Muscle Physiology Part 2 Flashcards
When 💡action potential is transmitted along the sarcolemma and then down the tubules, __ is released from the terminal cisternae SR into the myoplasm.
Calcium
Release of Ca raises intracellular Ca which promotes __; that is 💡Twitch.
Actin-myosin interaction and contraction
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
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
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
💡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
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
Skeletal muscle is able to contract in the absence of (1)__ or with mutated (2)__.
(1) extracellular Ca
(2) DHPR
Release of Ca from (1)__ -> conformational changes in (2)__-> opens (3)__- > release calcium in (4)__.
(1) terminal cisternae
(2) DHPR
(3) RYR
(4) myoplasm
o Located in 💡lumen of cisternae
o Allows Ca to be stored at 💡high concentration.
Calsequestrin
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
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
Skeletal muscle contraction is possible because it is innervated by __
Nerve
If denervated, the muscle will be __.
Paralyzed
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
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)
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
- Has 💡four binding sites
- Involved in 💡controlling and 💡enhancing interaction between trop I and trop C
Troponin C
Troponin C binding site is for what ions?
Calcium and Magnesium
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
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
1 attachment
power stroke
↑ power stroke generated
↑ force of contraction
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
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:
- ATTACHED STATE
- RELEASED STATE
- COCKED STATE
- POWER STROKE STATE
- ATTACHED STATE
- Hydrolyzed ATP > ADP > affinity of myosin to actin is high
- Myosin binds with actin
- 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)
- 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
- 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
- Latent period
- Period of Contraction
- 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:
- 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
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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
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
