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Cell Bio & Developmental Genetics > Lecture 17/18 - How do neurons communicate with other cells? > Flashcards

Lecture 17/18 - How do neurons communicate with other cells? Flashcards

1
Q

3 levels of communication based on how far/close

A
  1. Juxtacrine signalling
  2. Paracrine signalling
  3. Endocrine signalling
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2
Q

Juxtacrine signalling

A
  • signal targets adjacent cells
  • direct contact
  • fast
  • gap junction - electrical synapse
  • between 2 neurons
  • 2 cardiac cells
  • 2 astrocytes
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3
Q

Paracrine signalling

A
  • signal targets cells in the vicinity
  • short distances
  • proximal
  • chemical synapses involving a neurotransmitter
  • between 2 neurons
  • between a neuron and a muscle (neuromuscular junction)
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4
Q

Endocrine signalling

A
  • signal targets distant cells
  • long distant
  • hormones traveling in blood
  • eg ADH (antidiuretic hormone) produced by the hydrophyse - targets kidneys and blood vessels
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5
Q

2 types of synapses

A
  • chemical synapse

* electrical synapse

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6
Q

Chemical synapse

A
  • short distance
  • uses neurotransmitter
  • paracrine signalling
  • neuron-neuron communication
  • neuron-muscle communication
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7
Q

Electrical synapse

A
  • direct contact
  • juxtacrine signalling
  • neuron-neuron communication
  • muscle-muscle (cardiac cells)
  • astrocyte-astrocyte
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8
Q

Presynaptic

A

axon

• transmits info

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9
Q

Postsynaptic

A

dendrite

• gets info from many presynaptic

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10
Q

The membrane potential is

A

electric

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11
Q

Measuring the membrane potential

A 
•  inside axon more (-) than outside
= already imbalance
•  glass pipette to conduct electric charge
•  1 in axon, 1 just outside
= measure membrane voltage
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12
Q

Membrane potential

A

the electrical charge difference across a membrane

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13
Q

Resting potential

A

the steady state membrane potential of a neuron
• -60 to -70 mV
• membrane potential when not transmitting a signal

• electric difference = voltage

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14
Q

Voltage

A

electric potential difference

• force that causes charged particles to move between 2 points

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15
Q

Major charged particles (ions) that carry electric current in neurons

A
  • sodium (Na+)
  • potassium (K+)
  • calcium (Ca2+)
  • chloride (Cl-)

• there is 1 specific channel for each ion
(ions move to opposite charge -
most –> least concentrated)

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16
Q

Ions can diffuse in both directions depending on 2 gradients

A
  • electrical gradient

* chemical gradient

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17
Q

Electrical gradient

A

voltage difference across the membrane

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18
Q

Chemical gradient

A

concentration difference across the membrane

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19
Q

The net movement of ions depends on

A
  • the electrochemical gradient

* whether the gates for this ion are open or not

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20
Q

The sodium-potassium pump

A

constantly moves Na+ to the outside and K+ to the inside
(requires energy)

the pump establishes concentration gradients
in a resting neuron
• K+ more concentrated inside
• Na+ more concentrated outside

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21
Q

In a resting neuron, … channels are the most common opened channels

A

K+ channels are the most common opened channels
–> leak of K+ outside
• follows the concentration gradient created by the pump
• if too much K+ going outside, there will be an electrical imbalance (more negative inside) pushing the K+ back inside
[less (+) in = more (-) in]

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22
Q

Potassium equilibrium potential

EK

A

the membrane potential at which the net diffusion of K+ out of the cell ceases
• the point at which K+ diffusion out due to the concentration gradient, is balanced by its movement in due to the negative electric potential

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23
Q

Leak channels

A

like the K+ channel are ALWAYS OPEN and mainly create the resting membrane potential

