Neurons And Action Potential Flashcards
1
Q
Parts of a Neuron
A
- Dendrites
- Cell body
- Nucleus
- Axon hillock
- Axon
- Axon terminals
2
Q
Types of Neuron
A
- Bipolar
- Semi-bipolar
- Multipolar
3
Q
Function of the Cell Body
A
Houses organelles and nucleus
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
5
Q
Function of the Axon
A
- Nerve fibers
- ## Conducts action potentials away from the cell body toward the axon terminals
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
7
Q
Function of Axon Terminals
A
- Where axons synapse “with other neurons or the effector tissue
- Release chemical messengers
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
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
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)
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
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
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
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
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
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
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
Synapse
- 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
Convergence and Divergence
- Convergence: many axons unput into one dendrite
- Divergence: one axon inputs into many dendrites
- These are not mutually exclusive
27
Steps For NT Release and Effects
- 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
EPSP vs IPSP
- Excitatory Post-Synaptic Potential
- Inhibitory Post-Synaptic Potential
29
Factors That Affect Size of Post Synaptic Potential
- Calcium levels (fatigue)
- NT levels
- Desensitization or hypersensitization
- Pre-synaptic inhibition or facilitation
30
Spatial Summation
- Summation of many different EPSPs occurring at different locations on a dendrite at the same time
31
Temporal Summation
- Summation of many EPSPs occurring at the same location on the dendrite over a very short period of time
32
Pre-synaptic Facilitation / Inhibition
- 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
Neurotransmitters
- 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
Neuropetides
- Larger than NTs
- Take longer to break down/remove from synaptic cleft, causing longer responses
- Ex. Substance P, which causes the pain response
35
Acetylcholine (Ach)
- Cholinergic receptors
- Parasympathetic
- Muscarinic and Nicotinic receptors
- Broken down by acetylcholinesterase
- Associated with Alzheimer's disease
36
Catecholamines
- Epinephrine and Norepinephrine
- Sympathetic
- Affect BP, HR, consciousness, mood, and attention
- Adrenergic and noradrenergic receptors
37
Seratonin
- Excitatory on muscle control
- Inhibitory on sensory mediation
- Affects mood, anxiety, wakefulness
38
Ways a Drug Can Impact the Synapse
- 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
Agonistic vs Antagonistic Drug Interactions
- Agonists mimic NTs when they bind and amplify that NT's effect
- Antagonists bind but don't activate receptor sites, blocking them
40
Peak of AP mV
+30 mV
41
Threshold Potential mV
-55 mV
42
Neurotoxin
- May replace or mimic certain NTs
- May affect NT release or reuptake
- May affect NT interaction with postsynaptic membrane
