The Senses The General Senses Sensory receptors Specialized

The Senses

The General Senses Sensory receptors— • Specialized cells or cell processes that monitor external or internal conditions • Simplest are free nerve endings. Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The General Senses • Adaptation— • Reduction in sensitivity at a receptor or along a sensory pathway in the presence of a constant stimulus Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The General Senses General senses— • Temperature, pain, touch, pressure, vibration • Receptors located throughout the body Special senses— • Smell, taste, vision, balance, hearing • Receptors located in sense organs (e. g. , ear, eye). Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The General Senses Temperature • Thermoreceptors detect temperature change • Free nerve endings • Found in dermis, skeletal muscle, liver, hypothalamus • Fast adapting Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

Touch, Pressure, and Position • Mechanoreceptors—Receptors that respond to physical distortion of their cell membranes. • Tactile receptors— • Sense touch, pressure, or vibration • Baroreceptors— • Sense pressure changes in walls of blood vessels, digestive organs, bladder, lungs • Proprioceptors— • Respond to positions of joints and muscle Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The General Senses Chemoreceptors • respond to chemicals dissolved in body fluids that surround them and monitor the chemical composition of blood and tissues • Carbon dioxide, Oxygen, Hydrogen ion Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The Special Senses—Smell • Olfactory Organs • Sense of smell • Detect: • scent • pheromones Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The Special Senses—Taste (Gustatory) Receptors • Taste buds • Found within papillae on tongue, pharynx, larynx • Sense salt, sweet, sour, bitter Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The Special Senses—Vision Visual Physiology • Photoreceptors—Cells specialized to respond to photons, packets of light energy • Two types of photoreceptors • Rods • Highly sensitive, non-color vision • Cones • Less sensitive, color vision • Site of sharpest vision Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

The Special Senses—Vision The Visual Pathway • • Ganglion cells axon converge at optic disc Axons leave as optic nerve (CN II) Synapse in thalamus Thalamic neurons project to visual cortex • Located in occipital lobes Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

Equilibrium and Hearing Sensory Functions of the Inner Ear • Equillibrium • Hearing Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

Equilibrium and Hearing Receptors of the Inner Ear • Hair cells • Mechanoreceptors • Stereocilia on cell surface • Bending excites/inhibits hair cell Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

External acoustic canal Movement of sound waves Tympanic membrane Sound waves arrive at tympanic membrane. Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 9 -27 2 of 7

External acoustic Incus canal Malleus Stapes Movement of sound waves Tympanic membrane Sound waves arrive at tympanic membrane. Movement of tympanic membrane causes displacement of the auditory ossicles. Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 9 -27 3 of 7

External acoustic Incus Oval canal Malleus Stapes window Movement of sound waves Tympanic membrane Sound waves arrive at tympanic membrane. Movement of tympanic membrane causes displacement of the auditory ossicles. Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct. Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 9 -27 4 of 7

External acoustic Incus Oval canal Malleus Stapes window Movement of sound waves Tympanic membrane Sound waves arrive at tympanic membrane. Movement of tympanic membrane causes displacement of the auditory ossicles. Round window Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct. The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct. Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings Figure 9 -27 5 of 7

External acoustic Incus Oval canal Malleus Stapes window Vestibular duct (perilymph) Movement of sound waves Vestibular membrane Cochlear duct (endolymph) Basilar membrane Tympanic duct (perilymph) Tympanic membrane Sound waves arrive at tympanic membrane. Movement of tympanic membrane causes displacement of the auditory ossicles. Round window Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct. The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct. Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings Vibrations of the basilar membrane causes vibration of hair cells against the tectorial membrane. Figure 9 -27 6 of 7

External acoustic Incus Oval canal Malleus Stapes window Cochlear branch of cranial nerve VIII Vestibular duct (perilymph) Movement of sound waves Vestibular membrane Cochlear duct (endolymph) Basilar membrane Tympanic duct (perilymph) Tympanic membrane Sound waves arrive at tympanic membrane. Movement of tympanic membrane causes displacement of the auditory ossicles. Round window Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct. The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct. Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings Vibrations of the basilar membrane causes vibration of hair cells against the tectorial membrane. Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve VIII. Figure 9 -27 7 of 7

Equilibrium and Hearing Auditory Pathways • Hair cells excite sensory neurons • Sensory neurons located in spiral ganglion • Afferent axons form cochlear branch of vestibulocochlear nerve (CN VIII) • Synapses in cochlear nucleus in medulla • Neurons relay to midbrain • Midbrain relays to thalamus • Thalamus relays to auditory cortex (temporal lobe) in a frequency map Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings

Aging and the Senses Impact of Aging on Sensory Ability • Gradual reduction in smell and taste sensitivity as receptors are lost • Lens changes lead to presbyopia (loss of near vision) • Chance of cataract increases • Progressive loss of hearing sensitivity as receptors are lost (presbycusis) Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings