Lecture 2 Muscle Tissue Flashcards
what are the characteristics of skeletal muscle?
- attaches to bone, skin or fascia
- striated (with light & dark bands visible with scope)
- voluntary
- appear as long cylindrical fibers with many peripherally located nuclei
what are the 3 types of muscle tissue?
skeletal
smooth (visceral)
cardiac
what are the characteristics of Cardiac muscle?
- striated
- involuntary
- autorhymic bc of built in pacemaker
- branched cylinders usu with one central nucleus - intercalated discs join neighboring cells
what are the characteristics of smooth (visceral) muscl
- attached to hair follicles in skin
- in walls of hollow organs – blood vessels & GI
- nonstriated
- involuntary
- spindle-shaped with one centrally located nucleus
what are the functions of muscle tissue?
- produce body movt
- stabilize body position
- regulate organ volumes (sphincters)
- movt of substances within the body (blood, lymph, urine, air, food and fuids, sperm)
- produce heat (thermogenesis - shivering)
one of the properties of muscle tissue is excitability, what is it?
ability to respond to certain stimuli by producing electrical signals called action potentials (impulses)
one of the properties of muscle tissue is CONDUCTIVITY , what is it?
ability to propagate the electrical signals over membrane
one of the properties of muscle tissue is CONTRACTILITY, what is it?
ability to shorten and thicken (contract) generate force
one of the properties of muscle tissue is EXTENSIBILITY, what is it?
ability to be stretched without damaging the tissue
one of the properties of muscle tissue is ELASTICITY, what is it?
ability to return to original shape after being stretched
what is superficial fascia? what does it do?
loose connective tissue & fat underlying the skin
- it stores water and fat
- reduces the rate of heat loss
- provides mechanical protection against traumatic blows
- provides a framework for nerves and blood vessels to enter and exit muscle
what is DEEP FASCIA?
dense irregular connective tissue around muscle
what are the layers of the deep fascia?
what is the function of deep fascia?
- epimysium: surrounds the whole muscle
- perimysium: surrounds bundles (fascicles) of 10 - 100 muscle cells
- endomysium: separates individual muscle cells
FX: deep fascia separates muscles into groups, support nerves, blood vessels, and lymph vessels and fills in spaces between muscles
connective tissue layers of skeletal muscles extend beyond the muscle belly to form what?
tendon
each skeletal muscle is supplied by…
a nerve, artery and 2 veins
each motor neuron supplies…
multiple muscle cells (neuromuscular junction)
each muscle cell is supplied by…
1 motor neuron terminal branch and is in contact with 1 or 2 capillaries
(nerve fibers & capillaries are found in the endomysium between individual cells)
what is muscle fibers (myofibers)
100s or 1000s of very long cylindrical cells seen upon microscopic examination of muscles
sarcolemma
sarco= flesh; lemma = sheath
- the plasma membrane of a muscle cell.
- it surrounds the muscle fiber’s cytoplasm, which is known as sarcoplasm.
why is sarcoplasm red?
due to the presence of myoglobin
transverse tubules
tiny invaginations from the surface toward the center of each muscles fiber.
- allow the action potential to travel from the sarcolemma throughout the muscle fiber
why does typical cell have many nuclei?
bc of early embryonic fusion of muscle cells
these are found at the periphery of the cells
what is the mitochondria?
power house of the cell
- it is the main site where ATP is produced.
- mitochondria lie in rows throughout the muscle fiber, strategically close to the muscle proteins that use ATP during contraction
what is ATP?
ATP is the principal energy transferring molecule in living systems. When it transfers energy to a reaction it decomposes to ADP, a phosphate group, and Energy
ATP –> ADP + Phosphate + Energy
ATP is produced from ADP and phosphate group using energy supplied from various decomposition reactions, particularly glucose.
ADP + Phosphate + Energy –> ATP
sarcoplasmic reticulum
- a fluid filled system of tubules that surround each myofibril.
