~L7-8: Muscle Contraction & Energy

Describe the trade off of larger muscles:

Can produce higher peak tension but:

• Consumes more energy, adds weight, decreases mobility

ATP is generated from:

the breakdown/catabolism of glucose, lipids, organic molecules

________ is a form of anaerobic ATP synthesis and occurs within the ________ . It ________ O2.

glycolysis - cytosol - doesn’t -

____________ which involves the _________ and ________ is a form of aerobic ATP synthesis occurs within the ________ and ________ O2.

Aerobic metabolism - Citric acid cycle - electron transport chain - mitochondria - requires

___________ metabolism is faster but ___________ and cannot use __________

Anaerobic - produces 2 ATP/Glucose - fatty acids

___________ metabolism is slower but ___________ and __________

Aerobic - 30+ ATP/Glucose - uses fatty acids

Glycolysis:

____________ → __________+ __________

Glucose → Pyruvate + ATP

Aerobic Metabolism:

__________ + __________ → __________+ __________ + __________

Pyruvate + O2 → ATP + CO2 + H2O

• Besides ATP can react with ________ to produce _______, a higher energy phosphate bond compound.

• This process ______ O2 and is very fast/very slow, but _____________

• Creatine - creatine phosphate

• doesn’t require - very fast - rapidly depletes

Resting muscles use ________ respiration of _________ to build an ATP___________ and create ___________ and ___________ stores.

aerobic - free fatty acids - surplus - glycogen - creatine phosphate

Moderately active muscles use _________ respiration of _______and _______ from _________ stores to build an ATP ____________.

aerobic - free fatty acids - glucose - glycogen - requirement

• Muscles at peak activity use _________ respiration using up __________ and ___________ stores.

• Waste products ___________ and ___________ build up.

• Aerobic + Anaerobic - glycogen - CP

• Lactate - Creatine

Muscle fatigue: Reduced ___________ for the same ___________

contractile tension - stimulus

Muscle fatigue impairs a muscle’s ability to ___________ or ___________ the ___________ because of ___________.

initiate - maintain - contraction cycle - rapid ATP production

Fatigue factors that impact ___________:

• Depletion of ____ vesicles in the ______ neuron axon terminal

• Accumulation of ____ in the ________ due to repeated APs

Excitation

• ACh - motor

• K+ - T-tubules (ECF)

Fatigue factors that impact ______:

• Leakage of _____ into the sarcoplasm

• Microtears in _________

• Build up of _________

contraction

• Ca2+

• myofibrils

• Lactate and H+

Recovery from fatigue requires some coordination with the _________.

liver

For short term recovery from fatigue, how is lactate disposed?

• Used in aerobic metabolism at rest

• Goes through gluconeogenesis at the liver

In the long term, ___________ are rebuilt by ___________ cells which proliferate using ___________ in the blood.

myofibrils - myosatellite cells - amino acids

A muscle twitch is the ___________ response of a muscle fiber to a ___________.

contractile - single action potential

Describe the trade off that occurs at myofibrillar hypertrophy:

• Myofibrillar hypertrophy: more myofibrils within a fiber are produced.

• maximal tension production vs energy efficiency

  • Mitochondria can get squished

  • ATP is not sufficient → rapid fatigue

Muscle fibers can vary by ______ timing and ___________, ___________, and ___________ composition.

twitch - protein - tissue - organelle

Type I fibers are fatigue resistant/prone and fast/slow to recover.

resistant - fast

Type IIB are also known as ___________ fibers.

Type IIA are also known as ___________ fibers.

ast-glycolytic

fast-oxidative

Type II fibers are fatigue resistant/prone and fast/slow to recover.

prone - slow

Which type of fiber has slower, longer twitches? Why?

Type I: slow myosins and pumps

Which type of fiber has a higher maximum tension? Why?

Type II: More myofibrils

Which type of fiber is utilized for aerobic exercises? Why?

Type I: more mitochondria and steady oxygen supply (more capillaries) → higher aerobic capacity

Which type of fiber has higher levels of Creatine Phosphate?

Type II: fewer capillaries per fibre

Type IIA fibers will have the characteristic fast contraction speeds of type II fibers but have intermediate __________, __________, _________ and __________ density, and resistance/recovery from _________.

twitch durations - size/power - mitochondria - capillary - fatigue

Describe a motor unit’s activation pattern:

All or none, but not all motor units within a muscle need to be activated for a contraction.

What makes up a motor unit?

