71 Cards in this Set
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depolarize
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the inside of the cell is becoming more positive
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hyperpolarize
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the inside of the cell is becoming more negative
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repolarize
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inside of the cell is returning to baseline membrane voltage
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Three Box Model
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-Input: sensory in (PNS)
-Analysis: integration-goes to brain and spinal cord a decision is made(CNS)
-Output: Motor out (PNS)
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Forms of energy
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-Electromagnetic: changing form of energy to movement of Ions across a membrane
-Mechanical: touch
-Chemical: bind to receptor and opens channel allowing ions to move
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Transduction
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movement of energy
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Camillo Golgi
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-thought all neurons were connected by cytoplasmic bridges
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Santiago Ramon y Cajal
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-thought each neuron was a separate unit
-figured out information flow (dendrite to cell body to axon to axon terminal to next cell)
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Law of dynamic polarization
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flow from dendrite to axon terminal to next cell
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Functional nomenclature of neuron
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Dendrite and Cell body: input region
-Axon: conductile region
-Axon Terminal: output region
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Input region of neuron
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-all protein synthesis happens here
-responsible for synaptic potentials (transmembrane proteins are ligand-gated channels)
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Ligand-gated channels
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neurotransmitter operated channels
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Conductile region
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-predominately has voltage gated Ion channels (responsible for action potentials)
-vesicle from cell body is loaded onto kinesin and walks along axon
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Output region
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voltage-gated calcium channels, responsible for neurotransmitter release
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Fast Axonal Transport
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-vesicle and kinesin
-moving proteins that have been made on the rough ER (secreted proteins)
-200-400 mm/day
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Slow Axonal Transport
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-tubulin, actin, intermediate filament
-moves proteins made on free ribosomes (cytoplasmic proteins)
-0.5-2 mm/day
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Glia
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maintains the environment for neuronal function
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Types of Glia
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-Astrocytes (CNS)
-Oligodendrocytes (CNS)
-Microglia
-Schwann Cells (PNS)
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Astrocytes
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-only in CNS
-regulate extracellular potassium ion and neurotransmitter concentrations (uptakes if too much)
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Oligodendrocytes
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-only in CNS
-ensheates axons and forms an insulating layer
-regulates extracellular potassium concentrations
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Microglia
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-macrophases
-part of immune system
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Schwann Cells
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-glia cell of PNS
-maintains neurons/neuronal activity
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What happens after Astrocyte uptake neurotransmitters?
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-uptake of neurotransmitters
-converts N.T. to an inactive form
-the inactive neurotransmitter goes out of astrocyte and into the cytoplasm
-axon receptor picks it up again
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Potassium leak channels
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-only allows K+ ions to pass
-always open
-large anions (A-) keep all the potassium from leaking out
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When is an equilibrium reached for potassium?
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-when the tendency for potassium to leave is balanced by the electrical gradient
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What are the two forces that pull sodium ions into the cell?
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-positive charged Na+ ions are being pulled down since there is a negative charge in the cell
-Sodium diffuses down its concentration gradient
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Dominant permeable
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-if K+ channels are open, K+ channels are dominant permeable (leads to equilibrium of potassium)
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Membrane potential
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membrane potential seeks the equilibrium potential for the ion whose permeability is dominant
(say 400 Na+ channels are open, compared to 2 K+channels, Na+ has the dominant permeability)
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Na+ selective channels
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-voltage-gated (charge sensitive)
-doors open by charge
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Switching the membrane potential
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-starts as potassium as dominant
-after action potential is fired, sodium becomes dominant
-once the dominant permeability is sodium, then the membrane potential seeks end
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Threshold
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-the influx of sodium through sodium channels is balanced by the efflux of potassium through potassium channels
-sodium has to come in faster than it is leaving
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What happens at threshold?
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all v-gated Na+ channels open
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How do sodium voltage gates inactivate?
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ball and chain
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How do potassium voltage gates inactivate?
