Chapter 8: Neurons - Cellular & Network Properties Flashcards
1
Q
consists of brain and spinal cord
A
central nervous system
2
Q
Receives and processes information form sensory organs and the viscera to determine the state of the external and internal environment
A
central nervous system
3
Q
consists of afferent and efferent neurons
A
peripheral nervous system
4
Q
- transmit sensory and visceral info to CNS
- input
A
afferent neurons
5
Q
- are either somatic (control skeletal muscle) or autonomic (control smooth & cardiac muscle, endocrine glands)
- output
A
efferent neurons
6
Q
divided into sympathetic and parasympathetic systems
A
autonomic nervous system
7
Q
excitable cells
A
neurons
8
Q
support cells
A
glial cells
9
Q
- cell body
- contains nucleus and most organelles
A
soma
10
Q
reception of incoming information
A
dendrites
11
Q
Transmits electrical impulses called action potentials
A
axon
12
Q
Where axon originates and action potentials are initiated
A
axon hillock
13
Q
- synaptic knob, synaptic bouton
- Releases neurotransmitter
A
axon terminal
14
Q
what are the components of a neuron?
A
- soma
- dendrites
- axon
- axon hillock
- axon terminal
15
Q
-have a single process called the axon -During development, the dendrite fused with the axon.
A
pseudounipolar neurons
16
Q
have two relatively equal fibers extending off the central cell body
A
bipolar neurons
17
Q
have
no apparent axon
A
anaxonic CNS internuerons
18
Q
highly branched but lack
long extensions
A
multipolar CNS interneurons
19
Q
how many dendrites does a typical multipolar efferent neuron have?
A
has five to seven
dendrites, each branching
four to six times
20
Q
what are the forms of axonal transport?
A
- anterograde transport
- retrograde transport
21
Q
transport from soma to axon terminal
A
anterograde transport
22
Q
-transport from axon to soma
-microtubules & neurofilaments
-Slow: 0.5–40 mm/day
-Fast: 100–400 mm/day
~Vesicles
~kinesins
A
retrograde transport
23
Q
what are the steps of fast axonal transport?
A
- peptides made on rough ER & packaged by Golgi apparatus
- fast axonal transport walks vesicles & mitochondria along microtubule network
- vesicle contents released by exocytosis
- synaptic vesicle recycling
- retrograde fast axonal transport
- old membrane components digested in lysosomes
24
Q
the region where the axon terminal meets the target cell
A
synapse
25
what are presynaptic and postsynaptic cells separated by?
synaptic cleft
26
a chemical signal diffuses across the synapse
chemical synapse
27
gap junctions connect pre and postsynaptic cells (bidirectional and faster)
electric synapses
28
- provide structural integrity, chemical, and anatomical support of neurons
- "glue"
- 90% of cells
glial cells
29
what are the 2 types of glial cells of the peripheral nervous system?
1. schwann cells
| 2. satellite cells
30
wrap around axon and form insulating myelin sheaths
schwann cells
31
- gaps in the insulation of myelin sheaths
| - section of unmyelinated axon membrane
nodes of ranvier
32
form supportive capsules around the cell body, regulate the chemical environment
satellite cells
33
what are the 4 types of glial cells of the central nervous system?
1. Oligodendrocytes
2. Astrocytes
3. Microglia
4. Ependymal cells
34
form myelin sheath
Oligodendrocytes
35
take up and release chemicals, feed neurons, water-K+ balance, and part of blood-brain-barrier
astrocytes
36
provide immune defense by removing damaged cells and foreign invaders
microganglia
37
form the barrier between fluid compartments of the CNS and are a source of stem cell
ependymal cells
38
consists of multiple layers of cell membrane
myelin
39
difference in voltage between two points
potential difference (E)
40
difference in voltage across the plasma membrane; always given in terms of voltage inside the cell relative to voltage outside the cell
membrane potential
41
a relatively small change in the membrane potential produced by a stimulus that triggers the opening or closing of ion channels
graded potential
42
graded potentials produced in the post-synaptic cell in response to neurotransmitters binding to receptors
synaptic potential
43
graded potentials produced in response to a stimulus acting on a sensory receptor
receptor potential
44
a large, rapid change in the membrane potential produced by depolarization of an excitable cell's plasma membrane to threshold
action potential
45
the membrane potential that counters the chemical forces acting to move an ion across the membrane, thereby putting the ion at.........
equilibrium potential
46
what are the 2 factors needed to determine the resting membrane potential?
1. ion concentration gradients
2. membrane permeability to these ions
~ion channels
47
what is needed to establish the equilibrium potential?
1. hypothetical cell
2. ion distribution
~outside cell= sodium and chloride
~inside cell= potassium and organic anions
48
what is the potassium equilibrium potential?
- K+ chemical driving force= out of cell
| - K+ diffuses out of cell
49
what happens as K+ diffuses out of the cell?
the inside of the cell becomes more negative
50
what pulls K+ back into the cell?
electrical driving force
51
- opposite in direction
| - equal in magnitude
chemical and electrical driving forces
52
when is an ion at equilibrium?
- when there is no net force for it to move across the membrane
- Chemical force = negative electrical force
- Electrochemical force = 0
53
when is potassium at equilibrium?
When membrane potential = –90 mV
54
what is the sodium equilibrium potential?
- Na+ chemical driving force: into the cell
| - Na+ diffuses into cell
55
what happens as Na+ diffuses into the cell?
the inside of the cell becomes less negative (positive)
56
what pushes Na+ out of the cell?
electrical driving force
57
what are the 2 forces acting on Na+?
- chemical: to move in
| - electrical: to move out
58
*electrochemical force
~intially in, due to stronger chemical force
~but electrical force continues to increase
net force
59
when is sodium at equilibrium?
When membrane potential = +60 mV
60
is a neuron more permeable to potassium or sodium?
25x more permeable to potassium
61
what is the ion distribution of a neuron?
- outside cell: sodium and chloride
| - inside cell: potassium and organic anions
62
what are the chemical driving forces for the resting potential of a neuron?
- K+ out of cell
| - Na+ into cell
63
in what ratio does K+ and Na+ enter and leave the cell?
more K+ leaves the cell than Na+ enters
64
what is the result of more K+ leaving the cell than Na+ entering?
inside of cell becomes negative
65
what do the electrical forces for the resting potential of a neuron do?
- Na+ into cell
| - K into cell
66
what do the electrical forces of the resting potential for a neuron result in?
- K+ outflow slows
| - Na+ inflow speeds up
67
inflow of Na+ is balanced by outflow of K+
steady state develops
68
what is the resting membrane potential of a neuron?
-70 mV
69
-Predicts membrane potential that results from the contribution of all ions that can cross the membrane
Goldman-Hodgkin-Katz (GHK) Equation
70
determined by the combined contributions of the concentration gradient times the membrane permeability for each ion
Resting membrane potential
71
maintains the resting potential of a neuron
sodium pump
72
what is the resting membrane potential closer to?
the potassium equilibrium potential
73
what happens when the membrane potential is not at equilibrium for an ion?
- electrochemical force is not 0
- net force acts to move the ion across the membrane in the direction that favors its being at equilibrium
- strength of the net force increases the farther away the membrane potential is from the equilibrium potential
74
what are the forces on K+?
- Resting potential = –70 mV
- EK = –94 mV
- Vm is 24 mV less negative than EK
75
into the cell (lower)
electrical force on K+
76
out of the cell (higher)
chemical force on K+
77
net force on K+ is weak
K+ flows out of the cell, but the membrane is highly permeable to K+
78
what are the forces on Na+?
- Resting potential= –70 mV
- ENa = +60 mV
- Vm is 130 mV less negative than ENa
79
into the cell
electrical force on Na+
80
into the cell
chemical force on Na+
81
net force on Na+ is strong
Na+ flows into the cell, but the membrane has low permeability to Na+
82
high force, low permeability
Small Na+ leak at rest
83
low force, high permeability
Small K+ leak at rest
84
returns Na+ and K+ to maintain gradients
sodium pump
85
20% of the resting membrane potential is directly due to..........?
Na+/K+-ATPase
86
- Electrogenic: 3 Na+ out, 2 K+ in
| - Net: +1 out
Na+/K+ pump
87
80% of resting membrane potential is indirectly due to.......?
Na+/K+-ATPase
88
-produces concentration gradients
~Na+= high outside, low inside
~K+=low outside, high inside
80% of resting membrane potential is indirectly due to Na+/K+-ATPase
89
- a difference in potential across the membrane
| - membrane is polarized
membrane potential
90
-70 mV
resting potential
91
a change to a more negative value
Hyperpolarization
92
a change to a less negative value
Depolarization
93
when the membrane potential returns to resting
Repolarization
94
what are the components of a resting membrane potential?
1. ion concentration gradients
| 2. membrane permeability to these ions
95
what are the gated channels that control ion permeability?
- mechanically gated
- chemically gated
- voltage gated
96
varies from one channel type to another
threshold voltage
97
small changes in membrane potential that occur when ion channels open or close in response to a stimulus
graded potentials
98
such as neurotransmitter molecules binding to receptors on the dendrite or cell body of a neuron
chemical stimuli
99
such as touch or light acting on a sensory receptor
sensory stimuli
100
varies according to the strength of the stimuli
The magnitude of the change in membrane potential
101
occur in the membranes of excitable tissue (nerve or muscle) in response to graded potentials that reach threshold
action potentials
102
Once initiated, it is capable of being propagated long distance along the length of an axon without any decrease in strength
action potential
103
lose strength as they move through the cell due to current leak and cytoplasmic resistance
graded potentials
104
if strong enough, graded potentials reach the......?
the trigger zone in the axon hillock and initial segment
105
the ability to fire an action potential
Cell’s excitability
106
depolarizing
excitatory
107
hyperpolarize
inhibitory
108
- a graded potential starts above threshold (T) at its initiation point but decreases in strength as it travels through the cell body
- at the trigger zone, it is below threshold and, therefore, does not initiate an action potential
subthreshold graded potential
109
a stronger stimulus at the same point on the cell body creates a graded potential that is still above threshold by the time it reaches the trigger zone, so an action potential results
suprathreshold graded potential
110
when is an action potential triggered?
if the membrane threshold at the axon hillock is depolarized to threshold
111
what happens if the potential is below threshold?
no action potential will occur
112
adding effects of graded potentials
summation
113
- are graded potentials
| - can be summed
IPSPs and EPSPs
114
what are the types of summation?
1. temporal
| 2. spatial
115
- type of summation
| - one synapse through time
temporal
116
- type of summation
| - several synapses at the same time
spatial
117
what is the degree of depolarization at the axon hillock signaled by?
frequency of action potentials
118
- affects depolarization
| - influences frequency of action potentials
summation
119
More action potentials result in more neurotransmitter released, which leads to......?
a greater IPSP or EPSP in the next neuron
120
The degree of depolarization at the axon hillock is signaled by the frequency of action potentials
frequency coding
121
The regulation of communication across a synapse
presynaptic modulation
122
what are the two modulatory synapses?
- presynaptic facilitation
| - presynaptic inhibition
123
the high-speed movement of a action potential along an axon
conduction
124
how do action potentials move down an axon?
Not a single action potential (AP) that moves down the axon but rather many replenished AP’s
125
what do axons travelling down an axon form?
a wave of electrical signal at constant amplitude
126
also known as nerve spikes
action potentials
127
the principle that the strength by which a nerve or muscle fiber responds to a stimulus is independent of the strength of the stimulus. If that stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response; otherwise, there is no response
all-or-none law
128
what happens during the conduction of an action potential?
