AP CH 10 Muscle Tissue

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

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

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!

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)

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.

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

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

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

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 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*

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

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

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.

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.

Name the three ways for muscles to produce ATP

1. Creatine Phosphate 2. Anaerobic cellular respiration (lactic acid fermentation) 3. Aerobic cellular respiration

During relaxation, why is the level of Ca2+ in the sarcoplsm low?

because active transport pumps force Ca2+ back into the sarcoplasmic reticulum.

The use of ________ for ATP Production is unique to muscle fibers.

creatine phospate

A fiber is categorized as either slow or fast depending on______

depending on how rapidly the ATPase in its myosin head splits ATP.

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)

the number of impulses per second that arrive at the neuromascular junction is known as?

frequency of stimulation

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

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 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)

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

the main component of thick filaments?

Myosin

The process by which the number of contracting motor units is increased is called _____?

motor unit recruitment

what are individual muscle cells called?

muscle fibers--> each skeletal muscle organ composed of hundreds to thousands of muscle fibers

What is another name for an impulse?

nerve action potential i.e. moving ions across generates an electrical charge like walking on a carpet

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.

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

How long does the contraction cycle repeat for?

Releats for as long as ATP and Ca2+ are available in the sarcoplasm

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.

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

Neuromuscular Junction (NMJ)

the synapose between a motor neuron and a skeletal muscle fiber

To initiate skeletal muscle contraction, calcium ions must bind with

troponin!

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.

Mysium means?

"of the muscle"

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

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

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

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

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

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.

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

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 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

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

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

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

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)

Slow Oxidative Fibers (SO) Contraction Fatigue resistance Respiration Function

Contraction: slowest contraction Fatigue resistance: VERY fatigue resistant Respiration: aerobic respiration Function: posture and endurance

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

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

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)

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

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!)

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

Muscle contraction begins when....

Once an action potential is propagated along hte sarcolemma and into the T tubules, muscle contraction begins.

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.

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)

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

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

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)

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

The force of a muscle contraction becomes ____as more _____ are activated

The force of muscle contraction becomes greater as more motor units are activated

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 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

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

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

The darker the muscle, the more _____ it is storing

myoglobin (oxygen-binding red protein)

What is Fibrosis?

replacement of damanged skeletal muscle fibers with fibrous scar tissue instead of satellite cells. adhesions = example of fibrosis

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

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.

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

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

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.

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

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)

___ is the only direct source of energy for muscle fiber contraction.

ATP

What is the name of the neurotransmitter released at the NMJ?

Acetylcholine (ACh)

Proteins associated with thin filaments

Actin Troponin Tropomysin

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 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

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)

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