15 - MSK Muscle of A&P Flashcards
What are the three types of muscle
smooth
cardiac
skeletal
How do the types of muscle differ in
function
body location
morphology (shape)
method of activation
Where is smooth muscle found
lines hollow organs
Size of smooth muscle
small
What is the morphology of smooth muscle
no striation (no striping pattern)
one nucleus
spidle shaped
Contracts into a ball
Does smooth muscle have gap junctions
yes
all connected to each other (wave of contractions)
how is smooth muscle regulated
involuntary
ANS
pacemaker cells (set diff rates of contractions)
respond to stretching (contract to resist stretching)
hormones
Where is cardiac msucles found
heart
Size of cardiac muscle
large
What is the morphology of cardiac muscle
striated (striped) – makes heart more efficient pump
1-2 nuclei
branched
Does cardiac muscle have gap junctions
yes
intercalated disks
how is cardiac muscle regulated
involuntary
ANS
pacemaker cells
hormones
Where is skeletal muscle found
MSK system
Size of skeletal muscle
very large
slightly bigger than a strand of hair
What is the morphology of skeletal muscle
striated (striped)
multinucleated (5-5000 nuclei) –> because very large, needs many nuclei to make enough nutrients that cell needs
long and tubular
Does skeletal muscle have gap junctions
no
has fine tune control (can control specific muscle)
how is skeletal muscle regulated
voluntary
somatic NS
What us skeletal muscle made of
muscle fibers (myocytes/muscle cells)
peripheral nerves
vasculature (blood vessels)
Where do peripheral nerve axons originate from
lower motor neuron cell bodies in the ventral grey horn of the spinal cord –> goes through ventral or dorsal ramus
What does contraction of skeletal muscle do
accounts for all voluntary body movement
What are the three layers that skeletal muscle is wrapped in
1) endomysium
- surrounds individual muscle fibers
2) perimysium
- surrounds bundle of muscle fibres
3) epimysium
- surrounds the entire muscle
What is a tendon made of
all the layers of skeletal muscle tapering off to form tendon
continuous with the periosteum of bone
What are muscle composed made of
muscle fibers
What are muscle fibres
filled with thousands of myofirbils
What are myofibrils
millions of sacromeres in series
What are sacromeres
What are they composed of
basic contractile unit (from Z to Z)
smallest unit in muscles
2 filaments:
- thick filament (myosin)
- thin filament (actin)
What do the dark and light bands on sacromere structure do
gives rise to striations
What do the bands mean on sacromere structure
light I band = actin only
dark A band = myosin and actin
dark H zone = myosin only
What happens with muscle shortening
actin filaments pulled across myossin filaments to make distance between adjacent z discs to get smaller
thick filaments slide over thick filaments = contraction
both H zone and I band decrease in size during contraction
What is titan
largest protein in the body
acts as a string to keep myosin in the centre
What is the effect of exercise on muscle size
muscles enlarge with use (hypertrophy)
- exercise stimulates protein synthesis
(actin and myosin)
- Results in more sarcomeres and more myofibrils
Do the number of muscle cells increase
no!
