Muscle overview/skeletal muscles Flashcards
thin filaments of contractile apparatus
actin myofilaments
tropomyosin
troponin
troponin
a calcium binding protein that closely resembles calmodulin
thick filaments
myosin
myosin is made up of
- two heavy chains, each consisting of a tail and a globular head domain on a hinge, head contains an enzyme (myosin atpase)
- four light chains, two attached to each heavy chain head domain, light chains are particularly important in regulating the contraction of smooth muscle
layers of connective tissue
- epimesium
- perimesium
- endomesium
sarcomere
functional unit of skeletal and cardiac muscle
- arrangement of thick and thin filaments
- striated muscle between two z-disks (lines)
- smallest functional unit capable of contraction as the z-lines are pulled together
thin filaments attach to what?
attached to z-disks
thick filaments attach to what?
m-lines, with tail ends of the myosin oriented toward the m-line from both sides
what attaches the z-lines to the m-lines
titin
largest protein known?
titin
A-band
entire length of thick filaments
H-band
only thick filaments, no overlap like a band
m-line
attachment of thick filaments in the middle
I-band
only thin filaments
z-line
attachment of thin filaments
sliding filament theory
myosin pulls z-lines together
I bands and H bands get smaller, may disappear
-a band remains the same size
myosin atpase
gives the power for shortening of the sarcomere
Things needed for sarcomere contraction
- hinge region of myosin extends if it has ADP and/or phosphate bound and flexes if not
- myosin has a low affinity for actin if ATP is bound and high affinity if not
- in the absense of ATP, the myosin remains tightly bound to the actin. this only happens after death
- to make the muscle relax, the myosin is prevented from binding to the actin. control of myosin’s access to actin is known as excitation contraction coupling
excitation contraction coupling
control of myosins access to actin
-through tropomyosin and troponin
tropomyosin
thin filament protein, covers actins binding site for myosin
toponin
thin filament protein that binds Ca++, causes tropomyosin to move when cytoplasmic [Ca++] increases
Sequence of events during EC-coupling: contraction phase
- AP is conducted to presynaptic terminal of motor neuron
- synapse at neuromuscular junction-exocytosis of Ach onto motor end plate
- Ach binds to nicotinic receptors in the motor end plate. nicotinic cation channels open
- a muscle EPSP occurs and triggers an action potential in the sarcolemma
- muscle action potential travels across the sarcolemma and down into the t-tubules
- Dihydropyridine (DHP) receptors in the t-tubule membrane respond to the action potential by opening Ca++ channels known as ryanodine receptors (RyR) in the sarcoplasmic reticulum (SR)
- Ca++ diffuses into the cytoplasm through the RyR, causing increased cytoplasmic [Ca++]
- Ca++ binds to troponin, which causes tropomyosin to move away from actin’s binding sites for myosin
- myosin begins its ATPase cycle and pulls on actin, shortening the sarcomere
Sequence of events during EC-coupling: relaxation phase
- Ca++ is pumped back into the SR by Ca++-atpase. inside the SR it binds to calsequestrin, a protein inside the SR that allows more Ca++ to be stored
- Decrease in cytoplasmic [Ca++] causes troponin to be empty and allows tropomyosin to cover myosin binding sites, stopping myosin ATPase cycle
Muscle twitch
a response of a muscle to one single action potential
-twitch of a single muscle fiber is ALL-OR-NOTHING
latent period
time between stimulus and beginning of twitch. this is when EC-coupling is occuring
Contraction Phase
beginning of the twitch, when muscle active force is increasing
-force increases as [Ca++] increases, so the contraction phase is when Ca++ is diffusing out of the Sr into the cytoplasm
relaxation phase
end of the twitch, when active force is decreasing
-force decreases as [Ca++] increases, so the relaxation phase is when Ca++ is getting pumped out of the cytoplasm into the SR
Tetanic contraction
a muscle fiber responding to a high frequency of action potentials will experience temporal summation of twitches
unfused tetanus
lower frequency of action potentials
-individual twitches are still evident, variable force dependent upon frequency of action potentials
fused tetanus
higher frequency (above 20/sec)
- no individual twitches. fused tetanus of a single muscle fiber is all or nothing
- normal was of using a muscle fiber
series elastic components of skeletal muscle
tendons
-are stretched by either active contraction or passive elongation of the muscle
parallel elastic components
connective tissues (endomysium, perimysium, epimysium)
intracellular: titin
- are stretched by passive elongation, go slack during active contraction
pre-load muscle
length-tension relationship is isometric force as a function of muscle length (preload with a weight the muscle cannot move)
- tension on muscle before contraction
- no preload, cant contract
- more preload, more force produced
- too much, cant contract. need optimal preload
isometric contraction
- muscle fibers shorten
- tendon gets longer
- overall length does not change
isotonic contraction
force on muscle does not change
- muscle contracts, force is on tendons, muscle, tendons, no force on mysiums
- mysiums take force when relaxed
mixed contraction stages
Isometric: increasing force to move load
Isotonic: load moves up and down
Isometric: muscle relaxes
what stretches mysiums
preload
- stretches mysiums in a relaxed muscle
- will never feel the full weight of object lifted
what does not stretch mysiums
afterload.
