A&P Test 3

What are the three different types of muscle?

1.Sletetal 2. Cardiac 3. Smooth

What is a motor unit?

A motor neuron and all (four several hundred) muscle fibers it supplies.

what is the enery source used directly in contraction?

ATP (avalable stores of ATP are depleted in 4 to 6 seconds)

What much occur for contraction to continue, with regards to ATP?

ATP must be regenerated as fast as it is broken down

how is ACh destroyed?

Ach effects are quickly terminated by the enzyme, acetylcholinesterrase. prevents continues muscle fiber contraction in the absence of additional stimulation

Where are the synaptic vesicles located, what do they contain and what causes them to empty?

Axon terminal, contain neurotransmitter acetylcholine (Ach) they empty due to nerve impulse

what happens when the levels of calcium inside the cells are high?

Ca2+ binds to troponin, triponin changes shape and moves tropomyosin away from active sites, events of cross bridge cycle occue, when nervous stimulation ceases Ca2+ is pumped back into the SR and contraction ends.

What is a sarcomere?

Contractile element of skeletal muscle cells

Does contraction always cuse shortening?

Contraction- generation of force, doesn not necessarily cuase shortening of the fiber

What are the four steps in the cross bridge cycle?

Cross bridge formation- high engery myosin head attached to thin filament. Working power stroke- myosin head pivots and pulls thin filaments toward M line. Cross bridge detachment- ATP attched to myosin head and the cross bridge detaches. Coking of the myosin head- engery from hydrolysis of ATP cocks the myosin head back into high engery state

What is the sarcoplasm?

Cytoplasm of muscle cells

What are myofibrils?

Densely packed, rodlike elements, run parallel to fiber length, 80% of cell volume, hundreds of thousands in a single muscle cell, and contain sacromeres.

What happens when once ACh is bound to those receptors?

Electrical events lead to the gerneration of an action potential.

List the three connective tissue sheaths and what they surround?

Epimysium- dense irregular connective tissue surrounding entire muscle. Perimysium- fibrous connective tissue surrounding fascicles (groups of muscle fiber) Endomysium- areolar connective tissue surrounding each muscle fiber.

What are four special characterics of muscle tissue?

Excitability- (responsivenss to irritability) ability to recieve and respond to stimuli. Contractibility- ability to shorten when stimulated. Extensibility- ability to be stretched Elasticity- ability to recoil to resting length.

What are two requirements for contraction? What is the final trigger?

Generation and propagation of an action potential along the sacrolemma. Brief rise in intracellular Ca2+ levels

describe a sarcomere in its relaxed state and in a contracted state? ( What disappears)

In a relaxex state, thin and thick filaments overlap only slightly. During contraction, myosin heads bind to actin, detach and bind again to propel the thin filaments toward the M line, as H zones shorten and disappear sacromeres shorten, muscle cells shorten and the whole muscle shortens. ( H zones shorten and Disappear)

How many cuclei are in a typical skeletal muscle cell?

Multiple

What protein makes up the thick filament?

Myosin

What does actin have sites for?

Myosin head attachment during contraction

What channels close in repolorization? Which one opens?

Na+ voltage gated -K+

what ion comes rushing in when the ion channels open in depolarization?

Na+ as a result more Na+diffuses, so the interior of the sarcolemma become less negitive.

What is myoglobin?

O2 storage

What are the T tubules? Where are they found? What is their function?

Penetrate the cells interior at each A band - I band junction, associate with the paired terminal cisternae to form triads, T tubules cunduct impulses deep into muscle fiber, impulses cause Ca to be released from terminal cisternae.

What is the sarcolemma?

Plasma membran of muscle cells

What causes the striations?

Repeating series of dark and light bands.( dark bands- A bands, lighter midsection-H zone (bisected by M line), light bands- I bands (darker midsection Z disk

Where are ACh recepters located?

Sarcolemma

What is excitation-contraction coupling?

