Chapter 16 - Nervous System: Senses

Describe the general function of sensory receptors.

Detect temperature, pain, touch, pressure, and proprioception.

Name the auditory ossicles and explain how they function in hearing.

Auditory Ossicles - three smallest bones of the body. Amplify and transmit sound waves into inner ear. Vibrate when sound waves strike tympanic membrane. Cause stapes' footplate to move in and out of oval window. Movement initiating pressure waves in inner ear fluid. Malleus - attached to medial surface of tympanic membrane, resembles a hammer in shape. Incus - middle ossicle resembling an anvil. Stapes - resembles a stirrup, has disclike footplace fitting into oval window, marks lateral wall of inner ear. Stapedius and tensor tympani - restrict ossicle movement when loud noises occur, protect receptors in inner ear.

Terms to be covered in lab: conjunctivitis, cataracts, glaucoma, emmetropia, hyperopia and myopia and astigmatism.

Conjunctivitis: most common nontraumatic eye complaint. Inflammation and reddening of the conjunctiva. Due to viral infection, bacterial infection, allergens, chemicals, irritants. Trachoma - chronic, contagious for of conjunctivitis. Caused by Chlamydia trachomatis. Common cause of neonatal blindness in developing countries. Newborn affected as passes through birth canal. Inflammatory process causing scarring and thickening of conjunctiva. Cataracts: small cloudiness within the lens. Usually as a result of aging. Difficulty focusing on close objects. Reduced visual clarity and reduced color intensity. Needs to be removed when interferes with normal activities. Glaucoma: characterized by increased intraocular pressure due to increased aqueous humor. The individual over time may experience reduced vision, halos and if left untreated may result in irreversible damage. Emmetropia: normal vision, parallel rays of light focused exactly on retina. Hyperopia: trouble seeing up close (far-sighted). Only convergent rays from distant points brought to focus. Eyeball too short. Focus posterior to retina. Corrective convex lens. Myopia: trouble seeing faraway objects (near-sighted). Only rays close to eye focus on retina. Eyeball too long. Focus anterior to retina in vitreous body. Corrective concave lens. Astigmatism: unequal focusing. Due to unequal curvatures in one or more refractive surfaces.

Discuss the structure, location, and cranial nerve innervation of gustatory chemoreceptors.

Gustatory cells are specialized chemoreceptors. Dendritic ending of each formed by gustatory microvillus (extends through opening in taste bud, taste pore, to surface). Tastants, taste-producing molecules in food (dissolve in saliva, stimulate gustatory receptors through taste pore). Sensory neurons: dendritic ends associated with multiple gustatory cells, primarily components of facial and glossopharyngeal nerve. Project first to medulla to synapse. Secondary neurons projecting to thalamus. Teritiary neurons projecting to primary gustatory cortex.

Name the components of the olfactory epithelium and its mode of action. Identify the pathway from the olfactory chemoreceptors to the cerebrum.

Olfactory receptor cells (detecting odors) Supporting cells (sustaining receptors) Basal cells (replacing olfactory receptor cells every 40-60 days) 1. Olfactory hairs - house receptor proteins for detecting specific odorant molecule. 2. Olfactory nerves (CN I) - enter olfactory bulbs. 3. Olfactory bulbs - terminal ends of olfactory tracts. 4. Olfactory tracts - axon bundles that project directly to primary olfactory cortex in temporal lobe. (emotional association - limbic system)

Compare and contrast the two general types of photoreceptors, including their photopigments. Note their role in light and dark adaptation

Rods & Cones Rods: especially important in dim light, cannot distinguish color. Rhodopsin - opsin in rods. Involved in transduction of dim light. Cones: less numerous than rods. Activated by high-intensity light. Provide precise visual sharpness and color recognition. Subdivided into 3 different wavelengths - Blue, green, red. Photopsin - specific opsin associated with retinal in cone cells. three different proteins providing for different absorption in cones. Dark adaptation - return of sensitivity to low light levels after bright light. Cones initially nonfunctional in low light. Rods still bleached from bright light conditions. May take 20-30 minutes to see well. Light adaptation - adjustment from low light levels to bright light, turning on a light in a dark room. Rods become inactive and cones must adjust to brighter light. May take 5-10 minutes to see well.

Trace the path of a sound wave from outside the ear to stimulation of vestibulocochlear nerve (CN VIII).

Sound waves funneled by auricle of external ear. Enter external acoustic meatus. Make tympanic membranes vibrate. Sound waves amplified. Foot of stapes moving in oval window. Transmits sound waves into pressure waves within inner ear. Pressure waves continuing through perilymph. Cause deformation of cochlear duct. Displace specific regions of basilar membrane. Causes distortion of hair cells. Nerve signals initiated in cochlear branch of CN VIII. Vibrations in scala media transmitted to perilymph (absorbed at the round window).

Compare and contrast the bony labyrinth and the membranous labyrinth.

The bony labyrinth is the spaces within the temporal bone. Contains the membrane-lined fluid-filled tubes called membranous labyrinth.

Describe the structures of the outer, middle, and inner ear.

