Chapter 9 Flashcards
Name 3 types of muscle tissue
- skeletal
- cardiac
- smooth
Does the skeletal muscle tissue have the following:
- striations
- attachment sites…what are they?
- are they voluntary?
- how strong are they?
- yes to stripes
- attached to bones
- voluntary conscious control
- powerful
Does the cardiac muscle tissue have the following:
- striations
- what is their function?
- are they voluntary?
- yes to stripes
- pumps blood
- involuntary
Does the smooth muscle tissue have the following:
- striations
- where are they located?
- are they voluntary?
- no to stripes
- located in walls of hollow organs
- involuntary
Name 4 characteristics of muscle tissue
- excitability - responsiveness
- contractility - able to decrease in length
- extensibility - able to stretch
- elasticity - is able to recoil to original length
Name 4 muscle functions:
- movement of bones or fluid
- maintaining posture
- stabilizing joints
- heat generation
Name the 3 connective tissue sheaths that muscles are wrapped in
- epimysium
- perimysium
- endomysium
What does epimysium surround and what type of connective tissue is it?
surrounds the whole muscle
dense regular
What does the permysium surround and what type of connective tissue is it?
surrounds each fascicle
fibrous
What does the endomysium surround and what type of connective tissue is it?
surrounds each muscle fiber
areolar
What is the origin vs the insertion?
origin: attachment to bone that doesn’t move (usually proximal)
insertion: attachment to bone that does move (usually distal)
Describe how a muscle attaches directly.
the epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage
Describe how a muscle attaches indirectly
connective tissue wrappings extend beyond the muscle as a ropelike tendon or sheet-like aponeurosis
Which is the most common attachment method:
direct or indirect
indirect
What are bundles of actin and myosin myofilaments that are enclosed in sarcoplasmic reticulum called?
myofibrils
What is the membrane around the outside of the muscle cell (muscle fiber) called? and where is it located?
sarcolemma
located inside endomysium
Name 4 things the muscle cell cytoplasm contains and what is their function?
- mitochondria - ATP production
- glycosomes - stores glycogen
- myoglobin - stores oxygen
- myofibrils - for contraction
What is the name of the cytoplasm of the muscle cell?
sarcoplasm
What has terminal cisternae that store calcium ions?
sarcoplasmic reticulum
What are the channels from the sarcolemma into the cells called? and where are they located?
t-tubules
located at A and I band junctions
What are a pair of terminal cisternae and a t-tubule called?
triad
What volume of a cell does the myofibrils take up?
80%
Describe the striations exhibited by myofibrils and what are they called?
A bands - dark
I bands - light
What are the thick filaments in the myofibrils called?
myosin
What are the thin filaments in the myofibrils called?
actin
What are the two proteins called that act as a control switch for muscle contraction?
tropomysin
troponin
Described the functions of tropomysin vs. troponin.
tropomysin blocks the binding sites on actin in relaxed muscle
troponin holds tropomysin in position
What is the smallest contractile unit of a muscle fiber? and where is it located?
sarcomere
located in the region of a myofibril between two Z discs
What is a sarcomere composed of?
thick and thin myofilaments made of contractile proteins
What produces striations?
arrangement of myofilaments
What is the light band with Z disc in middle?
I band
What is the sheet of alpha actinin that anchors actin filaments?
Z disc
What are the dark bands that contain both myosin and actin?
A band
What is the lighter band in the middle of A band where there is only myosin present?
H zone
What is the middle of H zone; dark line containing myomesin which anchors myosin filaments?
M line
What protein are the elastic filaments composed of?
titin
Where does the elastic filaments stretch from and what is their purpose?
stretch from Z disc to M line through myosin
help sarcomere return to original length after being stretched
When does shortening occur in the contraction of a muscle?
only occurs when tension generated by cross bridges on the thin filaments exceeds forces opposing the shortening
Describe the sliding filament model of contraction
- myosin heads bind to actin, detach and bind again to propel actin towards the M line
- as H zone shorten and disappear, sarcomeres shorten, muscle cells shorten and whole muscle shortens
What are the 2 requirements for skeletal muscle contraction?
