muscle development Flashcards by Milleth Jane CAPANGPANGAN

EXCITATION OF SKELETAL MUSCLE:

Neuromuscular Transmission and Excitation-Contraction Coupling

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Transmission of Impulses from Nerve Endings to Skeletal Muscle Fibers:

The Neuromuscular Junction

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Each nerve fiber normally stimulates 3 fibers to several hundred________

skeletal muscle fibers

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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

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Vesicles Containing __________are Released into the Synaptic Space

Acetylcholine

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are innervated by large, myelinated nerve fibers that originate from large motoneurons in the anterior horns of the spinal cord

Skeletal muscle fibers

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on the inside surface of the neuronal membranes are linear dense bars, and to the side of these bars are __________

voltage-gated calcium channels

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When the action potential spreads over the nerve terminal, these
channels open, allowing __________ to diffuse into the terminal.

calcium ions

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The calcium ions are believed to exert an attractive influence on
the _________vesicles, drawing them adjacent to the dense bars

acetylcholine

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Some of the vesicles fuse with the neural membrane and empty
their acetylcholine into synaptic space via the process of
___________

exocytosis

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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

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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

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Acetylcholine Opens Acetylcholine-Gated Ion Channels on the

Postsynaptic Membrane

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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)

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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

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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

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This action creates a local positive potential change inside the muscle fiber membrane, called the _________

end plate potential

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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

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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

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Acetylcholine Released into the Synaptic Space is Destroyed by
___________ or Simply Diffuses Away

Acetylcholinesterase

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acetylcholine, once released into the synaptic space,
continues to activate the ___________ for as long as it
remains in the space

acetylcholine receptors

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Most of the acetylcholine is destroyed by the enzyme
__________

acetylcholinesterase

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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

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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.

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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.

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