muscle physiology Flashcards
structure of skeletal muscle include
muscle, muscle fibres , myofibrils ,
what is the role of myofibrils?
they are the contractile element in muscle fibres and have a pattern of dark and light bands
A band
known as dark bands and are made up of stacked thin and thick filaments that a re aligned parallel to each other
I bands
called light bands and a re made upon a portion of thin filaments that don’t extend to A bands
H zone
known as the lighter portion of the A band and hold myosin together in a stack
M line
proteins that hold the think filaments together ad runs down the centre of the H zone
z line
located in the middle of the I band , dismantle between 2 lines is known as a sarcomere , the functional unit of skeletal muscle
cross bridges
mobile myosin binding to the actin molecules in muscles
thin filament is made up of what proteins ?
actin , tropomyosin and troponin
thick filament is made up of ?
the motor protein known as myosin
head of myosin contain ?
important binding site for actin and a myosin ATPASE site
cross bridge formation from what ?
basis of sliding filament mechanism to allow for muscular contraction
contraction
activation of tension generating sites within muscle fibres, muscle will shorten
what happens to thick and thin filaments in contraction ?
thin filaments move inwards over the thick filaments , when this happens, z one move closer together when all the sarcomeres shorten to the same degree
concentric contraction
when a muscle shortens
powerstroke
refers to the interaction between myosin and actin which leads to a shortening of a sarcomere
what are the steps in the cross bridge cycle 4 things
1 binding, myosin cross bridge binds to actin 2 power stroke : myosin head bends pulling thin myofilament inwards
3: detachment : cross bridge detaches and returns to original formation
4 binding again
what is the result of a power stroke ?
actin molecules being pulled closer to he myosin , with each cross bridge actin is pulled over even more
excitation contraction coupling
process of converting electrical signal to a muscle contraction
structures of skeletal muscle that allow for transmit of signal to muscle fibres
T tubules and sarcoplasmic reticulum
sarcoplasmic reticulum
runs parallel to muscle fibres and acts as a storage site for calcium
T tubules
invaginations of the plasma membrane , run perpendicular to the fibres at junction of A and I bands
membrane depolarization in t tubules results in the release of ?
ca + from the sarcoplasmic reticulum
what happens in a relaxed muscle
cannot contract because tropomyosin is in the and troponin are in the way to prevent a cross bridge formation by blocking the myosin sites on the actin molecules
what happens when muscle is excited ?
Ca enters the muscle fibres which then binds to troponin which causes tropomyosin to move out of the way and exposing the myosin binding sites on actin molecules
muscle relaxation is caused by
decreased nerve activity at neuromuscular junction Ach in no longer released and acetylcholinesterase roves remaining ACH which stops the generation olfaction potentials in skeletal muscle
what happens without the release of ca +?
the troponin - tropomyosin complex can cover the the actin molecules , which results in muscle lengthening and relaxation
exposure of the actin binding sites allows for the
the ATP cross bridging cycling
what happens when ATPase binds withATP
splits into ADP and inorganic phosphate , stored energy is released and transferred to the myosin cross bridge
in the presence of ca +, the troponin and tropomyosin complex exposes actin , why happens to the cross bridge
?
cross bridge can bind with the actin molecule and causes a power stroke
when there is no Ca +?
cross bridge remains cocked and their is no contraction
what happens in power stroke ?
P is released and and ADP is released and cross bridge is still bound to actin
what happens when new ATP molecules bind ?
causes cross bridge to detach and return to its original shape
latent period
when cross bridging cycling begins, delay before contraction starts and action potential is complete
contraction time
where peak tension occurs , greatest tension reached by still creating force from the outside load , will end after all ca has Been removed
relaxation time
temporal relaxation between electrical stimulus and mechanical response
in order for muscles to have tension they must ?
have twitch which can happen through motor unit recruitment or frequency stimulation
muscle fibres in motor units are spread ?
throughout the entire muscle , activation of one mutter unit will only cause a weak contraction
when motor neuron is activated hat happens
causes muscle fibres in motor unit to contract
what happens when fatigue takes place ?
body can selectively rotate the activation of motor units so some rest and others take over
multiple action potential during muscle contraction allow for what ?
increase the contractile ability of the muscle
what happens if muscle fibre is restimulated after it has completely relaxed ?
the second twitch will be the same magnitude as the first twitch
what happens if muscle fibre is stimulated before it could relax?
second twitch is added to first twitch which results in twitch summation
what happens when twitches overlap ?
tetanic contraction occurs , unfused is when muscle fibres do not completely relax before the next stimulus
fused tetanic contraction
known as tetanus and their is no muscle relaxation between stimuli
length tension relationship
amount of tension generated at tetanus is dependant on the length of the muscle at onset of contraction
what happens when the length of the muscle is less than optimal ?
efficiency of contraction and tension will decrease as the thin filament is overlapping the thick filament without cross bridges. Thin filaments from opposite side of sarcomere cross over the z line
what happens if muscle fibre length is optimal ?
maximal number of cross bridging binding sites are available , thin filaments don’t overlap central region , muscle fibres at rest are at optimal length
what happens if it is greater than optimal length ?
during passive stretch the z lines will become further apart and the amount of overlap between thick and thin filaments decreases , less overlap means less cross bridges and less tension can be developed .. contraction won’t occur at all if the fibre is 70 % greater than the optimal fibre length
movement of bones is achieved through ?
muscle contraction or relaxation
how will a muscle shorten in contraction ?
it must exceed the forces that oppose the movement of the bone
muscle soreness or myalgia happen because ?
