Module 3: Lecture 5 Flashcards
where do we have very high concentrations of our voltage gated sodium and potassium channels?
nodes of ranvier
why are we able to generate an action potential?
due to our nodes of ranvier
why does action potentials not happen anywhere that there is myelin sheath?
because it is insulating and hydrophobic. it does not allow ions to cross across that membrane
the distance between two nodes of ranvier is short enough that?
local current can take place between an active node and the adjacent one
what is saltatory conduction?
the electrical impulse jumps from node to node
how come electrical impulses jump from node to node in saltatory conduction?
because there are no voltage gated ion channels within this myelin sheath area and its not exposed to the extracellular fluid si you are not going to generate an action potential at the myelin sheath because there is no mechanism to bring in the sodium ions so they just continue flowing along the cell membrane until it reaches the next node of Ranvier
what is a key factor affecting the conduction velocity of an action potential?
diameter of the fiber
what determines the magnitude of that potential?
the amount of charges that are ultimately moving across the membrane
what affects the resistance of electrical charge between two regions
fiber diameter
the larger the diameter of the fiber, the higher the?
velocity
what is multiple sclerosis?
loss of myelin –> slows or blocks the propagation of action potentials –> poor coordination, lack of sensation, partial paralysis
what is a synapse?
junction between axon terminals(output zone) from a pre-synaptic neuron and the dendrites(input zone) from a post-synaptic neuron
- the connection between two nerves, how they communicate with one another
what do we say when we talk about a nerve connecting to a gland or a muscle?
we say that nerve innervates that muscle or that gland
what do we call it when we talk about a nerve to nerve connection?
a synapse
how many synaptic inputs can the dendrites and the cell body receive?
as many as 100,000 synaptic inputs
can a neuron that is pre-synaptic to one cell be post-synaptic to another?
yes
when can we refer to it as pre-synaptic or post synaptic?
when it gets to the synapse
what are the two types of synapses?
- electrical (pre- and post=synaptic cells are joined together through gap junctions)
- chemical (neurotransmitter)
what is your synaptic cleft?
the space between your pre- and post- synaptic neuron
is an action potential an electrical signal?
yes
how do we transmit the signal from the pre-synaptic neuron to the post-synaptic neuron if there’s no physical connection?
through the use of neurotransmitters. a chemical signal.
- the physical gap will be jumped by the chemical neurotransmitter that will then induce the electrical signal within the postsynaptic neuron
what is inside of that synaptic neuron?
a whole bunch of synaptic vesicles
- these membrane lipid bound nodules/vesicles that contain the neurotransmitter
where are the receptors of the neurotransmitters in a chemical synapse?
on the subsynaptic membrane (membrane of the postsynaptic neuron)
why can we not just spread the action potential from one neuron to the next?
because of the synaptic cleft (10-20nm)
- prevents direct propagation
how are neurotransmitters released into the synaptic cleft?
neurotransmitters are stored in small synaptic vesicles encased in lipid bilayer membranes. Prior to activation, these vesicles are stored in the region of the synaptic knob (‘active zones’)
what initiates the release of a neurotransmitter?
when an action potential reaches the pre-synaptic axon terminal
when the neurotransmitter is released when an action potential reaches the pre-synaptic axon terminal, what does it open?
calcium-voltage gated channels on the synaptic knob region
where is there a high concentration of calcium?
in the extracellular fluid, on the outside of the cell
what happens when you open a voltage gated calcium channel?
in the region of the synaptic knob, it allows calcium to enter
what is the trigger that results in exocytosis of the neurotransmitters?
the influx of calcium from the calcium voltage-gated channels
what is generating your graded potentials?
chemical synapse
- neurotransmitters binding to their ligand gated ion channels that then open and result in the graded potential which if strong enough, will become an action potential
summary of the connecting of two nerve cells (synapse)?
- action potentials propagating down the axon
- sodium enters from channels
- causes a local depolarization event
- voltage gated calcium channels that open in response to depolarization and allows calcium to enter along the whole cell
- calcium induces the exocytosis of the neurotransmitters from these synaptic vesicles
- the neurotransmitters are released into the synaptic cleft
- they go and bind to the chemically or ligand gated ion channels on the post-synaptic membrane
- they open, allowing graded potentials to occur
what is the signal that allows the neurotransmitters to be released into the synaptic cleft?
calcium
what is caused if we increase the calcium concentration in the nerve cell?
it will cause the exocytosis
before calcium activation, are synaptic vesicles free floating in space?
no, they are loosely docked to the active zones of the docking site by the interaction of SNARE proteins anchored in both the vesicle membrane and axon terminal membrane
- docked to the cell membrane on the intracellular side through SNARE proteins
which protein senses the amount of calcium in the nerve to change the conformation of SNAREs?
synaptotagmin
- calcium binds to it
- changes the conformation of SNAREs (‘hold SNARE proteins together’) which induces the membrane fusion and neurotransmitter release
what allows membranes to fuse with one another and release the neurotransmitters into the synaptic cleft?
the binding and fusion of SNARE proteins
