How do neurons talk to each other?
Neurons communicate through specialized junctions called synapses, using chemical messengers called neurotransmitters. This process is fundamental to everything your brain does - from simple reflexes to complex thoughts and emotions.
In this exploration, you'll discover:
- How synaptic transmission works at the molecular level
- Different types of neurotransmitters and their functions
- The difference between excitatory and inhibitory signals
- How drugs and diseases affect synaptic function
Start by selecting a tab below to begin your exploration!
Synaptic Structure: The Communication Junction
💡 Interactive: Click on any part of the synapse to learn more about its function
Key Synaptic Components
Synapses are highly specialized structures that enable precise chemical communication between neurons:
Presynaptic Terminal
Contains synaptic vesicles, Ca²⁺ channels, and release machinery. Action potentials trigger neurotransmitter release here.
Synaptic Vesicles
Membrane-bound organelles storing ~5,000-10,000 neurotransmitter molecules each. Ready-releasable pool contains ~10-20 vesicles.
Synaptic Cleft
20-50 nanometer gap where neurotransmitters diffuse. Contains enzymes (AChE) and transporters for signal termination.
Postsynaptic Membrane
Contains neurotransmitter receptors and ion channels. Generates EPSPs or IPSPs based on receptor type.
Receptors & Channels
Ionotropic receptors (fast, ~1ms) directly gate ion channels. Metabotropic receptors (slow, ~100ms) use second messengers.
📡 Watch: The simulation shows medically accurate timing and molecular interactions during synaptic transmission. Each step is based on real neuroscience research!
Synaptic Transmission: Step-by-Step Process
Interactive Transmission Timeline
Follow the precise sequence of events during synaptic transmission. Each step occurs within milliseconds:
Transmission Steps
1. Action Potential Arrival (t=0ms)
Action potential depolarizes presynaptic terminal to +30mV, opening voltage-gated Ca²⁺ channels.
- Membrane depolarization activates Ca²⁺ channels
- Ca²⁺ influx increases from 0.1μM to 10-100μM
2. Calcium Influx (t=0.1-0.3ms)
Ca²⁺ enters through N-type and P/Q-type channels, binding to synaptotagmin sensors.
- Synaptotagmin acts as Ca²⁺ sensor
- SNARE proteins prepare for vesicle fusion
3. Vesicle Fusion (t=0.2-0.5ms)
Ca²⁺-triggered exocytosis: vesicles fuse with presynaptic membrane via SNARE complex.
- Fusion pore opens (~1-2nm diameter)
- ~5,000-10,000 neurotransmitter molecules released
4. Neurotransmitter Diffusion (t=0.1-1ms)
Neurotransmitters diffuse across 20-50nm synaptic cleft, reaching peak concentration in ~100μs.
- Diffusion time depends on cleft width
- Concentration peaks at ~1mM in cleft
5. Receptor Binding (t=0.1-2ms)
Neurotransmitters bind to postsynaptic receptors, causing conformational changes.
- Ionotropic: Direct channel opening
- Metabotropic: G-protein activation
6. Postsynaptic Response (t=1-10ms)
Ion channels open, generating EPSP or IPSP. Signal integration determines if action potential fires.
- EPSP: Na⁺/Ca²⁺ influx, depolarization
- IPSP: K⁺ efflux or Cl⁻ influx, hyperpolarization
7. Signal Termination (t=1-100ms)
Neurotransmitter removal by reuptake, enzymatic degradation, or diffusion.
