Human Physio Ch. 12 Muscle Physiology

Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules convey potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum.

3, 1, 2, 4

Step 4 at Neuromuscular Junction stimulating a muscle fiber

4. Na+ enters muscle cell causing AP along sarcolemma

Step 2 at Neuromuscular Junction stimulating a muscle fiber

2. Ca2+ enters NMJ through voltage-gated channels

The molecular event that occurs immediately after the power stroke is the

release of ADP from the myosin.

smooth muscle

slower than skeletal muscle but can sustain contractions for longer without fatiguing

__________ muscle tissue has No striations, single central nuclei, involuntary.

smooth

The function of the titin protein is to

stabilize the position of the contractile filaments.

tetanus

state of maximal contraction =if MAP is shortened the muscle fiber does not have time to relax completely between 2 stimuli resulting in more forceful contraction //incomplete or unfused =stimulation rate of muscle fiber is not at max and fiber relaxes between stimuli //complete or fused =stimulation rate is fast enought that muscle fiber does not have time to relax, reaching max tension and staying there

sliding filament theory of contraction

states that during contraction, overlapping thick and thin filaments slide past each other in an energy-dependent manner as a result of actin-myosin crossbridge movement

Skeletal muscle structure is ______

striated

What is name given to the regularly spaced infoldings of the sarcolemma?

transverse or T tubules //allow action potentials to move rapidly from the cell surface into interior of fiber =reaches terminal cisternae simultaneously

attachment sites for myosin

M line

Myosin light protein chains

MLCK phosphorylates _____ which activates myosin ATPase. This allows crossbridge power strokes

Where do we find smooth muscle tissue?

Lines wall of hollow organs and blood vessels

autonomic innervation, paracrines and hormones

cardiac and smooth muscles controlled by

in muscle contraction Myosin heads (crossbridges) bind to

actin

Excitation also means

action potential

motor unit

composed of a group of muscle fibers and one somatic motor neuron that controls them //when SMN fires AP all muscle fibers in unit contract =finer movement recruit more motor neurons and less muscle fiber to a unit =same unit must be same fiber type >>fast twitch and slow twitch motor units =force increase by recruiting more motor units //marathon runners have slow twitch fibers //sprinters have fast twitch fibers //conversion occurs in muscles that are being trained =endurance training inc capillaries and mitochondria in muscle tissue region =increasing aerobic activity

Tropomyosin physically blocks

cross bridges

muscle tension

force created by a contracting muscle

recruitment of additional motor units

force of contraction within a skeletal muscle can be increased by //neurons with the lowest threshold control fatigue resistant slow twitch fibers =genereate minimal force //neurons with highest threshold stimulate motor units of fatigue resistant fast twitch Oxi-glyco fibers =more motor units participate in contractions, greater force generated

Myofibrils

intracellular bundles of contractile and elastic proteins

Tension is maximal when sarcomeres are at what length

normal resting

Skeletal muscle has many peripheral _____

nuclei

varies

number of muscle fibers in a motor unit

TRUE or FALSE Cardiac muscle has striations

TRUE

TRUE or FALSE Contracting muscle can only move in 1 direction

TRUE

TRUE or FALSE Myosin is an ATPase

TRUE

TRUE or FALSE Not all skeletal muscle fibers (cells) are identical

TRUE

What is an area that contains many synaptic vesicles filled with acetylcholine

Axon terminal of motor neuron

In the Triad the T-tubule brings

AP into skeletal muscle fibers

What happens when calcium binds troponin?

Tropomyosin is pulled away from the actin active site.

sarcomeres (image)

* Sarcomeres are part of the myofibrils

myofibrils (image)

*Inside muscle fibers

myofilaments

*thick and thin * myofilaments found inside the Sarcomere

Step 1 at Neuromuscular Junction stimulating a muscle fiber

1. Incoming AP (Na+) from somatic motor neuron

3 different types of skeletal muscle fibers

1. SLOW 2. INT/FAST 3. FAST

runs the length of a thick filament

A band

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?

