Keywords

The perineurium is composed of multiple concentric single-cell layers enclosing individual nerve fascicles. Each layer has a thickness equivalent to the width of a perineurial cell. Groups of these cells join by means of tight junctions and desmosomes to form layers that function as a barrier against diffusion of particles across them. Perineurial internal layers have more of these specialized unions among perineurial cells, which are proximal to nerve fascicles [1–4].

Perineurial cells have basal laminas constituted by glycoproteins such as fibronectin, as well as heparin sulfate and laminin, and their nuclei are flattened. The cytoplasm is granular and contains few mitochondria and pinocytic vesicles. Measurements of the thickness of the perineurium are related to the number of layers contributing to its shape, which ranges from 8 to 16 perineurial layers. Extracellular matrix, together with collagen fibers and a few fibroblasts, occupies the spaces between perineurial laminas [1–6].

The membrane allows the axons a certain degree of mobility within the nerve fascicles, and it becomes progressively thinner as the number of fascicles increases. Tension exerted on the perineurium is transmitted successively toward the endoneurium, affecting the intracellular pressure in the axon. The perineurium, together with endothelial cells of intrafascicular capillaries, contributes to the blood–nerve barrier (Figs. 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19, 4.20, 4.21, 4.22, 4.23, 4.24, 4.25, 4.26, 4.27, 4.28, 4.29, 4.30, 4.31, and 4.32) [7–10].

Fig. 4.1
figure 1

Perineurium. A few nerve fascicles are enclosed in perineurium from a human sciatic nerve. Arrows indicate the perineural layer. Scanning electron microscopy, magnification: ×70 (From Reina [3]; with permission)

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Fig. 4.2
figure 2

Perineurium. Two fascicles are surrounded by perineurium from a human sciatic nerve. Tridimensional view shows details of the perineural layers (arrows). Scanning electron microscopy, magnification: ×150 (From Reina et al. [1]; with permission)

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Fig. 4.3
figure 3

Perineurium. Two fascicles are surrounded by perineurium from a human sciatic nerve. Tridimensional view shows details of the perineural layers (arrows). Scanning electron microscopy, magnification: ×200 (From Reina [3]; with permission)

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Fig. 4.4
figure 4

Perineurium. Two fascicles are surrounded by perineurium from a human sciatic nerve. Tridimensional view shows details of the perineural layers (arrows). Scanning electron microscopy, magnification: ×300

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Fig. 4.5
figure 5

Perineurium. Fascicles are surrounded by perineurium from a human sciatic nerve. Tridimensional view shows details of the perineural layers (arrows). Scanning electron microscopy, magnification: ×70

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Fig. 4.6
figure 6

Perineurium. Fascicles are surrounded by perineurium from a human sciatic nerve. Arrows indicate a perineural layer. Scanning electron microscopy, magnification: ×70

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Fig. 4.7
figure 7

Perineurium. Fascicles are surrounded by perineurium from a human sciatic nerve. Arrows point toward a perineural layer. Scanning electron microscopy, magnification: ×75 (From Reina et al. [11]; with permission)

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Fig. 4.8
figure 8

Perineurium. Perineural layers from a human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×500 (From Reina et al. [1]; with permission)

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Fig. 4.9
figure 9

Perineurium. Perineural layers from a human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×350

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Fig. 4.10
figure 10

Perineurium. Perineural layers from a human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×650

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Fig. 4.11
figure 11

Perineurium. Perineural layers from a human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×1,600

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Fig. 4.12
figure 12

Perineurium. Fascicles are surrounded by perineural layers of human sciatic nerve. Shown is a tridimensional view of perineural layers (arrows) and interfascicular tissue. Scanning electron microscopy, magnification: ×50

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Fig. 4.13
figure 13

Perineurium. Fascicles are surrounded by perineural layers of human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows) and interfascicular tissue. Scanning electron microscopy, magnification: ×75

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Fig. 4.14
figure 14

Perineurium. Perineural layers of human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×300

