Ch. 10: Muscle Tissue review
Describe the structural muscle proteins
Structural proteins = Titin and Dystrophin Titin anchors the Z disc to the M line (which helps stabalize position of the thick filaments) (Z disc is dense protein material that separates one sarcomere from the next sarcomere in the mofibril) (M line is the supporting protein in the middle of the sarcomere) Dystrophin links the sarcomere to sarcolemma (i.e. the thin filaments of the sarcomere attach to integral membrane proteins of the sarcolemma, which are attached to proteins in the connective tissue ecm that surrounds muscle fibers -keeps sarcomere conected to the plasma membrane -reinforces sarcolemma -transmits tension generated by sarcomeres to tendons
I band
Structure A
fascicle
Structure A
nucleus
Structure A
Z disc
Structure B
perimysium (around fascicle)
Structure B
periosteum
Structure B (fibrous covering of bone)
H zone
Structure C
satellite cell
Structure C
tendon
Structure C
M line
Structure D
epimysium
Structure D
mitochondrion
Structure D
endomysium
Structure E
A band
Structure F
myofibril
Structure F
perimysium
Structure F (covering)
muscle fiber (cell)
Structure G
thick filament
Structure G
epimysium
Structure G (same layer as E)
muscle fiber (cell)
Structure H
thin filament
Structure H
sarcolemma
Structure H (plasma membrane)
sarcomere
Structure I
sarcoplasm
Structure I (cellular fluid of muscle)
sarcoplasmic reticulum
Structure J
titin filament
Structure J
myofibril
Structure K
sarcolemma
Structure K
zone of overlap
Structure K
myofibril
Structure L
somatic motor neuron
Structure M
sarcoplasm
Structure M (fluid of this space)
blood capillary
Structure N
nucleus
Structure N
thick filament
Structure O
nucleus
Structure P
thin filament
Structure P
triad
Structure Q
striations
Structure Q (markings)
transverse tubule (T tubule)
Structure R
sarcoplasm
Structure R (fluid)
sarcolemma
Structure S
terminal cisterns
Structure S
filament
Structure T
mitochondrion
Structure T
sarcomere
Structure U
Z disc
Structure V
what do muscle action potentials travel through?
T tubules
Connective Tissue that Attaches Skeletal Muscle
Tendon: -Rope-like extension of the three connective tissue layers (epi/peri/endomysiums may extend beyond muscle fibers) -attaches a muscle directly to the periosteum of a bone EX: Achilles tendon attaches gastrocnemius muscle of calf to calcaneus of tarsus (heal bone) Aponeurosis: (basically a flat tendon) -Broad, flat sheet extension of the three connective tissue layers -attaches muscle to another muscle or bone EX: epicranial aponeurosis between frontal and occipital bellies of occipitofrontalis muscle
When a skeletal muscle fiber contracts, ___.
The H zone and the I bands narrow
The force of a muscle contraction becomes ____as more _____ are activated
The force of muscle contraction becomes greater as more motor units are activated
The total tension that a single fiber can produce depends on? The total tension that a whole muscle can produce depends on?
The rate at which impulses arrive at the neuromascular junction. The # of impulses per second is "frequency of stimulation" the total tension that a whole muscle can produce depends on the number of muscle fibers that are contracting in unison
Describe the various stimuli that trigger action potentials in muscle cells
The stimuli that trigger action potentials in muscle cells may be: 1. electrical signals arising in muscle tissue itself (like in the heart's pacemaker) 2. chemical stimuli (such as neurotransmitters released by neurons) 3. hormones distributed by blood 4. local changes in pH
Epimysium vs. Perimysium vs. Endomysium
These are three layers of connective tissues (within the muscle organ itself) Epimysium= STRONG! -dense connective tissue -outermost layer -encircles entire muscle organ Perimysium= Less strong, more RUBBERY! -layer of dense irregular connective tissue -surrounds bundles of muscle fibers called fascicles -each fascicle contains bundle of 10-100 or more muscle fibers (cells) Endomysium= LOOSE! -thin sheath of areolar connective tissue -penetrates interior of each fascicle -separates each muscle fiber within a fascicle
What regulates the cardiac and smooth muscle?
These involuntary muscle tissues are regulated by: 1. The autonomic (involuntary) division of the nervous system 2. Hormones released by endocrine glands
What is going on with actin and myosin during rigor mortis?
They are stuck becuase there is no ATP to allow for release. after a while the proteins die though, and your muslces release
Excitation-Contraction Coupling---Ca2+
This refers to the steps that connect excitation (a muscle action potential propagating along the sarcolemma and into the T Tubules) to contraction (sliding of the filaments) 1. An increase in Ca2+ concentration in sarcoplasm (all Ca2+ is in the sarcoplasmic reticulum and it gets released ) -increase starts muscle contraction -decrease stops it -calcium is typically low in sarcoplasm but stored in SR cisterns the Ca2+ release channels that are in SR, open when muscle action potential propagtes into T-Tubule -release Ca2+ ions into sarcoplams -bind to troponin, moving tryopomyosin and exposing mysosin binding sites on action, so now mysoin can bind to it and pull actin in. BUT THEY CAN'T DO THIS TIL THE ATP COMES IN!
What is the primary function of muscle?
To change chemical energy into mechanical energy to produce movement. i.e. you eat food and it gets broken down to make ATP and this gets converted to mechanical energy
Deep in word extensions of the sarcolemma from a tunnel like network in the muscle cell is known as ____
Transverse tubules (T tubules)
T/F? Decreased oxygen availability leads to muscle fatigue.
True
T/F? Electrical gradients exist because sodium and potassium ions are separated on either side of the plasma membrane.
True
T/F? Jack has decided to take up jogging as a way to enhance his endurance training.
True
True or False, all the muscle fibers in one motor unit contract in unison?
True *note that typically, muscle fibers of a motor unit are dispersed throughout a muscle rather than clustered together)
Mysium means?
"of the muscle"
What value best represents resting membrane potential of skeletal muscle cells?
-85 mV
Describe how an impulse excites a skeletal muscle fiber
1. Release acetylcholine...vescicles undergo exocytosis in repsonse to Ca2+ ions. -An impluse travels from the brain or spinal cord, along a motor neuron, to the muscle fiber. -Arrival of the impluse at the synaptic end bulb stimulates voltage-gated channels to open up. -Ca2+ ions flow inward through the open channels. -Ca2+ stimulates synaptic vesicles to undergo exocytosis. ACh released into synaptic cleft. ACh diffuses across synaptic cleft between motor neuron and motor neuron end plate 2. Activation of ACh receptors...bind to receptors to open Na+ ion channels -binding of 2 molecules of ACh to a receptor on the motor end plate opsn ion channel in the ACh receptor. Now ions mostly Na+ can flow across the membrane 3. Generation of muscle action potential...change in membrane potential triggers contraction -inflow of Na+ (down its electrical gradient) makes inside of muscle fiber more positively charged. -this change in membrane potential tribbers a muscle action ptoential -muscle action potential travels along sarcolemma into T tububles, stimulating contraction! 4. Termination of ACh activity...acetylcholinesterase enzyme (AChE) in the synaptic cleft breaks down existing ACh around muscles so they stop contracting. -breaks ACh down into acetyl and choline that cannot activate the ACh receptor
Creatine Phospate
1. an energy-rich molecule found only in muscle fibers -synthesized in liver, kidneys and pancreas, then transported to muscle fibers via blood stream. -the enzyme creatine kinase catalyzes transfer of high-energy phosphate group from excess ATP to creatine when muscle is relaxed.. 2. = First source of energy when contraction begins (it is the fastest way to get energy compared to all three ways) 3. During contraction, transfer of phosphate group to ADP to quickly form new ATP (when contraction begins and ADP level rises, creatine kinase enzyme catalyzes transfer back of high energy phosphate group from creatine phosphate back to ADP to make new ATP.) 4. sufficient only for short busts of activity; about 15 seconds
ways to make ATP in muscle fibers
1. from creatine phosphate 2. by anaerobic glycolysis (w/0 oxygen) 3. by aerobic repiration (w/ oxygen)
After prolonged exercise you have...
1. muscle fatigue 2. Recovery oxygen uptake (to fix the oxygen debt) -breathing rate/oxygen consumption remains above resting level -helps restore metabolic conditions 3. ongoing changes after exercize boost oxygen use so you have increase in body temp which speeds up all metabolism heart and respiratory muscles still working harder than at rest tissue repair processes are increased.
What are the benefits of the liver cells converting some of the lactic acid (produced in anaerobic respiration) back to glucose?
1. provides new glucose molecules 2. reduces blood acidity
Aerobic Cellular Respiration
1. series of oxygen-requiring reactions in mitochondria 2. Oxygen sources -diffuses into muscle fibers from blood hemoglobin -released by myoglobin in sarcoplasm 3. Series of oxidation reactions of nutrients -Pyruvic acid from glycolysis, or breakdown of fatty acids or amino acids -yields 36 ATP molecules, carbon dioxide, water, and heat 4. Provides most of energy for sustained muscle contraction
What are the 3 main categories of skeletal muscle fibers?
1. slow oxidative fibers 2. fast oxidadtive-glycolytic fibers 3. fast glycolitic
muscles controlling eye movements have _____ muscle fibers per motor unit
10-20
for how long do creatine phosphate and ATP provide energy for contraction?
15 seconds
a motor neuron makes contact with about how many muscle fibers?
150
how many molecules of ATP does anaerobic respiration generate?
2
how many thin filaments are there for every thick filament?
2
muscles that control voice production have _____ muscle fibers per motor unit
2-3
muscles in the arm and leg have ______ muscle fibers per motor unit
2000-3000
about how long does anaerobic respiration provide energy for?
30-40 seconds
each molecule of glucose yields about ____ molecules of ATP
36
aerobic respiration provides more then ____% of the needed ATP in activities lasting more than 10 minutes
90
Region that contains both THICK&THIN filaments
A BAND
darker middle part of the sacromere; thick (myosin) & thin (actin) filaments overlap eachother
A band
What begins contraction?
A muscle action potential propagating along a T Tubule opens Ca2+ release channels in the Sarcoplasmic Reticulum, and calcium ions flow into the sarcoplasm and contraction begins.
Which property do muscle tissues and neurons share?
Answer: electrical excitability
What properties do all muscle tissues have in common?
Answer: electrical excitability, contractility, extensibility, elasticity
What happens to acetylcholine once it has bound to its receptor?
Answer: it is broken down by acetylcholinesterase
Which portion of the sarcolemma contains acetylcholine receptors?
Answer: motor end plate
What is a motor unit?
Answer: one motor neuron and all the skeletal muscle fibers it stimulates
As each myosin head detaches from a thin filament, what stops the thin filament from sliding back to its original, relaxed position?
Answer: other myosin heads on the myosin filament are still attached
In what ways does motor unit recruitment assist muscle function?
Answer: produces smooth movements rather than a series of jerky movements
What are the general functions of muscle tissue?
Answer: producing body movements, stabilizing body positions, storing and moving substances within the body, generating hea
What are three functions of ATP in muscle contraction and relaxation?
Answer: provide energy for myosin head movement, detachment of the myosin head from actin, and for operation of the calcium active transport pump
What functions do fascia serve?
Answer: supports and surrounds muscles and other organs, allows free movement of muscles, carries nerves and blood and lymphatic vessels, and fills spaces
What is muscle fatigue?
Answer: the inability of a muscle to contract forcefully after prolonged activity
Arrange the following elements from smallest to largest: muscle fiber, thick filament, myofibril.
Answer: thick filament, myofibril, muscle fiber
What do skeletal muscle contraction share in common with smooth muscle contractions?
Both types of contractions result from thick and thin filaments sliding past one another
At the beginning of contraction, the sarcoplasmic reticulum releases ___ into the sarcoplasm.
Ca2+
Sliding Filament Mechanism
Contraction begins once an action potential is propagated along the sarcolemma and into the T-tubles Thin actin filaments at both ends of the sarcomere "slide" as they are pulled into the center of the sarcomere by myosin head activity (myosin stays put, actin slides back and forth) Z discs come closer together, shortening the sarcomere Shortening of individual sarcomeres causes shortening of whole muscle fiber, which in turn can lead to contraction of the whole skeletal muscle
Fast Glycolitic (FG) Contraction Fatigue resistance Respiration Function
Contraction: fastest strongest contraction Fatigue resistance: fatigue rapidly Respiration: use glycolysis Function: bursts of movement (don't last long, can't use it to run; good for strength like lifting something heavy)
Fast Oxydadtive-Glycolytic (FOG) Contraction Fatigue resistance Respiration Function
Contraction: intermediate contraction Fatigue resistance: moderate fatigue resistance Respiration: aerobic respiration and glycolysis Function: walking and sprinting *can increase your ratio of these*
Slow Oxidative Fibers (SO) Contraction Fatigue resistance Respiration Function
Contraction: slowest contraction Fatigue resistance: VERY fatigue resistant Respiration: aerobic respiration Function: posture and endurance
endomysium
Covering L
endomysium
Covering O
The main immediate source of ATP as muscle contractions begin comes from ___.
Creatine Phosphate
The sarcomere is situated BETWEEN two of these adjacent structures
Z DISC
What anchors thin and elastic filaments in place within the myofibril?