A myosin head bound to actin

I bands, A band, central H zone

A sarcomere is divided into

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

A series of proteins that control calcium release.

twitch

A single contraction-relaxation cycle is known as a

muscle fibers

A skeletal muscle is a collection of

Which of these structures would not change size during a muscle contraction? A. A band B. Sarcomere C. I band D. H zone

A. A band

Which of the following statements best describes the neuromuscular junction? Choose the best answer. A. the point of synapse between a motor neuron and the muscle fiber that it innervates B. the release of calcium from the sarcoplasmic reticulum as a result of the action potential traveling down the t-tubule C. the release of acetylcholine from the axon terminal of the motor neurons D. the act of myosin and actin sliding past each other in order to produce a contraction

A. the point of synapse between a motor neuron and the muscle fiber that it innervates

What is a structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+

ACh receptor-channel

________ is composed of multiple globular molecules polymerized to form long chains or filaments.

Actin

Tropomyosin covers what?

Actin and myosin binding site

What is a change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels

Action potential

ADP; rigor state

At the end of the power stroke, myosin releases ___. The cycle ends in the ___, with myosin tightly bound to actin.

The contraction cycle is triggered by the rise in ________ released from the sarcoplasmic reticulum (SR).

Ca2+

Which ion signals the beginning of skeletal muscle contraction?

Ca2+ //intracellular calcium signal =initiates muscle contraction //movement created when myosin hydrolyses ATP

power stroke

Ca2+ binding to troponin unblocks the myosin-binding sites and allows myosin to complete its

How does the process of smooth muscle contraction differ from contraction in skeletal muscle?

Ca2+ comes from the extracellular fluid as well as the SR. //smoth muscle has myosin filaments covered entirely with myosin heads surrounded by bundle of actin connected by dense bodies =has no troponin //smooth muscle operates over a range of length =found in walls of hollow organs and tubes //most skeletal muscles are attached to bone and operate over a narrow range of length //smooth muscle contracts and relaxes much more slowly than skeletal or cardiac muscle =uses less energy to generate and maintain a given amount of force >>use of ATP is lower and has fewer mitochondria >>relies more on glylolysis //smooth muscle sustains contractions for extended period of time without fatiguing =tonically contract =small spindle shaped cells with single nucleus //smooth muscle is initiated by electrical or chemical signal =skeletal muscle always begins with MAP //smooth muscle has varicosities instead of motor end plates //in smooth muscle Ca++ comes from ECF and SR =skeletal muscle is just SR //Smooth muscle has Ca++ signal that ends in MLCK and activation of ATPase.

Subjective feelings of tiredness and a desire to cease activity describes which phenomenon?

Central fatigue //pyschological fatigure first, then physical =protective mechanism at maximal exertion =ATP hydrolysis creates low pH environment is possibly cause for fatigue

Define Sarcomere:

Contractile unit of a myofibril

Which enzyme catabolizes the phosphorylation of ADP by creatine phosphate?

Creatine kinase

When does cross bridge cycling end?

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.

Smooth muscle cells lack which protein(s)? A. myosin only B tropomyosin only C. troponin and tropomyosin D. troponin only E. actin only

D. troponin only

Myosin phosphatase

During relaxation, Ca2+ is pumped out of the cytosine, and myosin light chains are dephosphorylated by _____

Ca2+-ATPase

During relaxation, the sarcoplasmic reticulum uses a ___ to pump Ca2+ back into its lumen

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. //sarcolemma is the cell membrane of muscle fiber =cytoplasm is sarcoplasm =myofibrils are intracellular structures >>highly organized bundles of contractile and elastic proteins that carry out the work of contraction =Sarcoplasm reticulum wraps around myofribrils >>concentrates and secretes Ca++ with help from Ca-ATPase =Ca release creates signal in contraction

TRUE or FALSE Tropomyosin is a regulatory protein and an ATPase

FALSE It is only a regulatory protein

antagonistic muscle

Flexor-extensor pairs are examples of

_____ and ______ are antagonistic pairs which allow force in two opposite directions

Flexors and extensors

Define Tension:

Force exerted on an object by a contracting muscle

FAST skeletal muscle fibers are Oxidative, Oxidative-Glycolytic, or Glycolytic?

