Senses are the means by which our brains understand our surroundings. Most of us were taught in school that humans possess five senses: sight, sound, smell, taste, and touch. We also learned that many animals have comparable senses, although their range may differ. For instance, while humans can detect red, green, and blue light, various bird species can perceive these colors as well as UV light; dogs, on the other hand, can only see yellow and blue light. Furthermore, humans can hear frequencies up to approximately 23,000 Hz, whereas dogs can hear sounds reaching 45,000 Hz. Nevertheless, these represent just five of the senses. Depending on how one defines a sense, many scientists suggest that humans have at least nine, with others positing that there might be several dozen! Additionally, numerous other animals possess extra senses as well. Here are just a few examples of these senses.
## Awareness of Your Body
Proprioception refers to the ability to perceive your body and its location, while kinesthesia pertains to the ability to sense movement. These senses are crucial for maintaining balance and applying the necessary force for daily activities. You can walk with your eyes closed because proprioception and kinesthesia function independently of vision. They depend on sensory organs in your muscles known as spindles. Each muscle spindle is wrapped around muscle fibers, and when a muscle is stretched, these spindles convey information about the length and velocity of the stretch to your spinal cord and brain, which then use this data to determine your body’s position.
## Pain
The experience of physical pain is referred to as nociception. When your tissue sustains damage from an injury, pain receptors known as nociceptors become active and transmit an electrical signal through a nerve to your spinal cord. The nerve fibers that convey pain signals differ from those that carry information regarding proprioception and touch. Once the spinal cord receives the signal, it may trigger a reflex action, such as recoiling from the pain source. Concurrently, the spinal cord sends signals to the brain, which interprets these signals, allowing you to perceive the pain. This process aids in avoiding the pain source in the future.
## Temperature
Humans possess various types of thermoreceptors capable of sensing warmth, cold, or both. Temperature information travels along the same nerve fibers as pain signals. This explains why extreme temperatures can elicit pain.
## Balance
Our equilibrium sense is supported by the vestibular system, situated within the inner ear. This system comprises three semicircular canals that contain fluid and hair cells to detect fluid movement. Each canal is tasked with sensing balance in a specific direction.
## Echolocation
As humans, we possess depth perception due to having two eyes that view the world from different perspectives. This enables the brain to gather sufficient information for judging distance. However, several animals, including nocturnal and burrowing species, cannot depend solely on vision to detect obstacles. These creatures, such as certain bats, toothed whales (including dolphins), and small mammals, utilize echolocation to measure distance. An animal generates clicking sounds and listens for the echoes of these sound waves bouncing off obstacles. Since sound requires time to travel, animals can determine their distance from an obstacle based on the echo’s return time. Bats utilize echolocation for hunting and navigation, emitting very high-pitched sounds, typically beyond human hearing, and accelerating their clicks as they approach their prey for greater precision. Toothed whales like dolphins also employ echolocation for similar reasons. These marine mammals possess a melon, a fatty structure on the top of their heads that enhances the clarity of the reflected sound waves. Intriguingly, humans can also learn echolocation techniques, which can assist visually impaired individuals in perceiving their surroundings.
## Electricity
Electroreception is predominantly observed in aquatic creatures due to air’s high resistance to electricity, making current detection challenging. Animals such as sharks, rays, other fish, and bees utilize electroreception. Sharks and rays, in particular, possess electroreceptors known as ampullae of Lorenzini embedded in their skin, allowing them to detect electrical currents from prey, even when concealed beneath sand. Furthermore, some fish species utilize electricity for communication, while bees employ electroreception to sense current from flowers.
## Magnetic Fields
Birds, turtles, bees, and numerous other animals can perceive the Earth’s magnetic field, which aids in annual migrations and ocean navigation. Scientists are not yet entirely certain how this sense, termed magnetoreception, operates.