Innervation of Fascia
David Lesondak, Angeli Maun Akey in Fascia, Function, and Medical Applications, 2020
Most peripheral nerves are enveloped in a three-layer fascial model. Their axons are surrounded by endoneurium, which offers only little mechanical support. Groups of endoneurium-covered axons are then enveloped by a think but dense perineurium, which offers strength in tension, and also maintains the so-called blood–nerve barrier. Finally, the perineurium is again covered by the epineurium, a thick and areolar layer of connective tissue that is highly vascularized and acts as a cushion for the whole nerve bundle. All three fascial layers of the nerve are innervated and contain a thin plexus of potential nociceptors that is likely responsible for some cases of nerve trunk pain. Experiments with rats have shown that inflammation tends to change respective neural axons by making them sensitive to mechanical stimuli.23 Such nerve trunk pain may then appear either as local tenderness of a nerve, or a “doorbell” type of response, where local spot palpation may evoke symptoms in a more distal region.
Neurophotonics for Peripheral Nerves
Yu Chen, Babak Kateb in Neurophotonics and Brain Mapping, 2017
Nerve fibers, both afferent and efferent, are grouped in fascicles surrounded by connective tissue in the peripheral nerve (Peters and Palay, 1991). The fascicular architecture changes with an increasing number of fascicles of smaller size from the proximal to the distal end of the nerve. These fascicles eventually give origin to branches that innervate distinct targets, either muscular or cutaneous. In addition to bundles of nerve fibers, the peripheral nerves are composed of three supportive sheaths: epineurium, perineurium, and endoneurium. The epineurium is the outermost layer, composed of loose connective tissue and carries blood vessels that supply the nerve. The perineurium surrounds each fascicle in the nerve. It consists of inner layers of flat perineurial cells and an outer layer of collagen fibers organized in longitudinal, circumferential, and oblique bundles. The perineurium is the main contributor to the tensile strength of the nerve, acts as a diffusion barrier, and maintains the endoneurial fluid pressure. The endoneurium is composed of fibroblasts, collagen and reticular fibers, and extracellular matrix, occupying the space between nerve fibers within the fascicle. The endoneurial collagen fibrils are packed around each nerve fiber to form the walls of the endoneurial tubules. Inside these tubules, axons are accompanied by Schwann cells, which either myelinate or just surround the axons (Peters and Palay, 1991).
The nervous system and the eye
C. Simon Herrington in Muir's Textbook of Pathology, 2020
Histologically, a peripheral nerve consists of longitudinally orientated nerve fibres running in a fascicle. Each fibre is surrounded by collagenous tissue called the endoneurium, each fascicle by perineurium, and all the fascicles in a given nerve by the epineurium. Within the endoneurium the myelinated axons are supported by Schwann cells which manufacture and maintain the myelin sheaths between the nodes of Ranvier. Unlike the oligodendrocyte of the CNS, which supports the internodal myelin of many axons, the Schwann cell supports the internodal myelin of only one segment of an axon. The thickness of the myelin sheath is proportional to the diameter of the axon.
Anatomic variations of the human falx cerebelli and its association with occipital venous sinuses
Published in British Journal of Neurosurgery, 2021
Safiye Çavdar, Bilgehan Solmaz, Özgül Taniş, Orhan Ulas Guler, Hakkı Dalçık, Evren Aydoğmuş, Leyla Altunkaya, Erdoğan Kara, Hızır Aslıyüksek
Falx cerebelli, is composed of fibroelastic, dense irregular connective tissue. The connective tissue consisted of cells predominantly of fibroblast which produced the ground substance and collagen fibers. Additionally, the connective tissue contained sensory nerve endings and blood vessels. The arterioles were composed of 1–2 layers of smooth muscle cells in the tunica media and the venules were composed of a single layer of endothelium with many erythrocytes in their lumens (Figure 10a). Furthermore, a large number of lymphatic vessels appeared to be undulated with a single layer of endothelium and a subendothelial layer (Figure 10b). Extravagated lymphocytes surrounding the lymphatic vessels were observed (Figure 10b). Near the vessels, a peripheral nerve characteristically formed a round bundle of nerve processes surrounded by connective tissue sheath perineurium was detected (Figure 10a).
Histological and ultrastructural study of AflatoxinB1 induced neurotoxicity in Sciatic nerve of adult male Albino rats
Published in Ultrastructural Pathology, 2020
Madiha M. M. Makhlouf
In the present study, light microscopic examination of semi-thin sections of sciatic nerves of both control and olive oil-treated groups showed the same normal histological architecture. The sciatic nerve was covered from outside by several layers of collagen fibers called epineurium (Figure 2). The connective tissue perineurium appeared as thin layers of collagen fibers containing blood vessels surrounding the nerve fascicles (Figure 1). These contained nerve fascicles were formed of myelinated axons of variable sizes. The axons were surrounded by a dense and thick deeply stained blue myelin sheath. They were separated by connective tissue endoneurium. The axon contained within each myelin sheath appeared pale in staining (Figure 2). Schwann cells exhibited a vesicular nucleus with prominent nucleolus and their cytoplasm stained paler blue than the myelin and could be seen surrounding the myelinated axons and small clusters of non-myelinated axons (Figures 1 and 2).
Distinguishing Benign from Malignant Circumscribed Orbital Tumors in Children
Published in Seminars in Ophthalmology, 2018
Yufei Tu, Frederick A. Jakobiec, Katherine Leung, Suzanne K. Freitag
Typically, schwannomas (Figure 2) of the orbit demonstrate variable but typically hyperintense T2 signal. Variability in T2 signal intensity can be seen, depending on the prevalence of Antoni A or B patterns.1 Tumors that are in the Antoni A group typically demonstrate on MRI uniformly T2 hypointense signaling. Lesions that are in the Antoni B group can exhibit heterogeneous T2 hyperintense signal, with cavitary change.1 Schwannomas are typically avidly enhancing, although areas of cystic/cavitary change can result in regions of heterogeneous enhancement.1,2 No aggressive osseous destruction of the orbital bone is seen on CT. Rather, schwannomas can result in smooth osseous bowing or expansion. In our patient, the schwannoma demonstrated relatively hypointense signaling on T2, isointensity to brain on T2-weighted images, and minimally hyperintensity to skeletal muscle. This would be consistent with the predominant Antoni A growth pattern. The schwannoma also demonstrates no significant restriction of diffusion. Smooth bowing of the lamina papyracea without aggressive erosion is often present on CT. The encapsulation of the tumor by a perineurium is responsible for its elegant circumscription. In an adult, a circumscribed neurofibroma can pose a diagnostic radiographic challenge, but in a child such a lesion is highly exceptional. Most pediatric neurofibromas are of the plexiform and diffuse types.