muscle development Flashcards
EXCITATION OF SKELETAL MUSCLE:
Neuromuscular Transmission and Excitation-Contraction Coupling
Transmission of Impulses from Nerve Endings to Skeletal Muscle Fibers:
The Neuromuscular Junction
Each nerve fiber normally stimulates 3 fibers to several hundred________
skeletal muscle fibers
The nerve ending makes a junction called the ______________, and the action potential in the muscle fiber travels in both directions toward the muscle fiber ends
neuromuscular
junction
Vesicles Containing __________are Released into the Synaptic Space
Acetylcholine
are innervated by large, myelinated nerve fibers that originate from large motoneurons in the anterior horns of the spinal cord
Skeletal muscle fibers
on the inside surface of the neuronal membranes are linear dense bars, and to the side of these bars are __________
voltage-gated calcium channels
When the action potential spreads over the nerve terminal, these
channels open, allowing __________ to diffuse into the terminal.
calcium ions
The calcium ions are believed to exert an attractive influence on
the _________vesicles, drawing them adjacent to the dense bars
acetylcholine
Some of the vesicles fuse with the neural membrane and empty
their acetylcholine into synaptic space via the process of
___________
exocytosis
In the synaptic space are large quantities of the enzyme _____________, which destroys acetylcholine a few
milliseconds after it has been released from the synaptic vesicles.
acetylcholinesterase
are located almost entirely
near the mouths of the subneural clefts lying immediately adjacent to the dense bars, where the acetylcholine is emptied into the synaptic space
acetylcholine-gated ion channels
Acetylcholine Opens Acetylcholine-Gated Ion Channels on the
Postsynaptic Membrane
The principal effect of opening the acetylcholine-gated channels
is to :
allow large numbers of sodium ions to move into the muscle fiber (end-plate potential)
Acetylcholine-gated cation channels Normally leads to opening of voltage-gated sodium channels,
which initiate an action potential at the muscle membrane,
causing _________
muscle contraction
principal effect of
opening the acetylcholine-gated channels is to allow SODIUM IONS to flow to the inside of the fiber, carrying _______ charges with
them.
positive
This action creates a local positive potential change inside the muscle fiber membrane, called the _________
end plate potential
After acetylcholine (Ach) has become attached and a
conformational change has opened the channel, allowing sodium
ions to enter the muscle fiber and excite contraction.
Note the negative charges at the channel mouth that prevent passage of
negative ions such as ________ions.
chloride
This end plate potential normally causes sufficient depolarization
to open neighboring __________, allowing
even greater sodium ion inflow and initiating an action potential
that spreads along the muscle membrane and causes muscle
contraction.
voltage-gated sodium channels
Acetylcholine Released into the Synaptic Space is Destroyed by
___________ or Simply Diffuses Away
Acetylcholinesterase
acetylcholine, once released into the synaptic space,
continues to activate the ___________ for as long as it
remains in the space
acetylcholine receptors
Most of the acetylcholine is destroyed by the enzyme
__________
acetylcholinesterase
The short period during which the acetylcholine remains in the synaptic
space – a ____________ at most – is always sufficient to excite the muscle fiber under normal conditions.
few milliseconds
Acetylcholinesterase is attached mainly to the spongy layer of fine connective tissue that fills the synaptic space between the ___________ & ____________
presynaptic nerve terminal
postsynaptic muscle
membrane.
Then the rapid removal of the ____________ prevents continued muscle re-excitation after the muscle fiber has recovered from its
initial action potential.
acetylcholine
Acetylcholine Produces an End-Plate Potential that Excites the
_________
Skeletal Muscle Fiber
The sudden insurgence of sodium ions into the muscle fiber when the acetylcholine-gated channels open causes the electrical potential inside the fiber at the local area of the end plate to increase in the positive direction as much as ______________,
creating a local potential called the end plate potential.
