intro to the nervous system Flashcards
1
Q
what is the CNS composed of?
A
brain + spinal cord
2
Q
what is the PNS composed of?
A
all sensory and motor neurones across our body
3
Q
what is the autonomic nervous system?
A
outputs from its fibers are directed to the hear and other internal organs (involuntary)
4
Q
what are efferent fibers?
A
motor neurons
5
Q
what are afferent fibers?
A
sensory neurons
6
Q
how many neurons compose the nervous system?
A
100 billion
7
Q
what are neurons
A
they are electrical cells
8
Q
how do neurons talk to each other?
A
communication occurs are the synapses, a specialized site in the cell
9
Q
what is the shape and size of a neuron?
A
they come in multiple and various shapes and sizes which are all extremly complex
10
Q
what are the common morphologic elements found in all neurons?
A
- cell body (soma)
- dendrites (branches)
- axon (single)
11
Q
what can the branching of a neuron say about that specific neuron?
A
the greater the branching the greater the input for that neuron will/can be
12
Q
can there be small branches found at the ends of the axons?
A
yes, these act with specialized structures of the presynaptic terminals
13
Q
how does information go across a neuron to another?
A
the output is given to the dendrite of an adjacent neuron and becomes the input of that neuron which passes through the cell body into the axon which can then transfer it as an output to presynaptic terminals or to dendrites of other neurons
14
Q
what is the typical resting potential of a neuron?
A
between -60 and -70 mV
15
Q
what is the negative charge of the resting potential caused by?
A
due to the small excess of negative ions inside the cell
16
Q
how is the resting membrane potential of neurons created?
A
by the concentration gradients of various physiological ions
potassium is high on the inside and strives to exit the neuron, Chloride and sodium are high on the outside and want to come in
17
Q
then why is their a slighlt negative imbalance?
A
when the membrane is at rest, it is more permeable to potassium than to the other ions allowing to flow out (selective permeability of the membrane)
18
Q
what happens when K+ leaks out of the membrane?
A
it leaves behind impermeant, negatively charged ions which give the negative membrane potential
19
Q
why does not all the K+ exit the cell due to its higher permeability?
A
the accumulation of unpaired negative ions will cause for an electrical gradient to pull back k+ into the cell
20
Q
what happens when the chemical and electrical gradient of the cell are equal?
A
the system is in equilibrium and so is the membrane potential
21
Q
what is the membrane potential at equilibrium described by?
A
Nernst equation
22
Q
what is the equilibrium potential for K+
A
-90 mV
23
Q
what is the resting permeability to k+ caused by? how does that happen?
A
leak channels
they form k+ selective pore through the membrane
24
Q
when are the K+ leak channels open?
A
they are open all the time, however ions can pass through at resting membrane potential
25
why is the resting membrane which is permeable to K+ at -70 mV rather than -90 mV?
-each ion has an equilibrium potential that is determined by its charges and internal/external concentration, hence if the equilibrium potentials for each ion is calculated this is how the -70 is obtained
26
what other ion leaks in the membrane and in what direction?
very small leakage for Na inwards
27
what is the membrane potential determined by?
concentration gradients and relative permeability
28
which of the 2 can change more? relative permeability or concentration gradients?
relative permeability
29
which relative permeability makes the greatest contribution to the membrane potential?
the dominant permeability, hence the permeability for potassium
30
how are the sodium and potassium gradients maintained?
by the Na-K-pumps
31
what type of energy is used by the Na-K pump?
energy produced by ATP hydrolysis
32
what is the net movement that results from Na-K pumps?
3 Na outwards
| 2 K+ inwards
33
what is the action potential?
it is the brief potential impulse that causes for axons to propagate info from one region of the NS to another
34
where do action potentials usually start off?
initial segment of the axon
35
where do action potentials end?
they propagte down the length of the axon and into presynaptic terminals
36
what is the action potential?
it is a transient depolarizing spike that moved swn the axon
37
at the action potential peak, what does the membrane potential approach?
Ena
38
when is the action potential initiated?
when the membrane potential depolarizes to a threshold level
39
what determines the threshold?
the properties of ion channels in the axon membrane, especially the voltage gated sodium channels
40
what is the depolarizing phase of the action potential cased by?
the sodium ions flowing into the cell through the voltage gated channels
41
what are the 3 critical properties of the sodium channels?