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they do not inactivate, they go through delayed rectifier
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propagation of potentials in membranes that lack v-gated channels (hose story)
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-voltage gated channels do not span across the membrane
-positive charge is leaving the cell through the potassium leak channels
-this makes it hard for the action potential to fire
because voltage is decreasing
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Action potential propagation in unmyelinated neurons
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-propagates action potentials at 1-2 m/sec
-channels are spread out equally
-voltage stays the same
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Capitance
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-ability to store charge
-separation of charge across a non-conducting medium
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High capitance
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-charges interact more since they are closer together (nothing in between)
-charge is stored near the membrane
-a lot more negative charges get through
-decreased velocity
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Low Capitance
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-myelination separates charges
-less interaction (less charge)
-depolarizes cell faster
-increased velocity
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Nodes of Ravier
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space between myelinated sections
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Action potential propagation in myelinated axons
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-v-gated Na+ and K+ channels are clustered at Nodes of Ravier
-100-115 m/sec
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How do the sodium ions that enter at the nodes of ravier open the channels at the next nodes of ravier?
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Na+ ions carry electromagnetic fields which opens the next Na+ channels at the next Nodes of Ravier since the electromagnetic field creates a positive charge
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Stretch Activated Channels
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stretch activated input region: changing the shape of the plasma membrane in the input region opens stretch activated channels
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How much sodium enters through stretch activated channels?
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-the number of sodium ions that enter the input region through stretch-activated channels is proportional to the amount stretch
-the harder we stretch plasma membrane the more the Na+ channels open, the more sodium comes in
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in which direction does the action potential propagate?
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the action potential propagates towards the CNS as sensory afferents
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Refractory period
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-a part after the action potential that makes it hard for another action potential to fire
-Na+ channels close during this time
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What is ganglion
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a cluster of neuronal cell bodies in the PNS
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Action potential frequency
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-the stronger the stimulus, the more frequent the action potential
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Otto Loewi story
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-frog heart with vagus nerve (transferred this water to the heart without nerve)
-the heart rate slowed down even without the vagus nerve
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Mechanisms for releasing neurotransmitters
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-voltage calcium channels allow Ca+ to enter the pre-synaptic element (axon terminal)
-the intake of calcium triggers for N.T. to release into synpatic cleft
-the Na+ then enters post-synaptic element and depolarizes the cell (excitatory post-synaptic potential)
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Neuromuscular synapse
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-there are extracellular proteins in the synapse
-enzymes replace astrocytes
-enzymes eat extra N.T. or break it down
-enzymes are called acetyl cholesterase (break N.T. into acetate and choline...these two then open receptor on dendrites)
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SNARE Hypothesis
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-Target snares
-Vesicle snares
1. Calcium enters the pre-synaptic element
2. Synaptotagmin binds to calcium
3. when synaptotagmin binds to calcium, 3 alpha helical transmembrane proteins bind together and pull the vesicle to the membrane and allow it to fuse and release N.T.
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T-SNARES
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-syntaxin: found in plasma membrane of axon terminal
-SNAP 25
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V-SNARES
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V.A.M.P.: found in membrane of vesicle
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synaptotagmin
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calcium sensor
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Neurotransmitter receptor on post-synaptic neurons
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-neurotransmitter-operated channels (ligand-gated, Ionotropic channels)
-binding of N.T. opens gates and allows ions to flow through (Na+)
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what opens v-gated Na+ channels?
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EPSP
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Trigger zone is a morphological site
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wherever the v-gated channels are clustered, this is where the trigger zone is
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Ohm's Law
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V=IR
(voltage=current x resistance)
-I is a fixed number
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Ohm's Law high resistance
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-few leak channels
-voltage increases
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Ohm's Law low resistance
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-many leak channels
-voltage decreases
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Spatial summation
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-EPSPs from spatially separate synaptic sites are summating
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Temporal summation
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-synaptic potentials must over lap in time
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Spinal cord
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-bilaterally symmetrical
-split into L/R and anterior/posterior
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White matter
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-characterized by myelinated axons
-conductile regions of neurons in CNS (tracts)
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tract
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bundle of conductile regions in CNS (oligodendrocytes)
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nerve
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a bundle of conductile regions in the PNS (Schwann cells)
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Gray matter
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-characterized by neuronal cell bodies
-input regions and output regions of neurons (synaptic sites)
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Anterior region of spinal cord
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primarily motor
-somatic efferent
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Posterior region of spinal cord
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primarily sensory
-point of input from the periphery into the CNS (primary sensory afferents)
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Spinal nerve
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-31 pairs
-carries motor and sensory neurons
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Muscle System