50 to 75 millivolts
The end plate potential created by acetylcholine stimulation is
normally far ________that necessary to initiate an action potential in the muscle fiber.
greater than
The weakness of the end plate potential at point C resulted from
the effect of ________
botulinum toxin
a bacterial poison that decreases the quantity of acetylcholine released by the nerve terminals
botulinum toxin
Drugs can Affect the Neuromuscular Junction by having
____, _____, & ____
Acetylcholine-Like Actions,
Blocking Neuromuscular Transmission,
Inactivating Acetylcholinesterase
Medication that stimulates drugs that have acetylcholine-like
actions:
methacholine,
carbachol,
nicotine
have the same effect on the muscle fiber as does
acetylcholine.
The only difference is that these drugs are not
destroyed or can only be slowly removed by
___________, unlike acetylcholine.
cholinesterase
Drugs that block neuromuscular transmission.
curariform drugs
ex. tubocurarine
prevent passage of impulses from the end plate into the muscle.
curariform drugs
can cause PARALYSIS , classic example is ___________which competes with acetylcholine for
the site, hence, affecting your membrane.
The acetylcholine cannot increase permeability to the
muscle membrane and acetylcholine channels
sufficiently initiates an action potential.
tubocurarine
Drugs that inactivate acetylcholinesterase. Three particularly
well-known drugs –
neostigmine
physostigmine
diisopropyl fluorophosphate
These will inactivate acetylcholinesterase so that
acetylcholine effect is prolonged, as a result this will increase levels of acetylcholine with successive nerve
impulses causing large amounts of acetylcholine to
accumulate and repetitively stimulate the muscle fiber
Drugs that inactivate acetylcholinesterase
potentially last for several hours, thereby allowing
acetylcholine to accumulate in the synaptic space
neostigmine and physostigmine
used as a nerve gas poison because the effect of
preventing acetylcholinesterase is longer (recorded to
be weeks, and is very dangerous)
Diisopropyl fluorophosphates
causes muscle paralysis.
Paralysis occurs because of the inability of the
neuromuscular junctions to transmit signals from the
nerve fibers to muscle fibers.
Myasthenia Gravis
Pathologically,
is thought to be an
autoimmune disease in which patients have developed
antibodies against their own acetylcholine-gated ion
channels.
The end-plate potential that occurs in the muscle fiber
is going to be weak to initiate any voltage-gated sodium channel, thus, the polarization will not occur
An antibody attacks the acetylcholine gated ion
channels on the muscular site, causing weakness to the point of paralysis
myasthenia gravis
If the disease is sufficiently advanced, the patient can
die of paralysis (paralysis of the respiratory muscles e.g.
diaphragm).
myasthenia gravis
myasthenia gravis can be ameliorated by giving _____________
Mu(anti-cholinesterase) which prevents the
destruction of acetylcholine.
neostigmine
This will result in the
accumulation/high levels of acetylcholine in the
synaptic cleft.
neostigmine against myasthenia gravis
The resting membrane potential is about ________ in skeletal muscle fibers, which is similar to that of large, myelinated nerve fibers which innervates the skeletal muscles
-80 to -90 millivolts
The duration of the action potential is only 1 to 5 milliseconds in the skeletal muscles which is ________ than in large,
myelinated nerve fibers.
five times longer
Myelination increases velocity
The velocity of conduction is 3 to 5 m/sec in skeletal
muscle, which is about _________ the velocity of conduction
in the large myelinated nerve fibers that excite skeletal muscle
1/18
Muscles eventually develop ______
which are important for the excitation contraction coupling.
Are internal extensions of the cell membrane.
Transverse Tubules (T Tubules)
run transverse to the myofibrils and begin at
the cell membrane of the muscle and penetrate from
one side of the muscle to the opposite side.
T tubules
internal extensions of the cell membrane,
when an action potential spreads over a muscle fiber
membrane, it also spreads along the T tubules to the interior of the muscle fiber
T tubules
Is Composed of Longitudinal Tubules and
Terminal Cisternae
Sarcoplasmic Reticulum
_________ of the sarcoplasmic reticulum run
parallel to the myofibrils and terminate in large chambers called
terminal cisternae
longitudinal tubules
In cardiac muscle, a single T tubule network for each sarcomere is located at the level of the
Z disk
In mammalian skeletal muscle, there are _______ T tubule networks
for each sarcomere located near the two ends of the myosin filaments, which are the points at which the mechanical forces of
muscle contraction are created.
