Muscle Physiology II

Question 1

Muscle Twitch

Answer 1

Contraction produced in a
muscle fiber in response
to a single action
potential
• Twitch is an all-or-nothing
event

Question 2

Preload

Answer 2

Preload is the load on a muscle

in a relaxed state

Question 3

Applying preload to the muscle

results in:

Answer 3

Stretching of the muscles
– Generation of passive tension
in the muscle

Question 4

Afterload

Answer 4

Afterload is the load the muscle

works against during contraction.

Question 5

tension

Answer 5

• Force exerted by contracting

muscle

Question 6

load

Answer 6

• Force opposing contraction (such

as weight to be moved)

Question 7

Isometric Contraction

Answer 7

•Length constant
•Contractile elements contract,
generating tension
•When load > tension
•Muscle does NOT shorten, load
not lifted
-Sarcomeres shorten while elastic elements stretch

Question 8

Isotonic Contraction

Answer 8

•Constant tension
•When tension > load
•Load is lifted as muscle shortens
- sarcomeres shorten more but, because elastic elements
are already stretched, the muscles shorten

Question 9

Concentric action

Answer 9

a shortening

action

Question 10

Eccentric action

Answer 10

lengthening actio

Question 11

Phases of Isotonic Contraction

Answer 11

Phase 1 Isometric contraction
Phase 2 Isotonic contraction
Phase 3 Isotonic relaxation
Phase 4 Isometric relaxation

Question 12

bell-shaped curve (force/time)

Answer 12

Isometric contraction

Question 13

flat-topped curve (force/time)

Answer 13

Isotonic contraction

Question 14

Passive tension generation

Answer 14

The elastic component of skeletal
muscle creates a resistance to
stretch.

Question 15

Re of Force

Preload and Passive Tension

Answer 15

Preload  Length  Passive

tension

Question 16

Force Velocity Relation-Increase Preload + Increase Fmax:

Answer 16

Shifts curve to the right.
• Increase crossbridge overlap
• increases maximum weight that can be
moved, max force generated.

Question 17

orce Velocity Relation-Increase Preload+Increase Velocity

Answer 17

Same weight/afterload can be moved
faster.
ATPase activity not altered
-No change Vmax

Question 18

Vmax is Determined by

Answer 18

myosin ATPase

activity → how fast crossbridge cycle spins

Question 19

Vmax and Different Muscle Types-Red (Type I, slow oxidative):

Answer 19

-less powerfu
-endurance
muscle
-Lower Myosin ATPase
-myoglobin
pigment
-High capacity for aerobic metabolism
-Slow twitch

Question 20

Vmax and Different Muscle Types-White (Type II, fast glycolytic):

Answer 20

• powerful
• utilized short-term
• High Myosin ATPase
• Low myoglobin
• High capacity for anaerobic glycolysis
• Fast twitch

Question 21

How do skeletal muscles regulate their force?

Answer 21

By Graded Muscle Contractions

Question 22

1. Temporal summation:

Answer 22

Tension produced by each fiber (due to high frequency stimulation)

Question 23

Spatial summation (recruitment)

Answer 23

Number of fibers contracting

Question 24

Factors Affecting Force of Individual Muscle Fiber

Answer 24

• Frequency of stimulation
• Fiber diameter
• Changes in fiber length

Question 25

Basis of Summation

Answer 25

Increases in frequency of action potentials in muscle fibers
increases tension
-Action potential causes Ca2+ release
-Contraction
- Contractions can overlap and sum

Question 26

Cause of Summation and Tetanus

Answer 26

-At high frequencies, release exceeds re-uptake
-Calcium increases in cytosol
– Eventually saturates system
-

Question 27

Tetanus

Answer 27

-Clostridium tetani.
-toxin that is released blocks the release of inhibitory neurotransmitters,
γ-aminobutyric acid (GABA)
-increase in the resting firing rate of motor
neurons.
-Increased repetitive stimulation

Question 28

Tetanus-Management

Answer 28

Antitoxin -neutralize circulating and unbound toxin.

Diazepam (GABA agonist)- to control spasm

Question 29

Force developed by the whole

muscle depends on

Answer 29

More fibers contracting → greater tension
-Recruit motor units
• Activate motor neuron activates all
muscle fibers in the motor unit
• Increases in tension occur in steps
proportional to size of motor unit