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what is a neuron

-specialized animal cell that purpose is to send, receive, and conduct signals


Name another cell type in the nervous system?

glial cells : provide structural support and electrical insulation neurons


define membrane potential

-the electrical charge difference across a cell membrane
-store up source of electrical energy


resting membrane potential

-when a neuron is not being excited or inhibited

-approximately -70mV
-inside more negatively charged than the outside


what maintains the resting membrane potential

-70 mV


voltage-gated channels

-an ion channel that opens or closes according to the value of the membrane potential (changes in nearby transmembrane voltage)


ligand-gated channels

-an ion channel that opens or closes in response to the binding of a specific chemical (Neurotransmitter) or physical stimuli


non-gated ion channels

-unregulated ion channels that are always open

-always allow the associated ion to pass through


describe the differential ion concentrations in the neuron at the membrane potential positive or negative at rest

-more negative at rest
-Na+ outside
-K+ inside
-more Cl- outside


describe the driving forces (electrical and chemical) on Na+ and K+ rest (i.e. how would the ions move if a channel opened)

-Na+= chemical and electrical forces IN

-K+= chemical OUT; electrical IN


purpose of Na+ K+ pump

-helps maintain differential concentrations of Na+ and K+ ions

-balances the ions by pumping Na+ out and K+ in



-making a membrane potential less negative




-making a membrane potential more negative

-closer to the firing threshold.



what happens during an action potential (STEPS)

1. membrane is at rest
2. depolarizing stimulus make the inside less negative and more likely to fire
3. depolarization causes Na+ to rush IN making the cell more positive
4. K+ channels open, K+ rushes OUT
5. Na+ inside causes sodium influx causing Na+ channels to close (no more Na+ enters cell)
6. inside more positive so K+ channels open and cause outflow of K+
7. outflow of K+ causes the membrane to return to rest
8. Na+ K+ pump resets and re-establishes resting membrane potential: K+ channels close, Na+ channels reset, extra K+ outside diffuses away


all-or-none law

-an action potential either occurs or does not occur

-once triggered, it travels without getting smaller to the end


how is the threshold of excitation of an action potential reached

-with enough excitatory postsynaptic potentials (EPSPs)

-if enough Na+ ions have entered the cell with the neurotransmitter binding then they add up until it reaches a threshold causing an axon Potential to be generated at the axon hillock


how can action potentials represent continuous information when action potentials fire in an all-or-none fashion

-variation of firing when on or off


absolute refractory period

-time when impossible to initiate another action potential
-Na+ channels are inactivated

-impossible to fire another action potential, because ions are in the wrong place


relative refractory period

-time when it takes a stronger stimulus to initiate an action potential
-during overshoot hyperpolarization
-harder to fire AP, takes more stimulation


absolute and refractory period similarities

-prevent the backwards movement of APs and limit the range of firing

-keeps it moving in one direction
-from the axon hillock, to the axon terminals


why does an action potential tend to move in one direction in the neuron

refractory period : keeps it moving in one direction


how does myelin affect the conduction of action potentials

-allows AP to happen only at the Nodes of Ranvier

-causes information to travel faster


define saltatory conduction

-conduction of action potentials by myelinated axons

-action potential appears to jump from one node of Ranvier to the next
-faster conduction


synaptic transmission

the process by which presynaptic neuron communicates with the postsynaptic neuron

-the sending of neurotransmitter between neurons to keep the message going


2 types of synaptic transmission

-chemical synapse: slower, but signal strength maintained

-electrical synapse/gap junctions: faster, but signal can degrade


what are dendritic spines, and what is their purpose

-"tree" branches off the soma
-RECEIVE INFORMATION from the terminal buttons of other neurons


describe the process of chemical synaptic transmission *

-AP reaches the terminal, causes Ca2+ channels to open
-Ca2+ flows into cell
-fusion pore widens and Ca2+ causes vesicles to bind with cell membrane (Ca2+ ions attach to the receptors of the vesicles of the neurotransmitter)

-release of neurotransmitter by exocytosis into the synaptic cleft

-transmitter binds with receptor and neurotransmitter to leave terminal button into the synaptic cleft


ionotropic receptor *

-contains a binding site for a neurotransmitter and is also an ion channel that opens when a molecule of thee neurotransmitter attaches to the bonding site


metabotropic receptor *

-contains a binding site for a neurotransmitter; activates an enzyme that begins a series of events that opens an ion channel elsewhere




-often result from Na+ or Ca2+ going into the cell