Neuronal Anatomy and Communication
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Transcript of Neuronal Anatomy and Communication
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Neuronal Anatomy and Communication
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Cells of the Nervous System: Neurons
Three types of neurons:Sensory neuronsMotor neurons Interneurons
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Neuronal structure
Soma Dendrites Axon Terminal
buttons Synaptic cleft
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Neuronal classifications
Bipolar neuron (a)
Unipolar neuron (b)
Multipolar neuron
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Internal structure Cell membrane Cytoplasm Mitochondria Nucleus
ChromosomesProteins
Microtubules
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Cells of the Nervous System: Glia
Glial cells support neural function
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Glial Cells Astrocytes
Arms wrap around blood vessels
and neuronal structures Isolate the synaptic cleftMaintain chemical
composition
of extracellular spaceClean up following cell
death
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Glial cells
Oligodendrocytes (CNS) & Schwann cells (PNS)Provide support and insulation
in the form of the myelin sheath
Myelin Nodes of Ranvier
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Glial cells
MicrogliaSmallest glial cellsBrain’s immune cells
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Blood-Brain Barrier
Composed of tightly-packed cells of the cerebral blood vessels.
Regulates chemicals in the CNS Protects the brain from toxins Semipermeable
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The withdrawal reflex: an example of neuronal communication
1. Sensory neuron detects
2. Message is sent
3. Neurotransmitter is released
4. Interneuron
5. Motor neuron sends a message
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Communication within a neuron
Based on changes in the membrane potential of the neuron.
Neurons have two basic potentials
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Resting membrane potential
The inside of a neuron is negatively charged relative to the outside
Due to concentrations of positively and negatively charged ions in the brainOutside the cell Inside the cell
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Resting membrane potential A concentration gradient pulls the sodium,
potassium and chloride ions toward the membrane; electrostatic forces prevent them from crossing it.
The balance between potassium and sodium ions in and out of the neuron is maintained
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Membrane potential
The membrane potential can change: Depolarization Hyperpolarization
-80
-70
-60
-50
-40
Depolarization
Hyperpolarization
Resting Membrane Potential
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Action potential
A hyperpolarization _________ communication within a cell.
A depolarization _________ the cell, and _________ the chances of communication within the cell.
Threshold of excitation
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Action potential
A massive, momentary reversal of the membrane potential.
Carried down the axon from the cell body to the terminal buttons.
Results in the release of a chemical message into the synapse.
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Action potential
Chemical messages from other neurons affect the neuron’s charge.
Excitatory Post-Synaptic Potentials (EPSPs) Inhibitory Post-Synaptic Potentials (IPSPs)
When the cell is depolarized to -65mV, an action potential begins.
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Steps of the action potential1. Ion channels in the
membrane rapidly open and Na+ enters the cell (-65mV +40mV)
2. As Na+ rushes in, K+ is forced out of the cell.
3. As the action potential peaks, Na+ channels close, and no more Na+ enters the cell.
4. K+ is forced out of the cell, which decreases the charge inside the cell and K+ channels close.
5. K+ ions trapped outside of the cell result in a temporary hyperpolarized membrane potential.
6. Ion channels reset and the Na+/K+ pump returns the ions to the normal gradients.
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All-or-None law
An action potential either occurs or it doesn’t.Magnitude is the same.Does not diminish in strength.
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Rate law The strength of a response depends on the
firing rate of the cell. More action potentials/second = strong
response, fewer = weak response.
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Action potential conduction Action potentials depend on sodium influx
from the extracellular fluid.Nodes of Ranvier.
Saltatory conduction
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Communication between neurons Within-neuron communication: electrical
signal Between-neuron communication: chemical
signal Synaptic transmission
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Synaptic structure Presynaptic membrane
Terminal buttonVesiclesTransporter molecules
Synaptic cleft Postsynaptic membrane
On the dendrite, soma or axonReceptors
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Neurotransmitter binding Binding sites Ligands
Molecule that fits into a specific binding site Endogenous ligands Exogenous ligands
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Synaptic firing
1. Initiated by an action potential in the cell
2. Neurotransmitter (NT) binds to the receptor
Prompting specific ion channels to open
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Types of receptors Ionotropic receptor
Neurotransmitter
ReceptorG-protein
Enzyme
Ion Channel
GateJoins the
ion channel
Second messenger
Metabotropic receptor
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Synaptic firing3. Postsynaptic potentials are produced by the
flow of ions in and out of the cell. Each NT produces a specific postsynaptic
potential Excitatory NTs Inhibitory NTs
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Synaptic firing
4. Neural integration is the summation of all postsynaptic potentials.
Determines the response to PSPs.
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Synaptic firing Remember – Each neuron has synaptic
connections with hundreds of other neurons, and must summate all incoming PSPs thousands of times each second!
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Synaptic firing
5. Removal of NT from the synapse terminates PSPs
Reuptake Enzymatic deactivation
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Autoreceptors
Found on the presynaptic membrane
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Types of synapses Axodendritic Axosomatic Axoaxonic