Unit 3: Synaptic Transmission & Neurotransmitters

Neurotransmitter

Chemical messengers that

1. is produced by a neuron

2. is in the presynaptic axon terminal & can produce biological effect

3. (as a drug), mimics a natural neurotransmitter in body

4. must be inactivated after release

Amine Neurotransmitter

Small molecule transmitters of amino acids in synaptic vesicles (occurs in axon terminals for chemical synapse)

ex. GABA

Neuropeptides

Large 3+ amino acid transmitters synthesized in the rough ER to be packed in the golgi

ex. endorphins

Synapse

The junction when a neuron communicates with another neuron or target cell

1. Electrical

2. Chemical

Electrical Synapse

A excitatory synapse of dendrite to dendrite where ions pass directly through the 3nm gap through the gap junction formed by connexons, allowing fast and synchronous communication

Chemical Synapse

A synapse of dendrite to axon terminal where neurotransmitters are released into the 20~50nm synaptic cleft by the action potential triggering the fusion of vesicles; it is slower

Gap Junction

The direct connection between dendrites formed by connexons

Connexons

The proteins forming the gap junction

Presynaptic neuron

The neuron that sends the signal with the action potential

Postsynaptic neuron

The neuron that receives the neuron

Synaptic Vesicles

Vesicles storing amine neurotransmitters in the chemical synapse

Synaptic Cleft

The small space between neurons at a chemical synapse

Removal of neurotransmitters from the synapse

1. Reuptake

2. Enzymatic breakdown

3. Diffusion (passive)

4. Astrocyte End Feet

Reuptake

The process of neurotransmitters being recycled into the presynaptic neuron

Acetylcholinesterase

Enzyme breaking down Acetylcholine in the synaptic cleft

Ionotropic Receptor

Ligand gated ion channel; fast and direct, only for small molecule amines

ex. Nicotinic ACh

Metabotropic Receptors

Receptor that activates G proteins that releases a second messenger; slow but amplified

G protein

A molecule containing alpha, beta, and gamma

When neurotransmitter binds, GTP is used to separate the alpha to activate effector enzyme to make and release a 2nd messenger  

Second messenger 

A molecule that directly signals to the target

ex. activating an potassium ion channel (cAMP)

GTP in GPCR signaling

A small molecule like ATP within the alpha subunit

The receptor which received the neurotransmitter activates the G protein to convert GDP into GTP in the alpha subunit, separating it to activate the effector

Receptor Agonist

Molecule that activates a receptor (drug or neurotransmitter)

Receptor Antagonist

Molecule that blocks a receptor (drug or toxins)

Nicotinic Receptor

Ionotropic excitatory acetylcholine receptor

Muscarinic Receptor

Metabotropic inhibitory acetylcholine receptor

Adrenergic Receptor

Metabotropic excitatory norepinephrine and epinephrine receptor

Serotonergic Receptor

Serotonin receptor for both excitatory, inhibitory, and metabotropic, ionotropic

Dopaminergic Receptor

Metabotropic dopamine receptor for both excitatory and inhibitory

GABA

Calming effect in the brain (inhibitory)

Glutamate

Learning and Memory

Dopamine

Reward pathway for pleasure

Serotonin

Sleep and Mood

Acetylcholine

Muscular Contractions

Histamine

State of Wakefulness

Epinephrine

Fight or Flight 

Norepinephrine

Energy in Fight or Flight

Endorphins

Opioid blocking pain

Glycine

Motor Coordination

SNARE complex

Group of proteins that pull the vesicles and membrane together for fusion

Synapsin

protein connecting vesicles to cytoskeleton until released by Ca2+

VAMP

SNARE protein on the vesicle x2

SNAP-25

SNARE protein on the membrane

Syntaxin

SNARE protein on the membrane