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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

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Biology 101 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
Q

Nernst equation

A

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)

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26
Q

If the membrane was permeable to only K+, the membrane potential calculated from the Nernst equation would be

A

-75mV

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27
Q

If actual mV from the Nernst equation doesn’t match predicted (-75mV) assume

A

other ions moving

permeable to many

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28
Q

In reality, the measured membrane potential int he squid axon is

A

-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

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29
Q

To calculate the real membrane potential, use the

A

Goldman equation

30
Q

The Goldman equation takes into account

A
  • all the ions that can diffuse across a membrane

* the relative permeability of the membrane to those ions

31
Q

The resting potential is mainly due to

A

K+

32
Q

Relative permeabilities (p)

A

• are expressed as percentagegs

33
Q

Membrane’s permeability to ions

A 
pK = 1.0
pNa = 0.05
pCl = 0.45

membranes permeability to potassium ions is the highest

34
Q

Goldman equation

A

Vm = RT / F ln [(pk ion1 out/pk ion1 in) (ion 2) etc]

35
Q

Which equation do you use to calculate the membrane potential

A

Goldman equation
should be around -60mV

• closer to actual bc account for all ions and permeability of each

36
Q

The membrane potential at rest =

A

-60 mV

37
Q

Some ion channels are “gated”

A
  • voltage-gated channels
  • chemically-gated channels
  • mechanically-gated channels

WHEN THEY OPEN AND CLOSE, GATED ION CHANNELS CHANGE THE RESTING POTENTIAL

38
Q

Voltage-gated channels

A

respond to change in voltage across a membrane

39
Q

Chemically-gated channels

A

depend on specific molecules that bind are alter the protein channel

40
Q

Mechanically-gated channels

A

respond to force applied to membrane

41
Q

Deplozarized plasma membrane

A

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
Q

Hyperpolarized plasma membrane

A

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
Q

Neurons have many dendrites that can form

A

synapses with axons of other neurons

44
Q

Graded membrane potentials

A

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
Q

Summation of excitatory and inhibitory postysynaptic potentials is how the nervous system

A

integrates information

46
Q

Each neuron receives … or more synaptic inputs

but has … output

A

1,000 synaptic inputs
only 1 output

an action potential in a single axon, or no action potential

47
Q

Excitatory and inhibitory potentials are summed over

A

space and time

too slow = accumulation of info fades, doesn’t result in action potential

binary information

48
Q

Spatial summation

A

adds up messages at different synaptic sites

49
Q

Temporal summation

A

adds up potentials at the same site in a rapid sequence

50
Q

The action potential is integrated at

A

the axon hillock

51
Q

Positive feedback

A

Na+ channel opens
more open

–> depolarized above resting potential
= action potential
(big rush of Na+ inside)

52
Q

Graded membrane potential is a

A

gradual change in the membrane potential proportional to the inputs received
• travels just locally

53
Q

Action potentials are

A

sudden, transient, large changes in membrane potential

• travel far

54
Q

At resting potential, the voltage gated channels are

A

closed

• SLIGHT DEPOLARIZATION causes them to open

55
Q

Voltage-gated Na+ channels are concentrated in the

A

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
Q

When enough voltage-gated Na+ channels are opened, the membrane is

A

depolarized about 5-10 mV above resting potential
THRESHOLD is reached
–> an action potential is generated

57
Q

How the axon comes back to resting potential

A
  1. voltage-gated Na+ channels close

2. voltage-gated K+ channels open

58
Q

Both Na+ and K+ voltage-gated channels are voltage sensitive, but their dynamic is different

A

• Na+ gated channels open faster than K+
(goes in = more + to make action potential)
• K+ channels stay open longer
(goes out = more -)

59
Q

The magnitude of the action potential

A

does not change between 2 - even far away - recording sites

60
Q

An action potential is an

A

all-or-none event

• positive feedback to voltage-gated Na+ channels ensures the maximum action potential

61
Q

An action potential is self-regenerating because

A

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
Q

The action potential moves in 1 direction because of the

A

refractory period

63
Q

Refractory period

A
  • K+ still open
  • Na+ closed
  • action potential not possible (requires delay)
64
Q

Schwann cells make

A

myelin

65
Q

Gap in myelin

A

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
Q

Action potentials travel faster in

A 
myelinated cells (100m/s)
than non myelinated (2m/s)
67
Q

Invertebrates have

A

large axons

68
Q

Vertebrates rely on

A

myelin

69
Q

Voltage-gated channels are clustered at

A

thus node

• thus the action potential can only be generated at the nodes

70
Q

When positive current reaches the next node

A

the membrane is depolarized -

another action potential is generated

71
Q

Action potentials appear to jump from node to node, a form of propagation called

A

saltatory conduction

72
Q

Much faster with myelin because

A

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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