Neurophysiology Basics

Na+

K+

-70 mV

Oligodendrocytes

To transmit action potentials

Saltatory conduction

To receive and transduce signals

Both depolarizing and hyperpolarizing stimuli

Depolarization, repolarization, hyperpolarization

A certain threshold voltage being reached

The diameter of the axon and myelination

-70 mV

Na+ and Cl-

K+

-70 mV

To allow ions to flow across the membrane in response to neurotransmitter binding

Myelination and axon diameter

Depolarization, repolarization, hyperpolarization

Depolarization of the membrane

Chemical and electrical stimuli

Oligodendrocytes

Voltage gates open when Vm reaches a certain threshold voltage

To reset the membrane potential (Vm) back to resting state

To generate action potentials

The diameter of the axon

To prevent the backward propagation of action potentials

Activation gates of voltage-gated Na+ channels opening

To initiate the depolarization phase

To initiate the repolarization phase

To reset the membrane potential (Vm) back to resting state

To generate action potentials

Sodium (Na+) channels

Postsynaptic potential (PSP)

Potassium (K+) channels

Axon hillock

Chemical signal

All of the above

Ligand-gated ion channels

To increase the speed of conduction

Nodes of Ranvier

Saltatory conduction

Oligodendrocytes in the CNS and Schwann cells in the PNS

Electrical and chemical signal transmission

Nodes of Ranvier

Depolarization

They are filled with neurotransmitter (NT) molecules and are responsible for the release of NTs into the synapse

Neurotransmitter clearance

Spatial summation, temporal summation, and cancellation

Adding up of potentials from different locations across the neuron at the axon hillock

Adding up of all potentials that reach the axon hillock based on time of arrival

EPSP-IPSP cancellation

The axon hillock is responsible for integrating incoming signals from the dendrites and deciding whether to initiate an action potential.

The axon initial segment (AIS) is responsible for generating and propagating action potentials along the axon.

The speed of action potential propagation is determined by the diameter of the axon and the presence of myelin sheath.

Depolarization of the membrane to the threshold level triggers the opening of voltage-gated sodium (Na+) channels.

The opening of voltage-gated potassium (K+) channels is triggered by the depolarization of the membrane during the rising phase of an action potential.

A postsynaptic potential (PSP) occurs when there is a brief change in the postsynaptic membrane potential (Vm).

Both excitatory and inhibitory stimuli can change the membrane potential (Vm) of a neuron.

Sodium (Na+) ion is highly concentrated outside of the cell.

Signal integration occurs at the axon hillock of a neuron.

The resting membrane potential of a neuron is approximately -70 millivolts (mV).

Leak channels, voltage-gated channels, and ligand-gated channels.

Depolarization is when the interior of the neuron becomes less negative than the resting membrane potential (Vrest). Hyperpolarization is when the interior of the neuron becomes more negative than Vrest.

The Na+/K+ pump moves 2 K+ ions into the neuron and 3 Na+ ions out of the neuron using 1 molecule of ATP. This helps keep the ion concentrations constant, ensuring that the diffusive force remains unchanged over time.

The five stages of an action potential are: initiation, depolarization/rising phase, repolarization/falling phase, after-hyperpolarization/undershoot, and return to rest.

Voltage-gated Na+ channels open when the membrane potential (Vm) reaches a certain threshold voltage.

Frequency-coding refers to the increase in the number of action potentials produced in response to increased stimulus intensity. Higher stimulus intensity leads to more action potentials being generated.

The speed of action potential propagation, also known as conduction velocity, is determined by the diameter of the axon and the presence of myelination.

The refractory period is a period of time after an action potential where the membrane is unresponsive to firing additional action potentials. This allows the neuron to reset and ensures that action potentials travel in a unidirectional manner.

Nodes of Ranvier are the gaps between sections of myelin where the axon is exposed. They play a crucial role in the conduction of action potentials by allowing the action potential to 'jump' from one node to another, which speeds up the propagation of the action potential.

Signal integration occurs at the axon initial segment (AIS) next to the axon hillock. It is here that the neuron determines whether the incoming signals are strong enough to generate an action potential.

