Chapter 15- Muscle structure and physiology (3) Flashcards
How can the size of a muscle contraction be varied?
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.
Small delicate muscles with fine degree of control consists of…
Motor units containing only a few muscle fibres.
Muscles that don’t require that much control consists of…
Motor units containing more muscle fibres.
Why are the motor units with the smallest muscle fibres activated first?
Because they are controlled by the smallest, most highly excitable neurons.
How does contractile strength increase?
When motor units with larger and larger muscle fibres begin to be excited.
The largest motor units are controlled by what and when are they activated?
They are controlled by the largest, least excitable (highest threshold) neurons
They are activated only when the most powerful contraction is necessary.
The higher the frequency,….
the greater the strength of contraction of a given motor unit.
What is a muscle twitch?
The response of a muscle to a single stimulus
What are the three phases of a muscle twitch?
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.
What are the two types of muscle contraction?
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
Is the cardiac muscle striated?
Yes
Unlike skeletal muscle, cardiac fibres…
Branch and there is only a single, central nucleus per fibre.
What do intercalated discs act as?
Gap junctions
What do intercalated discs and branching ensure?
Rapid conduction of action potentials throughout the heart
What is smooth muscle composed of?
Small spindle shaped cells
Is the smooth muscle striated?
No
What is its arrangement when it comes to the nucleus?
It has only one nucleus in the centre
What is the smooth muscle specialised for?
Specialised for weak, persistent motion
Is smooth muscle voluntary or involuntary?
Involuntary
What does the smooth muscle often line?
Often lines hollow organs
What does the sacromere arrangement of skeletal muscle ensure?
Rapid and powerful contractions.
When will the sarcomeres not contract?
If the muscle is too stretched as the actin and myosin no longer overlap.
It also cannot contract if the muscle is too compressed.
Which muscle has a more irregular arrangement of actin/myosin?
Smooth muscle
What muscle contracts without sacromeres?
Smooth muscle
Is contraction without sarcomeres more powerful or less powerful?
Less powerful
However, it uses less energy which is beneficial because the smooth muscle is continuously active.
