List of abbreviations
of micros-
specialist terms
explained in
English +

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

dieser Seite

Dr. med.
H. Jastrow

of use
Overview synapse (Synapsis):
Pages with explanations are linked to the text below the images if available! (Labelling is in German)
type I synapse
Cortex cerebri 1 (rat)
type I synapse
Cortex cerebri 2 (rat)
type I synapse
Cortex cerebri 3 (rat)
type I synapse
Cortex cerebri 4 (rat)
type I Synapse + mitochondrium
cerebral cortex (rat)
synapse en passant
smooth muscle cell (rat)
synapse (rat)
synapse on a Merkel
cell, skin (rat)
type I synapse
Cortex cerebri 5 (rat)
synapses in cerebral
cortex (rat)
ribbon synapses of the
retina (rat)
electrical synapse = gap junction = nexus
stereo image, pilar cell, inner ear (rat)
nexus, intercalated
disk, heart (rat)

A general distinction is made between electrical and chemical synapses.
Electrical synapses (non-vesicular synapses; Terminologia histologica: Synapses nonvesiculares; Synapses electricae) correspond to nexus (gap junctions; maculae communicantes; Terminologia histologica: Maculae communicantes; Nexus) and consist of tunnel proteins (further details here). They provide faster signal transduction than chemical synapses and by a process called electrotonic coupling generate an ultrafast balance of membrane potentials of coupled neurons. This allows a synchronized conduction of impulses in strands of cells coupled by nexus which is of importance e.g., during maturation of the brain in the foetal period. In adults, however, nexus are present in relevant number only in some few areas still: they synchronize inhibition of Purkinje's cells by coupling basket and stellate cells of the cerebellum; couple glial cells of the CNS, olfactory bulb (Bulbus olfactorius), sensory cortex of the Gyrus postcentralis (main sensory area for body perception). Nexus are bidirectional i.e., the signal transduction caused by direct flow of ions may run in both directions. Nexus are even present between epithelial cells of glands in order to synchronise their action.
mixed synapses (missing in Terminologia histologica: Synapses mixtae) partly show connexons typical for electrical synapses and directly adjacent chemical synapses. They are very rare and shall be restricted to few nuclei of brain nerves.
Chemical synapses (vesicular synapses; Terminologia histologica: Synapses vesiculares; Synapses chemicae) are typical for the central (brain and spinal chord) and the peripherical nervous system (all other kinds of nerve tissue). In spot-like nearly round areas with diameters of a few hundred nanometres chemical synapses in most cases are asymmetrical, i.e. pre- and postsynaptic membranes have different features causing a unidirectional conduction of impulses. Types of chemical synapses are descired below.
Presynaptic region (Terminologia histologica: Pars presynaptica)
The presynaptic side shows a widening of the terminating nerve cell process called axon (Terminologia histologica: Axon), which is termed terminal bouton (Terminologia histologica: Bulbulus terminalis). In many instances axons split into several axon collaterals (Terminologia histologica: Rami collaterales axonis) just shortly before their end which then form such boutons. Terminal boutons contain plenty of crista-type mitochondria providing energy by their ATP synthesis, further actin filaments (called neurofilaments here) as well as microtubules (termed neurotubules here) and some hundred to thousands of neurotransmitter vesicles (Terminologia histologica: Vesiculae synapticae; Vesiculae presynapticae: diameter: 40 - 60 nm). From point of view of function the latter are the most important component of the boutons. Synaptic vesicle linking strands (Terminologia histologica: Vincula vesicularum synapticorum) are 30 - 60 nm long, few nanometres thick, slightly electron-dense filamentous structures keeping the vesicles close to the cell membraneThey contain synapsin, a fibrous phosphoprotein and link the synaptic vesicles to actin- and spectrin filaments of the cytoskeleton. Further synapsin is the morphological correlate for fine filamentous interconnections of the vesicles to each other. It comprises ~6 % of all membrane proteins of these vesicles. Synapsin is the substrate of cAMP-dependent- and calcium-calmodulin-dependent proteinkinases being phosphorylated with raising level of calcium ions (Ca++) in the cytoplasm. This is required for disconnection of the vesicles from the cytoskeleton a prerequisite for their release.

An English page with much more detailed information and further images is available in the professional version of this atlas.

--> electrical synapse, synaptic bodies, nerve tissue, nerve
--> sensory organs, nerve fibres, nerve terminals, central nervous system, retina
--> Electron microscopic atlas Overview
--> Homepage of the workshop

Images, page & copyright H. Jastrow.