Question

Describe the special sense of vision in detail. How is the stimulus/signal received? How is it processed in our brain (pathway) and where

Describe TWO of four special senses, your choice (hearing, taste, smell, or equilibrium), in detail. How is the stimulus/signal received? How is it processed in our brain (pathway) and where

Answer 1

Visual pathways consists series of cells and synapses that carry information from our surroundings to the brain for processing, it consists of retina, optic nerve, optic chiasma, optic tract, lateral geniculate nucleus, optical radiation and striate cortex.

Visual pathway begins when light rays pass through cornea and centering at fovea and back of retina, the first cell in the pathway, the photoreceptor converts light energy into neuronal signal, this signal is passed on to the bipolar cells and amacrine cell and than to the ganglion cell, all these cells and synapse lie within the retina., the axons 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 eyes is combined and splits 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. This information from right visual feild (left side of brain) travel to left optic tract and vice-versa.. each optic tract terminate in the lateral geniculate nucleus (LGN). The LGN is the sensory relay nucleus in the thalamus of brain, the fibers leave the LGN as the optic radiata, the optic radiata 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 separated into ventral and dorsal pathway, the visual cortex which lies above cerebellum is responsible for processing the visual image.

The human ear is the organ responsible for hearing and for equilibrium or balance. The ear consists of three regions or areas: the outer (external) ear, the middle ear, and inner (internal) ear. Besides hearing, the inner ear is also concerned with balance.

Pathway of sound. Sound waves travel from the outer ear through the auditory canal causing the tymphanic membrane to vibrate, this in turn causes the three small bones known as ossicles, the hammer, the anvil and stirup in the middle ear to move, the vibrations move through the oval window to the fluid in the cochlea in inner ear, hair cell in organ of corti within the cochlea are stimulated, there are thousands of tiny hair cells, which in turn stimulate the cochlear branch of vestibulocochlear nerve. This cochlear nerve than transmits electrical impulse to the auditory region of the brain in the temporal lobe, this electrical impulse is finally perceived by the brain as sound.

Smell : Like taste, the sense of smell, or olfaction, is also responsive to chemical stimuli. The smell receptor neurons are located in a small region within the superior nasal cavity. For smelling to occur, chemicals in the air must enter the nostrils into the nasal cavity. There, they must be dissolved in the mucus covering the olfactory epithelium. Once dissolved, the chemicals bind to the olfactory hairs, stimulating the olfactory receptors to send nerve impulses along the olfactory nerves to the olfactory areas in the temporal lobes of the cerebral cortex. The brain interprets the impulses as a specific odor or odors.

The information of smell are sent to the limbic system, which are mainly concerned with emotional states and memory. Thus, the impressions formed by odors or smells are long-lasting and very much a part of an individual's memories and emotions.