4 functional zones of a neuron
- Input zone
- Trigger zone
- Conducting zone
- Output zone
Input zone
- Part where incoming signals are received
- Contains: dendrites and cell body
Dendrites
Projections from cell body that receive electrical and chemical inputs
Cell body
Location of the nucleus and other organelles
Trigger zone
- Where action potentials are initiated
- Contains: axon hillock
Axon hillock
Where the axon leaves the cell body
Conducting zone
- Where action potentials are conducted to their target locations
- Contains: axons
Axon
Tubular extension that conducts the action potential away from the cell body
Output zone
- Release chemical messengers
- Contains: axon terminals
Axon terminals
Release chemical messengers to communicate with other cells
What is conduction of an action potential?
- Action potentials trigger new ones in adjacent areas
- This repeats along the axon, keeping the signal strong with no decay
How is one-way propagation ensured?
- By refractory periods
- The voltage-channels become inactive
- They cannot be immediately reopened so the wave of excitation moves away from them
Neuronal firing rates
How often a neuron produces an action potential
Absolute refractory period
Under no conditions another action potential can be triggered
Relative refractory period
Still difficult but if the stimulus is strong enough, an action potential may be triggered
Oligodenedrocytes
Supporting cells of the central nervous system
Schwann cells
Supporting cells of the peripheral nervous system
What are nodes of Ranvier?
Gaps in myelin where axon is exposed; action potentials are regenerated here
What is myelin?
- A lipid-rich insulation made by oligodendrocytes (CNS) and Schwann cells (PNS) that wraps around axons
- They prevent current leakage, and speed conduction
Saltatory conduction
- In myelinated axons, action potentials jump from one node of Ranvier to the next
- makes conduction up to 50× faster than in unmyelinated axons
Synapse
- Junction between a presynaptic neuron and a postsynaptic neuron
- Includes the synaptic cleft between the 2 neurons
Presynaptic neuron
Neuron from which the action potential is coming from
Neurotransmitters
Chemical released into the synaptic cleft which activate ion channels on the postsynaptic neuron’s membrane
Synaptic cleft
Area of extracellular fluid between the pre and post-synaptic neurons
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Module 1: Section 1 + 256
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Module 1: Section 316
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Module 1: Section 413
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Module 1: Section 531
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Module 2: Section 120
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Module 2: Section 216
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Module 2: Section 332
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Module 2: Section 451
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Module 2: Section 511
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Module 4: Section 127
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Module 4: Section 235
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Module 4: Section 333
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Module 4: Section 426
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Module 4: Section 59
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Module 4: Section 628
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Module 5: Section 115
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Module 5: Section 234
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Module 5: Section 352
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Module 5: Section 47
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Module 5: Section 533
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Module 6: Section 121
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Module 6: Section 223
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Module 6: Section 344
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Module 6: Section 428
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Module 6: Section 512
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Module 6: Section 613
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Module 6: Section 743