Z disc
what passes through the center of each I band?
Z discs
In a relaxed muscle fiber, which is more plentiful in the sarcoplasm? ATP or Creatine Phosphate?
Creatine phosphate is three to six times more plentiful than ATP in the sarcoplasm of a relaxed muscle fiber.
What does each skeletal muscle fiber arise from?
During embryonic development, each skeletal muscle fiber arises from the fusion of a hundred or more small mesodermal cells called myoblasts. The result is one elongated, mutinucleated, amniotic muscle fiber
Ordinarily, pyruvic acid formed by glycolysis in the sarcoplasm enters the mitochondria, where it enters a series of oxygen requiring reactions called aerobic cellular respiration that produce lots of ATP. HOWEVER, during periods of heavy exercize, what happens?
During periods of heavy exercise, not enough oxygen is available to muscle fibers. In these situations, anaerobic reactons convert most of the pyruvic acid to lactic acid, which diffuses out of the skeletal muscle fibers into the blood. liver cells can convert some of the lactic acid back to glucose.
During periods of rest or light to moderate exercise, a sufficient amount of oxygen is available to skeletal muscle fibers. In such cases, ATP used for muscular activity is produced from a series of oxygen-requiring reactions called aerobic cellular respiration. During this process, ______ from glycolysis enters the _____, where it is completely oxidized in reactions that generate ____, carbon dioxide, water, and heat
During this process, pyruvic acid from glycolysis enters the mitochondria, where it is completely oxidized in reactions that generate ATP, carbon dioxide, water, and heat
At the Neuromuscular Junction (NMJ), what is the end of the motor neuron called? What does it divide into and what is inside this?
End of the motor neuron is called the AXON TERMINAL Axon terminal divides into a cluster of SYNAPTIC END BULBS. In each synapctic end bulb, there are membrane-enclosed sacs called SYNAPTIC VESICLES. Synaptic vesicles are filled with thousands of molecules of ACETYLCHOLINE (ACh) which is the nuerotransmitter relased at the NMJ
Which of the following wraps and surrounds an individual skeletal muscle fiber?
Endomysium
T/F? Both isotonic eccentric contractions and isotonic concentric contractions shorten the muscle.
False
T/F? Cardiac muscles perform peristalsis to pump blood through the heart.
False
T/F? Myofilaments shorten to produce muscle contractions according to the sliding filament mechanism.
False
During contraction, a muscle fiber synthesizes and uses a lot of ATP. What does the generation of ATP require and how is this delivered to the muscle fiber?
Generation of ATP requires oxygen, glucose, fatty acids and other stuff that gets delivered in blood
Middle portion of the A band that contains THICK filaments ONLY
H ZONE
center of each A band which contains thick (myosin), but no thin filaments
H zone
What does the contraction strength of a muscle depend on?
-size of the skeletal muscle's motor unit -number of motor units activated
Frequency of Stimulation
-the # of impulses per second -governs total tension produced by a single muscle fiber when stimulated -total tension in whole skeletal muscle organ depends on number of individual muscle fibers contracting at same time.
how many molecules of ATP does creatine phosphate generate?
1
what 4 things does oxidized pyrivic acid generate in aerobic respiration?
1) ATP 2) carbon dioxide 3) water 4) heat
3 ways that added oxygen is used to restore muscle cells to the resting level
1) convert lactic acid into glycogen 2) synthesize creatine phosphate & ATP 3) replace oxygen removed from myoglobin
3 ways that muscle fibers produce ATP
1) creatine phosphate 2) anaerobic cellular respiration 3) aerobic cellular respiration
3 layers of CT that extend from fascia
1) epimysium 2) perimysium 3) endomysium
4 properties of muscles
1) excitability 2) contractility 3) extensibility 4) elasticity
2 examples of muscles moving substances in the body
1) heart pumping blood 2) digestive tract
2 sources of oxygen for for muscle tissue
1) hemoglobin in blood 2) myoglobin in muscle cell
6 factors that contribute to muscle fatigue
1) inadequate release of ca++ from SR 2) depletion of creatine phosphate 3) insufficient oxygen 4) depletion of glycogen 5) buildup of lactic acid & ADP 6) failure of motor neuron to release enough ACh
2 types of filaments
1) myosin (thick) 2) actin (thin)
2 things that a huge amount of ATP is needed for
1) power contraction cycle 2) pump ca++ into SR
4 functions of muscles
1) produce body movements 2) stabilize body positions 3) move substances within the body 4) generating heat
4 things that maximum tension (force) is dependent on
1) rate at which nerve impulses arrive 2) amount of stretch before contraction 3) nutrient & oxygen availability 4) size of motor unit
3 types of proteins that myofibrils are built from
1) regulatory 2) contractile 3) structural
4 steps of nerve impulses eliciting a muscle action potential
1) release of ACh 2) activation of ACh receptors 3) production of muscle AP 4) termination of ACh activity
total strength of contraction depends on what 2 things?
1) size of the motor unit 2) number of motor units activated
what are 2 uses of Botox (botulinum toxin)?
1) strabismus (crossed eyes) 2) cosmetic treatment
What two changes permit relaxation of a muscle fiber after it has contracted?
1. a. when impulses cease being transmitted by the motor neuron, ACh release stops b. AChE rapidly breaks down any ACh present in the synaptic cleft. c. Ion channels close as action potential stops. d. Ca2+ release channels in the S.R. membrane close, stoping release of Ca2+ into sarcoplasm. 2. a. Ca2+ active txp pumps use ATP to move calcium ions back into SR Sisterns b. as Ca2+ level in sarcoplasm drops, troponin-tropomyosin complexes slide back over and cover the myosin binding sites on actin. c. muscle fibers return to their relaxed position
contraction cycle steps
1. ATP hydrolysis 2. attachment of myosin (in thick filament) to actin (in thin filament) to form cross-bridges, 3. power stroke (myosin bridge rotates towards center of sacromere) 4. detachment of myosin from actin
how long does the ATP inside muscle fibers power a contraction?
a few seconds
neuromuscular junction
a nerve action potential causes a muscle action potential. 1. release of Ach 2. activation of ach receptors 3. production of muscle action potential 4. termination of ach activity
synapse
a region where communication occurs between two neurons or a neuron and a target cell
aerobic respiration
a series of oxygen- requiring reactions that produce ATP, carbon dioxide, water and heat. pyruvic acid enters mitochondria. 1 glucose = 30 or so ATP, 2 sources of oxygen (oxygen that diffuses into muscle from blood), supplies ATP to muscles during periods of rest of light/moderate exercise
Muscle Tone
a small amount of tautness or tension in the muscle due to weak, involuntary, alternating contractions of a small number of motor units of a skeletal muscle, even at rest. -keeps skeletal muscles firm, but does not result in a contraction strong enough to produce movement
synaptic cleft
a small gap that separate the 2 cells
nerve impulses arriving at the synaptic end bulbs causes many synaptic vesicles to release ____ into the synaptic cleft
acetylcholine
ACh effects last only briefly because it is rapidly broken down by what?
