lect 11 pt 5

Why do we play the piano, video games, and type with our hands rather than our feet?

Part of it is learned coordination, and our hands are more equipped and conditioned to do these things.

What is another reason our hands can perform finer movements than our feet?

Our hands have more overall motor units.

What is the motor-unit difference between the hands and feet?

Hand muscles generally have more and smaller motor units than feet.

What does having smaller motor units in the hands allow?

More control and a better ability to gauge the amount of muscle fibers being used.

What does having smaller motor units allow you to do with your hand muscles?

Use $5\%$, $10\%$, or $15\%$ of the muscle fibers and make finer movements.

What type of motor control do the hands have compared with the feet?

Much better motor control.

How are the motor units in the feet different from those in the hands?

The feet have fewer overall motor units, and their motor units are larger.

What does a larger motor unit mean?

One motor neuron may go to a lot more muscle fibers.

What does having larger motor units in the feet do to control?

You cannot gauge things as well as you can with your hands.

What percentages does the lecture use to describe the larger steps of foot muscle recruitment?

$25\%$, $50\%$, or $100\%$.

What are feet generally like compared with hands because of their larger motor units?

Feet are more clumsy and cannot always gauge things as well as the hands.

What is the main reason hand muscles generally have better fine control than foot muscles?

Hand muscles generally have more and smaller motor units than feet.

What can muscles only do along their axis?

Muscles can only shorten along the axis.

What do muscles rely on to lengthen again?

An antagonist muscle most likely, but also passive elasticity and gravity.

What happens when fiber directions vary within a muscle?

The possible actions can also vary.

What happens when you strain a muscle?

Strain causes hypertrophy.

What happens during hypertrophy?

Sarcomeres are added and the muscles get bigger.

What happens when there is a lack of strain on a muscle?

Lack of strain causes atrophy.

What happens to sarcomeres during atrophy?

Some sarcomeres are removed and the muscles get smaller.

What happens to a chronically shortened muscle?

It removes sarcomeres for a new neutral joint position.

What happens to a chronically stretched muscle?

It adds sarcomeres for a new neutral joint position.

What happens when sarcomeres are added in parallel?

The cross-sectional area of the muscle increases.

What does adding sarcomeres in parallel do to muscle diameter?

It makes the muscle grow in diameter.

What does adding sarcomeres in parallel do to muscle strength?

It gives the muscle more strength.

What does "in series" mean for sarcomeres?

End to end, end to end.

What happens if you take a sarcomere off the end of a muscle?

You shorten the muscle.

What happens if you add sarcomeres in series?

You lengthen the muscle.

What is the difference between parallel and series sarcomeres?

Parallel increases cross-sectional area;

series lengthens or shortens the muscle.