- each section of the membrane is a different phase of the action potential
- a wave of electrical current passes down the axon
- each section of the axon is experiencing a different phase of the action potential
129
what are the steps of an action potential?
1. resting membrane potential
2. depolarizing stimulus
3. Membrane depolarizes to threshold.
Voltage-gated Na+ and K+
channels begin to open.
4. rapid Na+ entry depolarizes cell
5. K+ moves from cell to extracellular fluid
6. K+ channels remain open and
additional K+ leaves cell, hyperpolarizing it.
7. Voltage-gated K+ channels close,
less K+ leaks out of the cell.
8. Cell returns to resting ion permeability
and resting membrane potential.
130
How do you stop depolarization and this positive feedback loop?
Voltage-gated sodium channels have two gates
131
what are the two voltage-gated sodium channels?
- activation gates
| - inactivation gates
132
- responsible for opening sodium channels during the depolarization phase of AP
- closes the channel at the resting membrane potential
- Na+ enters the cell
activation gates
133
- (0.5 msec delay)responsible for the closing of sodium channels during the repolarization phase of AP
- Na+ entry stops
inactivation gates
134
what happens during repolarization caused by K+ leaving the cell?
the activation and inactivation gates reset to their original positions
135
- due to Na+ gates resetting
- Potential delay of 1-2 msec. between action potentials independent of intensity of trigger
- no stimulus can trigger another action potential
absolute refractory period
136
prevents backward conduction
refractory period
137
-follows an absolute refractory period
-only a larger-than-normal stimulus can initiate a new action
potential
relative refractory period
138
-spreads along adjacent sections of axon by local current flow
positive charge
139
-causes new section of the membrane to depolarize
local current flow
140
what are the phases of an action potential?
1. rising phase
2. peak
3. falling phase
141
what happens during the conduction of an action potential?
```
1. A graded potential above
threshold reaches the trigger zone
2. Voltage-gated Na+ channels
open, and Na+ enters the axon.
3. Positive charge flows into
adjacent sections of the axon
by local current flow.
4. Local current flow from the
active region causes new sections
of the membrane to depolarize.
5. The refractory period prevents
backward conduction. Loss of K+
from the cytoplasm repolarizes
the membrane.
```
142
what is the speed of an action potential in a neuron influenced by?
- diameter of axon
| - resistance of axon membrane to ion leakage out of the cell
143
how does the diameter of an axon affect the speed of an action potential?
larger axons are faster
144
how does the resistance of axon membrane to ion leakage out of the cell affect the speed of an action potential?
- myelinated axons are much faster
| - saltatory condution between nodes of ranvier
145
the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials
- Action potentials appear to jump from one node of Ranvier to the next
- Only the nodes have voltage-gated Na+ channels.
saltatory conduction
146
reduce or block conduction when current leaks out of the previously insulated regions between the nodes
demyelinating diseases
147
how can chemical factors alter action potentials?
-Binding of chemicals (neurotoxins, anesthetics) to Na+, K+, or Ca+ can alter the conduction of action potentials.
~blocking votage gated Na+ channels
-procaine hydrochloride (novacaine)
-tetrdotoxin (fugu toxin)
-K+ concentrations can also cause abnormal electrical activity in the nervous system
~hyperkalemia vs hypokalemia
148
```
increased
blood K+ concentration,
brings the membrane closer
to the threshold. Now a
stimulus that would normally
be subthreshold can
trigger an action potential.
```
hyperkalemia
149
```
decreased
blood K+ concentration,
hyperpolarizes the membrane
and makes the neuron less
likely to fire an action potential
in response to a stimulus that
would normally be above the
threshold.
```
hypokalemia
150
what is the type of signal in a graded potential?
input signal
151
where do graded potentials occur?
dendrites and cell body
152
what are the types of gated ion channels in neurons?
