MUSCLE Flashcards
what does muscle contain
contractile proteins
what is the function of muscle
convert chemical energy in ATP to sliding of protein filaments
what is muscle specialized for
contraction
what are 3 types of muscle cells
- skeletal
- smooth
- cardiac
what is skeletal muscle attached to
bones
what does contraction of skeletal muscle allow (2)
- supporting skeleton
2. moving skeleton
what does smooth muscle surround (2)
- hallow tubes
2. hallow organs
what does contraction of smooth muscle allow
- propelling contents of hallow tubes + hallow organs
2. regulating diameter of hallow tubes
what does contraction of cardiac muscle allow
propelling blood throughout body
what are characteristics of skeletal muscle
- striated
2. voluntary
what are characteristics of smooth muscle
- unstriated
2. involuntary
what are characteristics of cardiac muscle
- striated
2. involuntary
what are 4 functions of muscle
- move body
- manipulate external objects
- propel contents through hallow tubes and hallow organs
- empty contents to external enviro
what is myocyte
muscle cell
what is sarcolemma
PM of muscle cell
what is sarcoplasm
cyto of muscle cell
what is sarcoplasmic reticulum
ER in muscle cell
what is sarcomere
contractile unit of muscle
what is muscle fibre
single muscle cell
what does skeletal muscle consist of
muscle fibres bundled together by CT
how is muscle fibre formed
fusion of myoblasts
what are myoblasts
cells that are
a. undifferentiated
b. mononucleate
what kind of cell is muscle fibre
multinucleate
what are myofibrils made of
- thin filaments
- thick filaments
what are thin and thick filaments made of
- thin ==> actin
- thick ==> myosin
what does motor unit refer to
all muscle fibres that single motor nerve innervates
what does number of muscle fibres that single motor nerve innervates depend on
dexterity of movement
what does gross movement involve
1 nerve innervates hundred of muscle fibres
what does fine movement involve
1 nerve innervates 5 to 6 muscle fibres
what is NMJ
where motor neuron meets muscle cell
what separates motor neuron from muscle cell
synapse
what do synaptic vesicles contain
transmitter
where is transmitter released
synapse
what is motor end plate
area of muscle fibre that is directly under synaptic terminal
what happens at motor end plate
motor neuron innervates skeletal muscle
what happens when AP travels down axon of motor neuron
- synaptic terminal depolarizes
- Ca channels opens
- Ca rushes into synaptic terminal
- vesicles containing Ach migrate to mem
- vesicles fuse w mem
- vesicles release content into synapse
- Ach binds to receptrs on mem of muscle cell at motor end plate
- receptors on mem open to allow small amount of Na into muscle cell
9 small amount of pos charge opens Na channels - large amount of Na enters through Na channels
- muscle cell mem depolarizes + AP generates
what is required for skeletal muscle cell to contract
stimulation by axon of motor neuron
what does each efferent motor neuron innervate
multiple muscle cells
what does motor unit consist of
- motor neuron
2. all muscle fibres it activates
what does motor unit represent
smallest unit of force that can be generated
what is A band
dark region with slightly light region in centre
how much of thick filament lies within A band
entire width
what is H zone
slightly light region in centre of A band
what does H zone contain
- parts of tick filament
2. none of thin filament
what is M line
horizontal line in middle of H zone
what does M line contain
system of supporting proteins
what is I band
light region
what does I band contain
portion of thin filaments that do not project into A band
what is Z line
dark horizontal line in middle of I band
what does Z line connect
thin filaments of 2 adjacent sarcomeres
what is sarcomere
- distance from Z line to Z line
- smallest functional unit of skeletal muscle
why is sarcomere smallest functional unit of skeletal muscle
smallest unit that can contract
what kind of unit is sarcomere
repeating unit
what is responsible for striated appearance of skeletal muscle
sarcomere
what happens to intracellular Ca levels during excitatory response
rise from resting levels
what is actin filament
2 strands made of F actin wrapped together to form alpha helix
what is actin associated with
- tropomyosin
2. troponin
what is troponin composed of
- troponin T (TnT) ==> binds to tropomyosin
- troponin C (TnC) ==> binds to Ca
3, troponin I (TnI) ==> binds to actin to inhibit contraction
what is tropomyosin composed of
2 alpha helices
what is myosin molecule
double trimer
what does myosin molecule consist of
- 2 heavy chains
- 2 regulatory light chains (insides)
- 2 essential light chains (outsides)
what are 3 regions of heavy chains
- tail region
- hinge region
- head region
what region of heavy chain are alpha helices intertwined
tail region
what happens to molecule at hinge region
unwinds + flares open into 2 globular heads
what does each head of heavy chain form complexes with
2 light chains
- one regulatory light chain
- one essential light chain
what is function of regulatory light chain
regulate ATP ase activity of myosin
what is the function of essential light chain
stabilize head region
how are myosin head arranged
pointing outwards to leave bare spot in middle
what does myosin head bind
