spinule

Spinule is a term used in biology to refer to small spine-like or spike-like protrusions on the membrane of cells, particularly neurons. The word derives from Latin spina, meaning thorn or spine. In neuroscience, spinules are slender membranous protrusions that originate from postsynaptic dendritic spines and extend toward, or sometimes into, presynaptic terminals. They are typically hundreds of nanometers to about a micrometer in length and are observed using electron microscopy and advanced light microscopy.

Spinules are dynamic structures whose formation is associated with synaptic activity and plasticity. They can appear during development and in response to learning or synaptic stimulation. The functional role of spinules is not fully settled; they are thought to participate in structural remodeling of synapses, receptor trafficking between postsynaptic compartments, and trans-synaptic signaling. In some contexts, they may reflect endocytic or exocytic processes linked to synaptic function.

They are most commonly described at excitatory glutamatergic synapses in brain regions such as the hippocampus and cortex, but have also been reported elsewhere. Understanding of spinules continues to grow with advances in imaging methods, and they are considered one aspect of the broader field of synaptic ultrastructure and plasticity.