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

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.

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

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

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

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

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

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

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

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

Week 2: Structure of Muscle

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

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

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

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

Muscle Structure

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

Microscopic Structure Each individual muscle fibre is composed of MYOFIBRILS

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

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?

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

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

Sliding filament theory The whole ratchet mechanism occurs 50-100 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

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)

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

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

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

Week 2: Muscle Fibre Types Jack Walton

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

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

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

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

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

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

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?

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

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

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

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 –

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

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

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