Nerve & Synapse Flashcards
(129 cards)
1
Q
What makes up the CNS
A
The brain and spine
2
Q
What is the peripheral nervous system?
A
Sensory neurons, motor neurons
3
Q
What is the autonomic nervous system?
A
The autonomic nervous system is a component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal
4
Q
What is the enteric nervous system?
.
A
The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract
5
Q
of neutrons in nervous system
A
100 billion
6
Q
Neurons are _________ cells
A
Electrical
7
Q
Communications between neurons take place at sites known as
A
At specialized sites called synapses
8
Q
of synapses
A
Hundreds of trillions
9
Q
Do neurons have a specific morphology?
A
No, neurons come in an enormous range of shapes and sizes
10
Q
What are the characteristic structures of the neurons?
A
Cell body (soma), dendrites, a single axon, presynaptic terminal
11
Q
What are the things sticking off of the soma called and what is their use?
A
Generic term is processes, aka dendrites, they act like antennas for the neuron
12
Q
What is the soma’s role
A
Keeps neurons alive
Nucleus
DNA
Protein synthesis
13
Q
What is the Axons role?
A
Extend from neurons to brain
Propagate signals
Few millimeters to more than a meter
14
Q
Information moves along the ___ and is received by neurons at the ____ through the ____
A
Axon, dendrites, synapses
15
Q
Describe the flow of information
A
Dendrites, cell body (soma), axon, next neuron (dendrites)
16
Q
Resting Membrane Potential
A
Difference in charge between the inside and outside of the cell
Created by concentration gradient
17
Q
At rest, the neuronal membrane is highly permeable to __ and less permeable to ____
A
K+, the other physiological ions
18
Q
Why is the resting membrane potential important for cells in general?
A
It is a form of potential energy, starting point for the electrical properties of neurons
19
Q
Where do K+ ions leak to?
A
Out of cell
Down the concentration gradient
20
Q
The concentration of ____ inside the cell is high and ___ outside the cell
A
k+, low
21
Q
What creates the electrical gradient?
A
Accumulation of unpaired negative ions after sodium leaks
22
Q
What creates the electrical gradient?
A
Accumulation of unpaired negative ions after sodium leaks
23
Q
What does electrical gradient result in?
A
Pull K+ ions back into the cell
24
Q
When chemical and electrical gradients are equal, the system is _________
A
At equilibrium
25
Membrane potential at equilibrium is described by the
Nernst equation
| Eion= (2.3RT/zF)(log(ion/ion)
26
Why is the membrane permeable to K but not other physiological ions?
Because of Potassium leak channels (proteins that form pores in membrane for K+)
27
____ makes the inside of the cell less negative, and ____ makes the inside of the cell more negative
depolarization and hyper-polarization
28
Ek (equilibrium potential for K+)
-90 mV
29
Why does the membrane potential never quite get to Equilibrium K?
Because Na leaks in, adding positive charges, keeping it above -90 mV
30
Leak channels are ___
Proteins that form K+ selective pores through the membrane
| Open at the resting membrane potential
31
What is membrane potential determined by?
Concentration gradients and relative permeability of membrane to different physiological ions
32
What maintains the sodium and potassium gradient and what is its source of Energy?
Sodium Potassium Pump, uses energy produced by ATP hydrolysis to pump sodium out and potassium in against their concentration gradients
33
Action potentials are ___ ____ that carry information through the Axons
Electrical impulses
34
Describe the general pattern of action potentials?
Action potentials usually start at the initial segment of the axon and then propagate down the length of the axon to the presynaptic terminals (like a wave)
35
Action potentials start at ________ propagate down _________ to ________
Action potentials start at the initial segment of the axon propagate down the length of the axon to the presynaptic terminals
36
What is an action potential?
is a transient depolarizing spike that moves down the axon
37
What determines the threshold level of an action potential?
The threshold is determined by the properties of ion channels in the axon membrane, especially a class of channels called voltage-gated sodium channels
38
The AP is initiated when the ____ ___ depolarizes to a ___ level
membrane potential, threshold
39
The depolarizing phase of the action potential is caused by
sodium ions flowing into the cell through voltage-gated sodium channels
40
What are the three critical properties of voltage-gated sodium channels?
1) They are closed at the resting membrane potential, but open when the membrane depolarizes
2) They are selective for Na+
3) The open channel rapidly inactives, stopping the flow of Na+ ions
41
Where are voltage-gated sodium channels found, and what are the three states they can be found in?
closed, open, inactivated
42
___ channels are found everywhere on the neuron
K+ leak channels
43
What causes the sodium channels to reset?
The membrane potential has to reset to -70 mV
44
Depolarization of the membrane to threshold activates
a small fraction of sodium channels, which further depolarizes the membrane, resulting in activation of more sodium channels and so forth
45
What can be said of the amount of Na channels and Leak K channels on a particular segment of axon?
There are much more Na+ channels, so at peak action potential, the Na+ permeability swamps the resting permeability of K+ (which is why voltage shoots up)
46
At the peak of the actional potential the ___+ permeability ____ the resting permeability for __+
At the peak of the actional potential, the Na+ permeability swamps the resting permeability for K+
47
When do K gates channels open?