External Ear Auricle (pinna) - protects entry into ear and directs sound waves in External Acoustic Meatus - bony tube extending slightly superiorly from lateral head. Tympanic Membrane (eardrum) - vibrates when sound waves hit it. Transmits sound wave energy into middle and inner ear. Cerumen - waxlike secretion of ceruminous glands. May help impede growth of microorganisms. Middle Ear: contains air-filled tympanic cavity. Sounds transmitted through here via auditory ossicles. Bound medially by bony wall, houses oval window and round window. Auditory tube (Eustachian tube) - allows pressure to equalize within middle ear. Auditory Ossicles - three smallest bones of the body. Amplify and transmit sound waves into inner ear. Vibrate when sound waves strike tympanic membrane. Cause stapes' footplate to move in and out of oval window. Movement initiating pressure waves in inner ear fluid. Malleus - attached to medial surface of tympanic membrane, resembles a hammer in shape. Incus - middle ossicle resembling an anvil. Stapes - resembles a stirrup, has disclike footplace fitting into oval window, marks lateral wall of inner ear. Stapedius and tensor tympani - restrict ossicle movement when loud noises occur, protect receptors in inner ear. Inner Ear Bony Labyrinth - contains membrane-lined fluid-filled tubes (membranous labyrinth). Contains endolymph, similar to intracellular fluid. Perilymph - similar to interstitial fluid. In space between outer bony labyrinth and membranous labyrinth. Suspends, supports, and protects membranous labyrinth. Three partitions of bony labyrinth Cochlea - houses cochlear duct. Vestibule - contains two saclike, membranous parts. Utricle and saccule, interconnected and positioned at right angles. Semicircular canal - membranous labyrinth here termed the semicircular ducts.

Describe the accessory structures of the eye, and list their functions. Note tear composition.

External accessory structures Eyelids: united at medial and lateral palpebral commissures. Lacrimal caruncle - small reddish body at medial commissure Ciliary glands - form secretory products. contribute to gritty material around eyelids after waking Tarsal glands - keep eyelids from sticking. produce secretion to prevent tear overflow Conjunctiva continuous lining over external anterior eye: ocular conjunctiva continuous lining over internal surface of eyelid: palpebral conjunctiva does not cover surface of cornea: so blood vessels don't interfere with passage of light. Lacrimal apparatus Tears contain mostly water, with some salts, mucus, and lysozyme. Lubricates anterior surface of eye. Cleanses and moistens eye surface. Helps prevent bacterial infection: through action of antibacterial enzyme known as lysozyme. Lacrimal Gland - located in superolateral depression of orbit. Continuously produces lacrimal fluid which is distributed by blinking eyelids. Fluid transferred to lacrimal caruncle on medial eye. Lacrimal puncta - two small openings in each lacrimal caruncle. Drain fluid through lacrimal canaliculus into lacrimal sac. Nasolacrimal duct - receives fluid from lacrimal sac. Drains fluid into lateral side of nasal cavity (mixes with mucus). **1. Lacrimal fluid (tears) is produced in the lacrimal gland. 2. Lacrimal fluid is dispersed across eye surface when we blink. 3. Lacrimal fluid enters the lacrimal puncta, drains into the lacrimal canaliculi, and collects in the lacrimal sac. 4. Lacrimal fluid from the lacrimal sac drains through the nasolacrimal duct. 5. Lacrimal fluid enters the nasal cavity.

Classify the various types of sensory receptors based on each of the three criteria, receptor distribution - general vs special, stimulus origin, and modality.

General sense receptors: distributed throughout the body in the skin, muscle, joints, and internal organs. Detect temperature, pain, touch, pressure, and proprioception. Special sense receptors: located within head; specialized, complex sense organs. Stimulus origin: Exteroceptors - detect stimuli from external environment. Interoceptors - detect stimuli from internal organs. Proprioceptors - detect body and limb movements. Provide awareness of body joint position and skeletal muscle contraction. Modality of stimulus: classified into 6 groups. Chemoreceptors - detect chemicals dissolved in fluid. Eg taste buds on tongue. Eg. Chemoreceptors in blood vessels (monitor oxygen and carbon dioxide in blood). Thermoreceptors - respond to changes in temperature. Photoreceptors - detect changes in light intensity, color, movement. Mechanoreceptors - respond to touch, pressure, vibration, and stretch. Most curtaneous receptors (tactile- and also in the ear) Baroreceptors - specific type of mechanoreceptor, detect changes in stretch or distention. Involved in regulation of blood pressure, or stomach. Nociceptors - respond to painful stimuli.

Explain the components of the cochlea and how they function in the sense of hearing.

