Week 6 Muscle Physiology

Question 1

5 Functions of muscle tissue are

Answer 1

1.Producing body movements
2.Stabilizing body positions
3.Regulating organ volumes
bands of smooth muscle called sphincters
4.Movement of substances within the body blood, lymph, urine, air, food and fluids, sperm
5. Producing heat, involuntary contractions of skeletal muscle (shivering)

Question 2

5 Properties of muscle tissue are

Answer 2

Excitability- respond to chemicals released from nerve cells
Conductivity- Ability to propagate electrical signals over membrane
Contractility- ability to shorten and generate force
Extensibility- ability to be stretched without damaging the tissue
Elasticity- ability to return to original shape after being stretched

Question 3

3 Characteristics of Smooth muscle tissue

Answer 3

Attached to hair follicles in the skin
Not striated
Involuntary

Question 4

4 Characteristics of Cardiac muscle tissue

Answer 4

Only in the walls of the heart
Striated
Involuntary
Auto-rhythmic because of built in pacemaker

Question 5

3 Characteristics of Skeletal muscle tissue:

Answer 5

Attached to bones and skin
Striated
Voluntary an involuntary

Question 6

3 Types of muscle tissue are

Answer 6

Smooth, Cardiac, Skeletal

Question 7

Supaficial fascia is

Answer 7

loose connective tissue & fat underlying the skin

Question 8

Deep fascia is

Answer 8

dense irregular connective tissue around muscle

Question 9

Describe Epimysium

Answer 9

dense regular connective tissue surrounding entire muscle

Question 10

Describe Perimysium

Answer 10

fibrous connective tissue surrounding fascicles (groups of muscle fibers)

Question 11

Describe Endomysium

Answer 11

fine areolar connective tissue surrounding each muscle fiber

Question 12

Characteristics of Red fibres (Slow)

Answer 12

Small; high oxidative capacity; ATP from β-oxidation of fatty acids

Question 13

Describe the characteristics of White fibres “Fast-twitch”

Answer 13

Large; lower oxidative capacity; mostly anaerobic glycolysis;
Fatigue rapidly

Question 14

Briefly describe a myofibril

Answer 14

Densely packed, rod-like elements

Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands

Question 15

3 characteristics of a sarcomere

Answer 15

Smallest contractile unit of muscle is the sarcomere
Sarcomere contains the protein filaments actin &
myosin. Each muscle cell contains many thousands of sarcomeres.

Question 16

What are the two requirements for skeletal muscle contraction

Answer 16

Activation: neural stimulation at aneuromuscular junction
Excitation-contraction coupling:
Generation and propagation of an action potential along the sarcolemma
Final trigger: a brief rise in intracellular Ca2+ levels

Question 17

3 characteristics of thick filament’ head and tail

Answer 17

Composed of protein myosin
Tail- Interwoven, polypide chains
Head- binding sites for actin of thin filaments
Binding site of atp

Question 18

3 characteristics of thin filament (actin)

Answer 18

Twisted double strand of fibrosis protein of f actin
G actin bears active site for myosin head.
Tropomyosin and troponin- regulatory proteins bound to actin.

Question 19

What is the sarcoplasmic reticulum ?

Answer 19

Network of smooth endoplasmic reticulum surrounding each myofibril
Regulates intercellular ca2+ levels

Question 20

Briefly explain the innervation of a skeletal muscle

Answer 20

Stimulated by somatic motor neurons
Axons from motor neuron travel from the cns via nerves to skeletal muscles
Each axon forms server all branches as it enters a muscle.
Each axon ending forms a neuromuscular junction with each muscle fibre.

Question 21

Explain the 4 events that occur in local depolarisation

Answer 21

–ACh binding opens chemically (ligand) gated ion channels
–Simultaneous diffusion of Na+ (inward) and K+ (outward)
–More Na+ diffuses, so the interior of the sarcolemma becomes less negative
–Local depolarization – end plate potential

Question 22

Explain the 4 events of Generation and propagation of an action potential:

Answer 22

–End plate potential spreads to adjacent membrane areas
–Voltage-gated Na+ channels open
–Na+ influx decreases the membrane voltage toward a critical threshold
–If threshold is reached, an action potential is generated

Question 23

Explain the 3 events of re polarisation

Answer 23

• Na+ channels close and voltage-gated K+ channels open
• K+ efflux rapidly restores the resting polarity
• Ionic conditions of the resting state are restored by the Na+-K+ pump

Question 24

List the 2 requirements for skeletal muscle contraction.

Answer 24

1.Activation: neural stimulation at a
neuromuscular junction
2.Excitation-contraction coupling:
–Generation and propagation of an action potential along the sarcolemma
–Final trigger: a brief rise in intracellular Ca2+ levels

Question 25

Briefly describe Excitation-Contraction (E-C) Coupling

Answer 25

• Sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments
• AP is propagated along sarcomere to T tubules
• Voltage-sensitive proteins stimulate Ca2+ release from SR

Question 26

Explain the role of calcium in muscle contraction

Answer 26

•At low intracellular Ca2+ concentration:
–Tropomyosin blocks the active sites on actin
–Myosin heads cannot attach to actin
–Muscle fiber relaxes
•At higher intracellular Ca2+ concentrations:
–Ca2+ binds to troponin
–Troponin changes shape and moves tropomyosin away from active sites
–Events of the cross bridge cycle occur

Question 27

Describe the 3 stages to sliding filament model

Answer 27

• In the relaxed state, thin and thick filaments overlap only slightly
• During contraction, myosin heads bind to actin, detaches, and binds again, to propel the thin filaments toward the M line
• As the H zones shortens and disappears, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens

Question 28

What is the difference between small motor units and large motor units

Answer 28

• Small motor units in muscles that control fine movements

* Large motor units in large weight-bearing muscles