The Muscular System

1. The Muscular System Chapter 1

2. The Muscular System: An Overview • There are over 600 muscles in the human body which allow everyday movements • Without our muscles we would not be able to breathe, eat, walk or even keep our heart beating • The three major functions of the muscular system are: • Movement • Posture • Production of heat

3. Functions of muscles • Movement: most muscles are under voluntary control and are responsible for bodily movements; others are involuntary and work without our conscious control • Posture: the position of our bodies is effected by gravity; our skeletal muscles are continually working to keep our bodies balanced and aligned • Body heat: muscles require energy to produce movement and this releases heat; muscles play a role in maintaining body temperature

4. Types of muscles • Skeletal muscles: attached to bones in the skeleton that are under conscious control making them voluntary muscles. They are striped (striated) in appearance. • Smooth muscles: found internally in blood vessels and the walls of organs. We have no control over them because they are involuntary muscles. • Cardiac muscle: makes up the wall of the heart and works involuntarily. It has a striped appearance.

5. How are musculoskeletal movements possible? • Muscular movements are controlled by the brain • For movement to happen muscles must cross a joint between two bones • Nervous impulses are sent from the brain to muscles which causes the muscle to contract • Muscles never work alone, often several are involved in producing one movement • The prime mover (agonist) is the muscle that directly causes the movement, therefore the opposite muscle is the antagonist

6. Flexion / extension example • The bicep muscle is the agonist that causes flexion of the arm • When you pull your arm up towards yourself in a bicep curl the bicep contracts and shortens • At the same time, the triceps muscle which is the antagonist relaxes and lengthens • Both of these muscles must work together in unison to produce flexion • What happens during extension?

7. Types of muscular contractions • Isotonic: where the length of the muscle actually changes (e.g. sit-up). Concentric contractions shorten the muscle whereas eccentric contractions lengthen the muscle • Isometric: where the muscle length stays the same (e.g. pushing against a wall) • Isokinetic: when the tension within a muscle is maximal throughout a range of motion (only using machines). They work the muscle the most because they match the force that is exerted by the muscle

8. Anterior muscles • Frontalis (forehead) • Sternocleidomastiods (neck) • Obicularisoris (mouth) • Pectorals (chest) • Deltoid (shoulder) • Biceps (upper arm) • Rectus abdominis (abs) • Sartorious (inner thigh) • Quadriceps (thigh) • Tibialis anterior (shin)

9. Posterior muscles • Trapezius (top of back) • Rhomboids (middle of back) • Triceps (upper arm) • Latissimusdorsi (middle / lower back) • Gluteus maximus • Hamstrings • Adductors • Gastrocnemius (calf) • Soleus (ankle) • Achilles tendon

10. Arrangement of muscle fibres • The arrangement of muscle fibres determines how strongly they can contract • Fusiform muscle fibres run in the same direction as the tendon (lengthways) • Penniform muscle fibres run at angles to the tendon and make up about 75% of skeletal muscles • Penniform muscle fibres can be divided into three categories depending on how much they branch off the tendon

11. Types of Penniform muscle fibres • Unipennate muscle fibres only branch out to one side of the tendon • Bipennatemuscle fibres branch out on both sides of the central tendon • Multipennate muscle fibres branch out repeatedly from a number of tendons • Page 15

12. Muscle Fibre types • Slow twitch fibres • Red colour • Contract slowly over a longer period of time • Best suited for aerobic and endurance activities • Exert less force but can contract repeatedly • Fast twitch fibres • White colour • Contract rapidly over a shorter period of time • Best suited for anaerobic and high intensity activities • Exert great force in bursts of power and speed

13. The effect of age and gender • Your size, gender, age and physical training will determine the power that can be exerted by your muscles • During puberty boys begin to produce more testosterone than females causing them to develop more muscle mass • Females generally possess about 65% of the strength of adult males • Muscles are at their strongest between 20-30 and deteriorate by 1% each year after that

14. Microscopic muscle structure

15. Sliding Filament Theory • Myofibrils have several sections called sarcomereswhich run the length of the muscle • Within each myofibril are two types of myofilaments called actin (thin filament) and myosin (thick filament) • The lighter section of the sarcomere only contains thin actin filaments and is called the I-band • The darker section is where both actin and myosin overlap and is called the A-band • There is a small section in where only myosin is found called the H-band • During physical activity the myosin glides in between the actin and releases energy so that muscles can contract

16. The “all or nothing” principle • When a motor unit (lots of muscle fibres) receives a message from the brain all the muscle fibres in the unit will contract providing the stimulus is of significant intensity • If the stimlus is not intense enough the muscle fibres won’t respond and the muscle won’t contract