Muscles Flashcards
what do muscles do
generate force and movement
Name the three types of muscle
smooth, skeletal and cardiac
what muscle is striated
skeletal and cardiac
smooth muscle is not a striated but arrangement is
single unit cells, in a much more random arrangement
What muscle can divide and repair itself
smooth
Striated muscle is arranged in
Highly organised geometrical fashion of triangular and hexagons
striated muscle is highly packed so
squeezes out nucleus
cardiac muscle cells have what
intercalating disc
what does an intercalating disc do
allows electrical conductivity
Hard to depolarise heart due to
Multi connected heart providing alternative pathway due to the intercalating discs
What are striated muscle
arranged large protein filaments
what are muscles incased in
connective tissue sheaths
what are myoblasts
precursors for muscle
true or false myoblasts replace cells if damaged
false
what are damaged muscles replaced with
scar tissue
what happens if neighbouring cells die around muscle
makes it harder to contract
What are muscles attached to
Bones by tendons
what differentiates to form new muscle fibres when its damaged
satellite cells
Muscle cells never completely recover due to
limited stock of satellite cells
what do satellite cells move directly to
injury
What supplies muscles with oxygen for contractions
very deeply penetrating blood vessels
To much compression on blood vessels restricts muscles
oxygen levels, as can cut of supply
repeating units in striations are
sacromere
what lies between repeating units of sacromeres
Z line border
Do myosin fibres or actin fibres change in length
No
What causes contractions
Filaments slidding over each other and distance between them decreases
Thin filament and thick filament is
actin and myosin
What is the arrangement of actin
looks like a double helix
what is attached to actin
titin filament
cross head bridge is attached to what
Myosin filament
What generates the greatest force in muscle contraction
crosshead bridge moving actin
where does myosin cross head bridge head bind and latch on to
the binding site space on the double helix actin
what does the cross bridge head require to flip and detach itself from actin
ATP
Hydrolysis of ATP does what to cross bridge head
energises cross bridge attaching itself to actin
accumulation of ADP can cause what in contraction
muscle fatigue
what triggers contractions
fired AP causing an increase concentration of calcium ions
what does muscle do when relaxing
rid itself of calcium ions
what partially covers myosin binding site
Tropomyosin
Tropomyosin held in position by
troponin
Tropomyosin and troponin are an example of
cooperative bonding
What happens when calcium binds to troponin
pulls away Tropomyosin opening biding site for cross bridge head on myosin
Where is calcium ions stored
sacroplasm reticulum
what do transverse tubules deeply invaginated in the sarcolemma allow
depolarisation, conducting signal to release calcium ions
Depolarisation across cell membrane triggers
DHP to open calcium channel on sarcoplasmic reticulum
Why is relaxation powered
as ATP needed to remove calcium ions back into sarcoplasmic reticulum
How is paralysis prevented
muscle fibres within a motor unit may be scattered throughout muscle therefore hard to loose muscle activation
What is a motor unit
motor neurons and muscle fibres
Define Tension
force exerted by muscle
Load
force exerted on muscle
isometric
generates contraction without shortening muscle fibres
isotonic
shortens lengths of muscle fibres but tone of contraction kept consistent
lengthening
contractions with increasing lengths
Latent period
the time before excitation contraction starts
Contraction time
start of tension and time when we have peak tension
what is contraction time dependent on
calcium ion concentration
what has shorter latent period, but longer contraction event
Isometric contractions
what happens as load increases
contraction velocity and distance shortened decreases
What is a twitch
contraction of muscle fibre due to single AP being fired
Tetanus/ tetanic contraction
sustained level of contraction lev in any muscle fibre
what is an unfused tetanus?
stimulus not frequent enough, so cell can repolarise and depolarise again
If action potential is fired rapidly in the muscle what is it called
fused tension
why is a tetanic contraction better than a twitch tension
Calcium ions never get low for troponin to roebuck myosin biding sites
Less overlap over filaments means what about tension
there is less
Why cant we sustain titanic contraction for long
high calcium contraction for to long can cause cellular degradation
What happens if you overstretch muscle
Filaments interfere with each other to much and muscle does not contract
Optimal length for isometric tension is when?