- activation
2. excitation-contraction coupling
Describe activation
every muscle cell is in contact with a neuron
Describe excitation-contraction coupling
- generation and propagation of an action potential along the sarcolemma
- final trigger: brief rise in intracellular calcium levels
Where is the neuromuscular junction?
located half way along the muscle cell
What are the synaptic vesicles in the axon terminal called?
acetylcholine (ACH)
What contains the receptors for the ACH in the synaptic cleft?
sarcolemma
Where does the initiation of a contraction start?
neuromuscular junction
Describe what happens at the start of a contraction up to the release of ACH.
- nerve is stimulated (action potential) along axon to neuromuscular junction
- calcium channels in membrane of axon terminal open and calcium enters axon
- calcium ions trigger synaptic vesicles to release ACH by exocytosis into synaptic cleft
Describe what happens during the process of muscle contraction from when ACH is released into synaptic cleft and the action potential happens at the sarcolemma
- ACH diffuses across synaptic cleft and binds to receptors on sarcolemma of motor end plate
- permeability of sarcolemma changes and an action potential is initiated in the muscle cell
Where does the action potential travel?
along the muscle cell sarcolemma
What is ACH terminated by?
enzyme acetylcholinesterase
What is prevented in the destruction of ACH?
continued fiber contraction in absence of additional stimulation
What 2 things are happening during the latent period?
- time when E-C coupling events occur
2. time between AP initiation and the beginning of contraction
Describe the first 5 steps of the sliding filament model of muscle contraction (up to the binding of mysosin on actin)
- AP is propagated along sarcomere to t-tubules and calcium release from SR
- calcium binds to troponin
- troponin shape change moves tropomysin away
- ATP binds to myosin head and is hydrolyzed into ADP and Pi
- myosin heads are cocked and form cross bridges with action
Described steps 6-10 of the sliding filament model of muscle contraction (from where mysosin binds to action)
- myosin head changes shape to produce a power stroke
- ADP and Pi released from myosin head and new ATP binds
- myosin head detaches from actin and reattaches to new site on actin
- ATP hydrolyzed, head changes shape and new power stroke, etc…
- contractions continue as long as enough calcium ions are present and ATP available
What is the interval after a muscle contraction before another one can begin where the membrane needs to be repolarized before it can be stimulated again?
refractory period
Describe what happens at low intracellular calcium levels
- tropomysin blocks the active sites on actin
- myosin heads cannot attach to actin
- muscle fiber relaxes
- calcium levels are kept low in sarcoplasm
What proteins control the level of calcium in the sarcoplasm?
- calsequestrin
2. calmodulin
Describe what happens at higher intracellular
- calcium binds to troponin
- troponin changes shape and moves tropomysin away from active sites
- events of the cross bridge cycle occur
- when nerve stimulation stops calcium ions are pumped back into SR and contraction ends
Describe the 3 roles played by calcium in contraction
- action potential from neuron triggers calcium gates at axon terminal to open which then triggers release of ACH into cleft
- action potential in tubule and terminal cisternae triggers release of calcium from SR and removes inhibition by tropomysin
- when calcium binds to calmodulin it activates kinases - it then converts glycogen to glucose which is fuel for ATP production
What is it called when there is no shortening of a muscle. The muscle tension increases but does not exceed the load.
isometric contraction
What is is called when the muscle shortens. Muscle tension exceeds the load.
isotonic contraction
What is the most common isotonic contraction? and what does it do?
concentric isotonic
muscle shortens as it contracts
What type of isotonic contraction happens when the muscle is stretched by another muscle? What does it do and what is it important in maintaining?
eccentric isotonic
muscle contracts as it lengthens
maintains balance
What is a motor neuron and all muscle fibers it supplies?
motor unit
What do small motor units control?
muscles controlling fine movements (eg. fingers & eyes)
What do large motor units control?
large weight bearing muscles (eg. thighs & hips)
What is it called when all motor units do not fire at the same time? and why is this?
asynchronous
prevents fatigue
Name the 3 phases of a twitch and what happens during each phase
- latent - excitation contraction coupling
- contraction - cross bridge formation, tension increases
- relaxation - calcium ions reenter SR, tension declines to zero
What is a muscle twitch?
response of a muscle to a single brief threshold stimulus
What is a graded muscle response?
variation in the degree of muscle contraction
What are muscle responses graded by?