Snail-shaped spiral chamber within bone of inner ear. Houses the spiral-organ, responsible for hearing. Cochlear duct - membranous labyrinth that extends through cochlea. Roof formed by vestibular membranes. Floor formed by basilar membranes. Bony labyrinth partitioned by membranes into chambers - superior chamber is the vestibular duct. Inferior chamber is the tympanic duct. Merged through a small channel, helicotrema, at apex of cochlea. Two membranes connect the middle and inner ear. The oval window is a membrane that the stapes pushes against to generate pressure waves in the perilymph in the vestibular duct. The round window is a membrane at the end of the tympanic duct that dampens pressure waves in the tympanic duct. Spiral organ - within cochlear duct, resting on basilar membrane. Thick sensory epithelium consisting of hair cells and supporting cells. Hair cells - sensory receptors of inner ear for hearing. Release neurotransmitter molecules to sensory neurons. Covered on apical surface with long microvilli, stereocilia. Tectorial membrane - stereocilia extending into here. Sequence of stimulation - sound waves at tympanic membrane. Transmitted to oval window via ossicles. Initiate pressure waves in perilymph. Causes basilar membrane to flutter. Distorts hair cells, causing changes in neurotransmitter release. Sensory neurons stimulated (cell bodies housed within spiral ganglia in modiolus).

Explain how the utricle and saccule detect static equilibrium and linear movements of the head, and how the semicircular ducts function to detect rotational movements of the head.

Static equilibrium: when body is steady. Monitored by utricle and saccule. Linear Acceleration - tilting your head to look at shoes. Also detected by utricle and saccule. Macula - raised area of utricle and saccule. Each composed of layer of hair cells and supporting cells. Hair cells with stereocilia and one lone cilum, kinocilium. When both bent, changes in neurotransmitter released. * Detects linear acceleration. * Static equilibrium is the result of otoliths stimulating hair cells. Otolithic membrane - formed of gelatinous layer and otoliths. Otoliths, small masses of calcium carbonate crystals. Help increase weight of otolithic membrane covering hair cells. Position influenced by head position. Stereocilia and kinocilia embedded in gelatinous layer. Rotational Equilibrium: * the special sense which interprets balance when one is moving, or at least the head is moving. Angular Acceleration - rotational movements of the head. Monitored by semicircular ducts. Semicircular canal - semicircular duct connected to the utricle. Ampulla - expanded region within each semicircular duct. Crista ampullaris - elevated region on ampulla. Covered by hair cells and supporting cells. Cupula - overlying gelatinous dome. Kinocilia and stereocilia embedded here. Extends across semicircular duct to roof over ampulla. Detection of rotational movement - with head rotation, lagging of endolymph. Pushes against cupula, causing bending of stereocilia. Results in altered neurotransmitter released from hair cells. stimulation of sensory neurons. Bending of stereocilium in direction of kinocilium (leads to increased frequency of nerve signals). Response primarily to changes in velocity.

Describe the structures and function of the components of the eye. Know what makes up each tunic, locations and types of fluids

Fibrous Tunic, Vascular Tunic, Retina Fibrous tunic: composed of sclera and anterior cornea. Sclera - provides eye shape, protects eye's internal components, attachment site for extrinsic eye muscles. Cornea - convex transparent structure, contains no blood vessels, convex shape refracting light rays coming into the eye. Vascular Tunic: houses extensive blood vessels, lymph vessels; intrinsic muscles of the eye. Three regions choroid, ciliary body, iris. Choroid - most extensive posterior region. Cells filled with pigment from melanocytes. Ciliary body - composed of ciliary muscles and ciliary processes. Ciliary muscles - bands of smooth muscle. Suspensory ligaments extending from muscle to lens. Contraction changing tension on ligaments, altering lens shape. Ciliary processes - contain capillaries responsible for producing aqueous humor. Iris - most anterior region. Colored portion of the eye. Pupil - black opening at center of iris. Pupil size controlled by two smooth muscle layers. Controls amount of light entering the eye.

Distinguish between pitch (frequency) and loudness (intensity of sound) of sound.

Intensity: refers to sound's loudness. Measured in decibels (dB). Inaudible sound, no decibels. Louder sounds have a higher amplitude. Frequency: number of waves moving past a point during specific time. Measured in hertz (Hz). Classified as high, medium, or low. Interpreted as the pitch of a sound. Region of basilar membrane of spiral organ stimulated by pressure waves (caries according to sound frequency, high-frequency sounds stimulate near oval window).

Describe the structures of the inner ear involved in equilibrium.

Monitored by utricle, saccule, semicircular ducts.

Describe the structure and function of papillae of the tongue.

Papillae: epithelial and connective tissue elevations. Filiform papillae - do not house taste buds but assist in detecting texture and manipulating food. Faliate papillae - house only a few taste buds through early childhood. Fungiform papillae - contain a few taste buds. Vallate papillae - least numerous, largest papillae; arrange in inverted V on posterior dorsal tongue; most taste buds housed here.

Differentiate between a stimulus and a sensation and explain sensory adaptation.

Stimulus: changes in sensory information, Sensation: conscious awareness of sensory information. Sensory adaptation: A decrease in sensitivity to a continuous stimulus.

List the five types of tastes and explain the association of smell with taste.

Sweet, salt, sour, bitter, umami. Taste and olfaction: ability to taste heavily dependent on olfactory sense (food tasting bland during a cold). Taste from info from gustatory and olfactory receptors.