Neuro AM 03-24-25

Introduction to Neurotransmitters Focus on acetylcholine as the first neurotransmitter discussed. Review of synapses: Two synapses illustrated between neuron A and neuron B. An excitatory neuron releases neurotransmitter (e.g., glutamate) to neuron A, leading to depolarization, while an inhibitory neuron releases neurotransmitter (e.g., GABA) to neuron B, leading to hyperpolarization. Membrane Potential Changes Measurement of membrane potentials of neurons A and B is crucial for understanding neural communication. Excitatory neurotransmitter: When released, it causes depolarization by allowing positive ions (like sodium) to enter the neuron, making the membrane potential more positive (closer to the threshold for an action potential). Inhibitory neurotransmitter: Inhibitory neurotransmitters cause hyperpolarization by allowing negative ions (like chloride) to enter the neuron or by letting positive ions (like potassium) exit, making the membrane potential more negative, thus preventing action potential firing. Mechanisms of Action Neurotransmitters bind to specific receptors located on the postsynaptic neuron. This binding causes changes in membrane potential, which can lead to stimulation (depolarization) or inhibition (hyperpolarization). Some neurotransmitters can have both excitatory and inhibitory effects depending on the cell type they act upon; for example, acetylcholine is excitatory in skeletal muscles but inhibitory in heart muscle. Preparing for Exams Reminder about upcoming difficult exams that may include material on neurotransmitter functions. Importance of understanding neurotransmitters for success in exams is paramount, as they play a critical role in every neural process. A comprehensive understanding of their roles in different brain functions is essential for complex topics. Neurotransmitter Levels Issues can arise from either too low or too high levels of neurotransmitters: - Agonists may be used when levels are low to stimulate receptors, enhancing signaling. - Antagonists and reuptake inhibitors may be used when levels are high to dampen signals: - Antagonists block receptor binding, preventing neurotransmitter effects. - Reuptake inhibitors slow the reabsorption of neurotransmitters back into the presynaptic neuron, allowing more neurotransmitter to remain in the synaptic cleft, thus enhancing and prolonging their action. Acetylcholine Overview First neurotransmitter discovered; can be either excitatory or inhibitory depending on the target cell. Examples include its excitatory action on skeletal muscles that causes contraction and its inhibitory effect on heart muscle, which slows heart rate. Functions of Acetylcholine include: - Memory formation and learning: Acetylcholine is crucial for encoding new memories and facilitating neuroplasticity. - Attention and focus: It enhances alertness and cognitive processing. - Sleep regulation: Plays a role in transitioning between sleep stages, particularly in REM sleep. - Arousal mechanisms: Involved in stimulating the cortex to increase overall arousal and readiness. Disorders Related to Acetylcholine Levels include: - Alzheimer’s Disease: This neurodegenerative disease is associated with the loss of acetylcholine-producing neurons, leading to significant memory loss and learning difficulties. - Treatments include acetylcholine reuptake inhibitors, such as donepezil, to increase availability at synapses, aiming to alleviate symptoms by enhancing cholinergic signaling. Monoamines (Dopamine, Serotonin, Norepinephrine) A group of neurotransmitters with overlapping functions and effects that influence various psychological and physiological processes. - Serotonin: Functions in mood regulation, sleep, appetite, and overall emotional well-being. - Antagonists are used when serotonin levels are high (e.g., Zofran for nausea), while low levels are linked to mood disorders such as depression and anxiety; treatments include SSRIs (e.g., Prozac, Paxil) that inhibit the reuptake of serotonin to increase its availability at the synapse. - Dopamine: This neurotransmitter is vital for motivation, pleasure, attention, and movement control. High levels are linked to psychosis (e.g., schizophrenia) and are treated with antagonists. Conversely, low levels of dopamine are associated with attention deficit disorders (ADD) and depression; treatments focus on dopamine reuptake inhibitors (e.g., Wellbutrin, Ritalin) to increase dopamine availability. - Norepinephrine: Functions in attention and decision-making; treatments for norepinephrine-related disorders mimic approaches used for dopamine. Miscellaneous Neurotransmitters: - Glutamate: The major excitatory neurotransmitter in the CNS, critically involved in learning and memory processes. However, abnormally high levels of glutamate can lead to excitotoxicity and seizures, thus antagonists are sometimes used in treatment strategies. - GABA (Gamma-Aminobutyric Acid): The only primary inhibitory neurotransmitter in the brain, serving to calm nervous activity and promote relaxation. It helps to balance excitatory signals and prevent over-excitation of the nervous system. Conclusion Understanding neurotransmitters and their functions is essential for academic success and effective treatment of various neurological and psychological conditions. Regular review and study of neurotransmitter functions are important, as is preparation for any upcoming review sessions on this critical topic.