Neurophysiology

Ion

Atoms or molecules that bear a net charge due to an unequal number of protons and electrons.

Cation

Positively charged ions.

Anion

Negatively charged ions.

Current

The flow of electric charge, similar to the flow of water through pipes.

Voltage or Potential Difference

The separation of positive and negative electrical charges.

Resting Membrane Potential

The transmembrane potential of a resting neuron, typically around -70 mV.

Transmembrane Potential

The electrical potential difference across the cell membrane.

Graded Potential

A local change in membrane potential that can vary in strength depending on the strength of the stimulus.

Action Potential

A rapid rise and fall in membrane potential that carries an electrical signal along a neuron.

Refractory Period

The time following an action potential during which a neuron is unable to fire another action potential.

Absolute Refractory Period

The period during which no action potential can be generated, regardless of stimulus strength.

Relative Refractory Period

The period during which a stronger stimulus than usual is required to generate an action potential.

Synapse

The specialized site of contact between two neurons or a neuron and an effector that allows one-way flow of neural impulses.

Neuromuscular Junction

The synapse between a neuron and a muscle cell.

Neuroglandular Junction

The synapse between a neuron and a gland.

Excitatory Postsynaptic Potential (EPSP)

A postsynaptic potential that makes a neuron more likely to fire an action potential.

Inhibitory Postsynaptic Potential (IPSP)

A postsynaptic potential that makes a neuron less likely to fire an action potential.

Presynaptic Inhibition

The process by which one neuron decreases the amount of neurotransmitter released by another neuron.

Presynaptic Facilitation

The process by which one neuron enhances the effect of another neuron.

Neurotransmitter

Chemicals released by neurons that transmit signals across synapses.

Neuromodulator

A chemical that modifies the effect of neurotransmitters.

Acetylcholine (ACh)

A neurotransmitter that can have either excitatory or inhibitory effects depending on the target tissue.

Norepinephrine (NE)

A neurotransmitter that can also have excitatory or inhibitory effects depending on where it binds.

Dopamine

A neurotransmitter associated with reward and motivation, and deficiencies are linked to Parkinson’s disease.

Serotonin

A neurotransmitter that regulates mood, and low levels are linked to depression.

Calcium Channels

Channels that allow calcium ions to enter the neuron, triggering the release of neurotransmitters.

Graded

Describes potentials that vary in size, depending on the strength of the stimulus.

Decremental

Describes how the signal loses strength as it travels further from the site of stimulation.

Reversible

Describes potential changes that can return to resting state after removal of the stimulus.

All-or-none Rule

A principle stating that a neuron either fires an action potential at full strength or not at all.

Neural Coding

The process by which the nervous system converts information into patterns of action potentials.

Temporal Summation

The addition of stimuli close in time at a single synapse.

Spatial Summation

The addition of postsynaptic potentials from multiple synapses.

Resting Membrane Potential

The electrical potential difference across the membrane of a neuron at rest.

Hyperpolarization

An increase in the membrane potential that makes the inside of the cell more negative.

Depolarization

A decrease in membrane potential towards zero, making the inside of the cell more positive.

Sodium-Potassium Pump (Na+-K+ ATPase)

A pump that moves sodium out of the cell and potassium into the cell to maintain resting membrane potential.

Vesicles

Structures containing neurotransmitters released into the synaptic cleft during neurotransmission.

Exocytosis

The process by which neurotransmitters are released from vesicles into the synaptic cleft.

Acetylcholinesterase (AChE)

An enzyme that breaks down acetylcholine in the synaptic cleft.

Sodium Channels

Voltage-gated channels that allow sodium ions to enter the neuron, critical in action potentials.

Chloride Channels

Channels that when open, allow chloride ions to enter the neuron, contributing to inhibitory signals.

Ion Gradients

Differences in the concentration of ions across the neuron's membrane, crucial for action potentials.

Electrical Gradient

A difference in charge across a membrane that influences the flow of ions.

Chemical Gradient

A difference in the concentration of a chemical between two areas which influences how ions move.