Psyc 6 Action Potential

Cations have a _ charge

positive

anions have a _ charge

negative

ions important to the nervous system

Na+, K+, Ca2+, Cl-

what is the tertiary structure of a protein

a subunit composed of multiple a-helixes

characteristics of ion channels

no energy required (passive transport), can be gated or not

types of ion channels

always open, ligand gated, voltage gates, mechanically gated

characteristics of ion pumps

require energy, moves ions against their conc. gradient

neuron intracellular charge at rest

negative (-65mV)

K+ conc. at rest

more K+ inside cell, so it wants to get out

Na+ conc. at rest

more Na+ outside cell, so it wants to get in

at rest, there’s a higher concentration of Ca2+ _ the cell

outside

at rest, there’s a higher conc. of Cl- _ the cell

outside

sodium potassium pump function

uses energy to pump 3 Na+ out for every 2 K+ in

calcium pump function

uses energy to pump Ca2+ out

depolarization

getting less polarized (neurons get more positive)

pore loop function on voltage gated Na+ channel

attracts extracellular Na+

what causes the Na+ channel to open

when the neuron become more positively charged

describe the inactivated state of the Na+ channel

even if the channel is open, Na+ can not go through, occurs after depolarization

describe the neuron at rest

negative charge, Na+ and K+ channels are closed

membrane threshold voltage

-55mV

what happens immediately after threshold is reached

Na+ channels open and Na+ rushes in, causing rapid depolarization, K+ still closed

what happens after depolarization

repolarization, Na+ channels inactivate, K+ channels open allowing K+ to flow out, neuron becomes negative

what happens after repolarization

hyperpolarization, Na+ channels return to closed state, K+ channels still open leading to a very negative neuron (-100mV)

absolutely refactory periods

no chance of firing another action potential (depolarization and repolarization)

relatively refactory periods

small chance of another action potential because the neuron is already more negative than normal

tetrodotoxin

targets Na+ channels

A

resting potential

B

rising phase

C

overshoot

D

falling phase

E

undershoot

how do neurons communicate stronger signals through action potentials

higher frequency of action potentials (NOT higher voltage spikes)

why is conduction unidirectional in neurons

Na+ wants to diffuse forwards because it is more negative in that region, previously used Na+ channels are inactive

conduction occurs at a faster velocity in _ axons

wider

saltatory conduction

the action potential leaps from one node of Ranvier to another

EPSP

excitatory post synaptic potential - ligand gated Na+ channels open to make neuron more positive (easier to cause an action potential)

IPSP

inhibitory post synaptic potential - K+ and Cl- channels open, neuron become more negative (hyperpolarized) so its harder to cause an action potential

What does the picture show

close temporal spacing - two signals sent in close succession

What does the image show

simultaneous stimuli - two signals received at the same time

spatial summation

signals are received by dendrites that are close together and are summed

what determines if an action potential is fired

if the sum of all the incoming signals is enough to depolarize the membrane at the axon hillock past the threshold

vagus nerve stimulation showed that

messages can be sent through chemicals

how do ions travel between neurons in electrical synapses

gap junction channels

characteristics of electrical synapses

faster, weaker, usually large networks

A

axodendritic

B

axospinous

C

axoextracellular

D (2 types)

axosomatic, axosynaptic

E

axoaxonic

F

axosecretory (from axon to bloodstream or muscle)

neuromuscular junction characteristics

axon branches apart, junctional folds to trap neurotransmitters

4 types of neurotransmitters

amino acids, amines, peptides, gasotransmitters

3 main amino acid neurotransmitters

GABA, glutamate, glycine

4 stages of neurotransmission

neurotransmitter synthesis and storage, neurotransmitter release, receptor activation, neurotransmitter deactivation

synaptic vesicles hold

amino acids, amines

peptide synthesis process

made in cell body and packaged into secretory vesicles (rough ER and golgi)

snare protein function

tie vesicles to the cell membrane

process of neurotransmitter release

action potential depolarizes axon terminal, Ca2+ channels open, Ca2+ rushes in causing vesicles to fuse to membrane, vesicles dump out neurotransmitters (exocytosis)

receptor activation process

neurotransmitter binds to ligand gated channel which opens and lets ions in/out

receptor on presynaptic neuron that binds to its own neurotransmitters for regulation purposes

autoreceptor

neurotransmitter deactivation methods

glia uptake, enzyme degradation, diffusion, reuptake (endocytosis)

receptor where an ion actually passes through

ionotropic

receptor where nothing passes through but a conformational change occurs

metabotropic receptor/G-protein coupled receptor

what happens when a receptor binds to a metabotropic receptor

alpha subunit is kicked off and can bind to an ion channel or second messenger

how can the same neurotransmitter have different effects

different receptors, how fast the receptors open/close

agonist drug

binds to the receptor and mimics the natural chemical (increases effect of the natural chemical)

antagonist drug

binds to the receptor and prevents the natural chemical from binding (decreases effect of natural chemical)

cholinergic system neurotransmitter

acetylcholine (ACh)

cholinergic system RLF

choline (must come from diet)

cholinergic system synthesis process

ChAT synthesizes ACh from Choline and Acetyl CoA, ACh packaged by ACh transporter into vesicles

cholinergic system neurotransmitter deactivation process

ACh broken down by extracellular enzyme (AChE) and choline reuptake through choline transporter protein (uses Na+ to pull choline into cell)

where are the soma of cholinergic neurons found

basal forebrain complex (medial septum, basal nucleus of Meynert), PMT

where do the axons of cholinergic neurons go

spread across entire brain

ACh is important in

motor/muscle function, autonomic functions (heartbeat), learning, memory

catecholaminergic system neurotransmitters

dopamine (DA), norepinephrine (NE), epinephrine

catecholaminergic system precursor molecule

tyrosine

catecholaminergic system RLF

tyrosine hydroxylase (enzyme)

dopamine synthesis

enzyme makes DA from tyrosine, DA packaged into vesicles by transporter protein

catecholaminergic system neurotransmitter deactivation process

reuptake, some of the reuptaken neurotransmitters are broken down by monoamine oxidase (MAO) found on the mitochondria

where are dopaminergic soma found

substantia nigra, ventral tegmental area (both in brainstem)

where do dopaminergic axons go

frontal lobe, striatum

dopamine is important for

reward learning, addiction

how do cocaine and amphetamine work

cocaine blocks reuptake protein so dopamine is not deactivated (prolonged effect), amph sneaks into neurons and releases DA from vesicles so they freely diffuse out of cell through transporter proteins

how is norepinephrine synthesized

dopamine beta hydroxylase (DBH) enzyme within vesicles convert DA to NE

where are noradrenergic soma found

locus coeruleus (in brainstem)

where do noradrenergic axons go

spread over CNS and PNS

norepinephrine is important for

attention, sleep/wake, PNS response to stress

how is epinephrine synthesized

norepinephrine leaves vesicles, PNMT converts NE to E in cytosol, E packaged back into vesicles

serotonergic system precursor and RLF

tryptophan (must come from diet)

how is serotonin synthesized

tryptophan is converted by enzymes into serotonin, serotonin packaged into vesicles

serotonin deactivation method

reuptake

this neurotransmitter has MANY effects depending on the receptor

serotonin

where are serotonergic soma found

raphe nuclei (in brainstem)

where do serotonergic axons go

spread over CNS and PNS

serotonin is important for

sleep/wake cycle, mood and emotions

where are amino acidergic soma found

grey matter

glutamate and GABA precursor molecule

glutamine

method of amino acid deactivation

reuptake and glial uptake by astrocytes

inhibitory amino acids

GABA, glycine