Muscular System

Question 1

Types of muscle tissue

Answer 1

• Skeletal: voluntary, striated, attached to bones by tendons and other tissue
• Cardiac: involuntary, striated, only found within the heart
• Smooth: involuntary, non-striated, surround the body’s organs

Question 2

Types of muscle contraction

Answer 2

• Concentric: muscle fibres shorten
• Eccentric: muscle fibres lengthen
• Isometric: muscle fibres don’t change in length
• Contraction means that tension has generated, not that they have been shortened or lengthened

Question 3

Muscle Contraction During Exercise

Answer 3

• Isotonic Exercise: controlled shortening and lengthening of muscles (ex. Bicep curls)
• Isometric Exercise: no motion → muscle fibres maintain a constant length throughout contraction (ex. Plank or wall sit)
• Isokinetic Exercise: machines are used to control speed of contractions, combines both isotonic and isometric exercise

Question 4

Neuromuscular Junction

Answer 4

• The junction between the nervous and muscular systems
• When electrical impulse travelling along axon gets to neuromuscular junction, a chemical neurotransmitter (acetylcholine) is released
• Acetylcholine is detected by receptors on the muscle fibre and process of muscle contraction is initiated
• Acetylcholine goes from neuron and muscle, then floats around and gets received by muscles to then perform an action
• Energy transfer: electrical→ chemical→mechanical

Question 5

Role of Calcium

Answer 5

• Release of calcium ions is the trigger mechanism in muscle contraction
• Released into the sarcoplasm by the terminal cisternae (outer vesicles of the sarcoplasm)
• At rest myosin and actin filaments cannot interact because the binding sites on the actin are covered by troponin and tropomyosin proteins
• Troponin attached to tropomyosin and tropomyosin covers actin binding sites
• When calcium is released it binds to troponin which pulls tropomyosin out of the way to allow myosin to attach to actin

Question 6

Sliding Filament Theory

Answer 6

• Contraction occurs in the sarcomere (region on muscle fibres myofibril)
• Sarcomere contains actin and myosin filaments
• Actin: thin filaments on top, site of attachment, gets pulled across
• Myosin: thick filaments containing small bridges that bind to thin filaments
• Myosin crossbridges (bridges on filaments that extend to thin filaments) attach, rotate, detach and reattach rapidly which results in sliding overlap of myosin and actin → sarcomere then contracts