stretched

Question 16

Define responsiveness

Answer 16

(Excitability)

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

Question 17

Define conductivity

Answer 17

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

Question 18

What is the average myofiber size

Answer 18

5cm length

100um diameter

Question 19

How many sacromeres are there per myofiber

Answer 19

10000

Question 20

Describe sarcoplasm

Answer 20

Cytoplasm rich in glycogen to fuel contractions

Question 21

What is the structure of myosin

Answer 21

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

Question 22

How many myosin heads does each thick filament contain

Answer 22

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)

Question 23

What is the movement where the head moves and triggers contraction

Answer 23

Power stroke

Question 24

What chemical releases the initiation of muscle contraction

Answer 24

Ca2+

Question 25

What is the role of tropomyosin

Answer 25

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

Question 26

Describe the activation of a muscle contraction

Answer 26

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

Question 27

Describe type 1

Answer 27

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

Question 28

Describe type 2a

Answer 28

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

Question 29

Describe type 2b

Answer 29

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