3.01.10 - Muscles Muscles provide power for locomotion and...

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Muscles Muscles provide power for locomotion and other movements. Two important properties: contractility excitability Contractility is due to a set of contractile proteins -- actins, myosins -- that use ATP to power forceful shortening; evolutionarily conserved (found in nearly all animals) very diverse (many variants within and between species) Excitability is due to same general properties as axons -- distribution of ions across cell membrane + ability to rapidly change it. action potentials (all-or-nothing events) graded responses (varying intensity of events) Muscles provide power for locomotion and other movements. Two important properties: change it. action potentials (all-or-nothing events) graded responses (varying intensity of events) Muscles Muscles can only contract forcefully -- they cannot elongate forcefully. External force (stretching) must be applied in order for a muscle to elongate. many muscles arranged in antagonistic pairs Muscle types Smooth muscle: primarily in visceral organs and vascular system Usually exerts pressure on the contents a space (i.e., food in gut), or operates as a valve (i.e., vasodilation control) Not very differentiated; sheets of cells containing contractile proteins Lacks discrete synapses; neurotransmitter (or neurohormone) is released between smooth muscle cells Usually innervated by the autonomic nervous system ( sympathetic, parasympathetic ); also responds to hormonal stimulation Slow, graded contractions; very resistant to fatigue Muscle types Cardiac muscle: specialized to maintain heartbeat columns of cells connected with gap junctions (maintain & coordinate contractions) intrinsic contractile rhythm; overall heart contractility controlled by specialized cells (Purkinje fibers) that act as neurons pacemakers (clusters of electrically active fibers) generate and coordinate heartbeat: sinoatrial node, atrioventricular node responsive to load: extra filling --> strong contraction
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3.01.10 - Muscles Muscles provide power for locomotion and...

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