37.1 Muscles: Biological Motors That Generate Force and Produce Movement Flashcards
why are muscles the “biological motors” of the body?
because they generate force and produce movement
what does a muscle’s ability to produce movement depend on?
the electrically excitable muscle cells containing proteins that can be activated by the nervous system
basic features of muscle organization and function are conserved across the vast diversity of….
eukaryotes (cnidarians had the first muscle fibres-jellyfish and sea anemones)
what largely determines how muscles contract to produce force and movement?
the geometry and organization of proteins in muscles
fiber
in animals, a term for a muscle cell, which produces forces within an animal’s body and exerts forces on the environment
muscles are composed of elongated cells called:
muscle fibers
muscle fibres use:
ATP generated through cellular respiration to generate force and change length during a contraction
force
an interaction that changes the movement of an object, such as a push or pull by one object interacting with another object
the work performed by a muscle is equal to:
force times length change
muscles only exert pulling forces, therefore…
pairs of muscles are arranged to produce movements in two opposing directions at specific joints of the skeleton
all muscles contain the same contractile proteins that enable them to shorten and produce force, these proteins are:
actin and myosin
filament
in animals, a thin thread of proteins that interacts with other filaments to cause muscles to shorten. in plants, the part of the stamen that supports the anther
although all muscle fibres have filaments of actin and myosin, in different types of muscles…
the filaments are arranged differently
what are the two broad groups of muscles (based on function and appearance)
striated muscle and smooth muscle
striated muscle
skeletal muscle and cardiac muscle, which appear striped under a light microscope-actin and myosin filaments are arranged in a regularly repeating pattern
skeletal muscle
muscle that connects to the body skeleton to move an animal’s limbs and torso (elongated, many nuclei in each cell)
cardiac muscle
muscle cells that make up the walls of the atria and ventricles and contract to pump blood through the heart (less elongated when compared to skeletal muscle, tranches, only contain or more nuclei per cell)
smooth muscle
the muscle in the walls of arteries, the respiratory system, and the digestive and excretory systems; smooth muscle appears uniform under the light -actin and myosin filaments are irregularly organized
when compared to cardiac and skeletal muscles, smooth muscles contract….
slowly
whole muscles are made up of :
parallel bundles of individual muscle fibres (muscle cells)
myofibril
a long rodlike structure in muscle fibbers that contains parallel arrays of the actin and myosin filaments
each muscle finer contains hundreds of:
myofibrils (has a striated appearance due to their regular molecular organization)
each myosin molecule consists of:
two long polypeptide chains coiled together, each ending with a globular head
thick filament
a parallel grouping of myosin molecules that makes up the myosin filament
thin filament
two helically arranged actin filaments twisted together that make up the actin filament
tropomyosin
a protein that runs in the grooves formed by the actin helices and blocks the myosin-binding sites
Z disc
a protein backbone found regularly spaced along the length of a myofibril
sarcomere
the region from one Z disc to the next, the basic contractile unit of a muscle
what is the functional units of muscles?
sarcomeres-the shortening/contraction of a muscle is ultimately the result of the shortening of thousands of sarcomeres along a myofibril
titin, a third large protein, what is its function?
to help with assembly and protect the sarcomeres from being overstretched, thus contributing to muscle elasticity
what contributes to the striated appearance of skeletal muscles?
the regular pattern of actin and myosin filaments with sarcomeres along the length of the fibre
sliding filament model
the hypothesis that muscles produce force and change length by the sliding of actin filaments relative to myosin filaments
when myofibrils contracted to short lengths…
the sarcomeres had increased actin-myosin overlap
when myofibrils were stretched to longer lengths…
actin-myosin overlap decreased
the length of myosin and actin filaments…
never change
all of the length change during a muscle contraction results from:
the sliding of actin filaments with respect to myosin filaments within individual sarcomeres
the length change of the whole muscle fibbers is a sum of:
the fractions by which each sarcomere shortens along the fibre’s length
longer sarcomeres allow:
a greater degree of shortening
what causes a muscle finer to shorten and produce force?
interactions between the myosin and actin filaments
cross-bridge
the binding of the head of a myosin molecule to actin at a specific site between the myosin and actin filaments-how the myosin filaments pull the actin filaments toward each other
what allows the filaments to slide relative to each other?
the ability of the myosin head to undergo a conformational change and pivot back and forth
cross-bridge cycle
repeated sequential interactions between myosin and actin filaments at cross-bridges that cause a muscle finer to contract
movement of the myosin head is powered by:
ATP (needs it to detach from actin)
outline the steps of muscle contraction:
- myosin head binds ATP and detaches from actin
- myosin head hydrolyzes ATP resulting in a conformational change and myosin head is cocked back, ADP and P remain bound (myosin in in a high energy state)
- myosin head binds to actin (cross-bridge)
- once bound, ADP and P released, power stroke results
power stroke
the stage in the cross-bridge cycle in which the myosin head pivots and generates a force, causing the myosin and actin filaments to slide relative to each other
individual muscle contractions are the result of:
many successive cycles of cross-bridge formation and detachment
faster muscle fiber contraction=
faster rates of ATP hydrolysis
myosin functions as both a:
structural protein and an enzyme
each thick filament can interact with:
6 actin filaments
skeletal and smooth muscle fibres are both activated by:
the nervous system
skeletal muscles are innervated by:
the somatic nervous system
smooth muscles are innervated by:
the autonomic nervous system
motor endplate
the region on a muscle cell where acetylcholine binds with receptors, triggers opening of sodium channels
actin and myosin filaments can only form cross bridges when:
the myosin-binding sites on actin are exposed
at rest, the myosin-binding sites are blocked by:
the protein tropomyosin
sarcoplasmic reticulum (SR)
a modified form of the endoplasmic reticulum surrounding the myofibrils of muscle cells
when the muscle is at rest, the SR contains a large internal concentration of:
calcium ions which are transported in by calcium pumps in the membrane
a muscular contraction is initiated when depolarization of the muscle fibbers causes:
the SR to release calcium ions
troponin
a protein that moves tropomyosin away from myosin-binding sites, allowing cross-bridges between actin and myosin to form and the muscle to contract-does this when calcium binds to it
excitation-contraction coupling
the process that produces muscle force and movement, by excitation of the muscle cell coupled to contraction of the muscle
the muscle relaxes when:
neural stimulation ends-acetylcholine is broken down or reabsorbed, calcium ions actively transported back into sarcoplasmic reticulum, tropomyosin block myosin-binding sites
the smooth muscles can also be regulated by:
stretch of the muscle, local hormones, and other local factors (ex. pH, oxygen, carbon dioxide) by intracellular signalling
in smooth muscle, calcium ions also enter through:
voltage-gated and stretch-receptor calcium channels in the cell’s plasma membrane
smooth muscle lacks:
the troponin-tropomyosin mechanism for regulation contraction
calmodulin
a protein that binds with calcium ions and activates the enzyme myosin kinase that phosphorylates the smooth muscle myosin heads, causing them to bind to actin and begin the cross-bridge cycle, another enzyme dephosphorylates the myosin head to relax the muscle
smooth muscles use less…
ATP per unite time, contracts slower compared to skeletal muscle
