A2 Physiology  People are Awesome 2013 People are Awesome 2013

Sliding Filament Theory  Learning Outcomes:  All demonstrate understanding of the muscle structure.  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.  Read (p36-40 AQA A2 PE)and make notes on: - the three types of Muscle Fibres - describe a Motor Unit and explain how a Motor Neurone can stimulate muscle fibres.

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 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.

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. Actin Myosin

Sacromere movement  QPOhJc QPOhJc

Task 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.

Plenary Activity  Rearrange the sliding filament theory,