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| primary targets for synaptic input from the axon terminals of other neurons and are distinguished by their high content of ribosomes, as well as by specific cytoskeleton proteins. |
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| elongated nerve fibers that extend from the cell body to the terminal endings and transmits the neural signal. |
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| What makes a neuron capable of transmitting a signal faster? |
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The larger the axon, the faster the transmission of a signal.
If myelin is insulating the axon, expect to see faster transmission as well. |
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| What do action potentials facilitate in doing? |
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| carrying things from the cell body to the axon (presynaptic) terminal. |
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| Where are synaptic contacts made? |
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| made by axons ending on dendrites |
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| Where is an Action Potential's point of propogation? |
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| The cell body, particularly the axon hillock. |
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| What way does the action potential go? |
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| After being propogated at the axon hillock of the cell body, it goes to the terminus of the axon where synaptic contacts are made. The positioning of synaptic vesicles at the presynaptic membrane and their fusion initiate neurotransmitter release. The neurotransmitters released from synaptic vesicles modify the electrical properties of the target cell by bidning to receptors localized primarly at postsynaptic specializations. |
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| The chemical and electrical processes by which the information encoded by action potentials is passed on at synaptic contacts to target cells |
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| Presynaptic terminals and their postsynaptic specializations. Most abundant in all of the nervous system. |
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| The secretory organelles in the presynaptic terminal of chemical synapses that are spherical structures filled with neurotransmitter molecules. |
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| [ Anatomy of Synapses ]The synaptic contacts made by axon endings on dendrites represent... |
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| ...a special elaboration of the secretory apparatus found in most polarized epithelial cells. |
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| The axon terminal of the presynaptic neuron is immediately adjacent to a specialized region of postsynaptic receptors on the target. There is no physical connection between these two elements. pre- and postsynaptic componenets communicate via the secretion of molecules from the presynaptic terminal that bind to receptors in the postsynaptic cell. THESE MOLECULES MUST TRAVERSE AN INTERVAL OF EXTRACELLULAR SPACE BETWEEN PRE- AND POSTSYNAPTIC ELEMENTS CALLED THE SYNAPTIC CLEFT. |
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| [ Anatomy of Synapses ] Synaptic Cleft |
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| Site of extraceullular proteins that influence diffusion, binding, and degradation of the molecules secreted by the presynaptic terminal. |
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| More numerous than neurons by a ratio of 3-to-1. Glia also do not participate directly in synaptic interactions or in electrical signaling. Although their supportive functions help define synaptic contacts and maintain the signaling abilities of neurons. |
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| Restricted to the central nervous system. Elaborate local processes give these a starlike appearance. Maintains an appropriate chemical environment for neuronal signaling. |
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| Restricted to the central nervous system. Lays down a laminated, lipid-rich wrapping called myelin around some, but not all axons. |
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| Peripheral nervous system; cells that provide myelin. |
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Derived from hematopoietic precursos cells. Primarily scavenger cells that remove cellular debris from sites of injury or normal cell turnover.
Secrete signaling molecules that can modulate local inflammation and influence cell survival or death. |
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| In regards to membranes, what is meant by selective permeability? Why is this important in neurophysiology? |
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| Selective permeability establishes the idea that the cellular membrane only allows certain ions or molecules to be able to pass by. The selective permeability is due largely ti ion channels, proteins that allow only certain kinds of ions to cross the membrane in the directions of their concentration gradients. Thus, channels and transports basically work against each other, and in doing so they generate the resting membrane potential, action membrane potentials, and synaptic potentials and receptor potentials that trigger action potentials |
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| Na+ Voltage-gated Channels |
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Definition
These channels have one peptide.
Four domains.
Six transmembrane segments (each labaled S1-S6)
Selective filter for Na+ and an outer pore (called "P loops and are located along S5 to S6 of the segments)
On S6 there is an inner pore.
