The ability to hear and see is a result of the intricate workings of the sensory system.
The speakers create vibrations in the air that travel to your ear, where they are converted into signals that your brain can interpret.
Similarly, the screen emits groups of photons that travel at the speed of light and stimulate specialized cells in the eye, which then send signals to the brain to be decoded.
It’s not just hearing and sight that the sensory system is responsible for.
It also includes the sense of smell, taste, balance, proprioception, and various types of touch.
However, often these subsystems are discussed in isolation, without considering their similarities and how they work together as a whole.
Taking a holistic view of the sensory system can provide a deeper understanding of how we perceive and understand the world around us.
What is the sensory system
The nervous system’s component that processes sensory data is known as the sensory nervous system.
A sensory system is made up of neural networks, sensory neurons (including sensory receptor cells), and brain regions involved in sensory perception.
The sensory systems for vision, hearing, touch, taste, smell, and balance are the most well-known.
The physical world is translated by senses into the mental world, where people interpret the data to build their view of the environment.
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Receptors of the sensory system
Afferent neurons, or specialized cells that affect them, collect information from the external and internal environment in various forms of energy.
This energy is referred to as a stimulus, and when it activates a receptor, it is transformed into a graded or receptor potential.
This process is known as stimulus transduction.
Each receptor is specific to a certain type of stimulus, known as its adequate stimulus.
Additionally, receptors have a specific range of stimulus energies that they respond to.
However, if the intensity of a nonspecific stimulus is high enough, it can also activate a receptor.
Receptor potential of sensory system
The modulation of ion flow through specialized membrane receptors, known as gating, can lead to a fluctuation in the ion concentration across the membrane. This fluctuation is known as a graded receptor potential, which can trigger a nerve impulse, known as an action potential.
The frequency of these action potentials is determined by the intensity of the graded potential, rather than its overall magnitude. Factors that influence the magnitude of the graded potential include the strength of the stimulus, the combined effect of multiple receptor potentials, and the sensitivity of the receptors.
This sensitivity can decrease with prolonged exposure to a constant stimulus, a phenomenon known as adaptation.
Neural Pathways in Sensory Systems
An afferent neuron, along with its receptor endings, makes up a sensory unit.
When stimulated, the area of the body that triggers activity in a specific afferent neuron is known as the receptive field for that neuron.
Afferent neurons travel into the central nervous system, branching out and connecting with multiple interneurons. These afferent neurons are referred to as sensory or ascending pathways and are considered specific ascending pathways when they carry information about one specific type of stimulus.
The ascending pathways reach the cerebral cortex on the opposite side of where their sensory receptors are located.
Particular ascending pathways that transmit information from somatic receptors and taste buds go to the somatosensory cortex (parietal lobe), those from the eyes go to the visual cortex (occipital lobe), and those from the ears go to the auditory cortex (temporal lobe).
The sense of smell, or olfaction, is not represented in the cerebral cortex.
Nonspecific ascending pathways, made up of polymodal neurons, are activated by sensory units of various types.
These pathways are essential for alertness and arousal.
Cortical association areas, located outside of primary cortical sensory areas, play a role in more complex analysis of incoming information such as comparison, memory, language, motivation, emotion, etc.
Sensory Systems
Our senses allow us to experience the vast array of sights, sounds, smells, and tastes that surround us.
Our eyes perceive light, our ears detect sound waves, our skin senses touch, pressure, and temperature, our tongues taste the food we eat, and our noses detect scents in the air.
The human perceptual system is designed for precision, and people are incredibly skilled at utilizing the wide range of information available to them.
However, it is not just the sensation that we experience, but the perception that the brain creates from the information received through our senses.
When we look at a view of the countryside or the face of a loved one, we don’t just see a random assortment of colors and shapes, but rather a cohesive and meaningful image.
Sensory Receptors: Seeing
Humans rely heavily on their vision to understand the world around them.
A significant portion of the brain, known as the cerebral cortex, is dedicated to processing visual information.
This process starts when light enters the eye and is then transformed into electrical signals that travel to the visual cortex. Here, specialized neurons work to detect different aspects of the image such as color, shape, and movement.
This information is then combined to form a cohesive perception.
Research has shown that the human visual system has the capability to distinguish between up to seven million different shades of color.
This is possible due to the way our eyes perceive light, which is broken down into three primary colors: red, green, and blue. The specific wavelength of light that enters the eye determines the hue of a color, with shorter wavelengths appearing blue and longer wavelengths appearing red.
The intensity or amplitude of the light wave also plays a role in how bright or dim an image appears.
Sensory Receptors: Hearing
Hearing, like vision and the other senses, starts with the process of transmission. The sound waves that are captured by our ears are transformed into neural signals and sent to the brain, where they are combined with previous experiences and perceived as the sounds we hear.
The human ear can detect a broad range of sounds, from the faint ticking of a clock in a nearby room to the loud music of a rock band in a nightclub.
Additionally, we have the ability to discern slight variations in sound.
However, the ear is particularly attuned to sounds within the frequency range of the human voice.
For example, a mother can easily distinguish her child’s voice among a group of others, and when we answer the phone, we can quickly recognize a familiar voice.
This process happens in a fraction of a second, where the auditory system receives the sound waves, sends them to the auditory cortex, compares them to stored knowledge of other voices, and identifies the caller.
Sensory Receptors: Tasting
The sense of taste plays a critical role in our lives as it allows us to appreciate the food we consume and also helps us to identify the nutritional value of the food we eat.
It helps us to select foods that provide energy, such as those high in sugar, and avoid those that may be harmful.
Children who are picky eaters are biologically inclined to be cautious about the food they eat.
In addition to taste, our sense of smell also plays a vital role in maintaining our appetite, detecting potential dangers and helping us to avoid consuming poisonous or spoiled food.
Our ability to taste is made possible by the presence of taste receptors on the tongue. These receptors are responsible for detecting six different taste sensations, which include sweet, salty, sour, bitter, spicy and savory.
Sensory Receptors: Smelling
The sense of smell works by detecting different chemical molecules through various receptor cells in the nose.
These receptors, like a lock and key, are specifically designed to detect certain molecules, creating a unique smell.
Each smell is created by different combinations of these molecules that bind to different receptors.
The way these combinations are decoded is in the olfactory cortex, similar to how phone numbers are created by combining digits.
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However, as we age, the sense of smell peaks in early adulthood and then gradually declines, by the ages of 60 to 70, the sense of smell becomes significantly weakened.
Additionally, it is observed that women tend to have a sharper sense of smell than men.
Sensory Receptors: Touching
Touch plays a crucial role in human growth and development. Our skin, which is the largest organ of the body, is the primary sense organ for touch.
It is rich in nerve endings that are capable of sensing different types of pressures and temperatures.
Through touch, we can feel different sensations such as ticklishness, pain, cold and heatl, depending on the area of the body being touched.