Special Senses • Special sensory receptors – Distinct, localized receptor cells in head • Vision - 70% of body's sensory receptors in eye • Taste • Smell • Hearing • Equilibrium
The Eye and Accessory Structures
The Lacrimal Apparatus
Sense of Vision Ora serrata Sclera Ciliary body Choroid Ciliary zonule (suspensory Retina ligament) Macula lutea Cornea Fovea centralis Iris Posterior pole Pupil Optic nerve Anterior pole Anterior segment (contains aqueous humor) Lens Central artery and Scleral venous sinus vein of the retina Optic disc Posterior segment (blind spot) (contains vitreous humor) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball.
Circulation of Aqueous Humor
Inner Layer: Retina • Delicate two-layered membrane – Outer Pigmented layer • Absorbs light and prevents its scattering • Phagocytize photoreceptor cell fragments • Stores vitamin A – Inner Neural layer • Transparent • Composed of three main types of neurons – Photoreceptors, bipolar cells, ganglion cells • Signals spread from photoreceptors to bipolar cells to ganglion cells • Ganglion cell axons exit eye as optic nerve
Figure 15.6c Microscopic anatomy of the retina. Choroid Outer segments of rods and cones Nuclei of ganglion cells Nuclei of Nuclei of Axons of Pigmented bipolar rods and ganglion cells layer of retina cells cones Photomicrograph of retina
Figure 15.15a Photoreceptors of the retina. Process of bipolar cell Synaptic terminals Inner fibers Rod cell body Rod cell body Nuclei Cone cell body Mitochondria Outer fiber segment Connecting cilia Inner Outer segment Apical microvillus Pigmented layer Discs containing visual pigments Discs being phagocytized The outer segments of rods and cones Melanin are embedded in the Pigment cell nucleus granules pigmented layer of Basal lamina (border the retina. with choroid)
Chemistry Of Visual Pigments • Retinal – Light-absorbing molecule that combines with one of four proteins ( opsins ) to form visual pigments – Synthesized from vitamin A – Retinal isomers : 11- cis -retinal (bent form) and all- trans -retinal (straight form) • Bent form → straight form when pigment absorbs light • Conversion of bent to straight initiates reactions → electrical impulses along optic nerve
Figure 15.18 Signal transmission in the retina (1 of 2). Slide 1 In the dark cGMP-gated channels 1 Na + open, allowing cation influx. Ca 2+ Photoreceptor depolarizes. Voltage-gated Ca 2+ 2 Photoreceptor channels open in synaptic cell (rod) terminals. −40 mV −40 mV 3 Neurotransmitter is Ca 2+ released continuously. 4 Neurotransmitter causes IPSPs in bipolar cell. Hyperpolarization results. Bipolar Hyperpolarization closes 5 voltage-gated Ca 2+ channels, Cell inhibiting neurotransmitter release. 6 No EPSPs occur in ganglion cell. Ganglion cell No action potentials occur 7 along the optic nerve.
Figure 15.18 Signal transmission in the retina. (2 of 2). Slide 1 Below, we look at a tiny column of retina. The outer segment of the rod, closest to the back of the eye and farthest from the incoming light, is at the top. In the light 1 cGMP-gated channels Light close, so cation influx Light stops. Photoreceptor hyperpolarizes. Photoreceptor Voltage-gated Ca 2+ 2 cell (rod) channels close in synaptic terminals. −70 mV −70 mV No neurotransmitter 3 is released. Lack of IPSPs in bipolar 4 cell results in depolarization. 5 Depolarization opens Bipolar voltage-gated Ca 2+ channels; Cell neurotransmitter is released. Ca 2+ EPSPs occur in ganglion 6 cell. 7 Action potentials propagate along the Ganglion optic nerve. cell
Figure 15.15b Photoreceptors of the retina. 11- cis -retinal 2H + Rod discs Oxidation Vitamin A 11- cis -retinal Rhodopsin Reduction Dark 2H + Light Visual Opsin and pigment All- trans - consists of retinal • Retinal • Opsin Rhodopsin, the visual pigment in rods, All- trans -retinal is embedded in the membrane that forms discs in the outer segment.
Figure 15.17 Events of phototransduction. Slide 6 Recall from Chapter 3 that G protein signaling mechanisms are like a molecular relay race. Light 2nd Receptor G protein Enzyme Retinal absorbs light 1 (1st messenger and changes shape. messenger) Visual pigment activates. Phosphodiesterase (PDE) Visual pigment All- trans -retinal Light cGMP-gated cGMP-gated cation cation channel channel open in 11- cis -retinal closed in dark Transducin light (a G protein) 3 Transducin PDE converts 2 Visual pigment 4 5 As cGMP levels fall, activates cGMP into GMP, activates cGMP-gated cation phosphodiesteras causing cGMP transducin channels close, resulting e (PDE). levels to fall. (G protein). in hyperpolarization.
