Muscle physiology Week 12 Flashcards
what are the different muscle types
skeletal muscle
- striated, voluntary
cardiac muscle
- striated, involuntary
smooth muscle
- unstriated, involuntary
where can skeletal muscle be foud
attached to bones of skeleton
where can cardiac muscle be found
wall of the heart
where can smooth muscle be found
walls of hollow organs and tubes such as stomach and blood vessels
what is the function of skeletal muscle
producing movement
maintain posture & body position
stabilize joints
protect organs
generate heat
what is the function of cardiac muscle
pump blood out of heart
what is the function of smooth muscle
movement of contents within hollow organs
what is the arrangement of muscle fibers
parallel to one another and bundled together by connective tissue (fascia)
what are muscle fibers composed of
myofibrils with each being made of regular arrangement of thick and thin filaments
What is the ion responsible for muscle contraction
Ca2+
what controls calcium levels
motor neurons
what is the film holding all the myofibrils together
sarcolemma
what is the repetitive sequence of myofibrils
I - band (Z- disc)
A - band (H- zone)
what is the triad found on myofibrils
T-tubule
2 x terminal cisternae of SR
What does SR mean
sarcoplasmic retinaculum
what are A bands
thick filaments along with portions of thin filaments that overlap
what are I bands
remaining portion of thin filaments that do not project into A band (only thin filaments)
what are cross bridges
project from each thick filament in 6 directions toward surrounding thin filament
where can sarcomeres be found
between Z-lines
what does 1 myosin protein consist of
2 identical golf club like subunits
what forms the cross bridges
heads of myson
what can be found at the heads of myosin
actin binding site and ATPase site
what is the length of the tail of myosin
100nm
what is the main structural component of thin filaments
actin which forms actin helix
what does actin do
interacts with myosin cross-bridges
what are the components of thin filaments
actin helix + tropomyosin + troponin
what happens during relaxed state of cross bridging
no cross bridging because cross bridge binding site on actin is physically blocked by tropnin-tropomyosin complex
what happens during excited state of cross bridging
Ca2+ is released and binds to troponin which moves it aside for myosin to bind to actin helix
triggers power stroke that pulls thin filament inward during contraction
what regultaes myosin actin binding
Ca2+
what happens during power strokes
binding > power stroke > detachment > cycle repeats
- stroking motion pulls thin filament towards centre of sarcomere
what causes the muscle to shorten
repeated cross bridge binding & power stroke
how is contraction accomplished
by pulling thin filaments from opposite sides of each sarcomere sliding closer together between thick filaments
what are the changes of sarcomeres during contraction
H- zone & I-band shortens
A-band remains the same (proportionally bigger)
HAI = thick, thick + thin, thin
Ai = A remains the same, i-band shortens, H band disappear
what is the main motor neurotransmitter
Acetylcholine (ACh)
what do T tubules contain
dihydropyridine receptor which are voltage gated Ca2+ channel
what do SR contain
Ca2+ releasing channels which have ryanodine receptors
are action potentials in skeletal muscle able to occur rapidly
no due to the refractory period
what happens during depolarization of a muscle
ACh binds to receptors which opens Na+ channels but close K+ channels
ultimately action potential generated
what happens during repolarization of a muscle
closed Na+ channel but open K+ channel
what are T tubules
transverse tubules
what is close to SR
T tubules
how are Ca2+ release channels opened
activation of dihydropyridine receptors by local APs in T tubules
what happens to Ca2+ after contraction
majority is re-absorbed back into SR, small amount is pumped outside
when does contraction occur after AP
much time after AP was generated and contraction outlasts AP due to Ca2+ reuptaking needing time
what is rigor mortis
stiffness of death
what is the role of ATP in cross bridge cycle
Once the Ca2+ binds is present and myosin is able to move, it bends but ADP & phosphate ion detach
ATP then binds to myosin cross bridge and assumes original conformation
what happens to myosin upon death
myosin and actin remain bound in rigor complex
