Cara: I am glad that you took time out of your day to come and learn about building healthy brains. It is really important for us, as therapists, to understand posture. This is an intermediate course as I am hoping that everybody has a basic understanding of a child's sensory system.
Our distal coordination is contingent on our proximal stability. That is very critical for all function. We have to have this coordination of our entire bodies in order to access higher brain function.
Importance of Movement
There is a push in our country to have children learning at earlier and earlier ages and many kids are addicted to technology. They are using technology constantly even as little babies. We also have companies that want to help facilitate babies in these positions as shown in Figure 1 on the left.
Figure 1. Sedentary activities.
My kids had vibrating bouncy seats when they were little. These seats position the babies in a seated posture before they are ready. They do not have the strength and skills to sit up against gravity, but yet we are forcing them to do so. We also have kids that are sedentary due to using devices (picture on the right). There are wonderful apps that can be great, but they are so visually complex for our kids and we are giving them to our kids earlier. This becomes problematic as kids access higher level education. They need to fidget and with technology, we are asking them to sit still and pay attention. When our systems are not integrated, difficulties are going to occur. According to an article from the National Association for Sports and Physical Education, young children should never be sedentary for more than 60 minutes at a time. I think 60 minutes is actually too long. We need to implement activities a lot sooner than that.
I call the sitting devices containers. We are putting these babies into these containers for convenience or to free up our time to do other activities like cooking dinner. As you can see, this baby is stuck in a flexion pattern, and she is using sucking on a pacifier to organizer herself. The child on the right is in a W-sitting position to have the stability to use his electronic device. We need to understand our body so we can pull from this knowledge. Our body is designed to integrate our vestibular, proprioceptive, tactile, and visual systems to coordinate our body so that we can stabilize our body and move our eyes independently.
Vestibular System
This is a photo of the ear in Figure 2.
Figure 2. Ear anatomy.
There is the outer ear that we can see and then inside are the different organs. We are going to zoom in a little bit on this next slide and talk a little bit more in Figure 3.
Figure 3. Total of 5 vestibular receptors.
The first three are the semicircular canals that are oriented in three different directions: vertical, horizontal, and diagonal. There are also two otolith receptors, the utricle, and saccule, for a total of five vestibular receptors in the inner ear. They also transduce movement, and in particular linear accelerations.
Now we are going to talk about why the vestibular system is more than the inner ear. Integrated Learning Strategies are amazing and they have some cool graphics like Figure 4. The road starts at the top of the head and the visual system.
Figure 4. Overview of the vestibular system.
It tells the eyes what they are seeing in correlation with objects and words, what we hear, and what we process, store, and recall? It also helps us with motor planning. Our tactile system is receptors that tell us textures and sensory information.
Video #1
[Video Narrator] The function of the vestibular system can be simplified by remembering some basic terminology of classical mechanics. All bodies moving in three dimensions have six degrees of freedom. Three of these are translational and three are rotational. The translational components may be given in terms of movements along the X Y, and Z axes of the head. Rotations about the X, Y, and Z axes are commonly referred to as roll, pitch, and yaw. Buried deep in the temporal bone, the main peripheral component of the vestibular system is an elaborate set of interconnected chambers, the labyrinth, that has much in common, and in fact continuous with, the cochlea. The labyrinth consists of the two otolith organs, the utricle and saccule, and three semicircular canals. The vestibular hair cells, which like cochlear hair cells, transduce minute displacements into behaviorally relevant receptor potentials, are located in the utricle and saccule, and in three jug-like swellings called ampullae located at the base of the semicircular canals, next to the utricle. In the utricle and saccule, the sensory epithelium, or macula, consists of hair cells and associated supporting cells. Overlaying the hair cells and their stereocilia is a gelatinous layer. Above this layers is a fibrous structure, the otolithic membrane, in which are embedded crystals of calcium carbonate called otoconia. The crystals give the otolith organs their name. Otolith is Greek for "ear stones." The otoconia make the otolithic membrane considerably heavier than the structures and fluid surrounding it, thus when the head tilts, gravity causes the membrane to shift, relative to the sensory epithelium. The resulting shearing motion between the otolithic membrane and the macula displaces the hair bundles, which are embedded in the lower gelatinous surface of the membrane. This displacement of the hair bundles generates a receptor potential in the hair cells that is dependent upon the direction of tilt. Movement of the stereocilia toward the kinocilium causes potassium channels to open, depolarizing the hair cell. The depolarization results in neurotransmitter release and excitation of the vestibular nerve fibers. Movement of the stereocilia in the direction away from the kinocilium closes the channels, hyperpolarizing the hair cell, and thus reducing vestibular nerve activity. A shearing motion between the macula and the otolithic membrane also occurs when the head undergoes linear accelerations. Hair bundle displacement occurs transiently in response to linear accelerations and tonically in response to tilting of the head. The orientation of the stereocilia bundles, relative to the kinocilia, is such that given the utricle and saccule on each side of the body there is a continuous representation of all directions of body movement. Ultimately, variations in hair cell polarity within the otolith organs, produce patterns of vestibular nerve fiber activity that, at a population level, can unambiguously encode head position and the forces that influence it. Whereas the otolith organs are primarily concerned with head translations and orientation, with respect to gravity, the semicircular canals sense head rotations, arising either from self-induced movements or from angular accelerations of the head imparted by external forces.
