Muscle Structure and Function

Question 1

How much skeletal muscle is present in normal young people?

Answer 1

• About 40% male bodyweight

- About 30% female bodyweight

Question 2

What is the principle function of skeletal muscle and how does it do this?

Answer 2

• Principle function is contraction/ shortening distance between bones.
• Skeletal muscle moves bones attached to it by tendons.
• Muscle groups work together
• When a muscle contracts, its insertion is pulled towards its origin.

Question 3

Where does more force come from in skeletal movement?

Answer 3

• More complete activation of one muscle
• More activation of agonist muscle
• More inactivation of antagonist muscles.

Question 4

What are the levels of skeletal muscle structure from most superficial to deep?

Answer 4

• Whole muscle
• Fasicles
• Muscle fibre (cell)
• Myofibrils
• Sarcomeres

Question 5

What are fasicles?

Answer 5

-Bundles of cells surrounded by connective tissue

Question 6

What provides strength of muscle fibres?

Answer 6

-Strength of muscle fibres comes from bundling.

Question 7

What are the histological layers of skeletal muscle?

Answer 7

• Thick epimyseium
• Perimyseium
• Endomyseium

Question 8

What is a motor unit?

Answer 8

• A single motor neurone and all the muscle fibres it innervates.
• The functional units of motor control
• Final common pathway for info leaving the CNS.

Question 9

How many motor units does a muscle contain and how many muscle fibres would a motor unit contain?

Answer 9

• A muscle may contain 100’s of motor units and each motor unit may contain 100’s of muscle fibres.
• These ammounts will relate to the function of the muscle in question and the size of the muscle.

Question 10

What factors would impact no. of fibres, motor units and muscle fibres in a motor unit?

Answer 10

• No. of fibres = size of muscle
• No. of motor units = size and funtion
• No. of muscle fibres in a motor unit = function

Question 11

What are some things to be careful about when talking about motor units?

Answer 11

• Muscle characteristics are different species by species.
• In any one species, different muscles have different properties.
• In any one muscle in any one species, the motor units have very different properties.

Question 12

What are some classification properties of motor units?

Answer 12

-Mechanical: twitch responses; speed, force, rate of fatigue.
-Histological: metabolic profile; oxidative, glycolytic; aerobic or anaerobic, myosin ATPase activity
-Motor neurone properties: cell body size, axon diameter, synaptic inputs, axon branching
-Other: Colour; red/white
Use; phasic (tends to be pale, more glycolytic, faster contracting and fatiguing)/tonic (tends to be red, oxidative, slow contracting.

Question 13

What is the most simple and common motor unit classification?

Answer 13

-By speed of contraction and fatigue rate

Question 14

What are the 3 main types of motor units?

Answer 14

• Slow (S or type 1) (smaller twitch, slower fatigue)
• Fast fatigue resistant (FFR, 2a)
• Fast fatiguing (FF, 2b, 2x etc.) (larger twitch, faster fatigue)

Question 15

What determines the properties of motor units?

Answer 15

• Genetics
• Probably pattern of use
• Probably not training

Question 16

What is the training response in humans?

Answer 16

• Changes muscle size
• Changes properties like strength and endurance
• In humans evidence for changes in fibre type is poor.
• Thus it can be deduced that training in humans causes selective hypertrophy rather than type conversion.

Question 17

What is the muscles response to strength training?

Answer 17

• Early changes: better motor unit activation, less antagonist activation, improved glycolytic metabolism
• After 6 weeks: FF fibre hypertrophy

Question 18

What is the muscles response to endurance training?

Answer 18

• Enhanced oxidative metabolic profile
• More mitochondria
• Improved O2 supply
• More myoglobin
• Slow and FFR fibre hypertrophy

Question 19

What types of fibres are associated with high force output?

Answer 19

-Associated with more type II fibres

Question 20

What types of fibres are associated with endurance output?

Answer 20

-More type 1 fibres

Question 21

What is fatigue?

Answer 21

-Is a failure to produce the desired/expected force in the short/long term

Question 22

What stages of skeletal muscle activation are mostly affected by fatigue?

Answer 22

-In summary, mainly affects: failure of t-tubule system and less effective Ca+ release and uptake.