Today in class• Notes • Writing assignment• Vocabulary Activity

• Reminder – quiz tomorrow• Reminder – candy neuron

tomorrow – bring candy1

Neurons and Neuronal Communication:The Structure of a Neuron

There are billions of neurons (nerve cells) throughout the body.

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Action potential:a neural impulse that travels down an

axon like a waveJust as “the wave” can flow to the right in a stadium even though the people only move up and down, a wave moves down an axon although it is only made up of ion exchanges moving in and out.

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The neuron receives

signals from other

neurons; some are

telling it to fire and some are telling it not to fire.

The neuron receives

signals from other

neurons; some are

telling it to fire and some are telling it not to fire.

When the threshold is reached, the action potential starts moving.

Like a gun, it either fires or it doesn’t; more stimulation does nothing.

This is known as the “all-or-none” response.

When the threshold is reached, the action potential starts moving.

Like a gun, it either fires or it doesn’t; more stimulation does nothing.

This is known as the “all-or-none” response.

The action potential

travels down the axon

from the cell body to the

terminal branches.

The action potential

travels down the axon

from the cell body to the

terminal branches.

The signal is transmitted to another

cell. However, the

message must find a

way to cross a gap

between cells. This gap is also called the synapse.

The signal is transmitted to another

cell. However, the

message must find a

way to cross a gap

between cells. This gap is also called the synapse.

How neurons communicate(with each other):

When does the cell send the action potential?...

when it reaches a threshold

The threshold is reached when excitatory (“Fire!”) signals outweigh the inhibitory (“Don’t fire!”) signals by a certain amount.

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The synapse is also known as the “synaptic junction” or “synaptic gap.”

The SynapseThe synapse is a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron.

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NeurotransmittersNeurotransmitters are chemicals used to send a signal across the synaptic gap.

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Reuptake: Recycling Neurotransmitters [NTs]

Reuptake: After the neurotransmitters stimulate the receptors on the receiving neuron, the chemicals are taken back up into the sending neuron to be used again.

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Seeing all the Steps TogetherNeural Communication:

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Some Neurotransmitters and Their FunctionsNeurotransmitter Function Problems Caused by Imbalances

Roles of Different Neurotransmitters

Serotonin Affects mood, hunger, sleep, and arousal

Undersupply linked to depression; some antidepressant drugs raise serotonin levels

Dopamine Influences movement, learning, attention, and emotion

Oversupply linked to schizophrenia; undersupply linked to tremors and decreased mobility in Parkinson’s disease and ADHD

Acetylcholine (ACh)

Enables muscle action, learning, and memory

ACh-producing neurons deteriorate as Alzheimer’s disease progresses

Norepinephrine Helps control alertness and arousal

Undersupply can depress mood and cause ADHD-like attention problems

GABA (gamma-aminobutyric acid

A major inhibitory neurotransmitter

Undersupply linked to seizures, tremors, and insomnia

Glutamate A major excitatory neurotransmitter; involved in memory

Oversupply can overstimulate the brain, producing migraines or seizures; this is why some people avoid MSG (monosodium glutamate) in food 9

Serotonin pathways

Networks of neurons that communicate with serotonin help regulate mood.

Networks of neurons that communicate with dopamine are involved in focusing attention and controlling movement.

Dopamine pathways

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Hearing the messageHow Neurotransmitters Activate ReceptorsWhen the key fits, the site is opened.

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Keys that almost fit:Agonist and Antagonist Molecules

An antagonist molecule fills the lock so that the neurotransmitter cannot get in and activate the receptor site.

An agonist molecule fills the receptor site and activates it, acting like the neurotransmitter.

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RecapThe Structure of the Neuron

• Basic Building block of the nervous system• Consist of cells specialized for rapidly

communicating information

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Part Function

DENDRITES RECEIVE INFORMATION FROM ADJOINING NEURONS

SOMA (CELL BODY) RECEIVES AND STORES INFORMATION WITHIN THE CELL

NUCLEUS GOVERNS AND DIRECTS ACTION OF THE CELL

AXON TRANSMITS NEURAL IMPULSE DOWN LENGTH OF CELL

TERMINAL BUTTONS BRANCHING AT END OF AXON; CONTAINS NEUROTRANSMITTERS

TYPES OF NEURONS

• Sensory neurons – bring information from outside world to your brain

• Motor neurons – transmit responses from brain to muscles and glands

• Interneurons– Connect neurons to other neurons– Join sensory and motor neurons in spinal cord

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Synapses

• What are synapses – part of the structure of the Neuron

• What is the purpose of synapses?–They are the chemical (neurotransmitter)

connections between ALL neurons

So can you describe the structure of the Neuron? No, not yet.

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Next Question…

• What is the purpose of Glial cells?– Fact – most numerous cells within the nervous

system– Fact – Like glue – holding neurons together– Fact – assist and support activity of neurons– Fact – forms the myelin sheath (covering of the

axon)

–The myelin sheath – what is the myelin sheath?

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Myelin Sheath

• Fatty, protective covering on neuron axons• Forms over time, usually by age of 12• Nodes of Ranvier (gaps in myelin sheath) –

neural impulse may jump from node to node

• Fact – Multiple sclerosis (MS) – a condition that occurs from the destruction of myelin sheath

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How Neurons Communicate

• Ions involved: sodium, potassium, and chloride

• Resting potential – neuron not activated; cell has slightly negative charge

• Depolarization – stimulation leads sodium to enter cell; electrical charge now changed from negative to positive

• Action Potential – neuron fires down length of axon; called a neural impulse

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Importance of Neurotransmitters

• Synapse is tiny gap between one neuron and the next

• At synapse, the impulse changes from electrical to chemical

• Neurotransmitters are these chemical messengers across synapse

• Chemicals from adjacent neurons may either excit or inhibit cell firing

List 5 Neurotransmitters and explain what they do.

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Can you do the following? Do you need your outline to do it?

Take out a sheet of paper and do it.• 1. Describe the structure of a neuron.• 2. Describe the process by which an action

potential is triggered.• 3. Describe how nerve cells communicate, and

discuss the importance of neurotransmitters for human behavior.

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