2
Calcium lons Are Released From the __________ of the Sarcoplasmic Reticulum
Terminal Cisternae
From the nerve: post synaptic cleft of the muscle
membrane, goes to the T tubules, then T tubules
coordinate with the _________
terminal cisternae
After the contraction, a __________assists the removal of the
calcium ions to go back into the sarcoplasmic reticulum
Calcium pump
A continually active calcium pump located in the walls of the ___________ of the sarcoplasmic reticulum
pumps calcium ions AWAY from the myofibrils,
BACK into the SARCOPLASMIC TUBULES
longitudinal tubules
The pump can concentrate the calcium ions to about
__________ inside the tubules
10,000 fold
inside the
reticulum is a calcium-binding protein called
This protein can provide another 40 fold
increase in storage of calcium inside the
reticulum.
Calsequestrin
This transfer of calcium into the sarcoplasmic reticulum depletes calcium ions in the sarcoplasmic fluid, thereby _________
terminating the
muscle contraction
refers to the conversion of
action potential into a mechanical muscle contraction.
It is a process that happens in your muscles when you want to move.
Excitation Contraction coupling
The activation of a nerve, specifically a motor neuron.
Your brain sends a signal to your muscles, telling them to contract (get shorter and
tighter). This signal travels through your nerves like an
electrical message.
Excitation
The interaction (i.e. shortening) that
takes place between the actin and myosin filaments of the sarcomere.
Calcium is like a key that unlocks your muscle fibers, allowing them to shorten and contract.
Think of it as TURNING ON a switch that makes your
muscles work
Contraction
Lead to muscle action. When the electrical message reaches your muscle fibers, it needs to make them contract.
It does this by causing tiny storage units
in your muscles, called “calcium storage units,” to
release calcium
Coupling
calcium storage units
Coupling
At the beginning of this process, the sarcomere and/or muscle fiber is in a ___________.
Where there is just minimal overlap
of actin and myosin filaments.
resting position
Because communication is needed between the nervous and muscular systems, in order for contraction to occur, it makes
sense that there is a MEETING PLACE called the ____________for these systems to actually communicate
Neuromuscular
Junction
participants of neuro muscular junction:
motor neuron
synaptic terminal
motor end plate
synaptic cleft
sarcomere
synaptic vesicles
sarcoplasmic reticulum
nerve that connects to and powers the muscle fiber
motor neuron
represents the end component of the motor neuron
synaptic terminal
area that represents the part of muscle fiber in which the motor neuron sits
motor end plate
space between the synaptic terminal and end plate
synaptic cleft
travel along the axons of neurons and reach the synaptic terminal
action potential
release neurotransmitters called acetylcholine
synaptic vesicles
a receptor, where the acetylcholine binds in the motor end plate
nicotinic acetylcholine receptor
sodium begins to enter the muscle fiber, potassium leaves
more sodium enter, less K+ leaving 3:2
activation of sodium-potassium pump
action potential travels now in __________
initiating calcium from sarcoplasmic reticulum into sarcoplasm
t-tubules
muscle cell is also referred to as a
muscle fiber
Muscle cell membrane
Sarcolemma:
Muscle cell cytoplasm
Sarcoplasm
Muscle cell smooth endoplasmic
reticulum (SER)
Sarcoplasmic reticulum
the presence of these cells is a great issue
with the muscles because skeletal muscles have limited ability to proliferate and differentiate into muscle cells and
as a result, sometimes extensive injury to your muscles
would result into muscles not being fully repaired.
