BIOL2108H - Neutrotransmitters

neurons communicate with each other through…

synapses using neurotransmitters

what happens when the AP reaches the end of the axon?

neurotransmitter molecules cross the synapse and bind to membrane receptors on the postsynaptic cell

idrk what this means but

-neurotransmitters are stored in vesicles

-these merge with the neuron cell membrane to release NTs

-Nts diffuse across the synapse

-bind to receptor proteins on the other neuron

idrk what this means even longer

-neurotransmitters are stored in vesicles

-action potential reaches terminal branches → depolarization

-voltage-gated Ca2+ channels open

-Ca2+ enters neuron and binds to “docking proteins” on vesicle

-vesicle attaches (“docks”) to cell membrane and fuses

-NTs are released into synapse

-Ca2+ pump uses ATP to pump Ca2+ back out of neuron

terminal branches and dendrites

-terminal branches - sensory cell or pre-synaptic cell (neuron)

-dendrites - post-synaptic cell (neuron)

once released, NTs can…

-bind to receptors on the post-synaptic dendrites

-be re-absorbed by the pre-synaptic neuron

-diffuse away from the synapse

-be broken down by enzymes

neurotransmitters can either…

excite or inhibit an AP in the post-synaptic cell

neurotransmitters can eeither excite or inhibit an AP in the post-synaptic cell

-whether a signal is passed on or not depends on the overall effects of excitatory vs inhibitory NTs

-reuptake, diffusion, and degradation can all affect the amount of a particular NT that reaches the post-synaptic cell

NTs and ion channels

-neurotransmitters bind to ligand-gated ion channels in the post-synaptic dendrites → changes polarization

-these ion channels can either promote or inhibit the transmission of an AP

depolarization

closer to threshold potential

hyperpolariation

farther from threshold potential

recall

the axon hillock integrates multiple incoming signals to decide whether the transmit an AP or not (threshold potential

excitatory neurotransmitters

-open Na+ or Ca2+ channels

-depolarizes the neuron

-contributes to threshold potential and AP

inhibitory neurotransmitters

-open Cl- or K+ channels

-hyperpolarizes the neuron

-inhibits the threshold potential and AP

our nervous system processes a lot of stimuli

need both types of synapses to generate the right overall response

adenosine example

inhibitory NT that accumulates the longer we are awake → sleepiness and fatigue

with adenosine

-adenosine binds to its receptor

-opens special K+ channels on dendrites

-K+ concentration is slightly higher than equilibrium in the dendrites → flows out of dendrites

-hyperpolarization → inhibits AP

with adenosine and caffeine

-caffeine is an antagonist for adenosine → binds to receptor but doesn’t trigger the same response

-caffeine binds to adenosine receptor → blocks effect of adenosine

-not hyperpolarized → AP more likely

-other molecules are agonists → mimic NTs by binding to receptor and triggering the same response

lots of common medications affect neural regulation by:

-speeding up/slowing down enzymatic breakdown

-inhibiting reuptake channels

-preventing NT release

-inhibiting NT receptors

many drugs work by amplifying or weakening the effect of a particular neurotransmitter

antidepressants, allergy medications, some pain medication (morphine, oxycodone)

antidepressants

-strengthen effects of serotonin and/or dopamine

-SSRIs → serotonin reuptake channels are competitively blocked

-MAOIs → limit the enzymatic breakdown of serotonin and dopamine in the synapse

allergy medication

-weaken the effect of histamine

-inactivate histamine receptors

some pain medication (morphine, oxycodone)

mimics the effects of endorphins

neuroregulation

regulation of neural transmission

examples of neuroregulation

-how much neurotransmitter is produced/released (Ca2+ channels)

-how fast neurotransmitter breaks down within the synapse/ is reabsorbed

-how many receptors there are

-how many inhibitors/activators there are for NT receptors

-how many excitatory/inhibitory synapses there are

glutamate

most common excitatory NT, used throughout the brain

GABA

most common inhibitory NT, used throughout the brain

we can measure changes in…

voltage due to excitatory or inhibitory neurotransmitters

excitatory postsynaptic potential

small depolarization caused by an excitatory neurotransmitter = more likely to fire action potential

inhibitory postsynaptic potential

small hyperpolarization caused by an inhibitory neurotransmitter = less likely to fire action potential

summation

balance of EPSPs and IPSPs

opioid examples

-common pain medications including morphine, oxycodone, hydrocodone, fentanyl, codeine, etc

-illegal drugs including heroin and opium

understanding opioids

-some neurotransmitters are natural opioids, including endorphins

-produced by the pituitary and adrenal glands in the brain

-released in response to pain, stress, laughter, exercise, sexual activity, social activity, etc

-pain and stress relief, positive mood

synthetic opioids…

can bind to the same opiate receptors as endorphins and other opioid-based NTs

the brain’s reward pathway is largely controlled by 3 neurotransmitters

-dopamine = regulates pleasure/reward

-GABA = inhibitory NT

-endorphins = inhibitory NT, binds to opiate receptors

the brain’s reward pathway

prefrontal cortex, nucleus accumbens, ventral tegmental area, mesolimbic dopamine pathway

prefrontal cortex

-reward-based decision making

• learning associations of actions → rewards

• impulse control

• goal-seeking behavior

nucleus accumbens

-processing reward

• positive emotions

• motivation

• learning and reinforcement

ventral tegmental area

-produces dopamine in response to “reward” stimuli

• expectation of reward

• sugary foods

• sexual activity

• novelty

• unexpected reward

the ventral tegmental area is made up of ___ and also contains __

dopaminergic neurons, GABAergic neurons

dopaminergic neurons

neurons that synthesize and release dopamine in response to action potentials

GABAergic neurons

neurons that synthesize and release GABA in response to action potential

some neurons in the VTA have…

-opiate receptors on their dendrites

-opioid drugs like morphine can bind to these receptors to mimic naturally produced opiate neurotransmitters like endorphins