Lecture Notes - Chapter 17 PDF

**[Lecture Notes - Chapter 17]** **Introduction** - **Five *Special* *Senses*** 1. **Olfaction (smell)** 2. **Gustation (taste)** 3. **Vision (sight)** 4. **Equilibrium (balance)** 5. **Hearing (sound)** **17-1 -- Olfaction** = Sense of SMELL - **Olfactory Organ...

**[Lecture Notes - Chapter 17]** **Introduction** - **Five *Special* *Senses*** 1. **Olfaction (smell)** 2. **Gustation (taste)** 3. **Vision (sight)** 4. **Equilibrium (balance)** 5. **Hearing (sound)** **17-1 -- Olfaction** = Sense of SMELL - **Olfactory Organs** provide the sense of smell - Located in the nasal cavity - Paired -- one on either side of the nasal septum - Made up of two layers: 1. **Lamina propria** - Areolar connective tissue, blood vessels, and nerves - **Olfactory** **glands** - Produce secretions (mucus) that coat the surface of the olfactory organs 2. **Olfactory** **epithelium** - Has three types of cells a. Basal cells -- stem cells that divide & replenish the epithelium b. Supporting cells c. **Olfactory receptor cells** - - - - - - Olfactory reception involves detecting chemicals (**odorants**) which [dissolve] in the nasal mucous and interact with odorant-binding proteins on the olfactory receptor cells - **Olfactory Pathways** 1. Axons leave the **olfactory epithelium** and collect into 20 or more bundles (**olfactory nerves**) that penetrate cribriform plate of the ethmoid bone 2. Synapse with neurons in the **olfactory bulbs** 3. Axons leaving olfactory bulb travel along **olfactory tract** and extend directly to the olfactory cortex\* in the uncus of the temporal lobe, the hypothalamus, and portions of limbic system. - *Smell is the [only] sensation that reaches the cerebral cortex directly without having to pass through the thalamus* **17-2 -- Gustation** = Sense of TASTE - The sense of taste provides - information about the foods and liquids consumed - motivation to take in nutrients - The superior surface of the tongue contains epithelial projections called **lingual papillae** - Four Types of Lingual Papillae 1. **Filiform** **papillae** - Found on the anterior 2/3 of tongue - Provide friction to move food around mouth - The only type of papilla that does [not] contain taste buds 1. **Fungiform** **papillae \*** -- named for their "mushroom" shape - Scattered with a wide distribution on the tongue 2. **Vallate or Circumvallate** **papillae** \* - There are about 12 of these very large papilla on the tongue (form a "V" near the posterior margin of tongue). 3. **Foliate** **papillae** \* - Folds found on lateral margins of tongue - Except for filiform papillae, all lingual papillae contain **taste buds** - **Taste buds** are clusters of cells distributed on the tongue and portions of pharynx & epiglottis. - **Three types of cells are found in a taste bud:** a. **Basal cells are stem cells** that divide and replace old and worn out cells b. **Transitional cells** are immature gustatory receptor cells c. **Gustatory receptor cells** are specialized epithelial cells that associate with a sensory nerve ending - Survive only 10 days before replacement - Extend their **taste hairs** through the **taste** **pore of a taste bud** - **Taste hairs contact the food and contain either** - **Salt or sour ion channels or** - Na+ and H+ ions diffuse into the cell via leak channels, depolarizing the cell - **Sweet, bitter, or umami receptors** - Chemicals in food bind to receptors that are linked to G proteins called **gustducins**, activating a 2^nd^ messenger to ultimately stimulate the release of neurotransmitters - Gustatory Pathway 4. Neurotransmitters are released by gustatory receptor cell 5. Action potentials travel through sensory neurons in cranial nerves: - **Facial nerve VII** -- Anterior 2/3 of tongue - **Glossopharyngeal nerve IX** -- Posterior 1/3 of tongue - **Vagus nerve X** -- Pharynx & Epiglottis 6. Information travels to thalamus and then the gustatory cortex of the insula - Gustatory Discrimination is the result of 7. Four **primary** **taste** **sensations:** **Sweet**, s**alty**, s**our**, b**itter** 8. Additional Human Taste Sensations - **Umami** - Pleasant, savory taste imparted by the amino acid glutamate - **Water** - Detected by **water** **receptors** in the pharynx 9. **Temperature and texture of the food** - **This information is carried by the Trigeminal nerve V** 10. **The combination of taste and smell is important in order to experience the full flavor of foods** - Taste Sensitivity differs significantly among individuals 11. Many conditions may affect one's ability to taste - Some are condition-related - *For example: colds or nerve damage* - Some are inherited - *For example: 70 percent of Caucasians can taste