Question

a) Write out the complete pathway for vision

b) Write out the complete pathway for hearing

Answer 1

.a) Visual pathway begins when light rays paassing through cornea and centring at fovea, back of retina, the first cell in the pathway, photoreceptor cells converts light energy into neuronal signals, this signals is passed to the bipolar cells and amacrine cells than to the ganglion cell all thee cells synapse within the retina, the axon of the ganglion cell exit the retina through optic nerve, the optic nerve from both eyes meet and cross the optic chiasma,at this point information of both eye is combined and than split according to the visual feild, the corresponding halves of the feild of view i.e right and left are sent to the left and right halves of the brain to be processed the information from the right visual feild, which corresponds to the left side of the brain travel to the left optic tract and vice-versa , each optic tract converse at lateral geniculate nucles (LGN) in the thalamus. The fibers leave the LGN as the optic radiation, the optic radiation, one on each side of the brain carry information from the thalamic lateral geniculate nucleus to the layer 4, of the visual cortex, the visual pathway is than separated into ventral and dorsal pathway, the visual cortex is responsible for visual image.

b) Sound wave travels from the outer ear through auditory canal causing the tymphanic membrane to vibrate, this in turn causes the three small bones known as ossicles,which consists of hammer, anvil and stirrup in the middle ear to move, the vibrations than move through oval windows to the fluid in the cochlea in the inner ear, hair cells in the organ of corti within the cochlea are stimulated there are thousand of tiny hair cells which in turn stimulae the cochlear branch of the vestibulocochlear nerve, this cochlear nerve than transmits electrical impulses to the auditory region of the brain in the temporal lobe, this electrical impulse is finaly percieved by the brain as sound.