What are the factors effecting muscle size
muscle is highly expensive tissue because highly metabolically active (gobbles a lot of ATP)
if you dont use muscle, muscle will stop using protein and break down over time –> atrophy (no nutrition)
- immobilization, weightlessness, denervation (interfering signals)
building up muscle by muscle use –> hypertrophy
How does muscle contraction occur
sliding filament theory
- filaments slide past one another –> shortening
thin actin filaments slide over the myosin –> protein does not get smaller, but overlap between protein increases, making smaller
What shortens during muscle contraction
sacromere (z-z line shorter), H zone, I band
What stays the same during muscle contraction
A band
What is myosin
contractile globular protein (two heads)
thick
What is myosin composed of
composed of myosin molecules attached end to end to form a large myosin filament (tube-like structure)
globular heads contain actin binding sites and atp binding sites
- ATP provides energy to change the conformation (shape) of myosin heads
What is actin
glubules that form two coiled chains - the thin filmanet
What is actin made of
tropomyosin runs along actin - blocking myosin binding sites
troponin: holds tropomyosin in place regulated by Ca2+
How does actin contract
Add Ca2+ into cytoplasm –> Ca2+ binds troponin –> changes its confirmation –> pulls tropomyosin away from the mysoin-binding sites –> allows actin-myosin interaction to occur
When Ca2+ is removed, tropomyosin moves back to block myosin-binding sites (no actin-myosin interaction)
What is the contraction cycle
occurs as long as there is ATP (always present) and go signal (Ca2+)
cross bridge cycling: myosin bound to actin
- myosin heads hydrolyze (break down and store) ATP and become energized and oriented
- myosin head binds to actin to form a cross bridge
- myosin head pivots, pulling the thin filament past the thick filament toward centre of sacromere (power stroke)
- as myosin head binds ATP, the cross-bridge detaches from actin
What is rigor mortis
absence of ATP preventing myosin from disengaging with actin
slight state of contraction
very stiff becasue of all the cross bridges formed
What is excitaion-contraction coupling
process by which an electrical stimulus (excitation) triggers the release of calcium by the sarcoplasmic reticulum, initiating the mechanism of muscle sarcomere shortening (contraction(
What happens during excitation
AP in neuron coming down to axon terminal causes release of neurotransmitter (acetylcholine)
binds to acetylcholine receptors (nicotinic receptors on skeletal muscles) –> ACh-receptors at the motor end plate are stimulated
AP generated in muscle fiber and propagates along sarcolemma
How does AP in muscle contraction travel
AP travels as wave along the membrane and then must dive deep into the cell
AP propagated down T-tubules (transverse) = membrane invagination (allows go all the way down)
- T-tubules also have voltage gated ion channels (only way it would propagate): bring AP down
neurotransmission –> muscle action potential –> T-tubules –> SR (terminal cisternae) –> release of Ca2+ –> contraction
What is the sarcoplasmic reticulum
organelle
smooth endoplasmic reticulum specialized in skeletal muscle to be a place where you store calcium internally within that cell
right beside t-tubule
What is a triad
t-tubule and two sarcoplasmic reticulums surrounding it
How does AP cause calcium release
t-tubule bring AP down –> DHP receptor: changes shape & attached to ryanodine receptor –> pulls on plug –> calcium flows from sarcoplasmic reticulum to cytoplasm –> contraction
How to stop contraction
reuptake of Ca2+ in the SR
requires energy (pump using ATP) because concentration of Ca2+ very high in cytosol
SR Ca2+ pump
Takes a long time
Describe the electrical nad mechanical events that occur in a skeletal muscle cell
muscle fibre action potential occurs in about 3ms
latent period of about 10ms before muscle fibre shortening (lag phase)
- time it takes for calcium to flow across, bind….
1 AP generates certain amount of force and then disappears because brief release from AP and then circum pump put all calcium back into SR - no calcium, no contraction
Twitch contraction: 1 AP = 1 muscle contraction
What are the factors affecting force production
- muscle length
- degree of overlap before actin and myosin before telling the muscle to contract in the first place (~ half)
- if muscle is too contracted or too relaxed, can’t generate as much force if it there were some overlap between myosin and actin - Action potential frequency
- while muscle AP’s cannot be summed, calcium release events can
- the greater the frequency of stimulation, the greater the summation of intracellular calcium
Tetanic force: - number of fibres per motor unit and the cross-sectional area of those muscle fibres
- motor unit: single motor neuron –> all of the muscle fibres it innervates
- different types of muscle fibres in a muscle group
What is the size principle in motor unit recruitment
motor units are activated according to size; smallest to biggest
slow oxidative –> fast oxidative –> fast glycolytic
number of motor units recruited depends on force required for the task at hand
What is slow oxidative (muscle fibre type)
slow oxidative: always recruited first in contraction cause can make ATP using oxygen (fatigue resistance) –> posture and enduarance
What is fast oxidative-glycolytic (muscle fibre type)
fast oxidative-glycolytic: can make ATP using oxygen but can also break down glucose to make ATP in the absense of oxygen (less efficient) –> walking and sprinting
What is fast glycolytic (muscle fibre type)
fast glycolytic: biggest, only glycolytic processes (dont make ATP), short bursts of activity –> power movements), dont last very long