actin filament
how do all muscle cells (skeletal, cardiac, smooth) contact
cross bridge cycling
where in ATP hydrolyzed in cross bridge cycling
at cross bridge
what is energy in ATP converted to in cross bridge cycling
small movement
what are accessory proteins (4)
- titin
- C protein
- alpha actinin
- nebulin
what is the function of titin
anchor thick filaments to Z line
what is the function of C protein
hold thick filaments in place at M line
what is the function of alpha actinin
attach thin filaments to Z line
what is the function of nebulin
anchor thin filament to Z line
what is SFT
mechanism of muscle contraction
what happenes to A band during contraction
length remains constant
what happens to I band during contraction
length changes (i.e. shortens)
what happens to sarcomere during contraction
length changes (i.e. shortens)
what happens to Z lines during contraction
move closer together
what happens to H zone during contraction
gets smaller
what does sliding of actin past myosin generate
muscle tension
how is sarcomere shorted during muscle contraction
- filaments slide past each other
- filaments do not shorten
what does cross bridge cycling refer to
action of cross bridge (head + hinge region of myosin)
what pulls actin towards H zone
cross bridges
CROSS BRIDGE CYCLING what happens in first step (3)
- ATP binds to myosin head
- myosin reduces affinity for actin
- myosin head dissociates from actin
CROSS BRIDGE CYCLING what happens in second step (3)
- ATP breaks down to ADP + Pi
- ADP and Pi stay associated with myosin head
- myosin head pivots to cocked / resting position perpendicular to actin and myosin filament
CROSS BRIDGE CYCLING what happens when myosin head pivots
lies up w new G actin monomer
CROSS BRIDGE CYCLING what happens in third step (2)
- myosin head attaches to new G actin monomer
2. ADP and Pi have high affinity for actin
CROSS BRIDGE CYCLING what happens in forth step (1)
- Pi dissociates from myosin head triggering power stroke
CROSS BRIDGE CYCLING what happens during power stroke
- myosin head bends 45 degrees around hinge
2. myosin pulls actin towards tail
CROSS BRIDGE CYCLING what happens in fifth step (1)
- ADP releases from myosin head
CROSS BRIDGE CYCLING what happens in attached state
myosin (w head bend 45 degrees around hinge) remains attached to actin
CROSS BRIDGE CYCLING how long will myosin remain attached to actin
until ATP binds
RIGOT MORTIS when does rigor mortis develop
after death
when there is a lack of
ATP
RIGOT MORTIS what happens in rigor mortis
myosin head remains attached to actin in attached state
RIGOT MORTIS why does myosin head remain attached to actin in rigor mortis
lack of ATP
when can cross bridge cycling be controlled
3rd step
what happens when Ca conc less then 10 ^-7
- inactive cross bridges
- myosin (w ADP + Pi )cannot bind to actin - muscle relaxes
what happens when Ca conc greater than 10 ^-7
- active cross bridges
- myosin ADP + Pi can bind to actin - muscle contrats
what allows for Ca conc to become greater than 10 ^-7
AP
what happens at low Ca concentrations
- regulatory proteins (troponin + tropomyosin) inhibit actin -myosin interaction
what happens at low Ca concentrations
- Ca binds to regulatory proteins
- regulatory proteins do not inhibit actin -myosin interaction
- regulatory proteins undergo conformational change
what specifically causes conformational change that allows for actin-myosin interaction and cross bridge cycling
Ca binds to TnC of troponin
what surrounds myofibrils within muscle fibre
SR
what does SR contain
calcium release channels or ryanodine receptors
what does each ryanodine receptor on skeletal muscle contain
foot processes
what is terminal cisternae
enlarged region of SR that stores and releases majority of Ca
how is Ca in terminal cisternae stored
bound to calsequestrin
what is the function of Ca pumps in SR
pump Ca from cyto to ST after muscle contraction
what are the 2 Ca pumps in SR
- SERCA 1
2. SERCA 2A
what are SERCA 1 and SERCA 2A
Ca ATP ase
why are SERCA 1 and SERCA 2A Ca ATP ases
use en from ATP hydrolysis to pump Ca from cyto to SR
how does SR speed up muscle contraction
shorter distance from SR to contractile proteins compared to distance from outside of cell to contractile proteins
TRANSVERSE TUBULES what are T tubules
- envaginations of sarcolemma
2. system of ducts that synchronizes release of Ca from terminal cisternae of SR
TRANSVERSE TUBULES where do T tubules envaginate
junction bw A band and I band
TRANSVERSE TUBULES what part of T tubules couples w ryanodine receptors
DHP receptors / L type Ca channels
TRANSVERSE TUBULES what does couple of T tubules w SR allow
AP can be brought into close proximity to SR from T tubule
in all 3 muscle types what is intracellular signal that triggers and sustains contraction of msucle
increase in intracellular Ca concentration
what is triad composed of
1 T tubule sandwiched bw 2 SR cisternae
what kind of muscle can triads be found
skeletal
what is dyad composed of
1 T tubule next to 1 SR cisternae
what kind of muscle can dyads be found
cardiac
what do triads and dyads play role in
coupling excitation and contraction
what is equivalent to T tubule system in smooth muscle
caveolae
what are caveolae
rudimentary invaginations of smooth muscle fiber sarcolemma
what are carveolae in contact with
