PHILS 8

During contraction, muscle tension can...

be further increased if calcium release is prolonged. Increasing the frequency of action potentials increases calcium release in a process called summation.

During summation; the muscle contracted:

but did not return to resting length before it contracted again

incomplete tetanus

furthur inc in freq prod this where indiv contractions will be evident but intracellular calcium accumulation will inc ithe amount of tension above that seen during single twitches so before it can relax more calcium is pumped out

You applied a series of shocks to the muscle to induce contractions. What was the time interval between shocks when single twitches were observed?

greater than 250 ms

A contraction is produced by an increase in the level of calcium in the cytoplasm. Where is calcium stored when the muscle is at rest?

in the sarcoplasmic reticulum

In a resting skeletal muscle, calcium is stored

in the sarcoplasmic reticulum

An action potential that is

initiated by motor neuron activity travels around the muscle fiber and down the T-tubules to stimulate the SR to rel calcium into the sarcoplasm and produce a contraction

Sarcoplasmic reticulum

intracellular organelle that is wrapped around the myofibril and connected to the cell membrane by transverse tubule

An action potential in vertebrate skeletal muscle fibers increases intracellular calcium levels because:

it travels down the transverse tubules, stimulates voltage sensitive receptors, and opens calcium channels in the sarcoplasmic reticulum membrane

sarcomeres are

many of them conn to each other to form a chain

complete tetanus

max tension is achieved with no indiv twitches bc intracellular concentration of calcium will be essentially constant; all chanells open so rate of calcium release will be same as rate of calcium uptake stimulus so freq that timing between is diminishing a lot and it will prod fatigue

During a single-twitch contraction of a skeletal muscle fiber:

maximum tension is never achieved

single twitch contraction

muscle contracted and relaxed contraction

sumation

stimulation contracts but before it can relax its contracted again

During incomplete tetanus, the amount of tension increases above that seen with a single twitch because:

there is intracellular accumulation of calcium

Calcium initiates a contraction of skeletal muscle by binding with

troponin

Goals of lab

1. Dissect the gastrocnemius (calf) muscle from a frog and prepare for stimulation and recording. Record muscle tension at increasing stimulation frequencies.

Tetanus

A. When a muscle is stimulated repeatedly before it can fully return to a relaxed state, muscle tension increases in a process called incomplete tetanus. B. If a muscle does not relax at all between stimulations, muscle tension is maximum in complete tetanus.

Why would the rate of muscle relaxation be slower after tetanus than after a single twitch?

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

You applied a series of shocks to the muscle to induce contractions. What was the longest time interval between shocks when incomplete tetanus was first observed?

about 170 ms.

You applied a series of shocks to the muscle to induce contractions. What was the longest time interval between shocks when summation was first observed?

about 200 ms

You applied a series of shocks to the muscle to induce contractions. What was the longest time interval between shocks when complete tetanus was first observed?

about 70 ms

During single twitch-type contractions, the muscle contracted:

and returned to resting length before it contracted again

during muscle contraction

calcium is released from the sarcoplasmic reticulum to initiate actin and myosin binding. Calcium binds to the thin filament protein, troponin, which moves tropomyosin and reveals binding sites on actin. Myosin binds to actin, leading to the power stroke and sliding of the thin filaments over the thick filaments.

During incomplete tetanus, the muscle:

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

each sarcomere contains

overlapping thick and thin filaments and during a contraction the filaments slide over one another to dec length of sarcomeres and shorten muscle fiber

During complete tetanus, the muscle:

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