phenylthiocarbamide (PTC) it but 30 percent do not* - Some are age-related - The number of taste buds begins declining rapidly at age 50, which is why elderly individuals may find their food bland **17-3 -- Eye Anatomy** - Provide protection, lubrication, and support - Include: 1. The **palpebrae** (eyelids) - Blinking keeps surface of eye lubricated and free of dust and debris - **Palpebral** **fissure** - Gap between the upper and lower eyelids that exposes the eyeball - **Medial** **angle (commissure)** and **lateral** **angle (commissure)** - Where two eyelids are connected - **Lacrimal** **caruncle** - Mass of soft tissue at the medial angle that contains glands that produce the thick whitish secretions that appears after sleep - **Eyelashes** - Hairs that prevent foreign matter from reaching surface of eye - **Tarsal** **glands** - Large sebaceous glands associated with the eyelashes - Secrete lipid-rich product that helps keep eyelids from sticking together 2. The **conjunctiva** - superficial epithelium of eye - **Paplebral conjunctiva** is the epithelium covering inner surfaces of eyelids - **Bulbar conjunctiva** is the epithelium covering the anterior surface of the eye except for the cornea - **Conjunctivitis** (pinkeye) - Inflammation of conjunctiva 3. The **lacrimal apparatus** - Produces, distributes, and removes tears - **Lacrimal** **gland** (tear gland) - Produces secretions (tears) containing lysozyme, an antibacterial enzyme - Lacrimal ducts empty tears onto the surface of the eye - Pass from lateral \> medial, draining into: - **Lacrimal puncta (**2 small openings) \> **Lacrimal canaliculi** \> **Lacrimal sac** \> **Nasolacrimal duct** \> nasal cavity - **Orbital fat** - Cushions and insulates each eye - Three Layers of the Eye Wall 1. ***Fibrous* *layer (fibrous tunic)*** - **Cornea** -- transparent anterior section - **Sclera** -- white posterior section that extends from the cornea posteriorly - whites of the eye 2. ***Vascular* *layer (vascular tunic or uvea)*** A. **Iris** - The most anterior part of the vascular tunic - Contains blood vessels, melanocytes (give eye its color) - Contains 2 pupillary muscles (smooth muscles) that regulate the amount of light entering the eye by changing the diameter of **pupil** (central opening of iris) - **Pupillary [dilator] muscle -- sympathetic control** - **Pupillary [constrictor] muscle -- parasympathetic control** B. **Ciliary** **Body** - **ciliary** **processes -** secretes aqueous humor - **ciliary** **muscle** - hold the lens in place via **suspensory** **ligaments** - control the shape of the lens for focusing C. **Choroid** - Middle vascular layer posterior to the **ora serrata** - Jagged boundary between the ciliary body and the choroid - Provides route for blood vessels and lymphatics that supply tissues of eye, including the retina 3. **Sensory Layer** or **Retina** A. **Pigmented Layer** - Outer layer containing pigments that absorb light, preventing light scatter B. **Neural Layer** - Contains three layers of neurons i. **Visual receptors** (photoreceptors) - **Rods** - Highly sensitive to light but do not discriminate between colors - **Cones** - Provide color vision - Rods & cones converge and synapse on **bipolar** **cells** ii. **Bipolar cells** - Bipolar cells converge and synapse on **ganglion** **cells** iii. **Ganglion cells** - Axons converge at the optic disc - Horizontal and Amacrine cells facilitate or inhibit communication between photoreceptors & ganglion cells to alter sensitivity of retina - Specific areas of the retina: - **Macula lutea** - Contains a very dense concentration of cones but no rods - **Fovea centralis** is a pit in the middle of the macula - Highest concentration of cones thus the site of sharpest color vision (highest visual acuity) - When you focus on an image, THIS is where it lands for clear, sharp vision - Deterioration of the macula lutea is known as **macular degeneration** - - **Optic** **Disc** - Circular region just medial to the fovea - Where ganglion cell axons converge; origin of the optic nerve - Commonly called the **blind** **spot** because there are no photoreceptors (rods or cones) in this area - The Cavities of the Eye - The ciliary body and the lens divide the eye into two cavities: 1. Large **posterior** **cavity** - Filled with **vitreous body** - Gelatinous mass formed during embryonic development - Helps stabilize eye shape and supports retina - Collections of "debris" (cells) in the vitreous body can cast shadows on the retina known as **floaters** 2. Smaller **anterior** **cavity** - Has an **Anterior chamber** - Extends from cornea to iris - Has a **Posterior chamber** - Between iris and the lens - Filled with **aqueous humor** - Aqueous humor