- Reuptake transporters (DAT, SERT, NET)
- Enzymes (AChE, MAO, COMT)
Neurotransmitters: The Brain's Chemical Messengers
Over 100 different neurotransmitters have been identified, each with specific functions and effects. They can be classified by chemical structure and function:
Amino Acids
Glutamate
Primary excitatory neurotransmitter (~80% of synapses)
Function: Learning, memory, synaptic plasticity
Receptors: AMPA, NMDA, kainate, mGluR
GABA
Primary inhibitory neurotransmitter (~20% of synapses)
Function: Anxiety control, sleep, seizure prevention
Receptors: GABA-A (ionotropic), GABA-B (metabotropic)
Glycine
Inhibitory in spinal cord and brainstem
Function: Motor control, reflexes
Monoamines
Dopamine
Reward, motivation, motor control
Pathways: Nigrostriatal, mesolimbic, mesocortical
Disorders: Parkinson's, schizophrenia, addiction
Serotonin (5-HT)
Mood, sleep, appetite, pain
Receptors: 14 subtypes (5-HT1-7)
Disorders: Depression, anxiety, migraine
Norepinephrine
Attention, arousal, stress response
Source: Locus coeruleus
Cholinergic
Acetylcholine (ACh)
First discovered neurotransmitter (1921)
CNS: Attention, learning, memory
PNS: Neuromuscular junction, autonomic
Receptors: Nicotinic (ionotropic), muscarinic (metabotropic)
Degradation: Acetylcholinesterase (AChE)
Neuropeptides
Endorphins
Natural opioids, pain relief, euphoria
Function: Stress response, reward
Substance P
Pain transmission, inflammation
Function: Nociception, mood
Purines
ATP
Co-transmitter, fast synaptic transmission
Function: Pain, autonomic control
Adenosine
Sleep regulation, neuroprotection
Function: Caffeine antagonist
Gaseous
Nitric Oxide (NO)
Retrograde messenger, vasodilation
Function: LTP, blood flow
Neurotransmitter Receptors: Signal Detection
Neurotransmitter receptors are specialized proteins that detect and respond to chemical signals. They fall into two main categories:
Ionotropic Receptors
Ligand-gated ion channels that directly open when neurotransmitter binds
AMPA Receptors
Glutamate receptors, fast excitatory transmission
Ions: Na⁺, K⁺ | Speed: ~1ms
NMDA Receptors
Glutamate + glycine, voltage-dependent
Ions: Na⁺, K⁺, Ca²⁺ | Function: LTP
GABA-A Receptors
Primary inhibitory receptors
Ions: Cl⁻ | Drugs: Benzodiazepines
Nicotinic Receptors
Acetylcholine, neuromuscular junction
Ions: Na⁺, K⁺ | Location: NMJ, ganglia
Metabotropic Receptors
G-protein coupled receptors that use second messenger systems
Muscarinic Receptors
Acetylcholine, autonomic nervous system
Types: M1-M5 | Speed: ~100ms
Dopamine Receptors
D1-like (D1, D5) and D2-like (D2, D3, D4)
Function: Motor control, reward
Serotonin Receptors
14 subtypes (5-HT1-7), diverse functions
Function: Mood, sleep, appetite
mGluR
Metabotropic glutamate receptors
Types: Group I, II, III | Function: Modulation
Synaptic Integration: Computing with Neurons
Spatial and Temporal Summation
Neurons integrate multiple synaptic inputs to determine whether to fire an action potential:
Spatial Summation
Multiple synapses active simultaneously
- Different locations on dendrites
- EPSPs and IPSPs add algebraically
- Depends on input resistance
Temporal Summation
Same synapse active repeatedly
- Rapid succession of inputs
- Depends on membrane time constant
- Facilitation vs. depression
Synaptic Plasticity
Activity-dependent changes in synaptic strength
- LTP: Long-term potentiation
- LTD: Long-term depression
- Hebbian rule: "Cells that fire together, wire together"
Clinical Significance
Synaptic Disorders
- Myasthenia Gravis: Autoimmune attack on ACh receptors
- Lambert-Eaton: Reduced Ca²⁺ channel function
- Botulism: Blocks ACh release
Drug Targets
- SSRIs: Block serotonin reuptake
- Benzodiazepines: Enhance GABA-A function
- Antipsychotics: Block dopamine receptors
- Cholinesterase inhibitors: Alzheimer's treatment
Research Applications
- Optogenetics: Light-controlled neurotransmitter release
- Patch-clamp: Single channel recordings
- Two-photon microscopy: Live synaptic imaging