The medulla oblongata and spinal cord (central canal) are lit together; the roots of the accessory nerve begin in them, one in each; the nerve is not drawn on its own. The side (sagittal) slice button cuts through them. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Its fibres come from nerve cells in the upper spinal cord, from where the cord begins at the medulla oblongata down to about the sixth cervical segment (C6); they rise through the foramen magnum into the skull and leave again through the jugular foramen with the glossopharyngeal and vagus nerves. Traditional descriptions add a small cranial root from the medulla, which soon joins the vagus. [1]
Not a separate shape in this atlas; lit: the part it leaves the brain from. Lit: the whole medulla oblongata, where the traditional small cranial root of the accessory nerve comes from, and the spinal cord (central canal), the model’s only shape for the spinal cord, where the spinal root rises: it is just the top of the cord’s central canal, about 6 mm below the medulla, not the cord down to C6. The nerve itself has no shape in the BodyParts3D model, so nothing is drawn for it at a guessed point. [2][1]
Where it leaves: the fibres of the spinal accessory nerve originate solely in nerve cells of the upper spinal cord, from where it begins at its junction with the medulla oblongata to about the level of C6, in the spinal accessory nucleus of the anterior horn. The traditional cranial root comes from the nucleus ambiguus of the medulla; a 2007 study of twelve people found that in most of them this cranial part makes no distinct connection to the spinal part. Lit for the spinal root: the spinal cord (central canal), the top of the cord this model has. [1]
The rootlets from the upper spinal cord join into roots and then one nerve, which rises beside the cord through the foramen magnum, the large opening at the base of the skull. [1]
Inside the skull it runs along the inner wall towards the jugular foramen and leaves through it with the glossopharyngeal (IX) and vagus (X) nerves. Below the skull the cranial part leaves it to join the vagus, and the spinal part runs on alone, backwards and downwards. [1][3]
In the neck it crosses the internal jugular vein at about the level of the back belly of the digastric muscle, in front of the vein in about 80% of people and behind it in about 20%; it then passes through the sternocleidomastoid about 1 cm above Erb’s point and runs on to the front border of the trapezius. [1]
What it does
It works two muscles on each side. The sternocleidomastoid turns the head to the opposite side and tilts it; the trapezius, attached to the shoulder blade, shrugs the shoulder (its upper part lifts the scapula). [1][4]
The trapezius is worked from the opposite side of the brain, like most muscles; the fibres for the sternocleidomastoid are thought to cross twice, so it is worked from the same side of the brain. [1]
The cranial part, which travels on with the vagus, supplies muscles of the soft palate, the throat and the voice box. [1]
Connections
The spinal accessory nucleus in the upper cervical cord appears continuous with the nucleus ambiguus of the medulla, the source of the cranial part. Researchers disagree on how to classify the fibres it carries: special visceral efferent, general somatic efferent, or both. [1]
Other names
Cranial nerve XI (CN XI), eleventh cranial nerve; spinal accessory nerve; nervus accessorius (Latin). It is counted as a cranial nerve because part of it was once believed to come from the brain; since the cranial part soon joins the vagus, “accessory nerve” today usually means the spinal accessory nerve alone. [1]
Size
The model has no shape for the accessory nerve, so it is not measured here. The medulla oblongata, lit as a part one of its roots comes from, measures about 33 mm front to back, 41 mm top to bottom and 27 mm side to side on this model (the box it fits in, not its volume). [2]
The spinal cord (central canal), lit as a part one of its roots comes from, measures about 13 mm front to back, 36 mm top to bottom and 2 mm side to side on this model (the box it fits in, not its volume). [2]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.