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Neurons
N/A
42
Anatomy
Undergraduate 2
09/18/2012

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Cards

Term
interneurons
Definition
  • provide communication between other neurons
  • do not exit the CNS (brain and spinal cord)
Term
cell gradients
Definition
  • established between inside and outside cell
  • ions have a tendency to flow to equalize "pressure"
  • pumps move ions to increase gradient
  • we turn on faucets to let ions floor in
Term
electrochemical gradient
Definition
  • in neurons, gradient is established using electrical charge and molecular density rather than gravity pulling on water
  • using magnets, positive poles repel each other; whereas, opposite poles attract each other
  • ions- atoms that have either lost or gained an electron (negative particle)
  • causes them to acquire either positive or negative charge
  • positive ions will repel other positive ions, but positive ions will attract negative ions
Term
concentration gradient
Definition
  • molecules tend to move from area of higher concentration to area of lower concentration to equalize the concentration
  • analogy: tea bag in water
Term
electronephalography (EEG)
Definition
sum of much neural activity within brain, produced by 'generators'
Term
auditory brainstem response (ABR) testing
Definition
  • audiologist records electrical activity of neurons to determine whether auditory pathway is intact
  • he/she presents a stimulus such as puretone or click and then measure electrical emanations from brain stem area
  • done when baby is sleeping
Term
permeability
Definition
  • ease with which molecules may pass through a membrane 
  • tea bag is very permeable...plastic pouch is NOT
Term
semi-permeable
Definition
some ions may pass through it, given appropriate circumstances
Term
passive transport
Definition
  • no energy is expended to move ions across the barrier
  • rather, gradient established by inequalities between the two sides of membrane causes ion movement
Term
passive transport gatekeepers
Definition
  • voltage-sensitive proteins serve as gatekeepers
  • open channel when they receive adequate electrical stimulation
  • channel proteins also serve as gatekeepers
  • allow specific ions to pass through membrane
Term
active transport
Definition
  • active pumping is required to move ions across barrier
  • energy is expended to accomplish this task
  • ion pumps role is to move sodium and potassium ions against gradient 
  • energy used by Na-K pump proteins is in form of ATP (adenosine triphosphate); a product of mitochondria of cell
Term
sodium-potassium pumps
Definition
  • operate continuously
  • move 3Na+ ions out for every 2K+ ions moved in
  • active transport is required to readjust balance of ions across membrane
Term
intracellular space
Definition
minus signs indicate negative charge
Term
extracellular space
Definition
  • space between cells
  • positive signs indicate positive charge
Term
resting membrane potential (RMP)
Definition
-70mV (millevolts)
Term
action potential (AP)
Definition
change in electrical potential that occurs when cell membrane is stimulated adequately to permit ion exchange between intra- and extracellular spaces
Term
neuron "fires"
Definition
when critical threshold of stimulation is reached (-55mv), Na+ ions gates open up causing large number of Na+ ions to flood intracellular space
Term
depolarization
Definition
raising intracellular potential to +30mV very rapidly
Term
Time #1
Definition
  • cell membrane is depolarized to threshold
  • sodium gates open; Na+ is propelled into cell by its concentration and electrostatic gradient
  • membrane potential goes positive
Term
Time #2
Definition
  • sodium gates close
  • potassium gates open; K+ is propelled out of cell by its concentration and electrostatic gradients
  • membrane potential drops rapidly
Term
Time #3
Definition
  • potassium gates begin to close
  • sodium-potassium pump helps restore resting membrane potential
Term
absolute refractory period
Definition
  • time during which cell membrane cannot be stimulated to depolarize
  • no amount of stimulation will cause it to depolarize again
  • potassium channels open and K+ ions flow out of intracellular space
  • sodium inactivation- sodium gates spontaneously close and become inactivated
  • sodium-potassium pump- removes most of Na+ ions, while increasing intracellular concentration of K+ ions
Term
relative refractory period
Definition
  • period after absolute refractory period
  • period during which membrane may be stimulated to excitation again, but it needs a greater than typical amount of stimulation
Term
action potentials
Definition
  • critical threshold (~ -55mV)
  • for action potential to be generated, membrane channels have to break down
  • AP is not generated until you reach this critical threshold
  • if stimulation does not result in sufficient ion transfer to reach critical threshold, AP will not be triggered and sodium-potassium pump will restore RMP (-70mV)
Term
timing of entire cycle
Definition
  • RMP-->AP-->RMP ~ 1ms
  • neuron may respond every 1/1000 of second, or 1000x per second
  • even if stimulated 2000x per second, it will not be able to respond that rapidly because it won't have time to stimulate twice that rapidly
Term
ion concentration at #1
Definition
-70mV, resting membrane potential
Term
ion concentration at #2
Definition
stimulation is occurring
Term
ion concentration at #3
Definition
depolarization has occurred ; note plus signs in cell (+30 mV)
Term
ion concentration at #4
Definition
negativity is even greater than -70 mV; negative after potential (dips down below -70 mV)
Term
ion concentration at #5
Definition
sodium-potassium pump has restored RMP (-70 mV)
Term
propagation
Definition
  • spreading effect of wave action
  • wave of depolarization for APs
  • larger axon diameter results in increased rate
  • myelinated fibers facilitate an increased rate
Term
all-or-nothing manner
Definition
  • neuron either depolarizes or it does not
  • if neuron fails to depolarize, no AP is generated and no information is conveyed
Term
spike rate (rate of discharge)
Definition
frequency with which neuron is "turned on"
Term
nodes of ranvier
Definition
  • myelin is laid down on axon in "donuts" with nodes of exposed membrane between them
  • voltage-sensitive channels are found within the membrane at nodes
Term
saltatory ('leaping') conduction
Definition
  • propagating AP is "passed" from node to node
  • in long fibers, precious milliseconds can be saved by skipping from node to node
Term
synapse between two neurons
Definition
  • neurotransmitter travels across cleft very quickly (100 microseconds)
  • activates receptor proteins on postsynaptic neuron
  • presence of neurotransmitter in cleft triggers the ion channels to open
Term
excitatory effects
Definition
increase probability that neuron will depolarize
Term
inhibitory effects
Definition
decrease probability that neuron will depolarize
Term
excitatory postsynaptic potential (EPSP)
Definition
  • excitation causes depolarization; sum of their depolarizations will reach critical threshold
  • can continue to send the messages to the rest of the body
  • "voting" by neurons
  • hundreds or even thousands of neurons may make synapse on a given neuron
  • if sufficient number of these synapses are activated, then AP results
Term
inhibitory postsynaptic potential (IPSP)
Definition
  • inhibition causes hyperpolarization
  • greatly elevates threshold of firing
  • generally inhibitory synapses are found on soma
  • they stop message from continuing
Term
spatial summation
Definition
  • some neurons require many near-simultaneous synaptic activations
  • represents many points of contact arrayed over surface of post-synaptic neuron
Term
temporal summation
Definition
  • two or more closely successive impulses arrive
  • then synapse is established
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