Class 2 Flashcards
During development, all 3 types of muscle originate from where?
Somatic mesoderm
What migrates out of the somatic mesodermal germ layer to form muscle fibers
Myoblasts
Differentiation of myoblasts into their cell fate and what are believed to be highly correlated?
Cell lineage
Coelomic Graft model was used for?
To investigate whether muscle type differentiation is determined by myoblast cell lineage, independent of external influences
What is the coelom?
Body cavity formed during embryonic development when mesoderm is split into two layers
Satellite cells indicates that cell lineage is not as strong a determinant for what muscle type
Skeletal muscle type
Satellite cells are found where?
Between the basal lamina and plasma membrane
How are satellite cells activated?
After muscle injury or intensive exercise
Satellite cells fuse to what and why?
Fuse to themselves to create new muscle fibers or fuse to damaged muscle fibers to repair damage
A satellite cell can transform itself into a muscle fiber of what type?
Fast or slow MyHC isoforms
Nerve-evoked electrical activity is an external signal that can (-) muscle phenotype
Change
When a nerve from a fast muscle is transplanted into a slow muscle and vice versa —
Both re-innervated, muscles change phenotype
Type I motor units, receive (-) amounts of impulses delivered in (-) frequency sequences
High, low
Type II motor units, receive (-) amounts of impulses delivered in (-) frequency sequences
Low, high
Slow-to-fast muscle phenotype change
Difficult, or impossible
Fast-to-slow muscle phenotype change
Easy, possible
Why is it difficult to go from slow-to fast muscle phenotype?
The amount of background activity will dominate
Depolarization leads to what in muscle?
Shortening or mechanical tension
What is possibly more important for muscle activity? Neural or action potential?
Neural
Can muscles heal after atrophy?
Yes
Changes in muscle usage will lead to what?
Changes in muscle phenotype
Factors that can serve as messengers for muscle activity
- Free intracellular Ca
- Metabolites
- hypoxia
- tension
Regulation of force is a question of what?
Regulating fiber size
Size can be achieved by regulating three conditions that are?
- number of nuclei
- rate of protein synthesis
- rate of protein degradation
Hypertrophy is generally accompanied by:
Addition of new nuclei
How are new nuclei created in muscle cells?
Satellite cells fusing with pre-existing muscle fiber
What is myostatin?
Member of the trans-transforming growth factor B (superfamily)
Myostatin function
Role during development where it acts as inhibitor of muscle growth
Disruption of the myostatin gene leads to
Development of grossly enlarged muscles, increase in number of fibers and fiber size
Activity is regulated by IGF-binding proteins acting as carriers in blood, or locally binding IGF-I to the extracellular matrix describes what?
Insulin-like growth factor I
What organ supplies 75% of circulating IGF-I
Liver
What factor has been implicated as a factor promoting hypertrophy
IGF-1
IGF-1 function
- increase myotube diameter
- suppress proteolysis
- stimulate protein synthesis
- induce higher number of nuclei
- promote myoblast synthesis
Hormone for muscles
Testosterone
What is the structure where axonal branches of a motor neuron form contact to a group of target muscle fibers within a single motor unit through presynaptic buttons
Motor end-plate
There is one somatic motor neuron per (-)
One motor unit
Muscles for fine control have (greater, fewer) muscle fibers per motor unit
Fewer
There are/is (multiple, one) muscle fibers per motor unit
Multiple
Axonal branches from presynaptic motor neuron form swellings that occupy depression of the muscle fiber are
Presynaptic buttons
Is there direct contact between presynaptic button and the postsynaptic terminal
No
Synaptic button that occupies a depression is known as
Primary synaptic cleft
Sarcolemma of the muscle fiber that forms the infolding deep junctional fold is what?
Secondary synaptic cleft
What kind of synapse if the neuromuscular junction?
Chemical Synapse
What separates the presynaptic button and the postsynaptic terminal?
Synaptic clefts
Synaptic vesicles are derived from the what?
Neuronal soma (cell body)
What step is: acetylcholine is enclosed by synaptic vesicles and transported by kinesin along the axon by anterograde axonal transport
Step 1 in synaptic transmission within the neuromuscular junction of the skeletal muscle
What is a neuromuscular junction?
