Ions: Atom that has gained or lost an

electrical charge:

�� Anion: Negative Ion

�� Cation: Positive Ion

Oscilloscope: A

sensitive voltmeter to

measure the very small

and rapid changes in

electrical currents that

come from an axon.

Microelectrode: Small

electrode used to

record electric

potentials from living

cells.

The electrical charge

across a cell

membrane; the

difference in

electrical potential

inside and outside the

cell.

membrane potential.

Exists because

positively and

negatively charged

ions are distributed

unequally on two

sides of the

membrane.

ions, extremely resistant to passage of Na+, and slightlyresistant to passage of K

equilibrium potential at a membrane

potential to zero…

Pump: Protein found

in membrane of all

cells that exchanges

�� Counters Na+ leak.

Equation used to calculate the

equilibrium potential at a membrane

potential to zero…but doesn't cuz of sodium-ptassium pump which prevents Na+ leakage into the cell.

A sudden reversal in the membrane potential

(from negative to positive) caused by a brief

increase in the permeability of the membrane

increase in the permeability of the membrane

Na+ ions flow IN

K+ ions flow OUT.
-arise in axon hillock

If stimulation depolarizes

the membrane to –45mv

an action potential is

generated at the axon

hillock.

At the threshold level of depolarization, voltagegated

influx of Na+ into neuron. Only stay open for 1ms.

potential either occurs or does

not occur; once triggered, it is

transmitted down to the end of

the axon.

remains the same size,

without growing or

diminishing,

the stimulation is, the action

potential is always the same

is represented by the axon’s

rate of firing.

e.g: A high rate of firing

causes strong muscular

contraction, and a strong

stimulus (e.g., bright light)

causes a high rate of firing in

axons that serve the eyes.

action potential, another AP cannot be

generated, no matter what kind of input the

neuron receives. Followed by the:

can only be elicited by high levels of

stimulation.

generated at the axon hillock,

it travels passively along the

axonal membrane to the

sodium channels.

Na+ channels open andanother full

generated.

the axon in ‘waves’ of

depolarization.

hillock to the terminal buttons.

the membrane after depolarization.

terminals to the hillock (occurs when

terminals are stimulated).

Saltatory Conduction.

energy

faster; myelinated

axons conduct faster.

hillock, propagate

down the axon.

postsynaptic targets.

Depolarizations –

Decrease in

membrane potential

caused by excitatory

messages; increases

probability that the

neuron will fire.

Hyperpolarizations –

Increase in

membrane potential,

caused by inhibitory

messages; decreases

probability that the

neuron will fire.

1. They are graded;

signal.

2. They are transmitted decrementally;

size decays as a function of the square of the

distance.

3. They are transmitted rapidly.

�� passive, cable properties.

effect on firing of post‐synaptic neuron.

inhibitory and excitatory signals reaching the

axon hillock.

over time.

potentials that come

from different parts

of the cell.

and IPSPs) can

depolarize the cell at

the axon hillock ��

AP!

potentials that arrive

at the axon hillock at

different times.

arrive, the greater the

summation and

possibility of an AP.

is to cause local changes

in postsynaptic

membrane potentials,

through

synapses on a dendrite or

dendritic spine.

mediates presynaptic inhibition.

dendrites; found primarily in

olfactory bulb to mediate lateral

inhibition.

body.

presynaptic cell to release

transmitter, e.g., NO

down the axon to the

axon terminal.

channels open and

calcium ions (Ca2+) enter.

Calcium is key!

with membrane and

release transmitter into

postsynaptic receptors –

cause an EPSP or IPSP.

toward the postsynaptic

axon hillock.

removed – action is brief.

by presynaptic

autoreceptors, decreasing

release.

membrane of a particular neuron.

�� In most cases, do not control ion channels.

�� Instead, regulate internal processes.

neurotransmitter.

activate or block

them:

neurotransmitters and

hormones

drugs and toxins from

normal effects of the

receptor; facilitates

transmission.

receptor from being activated

by other ligands; inhibits

transmission.

an effect that is the opposite

of the normal function

Transmitter action is brief and can be terminated either by:

transmitter by an enzyme, e.g., acetylcholinesterase

(AChE) breaks down ACh and recycles it

2. Reuptake: transmitter is taken up into the presynaptic cell

reuptake.

vesicles.

areACh antagonists:

Molecules that interfere

with or prevent action of

transmitter.

�� Cause paralysis!

ACh agonists: Act like

transmitter at receptor.

in autonomic ganglia.

by parasympthetic neurons (e.g., heart,

intestines). Most common in brain.

both classes exist.