Muscular System Flashcards
muscles
convert chemical energy into mechanical energy
muscle functions
- motility
- maintain posture
- stabilize joints
- generate heat
characteristics of muscle tissue
excitability
contractility
extensibility
elasticity
excitability
receives and responds to stimuli
contractility
forcibly shortens in length
extensibility
stretched or extended
elasticity
recoil to original resting length
three types of muscle tissue
skeletal
cardiac
smooth
skeletal muscle tissue
attaches to and covers bony skeleton
responsible for body motility
contracts rapidly but fatigues easily
controlled at neuromuscular junctions
parts of muscle organ
muscle fibers
blood vessels (O2, nutrients, wastes)
nerves (control)
connective tissues (support and reinforce)
types of connective tissue sheaths
epimysium
perimysium
endomysium
epimysium
dense irregular tissue surrounding muscle
keeps fascicles together
perimysium
dense irregular tissue surrounding fascicle
keeps muscle fibers together
endomysium
areolar tissue surrounding fiber
direct muscle attachment
epimysium fuses to periosteum of bone
muscle to bone
indirect muscle attachment
connective tissue extends beyond muscle as tendon or aponeurosis to connect to bone, cartilage, or other muscle
sarcolemma
muscle plasma membrane
glycosomes- glycogen storage
myoglobin
mitochondria
T-tubules
invaginations of membrane
conduct electrical impulses to deepest region of muscle
stimulated by nervous system
cause release of calcium from SR
sarcoplasm
cytoplasm of muscle cell
sarcoplasmic reticulum SR
smooth ER that stores calcium and surrounds myofibrils
lies next to T-tubules
muscle fiber cells
each fiber is one long, multinucleated cell
10-100 micrometers diameter, 30cm long
made up of 80% myofibrils
myofibril
contractile organelle
made up of myofilaments and sarcomeres
myofilaments
actin (thin) and myosin (thick) motor proteins
sarcomere
smallest functional unit for contractions
region between two Z discs - stacked end to end within myofibrils
made up of myofilaments
striations
dark A bands- overlap of myosin and actin
light I bands- ends of sarcomere, not much overlap
elastic filaments
align myosin and actin
help with recoil after stretching
dystrophin
anchors actin filaments to sarcolemma and extracellular matrix
thick myosin filaments
compose central A band
rod-like tail with globular heads
head forms cross bridges
ATPase
thin actin filaments
globular proteins joined together to form filament
compose I band and partially overlapping A band
active sites for myosin binding
tropomyosin
regulates contractions
covers active sites on actin - prevents grabbing from myosin heads
troponin
regulates contractions
moves tropomyosin off active site
binds calcium
sliding model of contraction
myosin moves thin actin filaments toward center of sarcomere
entire muscle shortens as multiple sarcomeres contract in unison
cross bridge cycling steps
- myosin head attaches to actin forming cross bridge- attached ADP and Pi
- Pi released, initiating power stroke- myosin head pivots and bends as it pulls on actin sliding it toward M line, then ADP releases
- new ATP attaches to myosin head, releases link between myosin and actin
- ATP split into ADP and Pi, myosin head energized and cocked into high energy conformation
- repeat step 1
muscle needs to contract
ATP
calcium
signal from nervous system
rigor mortis
muscles stiffen 3-4 hours after death
dying cells cannot exclude calcium, still flows and stimulates muscle contraction
ATP no longer produced
cannot release actin and myosin filaments
muscle proteins eventually breakdown
nerve impulse
stimulates skeletal muscle contraction
creates action potential across sarcolemma and down T-tubules
stimulates release of calcium from SR
neuromusclar junction
motor neuron connects with muscle cell
3 components of neuromuscular junction
axon terminal
motor end plate
synaptic cleft
axon terminal
contains vesicles with neurotransmitter acetylcholine
motor end plate
contains acetylcholine receptors
synaptic cleft
space separating axon end from muscle fiber
excitation-contraction coupling
action potential reaches end of axons
Ach released to cleft
Ach binds to receptors on motor plate
depolarization
action potential propagates along T-tubules
calcium released from SR
calcium binds to troponin, troponin moves tropomyosin off actin binding site
depolarization
positive Na+ ions flood cell
creates action potential across membrane
when can cell be stimulated again?
