The structure and innervation of the sinu-atrial node of the mole heart.
The sinu-atrial node in the heart of the mole, Mogera wogera, contains myocytes which are devoid of atrial specific granules and which may be classified into two types: electron-lucent (majority) and dark (minority). Numerous unmyelinated axon terminals, containing synaptic vesicles, face the nodal myocyte surface with interspaces of less than 300 nm. There are about 6 terminals per myocyte profile and about 10 per profile at nuclear levels. Of a total of 2717 of these terminals 85.2% are 50-200 nm from the nodal myocytes, and 9.6% form closer neuromuscular junctions, with less than 50 nm interspace and some membrane specialization. Such specilizations are almost exclusively found in relation to the dark, minority-type of nodal myocyte. Myelinated nerve fibers are also numerous within the mole SA node, and may terminate almost directly on a nodal myocyte. A few nerve fibers contain many mitochondria and may represent afferent endings. Nodal capillaries are smaller and fewer than capillaries in the juxtanodal myocardium, probably indicating a lesser blood supply to the SA node than to the ordinary myocardium.
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D001699:Biometry; D002196:Capillaries / Q000648:ultrastructure; D007312:Eulipotyphla / Q000033:anatomy & histology*; D008854:Microscopy, Electron; D008971:Moles / Q000033:anatomy & histology*; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure; D009469:Neuromuscular Junction / Q000648:ultrastructure; D012849:Sinoatrial Node / Q000648:ultrastructure*