Lecture 4( mucle contraction) Flashcards
How much tension is in a muscle fiber when no actin is overlapping the myosin filaments
zero
at what point is the tension in the muscle the greatest
when actin filaments completely overlap myosin (sarcomere about 2.2 mirometers) until acin filament tips touch (sarcomere about 2micrometers long)
what is the length of the sarcomere at max tension
2.2-2 micrometers
Epimysium
Connective tissue surrounding entire muscle
muscle
made up of multiple fascicles
perimysium
CT surrounding individual fascicle
Fascicle
a bundle of myofibers
Endomysium
Delicate connective tissue around each myofiber
Sarcolema (plasmalemma)
Cell membrane of the muscle fiber
Myofibril
A chain of sarcomeres within a myofiber
Myofilament
Actin and myosin filaments that make up a sarcomere
what are T-tubules
invaginations of the sarcolemma
lie close to cisternae of sarcoplasmic reticulum
form triads with cisternae
two per sarcomere
what are z discs (z lines)
anchor actin filaments
located at each end of a sarcomere
What are the I-bands
Composed entirely of actin
width changes during contraction
Does the width of the I bands change with contraction
Yes
What are the A-bands
Composed of actin and myosin
- Think all filaments
- width does not change during contraction
Does the width of the A-bands change with contraction
No
What are the H-bands
Composed entirely of myosin
width changes with contraction
does the width of the H bands change with contraction
Yes
What Is the length of the sarcomere when the H band disappears
about 2 micrometers long
what is the length of the sarcomere when the I-bands are absent
about 1.65 micrometers, this is when the z lines are smashed up against the myosin filaments
do filaments themselves change length
No
where are nuclei and mitochondria located in skeletal muscle
On the periphery of the cell
what signals the release of Ach into the synaptic cleft
opening of voltage-gated calcium channels and influx of calcium into the axon terminal
what is the function of Ach on the sarcolemma
They open ligand gated sodium channels (creation of a local potential)
what are the voltage-gated channels on T-tubules called
DHP (dihydropyridine-channels)
What is the function of Dihydropyridine channels?
They interact and open ryanodine receptors on the SR membrane
What does calcium bind to in muscle fibers
Troponin C
how much does calcium concentration in the cytosol increase by after calcium release by the SR
Calcium is increased from 0.1micromols per liter to about 10 micromoles per liter
a conformational change in troponin C moves what away from active sites on actin
Tropomyosin
what are DHP receptors
Dihydropyridine receptors
voltage-sensitive L-Type calcium channels
located on the T-tubules
How are DHP receptors arranged
in quadruplets
do Dihydropyridine (DHP) receptors contribute to cytosol calcium levels?
Yes. They do so both actively and passively
A minute amount of calcium flows into the cytosol via these channels
They also cause a conformational change in the ryanodine receptors which then release more Calcium from the SR
where are RyRs (Ryanodine receptors located)
on the cisternae of the SR
What is the function of ryanodine (RyRs) receptors
Allow calcium into the cytosol from the SR
What is the function of SERCA
Sarcoplasmic Reticulum Calcium ATPases
uses ATP to pump calcium back into the SR
What is Calsequestrin
in the SR maintains an optimum calcium concentration gradient to facilitate return of calcium to SR
what is preload
load on a muscle in the relaxed state (before it contracts)
The greater the preload does what to the tension
increases the amount of passive tension in the muscle
Preload generates what kind of tension in the muscle
Passive tension
what is passive tension
The force of resistance a muscle has to an applied load
What is afterload
load the muscle works against
When does an isotonic contraction occur
When the muscle generates more force than the afterload
when does an isometric contraction occur
when a muscle generates less force than the afterload
What is an isotonic contraction
same tone
What is an isometric contraction
same length
What is passive tension
produced by the preload
what is active tension
produced by cross bridge cycling
what is total tension
sum of active and passive tension
when does cross-bridge cycling begin
when free calcium is available and attaches to troponin
is ATP required to form the cross-bridge linking to actin
No
is ATP required to break the cross-bridge link with actin
Yes
increased cross-bridges to actin filaments means what
greater force of contraction
Do cross-bridges act independently of all others
yes
