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NRSG 203 > Neurons And Action Potential > Flashcards

Neurons And Action Potential Flashcards

1
Q

Parts of a Neuron

A
  • Dendrites
  • Cell body
  • Nucleus
  • Axon hillock
  • Axon
  • Axon terminals
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2
Q

Types of Neuron

A
  • Bipolar
  • Semi-bipolar
  • Multipolar
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3
Q

Function of the Cell Body

A

Houses organelles and nucleus

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4
Q

Function of the Dendrites

A
  • Increases surface area for receiving signals
  • Sends graded potential towards the cell body/axon
  • “Input zone” for the neuron
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5
Q

Function of the Axon

A
  • Nerve fibers
  • ## Conducts action potentials away from the cell body toward the axon terminals
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6
Q

Function of the Axon Hillock

A
  • Where the cell body meets the axon
  • Trigger point for the all or nothing response
  • Where graded potentials summate
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7
Q

Function of Axon Terminals

A
  • Where axons synapse “with other neurons or the effector tissue
  • Release chemical messengers
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8
Q

Dyneins and Kinesins

A
  • The microtubule railway that carry products up and down the length of the neuron
  • Dyneins carry recycled vesicles and chemical messengers towards the cell body
  • Kinesins do the same but towards the axon terminals
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9
Q

Membrane Potential

A
  • Plasma membrane of the cell is polarized
  • Separation of opposite charges across the membrane
  • Due to differences in concentration and permeability of certain ions
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10
Q

Resting Membrane Potential

A
  • Constant charge in excitable tissues at rest
  • Created by permeability (ion channels), electrical gradient(charges drawn to each other), and concentration gradient (high to low concentration)
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11
Q

Na and K Nernst Potentials

A
  • Na = 60 mV
  • K = -89 mV
  • If only Na were allowed to move in or out of the cell, it would reach equilibrium at 60 mV. Same for K and -89. K’s equilibrium is so low because of opposing electrical and concentration gradients
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12
Q

How Membrane Potential is Maintained

A
  • Impermeable cell membrane
  • Na/K pumps
  • K leak channels open periodically and let K out of the cell
  • Anions (negative proteins) are too large to move out of the cell
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13
Q

Membrane States

A
  • Polarization: When the membrane potential is other than 0 mV
  • Depolarization: membrane potential is greater than -70mV and is rising.
  • Repolarization: When membrane potential is coming back down
  • Hyperpolarization: When membrane potential is below -70 mV
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14
Q

Graded Potential

A
  • initiated by mechanical, chemical, or electrical stimulus
  • Initiated in dendrites
  • Local, die away quickly
  • Can summate
  • The strength of a graded potential depends on stimulus strength
  • Can be excitatory or inhibitory (depolarizing or hyperpolarizing)
  • No refractory period
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15
Q

Action Potentials

A
  • Brief, rapid, large changes in membrane potential (100 mV)
  • Na and K gates open, Na floods the cell
  • Do not decrease in strength as they move
  • Na channels need time to reset after being opened (see Sl. 35)
  • Has 4 phases
  • Na/K pumps restore resting potential after
  • All or none, self propagating
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16
Q

Absolute vs. Relative Refractory Period

A
  • Absolute refractory period is where a second AP is not possible even with a large stimulus
  • Relative refractory period is where a second Ap is possible, but a greater than normal stimulus is required
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17
Q

Neuron At Rest

A
  • Resting Membrane potential is -70 mV
  • Na is moving out and K is moving in at a steady rate
  • The neuron has reached equilibrium
18
Q

Depolarization

A
  • Graded potentials reach threshold (-55 mV)
  • This triggers Na gates to open, and Na floods the cell while K stays in causing charges of +30 mv
  • Eventually, Na gates close and K gates open
  • K rushes out of the cell
19
Q

Repolarization

A
  • K rushing out of the cell causes the membrane potential to lower, repolarizing the cell
  • K gates are slow to close, so they may overshoot with how much they let out
20
Q

Hyperpolarization

A
  • When K gates overshoot, the charge lowers below resting potential, getting down to -80mV
  • This means that an additional 10 mV of graded potential are required to fire the neuron again. This is the refractory period
  • Na/K pumps gradually restore concentration gradients. Na is pumped out of the cell, and K is pumped in
21
Q

Types of Propagation - Myelinated vs Unmyelinated

A
  • Contiguous conduction: unmyelinated, APs spread along every portion of the membrane, slow and good for short distances
  • Saltatory conduction: myelinated, APs jump from node to node, rapid (approx. 50x faster), good for long distances
22
Q

