CH 12: Action Potential

membrane potential

cell have electrical charge difference from uneven ion distribution

membrane potential factor play

1. action of Na+/K+ pump (3Na out, 2K in)

   • maintain electrical gradient

2. 2 ion permeability

3. fixed anion unable to leave cell

catecholamine

synthesized and contain catechol group and mine group

acetylcholine

synthesize from choline in milk, egg, nut

reuptake

presynaptic neuron takes up and reuses most intact neurotransmitter molecules

drug/synapse

mimic neurotransmitter (Agonist)

block neurotransmitter (Antagonist)

drug/synapse: neurotransmitter effect

increase synthesis

cause vesicle leak

increase release

block reuptake/breakdown

tryptophan

serve as precursor for serotonin

large neurotransmitter

synthesized in cell body and transport down axon

resting membrane

sodium channel closed

potassium channel close to allow slow passage K+

• maintain -70mV

electrical signal types

action potential

graded potential

graded potential

short-distance signal

• stimulus to presynaptic cell

action potential

long distance signal

large graded potential

selective permeable

chem pass freely

sodium, potassium, calcium, chloride pass through channels

resting potential

-70mV

maintain: Na+ pump, K+ pump slowly

hyperpolarization

depolarization

threshold excitation

hyperpolarization

more neg than -70mV

hard to trigger AP

depolarization

toward 0

easy to trigger AP

threshold excitation

-55mV trigger AP

smaller neurotransmitter

synthesized in presynaptic terminal and held for release

drug properties

affinity: how well bind to receptor (strong or weak)
efficacy: how well activate a receptor

dopamine

drug can cause dopamine, release in nucleus accumbens

pleasure feeling

summation

temporal

spatial

temporal summation

repeat stimuli, short time, strong response

produce nerve impulse; weak

spatial summation

small stimuli produce reflex

synaptic input diff. effect, trigger nerve impulse

action potential characteristic

“all or none”: produce AP or not

absolute refractory period

relative period

absolute refractory period

no new AP

very hyperpolarized

relative period

block Na+ channels = no pain

propagation AP

begin: axon hillock

transmission

• unmyelinated axon: slow

• myelinated: faster, saltatory, conduction

saltatory conduction

saltatory conduction

AP “jump” from one node of Ranvier to next

amphetamine

behavior: excited, alert, happy, less tired

brain effect: boost dopamine and other transmitters

cocaine

behavior: excited, alert, happy, less tired

brain effect: block dopamine reuptake; dopamine stay loner

methylphenidate

ritalin

behavior: better focus

brain effect: slowly block dopamine reuptake

MDMA

ecstasy

behavior:

• low dose: stimulating

• high dose: sensory distortion

brain effect: release dopamine and serotonin; harm serotonin neuron

nicotine

behavior: mostly stimulant effects

brain effect: activate acetylcholine receptor, boost dopamine in reward areas

opiates

heroin, morphine

behavior: relax, less pain, withdrawal symptoms

brain effect: stimulant endorphin (natural painkillers) receptor

cannabinoids

marijuana

behavior: altered senses, less pain/nausea, more appetite

brain effect: activate feedback receptor, mimic body natural cannabinoids

hallucinogens

LSD

behavior: distorted sense

brain effect: stimulates serotonin 5-HT2A receptors