Week 4 - Muscle Structure

Question 1

How many skeletal muscles make up the human body

Answer 1

Human body contains up over 600 skeletal muscles. Which makes up 40-50% of body mass

Question 2

Functions of skeletal muscle

Answer 2

1. Force production for locomotion and breathing
2. Force production for postural support
3. Heat production during cold stress
4. Acts as an endocrine organ

Question 3

What are the muscle actions?

Answer 3

Flexors (decrease angle at the joint)
Extensors (increase angle at the joint)
Attached to bones by tendons (origin end(fixed), insertion end moves))

Question 4

Connective tissue surrounding skeletal muscle

Answer 4

Epimysium - surrounds entire muscle
Perimysium - surrounds fascicles
Endomysium - surrounds muscle fibers
basement membrane - just below endomysium
Sarcolemma - muscle cell membrane

Question 5

What are myofibrils

Answer 5

Contain contractile proteins, actin - thin filament, myosin - thick filament

Question 6

What does the sarcomere have

Answer 6

Includes Z line, M line, H zone, A band and I band

Question 7

What the role of sarcoplasmic reticulum
(ON SHEET)

Answer 7

Storage cites for calcium
Terminal cistercae

Question 8

Whats the role of transverse tubules
(ON SHEET)

Answer 8

Extend from sarcolemma to sarcoplasmic reticulum

Question 9

Whats the role of satelite cells
(ON SHEET)

Answer 9

Play a key role in muscle repair. During muscle growth satelite cells increase the number of nuclei in mature muscel fibres

Question 10

What is the myonuclear domain
(ON SHEET)

Answer 10

Volume of sarcoplasm surrounding each nucleus. Each nucleus can support a limited myonuclear domain.
More myonuclei allows for greater protein synthesis

Question 11

Whats the impact of increased or decreased myonuclei
(ON SHEET)

Answer 11

Increased myonuclei -> muscle hypertrophy
Decreased myonuclei -> muscle atrophy

Question 12

What is the neuromuscular junction

Answer 12

Junction between motor neuron and muscle fiber

Question 13

Whats the motor end plate

Answer 13

Pocket formed around motor neuron by sarcolemma

Question 14

Whats the neuromuscular cleft

Answer 14

Short gap between neuron and muscle fiber

Question 15

What is acetylcholine (ACh)
(ON SHEET)

Answer 15

It is a neurotransmitter released from the motor neuron.
Causes an end plate potential (EPP)
Depolarization of muscle fiber
Signal for muscle contraction

Question 16

What is the sliding filament model
(ON SHEET)

Answer 16

It is a model of muscle contraction. Muscle shortening occurs due to the movement of the actin filament over the myosin filament.
Reduction in the distance between Z lines of the sarcomere

Question 17

What is the cross bridge formation in the sliding filament model
(ON SHEET)

Answer 17

Actin and myosin form to create a power stroke

Question 18

What is muscle fatigue

Answer 18

A decline in muscle power output

Question 19

What leads to a decline in muscle power output

Answer 19

Decrease in muscle force production at the cross-bridge level
Decrease in shortening velocity

Question 20

Why are the causes of fatigue multifactorial

Answer 20

The cause of muscle fatigue depends on the exercise intensity that produce fatigue

Question 21

What are the steps of excitation-contraction coupling
(ON SHEET)

Answer 21

1. Signal from motor nerve fiber enters synaptic knob.
2. Synaptic vesicles release acetylcholine across synaptic cleft and to the ACh receptors on the sarcolemma of muscle fibre.
3. Release of ACh causes excitation of muscle fibre, which then travels to the T tubule and causes depolarization.
4. Depolarization opens calcium ion channels from sarcoplasmic reticulum and terminal cisterna of sarcoplasmic reticulum
5. Calcium ions bind to troponin on actin molecule, which causes a shift in the position of tropomyosin so that the myosin binding sites on actin are exposed. An ATP is used in this step.
   6-8. Energized myosin cross-bridge binds to the active site on actin and pulls on the actin molecule to
   produce a back and forth movement.
6. ACh release stops, and the muscle fiber is repolarised.
7. Calcium is pumped from the cytosol into the sarcoplasmic reticulum

Question 22

What are the main characteristics of moderate intensity exercise

Answer 22

Exercise intensity relative to lactate threshold - < lactate threshold
% maximal heart rate - 50 to 75%
%Vo2 max - <60%
Subjet perception of exercise intensity - light to somewhat hard

Question 23

What are the main characteristics of heavy intensity exercise

Answer 23

Exercise intensity relative to lactate threshold - >lactate threshold
%maximal HR - 76 to 85%
%Vo2 max - 60 to 75%
Subject perception of exercise intensity - Hard