acetylcholinesterase (AChE)
provide a site where a myosin head can attach
actin
thin filament
actin
2 types of contractile proteins
actin, myosin
activity that lasts longer than half a minute depends on what?
aerobic respiration
A neuromuscular junction includes all of the _____ on one side of the synaptic cleft, plus the ______ on the other side
all of the syjaptic end bulbs plus the mmotor end plate of the muscle fiber on the other side.
series of ATP producing reactions that do not require oxygen
anaerobic cellular respiration
broad, flattened tendon (attach the muscle to the structures that they move)
aponeurosis
axon terminal
at a neurotransmitter junction, the end of a neuron (motor neuron) that divides into a cluster of synaptic end pulbs
In response to physical inactivity, we expect to see muscles __________
atrophy
Sliding Filament Mechanism (the model describing the contraction of muscle)
1. Contractions begin once an action potential is propagated along the sarcolemma and into the T Tubules 2. Thin actin filaments at both ends of the sarcomere "slide" as they are pulled to the center of the sarcomere by myosin head activity. (myosin heads attach to and "walk" along the thin filaments at both ends of a sarcomere, progressively pulling the thin filaments towards the M line) 3. As filaments slide inward, Z discs come closer together, shortening the sarcomere 4. Shortening of individual sarcomeres causing shortening of whole muscle fiber, which in turn can lead to contraction of whole skeletal muscle
Name the three ways for muscles to produce ATP
1. Creatine Phosphate 2. Anaerobic cellular respiration (lactic acid fermentation) 3. Aerobic cellular respiration
Special Properties of Muscle Tissue that enable it to function and contribute to homeostasis:
1. Electrical Excitability -ability to produce action potentials (impulses) in response to certain stimuli. -shared property with neurons 2. Contractility -ability of muscle tissue to shorten forcefully when stimulated by an action potential, generating tension while pulling on attachment points. If tension is great enough to overcome the resistance of the object to be moved, the muscle shortens and movement occurs. (movement of skeleton like lifting a book off a table, or blood, or food, etc etc.) 3. Extensibility -ability to extend/stretch within limits without being damaged. (like when your stomach fills with food) 4. Elasticity -the ability of muscle tissue to return to original length/shape after contraction or extension
During relaxation, why is the level of Ca2+ in the sarcoplsm low?
because active transport pumps force Ca2+ back into the sarcoplasmic reticulum.
when is the number of skeletal muscle fibers set?
before birth
a-actin
bind to actin molecules and to titin
what is lactic acid carries away by?
blood
what 2 things is glucose derived from?
blood, glycogen
blocks release of ACh from synaptic vesicles
botulinum toxin
the muscle action potential propagates to the SR to release what?
ca+
What is required for excitation-contraction coupling?
calcium ions and ATP
where can the botulinum toxin be found?
canned foods
each muscle fiber is in close contact with one or more what?
capillaries
neurotransmitter
cells communicate to one another by sending these chemicals
proteins that generate force during contraction
contractile
myosin
contractile protein. main component of thick filaments. functions as a motor protein in all three types of muscle tissue (pull various cellular structures to achieve movement), looks like two golf clubs twisted together
actin
contractile protein. main component of thin filaments, individuals join to make a helix, have myosin binding sites
ability to contract forcefully when stimulated
contractility
in _____ muscle, calcium ion binding to toponin moves tropomyosin away from myosin-binding sites
contracting
the release of calcium ions triggers muscle ______
contraction
myofibrils (contractile organells) built from 3 kinds of proteins
contratile, regulatory, structural
The use of ________ for ATP Production is unique to muscle fibers.
creatine phospate
excess ATP is used to synthesize what? (energy-rich molecule)
creatine phosphate
ATP from creatine phosphate
creatine phosphate gives up a phosphate to create ADP. the result is 1 ATP
The binding of a myosin head to an actin molecule is termed a __________,
crossbridge
A fiber is categorized as either slow or fast depending on______
depending on how rapidly the ATPase in its myosin head splits ATP.
What are the connective tissues of the Skeletal Muscle Organ?
1. Hypodermis (areolar and adipose tissue) - separates muscle from skin -insulates -protects -attaches things 2. Fascia (dense connective tissue sheet) - supports and surrounds muscles and other organs -unites muscles with similar functions -allows free movement of muscles -carries nerves and vessels -fills spaces between muscles 3. Three layers that extend from the Fascia (Epimysium, Perimysium, Endomysium) -protect/strengthen skeletal muscle fibers 4. Tendon or aponeurosis -Tendon: epi/peri/endomysiums may extend beyond muscle fibers to form ropelike tendon that attaches a muscle to the periosteum of a bone (ex: achilles tendon) attaches calf muscle to calcaneus -Aponeurosis: when connective tissue layers extend as a broad, flat sheet ex: epicranial aponeurosis on top of skull btw frontal/occipital bellies of the occipitofrontalis muscle
After exercise what ongoing changes in your body help boost oxygen use to fix the oxygen debt?
1. Increased body temp speeds up all metabolism 2. Heart and respiratory muscles still working harder than at rest 3. Tissue repair processes are increased.
FUNCTIONS OF MUSCLE TISSUE Through sustained contraction or alternating contraction and relaxation, muscle tissue has 4 key functions. Name the functions and describe which muscles play a role in each one.
1. Produce body movements -shortening of muscle -integrated function of skeletal muscles, bones, joints 2. Stabilize body positions -skeletal muscle contractions without movement (i.e postural muscles contract continuously when you are awake to hold your head up) 3. Move substances within the body -All three kinds of muscles as part of different organ systems -Skeletal muscle: contractions promote flow of lymph and aid return of blood to heart. -Cardiac muscle: contracts heart to pump blood -Smooth muscle: sphincters prevent outflow of contents of stomach/bladder, and then contractions move food, bile, enzymes through GI tract, moves sperms/eggs 4. Generate heat to maintain normal body temp -Involuntary shivering of skeletal muscle
Why can skeletal muscle be considered an organ?
