Biology 220 Anatomy Physiology I Unit X SPECIAL

Biology 220 Anatomy & Physiology I Unit X SPECIAL SENSES Chapter 16 pp. 558 - 607 E. Gorski/ E. Lathrop-Davis/ S. Kabrhel

Special Senses • • • Vision Hearing Equilibrium Taste Smell

Vision 1. Location – receptors found in retina of eye (70% of all sensory receptors in the body) 2. Structure/receptors – rods - respond to light intensity (shades of gray) – cones - respond to light of specific wavelengths (color vision) ° Visible light = 400 - 700 nm Fig. 16. 13, p. 574

Vision 3. Nerve pathway – optic nerve carries impulse from eye (enters cranium through optic foramen) – fibers from medial portion of retina cross over at optic chiasma – fibers continue toward thalamus via optic tracts (some fibers to superior colliculi - visual reflex) 4. Relays (synapses) – fibers synapse in thalamus (lateral geniculate bodies) and are relayed to primary visual cortex

Vision 5. Final destinations – primary visual cortex on posterior medial occipital lobe – visual association area allows recognition of shapes, objects, letters, etc.

Visual Fields of the Eyes Fig. 16. 12, p. 584

Visual Fields Defects Right eye 1. 1 2 2. 3 3. 4. 4 Left eye

Hearing 1. Location – receptors found in inner ear 2. Structure/receptors – organ of Corti ° found in cochlea of inner ear ° contains “hairs” that respond to vibration 3. Nerve pathway – cochlear branch of vestibulocochlear nerve carries impulses from inner ear; enters cranial cavity through internal auditory meatus Fig. 16. 24, p. 587; Fig. 16. 27, p. 590

Hearing 4. Synapses – fibers synapse in medulla oblongata (twice) – fibers from medulla synapse in inferior colliculus (midbrain) – fibers from inferior colliculus synapse in thalamus and are relayed to primary auditory cortex 5. Final destination – primary auditory cortex (on temporal lobe) Fig. 16. 33, p. 595

Hearing Transmission of sound: • airborne sound enters external auditory canal --> strikes tympanic membrane causing vibration • vibration amplified by ossicles (malleus, incus, stapes) in middle ear and transferred to oval window • perilymph in inner ear moves basilar membrane --> endolymph in cochlear duct disturbed • hair cells of Organ of Corti pushed up against the tectorial membrane and stimulated --> send impulses through cochlear branch of vestibulocochlear nerve • pressure relieved when pressure waves enter scala vestibuli, move through and are relieved at round window

Cochlea/Resonance of Membrane Amplitude -intensity (energy) • healthy adult can pick up sounds between 1 -120 d. B – 130 d. B - pain Frequency - number of waves/time • range of human 20 -20, 000 Hz • most sensitive to 1500 -4000 Hz – low frequency sounds to apex – high frequency sounds to base Fig. 16. 31, p. 594

Equilibrium 1. Location - inner ear 2. Structure/receptors – receptors in utricle and saccule for static equilibrium (head position, linear acceleration changes in speed and direction) – receptors in semicircular canals for dynamic equilibrium (rotatory movements) Fig. 16. 34, p. 597

Equilibrium 3. Nerve pathways – vestibular branch of vestibulocochlear nerve carries impulse to brainstem (medulla) 4. Synapses - complex pathways 5. Final destinations – cerebellum – brain stem

Taste (Gustation) 1. 2. Location - oral cavity (mostly in papillae of tongue) Structures/receptors - chemoreceptors (respond to chemicals dissolved in saliva) 3. Nerve pathways from taste buds in: • mouth/tongue: facial (anterior 2/3 of tongue) and glossopharyngeal (posterior 1/3) • lower pharynx and epiglottis: vagus Fig. 16. 1, p. 560

Taste 4. Synapses – facial, glossopharyngeal and vagus nerves carry impulses to medulla – some fibers from medulla synapse with parasympathetic fibers to initiate reflexes for saliva and gastric juice secretion (also gagging or vomiting) – other fibers from medulla carry impulses to thalamus – fibers from thalamus carry impulses to gustatory area (parietal lobe), hypothalamus and cerebral limbic system

Taste 5. Final destinations: – gustatory area (parietal lobe), hypothalamus and cerebral limbic system • NOTE: – receptors for taste and smell complement each other and respond to many of the same stimuli – most (~80%) of what we call taste is really smell – mouth also contains: thermoreceptors, mechanoreceptors, nociceptors (carried by trigeminal nerve)

Smell (Olfaction) 1. Location – nasal mucosa in roof of nasal cavity 2. Structure/receptors – olfactory receptor cells in nasal mucosa (nerve I) – olfactory cilia (increase receptive surface area) • NOTE: these neurons (olfactory receptor cells) reproduce Fig. 16. 2, p. 562

Smell 3. Nerve – olfactory nerves enter cranium through olfactory foramina of cribriform plate (of the ethmoid bone) 4. Synapses – olfactory nerves synapse with neurons in olfactory bulb – fibers from olfactory bulb run through olfactory tracts – olfactory tracts carry impulses to thalamus or to other parts of the limbic system – fibers from thalamus eventually reach olfactory cortex of temporal lobe

Smell 5. Final destinations – limbic system (for emotional response to smell) – olfactory cortex of temporal lobe (for smell recognition)