- in relaxed muscles it stores calcium
- during muscle contraction, it releases calcium into the sarcoplasm
Myofibril
- at high magnification, the sarcoplasm appears stuffed with little threads, known as myofibrils
- contractile elements of skeletal muscle
- contains smaller structures called filaments
what are cross-striations of myofibril?
although myofibrils extend lengthwise within the muscle fiber, their prominent alternating light and dark bands make the whole muscle cell look striated or stripped, these bands are called cross-striation
thin filaments of myofibril are composed of?
composed of actin
thick filaments of myofibril are composed of?
myosin
elastic filaments of myofibril are composed of?
composed of titin
sarcomere
- the arrangement of myofilaments into compartments within a muscle fiber.
- are considered to be contractile unit of skeletal muscle
z disc (line)
separates one sarcomere from the other
A band
dark area which extends from one end of the thick filaments to the other and includes portions of the thin filaments where they overlap
I band
contains the rest of the thin filaments but no thick filaments. the Z discs pass through the center of the band
H zone
in the center of each A band contains thick but not think filaments
M line
formed by protein molecules that connect adjacent thick filaments
Myosin
contractile protein that forms the thick filament
- shaped like two gold clubs twisted together, the tails point toward the M line in the center of the sarcomere; the heads (cross bridges) extend out toward the thin filaments
Tropomyosin is a regulatory protein of Actin, what does it do?
it covers the myosin binding site on an actin molecule in relaxed muscle
Troponin is a regulatory protein of Actin, what does it do?
it binds calcium that is released during a muscle contraction. it helps to change the shape of actin by moving tropomyosin out of the way so that the myosin heads can bind to the actin molecule to allow muscle contraction
what does elastic filament composed of and what does it do?
composed of protein Titin.
It anchors the thick filaments to the Z discs.
Sliding Filament Mechanism
describe the process
- during muscle contraction, myosin heads pull on the thin filaments, causing them to slide inward toward the H zone at the center of the sarcomere
- the myosin cross bridges may even pull the thin filaments of each sarcomere so far inward that their ends overlap in the center of the sarcomere
- as thin filaments slide inward, the S discs come toward each other, and the sarcomere shortens, but the length of the thick and thin filaments do not change
- the sliding of the filaments and shortening of the sarcomere cause shortening of the whole muscle fiber and ultimately the entire muscle
during optimal overlap of thick and thin filaments, what takes place?
produces the greatest number of crossbridges and the greatest amount of tension
when muscles stretched past the optimal length, what happens?
fever cross bridges exist and less force is produced
if muscle is overly shortened, less than optimal, what happens?
- fever cross bridge exist & less force is produced
- thick filaments crumpled by Z discs
in normal conditions, the length of muscle fibers are?
resting muscle length remains between 70% to 130% of the optimum
what is the role of calcium in sliding filament mechanism?
increase in calcium in the sarcoplasm causes the sliding filament to start and a decrease in calcium in the sarcoplasm causes sliding filaments to turn off
name the 6 steps of how calcium affects the muscle contraction?
- a muscle action potential travels along the sarcoplemma
- calcium release channels open up in the SR
- calcium foods the sarcoplasm around the thick and thin filaments
- calcium combines with troponin
- this causes the troponin/tropomyosin complex to change shape and uncover the myosin binding site on the actin molecules
- the muscle contracts
what are the 5 steps of the power stroke and the role of ATP in muscle contraction?
- ATP from the mithochondria attaches to the myosin cross bridges (heads)
- ATP is split into ADP and Phosphate via an enzyme ATPase. The Energy reorients the myosin heads placing the myosin cross bridges in an activated state.
- When calcium levels increase, the troponin/tropomyosin complex moves allowing the activated myosin heads to bind to the actin molecules
- the myosin heads then swivel toward the center of the sarcomere. This swiveling is called the power stroke. as the heads swivel they release ADP, allowing another molecule of ATP to attach to the myosin head
- this process repeats over and over as lonf as there is enough ATP and as long as there is enough calcium
what are the 6 steps of relaxation of muscle tissue?