is continuously produced by capillaries in the **ciliary process** of the **ciliary body** - Released into the posterior chamber and circulates to anterior chamber - Drains from anterior chamber into **scleral** **venous** **sinus** (*canal* *of* *Schlemm*) to re-enter circulation - **Aqueous humor generates intraocular** **pressure** - Helps retain eye shape - When aqueous humor cannot drain intraocular pressure can get dangerously high causing **glaucoma** - **Pressure on the optic nerve that can lead to blindness** - The **Lens** - A transparent, biconvex, flexible disc posterior to the cornea - Made of - Outer capsule with elastic fibers - Keep the lens rounded unless a force is applied - Inner cells called **lens** **fibers** - Long, thin, transparent cells in the interior of the lens - Filled with proteins called **crystallins**, which provide clarity and focusing power to lens - **Cataract** - Condition in which the lens has lost its transparency **17-4 -- Focusing** - We rely more on **vision** than on any other special sense - Clear vision involves light being refracted (bent) in order to focus the image on the retina - Light is refracted (bent) by: 1. **Cornea** - **Does the majority of light refraction. [More than the lens!]** 2. **Aqueous humor** 3. **Lens** - - - - - - - - - - - - 4. **Vitreous body** (vitreous humor) - **Image reversal** - The image that arrives at the retina is - Upside down - Reversed left to right - The brain compensates for this - **Astigmatism** - Condition where light passing through cornea and lens is not refracted properly - Visual image is distorted - Can be caused by irregularities in the surface of the cornea or the lens - **Visual** **acuity** - Clarity of vision (how well you see) - Your vision is rated, by comparison, to a "normal" scale: - 20/20 means that you can see clearly at 20 feet what should be normally be seen at 20 feet - 20/40 means that you have to stand 20 ft from an object to see details that a person with normal vision can see from 40 ft away - 20/15 means that you can see details at 20 feet that a person with normal vision can only see at 15 feet away - **Behavioral optometry** - The use of eye exercises and lenses to improve various visual problems - "Physical therapy" for the eye - Methods are not used in conventional optometry and the practice is considered to be unorthodox **17-5 -- Visual Physiology** - The retina contains - 6 million **cones** - For color vision in bright light - Have characteristic ranges of sensitivity - **Red cones -- 74%** - **Green cones -- 16%** - **Blue** **cones -- 10%** - Their stimulation in various combinations is the basis for color vision - 120 million **rods** - For dim light conditions - Rods respond to almost any photon, regardless of the wavelength - Provide information about the presence of absence of light energy, but not specific colors - Anatomy of Rods and Cones A. **Outer segment** with membranous discs - Discs contain **visual** **pigments** - Is where light absorption occurs - Pigments are derivatives of **rhodopsin** - **Retinal** is synthesized from **vitamin A** - Rods and cones - All have the same pigment (retinal) - But have different opsins - Rods -- Have only one opsin which is sensitive to photons without much regard to wavelength - Cones -- each type of cone has a different opsin & thus is sensitive to different wavelengths of light - **Night blindness** - Vitamin A deficiency causes a decrease in the amount of visual pigments in the photoreceptors - The loss of vision is more apparent at night B. **Stalk** - A narrow stalk connects outer segment to inner segment C. **Inner segment** - Contains the metabolic machinery of the cell - **Photoreception** - **Resting State** (Darkness) - Na+ channels remain open, causing **dark current** - Na+ ions flow into outer segment, then to the inner segment, then out of the cell - Constant influx of Na+ ions causes membrane potential to be about -40 mV - Cell is constantly at threshold - action potentials are continuously generated and cause the photoreceptor to continuously release neurotransmitter - **Active State** (Light) - A photon of light strikes the retinal portion of rhodopsin molecule embedded in membrane of disc 1. Opsin is activated 2. Intracellular signaling takes place and causes..... 