1. Sport Sciences Human Anatomy Week 2: The Muscular System Types and functions

2. Learning Outcomes By the end of this session you should be able to:
Describe 3 types of muscle
List the three functions
Identify the major muscles of the body.

3. Did you know?
Muscle constitutes about 50% of total body weight
Muscle tissue weighs more than fat tissue
Muscle is made up of approx 30% protein and 70% salt solution

4. Student Task
Use the sticky labels provided to identify the major muscles on a partner

5. 3 Types of Muscle 1 Involuntary muscle (smooth muscle)
2 Cardiac muscle
3 Skeletal muscle (voluntary muscle)

6. Involuntary Muscle Muscles which we cannot control
Found in the body’s internal organs (e.g. walls of the intestine and in the blood vessels)
Work automatically without conscious control to keep us alive

7. Cardiac Muscle
Involuntary muscle
Found only in the walls of the heart

8. Skeletal Muscle
Sometimes called STRIATED or STRIPED (because of their striped appearance under a microscope)
Make up majority of muscles in the body
Under conscious control
Used primarily for movement

9. Skeletal Muscle Can be stimulated (by the nervous system)
Can contract (contractility) after stimulation
Can lengthen (extensibility)
Can return to normal length (elasticity)

10. 3 Important Functions 1 Movement 2 Support and posture
3 Heat production

11. Week 2: Structure of Muscle

12. Learning Outcomes By the end of this session you should be able to:
Explain the structure of skeletal muscle
Explain the sliding filament theory

13. Group Task
Work in groups of 2 or 3 to find out some information about one of the following:
The structure of muscle
Sliding filament theory
You have only 20 minutes to complete this task

14. Macroscopic Structure
Made up of parallel fibres
Fibres are specialised muscle cells
Long, narrow and cylindrical (about as thick as a human hair)

15. Fibres
Each fibre is surrounded by a layer of connective tissue (collagen) called ENDOMYSIUM
The fibres are bound together in bundles called FASCICULI
Each fasciculus is surrounded by a layer of connective tissue called PERIMYSIUM

16. Muscle Structure

17. The fasciculi are then bound together as one muscle, and are surrounded by a layer of connective tissue called EPIMYSIUM
At the end of the muscle, the layers of connective tissue combine to form a tendon
The tendon inserts into the periosteum of the bone to move the lever

18. Microscopic Structure
Each individual muscle fibre is composed of MYOFIBRILS

19. Myofibrils
Lie in parallel and give the fibre a striped (striated) appearance
A single muscle fibre is composed of several hundred to several thousand myofibrils
Myofibrils contain the contractile units of the muscle
These units are protein filaments called ACTIN (thin) and MYOSIN (thick)
These face each other like two combs with their teeth interlocked at the ends

21. Sliding filament theory
Under the microscope the myofibrils appear as extremely thin lines
The myofibril is composed of numerous longitudinal filaments of two types: thick and thin
The thick filaments are composed of myosin and the thin filaments of actin
Contraction of a muscle occurs by the thick myosin and thin actin filaments sliding between each other
But what propels the filaments to slide between each other?

22. Sliding filament theory
A bridge is formed between the actin and myosin filaments during muscle contraction – CROSS BRIDGE
The bridge then swings through an ‘arc’ pulling the actin filaments past the myosin ones – POWER STROKE
Each bridge then detaches itself from the thin filament and re-attaches itself at another site further along
This is called the ratchet mechanism

24. Sliding filament theory
The thin actin filaments also contain two other proteins - tropomyosin and troponin
When the muscles are relaxed, the tropomyosin molecules cover the attachment site and prevent the myosin bridges from binding with the actin filaments
Troponin displaces the tropomyosin and enables binding to occur
Calcium ions activate the troponin allowing it to displace tropomyosin

25. Sliding filament theory
The whole ratchet mechanism occurs times per second to bring about a contraction
Muscle contraction needs ATP as well as Calcium
ATP = Adenosine Tri-phosphate = High energy compound
1 cross bridge requires 1 x ATP molecule to move

26. Sliding Filament Theory
Myofibrils have dark and light bands (or striations)
These bands make up a SARCOMERE
Sarcomeres are the contractile units of the muscle
Each sarcomere consists of 2 protein filaments (actin and myosin)

