Question

outliline the similarity and difference between signaling in the visual and olfactory systems。what are the cell-types？ what kinds of receptors are involved？ how arw the signals transduced？ what is the end result of activation of these signals in terms of the response of the cell？

Answer 1

Working of Visual System:

he visual pathway consists of the series of cells and synapses that carry visual information from the environment to the brain for processing. It includes the retina, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus (LGN), optic radiations, and striate cortex The first cell in the pathway—a special sensory cell, the photoreceptor—converts light energy into a neuronal signal that is passed to the bipolar cell and the amacrine cell and then to the ganglion cell; all these cells and synapses lie within the retina. The axons of the ganglion cells exit the retina via the optic nerve, with the nasal fibers from each eye crossing in the optic chiasm and terminating in the opposite side of the brain. The optic tract carries these fibers from the chiasm to the LGN, where the next synapse occurs. The fibers leave the LGN as the optic radiations that terminate in the visual cortex of the occipital lobe. From various points in this pathway, information about the visual environment is transferred to related neurologic centers and to visual association areas.The visual pathway describes the anatomical pathway by which electrical signals generated by the retina are sent to the brain . The nerve fibers of the retina, representing the axons of the ganglion cells, collect together at the optic disc before passing out of the eye through the orbital bones and into the brain via the optic nerve (the second cranial nerve). The nerve fibers from different areas of the retina become more organized as they pass down the optic nerve. The optic nerves from each eye meet at the optic chiasm, a structure at the base of the brain. At this point, the nerve fibers that are associated with the nasal half of the retina from each eye cross over, so that on leaving the optic chiasm and passing into the optic tracts, the nerve fibers from the nasal retina of one eye travel down the optic tract with the nerve fibers originating in the temporal retina of the other eye. At the end of each optic tract, the retinal nerve fibers connect with other visual pathway nerves in a structure called the lateral geniculate nucleus (LGN) located in the midbrain. Some processing of the electrical signals occurs in the LGN before a series of radiating nerve fibers, the optic radiation, convey the information to the visual cortex in the posterior portion of the occipital lobe. Perception of sight ultimately derives from processing within this and adjacent areas of brain.

Working of Olfactory Sytem:

Our sense of smell begins with the nasal mucosa. Odors will travel to the nose’s mucous membrane, which engulfs the molecule and brings it to the olfactory nerve ending. Mucous is replaced roughly every 10 minutes in order to make room for new chemicals. The olfactory nerve—also known as cranial nerve #1—travels directly to the frontal lobe through a bone known as the cribriform plate at the top of the sinus.

This neural path is significant for two reason:

One, this is the only sense that does not travel to the thalamus before accessing the forebrain. The thalamus, if you remember, is the relay center for all sensory signals. Nearly all receptors send signals through the thalamus first, which then sends the signals to the proper areas of the brain for perception.

Two, the nerve’s placement makes it vulnerable to traumatic brain injury. In injuries that involve sudden acceleration or deceleration (shearing force), or a skull fracture at the front of the face, it’s possible for the olfactory nerve to be damaged or severed. This would result in the immediate loss of olfaction. Each side of the frontal lobe receives chemical signals through two olfactory bulbs, where it is processed by the brain. Interestingly, a person’s breathing rate will affect how sensitively odors are received and processed.