Download Lecture 2 (Neurons)

BIO 132
Neurophysiology
Lecture 2
Neurons
Lecture Goals:
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Understanding the basic function of the
nervous system.
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Understanding the parts of a neuron.
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Neuron – A specialized cell of the body that can
communicate information quickly by using ionic
currents and chemical signals called
neurotransmitters.
Nerve - Many neurons that are bundled
together and covered by a connective tissue
sheath.
Nervous System – The entire network of
interconnecting neurons.
Overall function of the nervous system:
To control motor output of the body based on
sensory information it detects from both the
internal and external environments of the body.
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There are ~100 billion neurons in the brain.
(Current population is less than 7 billion people.)
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Each neuron can make one to thousands of
connections with other neurons.
Glial cells are support cells of the nervous
system
There are ~10 times as many glial cells as there are
neurons.
 Used to nourish, insulate, direct growth of neurons.
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Neuron Morphology
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Parts of a typical neuron:
Dendrites
Cell body
Axon
Axon terminal
Cell Body (soma)
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Contains most of the cellular machinery of the neuron (nucleus,
ER, mitochondria, golgi complex, etc).
Is where most the synthesis of new cellular products occurs.
Cell body
Dendrites
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Means “tree” in Latin.
Main site where input is received from other neurons.
Dendrites
Axon
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Long projection from cell body that carries an ionic signal, called
an action potential, to other neurons.
Can be very short or very long (up to 6 feet in humans).
Can send off many branches (collaterals).
Axon
Axon Terminal
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Is at the end of each axon.
Contains vesicles filled with neurotransmitter.
Forms a connection with another neuron, called a synapse.
Axon terminal
Classifying Neurons
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There are several conventions for classifying neurons:
 By neurites (projections from the cell body).
 By dendrite shape.
 By connections.
 By neurotransmitter released
Classification By Neurites
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Unipolar neuron - A single neurite (projection from
cell body:
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Bipolar – Two neurites (both part of the axon)
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Multipolar – Many neurites (usually one axon and many
denrites)
Classification By Connections
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Primary sensory – dendrites detect external stimuli.
Stimuli
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Motor - makes a direct connection with skeletal muscle.
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Interneuron - only makes connections with other
neurons. (Most numerous type)
Classification By Neurotransmitter
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Based on the type of neurotransmitter released.
Examples:
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Cholinergic
Acetylcholine (ACh)
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Noradrenergic
Norepinephrine (NE)
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GABAergic
GABA
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Glutamatergic
Glutamate (Glu)
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Dopaminergic
Dopamine (DA)
Classifying Glia
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Astrocytes
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Most numerous
Fill the space between neurons
Envelope synapses to limit the spread of neurotransmitters
Regulate chemical content of extracellular fluid
Remove neurotransmitters from synapse
Myelinating glia – insulate axons from ion leakage
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Oligodentrites
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Found in Central NS and spinal cord
Can wrap around several axons
Schwann cells
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Found in peripheral NS
Wrap around a single axon