3.1 Major neurotransmitter systems

Neurotransmitters are the brain's chemical messengers, shaping our motivations and behaviors. From dopamine's reward-driven influence to serotonin's mood regulation, these molecules work together to create our emotional and cognitive experiences.

Understanding neurotransmitter systems is crucial for grasping how our brains drive behavior. By exploring their synthesis, release, and receptor interactions, we gain insight into the complex mechanisms underlying our thoughts, feelings, and actions.

Neurotransmitters in Motivation

Key Neurotransmitters and Their Roles

Top images from around the web for Key Neurotransmitters and Their Roles

• 

  Neurotransmission: The secret life of memory receptors | eLife View original

  Is this image relevant?

• 

  Chemical and Electrical Synapses | Biology for Majors II View original

  Is this image relevant?

• 

  Neurotransmission - Wikipedia View original

  Is this image relevant?

• 

  Neurotransmission: The secret life of memory receptors | eLife View original

  Is this image relevant?

• 

  Chemical and Electrical Synapses | Biology for Majors II View original

  Is this image relevant?

1 of 3

Top images from around the web for Key Neurotransmitters and Their Roles

• 

  Neurotransmission: The secret life of memory receptors | eLife View original

  Is this image relevant?

• 

  Chemical and Electrical Synapses | Biology for Majors II View original

  Is this image relevant?

• 

  Neurotransmission - Wikipedia View original

  Is this image relevant?

• 

  Neurotransmission: The secret life of memory receptors | eLife View original

  Is this image relevant?

• 

  Chemical and Electrical Synapses | Biology for Majors II View original

  Is this image relevant?

1 of 3

• Dopamine drives reward system functioning influences motivation, pleasure, and reinforcement learning
• Serotonin modulates mood, appetite, and sleep patterns affects emotional regulation and overall well-being
• Norepinephrine regulates arousal, attention, and stress responses impacts vigilance and reactivity to environmental stimuli (fight-or-flight response)
• Acetylcholine contributes to arousal, attention, and memory formation shapes cognitive processes related to motivated behaviors
• GABA acts as primary inhibitory neurotransmitter modulates anxiety and stress responses (calming effect)
• Glutamate functions as primary excitatory neurotransmitter involved in learning, memory, and synaptic plasticity (long-term potentiation)
• Endogenous opioids (endorphins) contribute to pain modulation and feelings of pleasure and reward (runner's high)

Neurotransmitter Interactions and Effects

• Neurotransmitters work in concert to regulate complex behaviors and emotional states
• Imbalances in neurotransmitter levels linked to various mental health disorders (depression, anxiety)
• Drugs of abuse often target specific neurotransmitter systems (cocaine affects dopamine)
• Neurotransmitter activity influenced by environmental factors, stress, and diet
• Genetic variations in neurotransmitter-related genes can affect individual differences in motivation and behavior
• Neurotransmitter systems exhibit plasticity adapting to repeated stimuli or experiences (addiction, learning)
• Interactions between neurotransmitter systems create complex feedback loops and regulatory mechanisms

Neurotransmitter Synthesis and Release

Synthesis and Storage

• Neurotransmitter synthesis occurs primarily in presynaptic neuron involves specific precursor molecules and enzymatic pathways
• Amino acid neurotransmitters (glutamate, GABA) synthesized from simple precursors
• Monoamine neurotransmitters (dopamine, serotonin) require more complex synthetic pathways
• Synthesized neurotransmitters packaged into synaptic vesicles via vesicular transporters
• Vesicles transported to presynaptic terminal along cytoskeletal elements
• Neurotransmitter synthesis regulated by feedback mechanisms and enzyme availability
• Some neurons can switch neurotransmitter phenotype in response to environmental cues (neurotransmitter respecification)

Release and Reuptake Mechanisms

• Neurotransmitter release triggered by action potential causes calcium influx through voltage-gated channels
• Calcium influx initiates vesicle fusion with presynaptic membrane via SNARE proteins
• Released neurotransmitters diffuse across synaptic cleft bind to receptors on postsynaptic neuron
• Reuptake mechanisms (transporter proteins) remove neurotransmitters from synaptic cleft
• Specific transporters exist for different neurotransmitters (DAT for dopamine, SERT for serotonin)
• Enzymatic degradation in synaptic cleft alternative termination mechanism (acetylcholinesterase for acetylcholine)
• Rate of synthesis, release, and reuptake regulated by various feedback mechanisms
• Drugs can target release and reuptake processes (SSRIs block serotonin reuptake)

Neurotransmitter Receptor Function

Receptor Types and Mechanisms

• Neurotransmitter receptors specialized proteins on postsynaptic membrane bind specific neurotransmitters
• Two main receptor types ionotropic (ligand-gated ion channels) and metabotropic (G-protein coupled receptors)
• Ionotropic receptors directly open ion channels upon neurotransmitter binding cause rapid changes in membrane potential
• Metabotropic receptors activate second messenger systems lead to slower but longer-lasting cellular responses
• Receptor activation can produce excitatory or inhibitory postsynaptic potentials depends on specific ion channels involved
• Receptor number and sensitivity modulated through up-regulation and down-regulation processes affect synaptic strength
• Different receptor subtypes for same neurotransmitter can produce varied cellular responses (D1 vs D2 dopamine receptors)

Signal Transduction and Cellular Response

• Ionotropic receptor activation leads to direct ion flow alters membrane potential rapidly (milliseconds)
• Metabotropic receptor activation triggers second messenger cascades can affect gene expression and protein synthesis
• Second messenger systems include cAMP, IP3, and DAG pathways
• Calcium often acts as a crucial second messenger in many signaling pathways
• Receptor activation can lead to short-term changes in neural excitability (ion channel modulation)
• Long-term changes in neural function result from altered gene expression and protein synthesis
• Cross-talk between different receptor systems creates complex intracellular signaling networks
• Desensitization mechanisms prevent overstimulation of receptors (beta-arrestin recruitment)

Excitatory vs Inhibitory Neurotransmitters

Mechanisms of Excitation and Inhibition

• Excitatory neurotransmitters (glutamate) increase likelihood of postsynaptic neuron firing action potential
• Inhibitory neurotransmitters (GABA) decrease likelihood of postsynaptic neuron firing action potential
• Neurotransmitter effect depends on receptor type and resulting ion flow not solely on neurotransmitter itself
• Excitatory neurotransmitters typically cause depolarization open sodium or calcium channels
• Inhibitory neurotransmitters cause hyperpolarization open chloride channels or close sodium channels
• Some neurotransmitters (acetylcholine, dopamine) can have both excitatory and inhibitory effects depends on receptor subtype and neural circuit
• Neuromodulators (serotonin, norepinephrine) influence excitatory or inhibitory effects of other neurotransmitters

Balance and Regulation of Neural Activity

• Balance between excitatory and inhibitory neurotransmission crucial for normal brain function
• Imbalance can lead to conditions like seizures (excessive excitation) or anxiety disorders (insufficient inhibition)
• Feedforward and feedback inhibition mechanisms help regulate neural circuit activity
• Tonic inhibition provides constant dampening of neural excitability (extrasynaptic GABA receptors)
• Phasic inhibition allows for precise timing of neural firing (synaptic GABA receptors)
• Excitatory-inhibitory balance can be altered by experience and learning (synaptic plasticity)
• Neurodevelopmental disorders often involve disruptions in excitatory-inhibitory balance (autism spectrum disorders)