different types of tissues function together 1. skeletal muscle tissue 2. connective tissue (surrounds and protects skeletal muscles) 3. nerve and blood supply (nerves and blood vessels bring nutrients, oxygen, ATP, and messages to tell muscles what you want them to do)
sliding filament mechanism
during contraction, the thick and thin filaments slide past one another. myosin heads 'walk' along the thin filaments, pulls filaments towards the m line
links thin filaments to the sacrolemma
dystrophin
ability to return to an original length
elasticity
separates individual muscle fibers from one another; innermost layer
endomysium
creatine phosphate
energy rich molecule, first source of energy when muscle contraction begins, formed from ATP when the muscle is relaxed.
the outermost layer; separates muscle fibers into fascicles
epimysium
ability to respond to stimuli
excitability
The degree to which a muscle cell can stretch depends on its __________.
extensibility
ability to stretch without being damaged
extensibility
dense sheet or broad band of irregular CT that surrounds muscles
fascia
the epimysium separates 10-100 muscle fibers into bundles called what?
fascicles
function in the contractile process; 2 types (thick & thin)
filaments
myomesin
forms the m line
the number of impulses per second that arrive at the neuromascular junction is known as?
frequency of stimulation
When muscle fibers are stimulated so frequently they do not have an opportunity to relax, they are experiencing __________.
fused or complete tetanus
contractile proteins
generate force during a contractoin (actin and myotin)
What is the basic function of all muscle tissue?
generate muscle tension
used to generate ATP when the supply of creatine phosphate is depleted
glucose
anaerobic glycolysis
glucose is catabolized. accoplished via glycolysis. breaks down each glucose molecule into 2 molecules of pyruvic acid. occurs in cytosol. produces 2 ATP and 2 lactic acid molecules. pyruvic actid is converted to lactic acid. lactic acid is recycled into glucose via liver, produces fewer ATP's than aerobic respiration, but is faster
used for the synthesis of ATP
glycogen
2 components of sarcoplasm
glycogen, myoglobin
breaks down glucose
glycolysis
A pathway of ATP production that results in the formation of lactic acid is __________.
glycolytic catabolism
what functions does fascia serve?
hat functions does fascia serve? allows free movement of muscles carries nerves, blood vessels, and lymphatic vessels fills spaces between muscles separates muscles of similar functions
contracting muscle produces what?
heat
regulatory proteins
help switch the contraction process on and off (tropomysosin, troponin)
properties enable muscle to function and contribute to ______
homeostasis
muscle growth occurs by this; an enlargement of existing muscle fibers
hypertrophy
Region that contains only THIN filaments
I BAND
lighter; contains thin (actin) filaments but no thick filaments
I band
What are the two types of muscle contractions?
Isotonic and Isometric Isotonic: involves a change in muscle length without a change in tension (force of contraction) -used for body movements and moving objects a. Concentric Isotonic (muscle shortens--pick up a book) b. Eccentric Isotonic (muscle lengthens--lower down a book) Isometric: tension generated is not enough to exceed the resistance of the object to be moved and the muscle does not shorten (or change length at all) ex: holding a book straight out in front of you maintaining posture, stabiliizing joints)
What type of contraction requires the greatest amount of tension?
Isotonic eccentric contraction
What is the M line?
It is the supporting protein in the middle of the sarcomere
Cardiac Muscle? What does it look like? Voluntary or Involuntary? Location?
Looks like: Striated every cell has only one nucleus looks branched intercalated discs between cells Involuntary: heart beats thanks to autorhythmicity, a built-in (intrinsic) rhythm Location: found only in the heart; forms most of the heart wall
Skeletal Muscle What does it look like? Voluntary or Involuntary? General Function?
Looks like: Striated (alternating light and dark protein bands are visible when tissue is examined under a microscope) Cells are long and multi-nucleated Voluntary: activity can be voluntarily controlled by the somatic (voluntary) division of the nervous system Function: most move bones of the skeleton (some skeletal muscles attach to and move the skin or other skeletal muscles)
Smooth Muscle? What does it look like? Voluntary or Involuntary? Location?
Looks like: not striated, looks smooth Usually involuntary: has some autorhythmicity when your GI tract propels food through it Location: Walls of hollow internal structures; blood vessels, airways, most organs in the abdominopelvic cavity, attached to hair follicles in the skin (arrector pilli muscle), iris of the eye
MIDDLE line of the A band
M LINE
supporting proteins that hold the thick filaments together in the H zone
M line
What is the folded region of the sarcolemma of the muscle fiber that is oposite the synaptic end bulbs? What is within this that can bind specifically to Acetylcholine (ACh)?
Motor End Plate has acetylcholine receptors that bind specifically to ACh. *Motor End Plate is folded because this increases surface area)
Describe Nerve and Blood Supply for Skeletal Muscles
Motor Neurons in Nerve -stimulate skeletal muscles to contract (can only stimulate to contract, to release it just removes the stimuli) -thread-like axon process of neuron extends from brain or spinal cord to a group of muscle fibers -axon end typically branches to extend to different skeletal muscle fibers Blood Vessels -generally each muscle has 1 artery and 2 veins of its own and does not sharet this -plentiful microscopic blood capillaries bring oxygen and nutrients and remove metabolic wastes -each mucle fiber is in close contact with one or more microscopic blood capillaries
Where are receptors for acetylcholine located?
Motor end plate
belly of skeletal muscle
Muscle Feature E
Contractile Proteins
Muscle Proteins 1. Myosin: -molecule shaped like two twisted golf clubs with tail and heads -converts chemical energy in ATP into mechanical energy of motion (grabs ATP, rips it in half, takes the energy from the bond and uses it!) 2. Actin: -thin myofilament component -has myosin-binding site for myosin head -this site is covered, and only calcium can makeit uncover. -basically just sits n waits for myosin to bind on to it
Structural Proteins
Muscle Proteins 1. Titin: anchors Z disc to the M line (z is the end) 2. Dystrophin: links sarcomere to sarcolemma (keeps sarcomere connected to plasma membrane
Regulatory Proteins
Muscle Proteins 1. Tropomyosin: Can cover myosin-binding sites on actin (like a scarf that wraps around the actin) 2. Troponin: -can bind Ca2+ and holds tropomyosin -if you give this a Ca ion, it pulls the tropomyosin off the active syte of myosin; i.e. calcium bonds to the tropomin which changes shape and pulls tropomyosin out of place and now the active site is open
Latrotoxin, produced by the poisonous black widow spider, increase the release of acetylcholine. How do muscle cells respond?
Muscle cells will experience fused or complete tetnus when excess acetylcholine exists.
Larry's muscle weekend while he played tennis for hours on a hot summer afternoon. the inability to maintain intensity is defined as ___.
Muscle fatigue
what type of tissue is fascia?
irregular CT
What is a myogram? Describe the phases of this.
