"Senses are 'food' for our brain. Each sense is a form of information. The brain constantly seeks different sensory 'food' for further development.“

(Ayres, 2002)

Types of Sensory Systems

Each individual perceives information from their environment uniquely through their sensory systems. When discussing sensory systems, most people immediately think of the five most well-known senses. However, in the field of sensory integration, three additional sensory systems are mentioned, bringing the total to eight sensory systems, which include (SPS, 2004):

a) Visual

b) Auditory

c) Tactile

d) Olfactory

e) Gustatory

f) Proprioception

g) Vestibular

h) Interoceptors

Visual System: How We See the World Around Us

The visual system enables the perception of light, color, shapes, and motion from the environment. Light enters the eye through the cornea and lens, focusing the rays onto the retina. Here, photoreceptors—rods that enable vision in low light and cones that allow the perception of color and detail—play a crucial role. Electrical signals from the photoreceptors are transmitted via ganglion cells to the optic nerve and the visual cortex, where the brain processes and integrates the information, enabling the recognition of objects and spatial surroundings (Kolb et al., 2007). Binocular vision allows depth perception through the overlapping visual fields of both eyes. The system also includes neural pathways for reflexive reactions, such as the pupillary reflex to light (Bear et al., 2015).

Auditory System: Sound Perception and Communication

The auditory system enables sound perception by detecting sound waves, which enter the ear through the external canal and cause the eardrum to vibrate. These vibrations are transmitted to the auditory ossicles of the middle ear and then to the oval window, which conveys them to the fluid in the cochlea of the inner ear. Movement of the basilar membrane within the cochlea stimulates hair cells, which convert the vibrations into electrical impulses. These impulses travel via the auditory nerve to the primary auditory cortex, where the brain recognizes the sound's frequency, intensity, and location. The auditory system also facilitates sound localization, which is essential for orientation and communication (Kandel et al., 2013).

Tactile System: How We Gather Information Through Touch

The tactile system enables the perception of touch, pressure, vibration, temperature, and pain, providing vital information about our environment. Tactile receptors located in the skin include mechanoreceptors (sensation of touch and pressure), thermoreceptors (sensation of temperature), and nociceptors (sensation of pain). Signals from these receptors travel through peripheral nerves to the spinal cord, where they are transmitted to the brain via somatosensory pathways to the parietal lobe. The information is processed there, allowing for conscious touch perception and spatial discrimination.The tactile system is crucial in motor skills, object recognition, and environmental interaction (Purves et al., 2012).

Olfactory System: The Importance of Smell in Everyday Life

The olfactory system, located on the underside of the brain's frontal region, detects and perceives odors through molecules that enter the nasal cavity and bind to receptors in the olfactory epithelium. Information about smells is transmitted from the nose to the brain via this center, which is crucial for accurate odor perception.This system serves four main functions: recognizing different odors, enhancing odor detection, filtering background odors, and facilitating higher brain regions associated with arousal and attention to more easily detect or distinguish odors (Doty, 2015).

Gustatory System: Taste as an Evolutionary Significant Factor

The gustatory system is responsible for taste perception and distinguishing safe from potentially harmful food through the specialized tongue, soft palate, pharynx, and epiglottis taste buds. Taste cells are sensitive to basic tastes—sweet, sour, salty, and bitter—while combinations of these create complex perceptions. The sweet taste, associated with the presence of carbohydrates, is most pleasing to humans, while a bitter taste often signals harmful substances. In smaller amounts, a sour taste can be acceptable, but evolutionary mechanisms protect us from consuming overly ripe or spoiled food. This system plays a crucial role in recognizing flavors, regulating dietary habits, and food selection, often overlapping with the olfactory system (Bear et al., 2015).

