3.5.3 Skeletal muscles are stimulated to contract by nerves and act as
effectors.
The sliding filament theory of muscle contraction
Gross and microscopic structure of skeletal muscle. The ultrastructure of a
myofibril.
The roles of actin, myosin, calcium ions and ATP in myofibril contraction.
The roles of calcium ions and tropomyosin in the cycle of actinomyosin
bridge formation.
Muscles as effectors
The role of ATP and phosphocreatine in providing the energy supply during
muscle contraction.
The structure, location and general properties of slow and fast skeletal
muscle fibres.
There are 3 types of muscle in our
body…
We have conscious
control over
skeletal muscle
only.
Muscles are made of many fibres, for
strength (think of a rope!)
Muscle cells have become
fused together to form
MUSCLE FIBRES
These share nuclei and
SARCOPLASM (cytoplasm in
muscle cells)
There are many
MITOCHONDRIA and
ENDOPLASMIC RETICULUM
The ultrastructure of a myofibril.
The arrangement of fibres
Close up of The Filaments…
The Bands…
Arrangement of Actin and Myosin
Evidence that filaments slide
• The A Band stays the same size!
Myosin
Actin
Actin and
Tropomyosin
The roles of actin, myosin, calcium ions
and ATP in myofibril contraction
The roles of calcium ions and
tropomyosin in the cycle of
actinomyosin bridge formation.
The Neuromuscular junction
Clip on Actinomyosin bridges
The role of ATP in muscle contraction:
1. To provide energy for the movement of the
myosin heads.
2. To provide energy for the active reabsorption
of Calcium ions, into the Sarcoplasmic
Reticulum, when the nervous stimulation has
ceased.
The role of Phosphocreatine
• In very active muscles, aerobic respiration may
not occur quickly enough to provide ATP
• Anaerobic Respiration may occur to
compensate since so much ATP is needed.
• Phosphocreatine is stored in muscle cells and
acts as a reserve supply of Phosphate so that
ATP can be regenerated quickly.
There are 2 types of Muscle Fibre…
• Slow Muscle Fibres (Slow-twitch)
• Fast Muscle Fibres (Fast-twitch)
Slow-Twitch Fibres…
• Function… Contractions over a long period of
time. E.g. running a marathon, keeping our body
upright.
• Location… Calf Muscles (or any place where
support to keep us upright is needed)
• Structure… Lots of MYOGLOBIN (stores lots of
oxygen so these muscles are very red), Numerous
mitochondria, a store of glycogen, huge blood
supply
Fast-Twitch Fibres
• Function… Rapid, Powerful contractions. E.g.
Weight-Lifting
• Location… Biceps (or any area where muscles
carry out short bursts of intense acticity)
• Structure… Thicker, more numerous Myosin
filaments. A store of phosphocreatine. More
enzymes for Anaerobic Respiration.