L6 Graded Potentials Flashcards
Which cells are excitable?
Nerves and muscles
Can undergo rapid changes in their membrane
Can change their resting potentials into electrical signals
Resting Vm
Voltage across plasma membrane in a cell with no changes in membrane permeability
Neural communication is based on
Rapid change in membrane permeability to ions
Direction of synapse
Unidirectional
Dendrites to cell body down axon to dendrites of other neuron
Graded potential is
Change in potential when a neuron releases neurotransmitter onto the dendrites/cell body of another neuron
Signal that travels down axon is known as
The action potential
Vm at rest is
Negative =polarized
If Vm becomes less negative
More positive
Less polarized/depolarized
If depolarized plasma membrane returns to negative Vm is
Repolarized (more negative)
If plasma membrane becomes more negative the Vm rest
Hyperpolarized
Step 1 of graded potentials
3
Resting membrane exposed to chemical stimulus (signal comes in from presynaptic to postsynaptic neuron)
Chemically gated channels open
Membrane potential changes
A graded potential that depolarizes the membrane potential makes the neuron
More pos
More likely to fire
A graded potential that hyperpolarizes the membrane potential makes the neuron
More neg
Less likely to signal
Graded potential step 2
Movement of ions through channel produces local current
Depolarizes or hyperpolarizes nearby regions of cell membrane
Change in potential is proportional to stimulus
Farther away from source=less graded potentials
Summarize graded potential
3
Vary with size of stimulus
Decays with distance
May be depolarizing or hyperpolarizing
Graded potentials depend on what and what are the two kinds?
Permeability changes induced by neurotransmitter of postsynaptic neuron
Excitatory postsynaptic potential- EPSP
Inhibitory postsynaptic potential- IPSP
EPSP causes what
Depolarization
More likely to fire
Na+ or Ca2+
IPSP causes what
Hyperpolarization
Less likely to fire
Cl- or K+
Summation of postsynaptic potentials
One neuron may receive input from 1000s of other neurons simultaneously
Whether it fires depends on whether net input is excitatory or inhibitory
For a neuron to fire it has to reach what voltage?
-50mV
Roughly +15mV change (-70 to -55)
Typically EPSP has a voltage of
0.5mV (lasts 20msec)
A typical neuron would need how many EPSPs to reach threshold?
30
Temporal summation
Single synapses receives many EPSPs in short period of time
1 neuron firing many times rapidly
Spatial summation
Single synapse receives many EPSPs from many presynaptic cells
Magnitude of graded postsynaptic potential (GPSP) depends on
Sum of activity in all presynaptic inputs
Only if EPSP is reinforced by other supporting signals through summation will info be passed on
Interaction of EPSPs and IPSPs allows
A fine degree of discrimination and control in determining what info will be passed on
