Neurotransmission:

Neurotransmission

The process by which neurons communicate with each other through synaptic transmission.

Neuron

A nerve cell that transmits information through electrical and chemical signals; the human brain has approximately 100 billion neurons.

Types of Synapses

Neurons communicate through electrical synapses (fast, direct ion flow via gap junctions) and chemical synapses(neurotransmitter release across the synaptic cleft).

Dendrites

Receive signals from other neurons.

Soma (Cell Body)

Processes information.

Axon

Conducts electrical signals.

Axon Terminals

Release neurotransmitters to communicate with other neurons.

Neuronal Membrane

A lipid bilayer that separates the intracellular and extracellular environments, regulating ion and molecule entry and exit.

Step 1 Neurotransmitter Synthesis

Neurotransmitters are produced in the neuron.

Step 2 Storage

Neurotransmitters are stored in vesicles in the axon terminal.

Step 3 Action Potential

Electrical signals travel down the axon.

Step 4 Calcium Influx

Voltage-gated Ca²⁺ channels open.

Step 5 Vesicle Docking

Vesicles prepare for neurotransmitter release.

Step 6 Exocytosis

Neurotransmitters are released into the synaptic cleft.

Step 7 Neurotransmitter Binding

Neurotransmitters bind to receptors on the postsynaptic neuron.

Step 8 Neurotransmitter Inactivation

Via reuptake, enzymatic breakdown, or diffusion.

Excitatory Neurotransmitters

Increase neuron firing likelihood (e.g., Glutamate).

Inhibitory Neurotransmitters

Decrease neuron firing likelihood (e.g., GABA).

Glutamate

Excitatory, involved in learning and memory.

GABA

Inhibitory, regulates anxiety and relaxation.

Dopamine

Controls reward, motivation, and movement.

Serotonin

Affects mood, appetite, and sleep.

Acetylcholine

Involved in learning, memory, and muscle control

Endorphins

Reduce pain and enhance mood.

Ionotropic Receptors

Fast-acting, directly open ion channels (e.g., AMPA, NMDA, GABA A receptors).

Metabotropic Receptors

Slow but longer-lasting effects, work via second messengers (e.g., Dopamine, Serotonin, GABA B receptors).

AMPA Receptors

Rapid excitatory transmission via Na⁺ and K⁺ ion flow.

NMDA Receptors

Involved in learning and memory, allows Na⁺, K⁺, and Ca²⁺ influx, requires depolarization to remove Mg²⁺ block.

Glutamate Excitotoxicity

Excessive glutamate leads to Ca²⁺ overload, causing cell damage, linked to stroke and neurodegeneration.

Nigrostriatal Pathway

From substantia nigra projections to neostriatum. Has a role in movement control (Parkinson’s disease).

Mesolimbic Pathway

From ventral tegmental area (VTA) to nucleus accumbent (NAcc) Role in reward and addiction.

Mesocortical Pathway

From VTA prefrontal cortex. Role in working memory and planning.

Serotonergic System

Originates in the Raphe nuclei, involved in mood, sleep, and emotion regulation.

Benzodiazepines

Enhance GABA function by increasing chloride ion flow, leading to neuronal inhibition, reduced anxiety, sedation, and muscle relaxation. Commonly prescribed for anxiety disorders and sleep issues.

Alcohol

Enhances GABA activity, leading to relaxation and sedation, while also inhibiting glutamate function, impairing cognitive abilities and motor coordination.

Cocaine

Blocks dopamine reuptake, causing an accumulation of dopamine in the synaptic cleft, leading to heightened alertness, euphoria, and increased energy. Prolonged use can lead to addiction and neurotoxicity.

SSRIs (e.g., Prozac)

Selective serotonin reuptake inhibitors prevent serotonin from being reabsorbed, increasing its availability in the synaptic cleft, improving mood, and treating depression and anxiety disorders.

MDMA (Ecstasy)

Increases serotonin release while inhibiting its reuptake, leading to enhanced mood, emotional bonding, and sensory perception. However, excessive use can deplete serotonin levels, leading to mood crashes and neurotoxicity.

Agonist

A drug or endogenous neurotransmitter which combines with a receptor on a cell to produce a cellular reaction.

Antagonist

A drug which reduces or completely blocks the activity of the agonist, no cellular effect after interacting with receptor.

Autoreceptors

A receptor on the neuron that releases neurotransmitters; it detects neurotransmitters in the synaptic cleft and, through G-protein mechanisms, regulates the synthesis and release of neurotransmitters without directly opening ion channels.