DAT bio chapter 11.5 Muscular system Flashcards
3 types of muscle
smooth, skeletal, and cardiac
Smooth muscle is present where? how many nucleus? striated? voluntary?
present in organs, airways, blood vessels.
one nucleus per cell
not striated
involunatary
Cardiac muscle is present where? how many nucleus? striated? voluntary?
present: heart
involuntary
1 nucleus per cell
striated
skeletal muscle is present where? how many nucleus? striated? voluntary?
present: around bone
voluntary
many nuclei per cell
striated
What does striated muscle contain
sarcomeres. Smooth muscle therefore lacks sarcomeres,
whereas cardiac and skeletal muscle contain them.
Cardiac muscles contain what
intercalated discs, which are made of desmomsomes and gap junctions
Skeletal muscle is composed of many _____ within ______
bundles within bundles
steps for muscle
Muscle → Muscle fascicles → Muscle fibers
muscle cells) → Myofibrils (contractile protein
What is the sarcolemma?
muscle fiber’s cellular
membrane, and it protects each muscle fiber.
What is the sarcoplasm
Cytoplasm of the muscle fiber holds the myofibrils
What causes muscle contraction?
Sarcomeres inside of myofibrils are the functional
unit of muscle fibers that are shorten to cause muscle contraction
Myofilament are contained within _____ and divided into ____ and ____
sarcomeres
thin actin filaments
thick myosin filaments
Stimulation of a muscle contraction (step 1
Action potential propagation reaches the end
of a motor neuron’s axon.
Stimulation of a muscle contraction (step 2
Acetylcholine is released as a
neurotransmitter between the presynaptic
motor neuron and postsynaptic skeletal muscle
fiber at the neuromuscular junction.
Stimulation of a muscle contraction (step 3
Acetylcholine binds to ligand - gated
sodium channels, causing sodium to enter
the cell, which creates graded potentials
on the muscle fibers.
Stimulation of a muscle contraction (step 4
The graded potentials trigger opening of
voltage-gated sodium channels, which may
produce action potentials on the muscle if the
stimulus is large enough.
The sarcolemma is the ____ of striated
muscle and ______ invaginations that
quicken action potential propagation on the
muscle.
cell membrane
T tubules
What is the sarcoplasmic reticulum?
endoplasmic reticulum of muscle fibers that
releases stored calcium ions into the
sarcoplasm through voltage-gated calcium
channels when triggered by the depolarization
of the muscle cell.
What does calcium ion bind to?
troponin, which removes tropomyosin from the myosin binding sites on actin, allowing myosin to interact with actin and cause sarcomere shortening, using sliding filament.
Cross bridge cycling step 1
Initiation: Calcium ions expose the
myosin-binding-sites on actin.
Cross bridge cycling step 2`
A cocked back, high energy myosin head
(containing ADP and Pi) forms a cross bridge
with the actin
Cross bridge cycling step 3
The myosin head contracts and the power
stroke occurs, bringing the myosin head back
to a low energy state and releasing ADP and
Pi. As a result, the sarcomere shortens.
Cross bridge cycling step 4
A new ATP molecule binds to myosin, causing
detachment of the myosin head from the
actin filament.
Cross bridge cycling step 5
The myosin head is an ATPase, and it
hydrolyzes the ATP into ADP and Pi
. This
causes the myosin head to re-enter a cocked
back, high energy state. (Return to Step 2 if
calcium ions present).
Cross bridge cycling step 6
Termination: Neuronal signaling from motor
neurons ends. The sarcoplasmic reticulum
pumps calcium back into itself, and troponin
brings tropomyosin back to cover
myosin-binding sites on actin.
Rigor mortis occurs Where?
dead animals when there is
no ATP available to release myosin from the actin.
The Z lines are the ____ of the sarcomeres. Thin
actin filaments branch from the Z lines towards
the middle of the sarcomere.
ends
The M lines are the _____ of the sarcomeres.
Thick myosin filaments branch from the M lines
towards the ends of the sarcomere.
midpoints
The _____ band is the area in the sarcomere where
only actin filaments are present. (Mnemonic: “I” is
a thin letter, representing thin actin filaments)
I
The ___– is the area in the sarcomere where
actin and myosin overlap.
A band
The _____ is the area in the sarcomere where
only myosin is present. (Mnemonic: “H” is a thick
letter, representing thick myosin filaments)
H zone
motor unit makes up what?
muscles,
motor unit refers to what?
all the muscle fibers innervated by a single
neuron.
Small motor units include
only a few muscle
fibers and are used in precision movement.
Large motor units
include many muscle fibers
that are innervated by a single neuron and are
used in powerful movements.
What is twitch contraction?
contraction of a
muscle fiber through motor unit stimulation.
Each twitch has the same ____ and ______
size and duration
The twitch contractions also follow
the all of none principle
what is the all of none principle?
depolarization will
cause all the muscle fibers to twitch if it is above
threshold potential but will not cause any
twitching if the depolarization is below threshold
potential.
3 phases of a twitch!
latent
contraction
relaxation
Latent
action potential spreads over
sarcolemma and T-tubules, signaling to
sarcoplasmic reticulum to release calcium.
Contraction
formation of cross bridges as
a result of calcium ions binding to troponin. H
zones shrink and muscle tension increases.
Relaxation:
calcium is pumped back into the
sarcoplasmic reticulum, ending cross bridge
cycling and decreasing muscle tension.
What is summation
process by which twitches add
up to create a larger overall contraction.
Twp types of summation
wave summation
motor unit summation
what is wave summation
depolarizing a motor unit again during the
relaxation phase. May cause tetanus, which
is when the muscle fibers cannot be further
stimulated due to a lack of relaxation.
Twitches blend together during tetany,
eventually causing fatigue (loss of muscle
contraction).
motor unit summation
different motor
units are stimulated at different times to
produce the intended amount of muscle
contraction. This is also known as the size
principle of motor unit recruitment
because smaller motor units are stimulated
first before larger motor units come in to
help.
Weak and involuntary twitches in _______ contribute to maintaining muscle
tone (muscle tonus).
small motor unit groups
