skeletal muscle structure and function

Question 1

how many skeletal muscle does the human body have?

Answer 1

• 600

Question 2

functions of skeletal muscle

Answer 2

• force production for locomotion and breathing
• force production for postural support
• heat production during cold stress
• acts an endocrine organ

Question 3

structure of skeletal muscle

Answer 3

muscle > fascicles > muscle fibres > endomysium >muscle cell membrane

Question 4

connective tissues in skeletal muscle

Answer 4

1. epimysium = surrounds entire muscle to keep intact
2. perimysium = surrounds fascicles
3. endomysium = surrounds fibres
4. basement membrane = below endomysium
5. sarcolemma = muscle cell membrane

Question 5

structure of muscle fibre

Answer 5

1. myofibrils
2. sarcomere
3. sarcoplasmic reticulum
4. transverse tubules

Question 6

describe myofibrils

Answer 6

• contains contractile proteins (actin thin and myosin thick)
• made up of the smallest contractile unit called sarcomere

Question 7

describe sarcomere

Answer 7

• actin and myosin filaments part of this structure
• includes Z line, M line, H zone, A band, I band

Question 8

describe sarcoplasmic reticulum

Answer 8

• storage site of calcium
• terminal cisternae

Question 9

describe transverse tubules

Answer 9

• extend from sarcolemma to sarcoplasmic reticulum

Question 10

what are satellite cells

Answer 10

• key in muscle growth and repair - in muscle growth they increase number of nuclei in mature muscle fibres
• near the sarcolemma

Question 11

what is the neuromuscular junction

Answer 11

• between motor neuron and muscle fibre
• comes down from spinal cord and sits on sarcolemma of muscle cell
  communicate through synaptic cleft
• synaptic vesicles containing neurotransmitter
• acetylcholine released cause EPP depolarising macula fibre and signal contraction

Question 12

what is the sliding filament model

Answer 12

• muscle contraction
• muscle shortening due to movement of actin filament over myosin filament
• cross-bridge formation- actin and myosin create power stroke
• troponin sits on actin filament covering calcium binding site on action
• tropomyosin intertwined around actin protein
• myosin - thick filament and its head binds to actin generating contraction
• actin - proteins covering the binding sites

Question 13

step by step of cross bridge cycle

Answer 13

1. energy required so one ATP molecule binds to myosin head
2. ATP hydrolysis to ADP+Pi = myosin head binds to actin site
3. release of Pi and ADP = power stroke where actin slides over the myosin filament
4. myosin relates from actin for ATP to bind to myosin head

Question 14

what is excitation-contraction coupling

Answer 14

• brings together neuromuscular junction and sliding filament theory
• the sequence of events where nerve impulse reaches muscle membrane and leads to muscle shortening by cross-bridge activity

Question 15

calciums role in contractions

Answer 15

• mediated by calcium
• increase of membrane potential and calcium release facilitates contractions to occur

Question 16

step by step excitation coupling

Answer 16

1. signal from motor nerve fibre enters synaptic knob
2. synaptic vesicles recast Ach across cleft and to receptors on muscle fibre
3. release of Ash causes excitation travelling to T tubule causing depolarization
4. depolarization opens calcium ion channels from sarcoplasmic reticulum
5. calcium ions bind to troponin on actin molecule, shift in tropomyosin so myosin binding sites on actin are exposed
6. myosin cross-bridge binds to active site on actin and pulls on actin molecule
7. Act release stops and fibres repolarised
8. calcium pumped from cytosol into sarcoplasmic reticulum

Question 17

explain muscle fatigue

Answer 17

• decline in muscle power due to decrease in muscle force production at cross-bridge level and decrease in muscle shortening velocity