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Fig. 4.15
figure 15

Perineurium. Perineural layers of human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×300

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Fig. 4.16
figure 16

Perineurium. Perineural layers of human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×600

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Fig. 4.17
figure 17

Perineurium. Perineural layers of human sciatic nerve. Shown is a tridimensional view of the perineural layers (arrows). Scanning electron microscopy, magnification: ×750

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Fig. 4.18
figure 18

Perineurium. Perineural layers of human sciatic nerve. Transmission electron microscopy, magnification: ×3,000 (a); ×7,000 (b) (Panel b from Reina et al. [9]; with permission)

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Fig. 4.19
figure 19

Perineurium. (a, b) Perineural layers of human sciatic nerve. Transmission electron microscopy, magnification: ×3,000 (a); ×1,100 (b) (Panel b from Reina et al. [9]; with permission)

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Fig. 4.20
figure 20

Perineurium. (a, b) Perineural layers of human sciatic nerve. Specialized membrane junctions are shown in detail. Transmission electron microscopy, magnification: ×20,000 (a); ×50,000 (b) (Panel a from Reina et al. [1]; with permission. Panel b from Reina et al. [9]; with permission)

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Fig. 4.21
figure 21

Perineurium. (a, b) Perineural layers of human sciatic nerve. Specialized membrane junctions and pinocytic vesicles are shown in detail. Transmission electron microscopy, magnification ×50,000 (a); ×30,000 (b) (Panel b from Reina et al. [1]; with permission)

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Fig. 4.22
figure 22

Perineurium. (a, b) Perineural layers of human sciatic nerve. Transmission electron microscopy, magnification: ×20,000 (a); ×7,000 (b)

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Fig. 4.23
figure 23

Perineurium. (a, b) Perineural layers of human sciatic nerve. Collagen fibers between perineural layers are shown in detail. Transmission electron microscopy, magnification: ×25,000 (a); ×30,000 (b)

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Fig. 4.24
figure 24

Perineurium. (a, b) Perineural layers of human sciatic nerve. The pinocytic vesicles are shown in detail. Transmission electron microscopy, magnification: ×80,000 (a); ×80,000 (b) (Panel b from Reina et al. [2]; with permission)

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Fig. 4.25
figure 25

Perineurium. Fibrous long spacing (FLS) collagen is seen among perineural layers of human sciatic nerve. Transmission electron microscopy, magnification: ×60,000 (a, b)

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Fig. 4.26
figure 26

Perineurium. FLS collagen is seen among perineural layers of human sciatic nerve. Transmission electron microscopy, magnification: ×150,000 (a); ×60,000 (b)

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Fig. 4.27
figure 27

Perineurium. FLS collagen is seen among perineural layers of human sciatic nerve. Transmission electron microscopy, magnification: ×100,000 (a); ×120,000 (b) (Panel a from Reina et al. [1]; with permission)

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Fig. 4.28
figure 28

Perineural cell. The rough endoplasmic reticulum is shown in detail. Transmission electron microscopy, magnification: ×100,000 (a); ×300,000 (b)

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Fig. 4.29
figure 29

Perineural cell. Pores on the membrane nucleus are shown in detail. Transmission electron microscopy, magnification: ×50,000 (a); ×120,000 (b)

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Fig. 4.30
figure 30

Perineurium. (a) Detail of mitochondria within a perineural cell. (b) Continuous capillary within perineural layers of human sciatic nerve. Transmission electron microscopy, magnification: ×150,000 (a); ×7,000 (b)

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Fig. 4.31
figure 31

Perineurium. (a) Detail of a continuous capillary between perineural cells. (b) Detail of a continuous capillary surrounded by the same perineural layer. Transmission electron microscopy, magnification: ×12,000 (a); ×7,000 (b)

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Fig. 4.32
figure 32

Perineurium. (a, b) Detail of a continuous capillary between perineural cells. Transmission electron microscopy, magnification: ×8,000 (a); ×10,000 (b)

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