- action potential stops
- Acetycholineesterase breaks down any ACh left in the synaptic cleft
- calcium release channels close in the SR
- calcium active transport pumps turns on in the SR and remove calcium from sarcoplasm
- calsequestrin (calcium binding protein) binds to calcium in the SR
- as calcium levels decrease, troponin/tropomyosin complex slides back into place over myosin binding sites
what is motor neurons?
neurons that stimulate muscle to contract
skeletal muscles are well supplied with nerves and blood vessels
what is Motor Unit?
a motor neuron and all the skeletal muscle fibers it stimulates
(- a motor unit delivers the stimulus that ultimately causes a muscle fiber to contract
- a single motor neuron makes contact with an average of 150 muscle fibers. this means that activation of 1 neuron causes the simultaneous contraction of about 150 muscle fibers
- all the muscle fibers of a motor unit contract and relax together
- stimulation of a motor neuron produces a contraction in all muscle fibers of a particular motor unit. accordingly, the total strength of a contraction depends, in part, on which motor units are activated
generally, where is the neuromuscular junction located in the skeletal muscle fiber? why?
since skeletal muscle fibers are often very long cells, they NMJ is located near the midpt of the fiber –> the muscle action potential then spreads from the center of the fiber toward both ends. this arrangement permits neraly simultaneous contraction of all parts of the fibers
what is neuromuscular junction (NMJ)?
=myoenural junction
end of axon nears the surgave of a muscle fiber at its mother end plate region (remain separated by synaptic cleft of organ)
what are synaptic end bulb?
swellings of axon terminals, they contain synaptic vesicles filled with acetylcholine (ACh)
what are synaptic cleft?
gap between neuron and muscle
what happens after a nerve signal?
- arrival of nerve impulse at nerve terminal causes release of ACh from synaptic vesicles
- ACh binds to receptors on muscle motor end plate opening the gated ion channels so that the Na+ can rush into the muscle cell
- inside of muscle, cell becomes more positive, triggering a muscle action potential that travels over the cell and down the T tubules
- the release of Ca+2 from the SR is triggered and the muscle cell will shorten & generate force
- Acetylcholinesterase breaks down the ACh attached to the receptors on the motor end plate so the muscle action potential will cease and the muscle cell will relax
what are the 3 sources of ATP production within muscle?
- creatin phosphate (unique to muscle cells)
- anaerobic cellular respiration
- aerobic cellular respiration
what is the role of ATP in muscle fibers?
- skeletal muscle quickly switches from inactivity & back
- muscle contraction requires huge amounts of ATP for: powering contraction; pumping Ca+ into SR (relaxation); other metabolic reactions
- only a few seconds of ATP is present inside muscle fibers
- if contraction continues for more than a fe seconds, more ATP is made
Creatin Phosphate
- while resting, muscle produces more ATP than needed, so excess ATP is used to synthesize creatin phosphate
- a phosphate is transferred from ATP to creatine forming creatine phosphate and ADP
- creatine phosphate is a 3-6x more plentiful than ATP in sarcoplasm of relaxed muscle
- during contraction ADP starts to rise (muscle is using ATP and creating ADP) and creatine then gives back the phosphate to ADP creating ATP
- together creatine phosphate and ATP provide enough for about 15 seconds (100 meter dash)
Anaerobic cellular respiration
- series of ATP-producing reaction which do NOT require oxygen
- glucose diffuses from blood into contracting muscle fibers
- glycolysis, a 10 step reaction, quickly breaks down each glucose molecule into 2 pyruvic acid
- these reactions net 2 ATP molecules (creates 4 but uses 2)
- normally pyruvate enters mitochondria and is further manipulated producing 36 ATP. these reactions require oxygen
- when oxygen is deficient, pyruvate is converted to lactic acid which diffuses into blood then to liver for conversion back to glucose
- anaerobic respiration can provide energy for about 30-40 sec (400-meter race)
Aerobic Respiration
- muscular activity lasting longer than 30 sec depends on aerobic respiration
- these series of oxygen-dependent reactions occur in the mitochondria
- when completely oxidize, pyruvate generates ATP, CO2, water & heat
- although slower than glycolysis, aerobic yields about 36 ATP for each glucose molecule (2 pyruvates)
- a typical fatty acid molecule yields more than 100 ATP
what are the 2 sourcs of oxygen of muscles used in aerobic respiration?
- O2 which diffuses in from blood
- O2 released from myoglobin within muscle: myoglobin found only in muscle is O2 binding protein similar to hemoglobin; they bind O2 when its plentiful and release it when scarce
what is muscle fatigue?
- inability of muscle to contract forcefully after a prolonged activity
what are the possible factors that contribute to muscle fatigue?
