EC Coupling Flashcards
(23 cards)
What is calsequestrin?
a Ca binding protein that reduces free Ca2+ in the SR
What is the structure of the sarcoplasmic reticulum (SR)? What does it consist of? What’s it function?
It is an extensive membranous sac structure inside each muscle fiber that consists almost entirely of Ca pumps and calsequestrin. These maintain a low intracellular Ca concentration by actively removing Ca2+ from the sarcoplasm.
What is excitation-contraction coupling?
a series of events whereby a depolarization leads to interactions between thick and thin filaments
What is the sequence of events that occur in EC coupling?
- Action potentials initiated near nmj travels along the surface of the muscle and into the T-tubules which open to the surface.
- the action potential in the T tubules activate a voltage sensor, located in the region of the triad
- the DHP receptor undergoes a conformatoinal change during which it interacts mechanically with the ryanodine receptor to open the Ca2+ channels in the sarcoplasmic reticlum
- Ca2+ leaves the sarcoplasmic reticulum and binds to troponin molecules
- The binding of Ca2+ to troponin produces a conformational change and tropomyosin moves and reveals myosin binding sites
- an interaction occurs between the actin and myosin and the fiber contracts
7. Ca pumps in the SR are activated, and Ca2+ concentration is rapidly returned to resting levels producing relaxation
What is Malignant Hyperthermia? What is the cause? What’s a symptom?
an autosomal dominant genetic disorder affecting 1 in 50,000 individuals. It’s triggered by inhalation anesthesics, and produced by an abnormality in the ryanodine receptor causing excessive Ca2+ release from the SR. A symptom is hyperthemia, as ATP consumption by Ca pumps of the SR liberates heat
What are sources of ATP necessary for contraction and relaxation for skeletal muscle?
ATP Pool
Creatine phosphate
Anaerobic metabolism (glycolytic)
Aerobic metabolism (oxidative phosphorylation)
Describe the ATP pool as a source for contraction and relaxation in skeletal muscle
The ATP pool is small.
Only supports a few seconds of maximal contractile activity
Describe creatine phosphate as a source of ATP for contraction and relaxation in skeletal muscle.
- an immediate high energy source for replenishing ATP
- creatine phosphate converts ADP to ATP
- provides energy for less than a minute of maximal activity
Describe anaerobic metabolism as a source of ATP for contraction and relaxation in skeletal muscle.
- occurs when oxygen supply is inadequate
- very rapid production of ATP from glucose or glycogen
- inefficient: 2 moles ATP/mole glucose
- Final product is lactic acid
Describe aerobic metabolism (oxidative phosphorylation) as a source of ATP for contraction and relaxation in skeletal muscle.
- occurs when oxygen is readily available
- slow process for ATP generation
- Fatty acids are the primary energy source
- Efficient: 36 mole ATP/mole glucose
- Final products are CO2 and H2O
What’s in a triad for EC coupling?
- Sarcoplasmic reticulum cisterna
- Transverse tube
- SR cisterna
Describe the dihydropyridine receptor
A two part voltage sensor receptor used in EC coupling that undergoes a conformational change and interacts with the ryanodine receptor to allow Ca channels in the SR to open
What is the ryanodine receptor?
The second part of the EC coupling mechanism that opens Ca channels in the SR reticulum to allow Ca2+ to leave the SR
What is oxygen debt? What’s it’s purpose?
The amount of oxygen equal to energy consumed minus that supplied by oxidative metabolism.
Purpose: to replenish metabolic stores using aerobic metabolism:
- creating phosphate and ATP levels are returned to normal - lactic acid turned back into glucose or glycogen or used to produced ATP
What are the types of skeletal muscle? What are they based on?
Types:
Type I
Type IIa
Type IIb
Based on contraction speed and metabolism
Describe Type I skeletal muscle.
- slow twitch, oxidative
- smallest diameter muscle fibers
- splits ATP at a slow rate
- high capacity for aerobic metabolism
surrounded by many blood vessels
contains myoglobin (aka. red fibers) and mitochondria - low glycogen content
- Fatigue resistant (b/c they rely on aerobic metabolism for energy production)
Describe Type IIb glycolytic fibers
- largest diameter muscle fibers
- contains a myosin that splits ATP at a high rate
- few mitochondria
- no myoglobin (white fibers)
- high glycogen stores
- fatigable (b/c rely on anaerobic metabolism)
Describe Type IIa fibers
an intermediate between Type I and Type IIb
- diameter between Type I and Type IIb
- it’s myosin splits ATP at a high rate but not as high as II b
- higher number of mitochondria thatn Type IIb
- contain myoglobin (red fibers)
- abundant glycogen stores (more than Type I, but less than TYpe IIb)
- fatigue resistant (has a greater capacity for aerobic metabolism than Type II b)
True or False: Most muscles are a mix of different fiber types
True
How are muscles classified in terms of their twitch capabilities?
Slow or fast twitch
What is an example of a fast twitch muscle?
Type IIb = lattismus dorsi
What’s a type of semi-fast twitch muscle
Vastus lateralis
What’s an example of a slow twitch muscle?
Soleus
