Chapter 50.5 Flashcards
What is muscle activity
a response to nervous system input
What is required for muscle function
protein filaments physically interacting
What does muscle cell contraction rely on?
thin filaments and thick filaments interacting
thin filaments
actin
thick filaments
staggered arrays of myosin
moves bones and the body
vertebrate skeletal muscles
characterized by a hierarchy of smaller and smaller units
skeletal muscle
consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle
skeletal muscle
What is each muscle fiber itself
a bundle of smaller myofibrils arranged longitudinally
Why is skeletal muscle also called striated muscle
How the myofilaments are arranged creates a pattern of light and dark bands
the functional unit of a muscle
sarcomere
what is sarcomere bordered by
Z lines
Z lines
where thin filaments attach
thin and thick filaments slide past each other longitudinally, what are they powered by?
myosin molecules
What does the sliding of filaments rely on
interaction between actin and myosin
What does muscle contraction require
repeated cycles of binding and release
what does the “head” of a myosin molecule
binds to an actin filament
What does the binding of the actin filament and the head of a myosin molecule form
a cross-bridge (and pulls the thin filament toward the center of the sarcomere
what two things generage the ATP needed to sustain muscle c ontraction
glycolysis and aerobic respiration
regulatory protein that binds to actin strands on thin filaments when a muscle fiber is at rest
tropomyosin and the troponin complex
What does the binding of tropomyosin and actin strands prevent
actin and myosin from interacting
What must be true for a muscle fiber to contract
myosin-binding sites have to be uncovered
how do myosin-binding sites become uncovered
when calcium ions bind to the troponin complex and expose the myosin-binding sites
When does contraction occur?
when there’s a high concentration of Ca2+
When does muscle fiber contraction stop
when the concentration of Ca2+ is low
what is the stimulus leading to contraction of a muscle fiber
an action potential in a motor neuron that makes a synapse with the muscle fiber
What does the synaptic terminal of the motor neuron release
the neurotransmitter acetylcholine
what occurs when acetylcholine depolarizes the muscle
it produces an action potential
How do action potentials travel to the interior of the muscle fiber?
along transvers (T) tubules
what does the action potential along T tubules cause
sarcoplasmic reticulum (SR) to release Ca2+
a specialized endoplasmic reticulum
sarcoplasmic reticulum
binds to the troponin comlex on the thin filaments
Ca2+
what does the binding of Ca2+ to the troponin complex do
exposes myosin-binding sites and allows the cross-bridge cycle to proceed
What happens when motor neuron input stops
the muscle cell relaxes
What do transport proteins in the SR do
pump Ca2+ out of the cytosol
What do regulatory proteins bound to thin filaments do
shift back to the myosin-binding sites
interferes with the excitation of skeletal muscle fibers
amyotrophic lateral sclerosis (ALS)
an autoimmune disease that attacks acetylcholine receptors on muscle fibers
myasthenia gravis
What does “contraction of a whole muscle is graded” mean
the extent and strength of its contraction can be voluntarily altered
Two basic mechanisms by which the nervous system produces graded contractions
- varying the number of fibers that contract
2. varying the rate at which fibers are stimulated
although each fiber is controlled by only one motor neuron, what could occur?
each motor neuron may synapse with multiple muscle fibers
consists of a single motor neuron and all the muscle fibers it controls
a motor unit
What does the strength of the resulting contraction depend on
how many muscle fibers the motor neuron controls
how many motor units may be in the whole muscle
hundreds
what does recruitment of multiple motor neurons result in
stronger contractions
what does a twitch result from
a single action potential in a motor neuron
what do more rapidly delivered action potentials produce
a graded contraction by summation
a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials
tetanus
There are several distinct types of skeletal muscles, each of which…
is adapted to a particular function
what are skeletal muscles classified by
either the source of ATP powering the muscle activity or the speed of muscle contraction
what do oxidative fibers rely mostly on to generage ATP
aerobic respiration
What do oxidative fibers have
- many mitochondria
- a rich blood supply
- a large amount of myoglobin
a protein that binds oxygen more tightly than hemoglobin does
myoglobin
what do glycolytic fibers use as their primary source of ATP
glycolysis
What is the difference between glycolytic fibers and oxidative fibers
glycolytic fibers have less myoglobin and get tired more easily
In poultry and fish, what is light meat composed of
glycolytic fibers
In poultry and fish, what is dark meat composed of
oxidative fibers
contract more slowly bus sustain longer contractions
slow-twitch fibers
what are all slow-twitch fibers
oxidative
contract more rapidly but sustain shorter contractions
fast-twitch fibers
what are fast-twitch fibers
either glycolytic or oxidative
What do most skeletal muscles contain in barying ratios
both slow-twitch and fast-twitch
In additon to skeletal muscle, what do vertebrates also have
cardiac muscle and smooth muscle
found only in the heart
cardiac muscle
consists of striated cells electrically connected by intercalated disks
cardiac muscle
what can cardia muscle do without neural input
generate action potentials
found mainly in walls of hollow organs such as those of the digestive tract
smooth muscle
contractions are relatively slow and may be initiated by the muscles themselves
smooth muscles
what may smooth muscle contractions also be caused by
stimulation from neurons in the autonomic nervous system