- closed at membrane potential, open when it depolarizes
- selective for Na+
- the open channel rapidly inactivates stopping the flow of Na+ ions
42
what type of process is the rising phase of the action potential?
a regenerative process
43
what positive feedback mechanisms is caused by depolarization?
depolarization to the threshold activates a small fraction of Na channels which further depolarizes the membrane resulting in the activation of more sodium channels
44
what does the positive feedback mechanism result in?
maximal activation of the sodium channel, a large sodium influx, and depolarization of the membrane from resting to new level
45
the density of the which higher?
| leak potassium channels or voltage gated sodium
the density of the voltage gated sodium channels is higher
46
what factors contribute to the falling phase of the action potential?
- sodium channel inactivation
| - the delayed activation of voltage gated potassium channels
47
when does sodium and potassium gradientrun down faster?
when the neuron is firing lots of action potentials because the pumps have to keep up with the neuronal activity
48
what is the propagation of the action potential caused by?
the spread of electronic currents from the site of the action potential which excites adjacent regions in the axon
49
why does the sodium not go back the other way?
since the voltage gated channels inactivate and don’t open again until the membrane returns to resting potential its allows for the impulse to move in only one direction
50
what is the period where sodium channels are completely unexcitable called?
the absolute refraction period
51
what happens during the absolute refraction period?
the axon is less excitable and is unlikely to fire an action potential
52
how could you describe the function of action potentials?
all or none event
53
how do neurons send information
by means of the frequency and pattern of the action potentials
54
sodium channels are the molecular targets for what?
naturally occuring toxins
- tetrodotoxin in pufferfish
- batrachotoxin in phyllobate frogs
- scorpions, anemonae, insecticides
55
what can block sodium channels?
therapeutical drugs such as local anesthetics and antiepiletic drugs
56
what feature of action potentials is important for survival?
the rapid propagation of the action potential
57
what strategry was adopted by squids to ensure rapid propagation of the action potential?
their body developped an axon 1000 times fatter than our axons
58
why does having a fatter axon improve the rate of propagation?
the rate of the action potential is proportional to the diameter of the axon
59
what did vertebrae neurons accomplish to have small axons with a high conductance velocity?
the axons are wrapped with myelin
60
what is myelin formed with?
schwann cells (PNS) and oligodendrocytes in the CNS
61
how does myelin function?
it acts as an electrical insulator, enabling electrotonic currents to travel farther and faster down the axon
62
what periodically interrupts myelin?
nodes of ravier
63
what is contained in the nodes of ravier?
these are regions of bare axons that contrain very high concentrations of voltage gated sodium channels
64
what do the nodes of ravier enable?
they enables that the signal gets regenerated at periodical intervals
65
are myelinated axons generally longer or shorter?
longer
66
what is a commun immune disease caused by the loss of myelin?
multiple sclerosis
67
which matter contains the most myelinated axons?
white matter
68
what matter is comprised of cell bodies, dendrites and synapses?
gray matter
69
what are the 3 main synapses?
axodendritic
axosomatic
axoaxonic
70
generally what type of synapses are spine synapses?
excitatory synapses
71
generally what type of synapses are shaft synapses?
inhibitory synapses
72
can a cell only make a single or multiple synapses with other neurons?
multiple, due to the branching axon
73
what is the purpose of presynaptic vesicles?
they serve as the back up vesicles and are stored in the presynaptic terminal
74
what are the active zones found in presynaptic terminals
the active zones contain vesicles that are release to release the chemicals into the synaptic cleft
75
what is the name of the dark regions found in the postsynaptic spine?
these are the postsynaptic density which are regions with high protein concentration
76
what is found between the presynaptic terminal and the post synaptic spine?
an extracellular space known as the synaptic cleft
77
what type of channel is found in the presynaptic terminal?
voltage gated calcium channels
78
how do voltage gated calcium channels function?
Ca in < Ca out causing for gradient to move inwards
79
when are the voltage gated calcium channels open?
at resting membrane potential
80
what is the function of voltage gated calcium channels in the presynaptic terminal?
they trigger the release of neurotransmitters
81
what type of channel can be found in the postsynaptic spine?
ligand gated ion channels
82
ligand gated ion channels are receptors for transmission where?
at the brain synapses
83
what are the fundamental steps of chemical synaptic transmission?
1- the action potential invades the presynaptic terminal Ca moves inwards
2- synaptic vesicles fuse with the presynaptic membrane and release transmitters into the synaptic cleft
3- transmitters diffuse across the clef and activate receptors of the postsynaptic membrane
84
what can the postsynaptic response to a neurotransmitter be?
