Nervous system Flashcards
1
Q
What are the two branches of the nervous system?
A
Central nervous system
Peripheral nervous system
2
Q
What constitutes the central nervous system? (2)
A
the brain
spinal cord
3
Q
What constitutes the peripheral nervous system? (3)
A
Motor output (efferent):
-Somatic nervous system: motor neurons (efferent fibers)
-Autonomic nervous system (in which we can find the enteric nervous system)
-Sensory neurons- (afferents fibers)
4
Q
True or false: The sensory information can not come from inside of the body, only the outside environment.
A
False: inside and outside
5
Q
What are the 2 reasons for which neurons are very specialized cells?
A
-They are electrical cells (enormous electrical properties and diverse)
-They communicate to each other (synapses)
6
Q
What are synapses?
A
Place where communication between neurons takes place
7
Q
What is the function of dendrites?
A
Dendrites are branching structures that receive
signals from outside/internal environment or other neurons.
8
Q
What is the function of the soma?
A
The soma is the cell body of a neuron that contains the nucleus and other organelles.
9
Q
What is the function of an axon?
A
An axon is a long, thin structure that carries signals away from the cell body to other neurons.
10
Q
What is the difference between afferent and efferent fibers?
A
Afferent fibers are sensory neurons that carry signals towards the central nervous system, while efferent fibers are motor neurons that carry signals away from the central nervous system.
11
Q
True or flase: the more dentrites there are, the more the inputs, the more synapses
A
true
12
Q
What is the resting membrane potential?
A
The inside of a typical neuron is -60 to -70 mV, compared to the outside.
13
Q
What does the resting membrane potential mean?
A
That there is a small excess of negatively charged ions inside the cell
14
Q
What are the 2 things causing the resting membrane potential?
A
-concentration gradients for the various physiological ions
-the selective permeability of the resting membrane to K+ ions
15
Q
What are the 4 ions focused in the class?
A
Na+
K+
Cl-
A- (anions, ex: amino acids)
16
Q
What is the main ion that the neuronal membrane is highly permeable to at rest?
A
K+
17
Q
What happens to K+ ions at rest?
A
They leak out of the cell, down their concentration gradient, leaving behind impermeant, negatively charged ions.
18
Q
What is the effect of unpaired negative ions inside the cell on the electrical gradient?
A
It creates an electrical gradient that tends to pull K+ ions back into the cell.
19
Q
What is the Nernst equation used for?
A
It is used to calculate the equilibrium potential of an ion across a membrane.
20
Q
What is the main factor determining the neuron resting membrane potential ?
A
The equilibrium potential for K+
= -90 mV
21
Q
What are leak channels?
A
Leak channels are proteins that form selective pores through the membrane and are open at the resting membrane potential.
22
Q
How does the resting membrane potential compare to the equilibrium potential of K+?
A
It’s a bit more positive due to a small inward leak of Na+.
23
Q
What is the equilibrium potential of Na+?
A
+70 mV
24
Q
What explains the -70mV of the resting potentials (and not -90mV like Ek) ?
A
The membrane is REALLY permeable to K+ and wants to push towards -90mV.
The membrane is a LITTLE permeable to Na+ and it wants to push towards +70mV.
Which creates a balance at around -70mV.
25
What maintains the sodium and potassium gradients?
The sodium and potassium gradients are maintained by the sodium-potassium pump, which uses the energy produced by ATP hydrolysis to pump sodium out and potassium in against their concentration gradients.
26
What would happen if the Na+/K+ pump don't work?
Potential slowly flows to 0
27
What are action potentials?
A brief electrical impulses that propagate information from one region of the nervous system to another.
A transient depolarizing spike that moves down the axon.
28
Where do action potentials usually start?
at the initial segment of the axon
29
Action potentials usually start
at the _________________ of the axon and then propagate down the length of the axon to the ________________________.
initial segment
presynaptic terminals
30
What is the threshold potential?
The membrane potential level at which an action potential is initiated.
= -50 mV
31
True or false: We produce an action potential at -49mV.
False, we haven't the threshold.
32
What are voltage-gated sodium channels?
A class of ion channels that are closed at the resting membrane potential but open when the membrane depolarizes
33
The reach of the threshold is determined by....
voltage-gated sodium channels
34
What is the definition of depolarize?
make more positive
35
What is the definition of hyperpolarize?
make more more negative
36
What causes the rising phase of the action potential?
Sodium ions flowing into the cell through voltage-gated sodium channels.