It is because it has very limited capacity to
regenerate
Satellite cells –
induce skeletal muscle
hypertrophy rather than hyperplasia
Muscle-building exercises
if you go further, it is a dense connective tissue
that surrounds each muscle fiber
Epimysium
contractile unit of your muscle
Sarcomere
has the capacity to regenerate
lots of tumors
smooth muscle
thin and long bundles that fill the muscle fibers
for each muscle fiber
myofibril
is the direct invagination of the muscle membrane
that terminally bathing the cisternae of sarcoplasmic reticulum
and it is quite important for your Calcium
T-tubules
less dark band with only thick filaments
middle portion of the A band
H band
faint line that anchors the thick filaments
midline of the A band
M line
light band
area with only thin filaments
loc. at lateral portions spanning 2 sarcomeres
I band
middle of I band
anchor thin filaments and mark the boundary of or sarcomeres
loc. at end margin of sarcomere, midline of I band
Z line (Z disc)
If you damage a motor neuron (that 3 to
several hundreds of muscular fibers)
and
there is no innervation of muscle there could be _______of
several groups of muscles.
atrophy
group of skeletal muscle fibers innervated by a single motor neuron that contracts together
motor unit
motor units:
large motor unit
small motor unit
large group of motor fibers innervated by a single motor neuron that typically generate a large contractile force but is relatively slow to respond as a whole
ex. muscles of posture that supports your back, thighs and buttocks
large motor unit
group of motor fibers innervated by a single motor neuron necessary for very DELICATE & FAST MOVEMENT
ex. muscles of the eyes, muscles of the fingers of the hands
small motor unit
3 types of skeletal muscles
type 1 (red, slow-twitch) fibers
type 2a (intermediate fibers)
type 2b (white, fast-twitch) fibers)
Small diameter; red appearance due to high
myoglobin content;
many mitochondria
Slow to contract but
resistant to fatigue;
undergo oxidative phosphorylation to produce maximum ATP
Postural muscles; large amount in muscles of endurance athletes
type 1 (red, slow-twitch) fibers
Medium-sized diameter;
slightly red due to good
amount of myoglobin;
many mitochondria;
glycogen storage
Faster to contract and
fairly resistant to fatigue;
generate ATP by both oxidative phosphorylation
and glycolysis
Large amount in mid-distance runners and swimmers
Type 2a (intermediate) fiber
Large diameter; light pink due to less myoglobin;
fewer mitochondria;
large glycogen storage
Fast to contract and prone
to fatigue; generate
ATP rapidly by anaerobic
glycolysis. Lactic acid by-products cause fatigue
Extraocular muscles,
muscles of the fingers;
large amount in short-distance runners and weight lifters
Type 2b (white, fast-twitch) fibers
are like tortoise: Slow moving but steady, and they
take first place
Type I fibers
are like the hare: Fast but Resting in the middle,
and they come in last place
Type 2b fibers
are between the other two, chronologically.
They
come in the middle and, hence, are intermediate fibers
Type 2a fibers
Usually the result at the time of death.
the dead body becomes rigid because the calcium leaks out and into the sarcolemma, and this causes actin and myosin
interaction, but due to a lack of developing ATP, the interaction cannot be separated. This results in MUSCLE RIGIDITY. Remember,
you need ATP also for muscle relaxation
Rigor mortis
Decrease in muscle cell volume with the loss of
myofibrils as the result of inactivity or loss of motor innervation
Atrophy
Episodic and progressive muscle weakness commonly as the result of autoimmune antibody binding and
blocking acetylcholine receptors at the neuromuscular junctions
Myasthenia gravis
often short with a single, oval Nuclei but they
have their own striations. They also store some form of glycogen
and what is characteristic is the presence of Intercalated disc, which are necessary to create a syncytium – that allows for
immediate transfer of action potential and stimulus.
cardiac muscleS
transverse portion of
the adhesion junctions and the lateral portion of the gap junctions
AND 1 terminal cisternae and T-tubules named______
DIAD
in sarcoplasmic reticulum of skeletal muscle, 2 T-tubules and cisternae
TRIAD
Injury and cell death at a region of the heart as a result of poor or blocked blood supply. Injured area s
replaced by scar tissue rather than new cardiac cells due to their inability to proliferate
Myocardial infarction (MI)
Benign smooth muscle tumors often arising in the
uterus; the most common neoplasm in women
Leiomyoma
Malignant smooth muscle tumors; 10% to 20%
of soft tissue tumors
Leiomyosarcoma
