Muscle Physiology Part 2 Flashcards by Adrian Tiglao

When 💡action potential is transmitted along the sarcolemma and then down the tubules, __ is released from the terminal cisternae SR into the myoplasm.

Calcium

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Release of Ca raises intracellular Ca which promotes __; that is 💡Twitch.

Actin-myosin interaction and contraction

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Skeletal Muscle (Electromechanical coupling)

i. Depolarization of sarcolemma is caused by Na
ii. Tropomyosin is covered
iii. Triad – association with two terminal opposing cisternae and T tubule
iv. Source from SR

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Cardiac Muscle (Electrochemical coupling)

*SA node = generates AP
*Ach = regulation (binds with GPR for inhibition)
*Catecholamine = calcium released = Inc. cardiac activity)

i. Depolarization sarcolemma is caused by Na
ii. Tropomyosin is covered
iii. Diad: 1 T tubule and 1 terminal
iv. Source from SR and ECF

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Smooth Muscle (Pharmacochemical coupling)

**Does not need AP but rather an agonist (IP3)

i. Depolarization sarcolemma is caused by Ca
ii. Tropomyosin is not covered; inactive
iii. No troponin instead it has calmodulin
iv. Myosin is inactive and needs to be activated by Ca-calmodulin complex
v. Membrane is leaky to Ca > Ca gets into the cell > bind to calmodulin > trigger release of Ca in SR > Ca-Calmodulin complex > activate myosin light chain kinase: activates tropomyosin/myosin
vi. Source from ECF and SR

**Thick filament regulated

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💡Feet:bridging proteins between t tubule and cisternae

i. Ca release channels in the membrane of cisternae
ii. Responsible for elevation in intracellular Ca in response to action potential
iii. Binds to ryanodine that is why called as ryanodine receptor

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At the 💡T tubule membrane 💡RYR interacts with __ receptor which is 💡critical for the ability of the action potential in the T tubule to 💡induce release of Ca from SR.

Dihydropyridine

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Skeletal muscle is able to contract in the absence of (1)__ or with mutated (2)__.

(1) extracellular Ca

(2) DHPR

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Release of Ca from (1)__ -> conformational changes in (2)__-> opens (3)__- > release calcium in (4)__.

(1) terminal cisternae
(2) DHPR
(3) RYR
(4) myoplasm

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o Located in 💡lumen of cisternae

o Allows Ca to be stored at 💡high concentration.

Calsequestrin

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o Bind both 💡RYR and 💡calsequestrin

o Increases 💡buffering capacity at the site of Ca release.

o 💡Histidine rich calcium binding Protein:
Binds to triadin

Triadin and Junctin

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o 💡Increases Ca uptake by SERCA (Sarcoplasmic endoplasmic Reticulum Calcium ATPase)

o Most 💡abundant protein in SR of skeletal muscle

o Transports 💡2 molecules of Ca for each ATP hydrolyzed.

Sarcalumenin

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Skeletal muscle contraction is possible because it is innervated by __

Nerve

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If denervated, the muscle will be __.

Paralyzed

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MUSCLE CONTRACTION MECHANISM

Activation of the nerve
Produce action potential
Travel along axon
Reach terminal button action potential
Depolarization
Ca++ voltage gated channel opens
Ca++ gets in

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MUSCLE CONTRACTION MECHANISM (detailed version)

Binding of 💡Ach to its nicotinic 💡Ach receptor
Opening of 💡cation channel (Na, K)
Sarcolemma 💡depolarization due to Na influx
Generation of 💡local potential (end plate potential) = open voltage gated = reach threshold
Generation of 💡action potential
Transmission of action potential along sarcolemma going to 💡T Tubule structure (used to transmit AP along sarcolemma to inner portion of the muscle fiber)
Activation of 💡DHP (voltage sensor) > undergo mechanical conformational
Activate 💡RYR
💡Release of Ca from terminal cistern (💡simple diffusion)
Ready to bind to 💡Trop C (translocation of tropomyosin laterally > exposed binding site > interaction between actin and myosin > initiate muscle contraction)

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MUSLE RELAXATION MECHANISM

💡Remove Ca
💡Release of Ca from the Trop C
Sequestration of Ca to SR
💡Muscle relaxation
💡Actin-Myosin Interaction: Cross Bridge Formation
Ca released by SR binds to 💡troponin C
Troponin C facilitates movement of associated 💡tropomyosin molecules towards the cleft of actin filaments
💡Exposes myosin binding site and allows 💡cross bridge to form
Generation of 💡tension

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Has 💡four binding sites

- Involved in 💡controlling and 💡enhancing interaction between trop I and trop C

Troponin C

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Troponin C binding site is for what ions?

