single-fibre and whole-muscle mechanisms

Question 1

what is tension

Answer 1

The force that a muscle exerts
on the joint when it is contracting is
called the tension of the muscle.

Question 2

what is the load

Answer 2

The force that is exerted on a
muscle by an object is called the load of
the muscle.

Question 3

what is the relationship between tension and load

Answer 3

Muscle tension must exceed the load in order for the muscle fibres to shorten, and
therefore move the object that is responsible for the load.
If muscle tension does not exceed the load then the muscle will either remain at
the same length, or it will lengthen.

Question 3

what is a concentric contraction

Answer 3

SHORTENING CONTRACTION (concentric contraction)
➢Constant load, muscle shortens
➢Tension > load

Question 4

what is an isometric contraction

Answer 4

Constant muscle length
* Free object: load = tension
* Fixed object: load => tension

Question 5

what is an eccentric contraction

Answer 5

• LENGTHENING CONTRACTION (eccentric contraction)
  ➢Muscle length increases
  ➢load > tension

Question 6

what is a twitch

Answer 6

The mechanical response of a
muscle fibre to a single action
potential

Question 7

what is the latent period

Answer 7

After the action potential, there is a
latent period(few milliseconds)
before the tension in the muscle
fibre begins to increase.

Question 8

what is the contraction time

Answer 8

The time interval from the beginning
of tension development (at the end
of the latent period) to the peak
tension is the contraction time.

Question 9

in a concentric contraction increasing the load will cause

Answer 9

• The latent period to increase
• The velocity of shortening to slow down
• The total duration of the twitch to become shorter
• The distance shortened to become less

Question 10

concentric contraction with the absence of load

Answer 10

a shortening contraction
reaches its maximum shortening velocity
* When the load increases to the point where the
muscle is not able to move it, then the contraction
becomes isometric
* When the load increases beyond the peak tension
that a muscle can produce, the contraction becomes
lengthening (eccentric)

Question 11

what is summation

Answer 11

The increase of muscle tension from successive action potentials

Question 12

what happens if you narrow the twitch times

Answer 12

you will get a larger and much longer duration of tension produced

Question 13

what is tetanus

Answer 13

when successive stimulation result in a sustained contraction

Question 14

what is unfsued tetanus

Answer 14

the muscle fiber has time to partial relax before the next stimulation, the tension then oscilliates

Question 15

what is fused tetanus

Answer 15

the muscle fiber has no time to relax

Question 16

length tension relationship

Answer 16

the shorter the muscle fiber leads to less cross bridges due to an overlap, the muscle can no longer shorten meaning their is less tension produced

at the optimal/ resting lengthen of the muscle their is maximal tension produced

at the muscle lengthened completely will produce lower tension due to cross bridges cant go together due to the distance between them

Question 17

what is passive tension

Answer 17

tension relased when the muscles starts to lengthen

Question 18

what are the 3 characters that differ between muscle fibers

Answer 18

• Primary mechanisms used to produce ATP
• Type of motor neuron innervation
• Type of myosin heavy chain expressed

Question 19

what are the 3 muscle fiber types

Answer 19

• IIx: Fast-twitch, fast-glycolytic fibres
• IIa: Intermediate fibres, fast-oxidative glycolytic fibres
• I: Slow-twitch, slow-oxidative fibres

Question 20

differences in slow twitch and fast twitch fibers

Answer 20

oxidative are red/black coloured aswell as surroned by mitrocondria

fast glycolic has a higher surface area

Question 21

muscle fiber differences

Answer 21

• On average 45 –55% type I fibres in arm and
  leg muscles
• No gender differences in fibre distribution
• Large intra-individual variation
• Trend in distribution consistent across
  muscle groups

Question 22

muscle fiber: production of ATP

Answer 22

Slow oxidative fibres:
Low ATPase activity, highly oxidative

Fast oxidative fibres:
High ATPase activity, highly
oxidative/moderately glycolytic

Fast glycolytic fibres:
High ATPase activity, highly
glycolytic

Question 23

what influences muscle contraction speed

Answer 23

• Muscle contraction speed (shortening velocity) depends on the rate
  of cross bridge cycling(calcium cycling)
• … which depends on the myosin heavy chain isoform
• Shortening results in changes in the I band but not the A band

Question 24

what mechanisms are involved with muscle fatigue

Answer 24

1.CONDUCTION FAILURE Caused by potassium accumulation in
the T-tubules Fast recovery

2.LACTIC ACID BUILDUP Acidic environment in muscle affects the
physiological functioning of proteins and the mechanisms involved in calcium release and re-uptake

3.INHIBITION OF CROSS-BRIDGE CYCLING Accumulation of ADP and Pi in muscle fibres slows down the cross-bridge cycling by preventing the release of cross-bridges from actin molecules

4.FUEL SUBSTRATES Muscle glycogen, blood glucose, dehydration.

5.CENTRAL COMMAND FATIGUE Failure to propagate signals from
the brain to the motor neurons

Question 25

what are the techniques to determine fiber type

Answer 25

Colour of fibre (~1900)
* EMG identification of motor units (~1950)
* Fibre speed and oxidative capacity (~1970)
* Myosin heavy chain isoform (~1990)
* Genomic nomenclature (~2000)
Gene expression e.g. slow / fast contractile speed families,
mitochondrial gene families