(07) Skeletal Muscle I Flashcards
What are the two main types of synapses?
(electrical) What kinds of connections are these?
What are the connections called?
What forms them?
Where found?
(chemical) What system do you usually find these in?
What do the junctions look like?
What are the attachments?
What neurotransmitter is released (in nerve to muscle)?
- electrical and chemical
- direct connections between the cells
- gap junctions
- proteins embedded in the PM (called connexions)
- smooth muscle and cardiac muscle
- Nervous system (nerve)
- neuromuscular juntion
- nerve to muscle
- Acetylcholine (ACh)
(Morphology of the Neuromuscular Junction)
What is the Active Zone?
What are the junctional folds?
What are the syaptic vesicles?
What is the synaptic cleft?
The area underneath the nerve terminal is enriched in what? What are these? What is the primary ion moving through these?
- Regions of the terminal where synaptic vesicles cluster
- invaginations of the post-synpatic membrane across from the active zones
- vescicles that contain neurotransmitter substances
- space between the pre and post-synaptic membranes
- nicotinic acetylcholine receptors, ligand gated ion channels, NA+
(Sequence of Events at the Neuromuscular Junction)
- An _____ travels down the
_______ axon to the _____. - Voltage-gated _____ open
increasing the _____
in the pre-synaptic terminal. - The rise in _____ triggers
docking of _____
with the membrane of the synaptic
terminal. - As the _____
fuse with the nerve terminal they
release their contents into the _____. - _____ diffuses across the cleft and
binds to its _____ on the post-synaptic
cell membrane. - Binding of the _____ to its _____
causes the receptor to open its’ _____
channel. - The _____ ions flow down their
concentration gradients through the
_____. The change in the ratio of
ions inside and outside the cell leads to a
_____ change in the membrane resting
potential (_____). - The depolarization spreads to the region
_____ and
triggers _____ in the muscle
cell membrane by opening voltage-gated
_____. - The _____ is broken down by
_____ into choline and
acetate. ______ is recycled by the
nerve terminal.
- Action Potential, motor neuron, nerve terminal
- Ca++, concentraion of calcium
- intracellular Ca++, neurotransmitter vesicles
- acetylcholine filled vesicles, synaptic cleft
- Acetylcholine, receptor
- acetylcholine, receptor, cation
- positive, receptor pore, local, end plate potential
- adjacent to the motor end plate, action potentials, Na Channels
9 acetylcholine, acetylcholinesterase, Choline
(The End Plate Potential)
- _____ depolarization due to _____ binding to its receptor.
- Spreads _____ from zone where _____ channels have opened
- Reaches its peak within _____
- Peak amplitude does not exceed _____ mV
- Local, acetylcholine
- passively, ACh
- 2 msec
- zero
(End Plate potential)
What must be reached by the EPP to cause action potential?
(the little hump at the beginning of the action potential is the end plate potential - occurs at the receiving at the synapse)
How big is the change in EPP? MEPP?
- The threshold voltage must be reached
- 30 mV, 1-2 mV
(Propagation of the EPP)
- Spreads ____ from zone where ___ channels have opened
- Decreases in _____ with distance
- Depolarization must reach _____ to cause _____
- What kind of conduction comes out of EPP?
- passively, ACh
- amplitude
- voltage gated Na+ channels, action potential
- electrotonic potential
(Ionic Mechanism of the EPP)
- Since the _____ receptor is a _____ cation channel, the _____ of the muscle membrane changes for both Na and K simultaneously
- concentrations of Na and K are _____, more ___ outside, more _____ inside, _____ that rushes through causes depolarization
- ACh, non-selective, permeability
- unequal, Na, K, Na
Changes in membrane permeability = Changes in _____
What equation says this?
Normally, _____ has a much higher permeability than _____. But when they become equal - can drive towards ___ equilibrium potential.
When you make the membrane potential more positive that is called a _____
- membrane potential
- Goldmann-Hodkin-Cats relationship
- K, Na, Na
- depolarization
Quantal Release of ACh
- Because ACh is packaged into ____ the release of _____ into the synaptic cleft occurs in a _____ that is referred to as _____.
- The vesicles are of ____ size and have a similar internal _____ concentration.
- The release of each vesicle of ACh can be detected as _______ of the _____ cell.
- These depolarizations are typically _____ (_____) and are called _____.
- vesicles, neurotransmitter, puls-type manner, quantal release
- similar, ACh
- transient depolarizations, post-synaptic
- small (less than 1 mV), miniature endplate potentials (MEPPs).
(Quantal Release of ACh)
- There is a _____ size distribution of MEPPs
- Analysis suggest vesicles containing roughly the same quantity of neurotransmitter with amplitude dependent on ______.
- narrow
- relative timing of vesicle release
(Excitation-Contraction Coupling)
- Nerve stimulation of the muscle at the _____ leads to muscle _____.
- Muscle contraction is controlled by the intracellular _____ concentration.
- Therefore an electrical signal (_____), must be converted into a ______.
- motor endplate, contraction
- Calcium
- action potential, chemical (signal) calcium
Transverse Tubules
- One of the ways that skeletal muscle cells are different that any other kind of cell is that they have a very specialized membrane called the _____.
- Each striated muscle cell is ______ by extensions of the plasma membrane that extend through the _____.
- The interior of these tubules is the same as that _____ fluid that _____ each cell.
- ______ travelling along the cell surface also travel through the _____.
Which muscle cells have this specialization?
What does it allow?
- sarcolemma
- invaginated, body of the cell
- interstitial, surround
- action potential, tranverse tubule system
- cardiac cells and muscle cells
- allows you to send signal to center of muscle as well as outside (important when considering large cells)
(Sarcoplasmic Reticulum)
- The SR is the primary ____ storage site in _____.
- ______ of the muscle plasma membrane triggers _____ from the SR through interaction with the _____.
- _____ is the activating signal to initiate skeletal muscle contraction.
- What type of proteins act as voltage sensor? What are they coupled to?
- calcium, skeletal muscles
- Depolarization, calcium, T-tubules
- Calcium from the SR
- DHP, a protein that is within the SR
(AGENTS AFFECTING NEUROMUSCULAR TRANSMISSION)
- Blocks ACh release from pre-synaptic terminals. Effect?
- Competes with ACh for receptors on motor end plate. effect?
- AChE inhibitor (anticholinesterase)
- Blocks reuptake of choline into presynaptic terminal
- Botulinum toxin – total blockade, paralysis of respiratory muscles, death
- Curare – decreases size of EPP, in maximal doses produces respiratory muscles and death
- Neostigmine - Prolongs and enhances action of ACh at motor end plate
- Hemicholinium
- Depletes – ACh stores from presynaptic terminal
What thing did Mick figure out?
- motor protein found in cells other than muscle, contributes to the trafficking between the cell nucleus and the nerve terminal - and therefore impacts health of the neuromuscular junction
(supposedly will talk more about this later…..)
