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Sensory Physiology: 1 Compiled and circulated by Dr. Parimal Dua, Assistant Professor, Dept. of Physiology, Narajole Raj college Sensory Physiology: 1. Distinguish between general senses and special senses. The human body has two major types of senses: special senses and general senses. Special senses have specialized sense organs and include vision (eyes), hearing (ears), balance (ears), taste (tongue), and smell (nasal passages). General senses are all associated with touch and lack special sense organs. 2. Classify the general senses. The general senses are pain, temperature, touch, pressure, vibration, and proprioception. Receptors for those sensations are distributed throughout the body. 3. What are receptors and their functions? Receptors are proteins or glycoproteins that bind signalling molecules known as first messengers, or ligands. They can initiate a signaling cascade, or chemical response, that induces cell growth, division, and death or opens membrane channels. 4. What are the different types of receptors in the body? a) Nociceptors (pain receptors) b) Thermoreceptors (temperature sensors) c) Mechanoreceptors (Pressure sensors) d) Chemoreceptors (Chemicals sensors) e) Photoreceptors (Light sensors) 5. Classify the special senses. The five special senses are: 1. Olfaction (smell) 2. Gustation (taste) 3. Vision (sights) 4. Equilibrium (balance) 5. Hearing Receptors for these senses are located in specialized areas called sense organs. 6. What is transducers? A transducer is an electrical device that is used to convert one form of energy into another form. In general, these devices deal with different types of energies such as mechanical, electrical energy, light energy, chemical energy, thermal energy, acoustic energy, electromagnetic energy, and so on. Page | 1 DSC1DT: Sensory Physiology, Endocrine and Reproductive System, Renal Physiology Compiled and circulated by Dr. Parimal Dua, Assistant Professor, Dept. of Physiology, Narajole Raj college 7. What is biotransducers? A biotransducer is the recognition-transduction component of a biosensor system. It consists of two intimately coupled parts; a bio-recognition layer and a physicochemical transducer, which acting together converts a biochemical signal to an electronic or optical signal. The bio-recognition layer typically contains an enzyme or another binding protein such as antibody. The physicochemical transducer may be electrochemical, optical, electronic, gravimetric, pyroelectric or piezoelectric. 8. Why receptors are called biological transducers? Receptors are called transducers because they 'convert' the energy contained in the stimulus into another form of energy, specifically into some sort of membrane potential. Receptors are termed selective because each type of receptor is highly specific (selective) with respect to the type of stimulus it responds to. 9. What is Muller's law? The law of specific nerve energies, first proposed by Johannes Peter Müller. The law of specific nerve energies states that an individual's mind cannot access objects in the natural environment except through the nerves. 10. What are Weber's law and Fechner's law? The Weber–Fechner law refers to two related hypotheses in the field of psychophysics, known as Weber's law and Fechner's law. Both laws relate to human perception, more specifically the relation between the actual change in a physical stimulus and the perceived change. This includes stimuli to all senses: vision, hearing, taste, touch, and smell. Weber's law states that the smallest change in the intensity of a stimulus capable of being perceived is proportional to the intensity of the original stimulus. Fechner's law states that the subjective sensation is proportional to the logarithm of the stimulus intensity. Since Weber's law fails at low intensity, so does Fechner's law. 11. Write down the mechanism of transduction of stimuli from sensory receptors. Transduction is the process that converts a sensory signal to an electrical signal to be processed in a specialized area in the brain. Page | 2 DSC1DT: Sensory Physiology, Endocrine and Reproductive System, Renal Physiology Compiled and circulated by Dr. Parimal Dua, Assistant Professor, Dept. of Physiology, Narajole Raj college The most fundamental function of a sensory system is the translation of a sensory signal to an electrical signal in the nervous system. This takes place at the sensory receptor. The change in electrical potential that is produced is called the receptor potential. How is sensory input, such as pressure on the skin, changed to a receptor potential? As an example, a type of receptor called a mechanoreceptor possesses specialized membranes that respond to pressure. Disturbance of these dendrites by compressing them or bending them opens gated ion channels in the plasma membrane of the sensory neuron, changing its electrical potential. In the nervous system, a positive change of a neuron’s electrical potential (also called the membrane potential), depolarizes the neuron. Receptor potentials are graded potentials: the magnitude of these graded (receptor) potentials varies with the strength of the stimulus. If the magnitude of depolarization is sufficient (that is, if membrane potential reaches a threshold), the neuron will fire an action potential. In most cases, the correct stimulus impinging on a sensory receptor will drive membrane potential in a positive direction, although for some receptors, such as those in the visual system, this is not always the case. Sensory receptors for the various senses work differently from each other. They are specialized according to the type of stimulus they sense; thus, they have receptor specificity. For example, touch receptors, light receptors, and sound receptors are each activated by different stimuli. Touch receptors are not sensitive to light or sound; they are sensitive only to touch or pressure. However, stimuli may be combined at higher levels in the brain, as happens with olfaction, contributing to our sense of taste. Page | 3 DSC1DT: Sensory Physiology, Endocrine and Reproductive System, Renal Physiology Compiled and circulated by Dr. Parimal Dua, Assistant Professor, Dept. of Physiology, Narajole Raj college Mechanoreceptor activation: (a) Mechanosensitive ion channels are gated ion channels that respond to mechanical deformation of the plasma membrane. A mechanosensitive channel is connected to the plasma membrane and the cytoskeleton by hair-like tethers. When pressure causes the extracellular matrix to move, the channel opens, allowing ions to enter or exit the cell. (b) Stereocilia in the human ear is connected to mechanosensitive ion channels. When a sound causes the stereocilia to move, mechanosensitive ion channels transduce the signal to the cochlear nerve. Page | 4 DSC1DT: Sensory Physiology, Endocrine and Reproductive System, Renal Physiology Compiled and circulated by Dr. Parimal Dua, Assistant Professor, Dept. of Physiology, Narajole Raj college Olfaction and Gustation: 12. Write down the structure of olfactory organ. Olfactory system, the bodily structures that serve the sense of smell. The system consists of the nose and the nasal cavities, which in their upper parts support the olfactory mucous membrane for the perception of smell and in their lower parts act as respiratory passages. The bony framework of the nose is part of the skull, but the outer nose is supported only by bone above; lower down, its shape is kept by cartilaginous plates. The expanded lower part of the side of the nose, the ala, is formed only of skin, both externally and internally, with fibrofatty tissue between the layers. The nasal cavities are separated by a septum covered in its lower two-thirds by thick, highly vascular mucous membrane composed of columnar ciliated epithelium with masses of acinous glands embedded in it, while in its upper part it is covered by the less vascular but more specialized olfactory membrane. Near the front of the lower part of the septum a slight opening into a short blind tube, which runs upward and backward, may sometimes be found; this is the vestigial remnant of Jacobson’s organ. The supporting framework of the septum is made up of ethmoid above, vomer below, and the septal cartilage in front. The outer wall of each nasal cavity is divided into three meatuses by the overhanging turbinated bones. Above the superior turbinated bone is a space between it and the roof known as the recessus sphenoethmoidalis, into the back of which the sphenoidal air sinus opens. Between the superior and middle turbinated bones is the superior meatus, which contains the openings of the posterior ethmoidal air cells, while between the middle and inferior turbinated bones is the middle meatus, which is the largest of the three and contains a rounded elevation, the bulla ethmoidalis. Above and behind this is often an opening for the middle ethmoidal cells; below and in front runs a deep sickle-shaped gutter, the hiatus semilunaris, which communicates above with the frontal air sinus and below with the opening into the antrum of Highmore or maxillary antrum. The inferior meatus is below the inferior turbinated bone, and, when that is lifted, the valvular opening of the nasal duct is seen. The roof of the nose is narrow, and it is here that the olfactory nerves pass in through the cribriform plate. The floor is wider so that a coronal section through each nasal cavity has roughly the appearance of a right- angled triangle. Page | 5 DSC1DT: Sensory Physiology, Endocrine and Reproductive System, Renal Physiology Compiled
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