Proprioception: The Sense of the Body in Space

The proprioceptive system enables the perception of the body's position and movement in space without relying on vision. It provides information about the state of muscles, joints, and tendons through receptors such as muscle spindles and Golgi tendon organs. These receptors detect changes in muscle length, tension, and movement, sending signals via peripheral nerves to the spinal cord and then to the cerebellum and somatosensory cortex. The system integrates information from the inner ear and muscle receptors to ensure precise movement, balance, and body orientation control. It is essential for daily activities and complex motor tasks, such as walking, eating with a spoon, or pouring liquids. Proprioception allows for posture correction and planning of complex movements to perform tasks successfully (Proske & Gandevia, 2012).

Vestibular System: Our Body Balance in Motion

The vestibular system in the inner ear is responsible for balance, body orientation in space, and gaze stabilization during movement. It consists of semicircular canals, which detect rotational movements, and otolithic organs, which register linear acceleration and changes in gravity. Information is transmitted via the vestibular nerve to the brain, where it is integrated with visual and proprioceptive data to coordinate movement and maintain balance. This system enables precise body adjustments to changes in position and stability during motion (Angelaki & Cullen, 2008).

Interoceptors: What the Body Tells Us from Within

Interoceptors, often an overlooked sensory system, enable the perception of the body's internal state by providing information about the functions of internal organs and homeostasis. Located in internal organs, blood vessels, and tissues, they detect bodily responses such as hunger, heartbeat, breathing, and the need to use the restroom. Signals from interoceptors are transmitted via the autonomic nervous system to the brain, particularly to the brainstem and hypothalamus, where they are integrated to regulate vital functions. The system works with the vestibular and proprioceptive systems, enabling the perception and regulation of the body's physiological states. It ensures proper awareness of internal needs and supports automatic responses to maintain homeostasis (Cameron, 2002).

SENcastle – A Sensory World in One Product

Sensory systems are essential for understanding the world and interacting with our environment. SENcastle, a compact sensory room, integrates input for five sensory systems—visual, auditory, tactile, vestibular, and proprioceptive—creating a unique multisensory experience. Through carefully designed elements, SENcastle encourages exploration, learning, and play, allowing users to develop and stimulate sensory integration in a safe and enjoyable environment. It bridges the sensory integration theory and practical application, helping children better understand their bodies and the world around them. SENcastle is a testament to the possibility of combining functionality and creativity to support each individual's neurological diversity and promote the harmonious development of individual sensory systems. 

References:

1.Angelaki, D. E., & Cullen, K. E. (2008): Vestibular system: the many facets of a multimodal sense. Annual Review of Neuroscience, 31, 125–150.

2.Ayres, J. A. (2002). Dijete i senzorna integracija. Naklada Slap, Zagreb.

3.Bear, M. F., Connors, B. W., & Paradiso, M. A. (2015): Neuroscience: Exploring the Brain (4th ed.). Wolters Kluwer.

4.Cameron, O. G. (2002): Visceral sensory neuroscience: Interoception. Handbook of Clinical Neurology, 104, 195–213.

5.Doty, R. L. (2015): Handbook of Olfaction and Gustation (3rd ed.). Wiley-Blackwell.

6.Kandel, E. R., Schwartz, J. H., Jessell, T. M., Siegelbaum, S. A., & Hudspeth, A. J. (2013): Principles of Neural Science (5th ed.). McGraw-Hill.

7.Kranowitz, C. S. (1998): The out of sync child. New York: The Berkley Publishing Group.

8.Kolb, H., Fernandez, E., & Nelson, R. (2007): Webvision: The Organization of the Retina and Visual System. University of Utah Health Sciences Center.

9.Proske, U., & Gandevia, S. C. (2012): The proprioceptive senses: their roles in signaling body shape, body position and movement, and muscle force. Physiological Reviews, 92(4), 1651–1697.

10.Purves, D., Augustine, G. J., Fitzpatrick, D., Hall, W. C., LaMantia, A.-S., & White, L. E. (2012): Neuroscience (5th ed.). Sinauer Associates.

11.SPS (2004): Understanding Sensory Integration. SPS.