Graded Potentials, Action Potentials&Synapse
Threshold Stimulus
-55mV=minimum amount of stimulus required to generate an action potential. Causes voltage gated channels to open and close. Constant amplitude.
Saltatory Conduction
A fast process on myelinated axons that involves the jumping of an action potential from node of ranvier to node of ranvier. Creates electrical current that depolarizes part of an axon. Neurons all conduct at different speeds.
Graded Potentials
A small deviation from the RMP that makes the membrane either more polarized (more negative inside=hyperpolarizing) or less polarized (less negative inside=depolarizing).
Subthreshold Stimulus
A stimulus less than -55mV.
Suprathreshold
A stimulus more than -55mV.
Resting State
All the voltage gated channels are closed but leakage channels are still operating. Membrane is most permeable to potassium. Positive on the outside (Na), negative on the inside (K).
Refractory Period
An action potential does not keep occurring, the neuron needs to rest.
Action Potential
An electrical event that is characteristic to a given neuron, they are constants that are not graded and do not vary, all or nothing concept, there is a certain amount of stimulus that is required to one.
Trigger Zone
An extensive number of sodium voltage gated channels at the plasma membrane.
Stimulus
Causes a change in environment in graded potentials.
Strong Stimulus
Causes a large depolarization in graded potentials.
Weak Stimulus
Causes a slight depolarization in graded potentials.
ESPSs
Excitatory graded potentials that are depolarizing.
Synaptic Cleft
Extracellular space between the two neurons.
Transmembrane Potential
Graded potential that is most changed at the site of stimulation and the effect decrease with distance (weaker and dies). Can be depolarizing or hyper polarizing. The stronger the stimulus the greater the change in the potential.
Postsynaptic Potentials
Graded potential that occurs in the dendrites or soma of a neuron in response to a neurotransmitter. They can be: Excitatory...EPSPs or Inhibitory...IPSPs.
Nerve Conduction Velocity
How quickly a nerve carries an impulse.
ISPSs
Inhibitory graded potentials that are hyper polarizing.
Spatial Summation
Involves many neurons firing repeatedly on one post synaptic neuron. Summation occurs and an action potential is generated.
Exocytosis
Involves transport of neurotransmitters across the plasma membrane.
Hyperpolarization
Opening of potassium channels. When K enters the cell it becomes negative.
Depolarization
Opening of sodium channels. When Na enters the cell it becomes positive.
Reverse Polarity
Positive on the inside and negative on the outside. Is SOMETIMES a result of depolarizing graded potentials.
Repolarization Phase
Potassium voltage gated channels open because of the delayed threshold stimulus, to get back to the resting polarization (negative on inside, positive on outside). Inactivation gate on Na channels closes. Potassium exits the cell and goes down the concentration gradient. Attempting to reach RMP (-70mV).
Continuous Conduction
Slow process on an unmyelinated axon that requires an entire plasma membrane to be depolarized. Trigger zone is located with sodium voltage gated channels. When there is a stimulus these channels will open and a current is going to be created. Depolarization serves as stimulus to the next segment of axon and continues to depolarize from axon to axon.
Depolarizing Phase
Sodium voltage gated channels open and the membrane potential is reaching 0 and goes to 30. Membrane is most permeable to Na during this phase. Inside is positive, outside is negative.
First Nerve Impulse
Step 1 in chemical synapse. The action potential arrives at the axon terminal. Can get there by continuous or saltatory conduction.
Calcium Voltage Gated Channels
Step 2 in chemical synapse. Located on the axon terminal in the plasma membrane. Ion is high on the outside and low on the inside of the synaptic end bulb plasma membrane . Action potential arrives and opens the voltage gated channels.
Synaptic Vesicles
Step 3 in chemical synapse.Contain neurotransmitters within them. Ca is responsible for the exocytosis of the neurotransmitters into the synaptic cleft. They merge/fuse with the plasma membrane and the neurotransmitters exit into the synaptic cleft.
Postsynaptic Cleft & Ligand Gated Channels
Step 4 in chemical synapse. Protein channels found within the postsynaptic membrane. Channels open from the neurotransmitter binding to the protein channel receptor.
Opening of the Ligand Channel
Step 5 in chemical synapse. Sodium diffuses into the cell going down its concentration gradient and depolarizes.
Postsynaptic Potential (EPSPs)
Step 6 in chemical synapse. Channel opens and goes into extracellular space that is high in sodium. Cytosol (inside) is low in sodium. Cleft (outside) is high in sodium.
Second Nerve Impulse
Step 7 in chemical synapse. Graded potential may not be big enough to generate an action potential but can be summated to generate an action potential.
Temporal Summation of EPSPs
Stimuli are subthreshold. When one neuron fires repeatedly hoping to summate with neuron number two to send out an action potential. Summate to -55mv to reach action potential.
Hyperpolarization Phase
The voltage gated potassium channels are still open and the sodium channels are now in the resting state. Sodium/potassium pump is doing final adjustment of Na and K levels. End up with resting membrane potential again.
Relative Refractory Period
Time at which a suprathreshold stimulus is required to generate another action potential.
Absolute Refractory Period
Time at which another action potential can never be initiated, absolute rest.
Depolarizing Graded Potentials
When the response makes the membrane less polarized (less negative inside). Occurs in the soma and dendrites of a neuron.
Hyperpolarizing Graded Potentials
When the response makes the membrane more polarized (more negative inside). Occurs in soma and dendrites of a neuron.
Summated Graded Potentials
When you add graded potentials that are close together. If one waits to long you cannot add together the stimuli and they die out.