During the decline of the action potential, making it come down much faster as K moves out by leak channels and gated channels
48
What are the two factors that contribute to falling phase of AP
sodium channel inactivation
delayed activation of voltage-gated potassium channels
49
How do action potentials propagate down the axon?
It is caused by the spread of electrotonic currents from the site of the action potential, which excites adjacent regions of axon (+30 mV of AP excites -70 of rest of neuron)
50
Action potential propagation is self-regulating/terminating
Action potential propagation is self-regulating
51
Why doesn't the AP move backwards on the axon?
Because of the inactivated Na+ Channels
52
What is the absolute refractory period?
The Na channels are inactivated and the membrane is completely unexcitable. While the K channels are open, the membrane potential overshoots its resting level.
53
After an AP ___ ___ are inactivated and the membrane is ____
Sodium channels, unexcitable
54
Relative refractory period
Longer period where the voltage gated potassium channels are open and the membrane potential overshoots its resting level
axons are less excitable and is unlikely to fire an action potential (-70 mV)
55
Neurons send information by means of the
frequency and pattern of action potentials
56
T/F: Each action potential is an all-or-none event.
T
57
Molecular targets for naturally occurring neurotoxins
Sodium channels (AP cannot reach)
58
Sodium channels can be modulated by
tetrodotoxin, batrachotoxin, pyrethroid insecticides as well as scorpion and anemone toxins
59
What is slow pain conducted by (like after burning your hand on stove top)?
They are called c-fibers (0.5-2.0 meters/sec)
60
propagation rate of the action potential is proportional to
Axon diameter (The larger the diameter the faster the AP can move)
61
How squids solved the problem of how to send fast-moving signals
making giant axons, 1000 times fatter than our axons
62
How do vertebrate neurons solve the problem of small axons with high conduction velocity?
The axon are wrapped by an insulator called myelin (formed by Schwann cells and oligodendrocytes)
63
What is the main responsibility of the Myelin?
Myelin acts as an electrical insulator, enabling charge to travel farther and faster down the axon
64
Where is myelin made in the CNS and PNS respectively?
In CNS -> oligodendrocytes
| In PNS -> Schwann cells
65
What happens to signals in unmyelinated axons?
The signal leaks out and fades away over short distances
66
nodes of Ranvier
periodic gaps in myelin
67
What is usually found at nodes of Ranvier and why is it important?
Nodes of Ranvier has high concentration of voltage gated sodium channels, allowing the signal to REGENERATE at periodic intervals
68
Multiple sclerosis is caused by
loss of myelin
| Demyelinated region
69
What myelin forming cells are affected by MS?
Oligodendrocytes (impacts CNS)
70
What is white matter?
Regions of the brain and spinal cord that contain mostly myelinated axons.
71
Gray matter
comprises cell bodies, dendrites and synapses
72
Three main types of synapses
Axondendritic
Axosomatic
Axoaxonic
73
A single neuron may make synapses with many other neurons through
its BRANCHING axon
74
What happens when an AP reaches a branch (fork) on an axon?
A full AP goes down each branch
75
Two axodendritic synapses
spine and shaft synapse
76
What are the components of the synapse?
The presynaptic terminal, the synaptic cleft, and the postsynaptic spine
77
What occurs on the presynaptic Terminal
Activation of voltage-gated calcium triggers neurotransmitter release
78
What occurs on the postsynaptic spine
Ligand-gated ion channels are postsynaptic receptors for transmission at brain synapses
79
What are the specialized regions that appear darker on the electron micrograph of the postsynaptic spine?
Postsynaptic density
80
Fundamental steps of chemical synaptic transmission
1. The action potential invades the presynaptic terminal. Calcium channels open, resulting in Ca2+ influx into the terminal
2. Synaptic vesicles fuse with the presynaptic membrane, releasing the transmitter into the synaptic cleft.
3. Transmitter diffuses across the cleft and activates receptors in the postsynaptic membrane.
81
How do the vesicles release the neurotransmitter into the synaptic cleft?
The vesicle (which is made from phospholipid), fuse to the membrane and releases contents
82
Transmitter diffuses across the ______ and activates _____ in the _________ _____
Transmitter diffuses across the cleft and activates receptors in the postsynaptic membrane.
83
What occurs at the active zone
Calcium-dependent fusion of a synaptic vesicle at an active zone
84
The postsynaptic response to neurotransmitter is either an ______ or _______
excitatory postsynaptic potential (EPSP)
| inhibitory postsynaptic potential (IPSP)
85
What occurs at the active zone
Calcium-dependent fusion of a synaptic vesicle at an active zone
86
excitatory postsynaptic potential
which depolarizes the postsynaptic membrane
87
inhibitory postsynaptic potential
hyperpolarizes the postsynaptic membrane
88
What does Botox do?
Botox chews up the proteins that are part of vesicles fusion process, therefore muscles cannot get activated (no neurotransmitters)
89
What is the main excitatory neurotransmitter in the brain?
