Skeletal and cardiac muscle physiology Flashcards
what are 2 types of striated muscle
skeletal
cardiac
what kind of contraction does skeletal muscle have
voluntary
what kind of contraction does cardiac muscle have
involuntary
dimensions of skeletal muscle
20-100 μm duameter, 12cm length
dimensions of cardiac muscle
brick shaped 10-20 μm diameter, 100 μm length
which is branches and unbranched out of skeletal and cardiac muscle
skeletal = unbranched
cardiac = branches
which one has a motor unit out of skeletal and cardiac muscle
skeletal = The motor unit: multiple fibres can be innervated by a single motor neuron
cardiac = No motor nerve (impulse arrives by conduction)
label this image of striated muscle
where do you find z lines
Z lines repeat along the length of the muscle approximately every 2 µm.
whats found in between 2 adjacent z lines
sarcomere - when we talk about sarcomere length we’re talking about the distance between two adjacent Z lines.
what does sarcomere contain
all of the protein filaments necessary for muscle contraction and these sarcomeric units simply repeat along the length of the muscle fibre.
what 2 structures are within the sarcomere
A band (which is the thick myosin filaments) and the I band (which is the thin actin filament) (which are anchored to the Z-line).
what is the a band
thick myosin filaments
what is the i band
thin actin filament
what are the small holes at every z line called
These are a blind-ended tubes of membrane called T-tubules
which is the thick and thin filaments in this diagram
what is a triad made up of?
1 T-tubule and 2 terminal cisternae
These T-tubules make junctions with the sarcoplasmic reticulum to form triads.
how many cisterns do skeletal cells have compared to cardiac cells
skeletal = triple (triad)
cardiac = double (dyad)
compare the mitochondria elvels in skeletal vs cardiac
more mitochondria in cardiac and bigger
arrangement of sarcoplasmic reticulum
repeating series of networks around myofibrils
where they meet is called terminal cisterna
what are t tubules surrounded by?
two terminal cisternae, called “triad”
what is the function of a t tubule
These t-tubules are necessary in larger cells to bring the action potential down into the centre of the cell and ensure synchronous coordinated contraction.
what cells are t tubules absent in
t-tubules are absent in small cells like atrial cells, neonatal cells and avian heart cells.
the association between Sarcoplasmic Reticulum and t tubule is essential for what
excitation-contraction coupling.
whats the difference between t tubules in skeletal vs cardiac
T tubules in cardiac muscle are fatter and the intracellular sarcoplasmic reticulum is less dense.
what are the 2 important periods in neuronal action potential
refractory period
relative refractory period
what is the refractory period
The refractory period is the period during which the ion channels have opened and inactivated but have not returned to that closed state to be ready and available to fire off another action potential. Remember that ion channels can enter an open state, then an inactivated state and they can only return to the close date to ready for the next action potential when the membrane has repolarized completely - so this period is called the refractory period.
And if a stimulus comes along during that period, we cannot generate another action potential.
what is the relative refractory period
In this period, the sodium channels have recovered from inactivation and they’re available and ready to go. But, because the membrane potential is now much more negative than it was at rest, during this green period, it is going to take a bigger depolarization to get up to that threshold level. So although the cell is available and able to fire off an action potential, it’s going to take a bigger trigger to get it there to get it up to the threshold voltage
key difference between refractory period and relative refractory period
refractory period - where you cannot fire off another action potential, and the relative refractory period (shown in green), where you can still fire off an action potential but it needs a larger triggering pulse.
in a cardiac action potential, does the ventricular muscle beat spontaneously?
no
in a cardiac action potential where does the wave originate
SA node
what is the refractory period like in cardiac action potential compared to relative refractory period
very long refractory period
what is the action potential like in skeletal muscle
short APD
whats the refractory period like in skeletal muscle
Short refractory period (allows tetany = involuntary muscle contractions ie spasms)
whats is skeletal muscle action potential triggered by
Triggered by activation of a motor neuron
what is skeletal muscle action potential initiated by
Excitation initiated in the neuromuscular junction
what is it called when action potentials happen back to back and cause contractions to fuse together
temporal summation
fused vs unfused tetanus
why do we have a long refractory period in cardiac muscles?
prevents tetany
protects against re-entrant arrythmias (, it stops the heart beating in that gap in between beats in a way that would compromise the hearts ability to pump. So if an arrhythmia comes along during the refractory period, is not going to trigger another action potential and another beat)
what happens if you remove calcium from the outside of a single ventricular myocye vs skeletal muscle
skeletal muscle can continue beating for at least 25 minutes without any extracellular calcium . Cardiac muscle, on the otherhand, is arrested almost immediately. Within milliseconds of removing external calcium cardiac muscle arrests.
what is the calcium transient
Within the time course of the action potential the calcium concentration returns to its resting level and hence this change is called the calcium transient.
in the cardiac muscle in excitation-contraction coupling, the action potential, when it sweeps down the surface membrane, sweeps into the T-tubule and in the T-tubule are voltage-gated calcium channels, this allows calcium to enter by diffusing across what
This calcium, when it enters the cell, diffuses across the very small space between the T-tubular membrane and the sarcoplasmic reticulum - the dyadic cleft.
in cardiac muscle excitation- contraction coupling, when Ca is elevated in this dyadic cleft, it binds to another channel (this time in the sarcoplasmic reticular membrane) what is the channel called
This channel is called the calcium release channel or the
ryanodine receptor because it binds a drug called ryanodine. (RyR)
the entire process of excitation-contraction coupling in cardiac muscles depends on what
started by calcium entering the cell through L-type calcium channels and triggering that release of a much larger amount of calcium from those intracellular stores.
what happens when an action potential arrives at the calcium channels in t-tubular membrane in skeletal muscle
the voltage-gated calcium channels change their conformation (just as they do in cardiac muscle). Howver, this time calcium entry is not required. In skeletal muscle, the channel is physically linked to the ryanodine receptor – you can se this indicated in blue on this diagram.
in skeletal muscle when the conformation of the calcium channel changes, in response to the change in voltage what happens
When the conformation of the calcium channel changes, in response to the change in voltage, this literally pulls the plug on the ryanodine receptor. This allows release of calcium into the cytoplasm. Calcium becomes elevated and that calcium binds to the myofilaments and brings about contraction.
larger ca transient gives you what compared to a smaller ca transient?
