NUERO 2/17

  • Neurotransmitters and Their Functions

    Second Messengers and G-Protein Coupled Receptors

    • Second messengers are molecules activated by G-proteins upon stimulation of metabotropic receptors.

    • Functions of second messengers may include:

    • Opening ion channels to allow ions (e.g., Na+, Ca2+) to flow into the cell.

    • Altering gene expression, which may lead to:

      • Increasing the number of receptor sites (increased sensitivity to neurotransmitters).

      • Decreasing the number of receptor sites (decreased sensitivity to neurotransmitters).

  • Types of Neurotransmitter Receptors

    • Neurotransmitters can bind to various receptor subtypes, influencing their effects throughout the body. For example:

    • Nicotine has two major receptor types.

    • Serotonin has multiple receptor subtypes (related to various bodily functions).

  • Classes of Neurotransmitters

    • Amino Acids:

    • Primary excitatory neurotransmitter: Glutamate.

      • Function: Increases neural activity (generates excitatory postsynaptic potentials, EPSPs).

    • Primary inhibitory neurotransmitter: GABA.

      • Function: Inhibits neural activity.

    • Amines:

    • Four major neurotransmitters:

      • Dopamine:

      • Role: Movement, motivation, reward, and addiction.

      • Acetylcholine:

      • Role: Functions both in the peripheral nervous system (muscle contraction at neuromuscular junctions) and central nervous system (learning/memory).

      • Norepinephrine:

      • Role: Fight-or-flight responses; operates within the sympathetic nervous system.

      • Serotonin:

      • Role: Mood regulation, sleep patterns, appetite control, and social behavior.

    • Peptide Neurotransmitters:

    • Example: Endorphins, function to alleviate pain and produce feelings of euphoria.

    • Gas Neurotransmitters:

    • Examples: Nitric oxide and carbon monoxide, signaling roles in the nervous system.

  • Functions of Serotonin

    • Affects many bodily functions:

    • Involved in sleep regulation (affects REM sleep duration).

    • Linked to mood and depression; SSRIs enhance serotonin availability to alleviate depressive symptoms.

    • Regulates appetite; increases appetite during food sight/smell and signals satiety after eating.

    • Influences social behavior; affects emotional states and connections with others.

  • Effects of Norepinephrine

    • Primary role in controlling the sympathetic nervous system (fight or flight):

    • Increases heart rate, dilates airways, and reduces digestive functions.

    • Chronic stress leads to excessive norepinephrine release, causing health issues.

  • Peptide Neurotransmitters:

    • Endorphins: Natural pain relievers that create feelings of euphoria and are released during physical activities (runner's high).

    • Oxytocin: Known as the "love hormone," it facilitates bonding and attachment behaviors.

    • Vasopressin: Influences social attachment and reproductive behaviors.

  • Pathways and Origins of Neurotransmitters

    • Different neurotransmitters originate from specific brain areas affecting their functions.

    • Cholinergic pathways: originate primarily in the basal forebrain (acetylcholine).

    • Dopaminergic pathways: originate in the substantia nigra (dopamine).

    • Norepinephrine pathways: originate in the locus coeruleus (norepinephrine).

    • Serotonergic pathways: originate in the brainstem (serotonin).

  • Psychoactive Drugs

    • Exogenous substances that influence the nervous system. Must cross the blood-brain barrier to have effects.

    • Typically categorized as agonists (enhance neurotransmitter activity) or antagonists (block neurotransmitter effects).

    • Tolerance: Body adapts to drug effects, necessitating more of the drug for the same effect.

    • Withdrawal Symptoms: Occur upon discontinuation of the drug due to physiological and psychological dependence.

  • Receptor Dynamics

    • Agonists bind to neurotransmitter receptors, enhancing their effects; may mimic neurotransmitters directly.

    • Antagonists bind to receptor sites, blocking neurotransmitter access and dampening their effects.

  • Examples of drugs include nicotine (agonist for acetylcholine), and others affecting various neurotransmitter systems to treat conditions or induce effects.