Motor unit

Question 1

What are the 4 factors that determine skeletal muscle contraction and duration?

Answer 1

1. sarcomere length within a muscle fiber
2. Summation of twitches within a muscle fiber
3. Recruitment of additional motor units
4. Properties of recruited motor units.

Question 2

The amount of muscle tensions that can be generated within a muscle a fiber has to do with what?

Answer 2

It has to do with the number of crossbridge formed/ bonds formed between actin and myosin.

Question 3

How does resting fiber length affect muscle tension?

Answer 3

Resting fiber length is the length of a muscle fiber before contraction begins. This affects the AMOUNT of tension/force a muscle can generate within that muscle fiber. The tension generated is proportional to the number of cross bridges that could form.

Question 4

What needs to happen in the resting fiber before it can create these optimal tensions in that muscle fiber?

Answer 4

Actin thin filaments need to line up with the myosin thick filaments and, sarcomere needs to have enough space to be able to shorten. For example, for a sarcomere to contract with optimal force, it needs to be at an optimal length. IF a sarcomere stretches or lengthens there will be less ability to form crossbridge and if it overlaps too much, there won’t be enough space for the muscle to shorten.

Question 5

What is the latent period?

Answer 5

a delay that occurs during the time for Ca2+ in the intracellular to increase and Ca2+ to bind to troponin. Shortly, this is the period between excitation of muscle fiber and the actual generation of muscle tension.

Question 6

How can muscle contractions be summed?

Answer 6

Contractions can sum, if multiple action potentials are exciting that muscle fiber. The more frequently the muscle fiber is excited, twitches can sum together, and overall muscle contraction can get longer.

Question 7

Why does low sarcoplasmic (cytoplasm/intracellular) concentration of Ca2+ causes the end for the events of muscle twitch?

Answer 7

Ca2+ will not bind to troponin, tropomyosin will not glide over the actin myosin binding site form the thin actin filaments, there will be no power stroke. Hence, end muscle contraction.

Question 8

What are single twitches?

Answer 8

In single twitches, muscle relaxes completely between stimuli. It’s like waves, at the end of each waves the twitch slowly dies down form the low conc of Ca2+ in the intracellular ICF, the beginning of the twitch starts with action potential exciting the cell.

Question 9

What is summation?

Answer 9

In summation stimuli are closer together, they do not allow muscles to relax fully. There is reduced duration of action potential.

Question 10

What is Unfused tetanus?

Answer 10

Stimuli/firing of action potential is far enough apart for letting muscles to relax SLIGHTLY between stimuli. When maximum tension is reached there is unfused tetanus. Muscle tensions some from the frequency of firing action potential and add up and get larger till they reach their maximum tension, as that point there is unfused tetanus.

Question 11

What is complete tetanus?

Answer 11

Muscle reaches steady tension, but when muscle feels fatigue, regardless of the continuous stimuli muscle tension decreases.

Question 12

What does the motor unit consist of?

Answer 12

The motor unit consists of 1 neuron and all the muscle fibers it innervates. One motor neuron can innervate multiple muscle fibers, who will all have similar properties, and the action potential generated by one motor neuron will travel down to all the muscle fibers in that motor unit.

Question 13

How are skeletal muscle fibers classified?

Answer 13

Skeletal muscle fibers are classified by speed and fatigue resistance.

Question 14

What is muscle fatigue?

Answer 14

It is the inability to maintain muscle tension during periods of sustained, repetitive activation.

Question 15

What is proprioception?

Answer 15

This is the real sixth sense. The sense of your body’s position, movement and effort.

Question 16

What are muscle spindles?

Answer 16

Muscle spindles are sensory organs, who provide information about length of the muscle and the change in the length of the muscle. They are fusiform (tapered in both ends) and contain intrafusal muscle fibers, sensory neurons, sensory receptors, and gamma motor neurons. They lie parallel to the rest of the extrafusal muscle fibers. They sense position and are located in the skeletal muscle fibers.

Question 17

What are Golgi tendon organs?

Answer 17

They are responsible for sensing load, located in tendons. Sensory organs who are located at the end of the muscles as muscles start to connect with tendons. As muscles contract Golgi tendon sensory organ’s fore action potential.
Suppose there is an increase in load, the muscle will contract this contraction happens by shortening of the sarcomere, it pulls up on the Golgi tendons and it causes all the collagen fibers to squeeze the sensory organs into firing action potential.

Question 18

What are reflexes?

Answer 18

Reflexes are the fastest synapses, less complex, doesn’t require cognitive processing, everything happens in the spinal cord level. They are mostly evoked by sudden, unexpected changes in the environment. They are a result of coordinated movement of a joint, they serve a protective role, and they are not equal to sensory receptor activity.

Question 19

What kind of reflex is this?

“Quickly removing a limb from a painful stimulus.”

Answer 19

Flexion crossed extension.

Question 20

What kind of reflex is this?

“Quickly returning a limb to its original position if it is unexpectedly/suddenly moved?”

Answer 20

Muscle spindles stretch reflex

Question 21

What kind of reflex is this?

“Quickly release muscle tension if tension becomes too great ?”

Answer 21

Loading reflex- Golgi tendon organs.