Vestibular Anatomy and Neurophysiology
Original Editor - Megyn Robertson
Top Contributors - Samuel Adedigba, Mandy Roscher, Megyn Robertson, Kim Jackson, Shaimaa Eldib, Wanda van Niekerk, Stacy Schiurring, Rachael Lowe, Lucinda hampton, Jess Bell, Olajumoke Ogunleye, Nupur Smit Shah and Tony Lowe
Introduction[edit | edit source]
The vestibular system is a sophisticated human postural control system (Hain, 2011). It is sensitive to two types of information: the position of the head in space and sudden changes in the direction of movement of the head (Shumway-Cook and Woollacott, 2007). The vestibular system is divided into a central and peripheral system. The vestibular system has both a sensory and motor component to help us sense and perceive motion and provides information about the movement of the head and its position with respect to gravity and other inertial forces (like those generated when driving in a car). This information is used to stabilize the eyes to our maintain gaze on targets of interest, with or without head movement. The vestibular system also employs complicated strategies to maintain blood pressure when one quickly goes from supine to an erect posture. It helps us to maintain good head and body orientation in relation to our environment, most often in an upright posture allowing us to maximise sensory integration of our senses (see, hear, smell).
The Peripheral Vestibular System (PVS)[edit | edit source]
The PVS is situated in the inner ear, behind the tympanic membrane. Inputs from the PVS are integrated by the central vestibular processor called the ‘vestibular nuclear complex’ which generates motor commands to drive the eyes and the body. The system is normally very accurate. To maintain accuracy, the vestibular system is monitored and calibrated by the cerebellum (Hain & Helminski, 2014).
Semi-Circular Canals[edit | edit source]
The Semi-circular canals (SCC’s) are specialised mechanoreceptors to help us access information regarding angular velocity. The sensory input received from the SCC’s enables the Vestibular Ocular Reflex (VOR) to generate an eye movement that matches the velocity of the head movement.
The 3 SCC’s are positioned at right angles to each other to give us feedback in 3 different planes of movement. Remember there are 2 ears, so effectively six SCC’s.
The six individual semi-circular canals become three coplanar pairs:
- right and left lateral
- left anterior and right posterior
- left posterior and right anterior
The planes of the canals are close to the planes of the extraocular muscles, so sensory neurons and motor output neurons can give quick information to individual ocular muscles. Inside the canals there are hair cells in endolymph, and with head movement, the swishing of endolymph displaces these hair cells of the coplanar pair in opposite directions with respect to their ampullae, and neural firing increases in one vestibular nerve and decreases on the opposite side. Endolymph displacement is proportional to angular head velocity, so the semi-circular canals transmit a velocity signal to the brain.
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