-causes contraction, muscles move
what feels the tension in series
tendon-fiber-tendon
what feels the tension in parallel
tendon-mysium-tendon
Isotonic contraction
- rare for just this type
- muscle stretches with preload, parallel muscle tension, muscle contracts=series
mixed contraction
- muscle does not feel load until after contraction
- isometric contraction until max weight is on muscle
- isotonic when pulling up
- no mysium stretching
key difference between pre-load and afterload
preload: stretches mysiums
afterload: give mixed contractions
power output of a muscle
power=force x velocity
corticospinal tract
upper motor neuron->lower motor neuron->muscle
what happens if you cut the upper motor neuron
spastic paralysis
what happens if you cut the lower motor neuron
complete paralysis
crossed extensor reflex (spinal reflex)
- step on tack
- leg beings to flex while other begins to extend
- foot on tack flexed, left leg extended
- then pain
- circuit causes flexion in muscles and extension in opposite
- circuit is also used for walking
what is pain
nociceptor afferent neuron
muscle spindles
- 1a fiber comes from spindle and synapses in gray matter to signal a muscle stretch
- gamma (y) motor neurons connect to muscle from gray matter. activate, stretches sensory part of muscle spindle, sends signal to CNS (through 1a fiber)
- muscle could be shortening, but if y activates then spindle stretches (called alpha/gamma contraction)
- activate gamma, stretch spindle, which stretches sensory spindle, 1a motor neuron sends signal to CNS, which sends signal down alpha motor neuron to muscle, muscle contracts
golgi tendon receptors
-axons arranged in between collagen fibers, axons get squished when you start pulling on tendons, send signal about force of contraction/tension
5 sources of ATP
- atp present in cytoplasm
- adenylate kinase reaction
- creatine kinase reaction
- glycogen breakdown (fermentation-lactic acid)
- fat mobilization (aerobic catabolism)
Adenylate kinase
- transfering phosphate
- ADP+ADPATP+AMP
- transfers phosphate to ATP
- does not last long (seconds)
creatine kinase
-muscles have creatine phosphate stored up (for emergencies)
-keep making ATP until exhausted (seconds)
Cr-P+ADP ATP+Cr
fermentation-lactic acid
- muscles contain glycogen
- 1 glucose-> 2 lactic acid, get 2 ATP per glucose
- lactic acid builds up, lowers acidic [] of blood
aerobic catabolism
- glucose-> krebs cycle
- use O2 and release CO2
reason for order of things and what do you use for sudden movement
- use all of these at once for sudden movement
- affiliated numbers are more for what gets used up the quickest
what role does epinephrine play
acting on B-adrenergic receptors (Gs-protein), causes increased glycogen breakdown in muscle fibers and fat mobilization by adipose tissues
Fiber types of muscle
- glycolitic fibers
2. oxidative fibers
glycolitic fibers
specialized in making fermentation ATP
-strong, high power quickly
oxidative
specialize in aerobic ATP production
-less power, longer production time
myosin types
- type 1 (slow myosin)
- type 2 (slow myosin)
- Type 2A (oxidative)
- Type 2B (glycolytic)
Type 1
goes through the cycle slower
- oxidative
- small diameter
- relatively small force
- lots of mitochondria
- myoglobin=red
type 2A
fast myosin
- oxidative
- very small diameter
- very small force
- lots of mitochondria
- myogloblin=red
type 2B
fast myosin
- glycolytic
- large diameter
- strong force
- few mitochondria
- no myoglobin-white
- glycogen granules
