Neural Communication

1
NeuralCommunication

• Signaling within
• a neuron
• Lecture 5

2
Postsynaptic Potentials

• Em changes
• dendrites soma
• Excitatory
• Inhibitory -

3
Postsynaptic Potentials - PSPs

• Chemically-gated ion channels
• Graded
• Summation
• Fast
• Decremental

4
EPSPs

• Excitatory Postsynaptic Potential
• Depolarization ()
• Em becomes more positive
• Na influx

5
EPSP

• Depolarization
• more likely to fire

Em
-65mv
- 70mv
AT REST
-
Time
6
Temporal Summation

• Repeated stimulation
• same synapse

Em
-65mv
- 70mv
AT REST
-
Time
7
Temporal Summation

more depolarization
Em
-65mv
- 70mv
AT REST
-
Time
8
Temporal Summation

more depolarization
Em
-65mv
- 70mv
AT REST
-
Time
9
Spatial Summation

• Multiple synapses

Em
-65mv
- 70mv
AT REST
-
Time
10
IPSPs

• Inhibitory Postsynaptic Potential
• similar to EPSPs
• EXCEPT opposite
• hyperpolarization (-)
• Em becomes more negative
• K efflux

11
IPSP

• Hyperpolarization
• less likely to fire
• also summate (max)

Em
- 70mv
AT REST
-
Time
12
EPSPs IPSPs summate

• CANCEL EACH OTHER
• Net stimulation
• EPSPs IPSPs net effects

13
EPSP IPSP
- 70mv
14
EPSP IPSP
Excitatory Inhibitory Depolarization Hyper
polarization Na influx K efflux or
Cl- influx more likely to fire less likely
15
EPSP IPSP
-70mV
16
Action Potentials

• Large and rapid change in membrane potential
• electrically-gated channels
• EPSPs
• threshold potential
• Occurs in axon
• triggered at axon hillock

17
AP Characteristics

• Voltage-gated channels
• All or none
• Slow
• Non-decremental
• Self Propagated
• regenerated

18
40
C E gradients drive Na into cell
Depolarization Na influx
0
-60
-70
-80
Time
19
outside
Na
K
axon
DEPOLARIZATION
20
outside
Na
Na
neg
Na
pos
Na
Na
Na
K
axon
DEPOLARIZATION
21
40
110 mV
Amplitude
Depolarization Na influx
0
- 70 mV to 40 mV
-60
-70
-80
Time
22
40
Repolarization K efflux
0
-60
-70
-80
Time
23
outside
Na
Na
neg
Na
pos
Na
Na
Na
K
axon
REPOLARIZATION
24
outside
Na
K
Na
K
pos
K
K
K
neg
Na
Na
K
Na
K
axon
REPOLARIZATION
25
40
0
-60
-70
-80
Time
26
outside
Na
K
K
K
K
pos
K
K
K
K
neg
Na
Na
Na
K
K
axon
AFTER-HYPERPOLARIZATION
27
Refractory Period

• after AP
• wont fire again
• relative absolute
• Relative
• during after hyperpolarization
• requires greater depolarization

28
Absolute refractory period

• Na channels deactivate
• will not trigger AP
• must reset
• Ball Chain Model

29
Na channel deactivation
30
Frequency Code

• Pattern Intensity of stimulus
• frequency of APs
• Place type of stimulus
• Visual, auditory, pain, etc.
• Brain area that receives signal
• Doctrine of Specific Nerve Energies

31
FREQUENCY CODE
Weak stimulus
Moderate stimulus
Strong stimulus
32
PSPs vs APs

• Graded All-or-none
• Summation
• longer duration short
• 1-2 msec
• chemical-gated voltage-gated
• passive spread propagated
• instantaneous slow
• decremental nondecremental

33
Saltatory Conduction

• Myelinated neurons
• oligodendroglia Schwann cells
• Transmit long distances
• APs relatively slow, regenerates
• EPSPs - fast, decremental
• Saltatory combines both types of current
• speed without loss of signal

34
Saltatory Conduction

• Nodes of Ranvier
• action potentials
• Myelinated
• like electricity through wire
• decremental but triggers AP at next node
• Safety factor - trigger AP across 5 nodes

35
Saltatory Conduction
36
Presynaptic Modulation

• Modifying PSP by influencing presynaptic neuron
• Presynaptic inhibition
• amount of NT released
• Presynaptic inhibition
• amount of NT released
• Effect on activity of postsynaptic neuron
• depends on nature of synapse

37
Presynaptic Inhibition
Excitatory Synapse

• A active
• B more likely to fire
• Add a 3d neuron

38
Presynaptic Inhibition
Excitatory Synapse

• axoaxonic synapse
• C is inhibitory

39
Presynaptic Inhibition
Excitatory Synapse

• C active
• less NT from A when active
• B less likely to fire

40
Presynaptic Inhibition
Inhibitory Synapse
-

• C active
• more NT from A when active
• B more likely to fire

41
Presynaptic Facilitation
Excitatory Synapse

• C active (excitatory)
• more NT from A when active
• B more likely to fire

42
Presynaptic Facilitation
Inhibitory Synapse
-

• C active
• more NT from A when active
• B even less likely to fire