Phils 8

what are thin filaments attacahed to

z discs

What was the longest time interval between stimuli when incomplete tetanus was first observed? About 210 ms. Greater than 250 ms. About 70 ms. About 170 ms.

About 170 ms.

What was the longest time interval between stimuli when summation was first observed? About 70 ms. Greater than 250 ms. About 170 ms. About 210 ms.

About 210 ms.

What was the longest time interval between stimuli when complete tetanus was first observed? Greater than 250 ms. About 170 ms. About 210 ms. About 70 ms.

About 70 ms.

What was the time interval between stimuli when single twitches were observed? Less than 70 ms. About 170 ms. Greater than 250 ms. About 200 ms.

Greater than 250 ms.

A contraction is produced by an increase in the level of calcium in the sarcoplasm. Where is calcium stored when the muscle is at rest? In the sarcoplasm. Outside the cell. In the sarcoplasmic reticulum. In the sarcomere.

In the sarcoplasmic reticulum.

Why would the rate of muscle relaxation be slower after tetanus than after a single twitch? The contraction was larger, so the rate of relaxation would be slower. Cross-bridges are formed during relaxation. It takes time for the large amount of calcium in the sarcoplasm to be taken up by the sarcoplasmic reticulum. There is maximum amount of overlap between the thick and thin myofilaments.

It takes time for the large amount of calcium in the sarcoplasm to be taken up by the sarcoplasmic reticulum.

what interaction is essential for excitation of a muscle fiber to result in contraction

SR and T-tubules

what causes the thin myofilaments to be pulled toward the center of the sarcomere

a subsquent shape change in the myosin heads

what results in the opening of voltage gated calcium channels in the SR membrane

action potential traveling down T-tubules

During summation, the muscle contracted: and the amount of tension created decreased. and did not return to resting length before it contracted again. and returned to resting length before it contracted again.

and did not return to resting length before it contracted again.

During single twitch contractions, the muscle contracted: and the amount of tension increased with each subsequent twitch. and returned to resting length before it contracted again. and did not return to resting length before it contracted again.

and returned to resting length before it contracted again.

why is a single brief contraction (or twitch) of the muscle is produced by a single action potential

because it creates a transient increase in sarcoplasmic calcium

how is maintaining elevated calcium levels achieved

by stimulating the muscle fiber to produce many action potentials in quick succession

___ diffuses out of the SR and into the sarcoplasm

calcium

what pumps in the SR membrane quickly to move calcium back into the SR

calcium pumps

what do thin myofilaments extend towards

center of the sarcomere

where are thick myofilaments located

center of the sarcomere

what does high frequency stimulation produce

complete tetanus

During incomplete tetanus, the muscle: contracted so that the single contractions created more tension than seen during single twitches. contracted and returned to resting length before it contracted again. produced a prolonged (fused) contraction, and single contractions could not be seen.

contracted so that the single contractions created more tension than seen during single twitches.

after the movement of tropomyosin, what can take place between the myosin and actin molecules to produce a shortening of the sarcomere?

cross bridge cycling

The sarcoplasmic level of calcium quickly ___, troponin releases ____ and returns to its original shape, and ____ returns to its original location blacking myosin-binding sites

declines calcium tropomyosin

after completion of this simulation, you will be able to use instruments to apply electrical stimuli ____ to the exposed muscle and display the evoked contraction as a deflection of a line tracing on the screen

directly

what is attached to the equipment stand and connected directly to the muscle

force transudcer

what of the muscle stimulation affects the evoked movement

frequence

In a resting skeletal muscle, calcium is stored: in the sarcoplasm of the muscle fibers. in the myofibrils. in the sarcoplasmic reticulum. in the sarcomere.

in the sarcoplasmic reticulum

this occurs when the muscle fails to relax between contractions

incomplete tetanus

what is the shaking effect elicited by

incomplete tetanus

what will further increases in stimulus frequency produce

incomplete tetanus

The process of cross bridge cycling ____ thin and thick myofilament overlap, ____ sarcomere length, and therefore causes ___ of the muscle fiber

increases decreasing contraction

what does prolonging the the period of elevated sarcoplasmic calcium do?

increases the time for cross bridge cycling

what are transverse tubules (T-tubules)

invaginations of the cell membrane

An action potential in skeletal muscle fibers increases sarcoplasmic calcium levels because: it travels directly to the sarcoplasmic reticulum, which then releases calcium into the cell. it directly stimulates the sarcomeres. it opens voltage-gated calcium channels in the sarcolemma, so that calcium enters the cell from the outside. it travels down the T-tubules, stimulating voltage-gated calcium channels in the sarcoplasmic reticulum membrane.

it travels down the T-tubules, stimulating voltage-gated calcium channels in the sarcoplasmic reticulum membrane.

