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19 Cards in this Set
- Front
- Back
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Axons
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-can carry electrical signal over long distances (meters)
-Release signal against target neuron -can be singular or may bifurcate into collateral processes -specialized for the conduction of electrical impulse (action potentials) |
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Saltatory conduction
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-allows the action potential to regenerate at each Node of Ranvier
-ensures that signals do not deteriorate as they travel along the axon |
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Glial cells
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-comprised the majority of cells in the CNS
-about a 10:1 ratio with neurons -Three main groups: Astrocytes, oligodendrocytes/Schwann cells, Microglia |
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Astrocytes
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-1/2 of the brain's cells
-Multiple functions -Support neuronal synapses -Buffer extracellular ions -Provide trophic support -Assist neuron-capillary exchange -Guide neuronal migration |
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PNS
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-Functional divisions: Somatic and autonomic
-Somatic- voluntary muscle control; sensory systems -Autonomic- Involuntary, visceral functions (Sympathetic: "fight-or-flight", Parasympathetic: "rest and digest", and enteric: GI control) -Nerves bundle together and intersect, forming a plexus (EX: brachial plexus- neck, shoulder, and arm nerves) |
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Characteristics of electrical synapse
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-close apposition of pre-and post-synaptic membranes
-Bi-directional signaling -Nondescript appearance (on electron micrograph) -Signaling through an electrical synapse is nearly instantaneous |
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Why is the chemical synapse slower?
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-activation of pre-synaptic machinery for neurotransmitter release (350us)
-Diffusion of neurotransmitter (50us) -response of post-synaptic receptors and associated proteins (150us) |
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Advantages of the electrical synapse
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-Faster (~0.5ms faster than chemical)
-Greater certainty of signal transfer -Still functional at low temperatures |
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Advantages of the chemical synapse
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-signal can be modified at various stages of transmission
-excitatory, inhibitory, or modulatory -multiple neurotransmitters from same terminal -synaptic plasticity |
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Neurotransmitters
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-Small compounds typically released in response to AP (when voltage-gated Ca2+ channels open)
-Must fulfill 5 criteria to be classified as a neurotransmitter: 1) synthesized in pre-synaptic cell; 2) AP-dependent release; 3) Exogenous application mimics endogenous effects; 4) Effects blocked by specific inhibitors; 5) Synapse must have mechanism to terminate signal |
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To end the signaling, the neurotransmitters may:
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1) diffuse away from the synaptic cleft
2) be taken up by the pre-synaptic neuron (or astrocyte) 3) be degraded by an enzyme Signaling by Ach and neuropeptides is terminated by enzymatic degradation Signaling by most other classic neurotransmitters is terminated by uptake |
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Neurotransmitter receptors can be:
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-Ligand-gated ion channels ("fast")- open ion channels directly
-G-protein coupled receptors ("slow")- indirect actions on the activity of ion channels |
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The effect of neurotransmitter can be:
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-Excitatory: depolarize post-synaptic cell
-Inhibitory: hyperpolarize post-synaptic cell -Modulatory: indirect effects on post-synaptic cell |
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Ion channel
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-Forms a hydrophylic pore through which ions flow from one side of the membrane to the other
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Voltage Gated
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-Open in response to changes in membrane potential
-Undergo channel inactivation (e.g. Na+ channel) -Show high specificity for ion permeability -Almost all are related in structure and function |
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Ligand Gated channels
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-Mechanism whereby fast AP transfer between two cells is manifest-fast conduction
-Receptor responsive to both voltage and ligand stimulation act as "Coincidence Detectors" |
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Metabotropic receptors
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-Basically, ligand-receptor interactions that transfer information by altering membrane "metabolism"
-Usually G-protein coupled receptors -More modulatory and slower acting than ionotropic receptors |
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Guidance Molecules
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-Produced by cells shown to guide neuronal migration
-Must be essential for guidance -Guided cells must have sensors/receptors for substance -Mislocate gradient must result in improper wiring -3 classes of guidance molecules: Ephrins, Semaphorins, and Netrins |
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Ephrins
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-Largest family of receptor tyrosine kinase
-receptor usually display specificity -receptor usually distributed in gradients along membrane -activation usually modulates GTPases (Roh, cdc42) that affect actin assembly |