Visual Pathway to the Brain and Visual Fields, Inferior View
Olfactory Epithelium and the Sense of Smell • Olfactory epithelium in roof of nasal cavity – Covers superior nasal conchae – Contains olfactory sensory neurons • Bipolar neurons with radiating olfactory cilia • Supporting cells surround and cushion olfactory receptor cells – Olfactory stem cells lie at base of epithelium • Bundles of nonmyelinated axons of olfactory receptor cells form olfactory nerve (cranial nerve I)
Figure 15.20a Olfactory receptors. Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air
Figure 15.20b Olfactory receptors. Olfactory Mitral cell tract (output cell) Glomeruli Olfactory bulb Cribriform plate of ethmoid bone Filaments of olfactory nerve Lamina propria Olfactory connective tissue gland Olfactory axon Olfactory stem cell Olfactory sensory Olfactory neuron epithelium Supporting cell Dendrite Olfactory cilia Mucus Route of inhaled air containing odor molecules
Figure 15.21 Olfactory transduction process. Slide 1 1 Odorant binds to its receptor. Odorant Adenylate cyclase G protein (G olf ) cAMP cAMP Open cAMP-gated cation channel Receptor GDP Receptor 2 G protein 3 Adenylate cAMP opens a 4 5 activates G activates cyclase converts cation channel, allowing Na + and protein (G olf ). adenylate ATP to cAMP. Ca 2+ influx and cyclase. causing depolarization.
Taste Buds and the Sense of Taste • Receptor organs are taste buds – Most of 10,000 taste buds on tongue papillae • On tops of fungiform papillae • On side walls of foliate and vallate papillae – Few on soft palate, cheeks, pharynx, epiglottis
Figure 15.22a Location and structure of taste buds on the tongue. Epiglottis Palatine tonsil Lingual tonsil To taste, chemicals Foliate papillae must – Be dissolved in saliva – Diffuse into taste pore – Contact gustatory Fungiform papillae hairs Taste buds are associated with fungiform, foliate, and vallate papillae.
Location and Structure of Taste Buds on the Tongue
Figure 15.22c Location and structure of taste buds on the tongue. Connective tissue Gustatory hair Taste fibers of cranial nerve Stratified Gustatory Basal Taste squamous epithelial epithelial pore epithelium cells cells of tongue Enlarged view of a taste bud (210x).
Basic Taste Sensations • There are five basic taste sensations 1. Sweet — sugars, saccharin, alcohol, some amino acids, some lead salts 2. Sour — hydrogen ions in solution 3. Salty — metal ions (inorganic salts) 4. Bitter — alkaloids such as quinine and nicotine; aspirin 5. Umami — amino acids glutamate and aspartate
Basic Taste Sensations • Possible sixth taste – Growing evidence humans can taste long- chain fatty acids from lipids – Perhaps explain liking of fatty foods • Taste likes/dislikes have homeostatic value – Guide intake of beneficial and potentially harmful substances
The Gustatory Pathway
The Ear: Hearing and Balance Three major areas of ear 1. External (outer) ear – hearing only 2. Middle ear (tympanic cavity) – hearing only 3. Internal (inner) ear – hearing and equilibrium • Receptors for hearing and balance respond to separate stimuli • Are activated independently
Structure of the Ear (1 of 2) Figure 15.24a Structure of the ear.
Structure of the Ear (2 of 2) Figure 15.24b Structure of the ear.
The Three Auditory Ossicles and Associated Skeletal Muscles Figure 15.25 The three auditory ossicles and associated skeletal muscles.
Membranous Labyrinth of the Internal Ear
Anatomy of the Cochlea
Anatomy of the Cochlea
Anatomy of the Cochlea
Transmission of Sound to the Internal Ear • Sound waves vibrate tympanic membrane • Ossicles vibrate and amplify pressure at oval window • Cochlear fluid set into wave motion • Pressure waves move through perilymph of scala vestibuli
Transmission of Sound to the Internal Ear • Waves with frequencies below threshold of hearing travel through helicotrema and scali tympani to round window • Sounds in hearing range go through cochlear duct, vibrating basilar membrane at specific location, according to frequency of sound
Pathway of Sound Waves • HIGH frequency sound detected here LOW frequency sound detected here
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