We have examined the origin of a set of precisely located sense organs in the notum and wing of Drosophila, in transformant flies where lacZ is expressed in the progenitor cells of the sense organs (the sensory mother cells) and in their progeny. Here we describe the temporal pattern of appearance and divisions of the sensory mother cells that will form the eleven macrochaetes and the two trichoid sensilla of the notum, and five campaniform sensilla on the wing blade. The complete pattern of sensory mother cells develops in a strict sequence that extends over most of the third larval instar and the first 10 h after puparium formation. The delay between the onset of lacZ expression and the first differentiative division ranges from 30 h, in the case of the earliest mother cells, to 2 h for the latest mother cells. The first division shows a preferential orientation which is also specific for each sensory mother cell. Up to this stage, there is no marked difference between the three types of mechanosensory organs.
The ear is a sensory organ that picks up sound waves, allowing us to hear. It is also essential to our sense of balance: the organ of balance (the vestibular system) is found inside the inner ear. It is made up of three semicircular canals and two otolith organs, known as the utricle and the saccule. The semicircular canals and the otolith organs are filled with fluid.
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Information coming from the vestibular system is processed in the brain and then sent on to other organs that need this information, such as the eyes, joints or muscles. This allows us to keep our balance and know what position our body is in.
In some situations, for example on a ship or airplane, different sensory organs (e.g. the eyes and the organ of balance) send contradictory messages to the brain. This can cause us to feel unwell, dizzy or nauseous.
The vestibular system is especially sensitive in children, and reacts more slowly to movements as we grow older. Inner ear infections and other problems may also affect how well our sense of balance works.
The human body can achieve an understanding of the world through its sensory systems. Sensory systems are widespread throughout the body including those that detect the world directly from the outside (exteroreceptors), those that detect information from internal organs and processes (interoceptors), and those detecting sense of position and load (proprioception).[1][2][3][1]
Sensory receptors occur in specialized organs such as the eyes, ears, nose, and mouth, as well as internal organs. Each receptor type conveys a distinct sensory modality to integrate into a single perceptual frame eventually. This information is achieved by the conversion of energy into an electrical signal by specialized mechanisms. In this report, we will discuss a basic overview of sensory systems, focusing on sensory receptors.
All impulses from the receptors transmit as nerve signals and what ultimately determines how we perceive the stimulus is where the nerve fiber terminates in the central nervous system. It is important to realize that what one senses is dependent on the receptor and any damage occurring from the beginning of the path to its end.
The inner ear senses balance. With head motion or pressure impulses of sound, the endolymph vibrates and creates a stimulus for the receptors of the vestibular system - the utricle and saccule. Inside the utricle and saccule are maculae containing hair cells with a membranous covering of microscopic otoconia that detect motion of the endolymph. Those in the saccule help sense vertical accelerations whereas those in the utricle sense horizontal accelerations. With changes in position, and thus changes in fluid motion, the shifting of these hair cells causes the opening of receptor channels leading to action potentials propagating from the hair cells to the auditory nerve. The rate of fluid motion, plus the quality of the fluid, gives more information about the motion. While the utricle and saccule detect linear motion, the semicircular ducts detect rotations in a similar fashion.[5]
The smell occurs by binding of odorant molecules to receptors on the membrane of the cilia, causing an action potential that sends this information to the brain. These systems utilize G-protein receptors along with adenylate cyclase. Initially, scientists believed that molecules bound directly to receptors and that each receptor potentially identified a specific type of smell. However, Yoshioka et al. proposed a more plausible theory, because hydrogen and its isotope are sensed as entirely different smells. The authors relate this to a postulate called the "molecule vibration model." When a substance is bound to its receptor, the substrate allows electrons to go down their gradient, and through their specific vibrational energies, it causes a flow of chemical changes and subsequent signaling to the brain.[4]