after repolarization is complete
refractory period- cant restimulate muscle cell after first stimulation
3 mechanisms to remove signal to repolarize
- acetylcholine destruction by acetylcholinesterase
- repolarization of membrane- back to resting potential
- resting intracellular calcium levels restored
mesodermal myoblasts
fuse together and develop sarcomeres for skeletal muscles
cannot divide again or repair itself
satellite cells
muscle stem cells, can give rise to new myoblasts and satellite cells
amount declines with age
muscle fibers can lengthen or thicken
motor unit
one motor neuron and all the muscle fibers it signals
number of fibers varies from 4 to hundreds
one nerve axon branches and forms many junctions
muscle twitch
response to single stimulation
latent period
action potential is spreading across sarcolemma
period of contraction
myosin fibers pull actin fibers
cross bridge cycling
period of relaxation
calcium pumped back into smooth ER
finished muscle contraction and cell resets
temporal/wave summation
frequent stimuli increase contractile force
produces smooth continual muscle contractions by rapidly stimulating specific fibers
relaxation time between twitches decreases, calcium gets higher
unfused tetanus
rapid stimuli
sustained muscle contraction
fused tetanus
higher stimulus frequency
no relaxation between stimuli
recruitment
overtime, stimulus recruits more and more muscle fibers to do work
multiple bigger motor units control strength of contraction
threshold stimulus
stimulus which first observable contraction occurs
maximum stimulus
all motor units recruited
strongest stimulus that causes contractile force
most contraction muscle can do
size principle
smallest/most excitable motor units activated first
largest/slowest motor units activated last
motor units stimulated asynchronously
some units in unfused tetanus, some resting
prolonged contractions by delaying fatigue
types of muscle contractions
muscle tone
isotonic
isometric
muscle tone
stretch receptors stimulate low level of contraction
maintains posture and joints
no net movement
keeps muscles healthy and ready
isotonic
muscle shortens
muscle develops enough tension to lift weight
isometric
no length change
load is greater than force possible to lift
reaches peak tension developing capability
the greater the load…
the briefer the duration of muscle shortening
the slower the muscle shortening
overload principle
forcing muscle to work promotes increased muscular strength
adapt to increasing demands- accumulate more organelles- gets larger
muscles must be overloaded to produce further gains
4 components that determine strength of muscle contraction
frequency of stimulation
number of muscle fibers recruited
size of muscle fibers
degree of muscle stretch (filament overlap)
3 sources of ATP generation
- creatine phosphate
- anaerobic glycolysis
- aerobic respiration
creatine phosphate
stored in muscle cells
maximum power for 15 seconds
CP + ADP –> ATP + creatine
anaerobic glycolysis
no oxygen required
one glucose = 2 ATP
energy for 30-40 seconds
aerobic respiration
requires oxygen and glycogen
glucose produces 32 ATP
slower- more energy for longer time periods
aerobic endurance
amount of time muscle can use aerobic respiration
anaerobic threshold
point at which muscle must convert to anaerobic glycolysis
what is used for short surges of power?
ATP stores in muscle
creatine phosphate
anaerobic glycolysis
what is used for long exercise?
aerobic respiration
what is used for prolonged/lack of oxygen exercise?