Na+ = Highly concentrated outside of the cell K+ = Highly concentrated inside of the cell Cl- = Highly concentrated outside of the cell

Neurotransmission = Process of transmitting information within neuronal cells through chemical and electrical signals Resting potential = The state of a neuron when no inputs are acting upon it, usually at about $-70$ millivolts Membrane potential = The charge difference between the interior and the exterior of a neuron

Action Potential = Brief change in the postsynaptic membrane potential Signal Integration = Process in which incoming signals from many neurons integrate to influence firing rate of a neuron Conduction Velocity = Determines the speed of action potential propagation

Resting membrane potential (Vrest) = Approximately $-70$ millivolts

Neurophysiology = Study of chemical and electrical signals within neuronal cells to process and transmit information Myelination = Process that increases conduction velocity Propagation = Process of transmitting an action potential from one location to another

Plasma or cell membrane = Separates intracellular environment from extracellular environment Neuron's interior = Usually more negatively charged than the exterior space Neurotransmission process = Provides baseline knowledge of neurotransmission

Neurophysiology = Study of how neurons process and transmit information Action Potential = Process that allows neurons to transmit information over long distances Signal Integration = Influences the firing rate of a neuron

Membrane Potential (Vm) = Electrical charge difference between the interior and the exterior of a neuron Resting Potential (Vrest) = State of a neuron when no inputs are acting upon it Action Potential = Brief change in the postsynaptic membrane potential

Na+ = Outside of the cell K+ = Inside of the cell Cl- = Outside of the cell

Membrane Potential = The electrical potential difference between the inside and the outside of a neuron Resting Potential = The stable, negative charge of a neuron when it is at rest Action Potential = The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell

Depolarization = Interior of neuron becomes less negative than Vrest, primarily due to Na+ currents Hyperpolarization = Interior of neuron becomes more negative than Vrest, primarily due to K+ and Cl- currents Afterhyperpolarization/Undershoot = Brief period of hyperpolarization after an action potential Refractory period = Period after an action potential where the membrane is unresponsive to firing additional APs

Depolarization/Rising Phase = Interior of neuron rapidly becomes more positively charged Repolarization/Falling phase = Interior of neuron rapidly returns to negatively charged status After-hyperpolarization/Undershoot = Neuron bypasses Vrest and is briefly hyperpolarized Return to rest = The neuron returns to Vrest

Voltage-gated Na+ channels (VGNC) = Trigger the rising phase by opening quickly at threshold Voltage-gated K+ channels (VGKC) = Trigger repolarization and hyperpolarization by slowly opening and closing Leak channels = Allow ions to cross the membrane, always open Gated channels = Open or close in response to environmental signals

Propagation = The movement of APs as Na+ spreads out and triggers APs in neighboring sections of the axon Axon initial segment (AIS) = The site where APs originate, next to the axon hillock Unidirectional travel = APs travel from AIS to axon terminals due to the refractory period Conduction velocity = The speed of AP propagation, determined by axon diameter and myelination

All-or-none principle = Neuron either fires or does not, and AP amplitude is always the same Frequency-coding = Increased stimulus intensity results in more APs produced Refractory period = Period after an AP where the membrane is unresponsive to firing additional APs Propagation = APs are not static, Na+ spreads out as it enters neuron, triggering APs in neighboring sections of the axon

Vm Concentration gradients = Presence of different ion concentrations across the cell membrane Diffusive force = Pushes ions down their concentration gradient Na+/K+ pump = Keeps ion concentrations constant by moving 2 K+ in and 3 Na+ out of the neuron using 1 molecule of ATP Ion channels = Allow ions to cross the membrane

Depolarization = Interior becomes less negative than Vrest, primarily due to Na+ currents Hyperpolarization = Interior becomes more negative than Vrest, primarily due to K+ and Cl- currents Graded potentials = Changes in Vm that are local and graded, decay back to Vrest over time Threshold = If reached, the cell will fire an action potential

Voltage-gated Na+ channels (VGNC) = Open quickly at threshold, triggering a strong depolarization Voltage-gated K+ channels (VGKC) = Open and close slowly, triggering a strong hyperpolarization Leak channels = Always open, allowing ions to cross the membrane Gated channels = Open or close in response to environmental signals

