Neurotransmitter pathways

Classification of NT's based on chemical structure:

• Structure determines which channels it can open. Quaternary and monoamines e.g. doamine, serotonin, noadrenaline, acetylcholine.
• Amino acids e.g. GABA, glutamate. Peptide transmitters (chains of amino acids) e.g. endorphins, oxytocin.Gas transmitters - nitric oxide. carbon monoxide. Synthesised, not stored

Classification of NT's based on function: Input-output functions:

• Glutamate - excitatory e.g. all senses except pain, GABA - inhibitory, especially local inhibitory interneurons, ACh - activates muscle fibres, muscle contracts

Information modulation --> ACh - activates cerebral cortex, facilitates learning. Dopamine - voluntary mobement, action planning, control. Noradrenalin - increases vigilance + readiness to act. Serotonin - Calming, reduces impulsive behaviour.

Neurotransmitter synthesis -Complex and can't be stored in large amounts so must be synthesised

Versatility of neurotransmitters (key-lock): Each NT only binds to a specific receptor and specific receptors will only accept one NT. Different receptors can be associated with different functions. At different synapses, the same NT can have different effects.

Dopaminergic Meso-Limbic-Cortical pathway: Fro midbrain to limbic system to frontal cortex using dopamine. Psychopharmacology - 3 target structures have different distributions of dopamine receptor subtypes.

Neurotransmitters and drugs: Substances able to cross blood-brain barrier may affect brain regardless of... 1. Whether produced by body (ENDOgenous substances)  2. Or enter blood from outside (EXOgenous substances).

• Drug = Substance that even in small quantities has major effects on bodily functions
• Psychoactive drug = Drug that affects CNS and alerts alertness, perceptual, cognitive and emotional. Interfere with brains NT's systems.
• Indirect inference: Interfere with production, release or removal of neurotransmitter

• Agonists - Increase availability of NT and increase production/prevent uptake
• Antagonists - Increase availability of NT, less likely gate will open

4 functional systems/categories:

• 1. Stimulants - increase neural activity or bodily functions e.g. caffeine, nicotine, cocaine
• 2. Depressants - decrease neural activity or bodily functions e.g. alcohol, valium
• 3. Analgesics - relieve pain e.g. morphine, heroin
• 4. Hallucinogens - cause hallucinations e.g. marujana, magic mushrooms, LSD

Direct inference: Postsynaptic receptor sites are specific to the molecular structure of a neurotransmitter. Similar molecules can bind as well.

• Agonists - mimic action of NT. Bind to receptor site and open channel.
• Antagonists - Prevent action of NT. Block receptor so no NT molecule can bind to it

Pathways identified in 2 ways:

• 1. Anatomically - nigro-striated pathway begins in substantia nigra and leads to straitum.
• 2. Chemically - dopaminergic pathwaybis one that was the neurotransmitter dopamine through all stages.

Parkinson's disease:

Movement disorder - trembling, slowness, problems initiating voluntary movement. Cause - degeneration of substantia nigra - under activity in NS, lack of dopamine. Treatment = L-Dopa (dopamine precursor). Side effects = Psychotic symptoms

Schizophrenia:

Delusions, hallucinations, emotional and cognitive dysfunction. Overactivity in MLC pathway. Overabundance of dopamine/over-sensitive receptor will open channels. Treatment = antipsychotic drugs, dopamine antagonist. Side effects - movement problems (Parkinsonism)