The maximum interaction of myosin heads to maximum number of actin binding
Movement of limbs requires what?
two antagonistic groups
define antagonistic muscle
muscle that opposes the action of another
What are muscle arranged in
Lever system
What does lever arrangement allow
Less muscular effort to be given to move a heavier load
What allows increased maneuverability
Lever system
What does ATP power for contraction
Ca2+ to be pumped back into sacroplasm reticulum
Binding to myosin hydrolysing Xbridge
What is fatigue due to
repeated muscle contraction
What is fatigue dependant on
fibre type,
length of contraction,
fitness of individual
When does rigor occur in muscles
when muscle uses up vast amount of ATP
what causes muscle fatigue during high intensity, short duration exercise
Increased lactic acid from glycolysis
increased ADP inhibiting xbridge
Conduction failure K doesn’t depolarise
what causes muscle fatigue during long-term, low intensity exercise
decreased muscle glycogen
decreased blood glucose
dehydration
What happens in central command fatigue
cerebral cortex cannot excite motor neurons, rest period
What are the two ATP forming pathways of skeletal muscle fibres
oxidative or glycotic
Skeletal muscle fibres are fast if myosin has
high ATPase activity, so xbridge can be energised quickly
what do oxidative fibres contain that glycolytic don’t have
myoglobin
red
Why are glycolytic fibres white
dont contain myoglobin pigment
What increases oxygen delivery in oxidative fibres
Increased mitochondria
increased vascularisation
low diameters
contain myoglobin
what fibres is coloured red
oxidative
What diameters do glycolytic fibres have
large
What do glycolytic fibres have an increase of compared to oxidative
glycogen
What size of neutrons are easiest to exit first and example
small therefore slow oxidative fibres activated first
What do slow oxidative resist more of compared to fast glycolytic
fatigue
Fast glycolytic fibres are the largest and produce the most force due to
containing the most myofibrils
What fibres are last to be activated
Fast glycolytic fibres
increasing load results in increasing
number of active motor units
when the number of active motor units is increasing its called
recruitment
Neural control of muscle tension depends on
Frequency of AP’s
Recruitment of motor units
What do muscles need to be able to survive
base line level of stimulation
what is denervation atrophy and what can be the cause
Muscle wastage due to destroyed nerve or NMJ
when muscle is not used what happens
Disuse atrophy
What is an increase in muscle mass called
Hypertrophy
How does exercise cause hypertrophy?
Proteins are taking up to repair muscle damage
What is smooth muscle innervated by
autonomic NS
Where does smooth muscle exist
in hollow organs
eg. GI tract, uterus, airways, ducts
Structure of smooth muscle
spindled shape
mononucleate
What muscle can divide through life
smooth muscle
How are filaments arranged in smooth muscle
diagonally across the cells anchored by dense bodies to cell membrane and cell structures
In smooth muscle what does calcium bind to during x bridge activation
calmodulin
What activates myosin light chain kinase
calcium calmodulin complex
What does activated myosin light chain kinase do in smooth muscle
phosphorylates myosin x bridge with ATP
How does smooth muscle relax
dephosphorylation of X-bridges
How can persistent stimulation s useful in blood vessels and can be maintained by
decreasing rate of ATP splitting
slow x bridge
Xbridge dephophorylated when still bound to actin
What muscle are only some sites activated by Ca2+
smooth muscle
In skeletal muscle ca2+ from one action potential saturates how many troponin sites
all
What muscle has the greatest range and control
smooth muscle
Depending on how many AP reach the cell is how smooth muscle does what
grade the contraction
What does it mean than smooth muscle has a tone
basically has a base level of Ca2+ causing constant level of tension
What factors affect the activity of contraction
Autonomic NT Hormones local factors stretching of muscles Spontaneous electrical activity in muscle membranes ie pacemakers
What are the two types of smooth muscle
single unit or multi unit
Many cells linked by gap junctions is what kind of smooth muscle type
single unit
What muscle type responds to stretch
single unit
How do signal travel in single unit and how do cells contract
signals travel between cells
contract synchronously
Smooth muscle sing unit fibres may contain what
pacemakers
examples of multiunit fibres
hair, airways, large arteries
Small blood vessels, GI tract and uterus are what smooth muscle fibres
single unit
