![]() ![]() In this field axon terminals are forming asymmetric and symmetric synapses with a dendritic spine.Ī version of Fig. Neuropil in layer 5 of area 46 in a 30 year old monkey. Other than area 46, the only other cortical structure in the monkey that appears to have been examined is the dentate gyrus, from which no age-related loss of synapses was found. Whether there is an age-related loss of synapses from all cortical areas has not been determined. That these profiles are of altered terminals is shown by the fact that they contain accumulations of synaptic vesicles at their peripheries, and are sometimes seen to be presynaptic to other structures in the neuropil. Generally the axoplasm of such terminals is filled with neurofilaments, sometimes surrounding a core of mitochondria ( Fig. It has been shown that with age some synapses are lost from the neuropil of prefrontal cortex area 46 and a few profiles of dystrophic axon terminals have been encountered in the cortical neuropil of old monkeys (Figs. 9.1 – 9.1B), the cell bodies of both excitatory and inhibitory neurons, and axon initial segments ( Figs. The postsynaptic elements at such synapses include dendritic shafts ( Fig. At symmetric synapses the synaptic cleft is narrower than at excitatory synapses, and the postsynaptic density is only about the same width as the presynaptic density. These synapses are formed by axon terminals that contain pleomorphic synaptic vesicles, which are somewhat smaller than the vesicles in axon terminals forming asymmetric synapses. The less common symmetric synapses are inhibitory in function. The postsynaptic elements of such synapses include dendritic shafts, dendritic spines, and the cell bodies of inhibitory neurons. The synaptic junction has a rather wide cleft and an obvious postsynaptic density. Asymmetric synapses are formed by axon terminals that contain spherical synaptic vesicles. 9.1 -9.3).Īsymmetric synapses, which are excitatory in function, predominate and account for about 80% of the total population of synapses. The adjectives refer to whether the pre- and postsynaptic densities associated with the synaptic junctions are of similar width (symmetric), or whether the postsynaptic density is thicker (asymmetric) and more prominent than the presynaptic one (Figs. Basically, there are two types of synapses in the cerebral cortex, and in material fixed using glutaraldehyde they are referred to as symmetric and a symmetric synapses. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |