The Muscular System More than 600 muscles in the human body attached to bones by tendons Exert force by converting chemical energy (food) into mechanical energy (muscle contraction)

Types of Muscles Skeletal Voluntary striated Most in human body e.g biceps Cardiac Involuntary e.g. heart only Smooth Involuntary/not striated Surrounds internal organs Contracts slowly but can sustain a contraction for a long period of time e.g. intestine lining

Properties of Muscle Fibres Irritability: muscle responds to stimulus Contractibility: shorten in length Elasticity: Ability to stretch and return to its normal position Extensibility: ability to extend in length Conductivity: can transmit nerve impulses

Skeletal Muscles Functions Movement Locomotion or movement of parts Heat Production Responsible for a major share of total body heat and maintaining homeostasis of temperature 3. Posture Partial contractions of man skeletal muscles

Muscle Structure Macroscopic Level: Muscles are surrounded by fascia Fascia is a thin, tight sheath of connective tissue Protects muscles, and prevent friction between muscles

Microscopic Level: Epimysium: large, strong sheath that envelopes entire muscle and becomes tendon (deep fascia) Perimysium: connective tissue that binds groups of fasciles Fasicles: bundles of individual muscles fibres Endomysium: sheath of connective tissue that surrounds individual muscle fibres

Sarcolemma: beneath endomysium/acts as a plasma membrane Sarcoplasm: muscle cell cytoplasm- inside sarcolemma (contains proteins, stores gylcogen and myoglobin)

Sarcomere: site of muscular contraction and house for myosin and actin Myofibril: thread like structure inside muscle fibre/house myosin and actin Sarcomere: site of muscular contraction and house for myosin and actin Myosin Cellular protein has a head and tail Head is attachment site for actin Actin Binding site for myosin 2 proteins Troponin – binding site for calcium Tropomyosin – covers the binding site on actin

The Neuromuscular System The NMS is linkage Muscular System Nervous System (nervous impulses originating in the CNS and sent through PNS) Use and practice improve the coordination between the two systems

Motor Unit Includes a neuron/nerve called the ‘motor neuron’, the axon and the muscle fibers it stimulates Where the motor neuron and muscle fiber meet is called the neuromuscular junction

How the Motor Unit Works Electrical impulse travels along nerve pathway Once at neuromuscular junction, a chemical neurotransmitter is then released (acetylcholine) ACh is detected by receptors on the surface of the muscle fiber resulting in muscle contraction SO….. Electrical energy-chemical energy-mechanical work

‘The All or None Principle’ When a motor unit is stimulated to contract, it does to its full potential Motor units can be small or large small: produce fine motor movements (threading a needle) large: produce big motor movements (kicking a ball)

Naming Muscles Action of the Muscle: flexion, extension e.g. flexor carpi ulnaris Direction of Fibres: rectus, transversus e.g. rectus abdominus Location of the Muscle: anterior, posterior e.g. tibialis anterior Number of Divisions: 2 or 3 heads e.g. biceps brachii Shape of Muscles: deltoid, trapezius e.g. trapezius looks like a trapezoid Point of Attachment: sternum, clavicle, mastoid e.g. sternocleidomastoid

How Muscles Attach to Bone Indirectly: epimysium extends as a tendon and then connects with periosteum Directly: epimysium adheres to and fuses with periosteum

Origin: point where muscle attaches to more stationary bones of the axial skeleton Insertion: point where muscle attaches to bone that is moved most

Agonistic pairs: skeletal muscles arranged in opposing pairs (e. g Agonistic pairs: skeletal muscles arranged in opposing pairs (e.g. flexors and extensors) Agonist: prime mover Synergists: assist the agonist, but not primarily responsible Antagonist: muscle that counteracts the agonist; lengthen when agonist contracts Fixators: Stabilize the joint See Table 3.3 in text

Types of Contractions Concentric- muscle fibres shorten Bicep shortens when lifting an object Eccentric- muscle fibres lengthen Bicep places weight on the grounds Isometric- muscle fibres stay the same Trying to lift something too heavy

Contraction during Exercise Isotonic Exercise: Shortening and lengthening contraction Isometric Exercise: Muscles maintain length Good for developing specific muscle groups (rehab) Isokinetic Exercise: Isometric and Isotonic exercise combined E.g. advanced high performance machines http://www.youtube.com/watch?v=By-Of-s1zN8

How do our skeletal muscles contract?

The Sliding Filament Theory Diagram of a Sarcomere

The Process Begins….. Message sent by brain (raise your hand) CNS PNS Neuromuscular junction (motor unit) ACh released (acetylcholine) Action potential generated opening up sarcolemma (membrane) Calcium ions is released into sarcoplasm due to ATP……

What is ATP: An energy carrying molecule that results from food metabolism Energy source behind the release of calcium Release of calcium is what triggers contraction Also detaches myosin from actin As you work, more and more ATP is used, and you must replace through food and metabolism

At Rest Calcium ion within sarcoplasmic reticulum ATP bound to myosin (thick filaments) Actin intact Contraction Calcium binds to troponin Tropomysoin swivels Binding sites are exposed Crossbridges from myosin bind to new sites on actin ATP breakdown = energy as heat and moves crossbridges causing sliding action Actin is drawn to center of sarcomere Crossbridge cycle repeats Z line is drawn together Sarcomere shortens

Back to Resting State… A Ch release halted and remaining is inactive Calcium ions back to sarcoplasmic reticulum by active transport Shape of actin is restored – no binding site available as they are covered by tropomyosin Crossbridges breakway

Visuals http://www.youtube.com/watch?v=EdHzKYDxrKc http://www.youtube.com/watch?v=Vlchs4omFDM&feature=related