Sliding Filament Theory
 Learning Outcomes:
 All demonstrate
understanding of the muscle
structure and the three types
of muscle fibres.
 Most gain understanding of
the sliding filament theory
through practical activity
 Few can apply the muscle
concept and are able to
lead the rest of the class in
practical activity.
Muscle Structure Starter
activity
 Describe
the structure of skeletal muscle
(4 marks)
Extension: draw a diagram to further
illustrate your understanding.
Muscle Structure Starter
activity
Max 2 marks:
 Muscles are covered in a layer of connective tissue
called Epimysium
 There are bundles of fibres surrounded by another
connective tissue called Perimysium
 Each muscle fibre is surrounded by a connective
tissue called Endomysium
Max 2 marks:
 Each muscle fibre contains hundreds of myofibrils
 These contain proteins responsible for muscles
contraction, actin and myosin.
 Together they form the contractile units, the
sarcomeres.
Home Work
 Complete
exam question on Sliding filament
theory: Handout p42 Q1 & 2.
 Watch Muscle fibre types A2 PE video (link on
weebly website), making notes.
 Complete table on characteristics of the three
muscle fibre types
 Complete Muscle fibre and me hand out.
The Sliding Filament Theory





Myofibril is - the contractile unit of the
muscle.
These can be divided into units called
Sarcomeres
Each sarcomere contains 2 types of protein
filaments - Actin & Myosin
During contraction these slide across one
another and connect or make cross bridges.
This overlapping creates a striped
appearance.
Practical Activity
http://www.youtube.com/watch?v=EdHzKY
DxrKc&feature=related
Pupils act out the movement of the actin
and myosin filaments.
Draw and clearly label a
Sarcomere
 Include
the following:
- Myosin, Actin, Sarcomere and Z line.

Extension – add to the diagram the
following:
- A band, I band and H zone
- explain what each of these are.
Myosin
Actin
Sacromere during relaxed state
Z lines – mark the boundary of each sacromere
A band – identifies where both actin and myosin exist
I band – identifies where only actin exists
H zone - identifies where only myosin exsists, this disappears during
contracted state.
Sacromere movement
 http://www.youtube.com/watch?v=ren_I
QPOhJc
Task
1. As a group go through the roles of the labels –
get them in the correct order and be able to
explain your role
2. In your own words describe the process that
occurs for the sarcomere to close together. (The
muscles to contract)
You can use your homework to help complete
this.
Sarcomere Movement
 At
rest the protein tropomyosin on the actin blocks
access to the myosin binding site
Step 1:
 These can be overcome by the release of calcium
from the sarcoplasmic reticulum – this occurs upon
receiving an action potential (signal to contract).
 The Ca binds to Troponin and neutralises the
Tropomyosin and releases the binding sites.
Step 2:
 Myosin has tiny protein projections that look similar
to golf clubs, they attach to the actin.
Step 3:
 Each projection contains ATPase which is an
enzyme used to break down ATP. This provides
the energy to bind the myosin crossbridge to the
actin filament. (enables the Myosin to pull the actin
inwards).
Step 4:
 It works like a ratchet mechanism where cross
bridges constantly attach and detach.
Step 5:
 Once the impulse has diminished Ca+ returns to
sacroplasmic reticulum and actin returns to its
resting position.
Muscle Fibres
 Within
skeletal muscle there are 3 types of
muscle fibres. All contain a mixture of all
three but not in equal proportions.
 This mix is mainly genetically determined.
 These fibres are grouped into motor units,
only one type of fibre can be found in
one unit.
 (Motor unit – the motor nerve and the
group of muscle fibres that it controls)
Muscle Fibres
 In
groups complete the I am type…..
sheet to demonstrate your knowledge of
the three types of fibres.
 Extension:
suggest?
 Although
Look at Fig 2.07 – what does it
fast twitch fibres generate much
greater forces they have a higher fatigue
index meaning shorter contraction time.
Plenary Activity
 Rearrange
the sliding filament theory,