Activation + Voltage sensors are S4, inactivation are D3-D4
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One peptide
Four domains
Six transmembrane segments (S1-S6)
Selectively filter for Ca++ and outer pore
P Loops on S5-S6
Inner pore is located on S6
Activation + Voltage Sensors -- S4 segments (also ligand-gated)
Inactivation is various |
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Definition
Four peptides (makes it a tetramer)
Six membrane segments (S1-S6), but two of these S segments will NOT BE VOLTAGE-GATED
Selectively filters for K+ and outer pore
P loop is S5-S6
Inner pore is S6
Activation + Voltage is S4 segments (also ligand-gated)
Inactivation is done through a C-terminus ("ball & chain") |
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| Nernst Equation and terms with it! |
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Definition
Eion = RT/ZF ln [ion outside]/[ion inside]
Eion = Nernst (equilibrium) potential of ion in mV
R = gas constant, T = ° Kelvin, F = Faraday constant
z = valence
[ion] = concentration of ion in mM |
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| When would one use the Nernst Equation? |
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| To predict the electrical potential generated across the membrane at electrochemical equilibrium can be predicted by thsi formula. For a simple hypothetical system with only one permeant ion species, the Nernst equation allows the electrical potential across the membrane at equilibrium to be predicted exactly. |
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| Describe and explain experiments that demonstrate how the Na-K-ATPase works: |
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| First off, this pump is crucial for brain function as it accounts for 20-40% of the brain's total energy consumption. Keynesand his colleagues found that this efflux ceased when the axon's supply of ATP was interrupted by reatment with metabolic poisons. Other conditions that lowered intracellular ATP also prevented Na+ efflux. These experiments showed that removing intracellular ATP also prevented Na+ efflux. Further studies with radioactive K+ demonstrated that Na+ efflux is associated with simultaneous ATP-dependent influx of K+. These opposing fluxes of Na+ and K+ are operationally inseparable. Removal of external K+ greatly reduces energy-dependent movements of Na+ and K_ implicated and ATP-hydrolyzing Na+/K+ pump in generation of th thought to alternately shuttle Na+ and K+ across the membrane in a cycle fueled by the transfer of a phosphate group from ATP to the pump protein. For every 3 Na+ removed, 2 K+ are transported. Cell pump generate an electrical current that can hyperpolarize that membrane potential. |
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Vm = RT ln PK[K+]outside + PNa[Na+]outside + PCl[Cl-]inside
F PK[K+]inside + PNa[Na+]inside + PCl[Cl-]outside |
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| When might one use the "Goldman Equation" to explain a resting membrane potential? |
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If the resting membrane potential were permeable to only K+, then the Goldman equation predicts that the membrane potential will vary in proportion to the logarithm of the K+ concentration gradient across the membrane.
When Hodkins and Huxley did this experiment they found that the resting membrane potential did change when the external K+ concentration was modified becoming less negative as external K+ concentration was raised. When the external K+ concentration was raised high enough to equal the concentration of K+ inside the neuron, thus making the K+ equilibrium potential 0mV, the resting membrane potential was also approx. 0mV |
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The event that carries signals over such distances is a self-regenerating wave of electrical activity. It is all-or-nothing change in the voltage across the nerve cell membrane that conveys information from one point to another.
[image] |
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| How might one use the Goldman equation to explain an action potential? |
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The equation is for a complex situation that may arise where Na+ and K+ are unequally distributed across the membrane. Ie., what would be the membrane potential if it was permeable to both Na+ and K+, when we know that when permeable to only K+ it would be +58mV.In this case it would depend on the relative permeability of the membrane to K+ and Na+. If more permeable to K+, potential would be approx. -58mV. If more permeable to Na+, potential would be closer to +58mV. This takes into account both the concentration gradients of the permeant ions and the relative permeability of the membrane to each permeant species.
What would happen if the membrane started out to be permeable to K+ and then switched to become more permeable to Na+? membrane potential would start out at a negative level, become positive while the Na+ permeability remained high, and then fall back to a negative level as the Na+ permeability level decreased again. This case essentially describes what goes on in a neuron during ana ction potential. In the resting state, Pk of the neuronal plasma membrane is much higher than PNa. since, as a result of the action of ion transports, there is always more K+ inside the cell than outside, the resting potential is always negative. As the membrane potential is depolarized, Pna increases. The transient increase in Na+ permeability causes the membrane potential to become even more positive, because Na+ rushes in.
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| Ion diffusion in a typical neuron found in your brain for K+, Na+, Ca++ |
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Definition
| Due to a higher concentration of K+ inside the membrane, it is going to want to diffuse out. Na+ concentrations are higher outside than in, so it wants to move inward. Ca++ concentration is higher inside than outside so, likewise, it wants to move inward. |
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| Different types of Ion channels |
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Definition
While ion channels are all selective, there are different subsets:
- voltage gated
- ligand-gated channels
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| What do Voltage sensors respond to? |
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| A change in membrane potential. |
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| What are three physiological characteristics of most ion channels? |
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Voltage sensor --> So that it may respond to changes in membrane potential
Selectivity Filter --> So that it creates a channel that is selectively permeable.
Diffused Ions are allowed along their gradient... |
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| Principles of Diffusion and how it applies to neurobiology |
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| Diffusion allows for areas of higher concentration to move to areas of lower concentration in order to establish equilibrium. In the field of neuroscience we want this for resting membrane potentials, whose voltage should be somewhere around 0mV. |
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There is an efflux of Na+, which is then reduced by removal of external K+. Recovery occurs when K+ is restored. Efflux decreased by metabolic inhibitors, such as dinitrophenol, which block ATP synthesis. Recovery when ATP is restored.
Also, when Na+ binds to pump you get a conformational change that releases 2K+ on the inside of the cell, and then releases 3Na+ on the outside of the cell as it takes in 2 more K+. So for every 3 Na+ lost, you gain 2 K+, leaving a -1 charge on the system. |
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| Membrane potential influences ion fluxes |
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Definition
| At -116 mV, there is no net flux of K+ from outside to inside, at -58 mV there is no net flux of K+. At 0 there is a net flux of K+ from inside to outside. |
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| Myelination and action potential conduction/propogation |
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Definition
Propagation speed is proportional to Rm/Cm
As myelination increases, Rm increases and decreases Cm.
This myelin "insulates" axon. Current flows through cytosol. |
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