Calcium and Magnesium

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SLIDING FILAMENT THEORY / CROSS BRIDGE CYCLING SARCOMERE SHORTENING

The 💡myosin cross-bridge is 💡pulling the actin thin filament 💡toward the center of the sarcomere, thereby resulting in an apparent 💡“sliding” of the thin filament past the thick filament; there is 💡sliding of myofilaments but 💡no shortening, there is 💡narrowing of or decreasing H zone

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The myosin cross-bridge is pulling the (1)__ toward the center of the (2)__, thereby resulting in an apparent (3)__ of the thin filament past the thick filament; there is sliding of myofilaments but (4)__, there is narrowing of or decreasing H zone

(1) actin thin filament
(2) sarcomere
(3) “sliding”
(4) no shortening

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1 attachment

power stroke

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↑ power stroke generated

↑ force of contraction

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When calcium binded with Troponin C, what will happen?

a. ATP is Hydrolyzed into ADP (Affinity is High)
b. Myosin crossbridge binds with Troponin
c. After Contraction, ADP will be Phosphorylated to ATP (Affinity is Low)
d. Remove Binding and back to Relaxed State

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It is an 💡excitation signal, needed to free myosin

Calcium

Absence of calcium

No binding, muscle is relaxed

It is needed for power stroke

ATP

The mechanism by which myosin produces force and shortens the sarcomere is thought to involve four basic steps:

1. ATTACHED STATE 2. RELEASED STATE 3. COCKED STATE 4. POWER STROKE STATE

1. ATTACHED STATE

- Hydrolyzed ATP > ADP > affinity of myosin to actin is high | - Myosin binds with actin

2. RELEASED STATE

- The head will pull it to the center and detach through ATP - ATP binds with myosin head - Dissociation of myosin to actin (detachment)

3. COCKED STATE

- ATP will be hydrolyzed again causing the head to move to another binding site - Binding of myosin head to another binding site of actin

4. POWER STROKE STATE

- Phosphate is released | - Detachment through ATP

Binding of ATP to myosin decreases the __, thereby resulting in the release of myosin from the actin filament

Affinity of myosin for actin

If myoplasmic [Ca++] is still elevated, the cycle __.

Repeats

If myoplasmic [Ca++] is low = __ results. The cycle continues until the SERCA pumps Ca++ back into the SR

Relaxation

If the supply of ATP is exhausted, as occurs with death, the cycle stops in cocked state with the formation of (1) __ causing (2) __.

(1) Permanent actin-myosin complexes | (2) Rigor mortis

💡Mechanical response of muscle brought about by a single 💡action potential which is composed of a 💡brief period of contraction and 💡brief period of relaxation

MUSCLE TWITCH

TWO ACTIVITIES OF MUSCLE TWITCH

* Electrical - Action potential | * Mechanical - Contraction

3 PHASES IN MUSCLE TWITCH **Take note that all phases require ATP

1. Latent period 2. Period of Contraction 3. Period of Relaxation

💡Between the start of depolarization and start of contraction -Includes the events happening 💡before contraction. **From binding Acetylcholine to the nicotinic receptors up to the binding of Ca2+ with Troponin C that causes Tropomyosin translocation

Latent period

From the 💡start of contraction to 💡peak of tension curve 💡All phase in sliding filament theory

Period of Contraction

- From 💡peak of tension curve up to the 💡end of muscular response - Includes events from 💡release if Ca2+ from Trop C, and 💡sequestration back to SR - Involves 💡SERCA

Period of Relaxation

SKELETAL MUSCLE TYPES | Two main groups according to the speed of contraction:

1. Fast-twitch Muscle Fibers | 2. Slow-twitch Muscle Fibers

* Contracts 💡very quickly in response to action potential, then 💡relaxes very quickly, which results in 💡short duration of contraction. * Can deliver 💡extreme amounts of power for few seconds to minute/s * Contain myosin isoforms that 💡HYDROLYZES ATP QUICKLY * Could contain 💡type IIa, 💡type IIx, or 💡type IIb myosin heavy chains * 💡Oxidative capacity ranges from relatively high (type IIa myosin heavy chain) to low (type IIb myosin heavy chains). * The 💡low oxidative capacity of fast type IIb muscle fibers, coupled with the 💡high myosin ATPase activity, increases the 💡susceptibility of these muscle fibers to fatigue.