3. Na+ channels to close 4. Dark current decreases and the membrane potential moves towards -70 mV - Cell is no longer at threshold and less action potentials occur and thus a reduction in release of neurotransmitter to the bipolar cell - THE [DECREASE] IN NEUROTRANSMITTER IS A SIGNAL TO THE BIPOLAR CELL THAT THE PHOTORECPTOR HAS ABSORBED A PHOTON! [ ] - Recovery after Stimulation - **Bleaching** - After absorbing a photon of light, rhodopsin molecule breaks down into retinal and opsin - Contributes to the lingering visual image (ghost image) after a camera flash - Eventually retinal is converted to its original shape and rhodopsin is reassembled - Requires ATP & takes time - Adaptation to Light or Dark Conditions - The sensitivity of the visual system varies with the intensity of illumination - **Dark-adapted state** - After about 30 minutes of darkness, visual pigments fully recover from bleaching - Photoreceptors are all restored and ready to respond - The visual system is extremely sensitive in this state = night vision! - If just 7 rods absorb photons, you'll see a flash of light - **Light-adapted state** - Initial exposure to light is unbearably bright - Sensitivity decreases as bleaching occurs - Eventually the rate of bleaching is balanced by the rate at which the visual pigments reassemble - Constriction of pupils by the *pupillary constrictor reflex* also reduces the amount light entering the eye - **The Visual Pathway** 1. Begin at photoreceptors which synapse with bipolar cells 2. Bipolar cells synapse with ganglion cells 3. Axons from ganglion cells converge on **optic disc** and penetrate the wall of eye 4. Proceed toward diencephalon as **optic nerve (II)** 5. Two optic nerves (one for each eye) reach diencephalon at the **optic chiasm** - Half of the fibers cross over to the opposite side of the brain 6. Proceed along the **optic tracts** towards the lateral geniculate nucleus of the **thalamus** 7. **Optic radiation** - Bundle of projection fibers linking the thalamus with visual cortex 7. End at **visual cortex** of cerebral hemispheres - The visual cortex in each hemisphere receives: - Visual information from the medial half of the field of vision from the eye on the SAME side - Visual information from the lateral half of the field of vision from the eye on the OPPOSITE side - Processing of Visual Information in the Visual Cortex - You perceive an image due to integration of this information arriving at the visual cortex. - When you look straight ahead the visual images from your left and right eyes overlap and the combined area is your **Field of Vision** - **Depth perception** is the ability to judge depth or distance by interpreting the 3-D relationships among objects in view - Obtained by comparing relative positions of objects within the images received by your two eyes (between left-eye and right-eye images) - Visual Processing in Other Areas of the Brain - Many areas of the brain receive visual information - **Superior collicuili** -- visual reflex center in the midbrain - **Pineal gland** - an endocrine gland in the epithalamus of the diencephalon - receives visual information in order to establish **circadian rhythms** - Is tied to day--night cycles via secretion of **melatonin** - Affects other metabolic processes, such as reproductive cycles **17-6 -- The Ear** 1. **External** **Ear** A. **Auricle** or **pinna** - Surrounds and protects the entrance to the **external** **acoustic** **meatus** - Channels sound waves towards the external acoustic meatus B. **External acoustic meatus (auditory canal)** - **Extends from the auricle to the** tympanic membrane - **Contains ceruminous** **glands** - Integumentary glands that secrete a waxy material (**cerumen**) - In combination with hairs, cerumen keeps foreign objects away from the tympanic membrane - Slows growth of microorganisms, reducing the risk of infection C. **Tympanic** **membrane** (eardrum) - Is a thin, semitransparent sheet - Separates external ear from middle ear - The tympanic membrane vibrates when sound waves hit it - Converts the energy in sound waves into vibrations 2. The **Middle Ear (tympanic cavity)** - Air filled chamber in the temporal bone - Communicates with nasopharynx via the **auditory** **tube** (Eustachian tube) - Permits the equalization of pressure on either side of tympanic membrane - Encloses and protects three auditory ossicles 1. **Malleus** (hammer) 2. **Incus** (anvil) 3. **Stapes** (stirrup) - They are the smallest bones in the body - Transmit vibrations from the tympanic membrane to the oval window - **Oval** **window** - Receives vibrations from the stapes and converts them into waves that travel through the cochlea - **Round** **window** - Allows pressure to be relieved from the cochlea - Infection in the middle ear is called **otitis media** 3. The **Inner Ear** - A **bony** **labyrinth** surrounds and protects a **membranous** **labyrinth** - Between the bony labyrinth and the membranous labyrinth is a fluid called **perilymph** - The membranous labyrinth contains a fluid called **endolymph** - Produced in the cochlear duct - Excess endolymph drains into the **endolymphatic** **duct** and is reabsorbed in the **endolymphatic** **sac** - The inner ear consists of three areas: the **vestibule**, the **semicircular canals**, and the **cochlea**: - The **vestibular complex** is the combination of the **vestibule** and the **semicircular canals** - For sensations of EQUILIBRIUM - The **cochlea** - For sensations of HEARING - The sensory receptors in all three sensory areas of the inner ear are called **hair cells** - They are separate receptor cells that associated with sensory neurons - Have stereocilia ("hairs") - When they bend, receptor output changes - Bend towards **kinocilium**, rate of action potentials increases - Bend away from kinocilium, rate of action potentials decreases 1. **Vestibule** - Contains **saccule** and **utricle** - - - - - - Crystals of calcium carbonate, called **otoliths** ("earstones"), sit on top of the hair cells - Tilting the head (via force of gravity) or linear acceleration causes the otoliths to shift to the side, bending the "hairs" - The hair cells in the **utricle** are sensitive to changes in [horizontal] movement & linear acceleration - The hair cells in the **saccule** are sensitive to changes in [vertical] movement & linear acceleration 2. **Semicircular canals** - Contains **semicircular ducts** - **Receptors provide information about DYNAMIC EQUILIBRIUM** stimulated by rotations of the head - **At the base of each semicircular** duct there is an expanded region called the **ampulla** - The hair cells are located in a structure the **crista ampullaris of the ampulla** - The "hairs" are embedded in a gelatinous **cupula** - When the head rotates, endolymph in the semicircular ducts lags behind, causing the cupula to bend, which in turn bends the "hairs" - Nodding stimulates the anterior semicircular duct - Shaking the head "no" stimulates the lateral semicircular duct - Tilting your head to the side stimulates the posterior semicircular duct 1. 2. - Relays information to the cerebellum - Relays information to motor nuclei in the brainstem and spinal cord - Relays information to the cerebral cortex for conscious awareness - Relays information to the superior colliculi - - - If spinning rapidly, eye jumps from point to point - - 3. **Cochlea** - Contains the **cochlear** **duct** - Receptors provide sense of HEARING - The cochlea contains three ducts: 1. **Scala vestibuli** (vestibular duct) - Contains perilymph - The **vestibular membrane** separates the scala vestibuli from the cochlear duct 2. **Scala tympani** (tympanic duct) - Contains perilymph - The **basilar** **membrane** separates the scala tympani from the cochlear duct 3. **Cochlear duct (scala media)** - Lies between the scala vestibuli and the scala tympani - Contains **endolymph** - Contains the **Spiral Organ of Corti** - Hair cells are located atop the basilar membrane - Hairs are in contact with an overlying **tectorial membrane** - Hearing 1. Sound waves arrive at tympanic membrane - - 2. The foot of the stapes presses in at the oval window causing a pressure wave in the perilymph of the scala vestibuli 3. The pressure wave will spiral through the scala vestibuli - Eventually it will transfer across to the scala tympani, causing the basilar membrane to vibrate - Vibrations of the basilar membrane stimulates hair cells by causing them to vibrate against the tectorial membrane 4. The pressure wave continues through the scala tympani and makes the round window bulge out - - - *Sound consists of waves of [pressure] conducted through a medium such as air or water* - - - - Frequency is the number of waves that pass fixed reference point at given time - Frequency is reported in **hertz**, and this is the number of cycles (waves) per second - Frequency determines which part of the cochlear duct is stimulated - - - - - Auditory Pathways 1. Stimulation of hair cells activates sensory neurons whose cell bodies lie in the **spiral ganglion** - Afferent fibers of these neurons form the **cochlear** **branch** of **vestibulocochlear nerve (VIII)** 2. Sensory neurons from CN VIII enter and synapses at the **cochlear nucleus** of the medulla oblongata - Much of the auditory information will cross over to the opposite side of the brain 3. Auditory sensations ascend to inferior colliculi, then to the media geniculate nucleus of the thalamus 4. Projection fibers deliver information to *auditory cortex* of temporal lobe - Hearing Range - - - 20-Hz (buzz) to 20,000-Hz (whine) - As people get older, their hearing range and abilities lessen due to the normal aging process and accumulated damage over time: - Tympanic membrane gets less flexible - Articulations between ossicles stiffen - Round window may begin to ossify - Damage to hair cell receptors