Chapter 2 Part B

Neuron Communication

Sending information by electrical/chemical signals

Electrical Signal

Travels within a neuron; message inside self

Chemical Signal

Neurotransmitters carry messages between neurons; message between cells

Principles of electricity

Rules including voltage, current, and resistance that explain how electrical signals are generated and move through neurons

Voltage

Difference in electrical charge of the inside and outside of a cell

Current

Movement of charged particles; measure of how particles move inside and outside of a cell

Ohm’s Law

The relationship between voltage, current, and resistance; Current (I)=V/R

Resistance

Physical barrier that separates inside and outside of a cell; limits current flow

Ion

an electrically charged particle (either positive or negative

Function of an ion

Moves across cell membranes and contributes to membrane potential

Anions

Negatively charged ion; more electrons than protons

Example of Anion

CI- (Chloride)

Cation

Positively charged ion; more protons than electrons

3 examples of Cation

Potassium (K+), Sodium (Na+), Calcium (Ca2+)

Na+

Sodium

K+

Potassium

Ca2+

Calcium

CI-

Chloride

Ion Distribution

Unequal concentrations of ions inside vs outside of the neuron when the cell is at rest.

Sodium, Chloride, and Calcium are more concentrated in

Extracellular Space

Potassium and Proteins are more concentrated in

Intra cellular space

Phospholipid Bilayer

Forms the neuronal membrane; a barrier controlling what can cross the membrane

Hydrophilic Heads of Phospholipid Bilayer

Attracted to water; settle in intercellular fluid and extracellular fluid

Hydrophobic Tails of Phospholipid Bilayer

Repels water; settles in center of phospholipid bilayer

Selectively Permeable

Allows some substances in but restricts others; potassium is more concentrated inside the cell

Membrane Permeability

How easily substances cross the membrane

Intracellular Fluid

Fluid inside the cell

Extracellular

Fluid outside the cell

Membrane Polarization

A difference in electrical charge across the membrane; allows an electrical potential to be maintained

Membrane Potential

Difference in electrical charge inside and outside of cell

Resting Potential

The neuron’s stable electrical state when not firing

Resting potential provides the

Baseline before generating an action potential

Ion movement

Movement of charged particles across the membrane; changes the membrane potential

Two forces that act on an ion to make it move

Diffusion and Electrostatic Pressure

Diffusion

Movement of molecules from regions of high concentration to regions of low concentration

Electrostatic Pressure

Forces of attraction or repulsion between particles

Ion Channel

Provides a passageway for ions; allows specific ions to cross the membrane

Voltage-gated ion channel

Ion channel that opens/closes in response to membrane voltage changes; controls ion movement when membrane potential changes

Ion channels are membrane spanning, meaning they

span the length of the phospholipid bilayer

Gating

The mechanism that controls whether an ion channel is open or closed

Ion Selectivity

A channel’s ability to allow certain ions through while excluding others

K+ Channels

Ion channels that allow potassium ions to cross the membrane

Na+ Channels

Ion channel that allows sodium ions to cross the membrane

Refractory period

Period after an action potential when another action potential is difficult or impossible

Ca2+ Channels

Ion channels that allow calcium to cross the membrane

Ion Pumps

Membrane proteins that use energy to move ions against their concentration gradients; maintains resting potential

Sodium Potassium pump

Ion pump that maintains action potential

What does sodium potassium pump move in and out?

3 Na+ out and 2 K+ in

Changes in membrane potential

Changes in electrical charge across membrane; allows neurons to receive and transmit signals

Depolarization

Membrane potential becomes less negative; moves closer to 0; less difference between inside and outside of cell

Hyperpolarization

The membrane potential becomes more negative; further from 0; bigger difference between inside and outside of cell

Action Potential

Rapid, temporary change in membrane potential

What does action potential do?

