Bipolar cells and many ganglion cells have concentric receptive fields with an on-center/off-surround or off-center/on-surround organization. Horizontal cells mediate this center-surround antagonism. Photoreceptor, bipolar, and horizontal cells respond to stimulation by modulating their membrane potential and their release of neurotransmitters,
Olfactionisnotgenerallyexaminedinaroutineneurologicalexamination.However,smellcanbetestedbyhavingthepatientinhaleandidentifyanodorant.Onenostrilshouldbeexaminedatatimewhiletheothernostrilisoccluded.Strongodorants,suchasammonia,shouldbeavoidedbecausetheyalsoactivatetrigeminalnervefibers.Smellsensationcanbelost(anosmia) afterabasalskullfractureorafterdamagetooneorbotholfactorybulbsortractsbyatumor(suchasanolfactory groove meningioma).Concussionscancauseanosmiabecausethesuddenmovementofthebraininsidetheskullcanshearthesmallunmyelinatedolfactorynervefibers.Anauraofadisagreeableodor,oftenthesmellofburningrubber,occursduringuncinate seizures, whichareepilepticseizuresthatoriginateinthemedialtemporallobe.
narrow range of gustatory receptors with the wide repertoire of olfactory receptors. In addition, via its intimate connections with limbic and, by extension, hypothalamic structures, it provides input to subconscious mechanisms related to emotions, memory, and sexual behavior.
but ganglion cells respond by generating action potentials.
5.
The axons of ganglion cells in the temporal retina project to the brain ipsilaterally; those in the nasal retina cross in the optic chiasm. Because the lens inverts the image that falls on the retina, each side of the visual field is projected to the contralateral side of the brain for both eyes. In the lateral geniculate nucleus (LGN) of the thalamus, the input from each eye terminates in separate layers, and the M ganglion cells (sensitive to movement) and P ganglion cells (sensitive to detail and color) project to separate layers as well.
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The LGN projects to primary visual (striate) cortex via the visual radiation and terminates largely in layer 4, where there is an orderly retinotopic map. Within the map, information from each eye maps to alternating adjacent points to create ocular dominance columns that extend vertically in the cortex. Striate cortical neurons outside of layer 4 respond best to bar or edge stimuli oriented in a particular way. Cells that “prefer” a particular stimulus orientation are grouped in orientation columns.
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The extrastriate visual areas have different functions. Some in the inferotemporal cortex are influenced chiefly by P cells, and they function in form detection, color vision, and face discrimination. M cells influence regions of the middle temporal and parietal cortex, which function in motion detection and the control of eye movements.
8.
A pure tone is characterized in terms of its amplitude, frequency, and phase. Natural sounds are combinations of pure tones. Sound pressure is measured in decibels (dB), in relation to a reference level.
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The pinna and auditory canal convey airborne sound waves to the tympanic membrane. The three small bones (ossicles) of the middle ear transmit the vibrations of the tympanic membrane to the oval window of the fluid-filled inner ear. Hearing is most sensitive at about 3000 Hz because of the dimensions of the auditory canal and the mechanics of the ossicles.
10.
The cochlea of the inner ear has three main compartments: the scala vestibuli, the scala tympani, and the intervening scala media (cochlear duct). The cochlear duct is bounded on one side by the basilar membrane, on which lies the organ of Corti, the sound transduction mechanism.
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