Cold receptors mainly sense temperatures between 25 to 30C. Temperatures below this cause release of bursting discharges. In touching dangerously hot objects (greater than 45C), there can be a brief sensation of cold due to the paradoxical firing of cold receptors. Warm receptors respond to the approximate temperature range of 30 to 46C. Higher temperatures may result in the decreased firing of these receptors.[8]
Nociceptors help signal pain that is related to temperature, pressure, and chemicals. As Dubin et al. discusses, most sensory receptors have low sensitivity to dictate all sensations to the brain. However, when it comes to pain, nociceptors only signal when the body has reached a point of tissue damage. Inflammatory markers increase during tissue damage, bind to receptors, and initiate pain signaling either externally or in the viscera. One of the ion channels families that are present on nociceptive neurons is called TRP (transient receptor potential) ion channels. Those signals that activate nociceptive receptors include extremes of temperatures, high pressures, and chemicals causing tissue damage [12]. Different fibers relay pain information; these are A-delta and C fibers. These fibers differ in their myelination and nerve diameter and thus speed of transmission. Painful temperatures, uncomfortable pressures, and chemicals mostly use C-fibers. C-fibers vary to be able to sense all three types of stimuli. A-delta fibers are small and unmyelinated and are primarily involved in thermal and mechanosensitive pain. Nociceptors utilize mostly glutamate but also substance P, calcitonin gene-related peptide, and somatostatin to signal pain.[12]
The mediation of the sense of load and position is through the specialized structures of muscle spindles and joint capsules which contain mechanoreceptors that detect joint angle, muscle length, and force.
As stated before, we have five sense organs that can receive and relay sensory information to the brain. These senses provide an organism with information crucial for perception. The different sense organs and the senses they provide are mentioned below:
These are the visual sensory organs in our body. These are sensitive to light images. The eyes vary in colour depending upon the amount of melanin present in our body. It helps in the sense of sight by detecting and focussing on the light images.
Ears are the auditory sense organs of our body. They help us to perceive sounds. Our auditory system detects vibrations in the air and this is how we hear sounds. This is known as hearing or audio caption.
Walking or kicking without looking at our feet, balancing on one leg, touching the nose with eyes closed and the ability to sense the surface on which we are standing upon, are a few examples of proprioception system.
A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. Although in some cultures five human senses were traditionally identified as such (namely sight, smell, touch, taste, and hearing), many more are now recognized.[1] Senses used by non-human organisms are even greater in variety and number. During sensation, sense organs collect various stimuli (such as a sound or smell) for transduction, meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of an organism's cognition, behavior and thought.
In organisms, a sensory organ consists of a group of interrelated sensory cells that respond to a specific type of physical stimulus. Via cranial and spinal nerves (nerves of the Central and Peripheral nervous systems that relay sensory information to and from the brain and body), the different types of sensory receptor cells (such as mechanoreceptors, photoreceptors, chemoreceptors, thermoreceptors) in sensory organs transduct sensory information from these organs towards the central nervous system, finally arriving at the sensory cortices in the brain, where sensory signals are processed and interpreted (perceived).
Sensory systems, or senses, are often divided into external (exteroception) and internal (interoception) sensory systems. Human external senses are based on the sensory organs of the eyes, ears, skin, nose, mouth and the vestibular system. Internal sensation detects stimuli from internal organs and tissues. Internal senses possessed by humans include spatial orientation, proprioception (body position) and nociception (pain). Further internal senses lead to signals such as hunger, thirst, suffocation, and nausea, or different involuntary behaviors, such as vomiting.[2][3][4] Some animals are able to detect electrical and magnetic fields, air moisture, or polarized light, while others sense and perceive through alternative systems, such as echolocation. Sensory modalities or sub modalities are different ways sensory information is encoded or transduced. Multimodality integrates different senses into one unified perceptual experience. For example, information from one sense has the potential to influence how information from another is perceived.[5] Sensation and perception are studied by a variety of related fields, most notably psychophysics, neurobiology, cognitive psychology, and cognitive science. 17dc91bb1f
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