In this summary you'll learn everything you need to know about the anatomy of the Vestibular system. This is one part of the anatomy that you need to know for the exam of the Cluster Locomotor System
Anatomy – Vestibular system
The vestibular system is a somatosensory portion of the nervous system that provides us with
the awareness of the spatial position of our head and body (→ proprioception) and self-
motion (→ kinesthesia). It’s composed of central and peripheral portions.
- The peripheral portion consists of the vestibular labyrinth, vestibular ganglion, and
vestibulocochlear nerve (VIII)
- The vestibular labyrinth is comprised of proprioceptive components located in the
inner ear
o The semicircular canals → contain cell that detect angular acceleration
o Utricle and saccule → contain cells that detect linear acceleration of the head
and position of the head in space (spatial orientation)
- The stimuli from these receptors are communicated to the vestibular ganglion, from
where they travel through the vestibular portion of the vestibulocochlear nerve (VIII)
into the central portion of the vestibular system → the vestibular nuclei in the
brainstem
- The vestibular nuclei send projections into the cerebellum, spinal cord, thalamus and
nuclei of the oculomotor (III), trochlear (IV) and abducens (VI) nerves
- Via these connections, the vestibular system contributes to the adjustments of the
head and neck movements, as well as the posture and balance of the whole body, the
vestibulo-ocular reflex and eye movements
- The left vestibular organ is more sensitive for movements to the left, and right
vestibular organ is more sensitive for movements to the right!
@MyMedicalPulse
, Labyrinth and semicircular canals
The vestibular labyrinth is a bony cavity located within the petrous portion of the temporal
bone → it consists of the 3 semicircular canals, 2 otolithic organs (utricle and saccule) and the
cochlea (= part of the hearing apparatus)
- Semicircular canals: 3 membranous channels located within the bony semicircular
ducts of the labyrinth filled with endolymph
o They are located in 3 planes, each plane making an angle of approximately 90
degrees with the other
▪ Anterior (superior) → sagittal plane
▪ Lateral (horizontal) → transverse plane
▪ Posterior (inferior) → frontal plane
o The terminal part of each canal ends with a dilation called the ampulla, which
opens into the vestibule
▪ The ampulla of each semicircular canal contains a cluster of
mechanoreceptor cells called the crista ampullaris
▪ Each crista is composed of the special sensory receptor cells, called the
hair cells
o The movement of the endolymph stimulates the hair cells → this way, each
semicircular canal detects when the head moves during the rotational
acceleration along its corresponding plane → thus it can detect head
movements such as nodding up/down, shaking side to side, tilting left/right
Figure 1: Adapted from a lecture of Raymond van de Berg
- Otolithic organs: 2 membranous cavities that lie in the bony vestibule of the inner ear
o Utricle: this lies in the posterior part of the vestibule
▪ On one end, it communicates with the semicircular canals, whilst on
the opposite end it forms a utriculosaccular duct with the saccule
▪ This duct passes through the temporal bone and reaches the posterior
surface of the petrous part of the temporal bone
@MyMedicalPulse
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