37
What are the 3 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 inactivates, stopping the flow of Na+ ions.
38
Where are voltage-gated sodium channels concentrated?
in the axon
39
What is the mechanism of the rising phase of the action potential?
It is a regenerative process that results from depolarization of the membrane to threshold,
activating a small fraction of sodium channels, which further depolarizes the membrane, resulting in activation of more sodium channels, and so forth.
-This positive feedback mechanism results very rapidly in maximal activation of sodium channels, a large sodium influx, and depolarization of the membrane from the resting level to a new level, near ENa.
-Inactivation terminates the sodium influx, causing the membrane to relax back to its original resting level.
40
Are the concentration gradients changing significantly during the action potential?
No, just a tiny imbalance
41
How does the density of voltage-gated sodium channels compare to the density of leak potassium channels in the axon membrane?
The density of voltage-gated sodium channels is much higher than the density of leak potassium channels.
42
What are the 2 factors contributing to the falling
phase of the action potential?
- sodium channel inactivation
- the delayed activation of voltage-gated potassium channels.
43
What is the mechanism of the falling phase of the action potential?
The inactivation of the Na+ VG channels stops the Na+ influx, causing the relaxation of the membrane to resting level.
After a delay, VG K+ open and they are at their peak during the falling phase, giving additional pathways for K+ to leave the cell and hence, repolarize the membrane.
44
True or false: the longer the AP, the more you can send per second.
False, the shorter the AP, the more you can send per second.
45
What happens to the sodium and potassium gradients when the neuron is firing a lot of action potentials? (pump)
They run down faster.
46
What happens if the Na+/K+ stops?
AP won't stop completely. will run for a while but eventually concentration gradients will run down and neuron can't fire AP.
47
What is the cause of action potential propagation?
Spread of electrotonic currents from the site of the action potential, which excites adjacent regions of axon.
48
Why doesn't the charge flow in the direction it came from? Why is the action potential unidirectional) (name not explanation)
absolute refractory period.
49
What is the absolute refractory period?
For a few milliseconds after the action potential, the sodium
channels are inactivated and the membrane is completely
unexcitable.
50
What is the difference between the absolute and relative refractory periods?
During the absolute refractory period, the axon is completely unexcitable.
Over a somewhat longer period, during which the voltage-gated potassium channels are open, the membrane potential overshoots its resting level. During this relative refractory period, the axon is less excitable and is unlikely to fire an action potential. (more far from the threshold)
51
How do neurons send information? (intensity of stimuli)
Neurons send information by means of the frequency and pattern of action potentials.
Intensity of stimuli is directly proportional to the frequency of the action potentials.
52
What are the molecular targets for naturally occurring neurotoxins?
VG sodium channels
53
Puffer fish make ___________,
an extremely potent __________ of sodium channels.
Phyllobates frogs secrete ____________, a powerful sodium channel ___________. Sodium channels are also modulated by pyrethroid ___________, as well as scorpion and __________ toxins.
tetrodotoxin
inhibitor
batrachotoxin
activator
insecticides
anemonae
54
What are some local anesthetics that block Na+ channels? (4)
Lidocaine, Benzocaine, Tetracaine, Cocaine.
55
What are some antiepileptic agents that block Na+ channels? (2)
Phenytoin (Dilantin)
Carbamazepine (Tegretol)
56
What is myelin?
An insulator that wraps around axons to increase conduction velocity.
57
The propagation rate of the action potential is proportional to axon ______________.
diameter
58
What is the function of nodes of Ranvier?
Nodes of Ranvier are periodic gaps in myelin that contain very high concentrations of voltage-gated sodium channels, enabling the signal to be regenerated at periodic intervals.
59
What is the difference between myelinated and unmyelinated axons?
myelinated axons impulse propagate a lot faster.
60
What is saltatory conduction?
The impulses fades through the axon and then gets a sudden boost, and fades, and gets another boost, etc allowing it to move faster.
61
What is the myelin called in the PNS and in the CNS?
PNS: Schwann cells
CNS: oligodendrocytes
62
What is multiple sclerosis?
Autoimmune disorder where the immune system degrades the myelin.
63
What is white matter?
White matter corresponds to regions of the brain
and spinal cord that contain mostly myelinated axons.
Myelin has a white appearance.
64
What is gray matter?
Gray matter comprises cell bodies, dendrites, and synapses.
65
What are the three main types of synapses?
axodendritic
axosomatic
axoaxonic
66
Can a single neuron make synapses with many neurons?
A single neuron, through its branching axon may make synapses with many other neurons.