Glycolytic

thick filaments only

H zone

thin filaments only

I bands

Myogenic contraction

In _____, stretch on the cell depo lorises it and opens membrane Ca2+ channels

Calmodulin; myosin light chain kinase(MLCK)

In smooth muscle contractions, Ca2+ binds to _____ and activates _____

Is Cardiac muscle voluntary or involuntary?

Involuntary

How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle?

It causes rotation of the myosin head back to 90°, thus "cocking" it.

AP(neuron)---(_____)--> AP (muscle) -----(Ca2+ released)---- >______ (muscle)

NMJ (Neuromuscular Junction) Contraction

What is an area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine

Motor end plate

phosphocreatine

Muscle fibers store energy for contraction in

Define Fatigue:

Muscle is no longer able to generate or sustain force

_______ filaments bind to and move _____ filaments, causing ____ ______ in skeletal, smooth, and cardiac muscles

Myosin actin muscle contraction

crossbridges

Myosin binds to actin, creating ____ between the thick and thin filaments

Myosin ATPase

Myosin converts energy from ATP into motion. ____ hydrolyzes ATP to ADP and Pi.

NMJ stands for

Neuromuscular Junction

_______ influence the contraction of muscles by causing changes in muscle membrane potential

Neurons

Z disks and the filaments between them

One sarcomere is composed of two

Define Motor unit:

One somatic motor neuron and all the skeletal muscle fibers (cells) it controls.

SLOW skeletal muscle fibers are Oxidative, Oxidative-Glycolytic, or Glycolytic?

Oxidative

INT/FAST skeletal muscle fibers are Oxidative, Oxidative-Glycolytic, or Glycolytic?

Oxidative-Glycolytic

________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle.

Phosphocreatine //transferred to ADP via creatine kinase aka creatine phosphokinase =muscle cells contain large amounts of this enzyme

Sarcolemma is the

Plasma membrane of muscle cell

What is it called when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere?

Power stroke

Ca2+-ATPase

Relaxation occurs when Ca2+ is pumped back into the SR by a

In the Triad extensive ____ assures that Ca2+ ions can readily diffuse to all troponin sites

SR

In the Triad a wave of depolarization stimulates

SR to release calcium ions

Define Muscle twitch:

Single cycle of contraction - relaxation in skeletal muscle fibers

1. fast-twitch glycolytic fibers -fatigue faster do to inc hydrolysis of ATP and inc pH - acidosis 2. fast-twitch oxidative-glycolytic fibers 3. slow-twitch (oxidative) fibers

Skeletal muscle fibers can be classified on the basis of their speed of contraction and resistance to fatigue into what 3 different twitch fibers

tendons

Skeletal muscles are usually attached to bone by

IP3 receptor channel

Smooth muscle sarcoplasmic reticulum ahas both RyR Ca2+ release channels and ______. calcium also enters the cell from the extra cellular fluid

Define Tetanus:

Sustained contraction/fusion of individual muscle twitches

Triad

T-Tubules plus the two end of the SR

Cardiac muscle has a central nucleus

TRUE

Sliding Filament Mechanism

The explanation of how thick and thin filaments slide relative to one another during striated muscle contraction to decrease sarcomere length

How does the myosin head obtain the energy required for activation?

The energy comes from the hydrolysis of ATP.

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.

What structure is the functional unit of contraction in a skeletal muscle fiber?

The sarcomere

Which protein spans the distance from one Z disk to the M line?

Titin

troponin

To initiate contraction, Ca2+ binds to //troponin C binds reversibly to Ca =pulls tropomyosin completely away from actin's myosin-binding site

T-tubule is the

Tunnel of sarcolemma

DHP receptors; RyR

Voltage-sensing Ca2+ channels called ___ in the t-tubules open ___ Ca2+ release channels in the sarcoplasmic reticulum

Calcium sensitivity

What smooth muscle can be altered by changing myosin phosphatase activity.?