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24
Q

Na+ channels

A

opened mainly by chemical stimulation

mostly closed at rest

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25
Nernst equation
calculates the value of K+ on both sides of the membrane • WHEN 1 TYPE OF ION CAN CROSS A MEMBRANE Eion = 2.3 RT/zF log (ion out/ion in)
26
If the membrane was permeable to only K+, the membrane potential calculated from the Nernst equation would be
-75mV
27
If actual mV from the Nernst equation doesn't match predicted (-75mV) assume
other ions moving | permeable to many
28
In reality, the measured membrane potential int he squid axon is
-66mV • the resting potential of the axon is not due solely to leak K+ channels • the neuronal membrane is slightly permeable to other ions, especially Na+ and Cl-, and movements of these ions influence the resting potential
29
To calculate the real membrane potential, use the
Goldman equation
30
The Goldman equation takes into account
* all the ions that can diffuse across a membrane | * the relative permeability of the membrane to those ions
31
The resting potential is mainly due to
K+
32
Relative permeabilities (p)
• are expressed as percentagegs
33
Membrane's permeability to ions
``` pK = 1.0 pNa = 0.05 pCl = 0.45 ``` membranes permeability to potassium ions is the highest
34
Goldman equation
Vm = RT / F ln [(pk ion1 out/pk ion1 in) (ion 2) etc]
35
Which equation do you use to calculate the membrane potential
Goldman equation should be around -60mV • closer to actual bc account for all ions and permeability of each
36
The membrane potential at rest =
-60 mV
37
Some ion channels are "gated"
* voltage-gated channels * chemically-gated channels * mechanically-gated channels WHEN THEY OPEN AND CLOSE, GATED ION CHANNELS CHANGE THE RESTING POTENTIAL
38
Voltage-gated channels
respond to change in voltage across a membrane
39
Chemically-gated channels
depend on specific molecules that bind are alter the protein channel
40
Mechanically-gated channels
respond to force applied to membrane
41
Deplozarized plasma membrane
if voltage-gated Na+ channels open Na+ diffuses in (electrochemical gradient) and the inside of the cell becomes less negative (or more positive) in comparison to its resting condition inside more (+) = depolarized
42
Hyperpolarized plasma membrane
if gated K+ channels open and K+ efflux increases over the normal leak rate the membrane potential becomes even more negative inside more (-) = hyperpolarized
43
Neurons have many dendrites that can form
synapses with axons of other neurons
44
Graded membrane potentials
small changes from the resting potential • the mix of excitatory and inhibitory activity determines whether the graded membrane potential is more positive or more negative than resting
45
Summation of excitatory and inhibitory postysynaptic potentials is how the nervous system
integrates information
46
Each neuron receives ... or more synaptic inputs | but has ... output
1,000 synaptic inputs only 1 output an action potential in a single axon, or no action potential
47
Excitatory and inhibitory potentials are summed over
space and time too slow = accumulation of info fades, doesn't result in action potential binary information
48
Spatial summation
adds up messages at different synaptic sites
49
Temporal summation
adds up potentials at the same site in a rapid sequence
50
The action potential is integrated at
the axon hillock
51
Positive feedback
Na+ channel opens more open --> depolarized above resting potential = action potential (big rush of Na+ inside)
52
Graded membrane potential is a
gradual change in the membrane potential proportional to the inputs received • travels just locally
53
Action potentials are
sudden, transient, large changes in membrane potential | • travel far
54
At resting potential, the voltage gated channels are
closed | • SLIGHT DEPOLARIZATION causes them to open
55
Voltage-gated Na+ channels are concentrated in the
hillock ``` Na+ channels open and Na+ rushes into the axon the influx of positive ions causes more voltage-gated channels to open and then more depolarization = positive feedback effect ```
56
When enough voltage-gated Na+ channels are opened, the membrane is
depolarized about 5-10 mV above resting potential THRESHOLD is reached --> an action potential is generated
57
How the axon comes back to resting potential
1. voltage-gated Na+ channels close | 2. voltage-gated K+ channels open
58
Both Na+ and K+ voltage-gated channels are voltage sensitive, but their dynamic is different
• Na+ gated channels open faster than K+ (goes in = more + to make action potential) • K+ channels stay open longer (goes out = more -)
59
The magnitude of the action potential
does not change between 2 - even far away - recording sites
60
An action potential is an
all-or-none event | • positive feedback to voltage-gated Na+ channels ensures the maximum action potential
61
An action potential is self-regenerating because
it spreads to adjacent membrane regions • when an action potential is stimulated in one region of the membrane, electric current flows to adjacent areas of membrane and depolarizes them • the advancing wave of depolarization causes more Na+ channels to open and the action potential is generated in the next section of the membrane • meanwhile, in the region where the action potential has just fired, the Na+ channels are inactivated and the voltage-gated K+ channels are still open rendering this section of the axon incapable of generating an action potential • hence the action potential cannot back up but continuously moves forward regenerating itself as it goes
62
The action potential moves in 1 direction because of the
refractory period
63
Refractory period
* K+ still open * Na+ closed * action potential not possible (requires delay)
64
Schwann cells make
myelin
65
Gap in myelin
nodes of Ranvier • regularly spaced gaps in the myelin along an axon • voltage-gated channels are clustered at the node thus an action potential can only be generated at the nodes • action potential moves 1 gap to another, travelling along the axon
66
Action potentials travel faster in
``` myelinated cells (100m/s) than non myelinated (2m/s) ```
67
Invertebrates have
large axons
68
Vertebrates rely on
myelin
69
Voltage-gated channels are clustered at
thus node | • thus the action potential can only be generated at the nodes
70
When positive current reaches the next node
the membrane is depolarized - | another action potential is generated
71
Action potentials appear to jump from node to node, a form of propagation called
saltatory conduction
72
Much faster with myelin because
ionic electric current flows much faster through the cytoplasm than ion channels can open and close • no channel where myelin is

Cell Bio & Developmental Genetics (27 decks)

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