- changing in the frequency of the stimulus
2. changing in the strength of the stimulus
What does a single stimulus produce?
a single twitch
What is it called when the muscle does not have time to relax completely between stimuli?
wave summation
What is it called when there is a further increase in frequency?
unfused (incomplete) tetanus
What is it called when stimuli are given quickly enough?
fused (complete) tetanus
What is the minimum stimulus strength that causes the first visible contraction?
threshold stimulus
What is the stimulus strength at which maximum contraction occurs?
maximum stimulus
What happens during recruitment?
stimulus strength increases
increasing number of motor units contract
Describe muscle tone
constant, slightly contracted state of muscles
even when resting
What is the function of muscle tone?
keeps muscles firm, healthy and ready to respond
What is the only source of energy used for muscle contraction?
ATP energy
What is ATP generated by?
phosphorylation of ADP by creatine phosphate
creatine PO4 -> PO4 + creatine
ADP + PO4 -> ATP
What are two components of muscle metabolism?
- anaerobic pathway
2. aerobic respiration
What is the physiological inability to contract and respond to stimulus?
muscle fatigue
When does muscle fatigue occur?
- ionic imbalance
- calcium depletion
- lack of ATP
What is caused when there is a total lack of ATP, during states of continuous contraction?
contractures or cramps
What is needed after excercise for replenishment of:
- oxygen reserves and myoglobin
- glycogen stores
- ATP and CP reserves
extra oxygen
How much of the energy produced during muscle activity is given off as heat?
60%
What 4 factors affect the force of muscle contraction?
- number of muscle fibers stimulated (recruitment)
- size of the fibers-hypertrophy of cells increase strength
- frequency of stimulation
- length-tension relationship-muscles contract most strongly when muscle fibers are 80-120% of their normal resting length
Muscle fiber are classified according to two characteristics. What are they?
- speed of contraction
2. metabolic pathways
Which type of fibers use aerobic pathways?
oxidative fibers
Which type of fibers use anaerobic glycolysis?
glycolytic fibers
What is influenced by muscle fiber type, load and recruitment?
velocity and duration of contraction (how fast and how long it contracts)
Name the 3 types of of muscle fibers?
- slow oxidative fiber
- fast oxidative fiber
- fast glycolytic fiber
At what rate does slow oxidative fibers work and what type of excercise would they be good for?
slow contracting & fatiguing
good for endurance - marathons
At what rate does fast oxidative fibers work and what type of excercise are they good for?
intermediate
good for walking, sprinting
At what rate does fast glycolytic fiber work and what type of excercise are they good for?
fast contracting & fatiguing
good for short term, high energy activites
Describe influence of load
increased load -> increased latent period, decreased contraction, and decreased duration of contraction
Describe influence of recruitment
increased recruitment -> faster contraction and increase in duration of contraction
What type of exercise leads to increased muscle capillaries, number of mitochondria, myoglobin synthesis?
aerobic exercise
What will aerobic exercise convert?
fast glycolytic fibers into fast oxidative fibers
What does aerobic exercise result in?
greater endurance, strength and resistance to fatigue
What type of exercise increases mitochondria, myofilaments, glycogen stores and connective tissue?
resistance exercise (typically anaerobic)
What is it called when muscles weaken and degenerate if not used regularly?
disuse atrophy
What shape is smooth muscle?
spindle shaped
What does resistance exercise result in?
muscle hypertrophy due to increased fiber size
What type of connective tissue does smooth muscle have?
endomysium only
Where is calcium stored in smooth muscle?
caveolae
What is caveolae?
indentations in the plasma membrane
What does smooth muscle not have in comparison to skeletal muscle?
does not have striations, sarcomeres, myofibrils and t-tubules
Where do the nerve fibers innervate smooth muscle?
diffuse junctions
What do the varicosities (bulbous swellings) of nerve fibers in smooth muscle release?
neurotransmitters
How does smooth muscle contract?
like a corkscrew
When the smooth muscle contracts cells are electrically coupled by what?
gap junctions
Describe stress-relaxation response.
responds to stretch briefly, then adapts to new length (ie. stomach filling up with food)
