Flashcards in Physiology Deck (76):
What proteins make up the thick filament?
myosin heavy chain; 2 light chains/head
Identify the thick and thin filaments.
What innervates skeletal muscle?
motor neurons in ventral horn
Each muscle fiber receives innervation from...
ONE motor neuron
Small motor neuron cell bodies innervate...
These are a.k.a (fast/slow) motor units
few muscle fibers that generally have a small cross sectional diameter
Large motor neuron cell bodies innervate...
These are a.k.a (fast/slow) motor units
many muscle fibers that generally have a large cross sectional diameter
What are the components of a motor unit?
muscle fibers innervated by motor neuron
What type of receptors are targeted by ACh at MEP?
What type of channels are at the nerve terminal?
monovalent cationic channels
What type of depolarizations are generated at the MEP?
How is an action potential generated at the MEP?
1. many nicotinic receptors activated
2. surrounding membrane depolarized
3. Na channels activated
4. AP initiated
5. propagation along muscle fiber membrane (~unmyelinated axon)
Why is AP propagation axial?
because muscle fiber has long length and small diameter
What is the transverse tubule system?
invanginations of the cell membrane, which bring it in close contact with SR
What is the "triad"?
close proximity of T-tubule, SR and intervening structure
What causes a conformational change in the dihydropyridine receptor?
depol of T-tubule membrane
What type of receptor is the ryanidine receptor? WHere is it?
voltage-dep Ca channal in SR
What activates the ryanidine receptor?
conformational change in the dihydropyridine receptor
What is the result of activation of the ryanidine receptor?
1. channel opens
2. passive efflux of Ca from SR causes rapid increase of intracellular [Ca]
What occurs when the t-tubule membrane repolarizes?
1. dihydropyridine receptor returns to its normal conformation
2. conf change causes the ryanidine receptor to close
3. Ca actively pumped back into SR, which decreases IC Ca
Sarcomeres are structural organizations of _____ proteins
What is an A band?
ordered hexagonal array of THICK filamentous proteins
What is an I band?
ordered hexagonal array of THIN filamentous proteins
What is a Z line?
where thin filamentous proteins of the I band anchor
From Z line to Z line =
What are the components of the myosin heavy chain?
1. globular head
2. filamentous tail
Directed outward in the thick filament:
globular myosin head
Permits ATPase activity in globular head
light chain of thick filament
What are the components of thin filaments?
What does actin form?
monomers form helical chains
High affinity for myosin head
Where is tropomyosin found?
along the length of thin filament, covering actin's myosin-binding site
What are the 3 types of troponin, and what do they do?
C = binds Ca
T = binds tropomyosin
I = maintains troponin conformation
Why is it important for troponin to maintain its shape?
so tropomyosin can cover the myosin-binding site on actin in absence of Ca
Structurally, low intracellular Ca results in:
tropomyosin blocks myosin-head binding site on actin
Structurally, high intracellular Ca results in what process?
1. Ca binds to troponin C
2. conformational change in tropomyosin/troponin complex
3. tropomyosin slides into the cleft between helical actin monomers
4. myosin-head binding sites opens
5. actin + myosin bind
1. ATP binds to myosin head and myosin undergoes conf change, which causes the release of myosin from actin
2. ATPase activity >> ADP + P (=higher affinity of myosin head for actin)
3. myosin binds to actin's (+) side (different site)
4. conformational change hinge, which pulls Z lines together for power stroke
How is power stroke released?
power stroke changes affinity of myosin head (increased ATP affinity), which results in release of actin
What is rigor mortis? (cause?)
decreased metabolism = decreased ATP; without ATP:
1. myosin/actin cross-bridges cannot release
2. no active pump for Ca into SR
How do changes in muscle length relate to tension?
as length increases, passive tension increases
(or as length decreases, passive tension decreases)
What is passive tension, at optimal length?
Passive tension occurs in (presence/absence) of contractile activity
(muscle opposes increases in fiber length naturally)
Total tension =
active + passive
What is optimal length?
the point at which every myosin binds every actin within a sarcomere
If the sarcomere is too long (i.e. compared to optimal length)...
every myosin does not bind every actin
If the sarcomere is too short (i.e. compared to optimal length)...
steric interaction hinders the optimal force
Active tension results from (what two factors):
AP and fixed length
When does a maximum active tension occur?
at a specific optimal sarcomere length
An isometric twitch is generated in response to:
a single AP
Maximal active tension occurs at skeletal muscle lengths when...
there is maximal overlap of thick and thin filaments
In an isotonic contraction, ____ remains unchanged and _____ changes
2. the muscle's length
(wikipedia; I don't get this at all)
If the weight on a muscle fiber is the same as peak tension, distance (does/doesn't) change.
If the weight on a muscle fiber is less than peak tension, distance (does/doesn't) change.
As force (weight) increases, the initial velocity from the muscle moving the weight will (increase/decrease)
_____ is at the x-intercept (where velocity = 0)
_____ is at the y-intercept (when force = 0)
isometric peak tension
maximum velocity of shortening
Why does a fast motor unit have a greater isometric twitch tension?
there are more fibers with the unit, and a larger cross sectional area
Why does a fast motor unit have a faster time to peak tension (TPT) and 1/2RT (time required to relax 1/2 peak tension)?
due to its Ca handling
Why does a fast motor unit have a faster velocity (y-intercept)?
increased cross bridging
At a given velocity, a fast motor unit generates greater ___ than a slow motor unit.
At a given force, a fast motor unit generates greater ___ than a slow motor unit.
How does the lower surface area of small motor neuron bodies affect depolarization?
fewer excitatory synapses are required for depolarization threshold to be met
Excitatory inputs first recruit _____ for AP's
small motor neurons
(when a greater number of inputs, large motor neurons are activated for APs)
When large motor neurons are recruited, small motor neurons fire...
at a higher frequency
(sorry, didn't know how to ask this)
What type of motor neuron will activate fewer muscle fibers in a motor unit?
An excitatory neuron will first activate few muscle fibers, which results in:
a smaller contraction; it then activates many fibers, resulting in a greater contraction
When a muscle is stretched to longer lengths, what 2 things are reduced?
1. the number of possible cross-bridges
2. active tension
What happens to fast and slow motor units at a frequency of ~10Hz?
fast: generate tension and completely relax
slow: cannot completely relax before next stimulus
What happens to fast and slow motor units at a frequency of ~20Hz?
fast:begin to sum tension
slow: reach a maximum GREATER than standard twitch tension (Tetanic Tension)
Slow units produce tetanic contraction at a (higher/lower) frequency than fast units
Slow units produce a (higher/lower) tetanic force than fast units.
How do graded contractions generate greater force?
recruiting more motor units with a higher frequency of contraction
Muscle fibers with a greater shortening velocity have more...
myosin ATPase activity
ADP >> ATP via...
creatine kinase (which removes P from creatine-P, forming creatinine)
How can you determine when an elevated creatinine and BUN is due to muscle disease rather than kidney disease?
in muscle disease the CK and LDH will be elevated (but will be nml in kidney disease)
Why are slow twitch fiber less likely to fatigue?
thet have a greater density of mitochondria = increased FA oxidation
Slow + fast twitch fibers (in combo) support what type of muscle contraction
intense, short term contraction