Chapter 15- Muscle structure and physiology (3)

Question 1

How can the size of a muscle contraction be varied?

Answer 1

1- By altering the number of motor units active. This is a form of spatial summation.

2- Another way is by varying the frequency of stimulation of a muscle. This is called temporal summation.

Question 2

Small delicate muscles with fine degree of control consists of…

Answer 2

Motor units containing only a few muscle fibres.

Question 3

Muscles that don’t require that much control consists of…

Answer 3

Motor units containing more muscle fibres.

Question 4

Why are the motor units with the smallest muscle fibres activated first?

Answer 4

Because they are controlled by the smallest, most highly excitable neurons.

Question 5

How does contractile strength increase?

Answer 5

When motor units with larger and larger muscle fibres begin to be excited.

Question 6

The largest motor units are controlled by what and when are they activated?

Answer 6

They are controlled by the largest, least excitable (highest threshold) neurons

They are activated only when the most powerful contraction is necessary.

Question 7

The higher the frequency,….

Answer 7

the greater the strength of contraction of a given motor unit.

Question 8

What is a muscle twitch?

Answer 8

The response of a muscle to a single stimulus

Question 9

What are the three phases of a muscle twitch?

Answer 9

1- Latent period- interval between stimulus and the beginning of contraction

2- Contraction phase- when the muscle is shortening.

3- Relaxation phase- during which tension declines.

Question 10

What are the two types of muscle contraction?

Answer 10

1- Isometric- There is no change in shape when tension is added

2- Isotonic- Muscle contracts and changes shape but no change in the tension

Question 11

Is the cardiac muscle striated?

Answer 11

Yes

Question 12

Unlike skeletal muscle, cardiac fibres…

Answer 12

Branch and there is only a single, central nucleus per fibre.

Question 13

What do intercalated discs act as?

Answer 13

Gap junctions

Question 14

What do intercalated discs and branching ensure?

Answer 14

Rapid conduction of action potentials throughout the heart

Question 15

What is smooth muscle composed of?

Answer 15

Small spindle shaped cells

Question 16

Is the smooth muscle striated?

Answer 16

No

Question 17

What is its arrangement when it comes to the nucleus?

Answer 17

It has only one nucleus in the centre

Question 18

What is the smooth muscle specialised for?

Answer 18

Specialised for weak, persistent motion

Question 19

Is smooth muscle voluntary or involuntary?

Answer 19

Involuntary

Question 20

What does the smooth muscle often line?

Answer 20

Often lines hollow organs

Question 21

What does the sacromere arrangement of skeletal muscle ensure?

Answer 21

Rapid and powerful contractions.

Question 22

When will the sarcomeres not contract?

Answer 22

If the muscle is too stretched as the actin and myosin no longer overlap.

It also cannot contract if the muscle is too compressed.

Question 23

Which muscle has a more irregular arrangement of actin/myosin?

Answer 23

Smooth muscle

Question 24

What muscle contracts without sacromeres?

Answer 24

Smooth muscle

Question 25

Is contraction without sarcomeres more powerful or less powerful?

Answer 25

Less powerful

However, it uses less energy which is beneficial because the smooth muscle is continuously active.