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 or

spike

see depolarization (change from negative inside neuron to more positive)

Neuron stimulated (either electrically or by receiving a “message”

action potential or

spike

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 or

spike

Hyperpolarization return to negative this is the refractory or recovery period

action potential or

spike

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

disease: Multiple Sclerosis progressive, autoimmune disease onset ~ 20 years of age early symptoms: motor symptoms, such as

weakness, leg dragging, stiffness, a tendency to drop things, a feeling of heaviness, clumsiness,

Advantages of Saltatory Conduction

What about communication between neurons?