Fast-twitch Muscle Fibers

``` Type 2 fiber Glycolytic White Muscle SERCA 2 Large Diameter Shorter duration of twitch ```

Fast Twitch

* 💡Slower to reach peak tension in response to an action potential, and then it 💡relaxes slowly * Provide 💡endurance, delivering 💡prolonged strength of contraction over many minutes to hours * Contain myosin isoforms that 💡HYDROLYZE ATP SLOWLY * Express 💡type I myosin heavy chain * 💡High oxidative capacity which in combination with the 💡low myosin ATPase activity contribute to the fatigue resistance of slow-twitch muscle fibers.

Slow-twitch Muscle Fibers

``` Type 1 fiber Oxidative Red Muscle SERCA 1 Small Diameter Longer duration of twitch ```

Slow Twitch

See anki

Se anki

TYPES OF MUSCLE CONTRACTION

A. Isometric Contraction B. Isotonic Contraction C. Isokinetic Contraction (in sports)

* One in which 💡muscle length is held constant, and the 💡force generated during the contraction is then measured * 💡“same length” * Muscle stays at a 💡fixed length * (-) shortening and lengthening (distance) * (-) change in length, (+) generation of force therefore,(-) work * Work = Force x Distance * Energy is converted to heat

Isometric Contraction

* One in which the 💡force (or tone) is held constant, and the 💡change in length of the muscle is then measured * (+) Length changes, whether lengthening or shortening * 💡Same tension but muscle length changes * (+) work because muscle length changes * Work = Force x Distance

Isotonic Contraction

(+) muscle shortening (+) work o Ex. your weight > weight of the load (force exerted > what is being lifted)

Concentric contraction

(+) muscle lengthening (-) work Ex. your weight < weight of the load (force exerted < what is being lifted) exerting force (-) o How to improve? Increase the force by increasing the mass of muscle (hypertrophy – exercise with load)

Eccentric contraction

** (+) in concentric contraction because some energy is (1)__; (-) in eccentric contraction because exerting more energy but (2)__; (0) in isometric because all energy is (3)__.

(1) converted to work (2) not converted to work (3) converted to heat but no work

Same 💡velocity of muscle shortening

Isokinetic Contraction

LENGTH-TENSION RELATIONSHIP

Resting length = physiologic length Beyond the resting length = overstretching

It is a tension generated when a 💡muscle at rest is 💡stretched. Muscles are made up of connective tissue or titin, when you stretch muscle: connective tissue resists the stretching → creates tension

Passive Tension

Passive Tension | ↑ Stretch = ?

↑ Passive tension = ↑ muscle fiber length

Passive Tension is __ to muscle length.

Directly proportional

It is a 💡tension generated when the 💡muscle is stretched and stimulated 💡Maximal at resting or optimal length

Active Tension

Active tension is not created by the connective tissue but of the number of __.

Power stroke

Active Tension | ↑ Stretch = ?

= expose more actin = ↑ power stroke = | ↑ Active tension

It is the 💡sum of passive and active tension

Total Tension

💡Before the resting length: | ↑ active tension, ↑ passive tension = ?

↑ Total tension **directly proportional

💡Beyond the resting length: | ↑ Passive tension

↓ Active tension (decrease in active is greater than passive) = ↓ total tension **inversely proportional

💡Stretch it further: | ↓ Active tension

↑ passive tension (increase in | passive is greater than active) = ↑ total tension

It is an 💡opposing/ reverse force to velocity

Load

LOAD VS VELOCITY OF SHORTENING ↑ Load = ? **inversely proportional

↓ Velocity of shortening

LOAD VS WORK PERFORMED ↑ Load = ? **directly proportional

↑ mass = ↑ force = ↑ work (acceleration | and distance are not yet affected)

If the too much load is added: ↑ Load = ?

↓ acceleration = ↓ shortening = ↓ work **inversely proportional

LOAD VS POWER ↑ Load = ?

↑ mass = ↑ force = ↑ work = ↑ power | initially directly proportional

But as you keep on contracting, there is also ↑ | time = ?

↓ power (inversely proportional)

In muscle contraction: Highest power of muscle =

within 10 seconds But, ↑ contraction = ↓ Power

ENERGY SOURCES DURING CONTRACTION

PHOSPHAGEN SYSTEM GLYCOGEN - LACTIC SYSTEM AEROBIC SYSTEM

PHOSPHAGEN SYSTEM

ADENOSINE TRIPHOSPHATE CREATINE PHOSPHATE

💡Immediate source for muscle contraction 💡ATP is the energy source used for this conversion.

PHOSPHAGEN SYSTEM

💡Stored ATP can sustain muscle contraction for?

3 sec

It is used to convert ADP to ATP and thus replenish the ATP store during muscle contraction.

CREATINE PHOSPHATE (phosphocreatine)

Stored ATP can sustain muscle contraction for?