Mygram = record of a twitch contraction (duration varies with type of muscle fiber...btw 10-100 msec Phases: Latent Period= brief delay, occurs btw application of stimulus and beginning of contraction. (here the muscle action potential is sweeping over the sarcolemma and calcium ions are released from the SR. ) Contraction Period= Powerstroke generates tension (details on this from the text book: calcium ions bind to troponin, miosin binding sites on actin are exposed, myosin heads attach to actin, and resulting power stroke generates force of contraction) Relaxation Period= cell events allowing muscles to resume original length (calcium ions are actively txp back into the SR; level of calcium ions in sarcoplasm decreases, myosin binding sites are covered by tropomyosin, myosin heads detach from actin, power strokes cease, and muscle fiber relaxes!)
The type of contraction in which length of the muscle fibers do not change is called __________.
isometric
Which statement best describes the function of myoglobin?
Myoglobin stores oxygen in muscle cells.
the main component of thick filaments?
Myosin
structual proteins
keep the thick and thin filaments in alignment, give the myofibril elasticity and extensibility, link the myofibrils to the sarcolemma and ECM (titin, a-actinin, myomesin, nebulin, dystrophin)
if oxygen levels are low, anaerobic reactions convert pyruvic acid into ______
lactic action
how long do most skeletal muscles fibers last?
lifetime
dystrophin
links thin filaments of the sacromere to integral membrane proteins in the connective tissue ECM
nebulin
long non-elastic protein helps anchor thin filaments during development
the axon of a somatic motor neuron typically branches ____ times
many
a motor unit consists of a ____ and the ____ it stimulates
motor neuron, muscle fibers
Neurons that stimulate skeletal muscle fibers to contract are called:
motor neurons Note: each motor neuron has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibers. muscle fiber contracts in response to muscle action potentials that arise at the neuromuscular junction
A single motor neuron together with all the skeletal muscle fibers it innervates is called a __________.
motor unit
The process by which the number of contracting motor units is increased is called _____?
motor unit recruitment
inability of muscle to maintain force of contraction after prolonged activity
muscle fatigue
after reserves are used up, ATP must be produced by what?
muscle fiber
what are individual muscle cells called?
muscle fibers--> each skeletal muscle organ composed of hundreds to thousands of muscle fibers
thread-like structures which have a contractile function
myofibrils
red colored protein that binds oxygen molecules
myoglobin
The darker the muscle, the more _____ it is storing
myoglobin (oxygen-binding red protein)
2 oxygen-binding proteins
myoglobin, hemoglobin
thick filament
myosin
thick filaments; functions as a motor protein which can achieve motion; converts ATP into energy of motion
myosin
Smooth muscle and skeletal muscle both possess __________.
myosin and actin filaments
projections of each myosin molecule that protrude outward
myosin head
binding of ACh to receptor opens ion channels and allows inflow of ______ to the inside of the muscle cell
na+
What is another name for an impulse?
nerve action potential i.e. moving ions across generates an electrical charge like walking on a carpet
The synapse of a motor neuron with a muscle fiber is known as the __________.
neuromuscular junction
the axon of a motor neuron branches out forming ____ with different muscle fibers
neuromuscular junctions
Does the length of individual thick and thin filaments change during contraction?
no, it is the amount of overlap between them that changes.
How is the contraction cycle like walking on a foot-powered, non-motorized treadmill?
one foot (myosin head) strikes the treadmill belt (thin filament) and pushes it back-ward (toward the M Line) Then the other foot comes down and imparts a second push. The belt (thin filament)moves smoothly while the walker (thick filament) remains stationary. Like the legs of a walker, each mysoin head needs a constant supply of energy to keep going...one molecule of ATP for each contraction cycle.
Each nerve impulse elicits?
one muscle action potential i.e. 1 nerve impulse can make one twitch.
production of ATP in muscle fibers
only use a modest amount when released, use high amount at high levels of activity, huge amount is needed to power a muscle contraction and to pump calcium into the sarcoplasmic reticulum
what does the binding of ACh to the receptor on the motor end plate trigger?
opening of ion channels
What does the myosin do?
Myosin grabs ATP, rips it in half, takes the energy from the bond and uses it. (i.e. it converts chemical energy in ATP into mechanical energy of motion) Will bind to Actin's myosin-binding site
How do motor neurons communicate with skeletal muscle fibers if they do not touch?
NEUROTRANSMITTER! The action potential from the motor neuron can't jump the gap (synaptic cleft) between the two cells. Instead, the motor neuron communcates with the muscle fiber indirectly, by releasing a chemical called nuerotransmitter
Through which ATP-generating mechanism can long-lasting muscle contractions be sustained?
oxidative catabolism
if sufficient _____ is present, pyruvic acid formed by glycolysis enters aerobic respiration pathways producing a large amount of ATP
oxygen
after exercise, heavy breathing and ______ remains above resting level
oxygen comsumption
the added oxygen that is taken into the body after exercise
oxygen debt
surrounds numerous bundles of fascicles; 2nd layer
perimysium
the inflow of Na+ makes the inside of the muscle fiber more _____ charged triggering a muscle AP
positively
_____ entering the mitochondria is completely oxidized generating
pyruvic acid
what 2 things does glucose break down into?
pyruvic acid, ATP
How does recruitment produce smooth movements rather than a series of jerky muscle movements?
recruit slow muscles first, than fast, which gives you one smooth movement
Oxygen Debt What does this term refer to?
refers to the added oxygen, over and above the oxygen consumed at rest, that is taken into the body after exercise. this oxygen is used to pay back/restore metabolic conditions to the resting level in 3 ways 1. convert lactic acid back into glycogen stores in the liver 2. resynthesize creatine phosphate and ATP in muscle fibers 3. replace oxygen removed from myoglobin
Between the start of the latent period and the start of the contraction period, there is a time interval during which the muscle cannot respond to another stimulus. This brief period is known as the __________.
refractory period
motor end plate
region of sarcolemma opposite the synaptic cleft that contain ACh receptors
proteins that switch the contraction process on and off
regulatory
Muscle contraction begins when....
Once an action potential is propagated along hte sarcolemma and into the T tubules, muscle contraction begins.
tropomyosin
regulatory protein. part of thin filament, blocks myosin by covering myosin binding sites
When do muscle fibers lose their ability to divide?
Once fusion of myoblasts occurs during embryonic development, the muscle fiber loses its ability to undergo cell division
When does the Contraction Cycle begin?
Once the sarcoplasmic reticulum releases Ca2+ into the sarcoplasm, the Ca2+ ions bind to troponin, which moves the troponin-tropomyosin complexes away from the myosin binding sites on actin. once the binding sites are uncovered, the contraction cycle begins.
troponin
regulatory protein. part of thin filament, holds tropomyosin in place
in ____ muscle, myosin is blocked from binding to actin
relaxed
contraction cycle
repeating sequence of events that causes the filaments to slide. thin filaments are moed past the thick filaments towards the center of the sacromere
What is Fibrosis?
replacement of damanged skeletal muscle fibers with fibrous scar tissue instead of satellite cells. adhesions = example of fibrosis
What is a Motor Unit?