- inadequate release of Ca+ from SR
- decline of Ca+ concentration in SR
- depletion of creatine phosphate
- O2 depletion
- lactic acid/ADP buildup
- surprisingly, ATP levels in fatigued muscles are not much lower than resting muscles
what is oxygen debt?
- after prolonged activity, heavy breathing continues for a while and O2 consumption remains above resting level
- recovery period may be just a few minutes or several hours
- oxygen debt refers to O2 over and above the resting O2 need
- extra O2 was used to “pay back” or restore metabolic conditions to resting levels in 3 ways:
- convert lactic acid back to glycogen
- resynthesize creatine phosphate and ATP
- replace O2 removed from myoglobin
why is “recovery oxygen uptake” a better term than “oxygen debt”?
bc it is now known that:
- only small amount of glycogen resynthesis occurs from lactic acid
- most glycogen is made much later from eating carbs
- lactic acid which remains is converted back to pyruvic acid and used for ATP via aerobic respiration in heart, liver, kidneys, skeletal muscle
- post exercise O2 use is boosted by elevated temp after strenuous exercise increases rate of chemical reactions (faster reaction uses more ATP and require more O2)
what happens if 2nd of stimuli occurs AFTER the refractory period is over?
muscle will respond to both stimuli
what happens if 2nd stimuli occurs AFTER refractory but BEFORE muscle has relaxed?
the 2nd contraction will be stronger than the first (wave stimulation)
what is Fused tetanus?
stimulation at a rate higher than 80 - 100 sec
what are the 2 types of isotontic contraction?
concentric isotonic - muscle is shortened
isotonic - muscle length increases during contraction (used during workout), muscle is contracting but is getting longer
what is isometric contraction
sustaning contraction for long time, works muscle harder and helps build up muscle mass
myosin-corssbriges generate tension but muscle doesn’t shorten bc force of loads equals muscle tension (used for maintain posture & support objects in fixed postion)
what is muscle tone?
small amount of tautness or tension in muscle due to weak involuntary contraction of motor unit
what is red muscle fibers?
skeletal muscle fibers that have high myoglobin content
what is white muscle fibers?
muscle fibers with low myoglobin content
- skeletal muscle fibers also contract and relax at different speed - the way they use ATP
slow oxidative (SO) fibers
- dark red (myoglobin and capillaries)
- creat ATP mainly via aerobic cellular respiration –> oxidative
- slow since contraction cycle of “rowing of myosin heads” is slower pace than “fast”
- very fatigue resistant
- capable of prolonged, sustanined contractions for many hours
- used in posture muscles, aerobic, endurance-type
fast oxidative - glycolytic (FOG) fibers
- intermediate diameter
- large amounts of myoglobin and many blood vessels, i.e. also dark
- create much ATP via aerobic cellular respiration
- moderately fatigue resistant
- high glyocogen content, i.e. generate ATP via glycolysis (anaerobic cellular respiration)
- speed of contraction faster than SO, since they breakdown ATP 3-5x faster than SO (myosin head rows faster)
- reach peak tension more quickly than SO but for briefer duration
- FOG used in walking, sprinting
Fast Glycolytic (FG) Fibers
- largest diameter (mostly myofibrils)
- generate most powerful contractions
- low myoglobin content and few capillaries
- contain large amounts of glycogen and generate ATP mainly via glycolysis (anaerobic cellular respiration)
- fast-twitch fibers used for short-duration of intense strength i.e. throwing a ball or weight lifting
- weigh lifting produces increases in size, strength, and glycogen content of fast glycolytic fibers
- FG fibers of weight lifters may be 50% larger than sedentary people
- fatigue quickly
most whole skeletal muscle are? and the proportions vary depending on?
mixture of all 3 types of fibers (SO, FOG, FG)
action of muscle
person’s training regimen
genetic factors
postural muscles have higher proportions of ?
SO fibers
muscles of arms / shoulder have higher proportions?
FG fibers
legs have large numbers of?
both SO & FOG
Skeletal muscle fibers of any given motor unit are? why?
