Module 3

Neural Communication

How do the different parts of our body COMMUNICATE?

ANSWER: via the endocrine and nervous systems

Why is it important for us to understand how cellular communication works?

Two cell types in the NS: 10% Neurons & 90% Glial Cells

A “typical” motor neuron is multipolar

Cell body (soma) is the “life hub” mediates cell metabolism, growth, division, contains DNA

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Axons are specialized to send information to other neurons

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Dendrites are specialized to receive information from other cells

A “typical” sensory neuron is unipolar or (rarely) bipolar

RARE

Most neurons in the brain are interneurons (aka association neurons)

Most interneurons don’t need a long axon… WHY?

They integrate

information

They carry sensory information and regulate motor activity.

Electrochemical communication between neurons

Outside has more

Sodium (+) and

Chloride (-)

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Inside has more

Potassium (+) and anions (-)

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lipid molecules

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Ion channels

Step 1: the neuron at rest (polarized) Inside is more negative than outside. -70mV

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What keeps the cell at -70 mV when at rest?

1. Concentration gradient

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ions want to move from an area of high to low concentration

2. Electrical gradient

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ions with the same sign (polarity) repel each other

ions with the opposite sign attract each other

The cell membrane. But pressure is building – some ions want in and others want out. Why?

Electrochemical communication between neurons

Outside has more

Sodium (+) and

Chloride (-)

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Inside has more

Potassium (+) and anions (-)

​

lipid molecules

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Ion channels

Step 1: the neuron at rest (polarized) Inside is more negative than outside. -70mV

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If it reaches approximately -55mV, our neuron will fire = action potential!

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If neighboring cells stimulate our neuron, sodium (+) will rush into the cell, making it less and less negative.

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Step 2: the neuron’s membrane potential begins to depolarize (inside becomes less neg.)

Eventually, the cell reaches its positive peak, sodium gates close, and potassium (+) gates open

Oops! Too far! No

worries, the Na – K

pump will bring us

back to normal ☺

Step 3: the neuron’s membrane potential begins to repolarize (inside becomes more neg.)

K+ rushes out, returning

the cell to negative

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The first action potential begins at the AXON HILLOCK

This creates a dominos effect of action potentials which end at the axon terminals

Step 4: the action potential starts at the axon hillock and then sweeps down the axon

The dominos effect

When the action potential reaches the terminal button, NT’s are released

Step 5 : neurotransmitters are released

Step 6 : NT’s diffuse across the synapse and bind to receptors on the post-synaptic cell

____ synaptic

____ synaptic

Pre

Post

Resting and action

Potentials - review

Once NT’s bind to receptors on the post-synaptic cell, what then?

Graded potentials are either inhibitory or excitatory

IPSP’s make the cell more negative, decreasing the

probability that the cell will fire

PSP’s are “local potentials” which are distinct from action potentials

Step 7 : neurotransmitters on receptors generate a GRADED POST-SYNAPTIC POTENTIAL

EPSP’s make the cell less negative, increasing the probability that the cell will fire

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Local potentials vs. action potentials

Analogous to a gentle nudge vs. a explosive push

Local potentials Action potential

Graded All-or-none

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Decremental Non-decremental

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Initiated in dendrite or soma initiated at the axon hillock

At any given time, MANY IPSP’s and EPSP’s are being generated

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The axon hillock “adds up” all the PSP’s… if the sum is ≥ -55mV …

Step 8 : PSPs travel to the axon hillock that then calculates the charge

How can local potentials have more “umph”?

Temporal summation & Spatial summation

What determines the firing rate for a cell?

Absolute Refractory Period

Immediately after the AP, �the cell cannot fire

How does the neuron code the intensity of the EPSP?

Relative Refractory Period

This occurs after the absolute �refractory period. Only a large �EPSP can get the cell to fire

Terminating synaptic activity

Re-uptake

Enzyme degradation

Regulating synaptic activity

Agonists

Antagonists

E

X

C

I

T

A

T

I

O

N

INHIBI

T

I

O

N

Graded vs Action potentials

What about Glial Cells in the nervous system?

The role of Glial cells in neurotransmission

1. They increase speed of conduction of the neural impulse

Local potentials travel faster down

the axon than action potentials

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AP’s occur at the nodes, local

potentials occur under the myelin.

This involves the passive diffusion of Na

under the sheath.

Without myelin, 100% of the signal would travel via �action potentials down the length of the axon.

This would take “forever”

slow

slow

slow

vey fast

2. They help to remove neurotransmitters from synaptic gaps

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• They remove K from synaptic spaces

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• They communicate electrically with neurons to modify the signals they send & receive

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• They release glial transmitters

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In other words, glial cells do a whole lotta shi

NEUROTRANSMITTERS

Chemical synapses

interaction

Review of

synapses

Chemical synapse Electrical synapse

The major players