The document discusses the physiology of balance. It describes that the inner ear, specifically the vestibular apparatus, provides the sense of balance and coordinates movements. The vestibular apparatus consists of the semicircular canals and otolith organs. The semicircular canals detect rotational head movements while the otolith organs detect linear movements and the position of the head relative to gravity. Sensations from the vestibular apparatus are transmitted through the vestibular pathway in the brain to control balance and eye movements.

1. Name: Mwale Kamukwamba ID #: 11468276 Programme: MBChB
Title: Physiology of balance
Special senses are defined as those senses with highly localized receptors that provide specific
receptors that provide specific information about the environment. Among the special senses are;
 sensation of vision
 sensation of hearing and balance
 sensation of taste
 sensation of taste
The ear is composed of three parts; external ear, middle and inner ears. Concerned with balance
is the inner ear. It is a membranous structure enclosed by a bony labyrinth in the petrous part of
the temporal bone. It consists of sense organs for hearing and balance. The sense organ for
hearing is the cochlea, while for balance is the vestibular apparatus, which h provides
information for the sense of balance and for coordinating head movements with eye and postural
movements. Equilibrium is the sense of body orientation and motion. Vestibular apparatus
consists of two sets of structures lying within a tunneled-out region of the temporal bone near the
cochlea – the semicircular canals and the otolith organs.
Semicircular canals detect rotational or angular acceleration or deceleration of the head, such as
when starting or stopping spinning, somersaulting or turning of the head. Acceleration or
deceleration movement cause fluid movement in the semicircular canals. Fluid not being
attached to the skull does not move with rotation because of its inertia it lags behind. As you

2. rotate the head fluid that is in the same plane as head movement is shifted to the opposite
direction. If head movement continues at the same rate in same direction, fluid catches up and
moves in unison with your head so that hairs return to their unbent position. When the head
slows down and stops the reverse occurs.
Otolith organs provide information about position of the head relative to gravity and detect
changes in the rate of linear motion. The otolith organs, the utricle and the saccule are saclike
structures housed within a big chamber situated between the semicircular canals and the cochlea.
Sensations of angular and linear movement will cause propagation of action potentials which are
transmitted through the vestibular pathway up to the cerebral cortex.
The vestibular pathway is as follows;
1. Sensation in the semicircular canals (joint receptors in the neck will also provide information
about balance)
2. Ganglion
3. Vestibular nerve
4. Vestibular nuclei
 superior (from here other fibres go to the reticular activating system)
 medial (other fibres go to eye muscles III, IV, VI via longitudinal fasciculus)
 lateral (to spinal cord to control antigravity muscles thus automatically controlling
equilibrium)
 lnferior (to spinal cord to control antigravity muscles thus automatically controlling
equilibrium)
5. Medial geniculate body
6. Cerebral cortex.
In conclusion, the vestibular apparatus is a non auditory part of the inner ear. It is stimulated by
movement or change in position of the head in space enabling balance to be maintained.
References
1. Nathan J. Siulapwa, Physiology lecture notes: Special senses, CBU-SoM, 2013.
2. Sherwood, L., Fundamentals of Human Physiology, 4th
Edition, Brooks/Cole Cengage
learning, California, 2012.
3. Mackenna, B.R., Callander, R., Illustrated Physiology, 6th
Edition, Churchill Livingstone,
London, 1997.
4. http://en.wikipedia.org