Activity 3. NERVOUS STIMULATION

Factors affecting tension produced in skeletal muscle

*frequency of action potential (nerve impulses) from a motor neuron *number of motor neurons

Based on the Sliding Filament Model of Muscle Contraction, what events are happening during the Contraction Period?

During the contraction period, calcium ions in the sarcoplasm have bounced to troponin, tropomysin has shifted away from the actin binding sites, and crossbridges have formed. This results to the sarcomeres actively shortening to the point of peak tension.

Describe the pattern of increase in the force generated by the muscle from 1.0V to 8.5V.

Incremental

Based on the Sliding Filament Model of Muscle Contraction, what events are happening during the Latent Period?

Period between when the action potential reaches the muscle until tension can be observed in the muscle. In the latent period, this is the first phase of twitch where there is accumulation of action potential in the sarcolemma which will stimulate the releasing of Ca2+ ions in the sarcoplasmic reticulum which is the one that activated the muscle twitch. However, there is no contraction or movement in this phase.

Based on the Sliding Filament Model of Muscle Contraction, what events are happening during the Relaxation Period?

Sarcoplasmic reticulum is receiving calcium ions that have been released from the sarcoplasm. Crossbridge cycling halts, and also at relaxing period the sarcomere goes back to rest.

Describe the process of muscle contraction based on the Sliding Filament Model.

The cross-bridge cycle is the name given to the molecular process by which myosin and actin myofilaments move over one another. Myosin myofilament heads swiftly bind and release in a ratcheting motion during muscle contraction, dragging themselves along the actin myofilament.

sliding filament model

The theory explaining how muscle contracts, based on change within a sarcomere, the basic unit of muscle organization, stating that thin (actin) filaments slide across thick (myosin) filaments, shortening the sarcomere; the shortening of all sarcomeres in a myofibril shortens the entire myofibril

Why was there no force generated even though the muscle was stimulated with 0.5V?

The voltage applied to the muscle does not reach the threshold needed for a muscle contraction to occur.

Why was the force generated using 8.5V and 9.0V the same?

There is no change in the force generated using 8.5V and 9.0V because the maximal stimulus is already at 8.5V. It marks the point when the muscle's fibers are all stimulated and reacting equally.

graded muscle responses

allows variation in muscle tension

incomplete (unfused) tetanus

frequency summation to a plateau, until it reaches its peak; quick cycle of contraction with short relaxation phase for each.

Tetanus

fusion of contraction to produce a continuous contraction

Twitch

isolated (single) contraction

Electromyograpy (EMG)

measures muscle response or electrical activity in response to a nerve's stimulation of the muscle; measures amount of tension produced over time

cross bridge cycling

myosin head attaches to actin binding site - pulls thin filament - ADP and phosphate released from myosin - linkage between actin and myosin break - ATP splits - goes back to original position

Series of action potential

necessary to produce a muscle contraction to produce work

wave summation

this occurs when a second stimulus is received before the muscle fiber has relaxed, creating a second contraction that is stronger than the first; because the second stimulus triggers the release of more ions

What is the effect if the muscle is stimulated several times before it has a chance to relax?

when the muscle is stimulated several times before it has a chance to relax, this causes more tension to occur resulting in a higher force generated.

complete (fused) tetanus

when the stimuli from the motor neuron is so rapid that there is no relaxation and the force development appears to form a plateau