ch. 50 muscles Flashcards
what does muscle cell contraction rely upon
interaction between thick and thin filaments
thin filament composition
mostly actin
thick filament composition
staggered arrays of myosin
what does vertebrae skeletal muscle move
bones and the body
what does a skeletal muscle consist of
bundle of long fibers, each a single cell, running along length of muscle
what is each muscle fiber composed of
bundle of smaller myofibrils arranged longitudinally
why is skeletal muscle striated
regular arrangement of myofilaments creates a pattern of light and dark bands
functional unit of muscle
sarcomere
what is a sarcomere bordered by
Z lines - where thin filaments attach
sliding filament model
thin and thick filaments ratchet past each other longitudinally, powered by myosin molecules
regions of each myosin
long tail and globular head
what does the head of the myosin molecule bind to
actin filament to form cross-bridge and pull thin filament toward the center of the sarcomere
what generates ATP needed to sustain muscle contraction
glycolysis and aerobic respiration
what happens when oxygen becomes limiting during intense muscle activity
ATP generated by lactic acid fermentation
- sustains contraction for only about 1 minute
steps of sliding filament model
- myosin head with low-energy configuration (ATP)
- with high-energy configuration (ADP + P) binds to binding sites on actin
- forms cross bridge
- thin filament moves toward center of sarcomere
- ATP back to myosin head
tropomyosin and troponin complex
set of additional proteins that bind to actins strands on thin filaments when a muscle fiber is at rest to prevent actin and myosin from interacting
how are myosin-binding sites exposed
Ca2+ binds to troponin complex
stimulus leading to contraction of a muscle fiber
action potential in motor neuron that makes a synapse with the muscle fiber
what does the synaptic terminal of the motor neuron release
neurotransmitter acetylholine
what does acetylcholine do
depolarize muscle, causing it to produce an action potential
transverse (T) tubules
where action potentials travel to the interior of the muscle
sarcoplasmic reticulum
releases Ca2+ from action potential in T tubules
what happens when motor neuron input stops
- muscle cell relaxes
- transport proteins in SR pump Ca2+ out of cytosol
- regulatory proteins bound to thin filaments shift back to their starting positions
steps at neuromuscular junction
- action potential arrives at synaptic terminal
- acetylcholine released
- binds at motor end plate
- sodium ions then rush into postsynaptic cell
- action potential appears in sarcolemma
- returns to initial state
amyotrophic lateral sclerosis
(Lou Gehrig’s disease) interferes with excitation of skeletal muscle fibers
- usually fatal
myasthenia gravis
autoimmune disease that attacks acetylcholine receptors on muscle fibers
- treatments exist
what is the contraction of the whole muscle?
graded - extent and strength of contraction can be voluntarily altered
2 basic mechanisms by which the nervous system produces graded contractions
- varying number of fibers that contract
- varying rate at which fibers are stimulated
motor unit
single motor neuron and all the muscle fibers it controls
recruitment
process by which more and more motor neurons are activated
what happens as recruitment proceeds
force developed by a muscle increases
twitch
results from single action potential in a motor neuron
what do more rapidly delivered action potentials produce
graded contraction through summation
tetanus
state of smooth/sustained contraction produced when the rate of stimulation is so high that muscle fibers cannot relax between stimuli
what are types of skeletal muscle fibers classified by
- source of ATP powering muscle activity
- speed of muscle contraction
3 types of skeletal muscle fibers
- slow oxidative
- fast oxidative
- fast glycolytic
slow oxidative
- slow contraction speed
- aerobic respiration
- slow rate of fatigue
- many mitochondria
- high myoglobin content
fast oxidative
- fast contraction speed
- aerobic respiration
- intermediate rate of fatigue
- many mitochondria
- high myoglobin
fast glycolytic
- fast contraction speed
- glycolysis
- fast rate of fatigue
- few mitochondria
- low myoglobin
oxidative fibers
- rely on aerobic respiration to get ATP
- have many mitochondria
- rich blood supply
- large amount of myoglobin
myoglobin
protein that binds oxygen more tightly than hemoglobin does
glycolytic fibers
- glycolysis as primary source of ATP
- less myoglobin
- larger diameter
- tire more easily
what is light meat composed of
glycolytic fibers
what is dark meat composed of
oxidative fibers
fast-twitch fibers
enable brief, rapid, powerful contractions
- glycolytic or oxidative
slow-twitch fibers
contract more slowly but sustain longer contractions
- less sarcoplasmic reticulum than fast fibers
- pump Ca2+ more slowly
- all oxidative
cardiac muscle
- found only in heart
- striated cells
- electrically connected by intercalated disks
how does cardiac muscle generate action potentials?
without neural input
where is smooth muscle foudn
walls of hollow organs (circulatory, digestive, reproductive)
smooth muscle contractions
- slow and may be initiated in muscles themselves
- may also be caused by stimulation from neurons in autonomic nervous system
why does smooth muscle lack striations
actin and myosin not regularly arrayed
is smooth muscle regulated by Ca2+?
yes but mechanism different
how are skeletal muscles attached
in antagonistic pairs - actions coordinated by nervous system
skeleton function
support, protection, and movement
3 main types of skeletons
- hydrostatic (fluid-based support)
- exoskeleton (external hard parts)
- endoskeletons (internal hard parts)
hydrostatic skeleton
fluid held under pressure in a closed body compartment
main type of skeleton in cnidarians, flatworms, nematodes, and annelids
hydrostatic skeleton
how to annelids use hydrostatic skeleton
for peristalsis - movement produced by rhythmic waves of muscle contractions from front to back
exoskeleton
hard covering deposited on the surface of an animal
skeleton of molluscs and arthorpods
exoskeleton
cuticle
jointed exoskeleton of arthropods which can be both strong and flexible
chitin
polysaccharide often found in arthropod cuticle
endoskeleton
hard internal skeleton buried in soft tissue
skeleton in organisms from sponges to mammals
endoskeleton
what do vertebrate endoskeletons consist of
cartilage bone, or combination
mammalian skeleton
- 200+ bones
- some fused together
- other connected at joints by ligaments
what is the position of legs relative to the body important for in mammals and birds
determining how much weight the legs can bear
locomotion
active travel from place to place
why is energy expended in locomotion
to overcome friction and gravity
air and locomotion
air poses little resistance
what is a prerequisite to walking, running, or hopping
maintaining balance
crawling challenge
must exert energy to overcome friction
challenge of locomotion in water
friction bigger problem than gravity
how do animals swim
- paddling with legs as oars
- jet propulsion
- undulating body and tail from side/side or up/down
what does active flight require
wings that develop enough lift to overcome downward force of gravity
