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15.1.1114-15 · Homeostasis and Control

Ultrastructure of Striated Muscle — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 7 parts Lesson 26 of 31 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

15.1.11 Ultrastructure of Striated Muscle — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the structure of a muscle fibre, myofibril and sarcomere.Location — muscles attached to the skeleton.Appearance — striated means striped or streaky.Muscle fibres — str…

  • Specialised unit
  • Mitochondria
  • Myofibrils
  • Sarcoplasmic reticulum
  • Thin filaments
  • Thick filaments

Part 1 of 5Striated muscle

Location
  • Location muscles attached to the skeleton.
Appearance
  • Appearance striated means striped or streaky.
Muscle fibres
  • Muscle fibres striated muscle is made of muscle fibres.

Part 2 of 5The muscle fibre

Specialised unit
  • Specialised unit contains an organised arrangement of contractile proteins in the cytoplasm.
Nuclei
  • Nuclei many nuclei, so it is not usually called a cell.
Membrane
  • Membrane surrounded by a cell surface membrane.
Normal cellMuscle fibre
Cell surface membraneSarcolemma
CytoplasmSarcoplasm

Part 3 of 5Contents of the sarcoplasm

Mitochondria
  • Mitochondria supply ATP.
Myofibrils
  • Myofibrils bundles of actin and myosin filaments that slide past each other in contraction.
Sarcoplasmic reticulum
  • Sarcoplasmic reticulum stores Ca2+.
T-tubules
  • T-tubules carry action potentials into the fibre.

Part 4 of 5Filaments

Thin filaments
  • Thin filaments made of actin.
Thick filaments
  • Thick filaments made of myosin.
Order
  • Order the two filaments are arranged in a particular order, creating different bands and lines.

Part 5 of 5Bands and lines of a myofibril

PartDescription
H bandOnly thick myosin filaments
I bandOnly thin actin filaments
A bandMyosin only in places and myosin overlapping actin elsewhere
M lineAttachment for myosin filaments
Z lineAttachment for actin filaments
SarcomereSection of myofibril between two Z lines

Key terms

TermMeaning
Striated muscleMuscle with a striped appearance, attached to the skeleton.
Muscle fibreMultinucleate contractile unit.
SarcolemmaSurface membrane of a muscle fibre.
SarcoplasmCytoplasm of a muscle fibre.
MyofibrilBundle of actin and myosin filaments.
SarcomereSection between two Z lines.
A bandBand containing myosin, including overlap with actin.

Avoid these mistakes

1
Calling muscle fibres single-nucleus cells — they have many nuclei.
2
Mixing up the I and H bands — I has actin only, H has myosin only.
3
Saying the A band is only myosin — it includes the overlap region.
4
Mixing up the M and Z lines — M holds myosin, Z holds actin.

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