Nerves and Muscles 3

Question 1

How many skeletal muscles are in the body/

Answer 1

650

Question 2

What are the different shapes of muscle?

Hint: There are 7

Answer 2

• Circular
• Cylindrical
• Parallel
• Multipennate
• Unipenntate
• Convergent
• Fusiform
• Bipennate

Question 3

What are the 3 types of muscle? What are there features?

Answer 3

Skeletal muscle: Voluntary muscle, striated, cells are multinucleate, non-branching, attached to skeleton

Cardiac muscle: Non-voluntary muscle, striated, cells are multinucleate, branched, heart muscle

Smooth muscle: Non-voluntary, not striated, cells have one nucleus, tapered, form walls of organs

Question 4

What is the organisation within a muscle?

Answer 4

A tendon attaches a muscle to bone. The epimysium is connective tissue that covers the whole muscle.

The perimysium is connective tissue that surrounds a fascicle. Fascicles are made up of thousands of myofibrils (chains of sarcomeres). Within this is a nerve and blood supply.

The endomysium is connective tissue that is between muscle fibres and cells.

A sarcoplasm is the cytoplasm of a muscle cell. The sarcolemma is the membrane of a muscle cell.

The sarcomere is the smallest contractile unit.

Question 5

What is the I band?

Answer 5

The band made up of the thin filaments - actin. This region is not superimposed by thick filaments.

Question 6

What is the M line?

Answer 6

A line made up of different proteins that connects myosin fibres. Other proteins help in the scaffold of the sarcomere and form structural support. This is formed of cross connecting elements of the cytoskeleton.

Question 7

What is the A band?

Answer 7

The band made up of thick filaments - myosin. This area is superimposed by the thin filaments.

Question 8

What is the H zone?

Answer 8

This is the one made up only of thick filaments - myosin. It is not superimposed by thin filaments and so is slightly lighter than the A band.

Question 9

What is Titin?

Answer 9

The longest protein isn human genome. Titin’s primary functions are to stabilize the thick filament, center it between the thin filaments, prevent overstretching of the sarcomere, and to recoil the sarcomere like a spring after it is stretched.

Question 10

What is the Z line?

Answer 10

The Z line separates the sarcomere.

Question 11

How many light chains make up the globular myosin head?

Answer 11

2

Question 12

What occurs at the neuromuscular junction in order to cause the release of calcium in the sarcomere?

Answer 12

1. The impulse travels down the presynaptic neurone and causes the release of acetylcholine.
2. Acetylcholine binds to the receptors on the postsynaptic membrane.
3. This causes depolarisation of the sarcomere as sodium ion channels are opened and an influx of sodium passes across the sarcomere.
4. This wave of depolarisation travels down the T-tubules.
5. This causes the release of Calcium from the sarcoplasmic reticulum.

Question 13

How does the Sliding Filament Theory hypothesis contraction occurs?

Answer 13

1. Calcium will bind to troponin.
2. This will cause a conformational change in the troponin complex causing tropomyosin to be moved out of the way exposing the myosin binding region.
3. ATP is hydrolysed in the myosin head and ADP and inorganic phosphate is released.
4. The myosin head then attaches to actin at the now exposed binding site. This is known as a cross-bridge.
5. When bound, the myosin head pulls the actin filament along reducing the length of the sarcomere. This is known as a power stroke.
6. ATP binds to myosin head causing the myosin head to dissociate from actin.

Question 14

What is a cramp and rigorous mortis?

Answer 14

There is not enough ATP and so myosin head does not dissociate from actin. As a result, the muscle remains contracted.

Question 15

What happens to a sarcomere in contraction?

Answer 15

The Z lines come closer together. The I band reduces in size however the A band stays the same.

Question 16

What happens in relaxation?

Answer 16

Calcium is taken up by the sarcoplasmic reticulum. Calcium moves away from troponin and so tropomyosin moves back meaning the myosin heads can no longer bind.

Question 17

What is an isotonic contraction?

Answer 17

A contraction in which the length of the muscle changes.

Question 18

What are the two types of isotonic contraction?

Answer 18

Concentric contraction: The overall length of the muscle shortens.

Eccentric contraction: Occurs when the muscle elongates when it contractions. This is less common and usually involves the control fo deceleration of movement being ignited by the concentric muscle agonist.

Question 19

What is an isometric contraction?

Answer 19

A contraction in which the length of the muscle stays the same. The amount of force a muscle is able to produced her is determined by the length of the muscle at the point of contraction.

Question 20

What is a twitch?

Answer 20

A mechanical response to an action potential by an individual motor unit, or a whole muscle.

Question 21

What are the three passes of twitch?

Answer 21

Latent period: Initial delay of a few milliseconds. The release of calcium begins.

Contraction period: The rate of release of calcium is greater than the rate of re-uptake.

Relaxation: The rate of uptake of calcium is greater than the rate of release from the sarcoplasmic reticulum.

Question 22

What are type I fibres?

Answer 22

Slow twitch fibres:

• Red due to high amount of myoglobin
• High number of mitochondria
• Do not fatigue
• The contraction produced is not very strong
• Contract slowly

Question 23

What are type IIa fibres?

Answer 23

Fast twitch fibres:

• Red in colour due to high concentration of myoglobin
• Resistant to fatigue (not as much as type I)
• Contract relatively quickly
• Produce a moderate amount of power when contacted

Question 24

What are type IIb fibres?

Answer 24

Fast twitch fibres:

• White as they rely heavily on aerobic respiration
• A high force is produced
• Contract quickly
• Fatigue easily
• No mitochondria

Question 25

How does the number of action potentials per second sent influence the force of contraction?

Answer 25

When the frequency of stimulation is so high that Ca++ levels rise to peak levels, summation results in the level of tension reaching a plateau called tetanus. When the frequency of stimuli is high enough to cause tetanus but tension oscillates around an average level, the tetanus is called incomplete or unfused. At greater frequencies of stimulus, levels of Ca++ peak and cause a maximum number of cross-bridges to cycle. At this point the tension plateau evens out and tetanus is called complete or fused. When the muscle is at maximum sustained tension it is said to have reached maximum tetanic tension. Complete tetanus can occur when lifting something heavy. Maximum strength

Question 26

How does the number of motor units recruited influence the force fo contraction?

Answer 26

To generate small forces, only a small number of motor units are recruited. When larger focus are needed, larger motor units are recruited. Initially type I fibres are recruited; as more action potentials are sent more type II motor units are recruited.

Question 27

How does the amount fo overlap between thick and thin filaments influence the force fo contraction?

Answer 27

The thick and thin filaments must be at a distance in which the thick filaments can pull the thin filaments across. If too far or too close this cannot occur. When the muscle is at the optimum length the number of active ceros bridges is the greatest.

Question 28

What are the causes of muscle disorders?

Answer 28

• Injury or overuse that cause inflammation (tendonitis)
  
  • Strains and sprains.
  • Cramp - inability to supply energy or generate and so unable to release action of myosin - occurs in activity.
• Can have a genetic predisposition. High CK levels
  • Muscular dystrophy - scaffold that attaches muscles to extracellular matrix is destroyed. Have high CK level
  • Inflammation - inflammatory muscle disease myotis, polymyalgia rheumatica
    Neurological disorder - issue with nerve supply