ALL THE SAME TYPE
- different motor units are recruited in specific order, depending on need
- if weak contraction is suffice only SO Motor units are activated
- if more force is needed, FOG motor units are recruited
- if max force is required FG motor units are called into action
what is genetically determined and helps account for individual difference in physical performance?
ratio of fast-twitchi & slow - twitch in each muscle
what causes gradual transformation of some FM and FOG?
endurance type (aerobic) exercises - these exercise also result in CV and respiratory changes so skeletal muscles receive better supplies of oxygen and nutrients
what produces a size and strength of FG fibers?
strength types exercise
- size increases is due to increased synthesis of thick and thin filaments resulting in hypertrophy
what is the anatomy of Cardiac Muscle
- striated, short, quadrangular-shaped, branching fibers
- single centrally located nucleus
- cells connected by intercalated discs with gap junctions
- same arrangement of thick and thin filaments
Cardiac versus Skeletal Muscle
???
what is autorhythmic cells?
contract without stimulation
it creates Cardiac Muscle to contract
conduction system of heart
SV –> right atrium –> Sinoatrial Node –> Atrioventrical node –> Bundle of HIs –> right and left (???)
describe the physiology of Cardiac Muscle
- autorhythmic cells (causes excitation)
- contracts 75 x per min & needs lots of O2
- larger mitochondria generate ATP aerobically
- sustained… (??_
what are the 2 types of smooth muscle?
- visceral (single unit): in the walls of hollow viscera & small BV; autorhythmic; gap junctions cause fibers to contract in unison
- Multiunit: individual fibers with own motor neuron ending; found in large arteries, large airways, arrector pili muscles, iris, and ciliary body
anatomy of smooth muscle
small, involuntary muscle cell - … (?)
in smooth muscle thick and thin myofilaments are arranged how? and what is the significance of this?
not orderly so they lack sarcomeres
anatomy of smooth muscle?
???
hypertrophy
immature skeletal muscl … ?
what controls muscle tension?
motor unit
increasing strength requires increasing motor unit recruitment
- typically different motor units in a whole muscle are not stimulated to contract in unison. While some are contracting, others are relaxing.
- weakest motor units are used first than additional motor units are added as needed until full contraction occurs
what is twitch contraction?
brief contraction of all muscle fibers in a motor unit in response to a single impulse (last from 20-200ms)
what is wave summation?
when 2nd stimuli occurs after the refractory period is over, skeletal muscle will respond to both stimuli
- if 2nd stimuli occurs after refractory but before muscle has relaxed, the second contraction will be stronger then the first - this phenomenon is called wave summation
unfused tetanus
when skeletal muscle is stimulated at a rate of 20-30x/sec it can only partially relax bt stimuli, the result is a sustained but wavering contraction called unfused tetanus
fused tetanus
sustained contraction in which individual twitches cannot be discerned, stimulation at a rate of higher than 80-100x/sec
unfused and fused tetanus both result from
addition of Ca+ released from SR bu 2nd and following stimuli
what are the 2 types of isotonic contraction?
concentric isotonic contraction & eccentric isotonic contraction
what is concentric isotonic contraction?
muscle shortens and pulls on another structure
ex: lifting a glass of water to your mouth, concentric isotonic contraction of your biceps muscle
eccentric isotonic contraction?
muscle length increase during contraction
ex: returning the glass of water from your mouth to rest it on the table. known as “negative” physical fitness
- myosin cross bridges resist movt of load and slows lengthening process
what is isometric contraction
myosin crossbridge generate tension but muscle doesn’t shorten bc force of load equals muscle tension
- used for maintaing posture & supporting objects in fixed position
muscle tone?
small amount of tautness or tension in muscle due to weak involuntary contraction of motor units
- to sustain muscle tone, small groups of motor units are alternatively active and inactive in a constantly shifting pattern
- muscle tone keeps skeletal muscles firm, but it does not result in a force strong enough to produce movt
skeletal muscle fibers that have high myoglobin content are referred to as? what are it’s characteristics?
red muscle fibers (or dark meat on chicken)
has more mitochondria and blood capillaries than white
muscle fibers with low myoglobin content are called?
white muscle fibers (or white meat)
what is myoglobin?
red colored protein that binds oxygen in muscle (similar to hemoglobin in RBC)
what re the 3 types of skeletal muscle fibers?
slow oxidative fibers
fast oxidative-glycolytic fibers
fast glycolytic fibers
which of the skeletal muscle fibers is the smallest in diameter and least power?
slow oxidative fibers
