Cellular Conduction

Electrochemical Information

What neurons communicate through the use of

Conduction

Information is transferred within the cell electrically

Transmission

Information is transferred between cells chemically

Action Potential

A rapid electrical signal that travels along the axon of a neuron

Neurotransmitter

A chemical messenger between neurons

Microelectrode

When inserted into a resting cell, shows that it is more negative than the extracellular fluid

Ion Channels

Proteins that span the membrane and allow ions to pass

Voltage Gated Ion Channels

Change conformation, opening or closing as a result of change in electrical potential in the cell membrane around them

Chemical Gated Ion Channels

Change conformation, opening or closing as the result of binding to a ligand

Selective Permeability

• Some channels are open all the time and allow only potassium ions to cross

• It allows K+ to enter or leave the cell freely but restricts the flow of other ions

Diffusion

Causes ions to flow from areas of high to low concentration, along their concentration gradient

Electrostatic Pressure

Causes ions to flow towards oppositely charged areas

Sodium-Potassium Pump

Pumps three sodium ions out for every two potassium ions pumped in

Equilibrium

When the movement out is balanced by the movement in

Nernst Equation

Predicts the voltage needed to counterbalance the diffusion force pushing an ion across a membrane

Goldman Equation

Predicts voltage potentials that are quite close to observed resting potentials

Axon Hillock

Where action potentials originate

Hyperpolarization

An increase in membrane potential, the interior of the membrane becomes even more negative

Depolarization

A decrease in membrane potential, the interior of the cell becomes less negative

Local Potential

AN electrical potential that spreads passively across the membrane, diminishing as it moves away from the point of stimulation

Threshold

The point where the membrane potential must reach (about -40 mV) for an action potential to be triggered

All-or-none Property

• Neuron fires at amplitude or not at all

• Does not reflect increased stimulus strength

Afterpotentials

Changes in membrane potential after action potentials

Voltage-Gated Sodium Ion Channels

Open in response to the initial depolarization

Refractory Period

Time when only some stimuli can produce an action potential

Absolute Refractory Phase

Time when no action potentials are produced

Relative Refractory Phase

Time when only strong stimulation can produce an action potential

Conduction Velocity

The speed of propagation of action potentials, varies with diameter

Saltatory Conduction

The axon potential travels inside the axon and jumps from node to node

Channelopathy

Genetic abnormality of ion channels

Postsynaptic Potentials

Brief changes in the resting potentials

Excitatory Postsynaptic Potential

Produces a small local depolarization, pushing the cell closer to threshold

Synaptic Delay

The delay between an action potential reaching the axon terminal and creating a postsynaptic potential

Inhibitory Postsynaptic Potential

Produces a small hyperpolarization, pushing the cell further away from threshold

Spatial Summation

the summing of potentials that come from different parts of the cell

Temporal Summation

the summing of potentials that arrive at the axon hillock at different times

Sequence of Transmission

1. Action potential travels down the axon to the axon terminal

2. Voltage-gated calcium channels open and calcium ions enter

3. Synaptic vesicles fuse with membrane and release transmitter into the cleft

4. Transmitters cross the cleft and bind to postsynaptic receptors and cause an EPSP or IPSP

5. EPSPs or IPSPs spread toward the postsynaptic axon hillock

6. Transmitter is inactivated or removed

7. Transmitter may activate presynaptic autoreceptors
   
   

v-SNAREs

Specialized proteins that attach to vesicles

t-SNAREs

Specialized proteins that attach to the presynaptic membrane

Synaptotagmin

A protein attached to the vesicle- is activated by calcium ions triggering the fusion of the vesicle with the presynaptic membrane, thus releasing a neurotransmitter

Ligands

Fit receptors exactly and activate or block them

Endogenous Ligands

Neurotransmitters and hormones

Exogenous Ligands

Drugs and toxins from outside the body

Ionotropic Receptors

Open when bound by a transmitter

Metabotropic Receptors

Recognize the transmitter but instead activate G proteins

Degradation

the rapid breakdown and inactivation of transmitter by an enzyme

Reuptake

Transmitter is taken up into the presynaptic cell

Axo-dendritic

Axon terminal synapses on a dendrite

Axo-somatic

Axon terminal synapses on the cell body

Axo-axonic

Synapse between two axons

Dendro-dendritic

synapse between two dendrites

Ectopic Tansmission

occurs outside of conventional synapses

Varicosities

Axonal swellings where transmitter may diffuse out

Neural Chain

A simple series of neurons