Neurotransmitters

3 types of Synapses

1. Neuron + neuron = neuronal

2. Neuron + muscle = neuromuscular

3. Neuron + gland = neuroglandular

Ionotropic NT Receptor

• Direct

• Immediate

• Brief

• Ion channels (ligand)

At rest —> channel is closed

When NT binds —> opens channel and allows ions to move by facilitated diffusion

Metabotropic NT Receptor

• Indirect

• Slow

• Long-lasting/ prolonged/ greater intensity

Often a G-Protein Coupled Receptor using cAMP as second messenger

Chemical Classification of NTs

1. Acetylcholine (unique)

2. Gas

3. Biological amines (NH2)

4. Lipid

5. Amino acid

6. Purine

7. Peptide (small protein)

3 Ascending Pathways

1. Spinocerebellar

• no crossing over

• body position/ movement awareness

• to cerebellum

2. Dorsal column-medial lemniscal

• cross over medulla

• touch, joint

• to parietal

3. Spinothalamic

• cross over spinal cord

• temp, pain

• to parietal

Acetylcholine (ACh)

• Neurons that release ACh are called: Cholinergic

• Functional Classification:

1. Response: Excitatory (depolarization) / Inhibitory (Hyperpolarization)

2. Cholinergic Receptors: a) Nicotinic - ionotropic —> open Na+ (excitatory), b) Muscarinic - metabotropic

• Chemical Classification: Acetylcholine

CNS: Hippocampus for creating long term memories

PNS:

1. Somatic motor neurons to stimulate skeletal muscle

2. Preganglionic autonomic motor neurons to stimulate post ganglionic motor neurons or adrenal medulla

3. Parasympathetic postganglionic motor neurons to their effectors

Hyposecretion: Alzheimer’s

ACh Receptors (2)

1. Nicotinic Receptors: Neuromuscular Junction, Autonomic Ganglia (Nicotine is an agonist, prolonging effects of ACh), CNS, Adrenal medulla

2. Muscarinic Receptors: Others

Alzheimer’s Disease and ACh

• Loss of cholinergic neurons (less release of ACh)

• Accumulation of abnormal proteins forming plaques

• Cholinesterase inhibitors:

- prevent ACh breakdown

- longer in synapse

Norepinephrine (NE)

• Neurons that release NE are called: Adrenergic

• Functional Classification:

1. Response: Excitatory (depolarization) / Inhibitory (Hyperpolarization)

2. Receptors: Adrenergic —> metabotropic

• Chemical Classification: Biological amines (NH2)

CNS:

1. Frontal lobe —> working memory (e.g. decisions, logic, reasoning)

2. Limbic —> feeling of well being

3. Reticular activating system (RAS) —> alert, consciousness

PNS: Postganglionic sympathetic motor neurons

*SM = smooth muscle

Disregard DA1

Glutamate

• Neurons that release glutamate are called: Glutaminergic

• Functional Classification:

1. Response: Excitatory

2. Receptors: Ionotropic (glutaminergic increase)

• Chemical Classification: Amino acid

CNS: Main excitatory neuron (important in memory formation)

Impaired reuptake: Alzheimer’s, repeated stimulus overstimulates neuron and causes death

Synaptic Plasticity

Neurons adapt to number/ repetitive stimuli

• Long term potentiation: 1) increase repetition, increase stimulus; 2) increase # of NT receptors or increased amount of NT released

• Long term depression: 1) few synapses, decrease stimulus or response of post synaptic cell; 2) decrease # of NT receptors or decreased amount of NT released