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Flashcards in 2.1 Neuron Properties Deck (67):
1

Dendrites

Receive synaptic INPUTS from neuronal axons

2

Cell Body (neuron)

Same organelles as any other cell

3

Trigger zone

Action potentials are started here, axon runs with them

4

Axons

Fire rapid impulses (APs) to synaptic terminals

5

Pre-synaptic terminal

Releases output signal to "post," releases neurotransmitters at synapse

6

Multipolar neurons are found in...

Brain, spine, motor

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Bipolar neurons are found in...

Retina, ear, nose

8

Unipolar neurons are...

Sensory receptor neurons

9

3 things necessary for cellular membrane potentials

1) Ions can be pumped through ion carriers embedded in cell membrane
2) Ions are maintained at different concentrations on either side of cell membrane (concentration gradient)
3)The ion (thus the potentials) can change by flowing through ion channels

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Major ions that are pumped in neurons

Na+, K+, Cl-, Ca2+

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What happens if there is not a constant source of energy for ion pumps?

Gradients erode very quickly, if you die from running out of energy it is probably because these pumps stopped working

12

Passive / Leakage (nongated channels)

Open randomly, important in maintaining the baseline neuronal membrane potential ; ion flow sensitive to concentration gradients
POTASSIUM

13

Ligand-gated channels

Open in response to binding of a ligand (neurotransmitters, hormones, etc)

14

Voltage-gated channels

Respond to changes in transmembrane potential (when it deviates from 'normal' resting membrane potential"

15

Mechanically gated ion channels

Respond to mechanical vibration; pressure
Activated by physical stretching of plasma membrane

16

Resting membrane potential

Baseline, status quo, where neuron sits most of the time, -70mV

17

Depolarization

Reduces the potential difference, brings it closer to zero.. Describes the state of flux when going more positive

18

Repolarizing

Potential is fluxing, getting more negative and returning to the reference point

19

Hyperpolarization

Increasing the potential difference; making it more negative (further away from 0) goes beyond -70mV

20

What does an RMP of -70 mV mean?

It's more negative inside the neuron's plasma membrane

21

Three compartments that matter to the RMP

1) Aqueous extracellular fluid (ECF) (aka interstitial fluid)
2) Non-conducting lipid barrier
3)Aqueous cytoplasm

22

What causes the potential difference?

1) Ion differences between ECF and cytoplasm
2) Ion pumps
3) Selective ion leakage

23

Ion differences

Phosphates and proteins are anions at physiological pH, they stay trapped in the cell
THEIR (-) CHARGES DOMINATE OVER THE IONS (Na/Cl/K)
-Primary reason the cytoplasm stays more negative

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Are anions more concentrated inside or outside cell?

Inside

25

Is K+ more concentrated inside or outside cell?

Inside

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Is Cl- more concentrated inside or outside cell?

Outside

27

Is Na+ more concentrated inside or outside cell?

Outside

28

Intracellular ions create...

An electrostatic force field (both attracts and repels more mobile ions)

29

Sodium-potassium pump

-3 Na+ ions out
-2 K+ ions in
ATP -> ADP +Pi
*Cl- also gets pumped out

30

What ion as many leak channels?

K+, the membrane is very permeable to K+

31

Inward forces on K+

1) Pumps push K+ into the cell (against gradient)
2) K+ tends to follow the anions into the cell (attracted to negative charge)
3) High Na+ in the ECF repels K+

32

Outward Force on K+

1) Leak channels (moving down the concentration gradient)

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Result of forces on K+

K+ going inside offsets anions slightly, pushes RMP towards (+)
(RMP is at -70 rather than -80 b/c of potassium)

34

Movers of Na+

Sodium potassium pumps
Very, very slow leak channels

35

Hyperkalemia

Increase in bloodstream (ECM) potassium
-Decreases gradient
-K+ doesn't diffuse out of cells as rapidly
-Membrane DEPOLARIZATION

36

Hypokalemia

Decrease in extracellular K+
-Increase in concentration gradient
-More diffusion of K+ out of the cell
-Membrane hyperpolarization

37

What keeps neurons at a resting membrane potential of -70 mV?

Electrostatic forces, Ion concentration gradients, Leakage channels and Pumps

38

What can cause a flux or change in the RMP of a neuron?

Physical stimuli or input from other neurons

39

Do all parts of the cell experience flux in RMP?

No, only regions near the plasma membrane

40

Graded Potentials

Have an amplitude (height)
-Results from a variable degree of divergence (big, med, small) from the RMP

41

Why does RMP change? (graded potentials)

It is changes in local ion permealbility
-Na+ going in will make the neuron RMP more positive (stimulatory)
-Cl- going in will make the RMP more negative (inhibitory)

42

What's the stimulus that elicits the Graded Potential?

-Ligands (neurotransmitters, hormones) bind ligand gated ion channels
-Mechanical stimulation
-Temperature change, etc

43

Summation

An additive effect on the amplitude when two or more stimuli occur at the same membrane locale at nearly the same time

44

Spatial summation

Many / multiple synapses release stimulus or inhibitory signal in the same locale on the target neuron

45

Temporal Summation

A single synapse may fire rapidly at a single point on the neuron

46

This is the consequence to RMP of a graded potential that causes the opening of Cl- channels

Hyperpolarization

47

Where are graded potentials in the neurons?

Dendrites, where summation and propagation of GPs to the trigger zone

48

Trigger zone

Decision point.. If the GPs are pushing to threshold (~50 mV) then ACTION POTENTIAL

49

Action potentials

Rapid, local reversals of the membrane potential
-All-or none (always same shape and amplitude)

50

What is the main mechanism for rapid communication along nerve axons?

Action potentials!

51

Why are action potentials triggered?

Because voltage-gated ion channels activated by crossing threshold in trigger zone

52

Sequence of AP

1. Stimulus (often graded potentials
2. Depolarizing phase
3. Repolarizing phase
4. Hyperpolarizing phase

53

What first happens when graded potentials cross threshold?

Voltage gated ion channels open, causes sharp depolarization

54

What happens after sodium channels are opened?

(+30mV) Na+ channels close and voltage gated K+ channels open

55

What happens when voltage gated K+ channels are opened?

Repolarization!

56

Why does hyper polarization occur?

Goes too far on downstroke, close K+ channels, returns to -70mV, prevents immediate location from having another action potential

57

Action potentials propagate...

UNIDIRECTIONALLY

58

Action potentials cannot go backwards due to...

Refractory period, membrane can't immediately fire an action potential due to channels being wide open & ion gradients exhausted

59

Saltatory conduction

Voltage gated ion channels are only located at nodes (between myelin sheath), action potential jumps from node to node

60

Information is encoded (strength of stimulus) in...

The FREQUENCY of action potentials

61

What is the final output of a neuron

Release of a neurotransmitter at synapse (NOT action potentials)

62

First step of synaptic transmission

AP triggers V-gated Ca2+ channels to open

63

Calcium influx into presynaptic neuron causes... (synaptic transmission)

Exocytosis of secretory vesicles carrying neurotransmitters

64

Are neurotransmitters stimulatory or inhibitory?

Both! (Could be either)

65

Once neurotransmitters are released into the synaptic cleft...

They commonly bind to ion channels on the post-synaptic neuron

66

What happens in an Excitatory Post-synaptic potential (EPSP)?

Postsynaptic neuron experiences depolarizing graded potential
ex: neurotransmitter (glutamate) opens Na+ channels

67

What happens in Inhibitory Postsynaptic Potential (IPSP)?

Hyper-polarizing graded potential
ex: Neurotransmitter GABA opens Cl- channels (Cl- rushes into post-synaptic cell)