The of firing in the vestibular neurons. When head

The vestibular system is responsible for sensing motion,
primarily acceleration, deceleration, and gravitational pull, which provides us
with a sense of security when moving (Ayres, 2005). The vestibular system is the foundation for the development
of balance reactions and motor development influencing muscle tone, posture control, bilateral motor coordination,
balance, orientation in space, and eye movements (Roley, Maillous, & Erwin, 2015). A healthy vestibular system is vital to
the integration of the other sensory systems, helping
one feel confident moving and interacting with surroundings (Ayes, 2015; Braley, 2014). 


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As seen in Figure 1,
the vestibular apparatus located on the inner ear, is
comprised of two otolith organs (the saccule and utricle) that sense linear
acceleration (i.e., gravity and translational movements) and three semicircular
canals that sense angular acceleration in three perpendicular planes (Lane,
2002). When the head

 moves (accelerates), inertia
causes the endolymph (fluid in the semicircular canals) to lag behind the head
movement causing pressure on the cupula triggering transduction, which is the displacement
of the cupula bending the hairs in the opposite direction of the head movement
(Lane, 2002). This
information is converted into neural signals conveyed by the vestibular nerve
to the vestibular nuclei in the brain stem contributing to: sensory information
about head movement and head position
relative to gravity, gaze stabilization,
postural adjustments, autonomic function, and consciousness (Lundy-Ekman,
2013). As shown in Figure 2, the flow
of endolymph in the canal moves the cupula and bends the hair cells, which
changes the pattern of firing in the vestibular neurons. When head
movement stops or decelerates, the inertia acts on the endolymph by placing
pressure on the cupula, bending the hairs in the same direction the head had
been moving, changing the transmission and activity of the vestibular nerve
(Lane, 2002).

Impact on Function and Participation

When the vestibular
system is fully functioning, one is secure and organized enough to attend and respond to all of the other senses encountered on a daily basis
(Braley, 2014). A child with a well-developed vestibular sense feels
confident and safe during movement activities being able to start and stop
movement activities calmly and with control (Bundy &
Murray, 2002). This child will feel comfortable with climbing, swinging,
somersaulting, and jumping knowing that their body will adapt and be able to stabilize and prevent himself/herself
from falling or getting hurt (Braley, 2014). As shown in Figure 3, the vestibular system assesses
the awareness of body position and
vision to trigger automatic responses by our head, trunk, arms, legs, and feet
to maintain balance as the girls jump through space (Ayres, 2005). If a child’s vestibular system is not
functioning correctly, they may be overly-sensitive or under-responsive to
movement (Ayres, 2005). As a
sensory system, the vestibular response not only provides an accurate
representation of one’s motion but is also vital in constructing an ‘internal
map’ of one’s center of mass in space with respect to gravity (Zalewski, 2015).
Aversive responses to movement, like gravitational insecurity causes a fear
of being out of the upright position or having one’s feet off the ground like
climbing stairs or walking on uneven
surfaces (Brundy & Murray, 2002; Fisher, 1991). These children may either
need to move persistently to feel satisfied or may be frightful of movement
because it makes them feel apprehensive and unbalanced (Ayres, 2005; Braley, 2014). Children with poor vestibular
responses may have difficulty coordinating
and planning motor tasks such as: jumping jacks, skipping, catching a ball with
two hands, crossing midline, coordinating
movements of the mouth, which may result in difficulty with speech production (Ayres, 2002; Braley,
2014; Roley, Maillous, & Erwin, 2015). Some signs include: moving in an
uncoordinated and clumsy manner, bumping into things, falling, or trouble with
walking or sitting in an upright position (Braley,
2014).  These symptoms often lead to a
child’s decreased participation in
areas of play, education, activities of
daily living, social participation,
coordination, balance, and play exploration
(Ayres, 2005).