13.9 Voluntary and involuntary muscles

Question 1

what are the 3 types of muscles in the body

Answer 1

1. skeletal muscle (bulk of the body, cells responsible for movement)
2. cardiac muscle (only in the heart, are myogenic)
3. involuntary muscle (found in many parts including walls of hollow organs, blood vessels and the digestive tract

Question 2

describe skeletal muscle

Answer 2

fibre appearance: striated
control: voluntary
arrangement: regularly arranged so muscle contracts in one direction
contraction speed: rapid
length of contraction: short
structure: muscles show cross striations, fibres are tubular and multinucleated

Question 3

describe cardiac muscle

Answer 3

fibre appearance: specialised striated
control: involuntary
arrangement: cell branch and connect so simultaneous contraction
contraction speed: intermediate
length of contraction: intermediate
structure: muscles have faint striations, fibres are branches and uninucleated

Question 4

describe involuntary muscle

Answer 4

fibre appearance: non-striated
control: involuntary
arrangement: no regularity so can contract in different directions
contraction speed: slow
length of contraction: long
structure: non-striated muscles, fibres are spindle shaped and uninucleated

Question 5

what makes up skeletal muscle

Answer 5

• bundles of muscle fibres

- each muscle fibre contains many myofibrils

Question 6

describe structure of muscle fibres

Answer 6

• enclosed within a plasma membrane (sarcolemma)
• number of nuclei
• longer than normal cells due to embryonic cells fusion together = stronger muscles as there are no junctions
• shared cytoplasm = sarcoplasm
• parts of sarcolemma fold inwards (T tubules) = spread out electrical impulse so whole fibre contracts at the same time
• lots of mitochondria = ATP for contraction
• sarcoplasmic reticulum extends throughout the fibre and contains Ca+ ions for contraction

Question 7

describe the structure of myofibrils

Answer 7

• long, cylindrical organelles made of protein
• collectively powerful
• lined up in parallel = provide max force when contracting
• alternating light and dark bands
• made up of two filaments:
  1. actin (thinner, 2 strands twisted around each other)
  2. myosin (thicker, long rod-shaped fibres with bulbous heads projecting to one side)

Question 8

explain the striped appearance of myofibrils

Answer 8

• light bands (region where actin and myosin filaments don’t overlap (also called I-bands))
• dark bands (presence of thick myosin filaments. darker edges as myosin and actin overlap)
• z-line (centre of the light band, shortens when muscle contracts)
• h-zone (lighter region in dark band where only myosin is present, decreases when muscle contracts)

Question 9

what is a sarcomere

Answer 9

• distance between adjacent z-lines
• functional unit of the myofibril
• shortens when muscle contracts

Question 10

histology of skeletal muscle

Answer 10

• individual muscle fibres (long and thin multinucleated fibres that cross with regular pattern of red/white lines)
• highly structured arrangement of sarcomeres (a-bands (dark) and I-bands (light))
• streaks of connective and adipose tissue
• capillaries running in between fibres