Chapter 1
The neuroscientist that was the main proponent of the Neuron Doctrine was
Cajal
Which type of potential will be decremental (amplitude decays with distance)?
Graded Potentials
In voltage-clamp recordings, the early inward current was eliminated when which ion was removed from the external solution?
Sodium
The larger the relative permeability of an ion, the greater its contribution to the membrane potential will be.
True
The reticular theory states that the nervous systems consists of...
a continuous network of fused cells and not individual cells.
What is meant by electrochemical equilibrium?
Electrochemical equilibrium occurs when there is an exact balance between two opposing forces: the concentration gradient (diffusional force) and the electrical gradient. At this point there is NO NET flux of the ion!
Why is the voltage clamp method so useful for studying neurophysiology?
The voltage clamp method allows simultaneous control of membrane potential and measurement of permeability changes! Can indicate how membrane potential affects ionic current flow.
All neurons have an axon and can generate an action potential.
False! Anaxonic neurons do not have an axon and thus do not fire action potentials. And not all neurons fire action potentials!
Which type of neurons have short axons and limited input, but consitute 99.9% of all neurons?
Local Interneurons
Why did Hodgkin and Katz propose that sodium was the predominant ion associated with the firing of an action potential?
Because the membrane potential approaches the equilibrium potential for sodium (+55mV) during the rising phase.
What is meant by membrane conductance? and how is this related to resistance?
Membrane conductance is the degree of permeability to certain ions. It is the inverse of resistance. Therefore when membrane conductance is HIGH, resistance is LOW (which means there are many channels open for a given ion).
All permeant ions experience an identical driving force at each time point during the course of an action potential.
False
What are three functions of glial cells?
1. myelination of axons 2. clear nts from the synapse 3. buffer extracellular K+ and other ions 4. scavenge debris 5. involved in injury response 6. help guide neuronal migration during development
How do active transporters and ion channels contribute to membrane potential?
Active transporters create and maintain ion concentration gradients and ion channels allow ions to diffuse down their concentration gradients which aids to the selective permeability of the membrane.
One way to determine which ion is responsible for the inward and outward currents is to use pharmacological agents. Which agent would you use to block Na+ current? K+ current?
Tetrodotoxin (TTX) can be used to block voltage-gated Na+ channels and TEA (tetraethylammonium) to block voltage-gated K+ channels.
The Na/K pump is electrogenic and therefore makes a major contribution to a neuron's resting membrane potential.
False, it only makes a minor contribution. Activity of the pump will slightly hyperpolarize the membrane just a few millivolts.
What are the input and output regions of a neuron? In which of these regions would you see graded potentials versus action potentials?
Input - dendrites and cell body Output - axon terminals. Graded potentials will occur in the dendrites and cell body, whereas action potentials will occur down the axon into the axon terminals
Why is resting membrane potential not exactly equal to the equilibrium potential for potassium?
Because the membrane has some resting permeability to ions other than potassium.
Here's a question on driving force... if ECl = -60 mV and Vm = -70 mV, would this resulting chloride current be negative or positive? inward or outward? Would it be a net influx or efflux of Cl-?
(Vm-ECl) = (-70 mV - (-60mV)) = -10 mV So this current would be negative (inward) and would result in an efflux of Cl-.
The refractory period prevents back propagation of the AP and also regulates the maximal firing frequency of APs.
True