ANIMAL CHP. 5
List the regions of a typical vertebrate motor neuron and summarize their functions.
Axon: signal conduction axon terminal: signal transmission dendrites: signal reception axon hillock: signal integration
Which will conduct an action potential more quickly - a myelinated or an unmyelinated axon? Why?
It insulates the axon and assembles specialized molecular structure at the nodes (It jumps). In unmyelinated axons, the action potential travels continuously along the axons.
Explain two ways in which graded potentials can be integrated to generate or to not generate an action potential.
subthreshold: no action potential generated; this is when a stimulus that is too small in magnitude to produce an action potential in excitable cells suprathreshold: action potential generated Threshold for most neurons to fire = -55 mV Action Potentials are Triggered by Net Graded Potentials at Axon Hillock
Explain in detail how chemical synapses work. Your answer should include the role of the action potential, voltage-gated calcium channels, intracellular calcium levels, secretory vesicles, neurotransmitter, and ligand-gated receptors.
1. action potentials arrive at the axon terminal 2. voltage-gated Ca2+ channels open 3. ca2+ enters the cell docked vesicles fuse with membrane and release neurotransmitter by exocytosis 4. neurotransmitter diffuses across the synaptic cleft and binds to receptors 5.binding of neurotransmitter to receptor activates signal transduction pathways
Can another action potential be generated during the absolute and relative refractory periods of a prior action potential? Be able to explain why or why not. What is the purpose of refractory periods?
Absolute refractory:axon CANNOT generate a new action potential; voltage-gated Na+ channels are inactive and resetting Relative refractory:axon CAN generate a new action potential, but only with a larger stimulus.because the membrane potential inside the axon becomes increasingly negative relative to the outside of the membrane, a stronger stimulus will be required to reach the threshold voltage, and thus, initiate another action potential. the refractory period limits the number of action potentials that a given nerve cell can produce per unit time.
Neurons operate via two types of electrical signals: name them.
Action and graded potential
How do the concentrations of sodium and potassium differ on the inside and outside of a neuron? How is this difference (or gradient) maintained?
K greater inside; Na greater outside. this is maintained by the ATPase pump
Compare and contrast the two major control systems in vertebrates. Your answer should distinguish these systems based on their major function in the body, types of effectors and chemical messengers used, specificity of action, and speed and duration of response.
Nervous: Effectors: neurons, muscles, glands Chemical signals: neurotransmitter Electrical signals: action and graded potential Speed of effect: FAST type of effect: specific Endocrine: Effectors: organs, tissues Chemical signals:hormone Electrical signals: N/A Speed of effect:slow type of effect: widespread
List and describe the mechanisms by which neurotransmitter signal transmission is shut off.
Neurotransmitter diffuses away from synapse Neurotransmitter is degraded by synaptic enzymes Neurotransmitter reuptake by presynaptic cell
An action potential is "all-or-none" so how do action potentials code information about stimulus intensity? How does this differ from how graded potentials code information about stimulus intensity?
Stimulus intensity is "coded" by the frequency of action potentials, NOT the size. graded potentials code information about stimulus by number of receptors and frequency of action potentials
Describe how ion concentrations and membrane permeability determine the resting membrane potential of a neuron.
The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion. ... Ions move down their gradients via channels, leading to a separation of charge that creates the resting potential
Differentiate between depolarization, repolarization, and hyperpolarization. What is happening in the neuron during these changes in membrane potential?
depolarization:(rising phase) = opening of voltage-gated Na+ channels (increased Na+ permeability) repolarization:(falling phase) = opening of voltage-gated K+ channels (increased K+ permeability hyperpolarization:(undershoot) = slow closing of voltage-gated K+ channels (slow decrease in K+ permeability)
What does the Nernst Equation estimate? What parameters does it use?
determines the equilibrium potential for a particular ion
What does the Goldman Equation estimate? What parameters does it use?
estimates resting membrane potential based on the concentration and permeability of many ions (potassium, sodium, and chloride)
Differentiate between an ion leak channel, a ligand-gated ion channel, and a voltage- gated ion channel. Where on a neuron is each type of channel found? Which type of channel plays a major role in generating resting membrane potential, graded potentials, action potentials?
ion leak channel: always open ligand-gated ion channel:activation by a specific chemical voltage-gated channel:They open and close in response to changes in transmembrane voltage. Voltage gated channels- open and close in response to changes in the voltage or membrane potential; involved in generating action potentials.
What effect may the evolution of myelination have had on the structure of nervous systems in vertebrates?
more complex nervous system; more connections throughout the body
Is the outside of a neuron membrane negatively charged or positively charged? The inside of the neuron membrane?
outside membrane -70mV
Explain what graded potentials are and why they occur. Why are they called graded? How do graded potentials code information about the intensity of a stimulus? On which portions of a neuron do graded potentials occur? Are graded potentials short or long-distance signals? Explain your choices.
result from binding of neurotransmitter to ligand-gated channels; vary in size. convert a chemical signal (neurotransmitter) to an electrical signal (change in membrane potential) Graded potentials can be summed, or added on top of each other to increase the change Stimulus intensity is coded by: 1) the number of receptors activated (population coding). 2) the frequency of action potentials (frequency coding). occur at the dendrites short distance (decay over distance); the membrane will always default to the resting membrane potential because ions are free to diffuse across the membrane
What does it mean when an ion is at its equilibrium potential? Resting membrane potential (-70 mv) is closest to the equilibrium potential of which ion? What does this tell you about the ion permeability of a neuron at rest?
the saturation of the momentary directional flow of charged ions at the cell membrane level. This phase typically features a zero charge inhibiting the flow of ions between either side of the membrane. resting membrane potential is closest to K; it is the ion the cell is most permeable to.
Explain what action potentials are and why they occur. On what region of the neuron are they first generated? On what region of the neuron are they conducted or propagated? How are action potentials examples of positive feedback?
triggered by net graded potentials at axon hillock. a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane conducted at the axon. Action potentials are caused by an influx of sodium ions in the nerve cell. If a small amount of sodium enters the nerve, it causes more channels to open which cause more sodium to rush in, creating a positive feedback loop that causes a large amount of sodium to enter the nerve and create an action potential.
Explain the relationship between diameter, myelination, and temperature and the speed of action potentials (or conduction velocity). Make sure you are familiar with the graph showing axon diameter vs. conduction velocity in various species that was shown in lecture.
wider diameter = faster speed myelinated = faster speed