Sensory Processing and the Eight Senses

What is sensory processing?

Sensory processing is the act of registering and interpreting sensory input. The body’s nerves, which are part of the nervous system, receive information from the environment and send signals to the brain. Different parts of the brain process and interpret the sensory information picked up by the nerves. During infancy and childhood, the neural pathways that are involved in processing sensory information are not fully developed. Therefore, it is very important for children to be exposed to a wide range of sensory experiences to facilitate efficient and effective sensory neural pathways.

What are the body’s eight senses?

Traditionally we are only taught about five basic sensory systems: visual (sight), auditory (hearing), olfactory (smell), gustatory (taste), and tactile (touch). However, there are three additional important sensory systems in the body: vestibular (balance and spatial orientation), proprioceptive (body awareness), and interoceptive (internal sensation).

1. Visual

- Sense of sight
- Visual sensory information is taken in through the eyes
- The retina of the eye contains receptor cells called rods and cones that respond to light
- Information picked up by the receptor cells is sent through the optic nerve to the brain
- The visual sensory information is processed in the occipital cortex, located in the back area of the brain

2. Auditory

- Sense of hearing
- Auditory sensory information is taken in through the ears
- Sound waves enter through the outer ear into the ear canal and reach the eardrum. The sound waves cause the eardrum to vibrate which causes three bones in the middle ear to vibrate (malleus, stapes, and incus). The vibration travels to the cochlea which is located in the inner ear and contains fluid. This vibration causes the fluid in the cochlea to create movement which moves auditory receptor cells called hair cells. When the hair cells move, cellular channels open which create an electrical signal which is carried by the auditory nerve to the brain.
- Auditory input is processed in the temporal lobe of the brain which is located behind the ears or temples on the left and right sides of the brain

3. Olfactory

- Sense of smell
- Olfactory sensory information is taken in through the nose
- Chemical substances (odor molecules) from the environment (carried through the air) enter the nasal cavity through the nostrils. These chemical substances dissolve in a mucous membrane on the upper portion of the nasal cavity and come in contact with olfactory receptor cells which transmit olfactory sensory information to the olfactory nerve which is transmitted to the brain.
- The olfactory sensory information is processed in the temporal lobe of the brain, on the left and right sides of the brain.

4. Gustatory

- Sense of taste
- Gustatory information is taken in through the tongue
- The surface of the tongue contains bumps called papillae which contain taste buds. Taste buds contain gustatory receptor cells which transmit signals created when the receptor cells come in contact with chemicals contained in foods. Signals from the gustatory receptor cells are sent to the brain through the facial, glossopharyngeal, and vagus cranial nerves.
- The gustatory sensory information is processed in the parietal lobe of the brain. The parietal lobe is located above the temporal lobe.

5. Tactile

- Sense of touch
- Tactile information is taken in through receptors all over the body but mostly in the skin
- There are multiple types of tactile sensory receptors, including free nerve endings, Merkel cells, Meissner’s corpuscles, Pacinian corpuscles, root hair plexuses, and Ruffini corpuscles, which respond to different types of tactile input. Different types of tactile input picked up by these receptors include pressure, vibration, temperature and pain. Tactile input is transmitted from these sensory receptors to sensory nerves which travel through the spinal cord to the brain.
- Tactile sensory information is processed in the somatosensory cortex in the parietal lobe of the brain

6. Vestibular

- The vestibular system provides information about motion, our head’s position, and spatial orientation
- This system also helps us maintain balance and posture, and stabilize the head and body while we are moving
- The vestibular system coordinates with the auditory and visual systems to organize the body’s balance, coordination, and eye control
- Vestibular information is taken in through the vestibular labyrinth which is located in the inner ear. The vestibular labyrinth is connected to the cochlea which contains fluid. There are three tubes called semicircular canals which are located in the vestibular labyrinth which detect head movement by detecting the movement of fluid through the semicircular canals.
- Difficulties with vestibular processing may lead to motion sickness, fear of heights, appearing clumsy, and bumping into objects
- Vestibular information is processed in the vestibular cortex within the parietal lobe of the brain.

7. Proprioceptive

- The proprioceptive system provides a sense of body awareness by sensing where the body is in space and providing information about the amount of force and pressure being exerted by the body’s muscles
- This system’s receptors are primarily located within the muscles and joints
- The proprioceptive system coordinates with the vestibular system and combines vestibular sensory input with input from stretch receptors in the muscles, joints, tendons, ligaments, and skin to provide information about the body’s location in space
- Difficulties with proprioceptive processing may lead to difficulty performing movements with the eyes closed, avoidance of physical activities (like sports), issues with balance, uncoordinated movements, and difficulty sensing the amount of pressure to use when performing tasks
- Proprioceptive information is processed in the somatosensory cortex in the parietal lobe of the brain

8. Interoceptive

- The interoceptive system provides a sense of internal body awareness by providing information about sensations within the body
- This system contributes to our emotions and sense of well-being as well as changes in the homeostatic (internal automatic) responses of the body and sensations within the internal organs
- Interoceptive receptors are located throughout the body, in all the major organs including the skin
- The interoceptive system provides information about hunger/fullness, thirst, heart and breathing rate, muscle tension, pain, itch, nausea, body temperature, alertness/sleepiness, need to urinate/have a bowel movement, etc.
- The interoceptive system coordinates with the vestibular and proprioceptive systems to control each individual’s internal perception of their body
- Difficulties with interoceptive processing may lead to difficulty recognizing hunger/fullness, difficulty sensing need to urinate/have a bowel movement, unusual responses to pain/stress/emotions, difficulty explaining symptoms when sick or injured, difficulty sensing body temperature (e.g. not noticing when overheated), disordered sleep
- Interoceptive information is processed in a part of the brain called the insula, which is located between the frontal and temporal lobes