- excitatory postsynaptic potential
| - inhibitory postsynaptic potential
85
what does the excitatory postsynaptic potential do?
it depolarizes the postsynaptic membrane (less negative)
86
what does the inhibitatory postsynaptic potential
it hyperpolarizes the postsynaptic membrane (more negative)
87
what is the main exictatory NT in the brain?
glutamate
88
what are the 2 types of ionotropic glutamate receptors?
AMPA
| NMDA
89
What are ionotropic receptors?
these are receptors that these are ions channels that will open in response to biunding of small molecules on their external surface
90
what are AMPA receptors responsible for at the excitatory synapse?
the fast EPSP
91
what is the first step so that allows the fast EPSP occurs at the excitatory synapses?
glutamate is released from the presynaptic terminals and binds to AMPA receptors
their
92
what does the binding of the glutamate to AMPA cause?
it allows for sodium cations to flow into the postsynaptic spine causing for a small transient depolarization
93
what is the voltage and duration of a single EPSP in typical depolarized brain synapses?
greater than a few milivolts
| lasts around 20 mili seconds
94
is the depolarization caused by a single EPSP sufficient to depolarize the axon segment to the threshold?
no
95
how many EPSP needs be be fired in order for their sum at the initial segment be sufficient to initiate action potential?
50-100 EPSPs
96
what can the EPSPs come from?
- multiple synpases acting in synchrony
| - individual synapses activated at high frequencies
97
what binds to NMDA receptors and opens them up?
glutamate
98
what are the key properties of NMDA receptors?
at resting membrane potential Mg2+ blocks the pore
| the pore is highly permeable to Ca2+
99
how is Mg2+ expelled from the pore?
depolarization
100
at -70 mV the majority of the synaptic current is carried how?
by Na+ through the AMPA receptors
101
at -70 mV what happens if the postsynaptic membrane is depolarized?
a substantial Ca2+ current will flow inwards through the NMDA receptors
102
what is synaptic plasticity?
when highly active excitatory synapses become stronger
103
what receptor is involved in synaptic plasticity?
NMDA receptors
104
long term potentiation (LTP) is a model of what?
synaptic plasticity
105
what happens when there is a burst of action potentials?
the high frequency activity depolarizes the postsynaptic spine and removes Mg2+ enabling Ca2+ to pass through
106
when are the EPSPs larger before, after or during the induction of LTP
hours after
107
what are the 3 phases of LTP?
control
induction
LTP
108
high concentrations of what can be toxic for neurons?
glutamate
109
what does excitotoxicity involve?
Ca2+ influx through NMDA receptors
110
what can excitotoxicity contribute to?
neuronal degeneration after a stroke or in cases of neurodegenerative diseases
111
what is the main inhibitory neurotransmitter?
GABA
112
what receptor is involved in the IPSP?
Gaba A receptor
113
what type of receptor si the GABA a receptor?
ionotropic
114
what does the activation of the Gaba A receptor cause?
influx of Cl- which hyperpolarizes the postsynaptic membrane
115
where are inhibitory inputs usually located?
neat the cell soma because that is where they can have the maximal effect
116
where are excitatory inputs usually located?
located on the dendritic spines
117
what determines if a neuron fires an action potention or not?
the relative balance between EPSP and IPSP
118
how does the output of the neuron differ on its firing of an action potential
the output follows a all of none firing of action potential
119
what do glutamate synapses have?
```
ionotropic receptors (AMPA and NMDA)
metabotropuc glutamate receptors (mGluRs)
```
120
what does the activation of mGluRs do?
it is activated by glutamate and will relat chemical signals to the inside of the postsynaptic neuron
121
what is generated by the activation of mGluRs by glutamate?
a chemical signa (second messenger) inside the postsynaptic spine
122
what is the function of second messengers?
they activate a range of cellular proteins such as ion channels, protein kinases and transcription factors
123
does GABA also activate a metabotropic receptor?
yes Gaba B receptor
124
what substances act mainly or entirely with metabotrophic receptors?
dopamine, serotonin, norephinephrine, neuropeptides (endorphins)
125
what is the name given to substances that interact with metabotrophic receptors?
neuromodulators
126
are neuromodulators directly involved in the fast flow of neural information?
no
127
what is the fct of neuromodulators?
they modulate global neural states, influence alertness, attention and mood
128
where do the neurones that release neuromodulators originate from?
in the brainstem or midbrain neuclei
129
neuromodulators are important targets for what?
a wide range of drugs
130
what does antidepressents such as prozac cause the transmission of?
serotonin
131
what does amphetamines such as cocaine affect the transmission of?
depamine and norepinephrine
