How do neurons communicate?
a
b
c
How do neurons communicate?
Need to think about this question 2 ways
How do neurons communicate?
1. within neurons –
2. between neurons-
Neuron receiving info
Information traveling down neuron
within neurons – electrically
between neurons – chemically◦ Synapse – space between neurons
How do neurons communicate
Ramon Y Cajal developed Golgi
Stain
first determined space between neurons
“synapse”
the “resting” state
the “active” state◦ neuron is firing◦ action potential
the “refractory” state
Neurons can exist in one of 3 states
giant squid axon
How do we know about what is happening in the neuron?
inside of the axon has a slightly negative charge relative to outside the axon◦ called the membrane potential◦ usually around -70mV
At rest:
inside of the axon has a slightly negative charge relative to outside the axon◦ called the membrane potential
why?
At rest:
action potential orspike
see depolarization (change from negative inside neuron to more positive)
Neuron stimulated (either electrically or by receiving a “message”
action potential orspike
see depolarization (change from negative inside neuron to more positive)
◦ “threshold” – if a great enough depolarization occurs, an action potential will occur
◦ action potential – very quick – milliseconds Other terms – spike, firing, generating an AP
Neuron stimulated (either electrically or by receiving a “message”
action potential orspike
Hyperpolarization return to negative this is the refractory or recovery period
action potential orspike
All axons and cells have a membrane thin lipid (fat) bilayer
The membranes have channels (to allow ions in or out)
Ions – molecules with a charge These channels can be open or shut
What causes these changes in electrical potential and the action potential?
Ions flowing across the membrane causes the changes in the potential
Ions are molecules that contain a positive or negative charge anion – negative charge cation – positive charge
What causes these changes in electrical potential?
Na+ sodium◦ HIGHER CONCENTRATION OUTSIDE THE AXON
Cl- chloride ◦ HIGHER CONCENTRATION OUTSIDE AXON
K+ potassium◦ higher concentration inside the axon
A- anions -large (-) molecules with a negative charge (stuck inside the axon)
Some important ions for neuronal communication
INSIDE AXON(intracellular)
OUTSIDE AXON (EXTRACELLULAR FLUID)
Na+
Na+
Na+
Na+
Na+Na+
Na+
Na+ and Cl- are in higher concentrationin the extracellular fluid
Cl-
Cl-
Cl-
Cl-Cl- Cl-
Cl-
Neuron at Rest
Na+
Na+
Na+
Na+Na+
Na+
Cl- Cl-
Cl-
Cl-
Cl-
Cl-
Cl-Cl-
A-
A-
A-
A-
A-
A-
INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID)
Na+
Na+
Na+
Na+
Na+A-
A-
K+ and negative anions are in higher concentrationin the intracellular or inside the axon
Cl-
Cl-
Cl-
K+K+ Cl-
K+
Neuron at Rest
K+
K+
K+
A-
A-
Na+
Cl-
K+
concentration gradient –◦ ions diffuse from higher concentration to lower
concentration
Some forces that play a role in maintaining membrane potential
example of concentration forces
Na+
K+
Cl-
What would each ion do if the ion channel opened based on the concentration gradient?
concentration gradient –◦ ions diffuse from higher concentration to lower
concentration
electrical gradient -◦ opposite charges attract so ions are attracted to
an environment that has a charge that is opposite of the charge they carry!
Some forces that play a role in maintaining membrane potential
example of electrostatic forces
Na+
K+
Cl-
What would each ion do if the ion channel opened based on electrostatic forces ?
INSIDE AXON(intracellular)
OUTSIDE AXON (EXTRACELLULAR FLUID)
Na+
Na+
Na+
Na+
Na+Na+
Na+
Na+ and Cl- are in higher concentrationin the extracellular fluid
Cl-
Cl-
Cl-
Cl-Cl- Cl-
Cl-
Axon depolarizing
Na+
Na+
Na+
Na+Na+
Na+
Cl- Cl-
Cl-
Cl-
Cl-
Cl-
Cl-Cl-
A-
A-
A-
A-
A-
A-
opening of Na+ channels and influx of Na+ ions
What drives the action potential?
What happens if sodium channels are blocked?
lidocaine, novocaine, cocaine
TTX – tetrototoxin
Sagitoxin-◦ red tides
Na+
K+
Cl-
ConcentrationGradient
ElectricalGradient
after the AP (+ intracellular)
INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID)
Na+
Na+
Na+
Na+
Na+A-
A-
K+ and negative anions are in higher concentrationin the intracellular or inside the axon
Cl-
Cl-
Cl-
K+K+ Cl-
K+
Neuron at Rest
K+
K+
K+
A-
A-
Na+
Cl-
K+
Sodium-potassium pump – active force that exchanges 3 Na+ inside for 2 K+ outside
INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID)
Na+
Na+
Na+
Na+
Na+A-
A-
K+ and negative anions are in higher concentrationin the intracellular or inside the axon
Cl-
Cl-
Cl-
K+
K+
Cl-
K+
After the action potential
K+
K+
K+
A-
A-
Na+
Cl-
K+Na+
Na+
Na+
Na+
Na+
myelin sheath (80% fat and 20% protein)◦ produced by glia
conduction or propogation of the action potential
http://www.blackwellpublishing.com/matthews/channel.html
nodes of ranvier
myelin sheath (80% fat and 20% protein)◦ produced by glia
◦ nodes of ranvier
conduction or propogation of the action potential
nodes of ranvier
myelin sheath (80% fat and 20% protein)◦ produced by glia
◦ nodes of ranvier
◦ saltatory conduction (200 ft/sec)
conduction or propogation of the action potential
http://www.blackwellpublishing.com/matthews/actionp.html
speed, efficiency of neurotransmission
Advantages of Saltatory Conduction
speed, efficiency of neurotransmission
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Advantages of Saltatory Conduction
What about communication between neurons?