67
What are presynaptic vesicles?
Presynaptic vesicles are membrane-bound structures within the presynaptic terminal that store neurotransmitters.
68
What is the active zone in a synapse?
The active zone is a specialized region within the presynaptic terminal where synaptic vesicles release neurotransmitters.
69
Describe the synaptic cleft in a synapse.
The synaptic cleft is a tiny gap or space between the presynaptic terminal and the postsynaptic membrane. Neurotransmitters are released into this gap, and they must diffuse across it to bind to receptors on the postsynaptic neuron.
70
What is the postsynaptic density (PSD), and what is its function?
A complex protein structure located on the postsynaptic membrane of a synapse. It contains receptors and signaling molecules that receive and process neurotransmitter signals
71
What type of channel is activated when the AP arrives at the PS terminals?
voltage-gated calcium channels
72
What do the activation of voltage-gated calcium channels trigger?
neurotransmitter release
73
What type of channels are found on the postsynaptic spine?
Ligand-gated ion channels
74
What are the 3 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 transmitter into the synaptic cleft.
3. Transmitter diffuses across the cleft and activates receptors in the postsynaptic membrane.
75
How does calcium (Ca2+) function in synaptic transmission?
acts as a biochemical signal that triggers a series of biochemical events in the presynaptic terminal, ultimately leading to the fusion of synaptic vesicles with the cell membrane.
76
What happens to do the vesicles once they have been used?
gets recycled and re-used
77
What are the 2 possible responses to neurotransmitter?
- excitatory postsynaptic potential, (EPSP) which depolarizes the postsynaptic membrane
-inhibitory postysnaptic potential (IPSP), which hyperpolarizes the postsynaptic membrane
78
What is the main excitatory neurotransmitter in the brain?
glutamate
79
What are the two primary types of ionotropic glutamate receptors involved in rapid excitatory synaptic transmission?
AMPA receptors
NMDA receptors
80
What are AMPA receptors and NMDA receptors, and what distinguishes them as ionotropic receptors?
AMPA receptors and NMDA receptors are ionotropic receptors. They are ion channels that open in response to the binding of small molecules, such as neurotransmitters, to receptor sites on their external surfaces.
81
Which type of receptor is responsible for generating the "fast" EPSP (Excitatory Postsynaptic Potential) at excitatory synapses?
AMPA receptors
82
What is the EPSP (Excitatory Postsynaptic Potential), and how would you describe its characteristics in terms of depolarization?
The EPSP is a small, transient depolarization of the postsynaptic spine. In typical brain synapses, the depolarization caused by a single EPSP is greater than a few millivolts and lasts for around 20 milliseconds.
83
Why is the depolarization caused by a single EPSP usually too small to depolarize the axon initial segment to threshold?
because it's a relatively small and brief change in membrane potential.
84
How many EPSPs, on average, are needed to initiate an action potential at the axon initial segment, and how can they sum together to achieve this?
From 50 to 100 EPSPs must sum at the initial segment to initiate an action potential. These near-simultaneous EPSPs can result from multiple synapses acting in synchrony and/or from individual synapses activated at high frequencies.
85
What is a key property of NMDA receptors at resting membrane potentials, and what prevents them from conducting ions under these conditions?
NMDA receptors have their pores blocked by Mg2+. This Mg2+ block prevents the receptors from conducting ions.
86
What happens to NMDA receptors when the postsynaptic membrane is depolarized, and how does this affect ion conduction?
Depolarization of the postsynaptic membrane expels Mg2+ from NMDA receptors, enabling their pores to conduct ions. This depolarization allows for the flow of a substantial Ca2+ current through NMDA receptors in addition to monovalent cations.
87
How does synaptic plasticity, involving NMDA receptors, affect the strength of highly active excitatory synapses?
Highly active excitatory synapses become stronger, meaning the EPSPs become larger. This process is called synaptic plasticity, and NMDA receptors are involved in mediating this phenomenon.
88
What is long-term potentiation (LTP), and how is it related to NMDA receptors?
Long-term potentiation (LTP) is a model of synaptic plasticity where high-frequency activity depolarizes the postsynaptic spine, removing the Mg2+ block of NMDA receptors. This enables NMDA receptors to conduct Ca2+. As a result, EPSPs are larger for hours after the induction of LTP.
89
What is the phenomenon of excitotoxicity likely to occur, and how is it related to NMDA receptors?
High concentrations of glutamate are toxic to neurons.