- mechanically gated
- chemically gated
- voltage gated
153
what are the ions involved in graded potential?
Na+, K+, Ca^2+
154
what is the signal type of graded potentials?
- depolarizing (Na+)
| - hyperpolarizing (Cl-)
155
what is the strength of the signal of a graded potential?
-depends on the initial stimulus, but it can be summed
156
what initiates the signal of a graded potential?
entry of ions through gated channels
157
what are the unique characteristics of a graded potential?
- no minimum level required to initiate
- two signals coming together in time will sum
- initial stimulus strength is indicated by frequency of a series of action potentials
158
what type of signal is an action potential?
regenerating conduction signal
159
where does an action potential occur?
trigger zone through axon
160
what are the types of gated channels involved in action potentials?
voltage gated channels
161
what are the ions involved in action potentials?
Na+ and K+
162
what type of signal is an action potential?
depolarizing
163
what is the strength of a signal of an action potential?
all or none phenomenon; cannot be summed
164
what initiates the signal of an action potential?
above-threshold graded potential at the trigger zone opens ion channels
165
what are unique characteristics of an action potential?
- threshold stimulus required to initiate
| - refractory period; two signals too close together in time cannot sum
166
what do neurons communicate at?
synapses
167
pass electrical signals through gap junctions (cytoplasm continuous)
electrical synapses
168
- signal can be bi-directional
- synchronizes the activity of a network of cells
- cardiac, smooth muscle, glial cells, CNS
electrical synapses
169
- use neurotransmitters that cross synaptic clefts
| - Make up majority of synapse in the nervous system
chemical synapses
170
- act at short distances
- released by a neuron
- diffuse across a narrow cleft to effect postsynaptic cell
neurotransmitters
171
- act over long distances
- released by neurons into the circulation
- exerts its effects on distant peripheral targets
neurohormones
172
what are the two types of neurocrine receptors?
1. receptor channels (ionotropic receptors)
| 2. metabotropic receptors
173
- mediate rapid response
| - alter ion flow across membranes
receptor channels (ionotropic receptors)
174
- G protein-mediated receptors
- mediate slower responses due to 2nd messenger system
- some open or close ion channels
metabotropic reeceptors
175
all neurotransmitters except..........., bind to specific receptors
nitric oxide
176
allows the same neurotransmitter to have different effects in different tissues
when receptors have multiple subtypes
177
either mimic or inhibit activity by binding to receptors
agonist and antagonist molecules
178
what are the seven classes of neurocrines by structure?
1. Acetylcholine (Ach)- derived from Acetyl CoA
2. Amines (biogenic amines)- derived from a single amino acid
3. amino acids
4. peptides
5. purines
6. gases - NO, CO, H2S
7. lipids
179
Neurons that secrete Acetylcholine and receptors that bind it
cholinergic
180
what is the site of release of acetylcholine?
- CNS and ANS synapses
| - neuromuscular junctions
181
what is the effect of acetylcholine?
- Excitatory in the CNS and neuromuscular junctions
| - Inhibitory or excitatory in ANS synapses
182
what is the agonist of acetylcholine?
nicotine
183
what is the antagonist of acetylcholine?
curare (plant derived)
184
how is acetylcholine synthesized?
- Acetyl CoA + choline ---> acetylcholine + CoA
- synthesized in axon terminal
- Choline acetyl transferase (CAT) = enzyme for synthesis
185
how is acetylcholine broken down?
- Acetylcholine ---> acetate + choline
- occurs in synaptic cleft
- Acetylcholinesterase (AChE) = enzyme of degradation
186
what are the cholinergic receptors of acetylcholine?
- nicotinic
| - muscarinic
187
- receptor of acetylcholine
- on skeletal muscle, in autonomic division of PNS and CNS
- monovalent cation channels --> Na+ & K+
nicotinic
188
- receptor of acetylcholine
- in CNS and autonomic parasympathetic division of the PNS
- G protein coupled receptors
muscarinic
189
- derived from tryptophan
| - Involved in regulating sleep, alertness, thermoregulation, and mood
amines (serotonin)
190
what is the site of release of amines (serotonin)?
