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The sacrum (pl.: sacra or sacrums [1]), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1–S5) between ages 18 and 30. [ 2 ] The sacrum situates at the upper, back part of the pelvic cavity , between the two wings of the pelvis .
It runs from the sacrum (the lower transverse sacral tubercles, the inferior margins sacrum and the upper coccyx [1]) to the tuberosity of the ischium. It is a remnant of part of biceps femoris muscle. The sacrotuberous ligament is attached by its broad base to the posterior superior iliac spine, the posterior sacroiliac ligaments (with which ...
The joint locks (or rather becomes close packed) on one side as weight is transferred from one leg to the other, and through the pelvis the body weight is transmitted from the sacrum to the hip bone. The motions of the sacroiliac joint Anterior innominate tilt of both hip bones on the sacrum (where the left and right move as a unit) Posterior ...
S1 supplies many muscles, either directly or through nerves originating from S1. They are not innervated with S1 as single origin, but partly by S1 and partly by other spinal nerves. The muscles are: gluteus maximus muscle; gluteus medius muscle; gluteus minimus muscle; tensor fasciae latae; piriformis; obturator internus muscle; inferior gemellus
S2 supplies many muscles, either directly or through nerves originating from S2. They are not innervated with S2 as single origin, but partly by S2 and partly by other spinal nerves. They are most commonly known to govern the toes. The muscles are: sphincter urethrae membranaceae; gluteus maximus muscle; piriformis; obturator internus muscle
The posterior divisions of the sacral nerves are small and diminish in size as they move downward; they emerge, except the last, through the posterior sacral foramina. The upper three are covered at their points of exit by the multifidus and divide into medial and lateral branches.
The superior gluteal nerve is a mixed (motor and sensory) nerve of the sacral plexus that originates in the pelvis. It provides motor innervation to the gluteus medius , gluteus minimus , tensor fasciae latae , and piriformis muscles; it also has a cutaneous branch.
Only skeletal and smooth muscles are part of the musculoskeletal system and only the muscles can move the body. Cardiac muscles are found in the heart and are used only to circulate blood; like the smooth muscles, these muscles are not under conscious control. Skeletal muscles are attached to bones and arranged in opposing groups around joints. [8]