Glutamate
90
What glutamate receptors are activated when glutamate is released into the synaptic cleft?
AMPA and NMDA receptors
91
What is meant by ionotropic receptors?
This means that they are ion channels, that open in in response to binding of small molecules (ie neurotransmitters) to receptor sites on their external surfaces
92
Which receptors are responsible for the fast EPSP?
AMPA
93
What occurs in AMPA receptors
Glutamate binds to AMPA, allowing Na+ to flow into the postsynaptic spine
94
What does EPSP stand for and what is it?
Excitatory PostSynaptic Potential is a small, transient depolarization of the postsynaptic spine
95
How long are EPSPs?
20 msec (have to have enough EPSPs to depolarize within this window)
96
The depolarization caused by a single EPSP is ____ millivolts
> a few millivolts
97
What happens after the depolarization caused by a single EPSP?
Nothing, it is too small to depolarization the axon initial segment
98
How do EPSPs get around this to depolarize the initial segment?
From 50 to 100 EPSPs must sum at the initial segment to initiate an AP (they can come from multiple synapses acting in synchrony and/or from individual synapses (activated at high frequencies)
99
The simultaneous EPSPs can come from either
multiple synapses acting in synchrony and/or from individual synapses, activated at high frequencies
100
What are key properties of NMDA receptors?
At resting membrane potential, the pore is blocked by Mg2+ (depolarizing expels Mg2+, which allows pore to conduct)
The open pore is highly permeable to Ca2+ as well as MONOVALENT cations
101
At -70 mW almost all the synaptic current at an excitatory glutamate synapse is carried by ___ through
AMPA receptors
102
What happens when excitatory synapses are highly active?
They become stronger (ie the EPSPs become larger).
103
synaptic plasticity
Highly active excitatory synapses become stronger (i.e. the EPSPs become larger) and involve NMDA receptors
104
Long-term potentiation (LTP)
is a model of synaptic plasticity
105
High-frequency activity depolarizes the postsynaptic spine, resulting in the
removal of Mg2+ block of NMDA receptors and enabling them to conduct Ca2+
106
What is the high concentration of glutamate being toxic to neurons called?
Excitotoxicity
107
Why is high concentration of glutamate toxic?
Too much calcium goes into Neuron -> neuron apoptosis
108
What do neurons release when they die?
Release tons of glutamate, which in cases like strokes, kills surrounding neurons, even if they were not affected by the stroke
109
The main inhibitory neurotransmitter in the brain
is y-aminobutyric acid (GABA)
110
Where are inhibitory synapses found on the neighbouring neuron?
Shaft of dendrite
111
Do neurons change roles during lifetime (ie excitatory to inhibitory)?
No
112
What is the name of the postsynaptic receptor called for the IPSP?
GABA(a) receptor
113
The GABA receptor is an _______ receptor
ionotropic receptor
114
Activation of the GABA(A) receptor causes an influx of ___ which ....
Activation of the GABAA receptor causes influx of Cl-, which hyper-polarizes the postsynaptic membrane
115
A typical cortical neuron receives
thousands of synaptic inputs, some excitatory, others inhibitory
116
inhibitory inputs are often clustered on or near
the cell soma, where their inhibitory effect is maximal
117
Whether or not a neuron fires an action potential at any given moment depends on
the relative balance of EPSPs and IPSPs
118
What are metabotropic receptors (function + names)?
Activated by neurotransmitters, but do NOT form ION CHANNELS
G-protein coupled receptors, GPCRs
119
Glutamate synapses have ionotropic receptors (AMPA and NMDA receptors) or metabotropic glutamate receptors (mGluR’s) or both
both ionotropic receptors (AMPA and NMDA receptors) and metabotropic glutamate receptors (mGluR’s)
120
Activation of mGluR’s by glutamate relays a
- chemical signal to the inside of the postsynaptic neuron
| - generates a chemical signal (changes conformation), called a second messenger, inside the postsynaptic spine.
121
What are some things secondary messengers can do?
```
Active ion channels
Activate proteins (like protein kinase)
Activate transcription factors
```
122
What are some examples of neurotransmitters that mainly, or entirely interact with metabotropic receptors?
Dopamine, Serotonin, norepinephrine, endorphins (neuromodulators, because they change global neural states, influencing alertness, attention and mood)
123
neuromodulators
dopamine, serotonin and norepinephrine
| neuropeptides such as endorphins
124
What kind of effects do neuromodulators have?
Global, broad effects
125
Where are neuromodulator neurons usually found, and how does their effect reach the entire brain?
Usually found in brain stem (or midbrain nuclei), and their axons (that branch A TON), go throughout the whole brain
126
Neurons that release neuromodulators, axons project
diffusely throughout the brain
127
Neuromodulator systems are important targets for a
| such as
wide range drugs
| antidepressants
128
antidepressants such as Prozac affect
serotonergic transmission
129
antidepressants such as amphetamines, cocaine and other stimulants typically affect
dopamine and norepinephrine transmission
