Neurotransmitters

Discussion focused on neurotransmitters in brain function and chemical communication.

Neurotransmitter: A chemical released by a neuron that communicates across a synapse to influence another neuron or target cell.
Distinction between neurotransmitters and hormones is emphasized; neurotransmitters work over short distances while hormones travel through the bloodstream.

Major categories of neurotransmitters include:
- Different types of neurotransmitters and their associations with behaviors.
- Neurotransmitters as a bridge between chemicals and behavior.
Debate on the number of neurotransmitters:
- Estimates range from 50-60 to upwards of 200-250.

Four essential criteria that define a neurotransmitter:
1. The chemical must be synthesized in the neuron.
2. The neurotransmitter must be released in response to an action potential.
3. The compound must have a specific receptor to bind to.
4. Binding should produce a defined physiological response.
Chemicals not meeting these criteria are not classified as neurotransmitters.
Some debate exists as to whether three out of four criteria are sufficient for classification.

Different neurotransmitters can be excitatory or inhibitory based on the receptor types they engage with.
- Example: Acetylcholine can be excitatory in skeletal muscles (e.g., hand clenching) but inhibitory in the heart muscle.
Explanation of neurotransmitter effects in the body is simplified for educational purposes, recognizing the complexity of real-world scenarios.

Acknowledgment that excess or deficiency in certain neurotransmitters can be associated with specific conditions (e.g., Alzheimer's disease, depression).
- However, relationships are not simple or linear (e.g., low dopamine not solely responsible for ADHD).

Generally, the largest group of neurotransmitters includes:
- Acetylcholine, Dopamine, Serotonin, Norepinephrine.
Characteristics:
- Simple chemical structures that allow for quick synthesis and action within the body.
- Origin from diet influences levels of neurotransmitters; for instance, acetylcholine derives from acetate and choline.

These are larger molecules generally related to protein synthesis, such as hormones.
They have a complex structure and require longer synthesis times.
- Examples include insulin, which regulates blood sugar.
- They take longer to act due to complexity and larger size.

Lipid-based neurotransmitters cannot be stored in vesicles due to their similarity to the vesicle membrane.
Important for systems like the endocannabinoid system.

This category includes gases like carbon monoxide and nitric oxide.
Gases cannot be stored; they are synthesized on-demand and diffuse rapidly, influencing physiological responses like vascular dilation.

Overview of Neurons and Behavior:
- Each neuron can release multiple neurotransmitters.
- Behaviors arise from the interaction of various neurotransmitter systems rather than isolated actions.
Cholinergic System:
- Predominantly uses acetylcholine.
- Key in maintaining alertness, memory functions, and interconnected with diseases like Alzheimer's, which is marked by cholinergic neuron loss.
Dopaminergic System:
- Governs both movement control and reward processing.
- Disorder of this system results in Parkinson’s disease due to loss of dopaminergic neurons, leading to mobility issues and cognitive decline.
Clinical Definitions and Challenges of Alzheimer's Disease:
- Alzheimer's is characterized by symptoms beyond memory loss, requiring a multifaceted understanding of cognition and behavior.
- Dementia is a broader category that includes Alzheimer's but also encompasses other disorders.
Parkinson's Disease Symptoms:
- Characterized by resting tremors, rigidity, bradykinesia (slow movement), and postural instability.
- Cognitive impacts also noticeable, leading to Parkinson's disease dementia.

Current treatments for neurodegenerative diseases focus on managing symptoms rather than providing cures.
Ethical considerations about the quality of life and care for patients with progressive diseases like Alzheimer's and Parkinson's are paramount due to increasing life expectancy and healthcare burdens.