Question 24

What are the main characteristics of very heavy intensity exercise

Answer 24

Exercise intensity relative to lactate threshold - >lactate threshold
%maximla heart rate - 86 to 100%
% Vo2 max - 76 to 100%
Subject perception of exercise intensity - Very hard

Question 25

What are the main characteristics of severe intensity exercise

Answer 25

Exercise intensity relative to lactate threshold- > lactate threshold %maximal heart rate - 100% %Vo2 max >100% Subject perception of exercise intensity - all out exercise

Question 26

What are some of the possible causes of fatigue due to heavy intensity exercise (ON SHEET)

Answer 26

Decreased Ca2+ release from sarcoplasmic reticulum Accumulation of metabolites that inhibit myofilament sensitivity to Ca2+

Question 27

What are some of the possible causes of fatigue due to moderate intensity exercise (ON SHEET)

Answer 27

Increased radical production Glycogen depletion

Question 28

What often causes EAMS

Answer 28

Likely caused by hyperactive motor neurons in spinal cord High intensity exercise can alter muscle spindle and golgi tendon organ function

Question 29

What are some strategies that can be used to alleviate EAMS

Answer 29

Passive stretching often relieves this type of muscle cramp Possible that activating ion channels in mouth/throat could send inhibitory signals to spinal cord, and thus inhibit overactive motor neurons

Question 30

What are the 3 main characteristics important to muscle fiber type function

Answer 30

Oxidative capacity Type of myosin isoform expressed Abundance of contractile protein within the fibre

Question 31

What are some of the main characteristics of type 2x fast fibers

Answer 31

Number of mitochondria - Low Resistance to fatigue - Low Predominant energy system - Anaerobic ATPase activity - Highest Vmax - Highest Efficiency - Low Specific Tension - High

Question 32

What are the key characteristics of Type 2a fast fibers

Answer 32

Number of mitochondria - High/moderate Resistance to fatigue - High/moderate Predominant energy system - Combination ATPase activity - High Vmax - High Efficiency - Moderate Specific Tension - High

Question 33

What are the key characteristics of type 1 slow fibers

Answer 33

Number of mitochondria - High Resistance to fatigue - High Predominant energy system - Aerobic ATPase activity - Low Vmax - Low Efficiency - High Specific Tension - Moderate

Question 34

How is the shortening speed different between fiber types

Answer 34

Speed of shortening is greater in fast fibres SR releases CA2+ at faster rate Higher ATPase activity

Question 35

Whats the effects of motor unit amount and speed for force productio

Answer 35

More motor units = greater force fast motor units = greater force

Question 36

How are muscle fibres innervated

Answer 36

Eahc mature fibre is innervated by a single axon

Question 37

What are the characteristics of motoneurons that supply larger faster motor units

Answer 37

Larger cell bodies Larger diameter axons Greater number of axonal branches Sparse afferent innervation More complex and extensive motor end plate of neuromuscular junction

Question 38

What is the Henneman Size Principle

Answer 38

Consistent pattern of recruitment. small = low force, large = high force Progressive recruitment of units, force increased in a step-wise manner

Question 39

Whats the size principle of motor units

Answer 39

Slow motor units have easily excited motor neurones Fast motor units have higher threshold motor neurones - harder to excite

Question 40

What is the muscle force velocity relationship

Answer 40

At any absolute force exerted by the muscle, the speed of movement is greater in muscles with a higher percentage of fast-twitch fibers Maximum velocity of shortening is greatest at the lowest force

Question 41

What is the muscle force-power relationship

Answer 41

At any given velocity of movement, the peak power generated is greater in a muscle with a higher percentage of fast- twitch fibers.

Question 42

Aging and muscle loss on muscle function

Answer 42

Age-related muscle loss-sarcopenia 10% muscle mass lost between age 25 to 50 years Additional 40% lost between age 50 to 80 years Also a loss of fast fibers and gain in slow fibers resistance training can delay age-related muscle loss

Question 43

Diabetes and muscle function

Answer 43

Disease related muscle loss-cachexia Associated with progressive loss of muscle mass Adds to the age-related loss of muscle mass Aerobic and resistance training are protective

Question 44

Cancer and muscle loss

Answer 44

50% of cancer patietns suffer cachexia Results in weakness, accounts for 20% deaths in cancer patients Regular exercise and nutrition therapy may counteract cachexia

Question 45

Muscular dystrophy and muscle function

Answer 45

Hereditary defects in muscle protein Results in loss of muscle fibers and weakness Duchene muscular dystrophy is most common in childhood