Contraction of skeletal muscles Flashcards
How many %of body is skeletal muscles
40%
Fibers of skeletal muscles are what diameter
10-80 micrometer
Sarcolemma consist of
true cell membrane which is the plasma membrane and outer covering of a thing
Polysaccharide layer which contains collagen fibers.
At the end of muscle fiber the sarcolemma
fused with the tendon fiber that collect into bundle to make muscle tendon that joins the muscle to the bone
Each myofibril contains how many actin and myosin filaments
1500 myosin and 3000 actin
wHat causes contraction
the projection out of myosin filament called cross bridges makes interaction between myosin and actin and causes contraction
Actin filaments is attached to the
z disk
Titin molecular weight
3 million
Characterists of titin and what does it do?
it is very springy and, it is filamentous and it keeps the interaction between myosin and actin in check, its springy molecules act as a framework and keep them in check so the contractile machinery of sarcomere will work
Attachments of titin
one end is attached to z disk that changes length of sarcomere as it contracts and other end of attached to myosin
titin molecules also acts as a?
template for the initial formation of portions of contractile filaments specially myosin
what does sarcoplasm contains (ions and etc)
potassium, magnesium, phosphate and enzymatic proteins
also contains mitochondria
functions of sarcoplasmic reticulum ?
regulations, reuptake and release of calcium and thus inturn regulation of muscle contraction,
general mechanism of action potential
- action potential travels to its ending to the muscle fiber
- nerve ending releases acetylcholine
- acetylcholine acts and causes to open acetylcholine gated channels
- na ions move inside thus causes voltage gates na channels to open
- action potential is initiated and depolarizes the muscle fiber, travels to middle and causes sarcoplasmic to release ca ions
- ca ions causes attraction of myosin and actin filaments and contraction occurs
- ca ions pumps back into the sarcoplasmic
sliding filaments mechanism
actin filaments are pulled inward among the myosin filaments so their end overlap to maximum extent, z disks have been pulled by actin filaments till the ends of myosin filament
myosin molecule has a molecular weight of
480,000
how many polypeptide chains myosin has
total 6 polypeptide chains 2 heavy (200,000) and 4 light chains (20,000)
define the stricture of heavy and light chain in myosin
the two heavy chains wind around each other to form a double helix, which makes the tail. the other end makes a globular polypeptide structure( the head ). each helix has 2 free heads. the light chains are a part of myosin head, 2 chains at each head
how many myosin molecules are there is myosin filament
200
cross bridges
part of the body of the myosin filament hangs to the side along with the head providing an arm to extend the head outwards. the head and arm is called cross bridges
each cross bridge is displaced by another cross bridge by
120 degrees
strcuture of actin filamengt
backbone of actin filament is made up of a double stranded F-actin proteins molecule which are represented by two lighter colored chain winded around each other to form a helix
f actin molecule is composed of polymerized G-actin molecule
molecular weight of g actin is
42,000
what is attached to G action molecule and what does it do
adp which are active sites of actin which attaches to the cross bridges of the myosin filaments
tropomyosin weight and length
70k and 40 nanometer
what is tropomyosin
it is wrapped spirally around f actin helix, covering the active site of actin in relaxed state
troponin
these ar attached to the side of tropomyosin. composed of 3 loosely bound proteins subunits
TI has affinity for actin
Tt has affinity for tropomyosin
Tc has affinity for calcium
it attaches the tropomyosin to actin and initiates the contraction due to affinity for ca ions
hypothetical mechanism of troponin tropomyosin and calcium molecules
the troponin binds to 4calcium ions, a conformational change takes place that pulls the tropomyosin deeper in the grooves of actin molecules by troponin. which exposes the active site on actin molecule and causes contraction.
where else energy is used than walk-along mechanism
- pumping back of Ca ions into the sarcoplasmic reticulum from the sarcoplasm
2 pumping of Na and K ions though the muscle fiber membrane to maintain the proper ionic environment for the propagation of action potential
first way of Atp is reconstitution is
phosphocreatine which is also has a high energy phosphate bond, it is cleaved and its released energy is used to combine a phosphate ion with adp to form atp
2nd most important source of energy is
glycolysis which is the breakdown of glycogen in muscle cell into pyruvic acid and lactic acid that liberates energy and used to convert adp into atp
the 2 importance of glycolysis
- it can happen without o2 so muscle contraction can be sustained for as long as one minute
- ATP formation from glycolysis is 2.5 times as rapid as atp formation from normal cellular nutrients reacting with o2
3rd source of energy
oxidative metabolism, combing oxygen with the end products of glycolysis and other cellular foodstuffs to liberate atp
how much energy is made from oxidative metabalism
95% energy is this energy that is used for sustained muscle contraction.
greatest proportion of energy comes from what
comes from fat for 2-4 hours
isometric contraction
when the muscle does not shortens during the contraction
isotonic contraction
when the muscle shortens during contraction but the tension in the muscle remains the same
which type of contraction is independent the load inertia
isometric
isometric contraction of ocular muscle and why?
less 1/50 second because for rapid movement of ocular muscle for fixation of eyes for proper vision
isometric contraction of gastrocnemius muscle and why?
1/15 of a second to provide suffienct velocity for limb movement for running and jumping
isometric contraction of soleus muscle and why
1/5 of a second for long term support of body against gravity
motor unit
all the muscle fiber innervated by single nerve fiber is called a motor unit
supply nerve fibers of small muscle fibers
small muscle fibers that react rapidly are innervated by several nerve fibers
large muscle fivers supplied by nerve fibers how
large muscle fibers have a single motor unit because they need less controlled contraction like the soleus muscle
summation
adding individual twitch contraction to increase the overall muscle contraction
summation occurs in 2 ways
- increasing the number of motor units contracting simultaneously ( multiple fiber summation)
- increasing frequency of contraction (frequency summation )
max strength of tetanic contraction
3-4kg/cm2 or 50pounds/inch2
staircase effect/treppe
when a muscle contracts after a long period of rest, its strength of contraction is as little as one half of his strength. 10-50 muscles twitches later
why staircase affect happens
high accumulation of ca ions in the cytosol
muscle tone
skeletal muscle in non contracted state are under tautness, this occurs due to low rate of nerve impulse coming from spinal cord which are controlled by nerve transmission of brain to spinal cord or by signals that originate in muscle spindles
muscle fatigue happens
due to glycogen depletion in muscles and interruption of blood flow
muscle hypertrophy occurs due to
increase in the number of actin and myosin filaments which in turn enlarges individual muscle fibers
atrophy occurs thorigh
atp dependent ubiquitin proteasome pathway
muscle stretch causes
hypertrophy which occurs with the muscle is stretched and new sarcomeres are added to the muscle fibers, where they are attached to the tendons
hyperplasia
increase in the number of muscle fibers due to the linear splitting of enlarged muscle fibers
what happens when a muscle loses its nerve supply
it degenerates in 2 months
final stage of denervation atrophy
muscle fibers are replaced by fibrous and fatty tissues
contracture
the fibrous tissues that replaced muscle fibers has tendency to become shorten for months called contracture
