lect 11 pt 4

What cellular characteristics can muscle fibers vary in?

The number of mitochondria, enzymes for aerobic versus anaerobic processes, and different myoglobin isoforms.

What do differences in muscle fiber cellular characteristics affect?

How fast, how forcefully, and for how long a muscle can contract.

What are slow oxidative fibers also known as?

Type I fibers.

What are fast oxidative fibers also known as?

Type II A fibers or intermediates.

What are fast glycolytic fibers also known as?

Type II X fibers.

What makes slow oxidative fibers appear much darker?

They have a lot of myoglobin.

What can slow oxidative fibers do for long periods?

They can contract all day long.

What are fast glycolytic fibers like in color?

They are much lighter in color.

What do fast glycolytic fibers provide?

Fast, powerful contractions.

What happens to fast glycolytic fibers after they provide powerful contractions?

They run out of gas pretty quickly.

What happens when you walk on a flat surface for a long time?

You can walk all day without a problem because of the steady activity.

What happens when you quickly walk up a hill?

You engage a lot of fast glycolytic fibers to power you up the hill quickly and efficiently.

What can happen to your calf muscles after quickly walking up a hill?

They can sting, and you can be out of breath.

What happens to the fast glycolytic fibers when you return to flat ground?

They relax and rejuvenate.

Which two muscles are discussed in relation to walking and powerful contractions?

Soleus and gastrocnemius.

What type of fibers is the soleus really full of?

Slow oxidative fibers.

What is the soleus described as being used for?

Walking all day.

What type of fibers does the gastrocnemius have mostly?

Fast glycolytic fibers.

What does the gastrocnemius provide?

Powerful contractions to motor you up a hill.

How can we lift both heavy and light objects with the same muscle?

We use exactly as much force as needed to lift the object.

How do we usually gauge how much force to use?

Through visual gauging and muscle memory.

What does muscle memory help us remember?

How heavy certain things are so we know how much force to apply.

What does visual preparation tell us?

How much of the muscle to use, or how many fibers to recruit.

What is a motor unit?

One motor neuron and all the muscle fibers it innervates.

What happens to all the muscle fibers innervated by a motor neuron when that neuron fires?

All of the fibers that it innervates will also contract.

Can motor units be different sizes?

Yes. You can have different-sized motor units with different motor neuron-to-fiber ratios.

What is recruitment of fibers?

Recruiting only as many fibers as are needed to get the job done.

What happens if you only need 50% of a muscle?

You fire 50% of your motor units.

What does the amount of force you generate depend on?

The number of motor units recruited.