Muscle

Question 1

Functions of Muscle

Answer 1

• organ protection
• skeletal stability
• peristalsis
• blood circulation
• voluntary and reflexive movement
• generates heat

Question 2

Skeletal Muscle

Answer 2

• striated
• unbranched
• multi-nucleated
• peripheral nuclei

Question 3

Sarcomere

Answer 3

I-band – light area around the Z-line consisting of thin actin
filaments not overlapped by thick filaments
A-band – dark area which spans the length of the thick filament
H-zone – light zone in the centre of the a-band where the thick
filaments are not overlapped by the thin filaments

Z-line – forms periphery of sarcomere where thin actin
filaments attach
M-line – found inside H-zone and forms the middle of the
sarcomere

Question 4

Hierarchy of skeletal muscle

Answer 4

Muscle = a bundle of fascicles
Muscle fasciculus = a bundle of fibres
Muscle fibre = a bundle of myofibrils
Myofibril = a bundle of myofilaments
Myofilaments = actin & myosin

*Muscle fibre = surrounded by endomysium
*Muscle fascicle = surrounded by perimysium
*Muscle = surrounded by epimysium

Question 5

Cardiac muscle

Answer 5

Myocardium - involuntary muscle found in the heart.
Contraction of cardiac muscle is intrinsic at nodes of
impulse-generating pacemaker muscle fibres;
autonomic nerves regulate the rate of contraction.
* Striated: Actin & myosin, organised as in
skeletal muscle.
* T-tubules and sarcoplasmic reticulum
present.
* Nucleus positioned centrally in fibre (cell).
* Cannot regenerate but can undergo
hypertrophy
* Branched cells joined together by
intercalated discs:
Fascia adherens (adhering junction)
Macula adherens (desmosome)
Gap junctions

Question 6

Smooth Muscle

Answer 6

• Visceral or involuntary muscle
• Found in tubular organs (gut, blood
  vessels, bile duct, uterus, urinary bladder,
  respiratory tract)
• Can regenerate and undergo hypertrophy
• Main histological features:
• Unbranched individual cells that are
  spindle shaped (long and tapered)
• Central nucleus, often corkscrew shaped.
• No striations
• No myofibrils - Actin and Myosin
  present, but not organised in regular
  way (i.e. no striations).
• Myofilaments attach to dense bodies
  (anchoring points - equivalent of Z-
  lines in striated muscle). Dense
  bodies connect to each other via
  intermediate filaments.
• Membrane invaginations called
  caveolae (equivalent of T-tubules)
  are important in Ca2+ transport.
• Most organelles stored at the poles
  of the nucleus, to avoid interference
  with contractile process

Question 7

Regeneration of Muscle Tissue

Answer 7

*Repair and regeneration can occur in skeletal muscle because of a population of reserve muscle satellite
cells that can proliferate, fuse, and form new muscle fibres.
*Cardiac muscle lacks satellite cells and has little capacity for regeneration.
*Regeneration is rapid in smooth muscle because the cells/fibres are small and relatively less differentiated,
which allow renewed mitotic activity after injury.