Motor units are a single MN + 1-1000 muscle fibers of the same type

The smallest motor units will have ______ fibers that are all type ____ while the largest will have _____ fibers that are all type _______

few - type I - many - type IIB

Explain the Size Principle for motor neuron activation in the spinal cord:

Weak stimuli in the spinal cord will only recruit the smallest motor units.

Synchronous Recruitment:

As stimulus intensity increases, the spinal cord will recruit more fibers which increase in size as per the intensity.

Describe asynchronous recruitment within a sustained contraction:

Similar-sized motor units take turns activating and resting dow the duration of the contraction.

Muscles enhance their peak tension by _________ through _________ or __________(the only one applicable to humans)

becoming larger - hyperplasia - hypertrophy

Hyperplasia:

More myofibers per fascicle → fascicle larger

Note: not possible in humans

Hypertrophy:

more myofibrils per myofibre → increase fiber diameter, larger fascicle

Why can humans only grow muscle size through hypertrophy?

After embryonic development, fibers can be repaired but not created.

Conversion between type ____ and ____ fibers is harder than type ____ and ____

I & II — IIA & IIB

Aerobic training leads to the hypertrophy of type ___ fibers.

Anaerobic training leads to the hypertrophy of type ____ fibres

type I - type IIb

The organelle which contracts within a muscle fiber is the ________, which consists of repeating units called _________ that are made of _________

myofibril - sarcomeres - myofilaments

The ___ band is the distance between the thin filaments.

The ___ band is the distance between thick filaments.

• H

• I

• Thin filaments intersect at the ___ line.

• Thick filaments intersect at the ___ line.

• The distance between two ___ lines is the length of a single sarcomere.

• Z

• M

• Z

Thin filaments have four components:

1. _______ and _______ frame around the helix

2. ______ forms a double helical fibre

3. _________ forms the Z line to interconnect filaments

• Tropomyosin - Troponin

• Actin

• Actinin

Thick Filaments are composed of ______ protein with a mobile head that binds to _______.

________ tethers the thick filament to the Z line

• myosin - actin

• Titin

During contraction, the ___ and ___ bands get shorter as the ____ and ____ filaments slide past each other.

H - I - Myosin - Actin

___________ Period

An action potential sweeps across the _________, then ___ ions will be released from the _________.

Latent - Sarcolemma - Ca+ - sarcoplasmic reticulum (SR)

___________ Phase

0. Ca+ interacts with the _______-________ complex to reveal active sites on _______ for ______ to bind to.

1. Cross bridges form as _____ binds to ______.

Contraction Phase

0. troponin-tropomyosin

1. actin - myosin

_________ Phase

2. The myosin head releases stored energy (_____+___)

3. Power stroke occurs as the myosin ____ pivots towards the ___ line.

Contraction Phase

2. ADP + P

3. neck - M

________ Phase

4. ATP binds to the myosin head to break the bond between ______ and _______

5. Myosin reactivates and ______ when ATP hydrolyzes into _____ and _____.

Relaxation Phase

4. myosin head - actin active site

5. recocks - ADP + P

Muscle tension is produced when ____ shorten. More ____________ increases tension.

sarcomeres - overlap between actin and myosin

Maximum tension is produced at an _______ resting sarcomere length.

intermediate

more Ca+ = more/less tension

more

A ‘twitch’ contraction involves 3 stages:

1. ___________

2. ___________

3. ___________

Maximum tension development occurs between steps ____ and _____.

1. Latent Period

2. Contraction Phase

3. Relaxation Phase

Between contraction and relaxation

________ occurs when a muscle fiber is stimulated repeatedly causing Ca+ build up because….

summation - more Ca2+ enters the cytosol before original Ca2+ is removed = more active sites

________ occurs when a muscle is under persistent tension and reaches maximum stimulation (all ________ is bound to _________)

Tetanus - troponin - calcium

Concentric contractions:

• load >/</= tension

• Muscle shortens/lengthens/neither

• movement/stabilization/slow-down of a joint

• Ex: ____________

• <

• shortens

• movement

• lifting a weight during a bicep curl

Eccentric contractions:

• load >/</= tension

• Muscle shortens/lengthens/neither

• movement/stabilization/slow-down of a joint

• Ex: ____________

• >

• lengthens

• slow down

• lowering a weight in a bicep curl

Isometric Contractions:

• load >/</= tension

• Muscle shortens/lengthens/neither

• movement/stabilization/slow-down of a joint

• Ex: ____________

• =

• neither

• stabilization (balance external load)

• Holding a bicep curl mid way