Chapter 2 Flashcards
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 rest….is 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
depolarization
- making a membrane potential less negative
- Na+
hyperpolarization
- making a membrane potential more negative
- closer to the firing threshold.
- K+
what happens during an action potential (STEPS)
- membrane is at rest
- depolarizing stimulus make the inside less negative and more likely to fire
- depolarization causes Na+ to rush IN making the cell more positive
- K+ channels open, K+ rushes OUT
- Na+ inside causes sodium influx causing Na+ channels to close (no more Na+ enters cell)
- inside more positive so K+ channels open and cause outflow of K+
- outflow of K+ causes the membrane to return to rest
- 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
EPSP *
- DEPOLARIZATION, EXCITATORY
- often result from Na+ or Ca2+ going into the cell
IPSP *
- HYPERPOLARIZATION, INHIBITION
- results from Cl- going into the cell or K+ going out
how is neurotransmitter action ceased in the synapse
-reuptake or enzymatic deactivation
what is the advantage of reuptake over enzymatic degradation in the termination of the neurotransmitter postsynaptic effect?
- terminates the effect in the synapse and takes the neurotransmitter back into the cell and recycles it to use later ,
- it inhibits a neurotransmitter causing its effects to last longer
- while the other destroys the neurotransmitter
spatial summation
g
temporal summation
g
electrical synapse function
-Electrical synapses are formed by gap junctions, places where multiple transmembrane proteins in the pre- and postsynaptic neurons connect to create pathways that connect the cytoplasms of the two neurons.
- rapid (used in escape neurons)
- less plastic than chemical synapses
4 types of glial cells
- astrocytes: support and nutrients
- oligodendrocytes: myelinate axons in the brain and spinal cord
- microglia: clean up debris and protect from invading microorganisms
- schwan: myelinate axons in the periphery body
2 differences between Oligodendrocytes and Schwann cells
- oligodendrocytes: in CNS form myelin, can myelinate multiple pieces of axons
- schwan: in PNS form myelin, can only myelinate one-to one axon