power stroke

When myosin releases Pi, the myosin head moves in the

attachment sites for actin

Z disks

in contraction, ________ are pulled closer together

Z-lines

T-tubules; sarcoplasmic reticulum

___ allow action potentials to move rapidly into the interior of the fiber and release calcium from the ____

Compared to skeletal muscle, contraction of smooth muscle cells is

a slower response to a stimulus and sustained without fatigue.

same fiber type

all fibers in a single unit are of the

series elastic elements

allow the fibers to maintain constant length even though the sarcomeres are shortening and creating tension (isometric contractions)

latent period

between the end of the muscle action potential and the beginning of muscle tension development represents the time required for Ca2+ release and binding to troponin

flexors

bring bones closer together

In all three types of muscle, myosin and actin are regulated by the availability of _____ ______

calcium ions

In smooth muscle cells, Ca2+ binds to ________ which activates the enzyme ________ to phosphorylate myosin and increase force.

calmodulin, myosin light chain kinase

The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a

channel for both Na+ and K+.

Sodium will ____polarize

depolarize

As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately

detaches from actin

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

Muscles contain many muscle

fibers

smooth muscle

has less myosin than skeletal muscle

titin and nebulin

hold thick and thin filaments in position //titin stabalizes position of contractile filaments =elasticity returns stretched muscle to their resting length //nebulin aligns the actin filaments of sarcomere

12-15

in smooth muscle, each myosin is associated with about how many actin molecules?

multi-unit smooth muscle

individual muscle fibers are stimulated independently //not linked together by gap junctions =not linked electrically =each muscle cell is independent //each muscle cell is assosciatted with axon terminal or varicosity =allows fine control of contractions =selective activation on individual muscle cells =increasing force means recruiting more fibers //iris and cilliary body of eye

Cardiac muscle has ______ disks

intercalated

muscle fibers

large cells with many nuclei in skeletal muscle

Creatine is produced by the

liver and kidneys

thin filaments

made mostly of actin

thick filaments

made of myosin

Changes in the ____ ______ of muscles are linked to internal changes in calcium release

membrane potential

somatic motor neurons

skeletal muscles controlled by

insertion

more distal or mobile attachment

extensors

move bones away from each other

Three types of muscle tissue

skeletal, cardiac, smooth

myofilament is a ______ protein

muscle

when you see Sarco this refers to

muscle (fleshy)

motion, force, and heat

muscles generate

tonic smooth muscles

muscles that are continuously contracted //always contains some level of tone =esophageal an urinary sphincters >>relax only when necessaryto allow material to enter or leave

Muscle fibers contain many

myofibrils

Sarcomeres contain many

myofilaments

Contraction of skeletal muscle causes movement of

skeleton

A motor unit consists of

one neuron and all the skeletal muscle fibers it controls.

Contraction of smooth muscle tissue pushes contents through _____

organs Example: small intestine

myoglobin

oxygen-binding pigment that transfers oxygen to the interior to reach mitochondria of the muscle fiber //oxidative muscle fibers have this =also small diameter fibers =myoglobin reaches mitochondria faste =thus more myoglobin and more capillaries bring in blood =better supply of O2 and ATP phosphorylation //glycolytic fibers lack myoglobin content and contrasts oxidative =relies on anaerobic glycolysis for ATP synthesis and fatigues rapidly

tropomyosin

partially blocks the myosin-binding site on actin in relaxed muscle

The function of transverse tubules is to

rapidly conduct action potentials to the interior of the muscle fiber.

ADP is combined with Pi from

phosphocreatine *Phosphocreatine stores are replenished at rest

muscle fatigue

reversible condition in which a muscle is no longer able to generate or sustain the expected power output //arises from excitation contraction failure in the muscle fiber rather than from failure of control neurons or neuromuscular transmission

Myofibrils contain many

sarcomeres

Contraction causes sarcomeres to

shorten

When a muscle contracts, it gets longer or shorter?

shortens *This pulls tendons which move bone at joint

excitation-contraction coupling

somatic motor neuron re- leases ACh, which initiates a skeletal muscle action potential that leads to contraction

When a skeletal muscle cell contracts and the muscle shortens,

some myosin heads are forming crossbridges as others are releasing them.

intercalated disks

structure that connects cardiac muscle cells (ONLY FOUND IN HEART)

