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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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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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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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