Factors That Affect Nerve Conduction

A
  • Neuron diameter
  • Myelination
  • Temperature
23
Q

A-delta vs C fibers

A
  • A-delta: Myelinated, large, fast, carry important signals such as pain receptors and motor neurons
  • C fibers: Unmyelinated, thin, slow, carry less urgent messages such as pH receptors
24
Q

Types of Glial Cells

A
  • Schwann Cells: Found in the PNS, make up myelin, can communicate and come together to preform some level of nerve repair
  • Oligodendrocytes: Found in the CNS, inhibit cell repair except in their embryonic state because we are so bad at it that it would just cause worse problems
25
Q

Synapse

A
  • Junction between two neurons
  • Primary means of neuron communication
  • Presynaptic neuron conducts AP toward the synapse
  • Synaptic knob contains synaptic vesicles
  • Synaptic vesicles store neurotransmitter
  • Synaptic cleft is the space between neurons where NTs are released
  • Postsynaptic neuron is excited or inhibited by these NTs, and its AP is conducted away from the synapse
  • Synaptic delay can be .2 to .5 msec
26
Q

Convergence and Divergence

A
  • Convergence: many axons unput into one dendrite
  • Divergence: one axon inputs into many dendrites
  • These are not mutually exclusive
27
Q

Steps For NT Release and Effects

A
  • AP arrives at terminal end
  • Voltage-gated Ca moves into knob
  • Ca binds to synaptotagmin
  • Synaptotagmin stimulates SNARE proteins, which ensnare vesicles, causing NT release
  • NT migrates across the synapse
  • NT binds to receptor site, opening ion gates and triggering graded potentials
  • These graded potentials are excitatory if the receptor is an Na channel and inhibitory if it is a K channel
  • These receptor sites can be Ionotropic Receptors (ion channels), or Metabotropic Receptors (2nd messenger activation channels)
28
Q

EPSP vs IPSP

A
  • Excitatory Post-Synaptic Potential
  • Inhibitory Post-Synaptic Potential
29
Q

Factors That Affect Size of Post Synaptic Potential

A
  • Calcium levels (fatigue)
  • NT levels
  • Desensitization or hypersensitization
  • Pre-synaptic inhibition or facilitation
30
Q

Spatial Summation

A
  • Summation of many different EPSPs occurring at different locations on a dendrite at the same time
31
Q

Temporal Summation

A
  • Summation of many EPSPs occurring at the same location on the dendrite over a very short period of time
32
Q

Pre-synaptic Facilitation / Inhibition

A
  • Neuron A is the presynaptic facilitator/inhibitor
  • Neuron B is the presynaptic neuron
  • Neuron C is the postsynaptic neuron
  • Neuron A releases NTs into neuron B that will either increase or decrease its NT release into neuron C
33
Q

Neurotransmitters

A
  • Vary from synapse to synapse
  • Same NT is always released at a particular synapse, and quickly removed from the synaptic cleft
  • Some common NTs include Ach, dopamine/serotonin, norepinephrine/epinephrine, histamine, glutamate, and GABA
34
Q

Neuropetides

A
  • Larger than NTs
  • Take longer to break down/remove from synaptic cleft, causing longer responses
  • Ex. Substance P, which causes the pain response
35
Q

Acetylcholine (Ach)

A
  • Cholinergic receptors
  • Parasympathetic
  • Muscarinic and Nicotinic receptors
  • Broken down by acetylcholinesterase
  • Associated with Alzheimer’s disease
36
Q

Catecholamines

A
  • Epinephrine and Norepinephrine
  • Sympathetic
  • Affect BP, HR, consciousness, mood, and attention
  • Adrenergic and noradrenergic receptors
37
Q

Seratonin

A
  • Excitatory on muscle control
  • Inhibitory on sensory mediation
  • Affects mood, anxiety, wakefulness
38
Q

Ways a Drug Can Impact the Synapse

A
  • Altering the synthesis, transport, storage, or release of NTs
  • Modifying NT interaction with the postsynaptic membrane
  • Influencing NT reuptake or destruction
  • Replacing deficient NTs with substitutes
39
Q

Agonistic vs Antagonistic Drug Interactions

A
  • Agonists mimic NTs when they bind and amplify that NT’s effect
  • Antagonists bind but don’t activate receptor sites, blocking them
40
Q

Peak of AP mV

A

+30 mV

41
Q

Threshold Potential mV

A

-55 mV

42
Q

Neurotoxin

A
  • May replace or mimic certain NTs
  • May affect NT release or reuptake
  • May affect NT interaction with postsynaptic membrane

NRSG 203 (18 decks)

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