Lecture 12 - Skeletal Muscle Performance and Plasticity

Question 1

what are the 3 types of muscle fibres?

Answer 1

type I fibres
type IIB fibres
type IIA fibres

Question 2

what are the 3 key differences between the fibre types?

Answer 2

type of myosin expressed
oxidative vs glycolytic energy production
type of SERCA pump expressed

Question 3

what is effect of the type of myosin expressed?

Answer 3

• determines fast or slow utilisation of ATP
• alters the speed of cross bridge cycling –> fast or slow speed of contraction
• fast or slow rate of utilisation of substrate for ATP generation –> fatigue prone or fatigue resistant

Question 4

what is the effect of oxidative vs glycolytic energy production?

Answer 4

• high oxidative activity from mitochondria can generate ATP continuously using O2 and substrates from blood but only relatively slowly (also high myoglobin)
• high glycolytic activity can generate ATP quickly from muscle glycogen but stores are limited and deplete quickly

Question 5

what is the effect of the type of SERCA pump expressed?

Answer 5

-faster or slower clearance of Ca2+ from the sarcoplasm into the sarcoplasmic reticulum (SR) –> faster or slower drop in tension

Question 6

what are muscle fibre distribution based on?

Answer 6

based on function

Question 7

where are fast twitch muscle fibres distributed?

Answer 7

distributed in muscles that aren’t often used but when they are used they are rapid power producing but susceptible to fatigue

Question 8

what is an example of a muscle composed of fast twitch muscle fibres?

Answer 8

the biceps brachii

Question 9

where are slow twitch muscle fibres distributed?

Answer 9

distributed in muscles that are low power and fatigue resistant as these muscles are used often

Question 10

what is an example of a muscle composed of slow twitch muscle fibres?

Answer 10

the soleus

Question 11

how does strength training effect skeletal muscle?

Answer 11

strength training generates more actin and myosin and this increases the diameter of muscle fibres which is called hypertrophy

Question 12

what is hypertrophy in terms of skeletal muscle?

Answer 12

increase in the size of tissues by the increase of cell size that generates more actin-myosin interactions producing more force

Question 13

how does endurance training effect skeletal muscle?

Answer 13

endurance training increases the oxidative capacity which increases the ability for sustained activity. This is because endurance training increases the number of mitochondria (more oxidative enzymes), increases capillaries + myoglobin, increases muscle stores of lipids and increases the ability of these lipids to be used directly from the blood

Question 14

what do mitochondria produce in terms of enzymes?

Answer 14

oxidative enzymes

Question 15

what is muscle contraction in terms of tension?

Answer 15

muscle contraction is the generation of tension

Question 16

what is isotonic contraction?

Answer 16

contraction where force is held constant while the muscle length changes

Question 17

what is isometric contraction?

Answer 17

contraction where length is held constant as the contraction does not require skeletal muscle shortening

Question 18

what is an eccentric contraction?

Answer 18

contraction where force exceeds the force of the muscle resulting in muscle lengthening

Question 19

what is a concentric contraction?

Answer 19

contraction where the force generated by the muscle is less than the muscle force at rest so the muscle begins to shorten

Question 20

what determines the amount of force skeletal muscle can generate in different types of contractions?

Answer 20

changes based on the length of the muscle and speed of contraction

Question 21

when is the length-tension relationship of skeletal muscle performed?

Answer 21

performed in an isometric contraction where skeletal muscle length is fixed at set points

Question 22

what is the relationship between skeletal muscle recoil and the amount of force applied?

Answer 22

skeletal muscle wants to naturally recoil due to its elastic properties and the more force applied increases the desire to recoil

Question 23

what is passive tension?

Answer 23

the longer muscle is stretched it means more force has been applied to stretch the muscle further

Question 24

what is the relationship between passive tension and stretching a muscle?

Answer 24

as you stretch a muscle you can measure greater and greater passive tension due to the elastic component of muscle causing it to act like a rubberband

Question 25

what is active tension?

Answer 25

when you electrically stimulate skeletal muscle resulting in a twitch

Question 26

what determines the size of a skeletal muscle twitch?

Answer 26

the length of skeletal muscle

Question 27

why does the active tension curve (graph) not go all the way down to zero?

Answer 27

because it is hard to get skeletal muscle shorter than its resting length

Question 28

what is the relationship between normal resting length of skeletal muscle and force generated from a muscle twitch?

Answer 28

at normal resting length you can generate the peak amount of force in a muscle twitch

Question 29

what is the active tension curve due to?

Answer 29

due to the amount of cross bridge interactions

Question 30

what allows a high velocity of muscle shortening?

Answer 30

if there is no external weight when shortening the muscle allowing it to occur very quickly

Question 31

what does speed or velocity of muscle shortening determine?

Answer 31

determines how much force can be generated by the number of cross bridges

Question 32

how does the nervous system regulate muscle force?

Answer 32

regulates muscle force by controlling activity in ‘motor units’

Question 33

what is a motor unit?

Answer 33

a motor neuron and all the muscle fibres it innervates

Question 34

what are the properties of motor units?

Answer 34

• all muscle fibres in one motor unit are the same metabolic type (fast or slow ATPase)
• all fibres in a motor unit activate at once

Question 35

what determines the maximum force generated from a motor unit?

Answer 35

the size of the motor unit which is determined from the size of the motor neuron cell body depending on the number of muscle fibres in one motor unit

Question 36

what is the muscle force regulated by?

Answer 36

regulated by changing the rate of activity in each motor unit (rate modulation/ mechanical summation) or by changing the number of units that are active (recruitment

Question 37

what is the order of motor unit recruitment?

Answer 37

the recruitment of motor units is ordered from smallest to largest