Ch.5: Synaptic Activity




The Structure of Chemical Synapses

Types of Chemical Synapses

The Release of Neurotransmitter Substance




Use and Refuse of Synaptic Vesicles

Excitatory Chemical Synapses

Inhibitory Chemical Synapses

The Disposal of Transmitter Substances

Presynaptic Inhibition

Spatial and Temporal Summation

Biochemistry of Neurotransmission

Receptors and Effectors

Enzymes, Substrates, and Products

Identifying Specific Neurotransmitters

    1. The substance should be present within the nervous system in quantities typical of transmitter agents. Thus, esoteric chemicals that may be produced in the laboratory or extracted from other species may have powerful synaptic effects, but if they are not detectable in the nervous system, they are not likely to be neurotransmitters.
    2. The substance must be present in the endfeet of neurons. Neurotransmitters are stored in vesicles within the terminal buttons; therefore, it is in these terminals that the substance should be concentrated.
    3. The substance must be synthesized within the neuron. Thus, the specific enzymes responsible for synthesizing the substance from its precursors must be present.
    4. There must be evidence of enzymes that inactivate or destroy the substance in the vicinity of the synapse.
    5. The substance must act on receptor sites. When applied to the postsynaptic surface as a drug, it should have exactly the same effect as the natural activation of the synapse.


The Repeal of Daleís Law

Neurotransmitters and Neuromodulators


The Nicotinic Receptor: A Chemically Gated Ion Channel

The Muscarinic Receptor: Neuromodulatory Effects

The Catecholamines

Tyrosine Hydroxylase

Tyrosine + Oxygen -------------------------> L-Dopa

Next, L-dopa is converted to dopamine by the enzyme dopa decarboxylase:

Dopa decarboxylase

L-Dopa --------------------> Dopamine

Norepinephrine is then synthesized from dopamine by the enzyme dopamine beta-hydroxylase:

Dopamine beta-hydroxylase

Dopamine ----------------------------->Norepinephrine

Thus, the catecholamines are a closely related family of neurotransmitter compounds, with dopamine and norepinephrine having important central nervous system effects.

The Dopaminergic Synapse

The Noradrenergic Synapse


Trytophan hydroxylase

Trytophan 5-HTP

5 -HTP decarboxylase

5-HTP Serotonin

Amino Acid Neurotransmitters