Carries an electrical signal along the axon

Order of Action Potential

Resting state, Depolarizing phase, depolarizing phase, hyperpolarization/overshoot

Threshold of excitation

Minimum membrane depolarization needed to trigger an action potential

Na+ Channels

Open at Threshold → Na+ enters → Causes depolarization

Rising Phase/Depolarization

Membrane becomes less negative as Na+ enters

Overshoot/Peak

Membrane briefly becomes positive

Falling Phase/repolarization

Na+ channels close and K+ leaves → membrane becomes negative again

Undershoot/after potential

Membrane becomes more negative than resting potential (hyperpolarization)

Return to resting

Membrane returns toward resting potential

Na+/K+ pumps during return to resting

Restores Na+/K+ concentration gradients

Absolute refractory period

Period when another action cannot occur

What do absolute refractory periods ensure

That action potentials travel in one directions

Relative refractory period

Period where another action potential can occur, but requires a stronger stimulus

What does relative refractory period limit

How quickly neurons can fire again

Ion movement during an action potential: Resting

K+ concentrated inside; Na+ outside

Ion movement during an action potential: Depolarization

Na+ enters

Ion movement during an action potential: Repolarization

K+ enters

Ion movement during an action potential: Undershoot

K+ continues exiting; membrane becomes more negative.

Ion movement during an action potential: Return to rest

Na+/K+ pump restores gradients.

All-or-none law

An action potential either occurs or does not occur

Rate Law

The strength of information is represented by the rate of action potentials; Stronger stimuli produce more frequent firing, not stronger action potentials

Stronger stimuli produce more _______ firing, not ___action potentials

Frequent; stronger

Axon Diameter

Larger diameter → faster action potential conduction

Myelination

Increases conduction velocity

Saltatory Conduction

Action potential “jumps” between nodes of ranvier; allows rapid conduction between myelinationed axons

Multiple sclerosis

Damaged myelin disrupts rapid neural communication.

Axodendritic

Synapse on a dendrite; neuron communicates with another through the dendrite

Axosomatic

Synapse on the soma; allows communication directly with the cell body

Exocytosis

Process where a synaptic vesicle fuses with the presynaptic membrane; releases NTs into the synaptic cleft

Ca²⁺ influx

Ca²⁺ enters the presynaptic terminal after an action potential; Triggers synaptic vesicles to release neurotransmitter.

Synaptic vesicle

Small membrane-bound sac containing neurotransmitters; Stores and releases neurotransmitter during exocytosis.

Ionotropic receptor

Receptor that directly controls an ion channel when a neurotransmitter binds; Quickly changes ion flow across the membrane.

Ligand-gated ion channel

Ion channel that opens/closes when a chemical (ligand) binds; Allows specific ions to cross the membrane.

Binding site

Specific location where the neurotransmitter attaches to the receptor; Initiates the receptor’s response.

Ion channel

Protein passageway through the membrane for ions; Allows selected ions to enter or leave the cell.

Metabotropic receptor

Receptor that affects ion channels through an indirect process involving a G protein; Produces slower, longer-lasting effects.

Binding site

Location where a neurotransmitter binds to a receptor; activates the receptor

G Protein

Protein coupled to the receptor; becomes activated and triggers intercellular effects

Second messenger

Molecule activated by the G protein; carries the signal inside the cell

Ligand

Chemical that binds to a receptor; Binding initiates the receptor’s response.

Postsynaptic potential

Local, graded change in the postsynaptic membrane potential; Changes the neuron’s likelihood of firing.

Excitatory Post Synaptic Potential (EPSP)

Depolarizing post synaptic potential

EPSP makes the neuron ____ likely to reach threshold

More

Inhibitory Post Synaptic Potential

Hyperpolarizing post synaptic potential

IPSP makes the neuron ____ likely to reach threshold

Less

Ion Movement in EPSP

Na+ enters → Depolarization

Ion Movement in IPSP

CI- enters or K+ Leaves → Hyperpolarization

Stimulus strength

Strength of the input producing the PSP