28. The sarcomere lies between the 2 Z lines
The I band contains only actin filaments
The H zone contains only myosin filaments
The A band contains both actin and myosin filaments

29. When a muscle contracts….
The I band shortens
The A band remains the same length
The H zone disappears
The myosin pulls the actin across so that the 2 filaments slide closer together, but the filaments themselves do not shorten in length

30. Learning Outcomes By the end of this session you should be able to:
Explain the structure of skeletal muscle
Explain the sliding filament theory

31. Week 2: Muscle Fibre Types
Jack Walton

32. Learning Outcomes By the end of this session you should be able to:
Identify 3 different types of fibres
Describe the characteristics of each type
Identify which sports use each type

33. Muscle Fibre Types
Muscles are composed of thousands and thousands of individual muscle fibres
Not all fibres are alike in structure and function
Can be classified into 3 types:
Type I
Type IIA
Type IIB

34. Type I Fibres Slow twitch or slow oxidative fibres: Red in colour
Large amounts of mitochondria, myoglobin and capillary network
Work slowly (split ATP at a slow rate)
Able to repeatedly contract or maintain contraction for a long duration
High resistance to fatigue
Fibres work mainly aerobically

35. Type IIA Fibres Fast twitch or fast oxidative glycolytic fibres (FOG)
Similar to Type I Fibres
Red in colour
Large amounts of myoglobin, many mitochondria and capillaries
Resistant to fatigue
Work rapidly to split ATP, fast contraction speed
Work aerobically or anaerobically
Used in high intensity, short duration activities such as 200m swim or 800m

36. Type IIB Fibres Fast twitch or fast twitch glycolytic (FTG) fibres
White in colour
Low number of myoglobin, few mitochondria, few capillaries
Fatigue easily
Fast contraction speed, split ATP quickly
Much stronger force of muscle contraction
These are used for activities of a very high intensity (anaerobic)
e.g. powerlifting or 100m sprint

37. Type IIC ?
Recent research has suggested that there may be a third muscle fibre type
Type IIc fast twitch glycolytic fibres
There is little known on these fibres at this point
Muscles tend to be composed of both fast twitch and slow twitch muscle fibre types
The amounts vary from muscle to muscle and from person to person

38. Fibre Mix Most skeletal muscle is a mixture of all 3 types
Proportion of types varies in relation to usual action of the muscle
For example – the postural muscles of the neck and back and leg have a higher proportion of Type I Fibres
Why do you think this is?

39. Fibre type and athletic success
Some outstanding athletes have a much higher percentage of whatever fibre type is most advantageous to their event
Elite distance runners - calf muscles composed of 90% slow twitch (Type I) fibres

40. Fibre type and athletic success
Sprinters - 92% fast twitch (Type II) fibres
What role does genetics play in determining this?
The slow and fast twitch characteristics of muscle fibres appear to be determined early in life, perhaps within the first few years

41. Fibre type and athletic success
Studies have revealed that identical twins have nearly identical fibre compositions
Little evidence showing change of fibre type from a few weeks training
More recent evidence suggests the possibility of fibre type change with high volume of training
However, the percentage of change is too small to make a difference in sports that require a high percentage of one fibre type to another

42. Fibre type and athletic success
Unlikely that a sprinters fibre type can be changed to a long distance runners
Therefore genetics do play a fairly important role in certain types of athletic events
This does not mean that people with a high percentage of slow twitch fibres cannot compete in sprinting events, it just reduces their capacity to compete at a high level
Russia - have attempted to fibre type young athletes to select their best sport –

43. Effects of Exercise on Fibre Type
Can change the characteristics of some fibre types
Some Type IIB fibres can transform into Type IIA fibres with long distance endurance training
Prolonged endurance training has been shown to increase the diameter of Type IIB fibres, increase the no. of mitochondria within the fibres, and increase the capillaries surrounding the fibres
The fibres can then use the aerobic energy system more efficiently

44. Effects of Exercise (cont)
Strength training can increase the size of Type IIB fibres (greater muscle mass - hypertrophy)
No increase in the number of fibres

45. Learning Outcomes By the end of this session you should be able to:
Identify 3 different types of fibres
Describe the characteristics of each type
Identify which sports use each type