over exertion , improper rest
motor unit contractions can be classified as
isotonic or isometric
isotonic contractions
muscle fibre tension increases as the fibre remains the same length known as static contraction
dynamic contractions are
at the level of the whole muscle, and contraction is dynamic and can be concentric or eccentric
concentric dynamic contractions
produce tension while muscle shortens this happens when lifting an object
eccentric dynmaic contactions
produce tension when muscle lengthens ex) controlled lowering movement of object using bicep muscle ( lowering a weight when doing bicep curls
what are the 3 ways ATP is important in the contraction relaxation process
1) splitting of ATP for power stroke
2) binding of the new ATP to myosin head to release the cross bridge
3) active transport of Ca back into the SR
muscle fatigue
when contractile activity cannot be maintained and tension in muscles declined
central fatigue
when CNS decreases its activation of motor neurons. characterized by the lowing down of activity even though the fibres are not fatigued
muscle fatigue
used to protect muscle cells, fatigue reduces contractile activity before ATP runs out
reasons for muscle fatigue
1) when ATP metabolites become too high, interferes with cross bridging cycle , 2) accumulation of lactic acid( reduction of ATP) 3)
accumulation of extracellular K ( NA and K pump cannot work without ATP ),
4) depletion of glycogen
slow twitch muscle fibres ( type 1)
contract and relax at slower rates and are innervated by type A2 motor neurons, they are smaller and have a slower conduction speed and lower activation threshold. Are also called slow oxidative because the create ATP by aerobic processes
fast twitch muscle fibres ( type 2)
contract and relax at much faster rates and are innervated by A1 motor neuronswhich are large and have high conduction speeds and higher activation threshold
fast oxidative glycolytic fibres
type 2 fast twitch fibre, which produce ATP by both anaerobic and aerobic metabolism
fast Glycolytic fibres
type 2 fast twitch fibres, produce ATP by anaerobic means
color of muscle fibres is determined by
how they produce energy
red fibres
slow oxidative and fast oxidative glycolytic fibres ,are highly vascularized an contain many mitochondria and contain myoglobin
myoglobin give the fibres ?
the red color
white fibres
fast glycolytic fibres which rely mainly on anaerobic metabolism and have few mitochondria and no myoglobin ( pale color )
muscle spindles
monitor changes in muscle length and plays key role in stretch reflexes. distributed throughout the muscle as specialized cell s found around extrafusal fibres ( regular muscle fibres )
intrafusal fibres
known as the specialized cells in muscle spindles , only the end is contractile
muscle spindles are innervated by
gamma motor neurons
central region of muscle spindles
contains sensory afferent fibres that are activated by stretch and transmit information on muscle length and rate of stretch on CNS
Golgi tendon organs
responds to changes in muscle tension , receptors found in the junctions of tendons and respond to both stretch and contraction of muscle
what happens when extrafusal fibres contract
resulting tensions pulls on the tendons and stretch activates the afferent fibres intertwined within the tendons, the stronger the pull of the tendons the the higher the rate of firing of the Golgi tendon organs . information is sent to brain for processing , most info is used subconsciously
different levels of input for motor control
afferent neurons, primary motor cortex, brains stem
afferent neurons
involved in spinal reflexes and are at the level of the spinal cord
primary motor cortex
contains the corticospinal motor system, which mediates fine motor movement of body parts such as hands and fingers
brain stem
multi neuronal motor system influenced by the the motor regions of the cortex and at the cerebellum and basal nuclei , system regulates overall body posture and involuntary movement
proprioception
your awareness of your body in the environment
what would happen to damage to brainstem nuclei
decreased input on Motor neurons which are responsible for excitation of muscle fibres , voluntary movement would become hindered
damage to muscle spindle ? what would happen ?
would effect the detection of muscle length which would hinder the afferent nerves to convey information to brainstem and primary motor cortex , bairn cannot coordinate purposeful muscle activity
smooth muscle does not have ?
sarcomeres
smooth muscle contains 3 kinds of filaments
thick myosin, thin actin that contain tropomyosin and intermediate filaments that don’t support contraction but eh cytoplasm skeletal framework
instead of z lines smooth muscle cells have
dense bodies that are positioned throughout the cell and the internal surface of the plasma membrane
dense bodies act as
anchors points for both the intermediate and contractile filaments
thick and thin filaments are arranged
not in the length of the cell but at angles forming diamond pattern
smooth muscle does not have which protein
troponin
myosin light chain
found in smooth muscle and skeletal muscle . is more relevant in smooth muscle.and aid in the cross bridge formation
step one in myosin cross bridge activation
in excitation , Ca enters and binds to calmodulin
step 2 myosin cross bridge activation
calmodulin complex binds to and activates myosin light chain kinase
step3 myosin cross bridge activation
phosphorylated myosin cross bridge can bind with actin
smooth muscle does not contain
T tubules and has small sarcoplasmic reticulum
calcium for smooth muscles comes from
Ca entry from ECF and release of Ca from the sarcoplasmic reticulum
dihydropryidine receptors acts as ?
calcium channels
calcium induced calcium released
release of ca can stimulate the SR to release more calcium
multi unit smooth muscle excitation
known as neurogenic stimulation , distinct groups or units of smooth muscles that are innervated by nerves to contract ( nerves of the autonomic nervous system. found in small air ways of lungs, hair follicles and in the eye
single unit smooth muscle excitation
represents the majority of smooth muscle muscle. fibres are all electrically connected to gap junctions and contract as a single unit or function syncytium. Found in hollow organs such as the digestive system , reproductive system and urinary tract