One motor neuron and all the skeletal muscle fibers the motor neuron stimulates. (i.e. the neuron and all the cells it talks to) -a single nerve impulse elicits a single muscle twitch contraction in all the muscle fibers that it innervates (A single motor neuron makes contact with an avg of 150 mucle fibers within a muscle)
How long does the contraction cycle repeat for?
Releats for as long as ATP and Ca2+ are available in the sarcoplasm
The Na+/K+ pump helps a muscle cell maintain a state of __________.
resting membrane potential
Muscle Proteins
Sarcomere is composed of protein! Contractile Proteins: 1. Myosin 2. Actin Regulatory Proteins 1. Tropomyosin 2. Troponin Structural Proteins 1. Titin 2. Dystrophin
the plasma membrane of a muscle cell
sarcolemma
How come the muscle fiber can experience simultaneous activation (and thus contraction)?
Skeletal muscle fibers are long cells and NMJ is usually located near midpoint. muscle action potentials arise at the NMJ and propagate toward both ends. This permits nearly simultaneous activation (and thus contraction) of all parts of the muscle fiber
compartments of arranged filaments; basic functional unit of a myofibril
sarcomeres
the cytoplasm of a muscle fiber
sarcoplasm
The storage and release of calcium ions is the key function of the __________.
sarcoplasmic reticulum
membranous sacs which encircle each myofibril
sarcoplasmic reticulum (SR)
retain the capacity to regenerate damaged muscle fibers
satellite cells
increases heat production when cold
shivering
Muscle Tone is established by....?
skeletal muscle contracts only after it is stimulated by motor neurons, so, muscle tone is established by BRAIN and SPINAL CORD (which activate muscle's motor neurson.
each branch of the axon extends to a different what?
skeletal muscle fiber
the model describing the contraction of muscle is known as the?
Sliding Filament Mechanism
What type of motor units control small precise movements? What type of motor units control larger, powerful movements?
Small precise movements: many small motor units control these (10-20 muscle fibers per motor unit) Ex: tongue, fingers Larger, powerful movements: BIG MOTOR UNITS MAKE BIG MOVEMENTS! -up to 3000 muscle fibers per motor unit Ex: quads, biceps (these may have more than one motor unit btw)
Type 1 fibers lack ___.
Speed
neurons that stimulate skeletal muscle to contract
somatic motor neurons
1 function of SR
stores calcium ions
proteins that align the thick and thin filaments properly
structural
titin
structural protein. connects z disk to m line, helps stabilize the position of thick filament
synaptic bulbs
synaptic vesicle, neural part of the NTJ, membrane closed sac that contain ACh
cords that attach a muscle to a bone
tendon
2 hormones that stimulate hypertrophy
testosterone, HGH
Twitch Contraction
the brief contraction of all the muscle fibers in a motor unit in response to a single nerve impulse in its motor neuron
Muscle Fatigue
the inability of a muscle to contract forecully after prolonged activity Contributing factors: 1. inadequate rlease of calcium ions from the SR, resulting ina decline of Ca2+ level in the sarcoplasm 2. depletion of creatine phosphate 3. insufficient oxygen 4. depletion of glycogen and other nutrients 5. buildup of lactic acid and ADP 6. failure of impulses in the motor neuron to release enough acetylcholine
Contraction Cycle
the repeating sequence of events that causes the filaments to slide; consists of 4 steps 1. ATP Splits -the myosin head has an ATP-binding site. An enzyme spits Adenosine Tri Phosphate splits into Adenosine Di Phosphate and a Phosphate. T - the split reorients and energizes the myosin head 2. Myosin attaches to actin -head attaches to a myosin bonding site on the actin -releases phosphate group -this triggers the power stroke (see below) 3. Power stroke occurs -during power stroke, myosin head rotates/swivels and releases the ADP -mysoin generates force as it rotates toward the center of sarcomere, sliding the thin filament past the thick filament toward the M line. 4. Myosin detaches from actin -at the end of the power stroke, the mysoin remains attached to actin until it binds with another molecule of ATP, and as ATP binds to the ATP binding site on the myosin head, the mysoin head detaches from actin.
Neuromuscular Junction (NMJ)
the synapose between a motor neuron and a skeletal muscle fiber
neuromuscular junction
the synapse between a somatic motor neuron (neurons that stimulate skeletal muscle fibers to contract) and a skeletal muscle fiber (movement)
tropomyosin & troponin are also a part of what?
thin filament
excitation-contraction coupling
this concept connects the events of a muscle action potential with the sliding filament model. an increace in the calcium level in the sarcoplasm starts the sliding of thin filaments. when calcium level declines or stops, sliding stops
what does your body do with the extra oxygen it takes in after you stop exercising?
this oxygen is used to pay back/restore metabolic conditions to the resting level in 3 ways 1. convert lactic acid back into glycogen stores in the liver 2. resynthesize creatine phosphate and ATP in muscle fibers 3. replace oxygen removed from myoglobin
stabilize the position of myosin; accounts for much of the elasticity & extensibility of myofibrils
titin
2 types of structural proteins
titin, dystrophin
tunnel in from the plasma membrane (sarcolemma)
transverse (T) tubules
in relaxed muscle, strands of _____ cover the myosin-binding sites
tropomyosin
2 types of regulatory proteins
tropomyosin, troponin
To initiate skeletal muscle contraction, calcium ions must bind with
troponin!
The fastest muscle contraction would be produced by a __________.
type IIb fiber
What characteristic is NOT descriptive of cardiac muscle tissue?
voluntary muscle contractions
Muscle tension can be increased to produce larger contractions when needed by increasing the frequency of impulses at the neuromuscular junction. This phenomenon is called
wave summation.
Compare the amount of red myoglobin in white muscle fibers vs. red muscle fibers
white muscle fibers are pale, with low myoglobin red muscle fibers are dark red with high myoglobin
IF motor neurons are damanged, what may occur?
your muscles may lose tone and become flacid
separate one sacromere from the next
z line
During the recovery period after exercise we breathe deeper and faster. the increased rate of respiration is known as ___.
(EPOC)Excess postexercise oxygen consumption
Satellite Cells
(Stem Cells) When skeletal muscle tissue arises from fusion of 100 or more small mesodermal cells called myoblasts, some myoblasts persist as satellite cells. They hang out around outside of muscle and regenerate muscle fibers in damaged mature skeletal muscle organs.
