L1-2 Revision

Question 1

What is the hierarchical structure of a muscle?

Answer 1

Sacromere -> Myofibrils -> Myofibres -> Fasicles

Question 2

What are the 3 myofibril orientations? And what does the pennation angle determine?

Answer 2

1. Fusiform
2. Unipennate
3. Bipennate

Pennation angle determines how much fibres able to be packed, Structure of the muscle → dictates function of muscle

Question 3

What is the mechanism of EC coupling?

Answer 3

1) AP down T-tubules
2) through DHP receptors
3) signals SR to release Ca²⁺

Question 4

What is the mechanism of the cross bridge cycle?

Answer 4

1. Rigor 45o bound
2. ATP binds → dissociate
3. ATP hydrolyses → ADP + Pi → swing → 90o bound
4. Release Pi → power stroke
5. ADP released → 45o rigor state

Question 5

Where is the location of the nucleus for healthy and injured muscle fibres?

Answer 5

healthy – periphery;

injured – centre

Question 6

What is the function of Titin?

Answer 6

provides elasticity and stabilises myosin

Question 7

What happens if you lose the cytoskeleton (actin, dystrophin, spectrin) of the muscle fibre?

Answer 7

Lose structure of muscles

Question 8

Which one is dark/light for actin and myosin?

Answer 8

 Actin = light (Thin)

 Myosin = dark (thick) - also has ATPase site & actin binding site

Question 9

What is Miometric and Pilometric?

Answer 9

 Miometric = Concentric

 Pilometric = Eccentric

Question 10

What does the ascending, plateau, and descending portion of the length-tension graph signify?

Answer 10

1. Ascending: Sacromere is short, overlap is not optimal
2. Plateau: Optimal overlap
3. Descending: Sacromere long, little or no overlap

Question 11

What happens during initial contraction?

Answer 11

Latent period where muscle is contracting isometrically → Until sufficient tension produced equal to the load

Question 12

What is power?

Answer 12

 Power = load x velocity

Question 13

What is a motor unit?

Answer 13

 Motor Unit = Motor Neuron + the Muscle Fibres it innervates

Question 14

Different fibre to nerve ratios?

Answer 14

 Delicate muscles (eye muscles): low fibre : nerve ratio

 Strong muscles (Quads): High fibre: nerve ratio

Question 15

What are the 3 different types of muscle fibres in humans?

Answer 15

1. Fast-fatigue (↑force) – fast glycolytic histochemical

 Type 2X – relies on glycolysis

2. Fast-resistant (mid force) – fast oxidative glycolytic

 type 2A – relies on oxidation & glycolysis

3. Slow (↓force) – slow oxidative

 Type 1 MyHc – relies on oxidation

Question 16

What is the Hanneman’s size principle?

Answer 16

• recruits slow (small) motor units first → ↑intensity → recruits stronger (large) motor units
• Therefore highly oxidative (slow) units are used most
• Fast Motor units are unsustainable → because of the depletion of glycogen
• Large Motor Units may sometimes be inexcitable → cannot be recruited voluntarily

Question 17

What is the muscle spindle reflex?

And what/where are the extrafusal & intrafusal muscle fibres located?

Answer 17

Muscle spindle reflex: Length detector; protective stretch reflex (In central part of intra)

Parallel to contractile extrafusal muscles (α-Motor Neurons)
Intrafusal contractile ends (innervated by γ-Motor Neurons) – 2o (flower spray) endings
Intrafusal central part lacks myofibrils – does not contract – 1o (annulospiral) endings wrap around → projects to spinal cord (fires when stretched)

Detects stretch & speed

Question 18

What is α-γ coactivation?

Answer 18

1) α innervates contractile extrafusal; γ innervates contractile intrafusal
2) Extrafusal and Intrafusal contracts
3) Centre of intra fibres stretched (caused by extrafusal contraction), needs to remain a constant length → stretch counteracted by intrafusal contraction stretching the centre of intrafusal the other way

Question 19

How is muscle tone maintained?

Answer 19

(Tonically active)

1) Fires AP when muscle is at resting length
2) AP → spinal cord → α-motor neurons
3) Tonic excitation in extrafusal
4) Maintains tone at rest

Question 20

What is the Golgi Tendon Organ reflex?

Answer 20

Golgi tendon organs: Force detector; Protects muscle from damage (In myotendinous junction)

Inhibits α-Motor Neurons → ↓contraction → Reflex relaxation

1) Responds to stretch and contraction
2) Muscles contract → Pulls tendon → GTO fire

Question 21

What is the knee jerk reflex?

Answer 21

Knee Jerk reflex: Monosynaptic reflex; Myotatic Unit (Collection of pathways controlling a single joint)

Reciprocal inhibition

1) Tap patellar → Stretch Quads
2) Spindles activated → Spinal Cord → Activate Quads & Inhibit Hamstrings

Question 22

What is the pain reflex arc?

Answer 22

Pain (flexion) reflex:

1) Nociceptors → sensory neurons
2) Move effectors away from stimuli
3) Maintain balance

Requires multiple excitations & relaxations