___ frequency stimulation produces single twitches, as seen when your eye twitches

low

what is the sarcoplasmic level of calcium in a resting muscle

low

what occurs at complete tetanus

maximum tension is achieved because the intracellular concentration of calcium is essentially constant all channels will be open so that the rate of calcium release will be the same rate of calcium reuptake

During a single twitch contraction of a skeletal muscle fiber: maximum tension is always achieved. maximum tension is never achieved. no tension is produced. calcium is not released from the sarcoplasmic reticulum.

maximum tension is never achieved.

when a ___ ___ excites a muscle fiber, the action potential travels down the T-tubules

motor neuron

during normal limb movements, ___ ___ produce action potentials at a sufficiently high frequency to elicit complete tetanus

motor neurons

skeletal muscles are composed of cells called ___ ___

muscle fibers

each muscle fiber contains many cylindrical structures called ____

myofibrils

what are myofibrils composed of

myofilaments arranged in sarcomeres

what forms cross bridges

myosin heads bind to actin

what are thick myofilaments made up of

myosin molecules

During complete tetanus, the muscle: contracted and returned to resting length before it contracted again. produced a prolonged (fused) contraction, and single contractions could not be seen. contracted so that the single contractions created more tension than seen during single twitches.

produced a prolonged (fused) contraction, and single contractions could not be seen.

muscle tesnion can be increased by ____ the period of elevated sarcoplasmic calcium

prolonging

when cross bridging ceases the muscle

relaxes

what are the fundamental contractile unit of skeletal muscle

sarcomeres

what occurs during incomplete tetanus

sarcoplasmic calcium accumulation increases the amount of tension beyond that of individual twitches

___ ___ is an organell that wraps around myofibrils and is linked to invaginations fo the cell membrane

sarcoplasmic reticulum

after the completion of this simulation, you will be able to determine the time taken for the ___ ___ to take up calcium after a single contraction

sarcoplasmic reticulum

sarcomeres are connected in a ____ to form a chain

series

In this lab you will apply electrical stimuli to a muscle, initially evoking ___ ____

single twitches

what will increasing the stimulus frequency result in

summation

after completion of this lab, you will be able to change the stimulus frequency and relate changes in the line tracing to ___, ____ ___, and ___ ____

summation, incomplete tetanus, and complete tetanus

increasing the stimulus frequency produces ___, ___ ____, and ____

summation, incomplete tetanus, and tetanus

during a single twitch, the brief period of cross bridge cycling generates only a small amount of ____

tension

this occurs when prolonged, elevated calcium levels in the sarcoplasm increase muscle tension

tetanus

why is the influx of calcium into the sarcoplasm short lived?

the action potential is brief and the voltage gated calcium channels quickly close

what does the force transducer detect

the amount of tension produced by the contracting muscle

calcium binds with a ____ myofilament protein called ____

thin troponin

what overlaps with thick myofilaments

thin myofilaments

what is cross bridge cycling initiated by

the movement of calcium from the SR to the sarcoplasm

when tropomyosin moves out of the way, what is exposed

the myosin binding sites on the actin molecules of the thin myofilaments

where is calcium stored in a resting muscle

the sarcoplasmic reticulum

what occurs during summation

the twitches "piggyback" on one another

During incomplete tetanus, the amount of tension increases above that seen with a single twitch because: there is accumulation of calcium in the sarcoplasm. sarcoplasmic calcium levels drop. maximum tension is achieved. the muscle twitches fuse into a single, maximum contraction.

there is accumulation of calcium in the sarcoplasm.

each sarcomere contains overlapping ___ and ___ myofilaments capable of causing contraction

thick and thin

mysoin heads of the ___ ____ are capable of binding actin of ___ ____

thick filaments thin filaments

Calcium initiates a contraction of skeletal muscle by binding with: actin. tropomyosin. myosin. troponin.

troponin

what happens when troponin binds to calcium

troponin changes shape and tropomyosin moves out of the way

you will change the time interval between the stimuli to observe ___, ___, and ____

twitches, summation, and tetanus

the force produced by the muscle is then controlled by changing the number and type of contracting muscle fibers

under normal conditions