Skeletal muscle is attached to bones by

tendons //lever fulcrum system where fulcrum is positioned at one end of the lever =requires large amounts of force to move/resist a small load =advantage of this is that it maximizes mobility and speed >>making for much larger movements at the hand >>speed of contraction at insertion point is amplified at the hand =lever fulcrum system amplifies distance load is moved and speed at which movement takes place //contraction is fastest when the load on the muscle is zero

Cardiac heart muscle pumps blood through

the body

origin

the end of the muscle attached closest to the trunk or to the more stationary bone

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated cation channels

Where does calcium bind?

the regulatory protein troponin

After death, when metabolism stops, in which step of the contractile cycle must skeletal muscles remain?

the rigor state

The H zone contains

thick filaments.

The I band contains

thin filaments only.

The two contractile protein are

thin----> actin thick ----> myosin

skeletal, cardiac and smooth

three types of muscles

Contraction occurs when Ca2+ ions bind to ______ and the complex pulls ______ away from the cross-bridge binding site *Myosin can now bind actin

troponin tropomyosin *Myosin can now bind actin

Calcium, released by the sarcoplasmic reticulum, binds to ________ to move the ________, which allows actin to form a high-force crossbridge with myosin.

troponin C, tropomyosin

Two regulatory proteins are

troponin and tropomyosin

Relative to skeletal muscle, smooth muscle

uses less energy to generate a given amount of force, can sustain contractile force without fatigue and uses calcium from the sarcoplasmic reticulum and extracellular space.

Is Skeletal muscle voluntary or involuntary?

voluntary

load

weight or force that opposes contraction of a muscle

Single-unit smooth muscle

what muscle contracts as a single unit when depolarizations pass from cell to cell through gap junctions //connected through gap junctions =aka unitary smooth muscle //aka visceral smooth muscle =forms walls of internal organs -intestinal tract //amount of calcium that enters cell determines force of contraction

smooth muscle

what muscle lacks troponin?

some smooth and cardiac

what muscles are autorhythmic and contract spontaneously

phasic muscles

what muscles usually relaxed or cycle through contractions //phasic smooth muscles =wall of the lower esophagus >>contracts only when food passes through it -cycle rhythmically through contraction and relaxation

Which fibers fatigue sooner? A. slow-twitch fibers B. fast-twitch fibers

B. fast-twitch fibers

Step 3 at Neuromuscular Junction stimulating a muscle fiber

3. ACh release from axon terminal, diffuses across synapse, binds to receptors on motor end plate

Which of the following is the most direct cause of muscle relaxation? Choose the best answer. A. Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites. B. The voltage created along the t-tubule fades and the muscle fiber membrane returns to a resting potential value. C. The cytoplasm of the muscle fiber exhausts all of its available ATP. D. The delivery of action potentials from the motor neuron stops.

A. Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.

Calcium entry into the axon terminal triggers which of the following events? A. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. B. Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal. C. Acetylcholine binds to its receptor. D. Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal.

A. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.

Match the structures with the accurate description. A. muscle fiber B. fascicle C. sarcolemma D. myofibril E. t-tubules a single muscle cell

A. muscle fiber

______ may be used up faster than it can be created through cellular respiration

ATP

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ATP binds to the myosin head.

Which of the following best describes the contraction phase of the excitation-contraction coupling reaction? Choose the best answer. A. An action potential travels down the axon of a motor neuron in order to release acetylcholine onto the motor end plate. B. Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together. C. An action potential travels down the t-tubule in order to release Ca2+ from the sarcoplasmic reticulum. D. Actin pushes on myosin to shorten its length, thereby shortening the muscle.

B. Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.

Which of the following best summarizes the events of excitation-contraction coupling? Choose the best answer. A. An acetylcholine signal from the motor neuron is converted into an electrical signal in the muscle fiber. B. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle. C. The actin filament slides towards the sarcomere and the muscle contracts. D. Cross-bridges release and the muscle relaxes.

B. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.

