the sense organ contain thousand of _
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cels
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the sence organ contain thousands of cells .
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Answer:
Sense Organs
The nervous system is responsible for sensing the external and internal environments of an organism, and for inducing muscle movement. Human sensation is achieved through the stimulation of specialized neurons, organized into five different modalities—touch, balance, taste, smell, hearing, and vision. The touch modality includes pressure, vibration, temperature, pain, and itch. Some animals are also able to sense magnetism and electric fields. Modality, timing, intensity, and location of the stimulus are the four features that allow the brain to identify a unique sensation.
Sensation Receptors
The neurons specialized to detect sensation are also called receptors because they are designed to receive information from the environment. Each receptor responds only to a stimulus that falls within a defined region, called its receptive field. The size of the stimulus can affect the number of receptors that respond, and the strength of the stimulus can affect how much they respond. For example, when a cat sits on your lap, a large population of receptors responds to the cat's weight, warmth, claws, and the vibrations from its purring.
Touch receptors.
Touch receptors are a type of mechanoreceptor because they are activated by mechanical perturbation of the cell membrane. The axon is located in either shallow or deep skin, and may be encapsulated by specialized membranes that amplify pressure. When the appropriate type of pressure is applied to the skin, these membranes pinch the axon, causing it to fire. The action potential travels from the point of origin to the neuron's cell body, which is located in the dorsal root ganglion. From there, it continues through another branch of the axon into the spinal cord, even as far as the brainstem.
Vision receptors
Vision receptors are called photoreceptors because the stimuli that activate them are photons of light. The two types of photoreceptors are called rods and cones. Rods only sense the intensity of light, while cones can sense both intensity and color. While cones function best in bright light, rods function better in dim light. Furthermore, rods are located diffusely over the retina at the back of the eye, but cones are located in the central line of vision in a region of the retina called the fovea. For this reason, dim objects in the darkness can be viewed better from peripheral vision than from direct focus. There are three kinds of cones in the vertebrate eye—one responsive to wavelengths of light corresponding to the color blue, one responsive to red wavelengths, and one responsive to green wavelengths. These three colors form the entire range of colors that humans can perceive.
Hearing receptors.
Hearing receptors, or hair cells, are mechanoreceptors located within a bony spiral structure called the cochlea. Sounds are interpreted by the brain from patterns of air pressure caused by the vibration of objects. Sounds can also travel through water or solid objects. In mammals, the pressure in the air is transformed into mechanical pressure by three ear bones called the malleus , incus , and stapes , located in the middle ear. .
Smell receptors.
Smell receptors, or olfactory sensory neurons, are chemoreceptors , meaning that the binding of molecules causes these neurons to fire. Olfactory neurons extend a single dendrite to the surface of the skin in the nose, where it expands—along with dendrites from other neurons—to form a large knob. Thin hair-like projections extend from this knob into the thin layer of mucus within the nose. These projections contain a diverse array of receptors for odorants, so that all olfactory neurons are able to respond to a particular scent. The number that actually do respond is relative to the concentration of the scent molecules in the air.
Taste receptors.
Taste-detecting, or gustatory, organs are also chemoreceptors and are located in functional groupings called taste buds on the tongue, palate, pharynx, epiglottis, and the upper third of the esophagus. Taste cells have a very short life span, which is why each unit contains a population of stem cells that continuously divides, producing progeny cells to replace the dying taste cells. The remainder of the cell types in the taste bud has hair-like projections called microvilli that extend into a pore at the top of the taste bud. When taste molecules bind or interact with the microvilli, the taste cell undergoes an electrochemical change that is conveyed to an associated neuron; however, taste cells are not neurons. Four basic taste sensations can be distinguished by humans: bitter, salty, sour, and sweet.
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