SR
what is “excitation” in coupling referring to
excitatory AP
what is “ contraction” in coupling referring to
contraction of muscle fibre
what happens when AP travels from surface mem to T tubule system
triad region depolarizes
what happens when triad region depolarizes (5)
- L type Ca channels undergo conformational change
- L type Ca channels open
- L type Ca channels release Ca from T tubule to cyto
- Ryanodine receptors open
- SR releases Ca through ryanodine receptors to cyto
what allows for ryanodine receptors to open when triad depolarized
mechanical coupling w L type Ca channels w foot processes of ryanodine recepotrs
what happens when Ca leaves ryanodine receptors
- Ca binds to troponin
- regulatory proteins undergo conformational change
- actin-myosin interaction
what is involved in Ca removal from intracellular space through PM (2)
- Na / Ca exchanger (NCX)
2. surface Ca pump (PMA)
how does NCX work
extrudes 1 Ca from cell in exchange for 3 Na
how does PMA work
pumps Ca out of cell using ATP hydrolysis
why does extrusion of Ca through NCX and PMA play a small role in intracellular Ca removal
deplete Ca
what is responsible for Ca re-uptake into SR
SERCA
what is the function of calsequestrin
- bind to Ca
2. keep Ca lvls low
what happens when Ca conc in SR becomes too high
inhibits SERCA
what does bnding of calsequestrin to Ca allow
“keep Ca low” to allow SERCA to continue pumping Ca into SR
what is immediate source of energy for muscle contraction
ATP
how many ATP molecules consumed per 1 round of cross bridge cycling
1
what is ATP synthesized from
- lipid metabolism (fatty acids)
2. carb metabolism (glucose)
where does most rapid and most readily available pool of energy come from
phosphorylation of ADP by creatine phosphate (CrP)
what happens during intense exercise
fast twitch fibres quickly convert glycogen to ATP
how do fast twitch fibres convert glycogen to ARP
- glycogen broken down into glucose
2. glucose converted to 2ATP + lactic acid
what are 2 types of muscle contraction
- isometric
2. isotonic
what happens in isometric contraction
- length of muscle remains constant
- length of sarcomere remains constant
- tension developed (by muscle)
what is measured during isometric contraction
force produced
when does isometric contraction occur
- lifting load that is too heavy
2. pushing load that is too heavy
what happens in isotonic contraction
- length of muscle changes
2. tension remains constant
what is measured in isotonic contraction
change in length
when does isotonic contraction occur
- lifting load that is not too heavy
2. pushing load that is not too heavy
why does tension remain constant during isotonic contraction
weight of load being lifted or pushed does not change
what is a twitch
response of muscle to single AP
what happens during twitch
contraction phase followed by relaxation phase
what is summation
second AP fired before giving previous twitch time to fully relax
TEMPORAL STIMULATION what does temporal stimulation mean
AP s more frequent
TEMPORAL STIMULATION what happens during temporal stimulation
- before next twitch tension developed by muscle falls small amount
- before next twitch muscle has little time to relax
- built up of tension
TEMPORAL STIMULATION why is there a build up of tension
there is still residual tension from previous twitch
UNFUSED TETANUS what does unfused tetanus mean
AP s even more frequent
UNFUSED TETANUS what happens during unfused tetanus
- before next twitch tension developed by muscle falls very small amount
- before next twitch muscle have very little time to relax
- build up of even more tension
TETANUS what does tetanus mean
AP s most frequent
TETANUS what happens during tetanus
- before next twitch tension developed by muscle does not fall
- before next twitch muscle has no time to relax
- build of most tension
TETANUS what is tetanus
individual muscle twitches become indistinguishable from each other
what does it mean if muscle fibres have no time to relax in between AP stimulation
no time for Ca to be returned to SR
what does not generate force changes in muscle
what does generate force changes in muscle
individual fibres // motor units (1 neuron + all muscle fibres it innervates)
how are changes in force brought about
recruiting more motor units
during voluntary contraction what order are motor units activated
1. small (more excitable) 2 large (less excitable)
how can tension developed in muscle during contraction be altered
altering length of muscle fibre
what is optimal muscle length
length at which muscle fibre develops greatest isometric tension
100% of muscle length
what happens as muscle length increases to 100% muscle length
tension increases to 100% isometric tension
what happens as muscle length increases past 100% muscle length
tension decreases from 100% isometric tension
what happens when length is below optimal
- sarcomere not stretched out
- some myosin unable to interact w correct actin
- max number of cross bridges not formed
what happens when length is at optimal
- sarcomere stretched out
- all myosin able to interact w correct actin
- max number of cross bridges formed
what happens when length is below optimal
- sarcomere too stretched out
- some myosin able to interact w correct actin
- max number of cross bridges not formed