what is located on the myosin heads
ATP-ase
what is a sarcomeres resting length
about 2 micrometers
Tension in a muscle decreases when it is stretched beyond what length
2.2 micrometers
where is ATP required for muscle contraction
most is used for sliding filament mechanism
pumping of calcium ions from sarcoplam back into SR
pumping of sodium and potassium ions through the sarcolemma to reestablish resting potential
what is the concentration of ATP in a muscle fiber
about 4mmol
enough to maintain contraction for 1-2 seconds
how long can the concentration of ATP in a muscle fiber maintain contraction
about 1-2 seconds
what is the purpose of phosphocreatine in muscles
- Releases energy rapidly
- Reconstitues ATP
- ATP=Phophocreatine provides enough energy for 5-8 seconds of contraction
ATP + phosphocreatine provides enough energy for how many seconds of contraction
about 5-8 seconds
How long can glycolysis sustain contraction
about 1 minute
what is a product of glycolysis in muscle contraction
lactic acid
what provides more than 95% of all energy needed for long-term contraction
Oxidative metabolism
What is Isometric contraction
contraction that occurs when there is an increase in tension but not in length
what is isotonic contraction
Muscle length changes
- two types Eccentric and concentric
what is eccentric contraction
type of isotonic contraction
- occurs when the muscle lengthens
What is a concentric contraction
type of isotonic contraction
- occurs when the muscle shortens
what determines the myofiber type
The innervating neuron
how are muscle fibers classified
resistance to fatigue and speed of contraction
Characteristics of Fast (white) muscle
contract rapidly, but less endurance fewer mitochondria primarily use anaerobic respiration resulting in buildup of pyruvic and lactic acid little myoglobin larger concentration of ATPase
Characteristics of Slow (Red) muscle fibers
contract slowly but have more endurance more mitochondria primarily use aerobic respiration more myoglobin smaller concentration of ATPase
Can number of myofibers be increased after birth
NO
Can the number of myofibrils be increased after birth
yes
What is lost muscle tissue replaced by
Scar tissue (fibrous connective tissue
The mass of a myofiber and muscle may increase by what mechanism
increase in the number of MYOFIBRILS
what type of muscle is the soleus mostly composed of
Dark (slow twitch)
What type of muscle is the gastrocnemius mostly composed of
Light (fast twitch)
what is a motor unit
a neuron ad the myofibers it innervates
When a neuron fires does all of the myofibers in the motor unit contract
Yes
what effect would increased number of motor units have
increased force of contraction
What is summation
electrical events occur faster than mechanical events
increased speed in cycling
increases muscle tension
each additional spike adds to the effects of the previous spikes
How does summation increase the rate of cycling
additional spike occurs before previous calcium ions have been returned to the SR. This increases the total amount of calcium ion in the cytosol and increases the rate of cycling between the myosin and actin cross-bridges
what is tetany
Frequency of spikes is fast enough, that there is no time for a relaxation between spikes
- the muscle remains at maximal contraction
what is the position of the fulcrum in a first-class lever system
in the middle
Which direction do the in and out forces move in a first-class lever system
Opposite directions
In what direction and position are the forces in a second-class lever system
In and out forces move in the same direction and on the same side of the fulcrum
example raisin the body onto the ball of the foot
define a third-class lever system
effort (in-force) is in the middle
both in and out forces move the he same direction and are on the same side of the fulcrum
ex. lifting a weight in the palm of your hand
what term refers to a chain of sarcomeres
Myofibril
what sarcomeric band does not undergo a change in length during the contraction of skeletal muscle
A-band
what sarcomeric band is composed entirely of actin filaments
I-band
Dihydropyridine (DHP) channels are part of what structure
T-Tubules
Ryanodine-sensitive calcium ion release channels are part of what structure
SR
by what factor does calcium concentration in the cytoplasm increase after calcium is released by the SR
100
What maintains an optimum calcium concentration gradient to facilitate return of calcium to SR
Calsequestrin
Are fast twitch muscle fibers more fatiguable than slow twitch
Yes
Give an example of eccentric contraction
The triceps muscle while lowering the body to the floor during a push-up
