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Key Words

Myosin - A thick, contractile protein filament, with protusions known as Myosin heads

Powerstroke - the action of the myosin head in musclar contraction. The head group attaches to the actin filament and tilts backwards, pulling the think filament to overlap with the thin filament

Calcium - These ions attach o the troponin causing it to change shape

Actin - A thin, contractile protein filament, containing 'active' or 'binding' sites

Tropomyosin - A actin-binding protein which regulates muscle contraction

Cross-bridge - In volutary muscles, the joining of a myosin head group to an actin thin filament in the prescence of calcium ions

Sarcoplasmic Reticulum - A specialised endoplasmic reticulum

Myofibril - a cylinderical organelle running the length of the muscle fibre, containing Actin and Myosin filaments

Sacromere - smallest contractile unit in voluntary muscle, consisting of thin & think filaments

Troponin - A complex of three proteins, attached to Tropomyosin

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Involuntary Muscle/Smooth Muscle

...innervated by neurones of the autonomous nervous system and contraction is relatively slow annd the muscle tires very slowly

  • Not Striated
  • Spindle shaped cells
  • contain bundles of action and myosin
  • uninucleate
  • 500um long and 5um wide


Walls of the Intestine - Circular/longitudinal bundles -> Peristalsis

Iris of the Eye - Circular/Radial bundles -> Contraction of radial dilates the pupil, contraction of the circular constricts the pupil

Walls of arteries/arterioles - circular bundles -> regulates temperature, blood flow and direction of bloodflw. Contraction narrows the vessel, reducing blood flow while Relaxation causes dilation, increasing blood flow

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Voluntary (skeletal) Muscle

...leads to the movement of the skeleton at a joint, thereby moving the limb

  • 100um in diameter
  • multinucleate
  • cell surface membrane is called the sarcolemma
  • Sarcoplasm contains:- mitochondria, extensive sarcoplasmic reticulum, myofibrils of sacromeres
  • striated
  • contracts quickly and powerfully but fatigues quickly
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Cardiac Muscle

...makes up the heart and there are three types

  • Atrial
  • Ventricular
  • Specialised excitatory and conductive muscle fibres

Atrial and Ventricular contract like skeletal muscle but with larger contraction duration. Excitatory fibres contract feebly but are myogenic so generate and conduct their own electrical impulses

Neurones of the autonomic system carry impulses to the heart to regulate contraction rate (sympathetic increases it and parasympathetic decreases it) 

  • Striated
  • continuous contraction and relaxation
  • powerfull contractions
  • no fatigue
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