L1-2 Revision Flashcards
What is the hierarchical structure of a muscle?
Sacromere -> Myofibrils -> Myofibres -> Fasicles
What are the 3 myofibril orientations? And what does the pennation angle determine?
- Fusiform
- Unipennate
- Bipennate
Pennation angle determines how much fibres able to be packed, Structure of the muscle → dictates function of muscle
What is the mechanism of EC coupling?
1) AP down T-tubules
2) through DHP receptors
3) signals SR to release Ca2+
What is the mechanism of the cross bridge cycle?
- Rigor 45o bound
- ATP binds → dissociate
- ATP hydrolyses → ADP + Pi → swing → 90o bound
- Release Pi → power stroke
- ADP released → 45o rigor state
Where is the location of the nucleus for healthy and injured muscle fibres?
healthy – periphery;
injured – centre
What is the function of Titin?
provides elasticity and stabilises myosin
What happens if you lose the cytoskeleton (actin, dystrophin, spectrin) of the muscle fibre?
Lose structure of muscles
Which one is dark/light for actin and myosin?
Actin = light (Thin)
Myosin = dark (thick) - also has ATPase site & actin binding site
What is Miometric and Pilometric?
Miometric = Concentric
Pilometric = Eccentric
What does the ascending, plateau, and descending portion of the length-tension graph signify?
- Ascending: Sacromere is short, overlap is not optimal
- Plateau: Optimal overlap
- Descending: Sacromere long, little or no overlap
What happens during initial contraction?
Latent period where muscle is contracting isometrically → Until sufficient tension produced equal to the load
What is power?
Power = load x velocity
What is a motor unit?
Motor Unit = Motor Neuron + the Muscle Fibres it innervates
Different fibre to nerve ratios?
Delicate muscles (eye muscles): low fibre : nerve ratio
Strong muscles (Quads): High fibre: nerve ratio
What are the 3 different types of muscle fibres in humans?
- Fast-fatigue (↑force) – fast glycolytic histochemical
Type 2X – relies on glycolysis
- Fast-resistant (mid force) – fast oxidative glycolytic
type 2A – relies on oxidation & glycolysis
- Slow (↓force) – slow oxidative
Type 1 MyHc – relies on oxidation
What is the Hanneman’s size principle?
- 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
What is the muscle spindle reflex?
And what/where are the extrafusal & intrafusal muscle fibres located?
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
What is α-γ coactivation?
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
How is muscle tone maintained?
(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
What is the Golgi Tendon Organ reflex?
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
What is the knee jerk reflex?
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
What is the pain reflex arc?
Pain (flexion) reflex:
1) Nociceptors → sensory neurons
2) Move effectors away from stimuli
3) Maintain balance
Requires multiple excitations & relaxations
