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*5 PAIRS*
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The sacral nerves are the five pairs of spinal nerves which exit the sacrum at the lower end of the vertebral column. The roots of these nerves begin inside the vertebral column at the level of the L1 vertebra, where the cauda equina begins, and then descend into the sacrum.[2][3]
There are five paired sacral nerves, half of them arising through the sacrum on the left side and the other half on the right side. Each nerve emerges in two divisions: one division through the anterior sacral foramina and the other division through the posterior sacral foramina.[4]
The nerves divide into branches and the branches from different nerves join with one another, some of them also joining with lumbar or coccygeal nerve branches. These anastomoses of nerves form the sacral plexus and the lumbosacral plexus. The branches of these plexus give rise to nerves that supply much of the hip, thigh, leg and foot.[5][6]
The sacral nerves have both afferent and efferent fibers, thus they are responsible for part of the sensory perception and the movements of the lower extremities of the human body. From the S2, S3 and S4 arise the pudendal nerve and parasympathetic fibers whose electrical potential supply the descending colon and rectum, urinary bladder and genital organs. These pathways have both afferent and efferent fibers and, this way, they are responsible for conduction of sensory information from these pelvic organs to the central nervous system (CNS) and motor impulses from the CNS to the pelvis that control the movements of these pelvic organs.[7]
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/ˈsækrəm/ or /ˈseɪkrəm/
*plural* –> sacra / sacrums)
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*the sacrum in ‘human anatomy’ is a large, triangular bone at the base of the spine, that forms by the fusing of sacral vertebrae ‘S1–S5’ between 18 – 30 years of age*
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(the sacrum is situated at the upper, back part of the pelvic cavity, between the two wings of the pelvis. It forms joints with four other bones)
(the two projections at the sides of the sacrum are called the ‘alae’ (wings), and articulate with the ilium at the L-shaped sacroiliac joints)
(the upper part of the sacrum connects with the last lumbar vertebra, and its lower part with the coccyx (tailbone) via the sacral and ‘coccygeal cornua’)
(the sacrum has three different surfaces which are shaped to accommodate surrounding pelvic structures)
(overall it is concave (curved upon itself))
(the base of the sacrum, the broadest and uppermost part, is tilted forward as the sacral promontory internally)
(the central part is curved outward toward the posterior, allowing greater room for the ‘pelvic cavity’)
(in all other ‘quadrupedal vertebrates’, the pelvic vertebrae undergo a similar developmental process to form a sacrum in the adult, even while the bony tail (caudal) vertebrae remain unfused)
(the number of sacral vertebrae varies slightly)
(a horse will fuse S1–S5, but a dog will fuse S1–S3)
(for example, the rat fuses four pelvic vertebrae between their lumbar and the caudal vertebrae of their tail)
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(the stegosaurus dinosaur had a greatly enlarged ‘neural canal’ in the ‘sacrum’, characterized as a “posterior brain case”)
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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