Skeletal Muscle

Question 1

What is the function of skeletal muscle?

Answer 1

Movement, stability, posture, thermoregulation and storing and moving substances

Question 2

What is the anatomy of the muscle?

Answer 2

Muscle belly consists of the epimysium (deep fasciae wrapped around everything) Fascicle - surrounded by the perimysium - one bundle of muscle fibres Endomysium- between tissue
Muscle fibre - multinucleated - myonuclear domain ceiling - amount of muscle fibre that it can interact with
Sarcoplasm - cytoplasm of muscle cell
Membrane around this is the sarcolemma
Myofibrils - contain sarcomere

Question 3

What is the structure of the sarcomere?

Answer 3

Joined in series and parallel to one another made of myofilaments - the functional units of muscle

Question 3

Outline the structure of myosin

Answer 3

Thick, darker band
2 subunits
S1- Globular heads - actin binding sites
S2 - Flexible region and tail

Question 4

Outline the structure of actin

Answer 4

Thin filament
Double helical strands
Tropomyosin interacts with actin and cover binding sites for myosin

Question 5

What is the overall structure of the sarcomere?

Answer 5

Z line - end of one sarcomere
I band - only actin
M line - middle line
A band - both actin and myosin
H zone - only myosin

Question 6

What are the structural proteins?

Answer 6

Titin - spring like if the muscle is stretched then titin will bring the fibres back to their position
Nebulin and desmin - support parts of the cell keeping them in place

Question 7

What is the sliding filament mechanism?

Answer 7

When contracting filaments slide past each other they are unchanged in length but the gross muscle length changes

Question 8

What is the sarcoplasmic reticulum?

Answer 8

Interconnected tubules surrounding myofibrils
Stores and releases calcium

Question 9

Outline the cross bridge cycle

Answer 9

1. AP arrives
2. Ca2+ released from SR
3. Ca2+ attaches to troponin
4. Tropomyosin moves uncovering binding sites
5. ATP hydrolysed which changes angle of the myosin head forming the cross bridge
6. Pi released from myosin head changes angle of it leading to the powerstroke ( movement)
7. Myosin head picks up another ATP and bond with actin is released
   8.Repeats until Ca2+ or ATP levels drop

Question 10

What is the length tension relationship?

Answer 10

When filaments overlap they cant generate tension
When the muscle stretches no longer butting against the z line so able to produce tension
When the sarcomeres are elongated so low tension as no overlap between actin and myosin

Question 11

What is the force velocity relationship during shortening?

Answer 11

Force in shortening is less than the isometric force as the faster the movement the less time myosin heads have to attach to binding sites

Question 12

What is the force velocity relationship is lengthening?

Answer 12

Force during lengthening is greater than the isometric force
Compliant portion of myosin is stretched further than during the isometric force
Forcible detachment of the myosin heads with the stretch

Question 13

What are the qualities of type 1 muscle fibres?

Answer 13

Small cross sectional area
MHC 1
Low force
slow shortening velocity
weak power
Red
Oxidative / fat
High mitochondrial density
High endurance

Question 13

What are the qualities of type IIa?

Answer 13

Medium cross sectional area
MHC IIa
Intermediate force
Fast shortening velocity
Intermediate power
Pink
Fat and glycogen
Intermediate mitochondrial density and endurance

Question 14

What are the qualities of type IIX?

Answer 14

Large cross sectional area
MHC IIX
High force
Very fast shortening velocity
Strong power
White
Glycogen/ PCr
Low mitochondrial density and endurance

Question 15

What is a motor unit?

Answer 15

A single motor neuron and all the fibres it innervates
Fine and gross movements have different sized motor units

Question 16

What is the neuromuscular junction?

Answer 16

Motor neuron meets the muscle fibre
Motor end plate - pocket formed around motor neuron by sarcolemma
Synaptic cleft - short gap between neuron and motor end plate
Ach - released from motor neuron leading to depolarisation of motor end plate

Question 17

What is the golgi tendon organ?

Answer 17

Detects tension in the tendon when the muscle contracts
Has an inhibitive afferent neuron
Large forces causes the GTO to decrease muscle activation

Question 18

What is the muscle spindle?

Answer 18

Highly specialised intrafusal muscle fibres positioned parallel to normal muscle fibres
Detects changes in length
Efferent neuron cause the spindle to contract to maintain tension in the middle of the fibres
Hence if muscle is stretching rapidly a contraction occurs preventing overstretching