CNS synapses
191
what is the effect of serotonin?
- inhibitory and excitatory
| - serotonergic receptors
192
- used to treat depression
| - block serotonin symporters
SSRIs (prozac & zoloft)
193
- derived from tyrosine
- Highly concentrated in substantia nigra control of skeletal muscles, involved in elevation of mood, motivation, and reward
amines (dopamine)
194
what is the site of release of dopamine?
Selected CNS synapses, some ANS synapses
195
what is the effect of dopamine?
inhibitory and excitatory
196
blocks dopamine transporters, which increases levels in synaptic cleft
cocaine
197
- derived from tyrosine
- involved in dreaming, waking, and mood, excited cardiac muscle, excite or inhibit smooth muscle and glands
- Adrenergic Receptors (alpha and beta)
amines (norepinephrine/epinephrine)
198
what is the site of release of norepinephrine/epinephrine?
Selected CNS synapses, some ANS synapses
199
what is the effect of norepinephrine/epinephrine?
inhibitory and excitatory
200
what are some important amino acids?
- glutamate
- glycine
- GABA (ƴ-aminobutyric acid)
201
accounts for about 75% of all excitatory synaptic transmission in the brain, involved in learning and memory
glutamate
202
- inhibitory brain, most common inhibitory neurotransmitter in the spinal cord
- enhances the excitatory effect of glutamate
glycine
203
most common inhibitory neurotransmitter in the brain
GABA(ƴ-aminobutyric acid)
204
peptide neurotransmitters involved in pain
substance P and opioid peptides
205
AMP and ATP bind to receptors in the CNS
purine neurotransmitters
206
gas neurotransmitters that diffuse in the cells
NO, CO, H2S
207
Eicosanoids, endogenous ligands for cannabinoid receptors
lipid neurotransmitters
208
what happens when an action potential reaches an axon terminal?
opens voltage-gated Ca+ channels due to depolarization
209
once the Ca+ channels are open what happens?
Ca+ enters axon terminal and initiates exocytosis of synaptic vesicles containing neurotransmitter
-H+ dependent antiporters. Exchange H+ for neurotransmitters in vesicle
210
-rapid removal or inactivation in the synaptic cleft
termination of neurotransmitter activity
211
what happens during the rapid removal or inactivation in the synaptic cleft?
- diffusion out of the synaptic cleft into the ECF
- enzymatic breakdown
- Intact or broken down neurotransmitters are taken up by presynaptic axon terminal or glial cells
212
determines how much neurotransmitter is released
frequency of action potentials
213
releases little neurotransmitter
weak stimulus
214
causes more action potentials and releases more neurotransmitter
strong stimulus
215
what is involved in the integration of neural information transfer?
- divergent and convergent (branching) pathways at synapses
| - synaptic plasticity
216
a change of activity at the synapses (i.e. enhance or decrease activity)
synaptic plasticity
217
one presynaptic neuron branches to affect a larger number of postsynaptic neurons
divergent pathway
218
many presynaptic neurons provide input to influence a smaller number of postsynaptic neurons
convergent pathway
219
nearly covered with synapses providing input from other neurons.
cell body of a somatic motor neuron
220
Which of the following glial cells become part of the blood-brain barrier?
astrocytes
221
If the ECF K+ concentration increases from 3 mM to 5 mM, what happens to the resting membrane potential of cells?
it becomes less negative
222
A neuron under the influence of a neurotransmitter that opens K+ channels will......
- become hyperpolarized
| - be less likely to fire an action potential
223
What effect does hyperkalemia, an increase in plasma K+ concentration, have on the resting membrane potential of neurons?
- less K+ leaves the cell so membrane potential becomes less negative.
- Shifts it closer to threshold so the neuron is more likely to depolarize.