Anaerobic Cellular Respiration
1. Series of ATP-producing reactions in sarcoplasm that do not require oxygen *when muscle activity continues past 15-second mark, supply of creatine phosphate is depleted and now glucose is going to make ATP* 2. Glycolysis (series of reactions) -breakdown of glucose from blood stream or from breakdown of glycogen stores in sarcolemma -yields 2 ATP molecules and 2 pyruvic acid molecules 3. Pyruvic Acid -converted to lactic acid in absence of oxygen -lactic acid moved into blood and carried to liver for reconversion to glucose 4. Succifient energy for 30-40 Seconds of activity (this is from creatine phosphate and the glycolysis)
1. Synapse 2. Synaptic Cleft
1. Synapse = a region where communication occurs between aneuron and another cell such as a skeletal muscle fiber. 2. Synaptic Cleft = a gap between two cells (intracellular space) that separates the cells so they can't physically touch.
creatine phosphate transfers its high energy phosphate group to _____ regenerating new ATP
ADP
___ is the only direct source of energy for muscle fiber contraction.
ATP
myoglobin releases oxygen when it is needed for the synthesis of what?
ATP
What is the name of the neurotransmitter released at the NMJ?
Acetylcholine (ACh)
Proteins associated with thin filaments
Actin Troponin Tropomysin
During muscle contraction myosin cross bridges bind to active sites on ___.
Actin filaments
How does the myosin bonding site on actin protein open up?
Actin has myosin bonding site for the myosin head and it sits and waits for the myosin head. While Actin is sitting there waiting, it's myosin-binding site is covered by a scarf (Tropomyosin). When Ca2+ comes to the Troponin protein, it binds and then the Troponin pulls the tropomyosin off the actin's myosin-binding site, so the myosin and actin can bine and then contraction hapens.
Describe the arrangement of filaments within a sarcomere
Alternating bands form striations A Band- darker middle with thick and thin overlapping H Zone - narrow cetner with only thick filaments I band - near Z discs with only thin filaments ** M Line - supporting protein in middle of sarcomere **
An action potential releases _____ ions that allow ____ filaments to bind and pull _____ filaments toward the center of the _____
An action potential releases CALCIUM ions that allow THICK filaments to bind and pull THIN filaments towards the center of the SARCOMERE
Which ATP-producing reactions provide ATP during a 1000-meter run? Which occur within mitochondria?
Answer: (a) energy transfer from creatine phosphate, anaerobic cellular respiration, and aerobic cellular respiration; (b) aerobic cellular respiration
What happens to the distance between neighboring Z discs when thin filaments in a sarcomere slide toward the M line? When thin filaments slide away from the M line?
Answer: (a) it decreases; (b) it increases
. What type of proteins compose thick filaments? Thin filaments?
Answer: (a) myosin (b) actin, tropomyosin, and troponin
Which events occur during the latent period of a twitch contraction? During the relaxation period?
Answer: (a) the muscle action potential sweeps over the sarcolemma, calcium ions are released from the sarcoplasmic reticulum and bind to troponin which allows the myosin heads to start binding to actin; (b) calcium ions are transported back into the sarcoplasmic reticulum, the level of calcium ions decreases in the sarcoplasm, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, power strokes cease, the muscle fiber relaxes
Which molecule is the only direct source of contraction energy for a muscle fiber?
Answer: ATP
Why are some skeletal muscle fibers classified as "fast" and others are said to be "slow"?
Answer: Because of how quickly ATPase in myosin heads split (hydrolyze) ATP
Describe the steps that occur for an action potential arriving at a synaptic end bulb to result in an action potential in a muscle fiber.
Answer: Step 1- calcium ions enter synaptic end bulb which leads to acetylcholine release into synaptic cleft; Step 2-ACh binds to ACh receptors causing their activation; Step 3- inflow of sodium ions across the sarcolemma cause the generation of a muscle action potential
What are the functions of T tubules, myoglobin, and sarcoplasmic reticulum, which are all unique to muscle fibers?
Answer: T tubules: propagate action potential into the muscle fiber; myoglobin: binds oxygen molecules that diffuse into muscle fibers from interstitial fluid and releases oxygen when mitochondria need it for ATP production; sarcoplasmic reticulum: stores calcium ions
How does sarcomere shortening result in shortening of an entire muscle and movement of a bone?
Answer: Z discs pull on neighboring sarcomeres, whole muscle fiber shortens, entire muscle shortens, which tightens tendons, moving the associated bone
How does a skeletal muscle fiber relax?
Answer: calcium ion release channels in the SR close and calcium ion active transport pumps use ATP to restore low levels of calcium ions in the sarcoplasm, the troponin-tropomyosin complex slides back into position where it blocks the myosin-binding sites on the actin molecules, then the muscle relaxes
Atrophy Hypertrophy Hyperplasia
Atrophy = muscles get smaller Hypertrophy= enlargement of existing muscle fibers Hyperplasia = increase in number of muscle fibers from satellite cells (happens a lot as a kid)
The increase in muscle tension that is produced by increasing the number of active motor units is called ___.
Recruitment
The plasma membrane of the muscle cell is known as the _____
Sarcolemma
What is the function contractile unit of the myofibril?
Sarcolemma
Skeletal Muscle Fiber Structure: Name elements and describe each in detail
Sarcolemma = plasma membrane of a muscle fiber; -muscle action potentials travel along the sacrolemma Transverse Tubules (T-Tubles) = -many invaginated, tunnel-like extensions of sarcolemma -open to cell's exterior thus filled with interstitial fluid -muscle action potentials travel along the sarcolemma and thru the T-Tubules and quickly spread throughout the muscle fiber. Sarcoplasm = cytoplasm of muscle fiber -contains organelles, glycogen (glucose storage molecule) and myoglobin (oxygen-binding red protein) Myofibrils = long contractile organelles (i.e. they lengthen or shorten) -inside sarcoplasm, extends entire length of muscle fiber -arrangement of filaments gives striated appearance. Sarcoplasmic Reticulum = smooth ER, stores calcium -fluid-filled, membranous organelle similar to smooth ER of non-muscle cells -wraps around each myofibril (looks like a web) -dilated end sacs are terminal cisterns, associated with either side of a T-tuble to form a triad -stores and releases calcium ions (Ca2+) that trigger muscle contraction (i.e. when calcium is needed for contractions, it lets it out) Filaments = Within myofibrils are these smaller protein structures that don't extend the enitre length of a muscle fiber. they are arranged in compartments called Sarcomeres Sarcomere = basic functional unit of contraction within myofibrils (made of proteins) -Myofibrils extend the length of the muscle fiber -Thick and thin myofilaments in myofibril do not extend entire length of muscle fiber Z disc = dense protein material that separates one sarcomere from next in myofibril
