Muscular system

Function Movement – Contraction of the muscle Posture – Anti-gravity Respiration Heat generation Communication

Functional characteristics – Structures for contraction – Metabolism Energy generation – Muscle contraction – Ion concentration gradient maintenance – Heat

Physical property Contractility – Movement of structure – Increased pressure Vessels and hollow organs Excitability – Responsiveness to stimuli Extensibility – Ability to contract after being stretched Elasticity/recoil – Diaphragm

Types of muscles

Skeletal muscles – Locomotion – Facial expression – Posture – Respiration – Voluntary contraction Exclusive control by nervous system

Smooth muscle – Most widely distributed – Walls of hollow organs – Blood vessels – Some autorhythmic Spontaneous excitation and contraction Independent of stimulation Contraction regulated by various factors

Connective tissues – Attachment Tendons (extension of fascicles) – Covering Endomysium (fiber) Perimysium (fascicli) Epimysium (muscle) Muscular fascia – Separates/compartmen talizes muscles

Nerves – Motor neurons Blood vessels

Muscle fibers Myofibril – Actin (thin) – Myosin (thick) – Actin and myosin are called myofilaments and form sacromeres

Sacromeres

Function of myosin head – Interaction with actin Cross-bridge formation – Contraction of muscle Bending and recoiling – ATP metabolism

Which band/zone corresponds to each figure?

Sliding filament model Actin filament sliding over the myosin – Shortening of sacromere – Responsible for muscle contraction Shortening of myofibril Relaxation – Increased sacromere length Contraction of antagonist muscle Gravity

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Membrane potential Axon from motor nerve – Excitation of muscle fiber Generation of action potential Differences in electrical charges between inside and outside of the plasma membrane – Differences in amount of Na and K ions – Membrane permeability K>Na

Membrane permeability – Channels Voltage-gated Chemical/ligand-gated

Action potential Stimulation

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Na Channels open K channel closed Na Channels closing K channel opening Na Channels closed K channels open

All or nothing principle Propagation of action potential (animation) – Movement from one spot to the next Frequency – # AP/time period – Increased AP frequency, increased strength of stimuli

Source of muscular action potential – Signals from nerve fibers Communicated via the neuromuscular junction

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Clearance of acetylchorine – Rapid Acetylchorinesterase 1 presynaptic AP=1postsynaptic AP – Recycled within the axon after metabolism

Excitation-Contraction coupling Conversion of neural signals into physical process of contraction – Generation of muscular action potential Neural action potential – Contraction Movement of intracellular Ca in response to muscular action potential

Ca ions – Stored in sacroplasmic reticulum Modified ER – Released in response to muscular action potential Transverse/t-tubule

General mechanism of contraction Eight steps – Action potential from the nerve reaches the nerve ending on the muscle fiber – Release of acetylchorine (neurotransmitter) – Opening of multiple acetulchorine-gated channels – Increased flow of Na ions (muscular action potential) – Propagation of action potential across muscle fiber

General mechanism of contraction Eight steps – Depolarization of membrane and release of Ca ions from SR Traveling of action potential into the inside of the fiber – Attraction of actin and myosin fiber by increased Ca Sliding of filaments – Removal of Ca into SR Restoration of filaments

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Cross-bridge movement Repeated interaction of myosin head and actin myofilament – Sliding of actin along the myosin surface – Repeated attachment and detachment of myosin and actin – Requirement ATP hydrolysis Ca ion

Power stroke – Movement of myosin while attached to actin Recovery stroke – Restoration of myosin head to its original position

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Muscle relaxation Factor that is essential for muscle contraction – Ca Access to actin active sites – Removal of Ca into SR Covering of actin active site with troponin-tropomyosin complex – Energy-dependent process Active Ca pumpus Restoration of membrane potential – Na-K pumps