Skeletal Muscle Physiology Flashcards
Skeletal muscle
- voluntary muslces
- with strated: sarcomeres which respond to calicum release to contract
- skeletal muscle spans joints and acts as lever for extension and flexion
- the origin: connective tissue to a bone via a tendon
Muslces, surrounded in epimysium, are grouped into fasciles, surrouned by perimysium (blood vesselsand nerves contained here) which are made of muscle fibers, surroudned by endomysium
the connective “mysium” tissue layers that sourrned are continuations of tendones & made of
- elastin
- collagen
- & provide passive tension
the structure and function of actin and myosin for muscle contraction
actin: when in its relaxed state, has its active sites cover by the molece tropomyosin : this binds myosin from being able to bind
(individual actin = globular, a long strain of globular actin = filamentous actin)
when contraction needs to occur
tropomyosin in moved, (by troponin, because that is activated by Calcium release to let go of tropomyosin and therefore freeing the active site) allowing the myosin heads to bind at the active sites of the actin body and contract
Myosin
- connected and anchored to the Z line, with its heads on each myosin
- neck: has light chains which have ATP activity
how does the ACH trigger from the motorneuron trigger muscle contraction
through the junction, Ach is release, binds onto nicotinic receptors which trigger an AP to travel and spread to the muscle cells and into the T tubules which continue to pass the signal along to other cells deeped
this process if very fast, < 5ms!!
the AP travels down the sarcolemma of the muscle fiber and down teh T tubules
- this triggers within the terminal cisternae specific receptors to open calcium channels and allow calcium to flow into the cell from the storage (sarcoplasmic reticulum)
- this release of calcium allows troponin to release tropomyosin and allow myosin to bind to actin active sites and contraction occurs
- the myosin binds: but is connected to Z line so it binds to actin bringing it closer to the midline as it shortens
The t tubles have DHPR & Ryanidine receptors on teh terminal cisterna: which open teh door for calcium to be released from the terminal cisterna, calcium travels through T tubule to the actin (troponin to bind)
SERCA: is a recycle protein for calcium to be recycled back into the SR
The force of a muscle contraction is proportional to the amount of calcium released
Crossbridge Cycling in Muscle contraction
in the presecence of ATP -> myosin binds and pulls actin to shorten
but ATP is also needed for release of tehmyosin from actin: thus: in tha absence of ATP, myosin cant unhook from actin: muscle stays contracted : rigor mortis
- if intracellular Ca+ remians elevated after a crossbridge cycle, another cycle will be stimualted to occur and reoccur – this will happen until ca+ sequestered into the SR
- the only other way that this cycle will stop is if ATP is no longer avalible
Fast v Slow Twitch Fibers
Fast = quick muscle contraction response (type IIa and IIb)
slow twich = (Type 1)
Fast Twithc Fibers: fatigue quickly becauase they rely on glycogen/glycolysis for energy: and this a a finite resources
slow twich fibers: doent faituge quickly becuase thy rely on oxidative energy production via myoglobin
Explain how Recruitment impacts force of muscle contraction
Recruitment: the main way to increase force is to increase the number of fibers (cells)
- all muslce fibers in a motor unit (from one neruon) are actiated simultaneously
- all muscle fibers within a motor unit are the same type
- in a mized muslce: slow twich are recruited first, then fast = spatial recruitment
Explain how Tetany impacts force of muscle contraction
- action potentials are uniform in skeletal muslce & lead to regular pulses of calcium release from the sarcoplastic reticulum
a single AP will initiate a muscle “twitch” or force
a second AP before muscle relaxation will INCREASE the force of the contraction of the muscle = amplification
increasing the APs which occur = maximal force of contraction via temporal recruitment = TETANY
aka, the fibers dont have time to releax and repolarize before another AP is triggered thus a continued contraction occurs (tetany)
Explain the Force of Contraction in Strech Reflexes
sensory fibers of the muscle run parallel to the muscle fibers & detect the stretch and speed of the contraction
Stretch Reflex: streching of the muscle lengthens spindles and results in high requence APs that travel to the spinal cord
the motor neurons are innervaed and activated in response to maintain a spcific angle of the muscle during contraction
Spindle = stimuli of teh muscle strech: triggers nerve signal to go to spinal cord
triggers motor neuron response to contract the muscles
Skeletal Muscle Tone
- at rest: muscles are normally partially contracted
- a reflex arch: or the sensory to motor stimualtion occurs without needing to go to the brain but just signals which are processed through teh spinal cord
- inturruption of the reflex arc by section of sensory afferent fibers alters the resting tone of a musle
what are muscle energy sources
ATP
Creatine Phosphate
ATP: used and converted to energy, small amoutn and needs to be constatnly replensihed
Creatine phosphate: used to convert ADTp to ATP to replenish the need for ATP stores during contraction
Creatine phosphokinase (CPK) helps turn ADP into ATP + creatine
- the limitng factor here is the ATP pool, because you can have excess creatine but if you dont have the ADP to recylce it wont help
Energy SOurce for Msucles
gycogen
glucose
FFAs
Glycogen: metabolized during contraction to provide glucose for ATP creation anf ATP storage repletion
Glucose: can be used (need insulin to push it inot cells)
glycolysis: provides 36-37 ATP per mole of glucose but needs O2
for anaerobic conditions, glycogen and glucose can only give 2-3 ATP
FFAs
- can be used for prolonged exercise
- beta-oxidation in teh mitocondria to form acetyl coA to CAC to create ATP
Explain how fatigue occurs
Fatigue: not due to loack of ATP but due to the build up of metabolic byproducts
- periods of tetany, oxygen supply is adequate as long as circualtion is ok
los of glycogen and creating of lactic acid creates the fatigue
how does muscle growth occur
- small ability to form new muscle fibers (hyperplasia) but a larger ability to grow the fibers (hypertropy)
increased length = increase velocity and extent of shortening can occur
increased diameter = increased force (in parallel)
atrophy occurs with immobilization
so doubling the SIZE (diameter) will increase force of the muscle contraction
doubling the lengthof the muscle (in series) will increase the speed/velocity of the contraction
Learning = length (increase rate and accuaracy/speed)
weightlighitng = increased in parallel (to increase force of contraction
Length-Tension Relationship
isotonic v isometric
when a muscle contract, the force is generated and length is decreased
Isometric: contractions when the length is held constant, and the force is measured during the contraction
isotonic: the force is held constant and the lengthis measured
contractile forces of a muscle are increased with muscle length to a POINT, after this point, ther ability to contract with force decreases
- this is related to sliding filament theroy
Force-velocity relationship
the velocity (speed) at which a muscle shortens is depndent on the force that the muscle develops
without a laod: the shortening velocity of the muslce ins at its max: it will happen quickly!
increasing the load: will decrease the speed the muscle can shorten until, at the ma laod it cannot contract and lift the load anymore
