Lecture 4: Graded and Action Potentials Flashcards
nerve and muscle cells are _____ tissues that can change their resting potentials into _____ signals
EXCITABLE tissues that can change their resting potentials into ELECTRICAL signals
Neural communication is based on ______ changes in membrane permeability to _____
RAPID changes in membrane permeability to ION
why is ion permeability changes used for cell to cell signaling in the brain over a second messager system or hormones?
SPEED, ion permeability change is FASTER
Graded potentials depend on the _______ changes induced by the neurotransmitter in the postsynaptic neuron
PERMEABILITY CHANGES
What determines whether a neuron fires or not?
based on if the net input is inhibitory or excitatory
When does temporal summation occur
when a single synapse receives many EPSPs (excitatory postsynaptic potentials) in a short period of time
when does spatial summation occur
when a single synapse receives many EPSPs from MANY presynaptic cells
what are the two gates in a Voltage-gated Na+ channel?
ACTIVATION and INACTIVATION gate
How many gates does a Voltage-gated K+ channel have?
One and its either open or closed
All voltage-gated channel gates are triggered to respond at ________ ?
threshold
3 conformations of voltage-gated sodium channels
resting
- closed but can open (-70mV)
activated
- open (from threshold to peak potential -50 to +30 mV)
inactivated
- closed and not capable of opening (+30 to -70mV)
2 Conformations of the voltage-gated Potassium channels
Closed
- at resting potential
-delayed opening occurs at threshold
- remains closed from -70 to +30 mV
Open
- from peak potential till after the hyperpolarization phase (+30 to -80mV)
what is the Absolute Refractory Period
interval during which NO stimulus can elicit an action potential
- most Voltage gated Na+ channels are inactivated
what is the Relative refractory period?
interval when a very large graded potential stimulus is required to elicit an action potential
due to elevated gK coupled w/ residual inactivation of Voltage gated Na+ channels
gk = membrane conductance to potassium ions
What is the purpose of a refractory period
- ensures one-way propagation of the action potential
- limits the frequency of action potentials
- energy conservation and prevents seizures
action potentials will always be of the same _______ for a particular axon regardless of how large the stimulus is
will always be the same MAGNITUDE
if a stimulus exceeds the threshold, an action potential will be ______
INITIATED, all or none response
the strength of a stimulus is determined by the _____ of action potential firing
FREQUENCY of action potential firing
A weak stimulus would cause ____ action potentials to be fired compared to a strong stimulus
FEWER
what determines the speed of conduction
DIAMETER of the FIBER
- larger diameter = slower internal resistance = faster conduction
-rapid fibers (large diameter) ex: motorneurons
-slow fibers (small diameter) ex: internal organs gut, glands
DEGREE OF MYELINATION
-lipid insulator of nerve fibers increases conduction velocity
What are the 2 types of conduction
CONTINUOUS CONDUCTION
- conduction in unmyelinated fibers
- action potential spreads along every portion of the membrane
SALTATORY CONDUCTION
** 50x faster
- impulse jumps over sections of fiber that is covered w/ insulating myelin
increasing ECF K+ will cause the RMP to ??
RMP will decrease, causing the inside of the cell to become more + = depolarization
Repolarization is ?
The return to resting potential after depolarization
When treating critically ill patients with intravenous fluids, which two ions are most important to the neuronal membrane potential?
Na+ and K+
