BIOL 005B Lecture Notes - Lecture 15: Canidae, Troponin, Endoplasmic Reticulum
BIOL 005B Lecture 15: Muscles and Locomotion
●Muscles provide power for locomotion and other movements
○Two important properties:
■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 the same general properties as axons -- distribution
of ions across cell membrane and ability to rapidly change it
●Action potentials (all-or-nothing events)
●Some have graded responses (varying intensity of events)
○Basic Muscle Facts:
■Muscles generate force via contractions
■Muscles can only contract forcefully: they cannot elongate forcefully
●External force (stretching) must be applied in order for a muscle to
elongate
■To generate that force, muscles must attach to something (a bone, a
tendon, or other skeletal element) and must use ATP
■Most muscles act in “antagonistic pairs”; one that extends and one that
flexes
●Skeletal Muscle Anatomy
○A skeletal muscle is composed of many muscle fibers
○Each fiber (muscle cell, or myocyte) has a single plasma membrane (sarcolemma)
but is multinucleate
○Fibers are arranged in bundles, and the bundles are arranged to form the muscle
○Each fiber is innervated by a motor neuron to cause contraction (one motor
neuron can innervate many fibers)
○Each fiber is composed of many myofibrils
○Myofibrils contain sarcomeres
●Within the Sarcomere
○Thick filaments: many different myosin molecules lined up in a staggered array
○Thin filaments: are actually two strands of actin and a regulatory protein wrapped
around each other
○Think in 3-D: each thick filament surrounded by 6 thin
●Sliding Filament Model of Muscle Contraction
○For the muscle to contract, the actin and the myosin must interact so that the actin
can be pulled inward
○Components do not shorten; they overlap
○Actin-myosin crossbridges are formed such that the actin is pulled inwards
towards the M-line
○Energy (ATP) is required. This process is gradual and the number of attachments
formed is dependent on the degree to which the muscle is contracted
○Why doesn’t backsliding occur?
Document Summary
Muscles provide power for locomotion and other movements. 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 the same general properties as axons -- distribution of ions across cell membrane and ability to rapidly change it. Some have graded responses (varying intensity of events) Muscles can only contract forcefully: they cannot elongate forcefully. External force (stretching) must be applied in order for a muscle to elongate. To generate that force, muscles must attach to something (a bone, a. Most muscles act in antagonistic pairs ; one that extends and one that tendon, or other skeletal element) and must use atp flexes. Within the sarcomere but is multinucleate neuron can innervate many fibers) A skeletal muscle is composed of many muscle fibers.