Local = Potential travels away from its source and across the membrane, it decays Graded = Larger stimuli result in larger responses and vice versa Threshold = If reached, the cell will fire an action potential Refractory period = Period after an AP where the membrane is unresponsive to firing additional APs

Initiation = Neuron is depolarized to threshold Depolarization/Rising Phase = Interior of neuron rapidly becomes more positively charged After-hyperpolarization/Undershoot = Neuron bypasses Vrest and is briefly hyperpolarized Return to rest = The neuron returns to Vrest

Oligodendrocytes = Cells responsible for producing myelin in the Central Nervous System Internodes = Sections of axon covered by myelin Nodes of Ranvier = Gaps between sections of myelin where the axon is exposed Myelination = The process that allows for faster conduction of action potentials

Synaptic vesicles = Small, spherical organelles located in the presynaptic terminal filled with neurotransmitter (NT) molecules Voltage-gated calcium channels (VGCCs) = Channels expressed densely on presynaptic terminal, which open upon depolarization leading to Ca2+ influx Neurotransmitter (NT) = Endogenous chemical specialized for transmitting information between neurons Receptors = Proteins that receive and transduce signals, typically located postsynaptically

Excitatory postsynaptic potential (EPSP) = Depolarizing postsynaptic potential that pushes the postsynaptic Vm toward the AP threshold Inhibitory postsynaptic potential (IPSP) = Hyperpolarizing postsynaptic potential that pushes the postsynaptic Vm away from the AP threshold Spatial summation = Adding up of potentials from different locations across the neuron at the axon hillock Temporal summation = Adding up of all potentials that reach the axon hillock based on time of arrival

Degradation = Rapid breakdown/inactivation of NT by an enzyme Reuptake = Process where NT is reabsorbed by transporters in presynaptic terminal to be reused Diffusion = Process where NT molecules diffuse out of the synapse EPSP-IPSP cancellation = Process where an IPSP spatially coincides with an EPSP and partially or totally cancels it out

Saltatory conduction = Process where the action potential appears to 'jump' from node of Ranvier to node of Ranvier Axon hillock = Location where integration of signals happens Schwann cells = Cells responsible for producing myelin in the Peripheral Nervous System Ligand-gated ion channels = Receptors that open in response to ligand binding and cause very fast changes in membrane potential

Calcium ions (Ca2+) = Ions highly concentrated outside the neuron Depolarization = Process that opens voltage gate on VGCCs leading to Ca2+ influx Exocytosis = Process where vesicles fuse with membrane and NTs flow down concentration gradient into synapse Endogenous = Naturally occurring, originating from organism itself

Signal integration = How postsynaptic potentials interact on the postsynaptic neuron to influence its firing Binding sites = Areas on receptors dedicated to detecting/binding NTs Internodes = Sections of axon covered by myelin Nodes of Ranvier = Gaps between sections of myelin where the axon is exposed

Neurotransmitter (NT) = Endogenous chemical specialized for transmitting information between neurons Receptors = Proteins that receive and transduce signals, typically located postsynaptically Synaptic vesicles = Small, spherical organelles located in the presynaptic terminal filled with neurotransmitter (NT) molecules Voltage-gated calcium channels (VGCCs) = Channels expressed densely on presynaptic terminal, which open upon depolarization leading to Ca2+ influx

Excitatory postsynaptic potential (EPSP) = Depolarizing postsynaptic potential that pushes the postsynaptic Vm toward the AP threshold Inhibitory postsynaptic potential (IPSP) = Hyperpolarizing postsynaptic potential that pushes the postsynaptic Vm away from the AP threshold Spatial summation = Adding up of potentials from different locations across the neuron at the axon hillock Temporal summation = Adding up of all potentials that reach the axon hillock based on time of arrival

Degradation = Rapid breakdown/inactivation of NT by an enzyme Reuptake = Process where NT is reabsorbed by transporters in presynaptic terminal to be reused Diffusion = Process where NT molecules diffuse out of the synapse EPSP-IPSP cancellation = Process where an IPSP spatially coincides with an EPSP and partially or totally cancels it out