A chemical synapse between a motor neuron and a muscle fiber
Acetylcholine is enclosed by the membrane-bound (-)
Synaptic vesicles
Where are synaptic vesicles located where?
Presynaptic terminals
Molecular motor proteins are what?
Kinesin
What is the highway of the axon?
Microtubule of the axon
What step is: depolarization of the axon terminal activates the voltage-gated Ca channels, increase in Ca induces exocytosis of synaptic vesicles, releasing ACh?
Step 2
Vesicular docking proteins are found where?
Synaptic vesicles
What do vesicular docking proteins allow synaptic vesicles to do?
Attach at the presynaptic terminals rich in membrane docking proteins
Depolarization triggers (influx, or efflux) of Ca
Influx
Increase in Ca concentration induces what?
Exocytosis of synaptic vesicles and releasing ACh
What step is AChE terminates the signal by hydrolyzing Ach into forming choline and acetyl CoA?
Step 3
How can Ach be enzymatically degraded and where?
In the synaptic cleft by acetylcholinesterase (AChE)
Where is AChE found?
Located in the post-synaptic membranes
Hydrolyzing ACh forms what?
Choline and acetyl CoA
Choline can be re-uptaked back to pre-synaptic terminal and recycled back into forming (-) by (-)?
ACh by Choline acetyltransferase
Kinesin-mediated that carries cargos from axon terminal toward soma are (anterograde, retrograde)
Anterograde
Dynein-mediated that carries cargos from axon terminal toward soma are (anterograde, retrograde)
Retrograde
Axonal transport requires 3 things:
- axonal cytoskeleton
- motor proteins (kinesin and dynein)
- hydrolysis of ATP
What are the 2 motor proteins?
Kinesin and dynein
Anterograde transport of vesicles and mitochondria is mediated by what?
Kinesin
Retrograde transport of a vesicle along a microtubule is mediated by what?
Dynein
Rabies virus is a neurotropic virus that is able to infect what?
Nerve cells
Rabies virus is capable of binding to the (-) and replicates in the (-)
Acetylcholine receptor, muscle tissue
The viral rabies particle migrated by (-) to the (-)
retrograde axonal transport to the cell body of neurons supplying affected muscle
Does rabies virus continue to replicate within infected neurons? Where does this occur?
Yes, in the CNS
Rabies virus is transported by (-) by the peripheral nerves to the (-)
Anterograde axonal transport, salivary glands
How is rabies transported?
Transmitted by the bite
A potent neurotoxin produced by clostridium tetani is what?
Tetanus
Tetanus uses (-) to enter the (-)
Retrograde axonal transport to enter the CNS
What does tetanus cause?
Spasm contraction of jaw, exaggerated reflexes, respiratory failure
Tetanus blocks the release of (-) a the spinal synapse
Inhibitory mediators
Varicella zoster causes
Chicken pox and shingles
Zoster virus enter the nerve body using (retrograde, anterograde) axonal transport and stay (-) in the nerves
Retrograde, dormant
Zoster virus reactivated by (-) and uses (anterograde, retrograde) axonal transport to move to nerve ending
Stress, anterograde
Shingles starts at the muscle and then is transported to the skin (T/F)
True
Curare produces what symptoms?
Muscle paralysis
Curare bind to Ach receptor and prevents binding of Ach to the (-)
Nicotinic acetylcholine receptors
Nicotinic acetylcholine receptors are located where?
Postsynaptic membrane
Botulinum toxin is an exotoxin that prevents the release of (-) at the (-)
Acetylcholine at the presynaptic terminal
Botulinum toxin produces what symptoms?
Muscle paralysis and dysfunction of the autonomous nervous system
Myasthenia gravis is an autoimmune disease with antibodies against (-) which
Ach receptors which prevent binding of Ach to the nicotinic acetylcholine receptors
Myasthenia gravis symptoms
Muscle weakness
Lambert-Eaton myasthenic syndrome is an autoimmune disease with antibodies against (-)
Voltage-gated Ca channels
Lambert-Eaton myasthenic syndrome reduces (-) into intracellular space
Calcium
Lambert-Eaton myasthenic syndrome symptoms
Muscle weakness