This phenomenon, called excitotoxicity, is thought to
involve calcium influx through NMDA receptors.
90
Excitotoxicity is likely to contribute to...
neuronal degeneration after stroke and in some neurodegenerative diseases.
91
What ions primarily carry the synaptic current at an excitatory glutamate synapse when the membrane is at a resting potential of -70 mV, and what change in the postsynaptic membrane potential leads to a substantial flow of Ca2+ through NMDA receptors?
At a resting potential of -70 mV, almost all the synaptic current at an excitatory glutamate synapse is carried by Na+ through AMPA receptors. When the postsynaptic membrane is depolarized, this change in membrane potential allows a substantial Ca2+ current to flow through NMDA receptors.
92
What does an inhibitory synapse do?
Releases a neurotransmitter that will hyperpolarize the next neuron which will bring it further away from the threshold.
93
What is the main inhibitory neurotransmitter in the brain? What is the postsynaptic receptor responsible for the IPSP called?
Y-aminobutyric acid (GABA)
GABAa receptor
94
The GABAa receptor is an __________ receptor. Activation of the GABAa receptor causes influx of ______, which ___________ the postsynaptic membrane.
ionotropic
Cl-
hyperpolarizes
95
What is the mechanism of pharamalogical drugs like benzodiazepines (Valium, Xanax), barbiturates (phenobarbital, pentobarbital) and ethanol ?
They bind to GABAa receptor and potentiate the receptor, meaning they make the receptor more sensitive to GABA, which enhances the inhibition.
(that's why it makes us sleepy)
96
True or false: Barbiturates are much stronger than benzodiazepines.
True
97
What is the message given by an action potential? (3 things)
-pattern
-frequency
-timing
of an action potential
98
What determines whether a post-synaptic neuron fires an action potential at any given moment?
The relative balance of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) determines whether a neuron fires an action potential at any given moment.
99
True or false: a neuron can be both excitatory and inhibitory?
False, a neuron is either excitatory or inhibitory. It either releases Glutamate or GABA, not both.
100
True or false: Inhibitory neurons have excitatory synapses.
True, they need an action potential to communicate their inhibition (neurotransmitter).
101
If inhibition stops completely, we could risk having...
an electrical storm- epilepsies
102
Metabotropic receptors are receptors for __________ but they are not ______________.
neurotransmitters
ion channels
103
What are the 3 type of receptors found in Glutamate synapses?
ionotropic receptors:
-AMPA receptors
-NMDA receptors
-metabotropic glutamate receptors (mGluR’s)
104
What does the activation of mGluRs by glutamate in a postsynaptic neuron generate?
generates a chemical signal, known as a second messenger, inside the postsynaptic spine
105
What cellular proteins can be activated by second messengers generated through the activation of mGluRs by glutamate?
a range of cellular proteins, including ion channels, protein kinases, and transcription factors.
106
Explain the synthesis of second messengers?
Upon binding the neurotransmitter, mGluRs change their configuration which allows to initiate biochemical sequences involving multiple proteins (inclusing G-protein) allowing the synthesis of second messengers, which build up in the cell and then diffuse.
107
What is the role of kinase proteins? (once activated by second messengers)
Kinase proteins phosphorylate target proteins to activate them.
108
What is the role of transcription factors? (once activated by second messengers)
proteins that control gene expression, regulate transcription
109
How long does the activation of second messengers typically last?
The duration of second messengers' activation in cellular signaling is usually very long, often on the order of seconds to minutes to hours. They are slow to turn on and slow to turn off.
110
What are mGluRs and GABAB receptors?
The metabotropic glutamate and
GABA receptors
111
What is the term used for neurotransmitters that interact mainly with metabotropic receptors and modulate global neural states rather than fast neural information flow?
Neuromodulators:
Neurotransmitters like dopamine, serotonin, norepinephrine, and neuropeptides such as endorphins are often referred to as neuromodulators because they modulate global neural states like alertness, attention, and mood.
112
Where do neurons that release neuromodulators often originate, and how do their axons project throughout the brain?
Neurons that release neuromodulators often originate in small brainstem or midbrain nuclei, and their axons project diffusely throughout the brain to influence neural states on a global level.
113
Why are neuromodulator systems important targets for various drugs, and what are some examples of drugs that affect these systems?
Neuromodulator systems are important drug targets because they can influence mood and neural states.
114
Antidepressants like Prozac affect __________ transmission, while stimulants like amphetamines and cocaine typically affect _________ and ______________ transmission.
serotonin
dopamine
norepinephrine