anaerobic glycolysis
muscle fatigue
inability to contraction despite stimulus
due to ionic imbalances or decreased glycogen
ionic imbalances in muscle fatigue
K ions accumulating in T tubules interferes with SR calcium release
inorganic phosphate released from creatine interfere with SR calcium or myosin release
recovery
oxygen reserves in myoglobin replenished
lactic acid converted to pyruvic acid/glucose
glycogen, ATP, and CP stores replenished
excess postexercise oxygen consumption
extra amount of O2 needed to restore balance
fast vs slow muscle fiber types
different speeds of contraction based on:
myosin ATPase rate
activity of motor neuron
release of calcium
oxidative vs glycolytic muscle fiber types
rely on different ATP production rates
fast glycolytic fibers
anaerobic respiration
fatigue easily
thick, rapid power
hitting baseball
slow oxidative fibers
aerobic respiration
fatigue resistance, endurance
thin, little power
marathoners
fast oxidative fibers
in between
contract quickly
oxygen dependent
sprinting, walking
aerobic exercise increases:
muscle capillaries
number of mitochondria
myoglobin synthesis
resistance exercise increases:
muscle fiber hypertrophy
number of mitochondria
myofibrils
glycogen stores
connective tissue sheaths
powerful levers
effort further away from fulcrum than the load
mechanical advantage
speech levers
effort is closer to fulcrum than load
mechanical disadvantage
first class levers
fulcrum between effort and load
strength or speed
second class levers
load between fulcrum and effort
wheelbarrow
strength
least common
third class levers
effort between fulcrum and load
tweezers
speed/range of motion
most common
cardiac muscle tissue
only found in heart
pacemaker sets contraction rate - gap junctions
intercalated discs connect cells
doesn’t fatigue
lots of mitochondria
characteristics of smooth muscle
sheets of spindle shaped cells
connected by gap junctions
endomysium surrounds them
location of smooth muscle
hollow visceral organs
respiratory, digestive, urinary, reproductive tracts
peristalsis
alternating contraction of longitudinal and circular layers of smooth muscle
2 layers are running perpendicular to each other
longitudinal layer contraction
organ shortens, circumference increases
circular layer contraction
organ elongates, circumference decreases
varicosities
swollen regions of autonomic nerve fibers on smooth muscle fibers
diffuse junctions
wide synaptic cleft where varicosities release neurotransmitters
regulation of smooth muscle contraction
neural
hormonal
chemical
neural regulation of smooth muscle
autonomic nervous system uses variety of different neurotransmitters to determine contraction or relaxation
hormonal/chemical regulation of smooth muscle
neuronal signal not always needed
spontaneous contractions
hormones or chemicals can alter calcium
differences between smooth and skeletal
smooth :
greater stretch and tension
slow, prolonged contractile activity
calcium from extracellular space
calmodulin regulation (no troponin)
actin and myosin arranged diagonally with intermediate filament bundles
regenerate throughout adulthood
stress relaxation response
adaption to stretch/larger volume
allow time before contracting
smooth muscle contraction
spontaneous general depolarization
cells connected by gap junctions
calcium floods from extracellular space and SR
calcium binds to calmodulin to activate myosin light chain kinase
actin and activated myosin create sliding filaments with ATP
calcium released back to extracellular space after
prolonged contraction in smooth muscle
myosin takes longer to release from actin
slow ATPase activity
multiunit smooth muscle
innervated independent fibers activated by hormones or neurotransmitters from autonomic system
lungs airways, large arteries, pupils, arrector pili
unitary smooth muscle
innervated by varicosities activated spontaneously or by hormones/neurotransmitters, signal transduced through gap junctions
lining of all hollow organs except heart
muscle cramps
sudden involuntary contractions of skeletal muscle
overexertion, dehydration, poor blood flow, ionic imbalance
stretching
twitching eyelids
involuntary spasm of eyelid muscle
fatigue, stress, caffeine
repeated twitching, light sensitivity, blurry vision
more sleep, less caffeine, eye drops
muscular dystrophy
muscle destroy disease
fibers atrophy and replaced by fat and connective tissue deposits
Duchenne’s muscular dystrophy
x-linked recessive disease (mother to son)
progresses upward from extremities
die of respiratory failure in 20-30s
lack of dystrophin protein that connects actin to ECM
steroids, PT, drugs, ventilation, experimental
Becker’s muscular dystrophy
dystrophin is partially functional
slower and less predictable
survive to mid to late adulthood
myasthenia gravis
autoimmune disorder with unknown cause
loss of acetylcholine receptors on motor end plate
muscle weakness
drugs
dystonia
involuntary sustained contractions
miscommunication between brain and muscle
tremor and twitching
drugs, therapy, surgery, brain stimulation
ptosis
drooping eyelid
weakness of muscle that raises eyelid, damage to nerves that control that muscle
caused by aging, injury, disease
surgery
osgood-schlatter disease
painful swelling of bump on anterior tibial tubercle
overuse and repetitive injuries during growth
seen in youth sports
rest and reduce stress
strabismus
eye muscles are not properly coordinated