what are the 4 steps in excitation, contraction and relaxation
- splitting ATP by myosin ATPase
- binding ATP to myosin breaks cross bridge
- active transport of Ca2+ back into lateral sacs of SR during relaxation (SERCA)
- activity of Na+ & K+ pump during AP production
what does SERCA mean
Sacro/Endoplasmic Reticulum Ca2+ ATPase
what are alternative pathways to form new ATP
creatine phosphate
glycolysis
oxidative phosphorylation
what does creatine phosphate do
supports short burst of high intensity contraction
fast reaction requires only 1 enzyme but not efficient
what are products of glycolysis
2 ATP & 2 Pyruvic acid
what can glyolysis support
anaerobic high intensity exercise
what happens to pyruvic acid with or without o2
with o2 = krebs cycle
w/o o2 = lactic acid
what does oxidative phosphorylation do
supports aerobic or endurance exercise
1 glucose = 36 ATP
Mitochondria & O2 involved
what happens when muscle fatigue occurs
when muscle can not respond to stimulation with same degree of contractile activity
- increase of phosphate
- Ca2+ leak
- depletion of glycogen
central fatigue occurs when CNS cannot adequately activate motor neurons
what are the origins of fatigue
muscle or central origin
what is needed to recover from exercise
increased o2 consumption
- excess post exercise o2 consumption
what are the different types of skeletal muscle fibers
based on differences in ATP hydrolysis and synthesis
1. slow oxidative fibers (type I)
2. fast oxidative fibers (type iia)
3. fast glycolytic fibers (type iix)
what are the colours of the different skeletal muscle fibers
type i = red
type iia = red
type iix = white
what is the glycogen content in the different skeletal muscle fibers
type i = low
type iia = intermediate
type iix = high
what is responsible for red colored meat
myoglobin
what has been proven to minimise sarcopenia
weight training / resistance training
what are the causes of sarcopenia
motor neuron death
changes in testosterone, activity, protein metabolism
mitochondria dysfunction
what does a loss of muscle protein lead to
hinders immune system, insulin absorption
increased risk of type ii diabetes
which muscle fiber is more affected than the other
type ii muscles are more severely affected than type i
when does gradual muscle loss begin
after 40
- loss through inactivity is ~1% and more so after 50
What are the differences between the skeletal muscle fibers
Fast vs slow fibers
- Myosin ATPase in Fast fibers > slow fibers
Oxidative vs glycolytic fibers
- fiber types differ in ATP synthesizing ability
Genetic endowment of muscle fiber types
- largely determined by type of activity for which muscle is specialized in
How do muscle fibers adapt
improvement in oxidative capacity (aerobic endurance)
muscle hypertrophy (anaerobic high intensity training)
Testosterone influence
interconversion between fast and slow muscle types under training
type I to II conversion during spinal cord injury/low gravity
muscle atrophy
muscle repair
What does anaerobic high intensity resistance training
increase myosin and actin filaments
What happens to satellite cells when muscle damage occurs
They become myogenic precursor cells that repair muscles
what causes muscle atrophy
disuse, denervation, aging
What are the primary types of contraction
isotonic (constant tension) = load remains constant as muscle changes
isokinetic (constant motion) = velocity remains constant as muscle fibers shorten
isometric (constant length) = muscle length remains constant as tension increases
What are secondary types of contractions
concentric contractions = muscle shortens
eccentric contractions = muscle lengthens
Which muscle fibers are more susceptible to eccentric exercise induced damage
fast twitch fibers
What are graded contractions
contractions of a whole muscle of varying strength
what are the factors that can help produce graded contractions
number of muscle fibers contracting
tension developed by each contracting fiber
what are the factors affecting contraction
no. of fibers contracting within muscle depending on extend of motor unit recruitment (stronger contraction = more motor units)
frequency of stimulus can influence tension develop by each muscle fiber
what is twitch summation
increase in tension accompanying repetitive stimulation of muscle fiber
what is tetanus contraction
smooth, sustained contraction of maximal strength