Sequence of events by which transmission of an A-P along the sarcolemma leads to sliding of the myofilaments

Motor units with what type of fibers are activated first?

Smallest

what is the threshold stimulus?

Stimulus strength at which the first observable muscle contractionoccurs

What is the space between the axon terminal and muscle fiber called

Synaptic cleft

What three structures make up the triad?

T tubules and paired terminal cisternae.

What protein makes up the thin filament?

Tehy run the length and part way into A bands

Gvie an example of isometric contractions?

The load is greater than the tension the muscle is able to develop (lifting a car). Tension increases to the muscle's capacity but the muscle neither shortens nor lenghthens.

What is the latent period, what is happening?

Time when E-C coupling events occur. Time between AP initiation and beginning of contraction

What are the three types of portein included in the troponin complex?

Tnl, TnT, and TnC

What happens when the levels of calcium inside the cells are low?

Tropomyosin blocks the active sites on actin, myosin heads cannot attach to actin and cuscle fiber relaxes.

What do the myosin heads have sites for?

Two maller, light polypeptide chains act as cross bridges during contraction, binding sites for actin of thin filaments, and binding sites for ATP and PTPase enzymes

What are the two ways muscle responses are graded?

changing the frequency of stimulation and c hanging the strengh of the stimulus

What are gylcosomes?

clycogen storage

What are the two types of isotonic contractions? give examples of each

concentric- the muscle shortens and does work (kicking a ball) Eccentric- the muscle contracts as it lengthens ( in calf -climbing steep hills)

What is muscle tone?

constant, slightly contracted state of all muscles

What is tension?

force exerte4d on an object by muscle

What is load?

force exterted on muscle by object

What is the rationale behind motor units contracting asynchronously?

helps prevent fatigue

Which type of muscle attachemt is more common in the body?

indirect (durable and small)

What are isometric and isotonic contractions?

isometric contraction- no shortening muscle tension increases by does not exceed the load (lifting a car) Isotonic contraction- muscle shortens becuase muscle tension exceeds the load .

what happens at each phase? Latent period period of contraction period of relaxation

latent period- events of excitation-contraction coupling (muscle tension is increasing) period of contraction- cross bridge formation, tension peaks period of relaxation- Ca2+ re entry into the SR, tension declines to zero

What are four major functions of muscle?

movement of bones or fluids (blood), Maintaining posture and body position, stabilizing joints, and heat generation (especially in skeletal muscle)

What is recruitment

multiple motor unit summation, which brings more and more muscle fibers into action (presisely controls contraction force)

What will result from prolonged tetanus?

muscle fatigue, muscle in unable to contract

What is another name for muscle cells

muscle fibers

List the structures in order from largest to most iicroscopic, starting with muscle and ending with myofilaments.

muscle, fascicle, miscle fiber, myofibril, sacromere, myofilament.

Where are small motor units found?

muscles that control fine movements (fingers and eyes)

What is the function of the sarcoplasmic reticulum?

network of smooth endoplasmic reticulum surrounding each myrofibril, most tubules run longitudunall.

What are the terminal cisternae & Where are they found?

pairs of terminal cisternae form perpendicular cross channels at A band- I bank junction

What is the muscle twitch? What are the 3 phases?

response of a muscle to a single, brief threshold stimulus latent period, period of contraction, and period of relaxation

How are the types of muscle alike and different?

skeleltal- attaches to and covers bones, striated, voluntary, powerful and adaptable. Cardiac- only in heart, striated and involuntary Smooth- in walls of hollow organs (stomach, urinary bladder, airways) forces fluids and other substances through internal channels, not striated, involuntary, and slow sustained contracts.

What do troponin and tropomyosin do?

tropomyosin- rod shaped protein, stiffens and stabilizes actin. Troponin- Three polypeptide complex, Tnl- inhibitory, binds to actin, TnT-binds to tropomyosin, positions it on actin, TnC- binds to Ca ions

Where are large motor units found?

weight bearing muscles (hips and thighs)