Righting reflex
The righting reflex, also known as the
The righting reflex has also been studied in cats and other non-human mammals.
Overview
Vestibular system
The vestibular system is composed of inner ear organs forming the "labyrinth": the
. The section below is an overview of the vestibular system, as it is crucial to the understanding of the righting reflex. Sensory information from the vestibular system allows the head to move back into position when disturbed as the rest of the body follows. The semicircular canals (brown, see figure) are arranged at angles to the horizontal plane of the head when it is in its normal vertical posture. Each canal has a widened base, called anThe semicircular canals have a superior, posterior, and horizontal component. Studies have shown that the horizontal canal is most correlated with agility, as shown with several mammals.[3] Curvature and size of these canals seems to affect agility, and may be due to the environments in which animals navigate, such as a mostly two-dimensional landscape as compared to three-dimensional spaces (i.e. in the air, the trees, or the water).[4]
The otoliths have two components: the
Signal transduction
Vestibular afferent signals are carried by type I or type II hair cells, which are distinguished by a larger amount of stereocilia per cell in type I cells than in type II cells.
Function
The righting reflex involves complex muscular movements in response to a stimulus. When startled, the brain can evoke anticipatory postural adjustments, or a series of muscle movements, which involves the function of the midbrain.[7] However, the mechanisms of such an origin are yet to be elucidated. Data support the generation of these movements from circuits in the spine connected to the supplementary motor area, the basal ganglia, and the reticular formation.
Reference frames
Visual input for proper righting reflex function is perceived in the form of reference frames, which create a representation of space for comparison to expected orientation. Three types of reference frames are used to perceive vertical orientation; they are consistently updated and quickly adapting to process changes in vestibular input.[8]
Allocentric reference frame
The allocentric reference frame describes a visual reference frame based on the arrangement of objects in an organism's environment. To test for the use of an allocentric reference frame, a "rod-and-frame" test, in which a subject's perception of virtual objects in an environment are altered, can be used to cause a body tilt as the subject believes to be correcting for the shift.[8]
Egocentric reference frame
The egocentric reference frame refers to a proprioceptive reference frame using the position of an organism's body in a space. This reference frame relies heavily on somatosensory information, or feedback from the body's sensory system. Muscle vibrations can be used to alter a subject's perception of the location of their bodies by creating an abnormal somatosensory signal.[8]
Geocentric reference frame
The geocentric reference frame involves visual inputs to help detect the verticality of an environment through gravitational pull. The sole of the foot contains receptors in the skin to detect the force of gravity, and plays a large role in standing or walking balance. The abdominal organs also contain receptors that provide geocentric information. "Roll-tilt" tests in which a subject's body is mechanically moved can be used to test for geocentric reference frame function.[8]
Pathways
The righting reflex can be described as a three-neuron arc system composed of primary
These automatic postural adjustments can be explained in terms of two reflexes similar to the righting reflex: the vestibulo-ocular reflex (VOR) and the vestibulocollic reflex (VCR).[10] The VOR involves movement of the eyes while the head turns to remain fixated on a stationary image, and the VCR involves control of neck muscles for correction of the head's orientation.[11] During the VOR, the semicircular canals send information to the brain and correct eye movements in the direction opposite head movement by sending excitatory signals to motor neurons on the side opposite to the head rotation.[11] Neurons in the otoliths control not only these signals for control of eye movements, but also signals for head movement correction through the neck muscles.[11] The righting reflex utilizes the VOR and VCR as it brings the body back into position. Visual information under the control of these reflexes creates greater stability for more accurate postural correction.[12]
Tests for righting reflex function
Vestibular function can be tested through a series of visual acuity tests. The static visual acuity test investigates a patient's ability to see an object from a distance by placing a subject at a certain distance from a letter fixed on a screen. The dynamic visual acuity test involves a patient's ability to control eye movements by following letters that appear on a screen. The difference between these two test results is the patient's fixation ability and vestibuloocular reflex (VOR) efficiency.[13]
Vestibular reflexes can also be examined using body tilt experiments. Patients with vestibular disorders may go through the
Proprioceptive ability tests are important in testing for righting reflex function. A therapist may ask a patient whether they know where a certain limb or joint is located without looking at it. These tests are often conducted on uneven surfaces, including sand and grass.[1]
Recently, vestibular reflexes have been investigated using leg rotation experiments. A leg and foot rotation test can be used to investigate changes in neuron activity within the
Plasticity
Because visual input is so critical in proper righting reflex function, impairment of vision can be detrimental.
Disorders
Many inner ear disorders can cause dizziness, which leads to dysfunctional righting reflex action. Common inner ear disorders can cause vertigo in patients, which can be acute or chronic symptoms.[1] Labyrinthitis, or inflammation of the inner ear, can cause imbalances that must be overcome through therapeutic exercises. Labyrinthectomy, or removal of inner ear organs, is an operation conducted for patients with severe inner ear disorders whose vertigo is debilitating. Imbalances result from the procedure, but therapy can help overcome the symptoms.[16]
Benign paroxysmal positional vertigo
Ménière's disease
Other causes of righting reflex disorders
Vestibular and balance disorders can have a number of contributing factors. Dietary factors such as a high-salt diet, high
Righting reflex in animals
The righting reflex is not exclusive to humans. A well-known righting reflex in cats allows them to land on their feet after a fall. As a cat falls, it turns its head, rotates its spine, aligns its hindquarters, and arches its back to minimize injury.[18] The cat reaches free fall to accomplish this, which is much lower than that of humans, and they are able to hit the ground in a relaxed body form to prevent serious injury.
Bats, however, have a unique vestibular system anatomy. Their balance system, at an orientation 180 degrees opposite to that of humans, allows them to perform powerful feats of flight while hunting in the dark. This ability couples vestibular function with sensory
References
- ^ OCLC 52858223.
- ^ OCLC 144771764.
- PMID 20002227.
- PMID 21930662.
- PMID 15201311.
- ^ PMID 22245372.
- S2CID 23629664.
- ^ S2CID 2704908.
- PMID 22198575.
- PMID 7627376.
- ^ S2CID 1545618.
- S2CID 338434.
- ^ Badaracco C, Labini FS, Meli A, Tufarelli D: Oscillopsia in labyrinthine defective patients: comparison of objective and subjective measures. Am J Otolaryngol 2010, 31(6):399-403.
- ^ Grasso C, Barresi M, Scattina E, Orsini P, Vignali E, Bruschini L, Manzoni D: Tuning of human vestibulospinal reflexes by leg rotation. Hum Mov Sci 2011, 30(2):296-313.
- ^ PMID 17392406.
- ^ Lao Z, Sha Y, Chen B, Dai C-F, Huang W-H, Cheng Y-S: Labyrinthine sequestrum: four case studies. Otolaryngology–Head and Neck Surgery 2012, 147(3):535-537.
- ^ Nguyen, H: "How does a cat always land on its feet?" Georgia Institute of Technology, Department of Biomedical Engineering. "My Third Page". Archived from the original on 2001-04-10. Retrieved 2014-08-23.
- ^ "Cats: A Cat's Nine Lives." Video. National Geographic 2012
- ^ Forman S: "Bats with frikkin' lasers." The Brown Daily Herald. 10 March 2010. http://www.browndailyherald.com/bats-with-frikkin-lasers-1.2186630#.UKqC2rvK3B8
- ^ Fejtek M, Delorme M, Wassersug R: Behavioral reactions of the bat Carollia perspicillata to abrupt changes in gravity. Uchu Seibutsu Kagaku. 1995, 9(2):77-81.