Which is the smallest structure? A. Muscle fiber B. Myosin C. Myofibril D. Myofilament

B. Myosin

Which loss of function would occur if you introduced a chemical that functioned as an inhibitor of the ryanodine receptor channel? Choose the best answer. A. Na+ ions would not be able to flow into the muscle cell in order to depolarize it B. Myosin would not be able to bind to actin in order to cause shortening of the sarcomere C. Ca2+ ions would not be actively pumped back into the sarcoplasmic reticulum D. The axon terminal of the motor neuron would not release acetylcholine

B. Myosin would not be able to bind to actin in order to cause shortening of the sarcomere

Match the structures with the accurate description. A. muscle fiber B. fascicle C. sarcolemma D. myofibril E. t-tubules a bundle of adjacent muscle cells

B. fascicle

Match from the following list. A. A band B. I band C. Z disk D. H zone E. M line The structures that serve as the attachment site for the thin filaments and mark the boundaries for one sarcomere.

C. Z disk

Sarcoplasmic Reticulum (SR) stores

Ca2+ ions

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

Calcium ions are stored in the sarcoplasmic reticulum.

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape.

Which of the following would cause muscle relaxation to occur?

Calcium ions pumped into the SR

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

Calcium ions. contraction //ACh is released into synapse from NMJ =ACh binds to AChR on MEP =depol happens channel opens =NA and K come in =depol creates EPP that always reaches threshold and MAP =MAP depol reaches L-type calcium channels in Ttubules causing release of Ca from SR's ryanodine receptors =Free Ca binds to troponin =tropomyosin moves out and reveals actin myosin binding site = myosin power stroke Relaxation //calcium must be removed from cytosol =SR pumps Ca back into lumen using Ca-ATPase =disequilibrium of bound and unbound Ca occurs =Ca releases from tropnin =tropmyosin slide back to block binding sate =crossbridges release and muscle fiber relaxes with help of elastic fibers

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Calcium release from the sarcoplasmic reticulum initiates the contraction

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine? A. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis. B. Acetylcholine diffuses away from the cleft. C. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. D. Acetylcholine is degraded by acetylcholinesterase

D. Acetylcholine is degraded by acetylcholinesterase

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction? A. Acetylcholine is released and moves across the synaptic cleft bound to a transport protein. B. When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal. C. Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein. D. Acetylcholine is released by axon terminals of the motor neuron.

D. Acetylcholine is released by axon terminals of the motor neuron.

Which of the following best describes the role of calcium (Ca2+) in the excitation-contraction coupling reaction? Choose the best answer. A. Ca2+ gives the myosin heads the energy necessary for the power stroke. B. Ca2+ binds to specific receptors which control the release of ATP into the cytoplasm of the muscle fiber. C. Ca2+ will bind directly to tropomyosin, resulting in a conformational shift which reveals the binding sites for myosin on actin. D. Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.

D. Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.

Which of the following structures is/are necessary to initiate the muscle action potential? Select all that apply. A. actin B. t-tubule C. tropomyosin D. motor end plate E. muscle fiber F. troponin G. acetylcholine H. calcium I. ACh receptor-channels J. myosin K. ryanodine receptor L. Ca2+-ATPase M. motor neuron

D. motor end plate E. muscle fiber G. acetylcholine I. ACh receptor-channels M. motor neuron

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron //satellite cells lie outside muscle fiber membrane =activate and differentiate into muscle hen needed form muscle growth or repair

Myosin head rotates on its hinge, sliding __________ past it (powerstroke)

actin filaments

isotonic contraction

creates force as the muscle shortens and moves a load //any contraction that creates force and moves a load //lengthening contraction or eccentric contraction =when you put weight down bending at the elbow -leads to muscle delayed muscle soreness //force created without moving anything is isometric contractions

isometric contraction

creates force without moving a load //how you ask? =elastic fibers in tendons and connective tissue that attach muscle to bone and between muscle fibers =all behave collectively as if they were connected to contractile elements on muscle >>called series elastic elements >>when sarcomeres shorten in isometric contraction elastic elements stretch help fiber maintain constant length >>once elastic elements are stretched and force generated by sarcomeres equal load, muscle shortens and isotonic contraction occurs.

skeletal and cardiac

striated muscles