Neurotransmitter Systems

Communication between Neurons

The nervous system uses various neurotransmitters for communication between neurons.
Different groups of neurotransmitters are categorized into systems, each with unique neurotransmitters.

Key Neurotransmitter: Acetylcholine
Functionality: Operates at the neuromuscular junction, autonomic nervous system, and throughout the brain.
Types of Receptors:
- Nicotinic Receptors: Found at the NMJ and various synapses; activated by nicotine and acetylcholine.
- Muscarinic Receptors: Interact with muscarine from certain mushrooms; do not bind to nicotinic receptors and have distinct roles.

Key Neurotransmitters: Glutamate, GABA (gamma-aminobutyric acid), and glycine.
Systems:
- Glutamatergic: Corresponds to glutamate; excitatory.
- GABAergic: Corresponds to GABA; inhibitory.
- Glycinergic: Corresponds to glycine; inhibitory.
Reuptake Mechanism: Neurotransmitters removed from synapses via reuptake by presynaptic cells or glial cells.

Composition: Enzymatically made from amino acids; lack carboxyl groups.
Key Neurotransmitters:
- Serotonin: Made from tryptophan; belongs to the serotonergic system.
- Dopamine: From tyrosine; involved in the dopaminergic system.
- Norepinephrine and Epinephrine: Similar and part of the adrenergic system; produced in adrenal glands.
Reuptake Process: Each neurotransmitter is transported back into presynaptic cells for recycling.

Definition: Chains of amino acids linked by peptide bonds, serving as neurotransmitters.
Examples: Met-enkephalin (5 amino acids) and beta-endorphin (31 amino acids).
Functionality: Released with other neurotransmitters; can act as hormones (e.g., vasoactive intestinal peptide, substance P).
Effect on Postsynaptic Cell: Varies with receptor - can cause depolarization or hyperpolarization.
- Acetylcholine Example: Binds to nicotinic receptor (depolarization) vs. muscarinic receptor (varied effects).

Overview of characteristics including neurotransmitters, receptors, degradation methods, and postsynaptic effects.
- Cholinergic System: Acetylcholine, nicotinic/muscarinic, eliminated by acetylcholinesterase.
- Amino Acids: Glutamate and GABA, reuptake by neurons/glia, predominantly excitatory/inhibitory effects.
- Biogenic Amines: Serotonin, dopamine, norepinephrine/epinephrine, reuptake, varied postsynaptic effects.
- Neuropeptides: Variable length peptides, degradation by peptidases, diverse receptor effects.

More complex; involve G proteins and effector proteins.
Mechanism: Neurotransmitter binds, activating G protein, results in production of second messengers (e.g., cAMP, IP3).
Effects in Neurons: Changes in enzyme activity and potential gene transcription impacts, influencing strength in neuronal connections (learning/memory).

Proteopathy: Accumulation of misfolded proteins causes neurodegenerative diseases like Alzheimer’s and Parkinson’s.
- Alzheimer's Disease: Linked to beta-amyloid plaques.
- Parkinson's Disease: Associated with toxic alpha-synuclein.
Mechanism: Proper folding of proteins is critical; disruption leads to toxicity and accumulation.

Proteopathy: Diseases characterized by abnormal protein accumulation.
Reuptake: Process of taking neurotransmitters back into neurons post-release.
Neurodegenerative Diseases: Conditions where nerve cells progressively deteriorate (e.g., Alzheimer’s, Parkinson’s).

Brain Utilization Myth: The idea that humans only use 10% of their brains is false.
Measurement through functional magnetic resonance imaging (fMRI) shows high brain activity across various regions during tasks (approximately 80% utilized).
Example Task: Subject performs Visual Recognition Task; fMRI measures activity across sensory and motor areas.