5-8 sec

Short term source for muscle contraction

GLYCOGEN - LACTIC SYSTEM

Long term source for muscle contraction

AEROBIC SYSTEM

Oxygen debt ≅ Energy consumed during exercise minus that supplied by oxidative metabolism.

True

* It is a condition characterized by 💡sustained contraction | * Transport Ca to the SR is 💡inhibited therefore 💡relaxation does not occur even though there are no more AP

CONTRACTURE

It is a 💡state of rigidity of the muscle that occurs after death

RIGOR MORTIS

In rigor mortis. there is complete depletion of __ that almost all of the myosin heads are attached to actin but in an abnormal, fixed, and resistant way

ATP

EFFECTS OF DENERVATION LOWER MOTOR NEURON

MUSCLE ATROPHY FASCICULATION MYASTHENIA GRAVIS

💡Denervation hypersensitive (fibrillation) not usually visible contraction

MUSCLE ATROPHY

• It is 💡jerky visible contractions or small, irregular contractions of groups of muscle fibers caused by 💡release of acetylcholine from the terminals of the degenerating distal portion of the axon. * Example: upper eyelid * Fatigue

FASCICULATION

It is characterized by 💡spontaneous, repetitive contractions. At this time, the 💡cholinergic receptors have spread out over the entire cell membrane, in effect reverting to their preinnervation embryonic arrangement. It reflect supersensitivity to acetylcholine.

Fibrillation

TYPES OF HEAT PRODUCTION IN MUSCLE

Resting Heat Initial Heat Recovery Heat Relaxation Heat

It is the heat given off at 💡rest basal metabolic process. (Na-K pump)

Resting Heat

It is the heat produced in 💡excess of resting heat during contraction

Initial Heat

It is the heat produced 💡during contraction

Activation Heat

It is a 💡distance the muscle shortens

Shortening Heat

It is the heat liberated by the 💡metabolic processes that 💡restore the muscle to its💡 precontraction state; equal to initial heat

Recovery Heat

It is the 💡extra heat in addition to the recovery heat

Relaxation Heat

It is the 💡functional contractile unit of 💡muscle. It consists of the 💡motor nerve and 💡all the muscle fibers innervated by the nerve.

MOTOR UNIT

It is the 💡functional contractile unit of 💡“muscle fibers”

Sarcomere

Activation of motor units with a small number of fibers facilitates __.

Fine motor control

Innervation Ratio

motor neuron:muscle fiber

It is a 💡neuromuscular junction formed by the α motor neuron.

Motor end plate

<500 muscle fibers/motor unit =

for fine, graded, and precise movement

>500 muscle fibers/motor unit =

for postural, and gross movement Motor Unit

Excitability relies on?

Size **Inversely proportional

Smaller size = ?

More excitable

Larger size= ?

Less excitable

see anki

What is the other term of 💡Spatial Summation?

Multiple fiber summation / Recruitment of motor units **Quantal / Graded Response- old name

A simple means of increasing the force of contraction of a muscle is to recruit more muscle fibers.

Recruitment

Because all the muscle fibers within a motor unit are activated (1)__, a muscle recruits more (2)__by recruiting more (3)__.

(1) simultaneously (2) muscle fibers (3) motor units

The process of increasing the force of contraction by 💡recruiting additional motor units Apply 💡several stimuli in 💡increasing intensity Increase of motor units activity = increase in force contraction

Spatial Summation

Because all fibers in a motor unit are innervated by a single (1)__, all fibers within a motor unit are of the __.

(1) α motor neuron | (2) same type

Once reached, contraction force 💡won’t increase even with the recruitment of more motor units

Maximal Force of Contraction

What is the other term of Temporal Summation?

Frequency/ tetanization

* Several stimuli of 💡increasing frequency | * Increase in frequency= increase force of contraction

Temporal Summation

If the muscle is stimulated a second time before it is fully relaxed, the force of contraction increases. Thus twitch forces are amplified as stimulus frequency increases. At a high level of stimulation, intracellular [Ca++] increases and is maintained throughout the period of stimulation, and the amount of force developed greatly exceeds that observed during a twitch.

Complete Tetany

At intermediate stimulus frequency, intracellular [Ca++] returns to baseline just before the next stimulus. However, there is a gradual rise in force.

Incomplete tetany

Similar to tetany but 💡allows full relaxation between each stimulus

Treppe / Staircase Phenomenon

● 💡Decreased ability of the muscle to generate force due to prolonged and strong contractions ● 💡Directly proportional to the rate of depletion of glycogen and creatine phosphate, but 💡not of ATP ● Lactic acid and inorganic phosphate accumulation. 💡Protective mechanism to minimize the risk of muscle cell injury death

FATIGUE

Muscle Physiology Part 2 Flashcards

(119 cards)