Muscular System Flashcards
functions
- body movement
- stabilization of body position
- substance movement throughout body (pumping force in veins/lymp)
- generating heat
muscle types
smooth, cardiac, and skeletal muscle
smooth muscle
- present in organs, airways, blood vesseks
- involuntary
- 1 nucleus per cell
- not striated
cardiac muscle
- present in heart
- involuntary
- 1 nucleus per cell
- striated (contains sarcomere)
skeletal muscle
- present around bone
- voluntary
- many nuclei per cell
- striated (contain sarcomere)
skeletal anatomy
muscle > muscle fascicles > muscle fibers (muscle cells) > myofibrils (contractile protein)
sarcolemma
skeletal M. anatomy
cell membrane
sarcoplasm
skeletal M. anatomy
cytoplasm of m. cells
protective sheaths
skeletal M. anatomy
- epimysium (covers muscle)
- perimysium (covers muscle fasicles)
- endomysium (covers muscle fibers)
sarcomere
functional unit inside myofibrils, contains thin (actin) and thick myosin filaments that cause contractions
actin
- thin
- Z line/ I band
myosin
- thick
- A band/ H zone
sarcoplasmic reticulum (ER)
surrounds many sarcomeres arranged in fibers
* releases stored calcium into sarcoplasm when muscle cell is depolarized
sarcolemma
wraps SR, sarcomeres, to form muscle
* contains T tubule –> makes AP faster
Z line
- ends of sarcomere
- thin actin filaments branch from Z line to middle of sarcomere
M line
- midpoints
- thick myosin filaments branch from M lines towards Z lines
I band
only actin filaments
A band
- actin and myosin overlap
- does NOT change size during contraction
H zone
only myosin present
muscle contraction stimulation
- AP reaches motor end plate
- Ach is released at neuromuscular junction
- Ach bind to ligand-gated Na+ receptors –> Na+ enters cell = graded potential created
- graded potential trigger voltage gated Na+ channels to open
* can produce AP on muscles IF stimulus is large enough
* AP travels to T-tubules and causes Ca++ release
cross bridge cycling
- initially actin/myosin unbound because tropomyosin blocks binding site on actin
- neuron sends signal to muscle at neuromuscular synapse, releasing ACh
- ACh causes AP in muscle cells which spread out quickly via T-tubules
- due to AP, SR releases many Ca++ ions into muscle cell
- Ca++ causes troponin to move tropomyosin, allowing myosin to bind to actin
* myosin is attached to ADP + Pi in higher energy “cocked” position
cross bridge cycling (6-9 steps)
- release of ADP + Pi causes power stroke where myosin moves along actin
- ATP binds causing release of actin from myosin
- ATP is hydrolyzed to ADP + Pi causing myosin to become “cocked” again
when does rigor mortis occurs?
when there is not more ATP to release myosin
motor unit
all the muscle fibers innervated by a single neuron
small motor unit
few muscle fibers for precise movement
large motor units
many muscle fibers used in powerful movements
type 1 (slow twitch)
type of fiber
- high myoglobin so looks red
- slow to fatigue but slow contraction velocity–> slow oxidative (oxidative phosphorylation)
- mitochondria are in higher numbers
type 2 (fast twitch)
type of fiber
- low myoglobin so looks white
- fast to fatigue, but fast contraction velocity
- muscle cells don’t divide, just grow more/thicker/longer sarcomeres
- type ll a: fast oxidative glycolytic fibers
- type ll b: fast glycolytic fibers
twitch contractions
- contraction of a m. fiber through motor unti stimulation @ same size and duration
- all or non principle: depolarization will cause all m. fibers to twitch if above threshold but will not cause any twitching if the depolarization is below threshold
latent
twitch contraction phase
AP spreads over sarcolema and T-tubules, signaling SR to release Ca++
contraction
twitch contraction phase
cross bridges form as Ca++ binds to troponin
* muscle tension increases
relaxation
twitch contraction phase
Ca++ is pumped back into SR
* muscle tension decreases
twitches can add up to create?
summation = larger overall contraction
wave summation
- depolarizing motor unit during relaxation (can cause tetanus)
- resulting depolarization is larger but can eventually cause fatigue
motor unit summation
AP to different motor units at different times
* small (most excitable), larger (least excitable)
tetanus
stimulated frequently meaning no relaxation period
* sustained until muscle fibers are fatigued
muscle tone
caused by weak, involuntary twitches
skeletal muscle types
agonists, antagonists, synergists
