Ever wondered why do you feel dizzy during a roller coaster ride but not while jogging? The answer may lie in your ears!
Scientists have found that an organ located in the inner ear helps our body maintain balance while jogging.
The active movements of a jogger’s arms and legs are accompanied by involuntary changes in the position of the head relative to the rest of the body. However, a jogger does not experience dizziness like those induced in the passive riders of a roller coaster.
The answer for the difference lies in the vestibular organ (VO) located in the inner ear, which controls balance and posture, the researchers said.
The VO senses ongoing self-motion and ensures that, while running, a jogger unconsciously compensates for the accompanying changes in the orientation of the head.
The capacity to adapt and respond appropriately to both slight and substantial displacements of the head in turn implies that the sensory hair cells in the inner ear can react to widely varying stimulus intensities.
In collaboration with Dr John Simmers at the Centre national de la recherche scientifiqu (CNRS) at the University of Bordeaux, neurobiologists Dr Boris Chagnaud, Roberto Banchi and Professor Hans Straka at Ludwig-Maximilians-Universitat Munchen’s Department of Biology II, have now shown, for the first time, how this feat is achieved.
The findings show that cells in the spinal cord which generate the rhythmic patterns of neural and muscle activity required for locomotion also adaptively alter the sensitivity of the hair cells in the VO, enabling them to respond to the broad range of incoming signal amplitudes.
“We are not really aware of what movement actually involves because our balance organs react immediately to alterations in posture and head position,” said Chagnaud.
“The hair cells, which detect the resulting changes in fluid flow in the semicircular canals in the inner ear, enable us to keep our balance without any conscious effort,” said Chagnaud.
Using tadpoles as an experimental model system, the researchers investigated how the hair cells manage to sense both low- and high-amplitude movements and produce the signals that control the appropriate compensatory response.
The tadpole’s balance organs operate on the same principle as the bilateral VOs in humans, and the nerve circuits responsible for communication between the hair cells and the motor neurons in the spinal cord are organised in essentially identical ways, the researchers said.
When a tadpole initiates a voluntary movement, nerve cells in the spinal cord send copies of the motor commands to efferent neurons in the brainstem that project to the hair cells in the inner ear.
By dampening the intrinsic sensitivity of the hair cells, the input from the spinal cord effectively adapts the VO’s dynamic range. This process enables the balance organ to maintain responsiveness to high-amplitude “afferent” stimuli from the periphery, and thus to modulate the head movements.