What is the primary drive of twitch summation
sustained elevation in cytosolic Ca2+
when does maximal tension occur
optimal muscle length
what is the difference between whole muscles and tendons
whole muscles are groups of muscle fibers bundled together & attach to bones
tendons attach muscle to bones
where is tension formed during muscle tension
produced internally in sarcomeres
what are the differences between type I and II fibers
Z-disk, Titin, Nebulin, dystrophin sizes
- Type I > Type II
Membrane strain
- Type I < Type II
For effective control of motor output, what does CNS continuously monitor
changes muscle length and tension
what monitors changes in muscle length & tension
muscle spindles = monitor muscle length
golgi tendon organs = monitor tension changes
what is the interactive system of skeletal muscles, bones and joints
Lever system
- bones are levers
- joints are fulcrum
- skeletal muscles provide force to move bones
what is stretch feedback
local negative feedback mechanism to sense and resist changes in muscle length when additional load is applied
what does the muscle spindle structure consist of
collection of specialized muscle fibers such as intrafusal fibers
what does alpha gamma coactivation lead to
contracts both intra- and extra- fusal muscle fibers
what do cardiac muscle feature
blends both skeletal and smooth muscle features
where can cardiac muscles be found
only in the heart
what are the fibers of cardiac muscles like
highly organized, striated, slender and short fibers
innervated by ANS
What is the advantage of smooth muscle
can develop tension and yet be relaxed when stretched as part of stress relaxation response
what are smooth muscles like
slow and economical based on latch phenomenon which allows them to stay attached longer
What is the Ca2+ dependent phosphorylation of myosin like
Ca2+ + Calmodulin = Ca2+ - Calmodulin > activates myosin light chain kinase > phosphorylates myosin cross bridge to bind with actin
Is troponin found in smooth muscle
no
does tropomyosin cover actin in smooth muscle
no
is smooth muscle myogenic
yes, they are pacemakers with slow wave potentials
What are 3 forms of ATP production
Creatine phosphate
Glycolysis
Oxidative phosphorylation
What is an example of a muscle that does not attach to bones at either ends but still produce movement
tongue
what are the factors affecting contraction
- frequency of stimulation
- fiber length at contraction onset
- fatigue extent
- fiber thickness
what are the neurons that assist with reflex
- excitatory neurons which stimulate flexion
- inhibitory neurons which inhibit extension
what controls motor contraction in NS
- motor cortex
- brain stem
- spinal cord
- cerebellum
- somatic & autonomous NS
For the myofibrillar domain to remain constant, what needs to change
changes in myofibrillar proteins and cross sectional area either increase or decrease in hypertrophy or atrophy respectively
Which component of the sarcomere acts as an ATPase?
myosin
Which of the following describe the characteristics of slow muscle fiber?
- small diameter, rich in myoglobin and very vascular
What are the two membranous structures within the muscle fiber that play important roles in linking excitation to contraction?
- transverse tubules and sarcoplasmic reticulum
Which of the following describes the neuromuscular junction?
special intercellular connection between axon branches and a skeletal muscle fiber
What happens to a muscle during an isometric contraction
prevented from shortening
During muscle contraction, what becomes smaller?
H-zone
What happens when two or more overlapping action potentials are “added” together within a muscle?
twitch summation
How would a drug that blocks acetylcholine (ACh) release affect muscle contraction?
contraction prevented
What two molecules participate in cross-bridge interactions?
actin & myosin
In skeletal muscles, action potentials travel down the _____ to initiate calcium release.
T-tubules
___ released from the lateral sacs of the sacroplasmic reticulum, binds to ___, which
induces contraction.
Ca2+, troponin
if u sever the tendon attached to a muscle, how would it affect the muscle’s ability to move a bod part
no movement possible without muscle - bone connection
what aspect of creatine phosphate allows it to supply energy to muscle
phosphate bonds
what molecule forms the thick filaments within muscle
myosin
