A simple nervous system
includes sensory information, an integrating center, and effectors.
Most of the neurons in the human brain are
interneurons
The nucleus and most of the organelles in a neuron are located in the
cell body
The point of connection between two communicating neurons is called the
synapse
In a simple synapse, neurotransmitter chemicals are released by
the presynaptic membrane
Although the membrane of a "resting" neuron is highly permeable to potassium ions, its membrane potential does not exactly match the equilibrium potential for potassium because the neuronal me
slighty permeable to sodium ions
The operation of the sodium-potassium "pump" moves
sodium ions out of the cell and potassium ions into the cell
A cation that is more abundant as a solute in the cytosol of a neuron than it is in the interstitial fluid outside the neuron is
K+
The membrane potential that exactly offsets an ion's concentration gradient is called the
equilibrium postsynaptic potential
ATP hydrolysis directly powers the movement of
Na+ out of cells
Two fundamental concepts about the ion channels of a "resting" neuron are that the channels
open and close depending on stimuli, and are specific as to which ion can traverse them.
Opening all of the sodium channels, with all other ion channels closed–which is an admittedly artificial setting–on an otherwise typical neuron should move its membrane potential to
+62 mV
The "selectivity" of a particular ion channel refers to its
permitting passage only to a specific ion.
For a neuron with an initial membrane potential at -70 mV, an increase in the movement of potassium ions out of that neuron's cytoplasm would result in the
hyperpolarization of the neuron.
A graded hyperpolarization of a membrane can be induced by
increasing its membrane's permeability to K+.
Self-propagation and refractory periods are typical of
action potentials
The "threshold" potential of a membrane is the
minimum depolarization needed to operate the voltage-gated sodium and potassium channels
Action potentials move along axons
more rapidly in myelinated than in nonmyelinated axons
A toxin that binds specifically to voltage-gated sodium channels in axons would be expected to
prevent the depolarization phase of the action potential
After the depolarization phase of an action potential, the resting potential is restored by
the opening of voltage-gated potassium channels and the closing of sodium channels.
The "undershoot" phase of after-hyperpolarization is due to
sustained opening of voltage-gated potassium channels
Immediately after an action potential passes along an axon, it is not possible to generate a second action potential; thus, we state that the membrane is briefly
refractory
The fastest possible conduction velocity of action potentials is observed in
thick, myelinated neurons
In the sequence of permeability changes for a complete action potential, the first of these events that occurs is the
opening of voltage-gated sodium channels
Saltatory conduction is a term applied to
jumping from one node of Ranvier to the next in a myelinated neuron
Two fundamental principles that characterize gated ion channels in the neuronal membrane are that the channels
open and close depending on stimuli and are specific as to which ion can traverse them.