Lecture 12: Special Senses Flashcards
General senses
Large group of different types of touch receptors
Special senses
Taste, smell, sight, hearing, and balance; localized (confined to the head region)
Taste
Gustation; chemoreceptors that respond to food dissolved in saliva fluids
Filiform papillae
Most numerous papillae on tongue; small and conical pointed; parallel rows; grasp and manipulate; do NOT contain taste buds
Fungiform papillae
Mushroom shaped and spread over anterior 2/3rds of tongue surface; contain taste buds
Vallate papilllae
V-shaped row bordering posterior third of tongue and directly anterior to terminal sulcus; contain taste buds
Taste buds
On fungiform and vallate papillae; taste receptors; 50-100 epithelial cells; two cell types (gustatory epithelial and basal epithelial cells); long microvilli (gustatory hairs); replaced every 7-10 days
Five qualities of taste
Sweet, sour, salty, bitter, and umami (glutamate “pleasant savory taste”)
Gustatory pathway
Reaches cerebral cortex through facial (VII), glossopharyngeal (IX), and vagus nerve (X); bitter taste receptors found in stomach; synapse in solitary nucleus of medulla transmitted to thalamus and ultimately to gustatory area of cerebral cortex in insula
Smell
Olfaction; chemoreceptors respond to airborne chemicals that dissolve in fluids of nasal mucosa
Olfactory epithelium
Pseudostratified simple columnar with three cell types (olfactory sensory neurons, supporting epithelial cells, basal epithelial cells)
Cell body to epithelium
Cell bodies of olfactory sensory neurons; apical dendrite ends in a knob from olfactory cilia radiate; olfactory cilia act as receptive structures for smell; mucus captures and dissolves odor molecules
Cell body to brain
Bundles of axon filaments of olfactory nerve; pass through cribriform plate of ethmoid bone; attach to olfactory bulbs and synapase at mitral cell; transmit pulses along olfactory tract to limbic system and piriform lobe of cerebral cortex
Anosmia
Absence of sense of smell (due to injury, colds, allergies, or zinc deficiency)
Uncinate fits
Distortion of smells or olfactory hallucinations (from irritation of olfactory pathways or after brain surgery/head trauma)
Visian
70% of all sensory receptors in eye; 40% of cerebral cortex involved in processing visual information; only anterior 1/6 of eye surface is visible
Accessory structures of eye
Eyebrows (hairs on superciliary arches); eyelids (palpebrae) separated by palpebral fissure (meet at medial and latera angles; lacrimal caruncle: reddish elevation at medial canthus; tarsal plates: connective tissue within eyelids; tarsal glands: modified sebaceous glands)
Conjuctiva
Transparent mucous membrane (palpebral tarsal conjuctiva); bulbar conjuctiva; conjuctival sac
Lacrimal apparatus
Keeps surface of eye moist; lacrimal gland: produces lacrimal fluid; lacrimal punctum; lacrima canaliculus; lacrimal sac: fluid empties into nasal cavity; nasalacrimal duct; inferior meatus
Extrinsic eye muscles
Control movement of eye; originate in walls of orbit; insert on outer surface of eyeball; annular ring; lateral rectus and medial rectus; superior rectus and inferior rectus; superior oblique and inferior oblique
Posterior segment of eye
Filled with vitreous humor; clear, jelly-like substance; transmits light; supports the posterior surface of lens; helps maintain intraocular pressure
Olfactory cortex
Process smell; transmit impulses to olfactory cortex; medial aspect of cerebrum in piriform lobe
Rhinencephalon
Includes parts of cerebrum that receive olfactory signals: piriform lobe, olfactory tracts, and olfactory bulbs; connect to limbic system; consciously identifying and recalling specific smells
Visceral sensory areas
Deep within lateral sulcus on insula lobe; receives general sensory input (pain, pressure, hunger) from abdominal and thoracic organs
Fibrous layer
Most external of eyeball; dense connective tissue; includes sclera and cornea
Sclera
Posterior 5/6 of tunic; white, opaque region; provides shape and anchor
Cornea
Anterior 1/6; epithelium; thicker layer of dense collagen-rich connective tissue; endothelium; avascular but gets oxygen from air and nutrients from aqueous humor behind; richly supplied with sensory nerve endings (most pain receptors)
Limbus
Junction between sclera and cornea
Scleral venous sinus
Allows aqueous humor to drain
Vascular layer
Middle coat of eyeball; includes choroid, ciliary body, and iris
Choroid
Vascular; darkly pigmented; forms posterior 5/6 of vascular tunic; brown color from melanocytes; prevents scattering of light rays within eye; responds to arachnoid and pia maters
Ciliary body
Thickened ring of tissue which encircles lens; smooth muscle called ciliary muscle which focus on lens
Ciliary processes
Posterior surface of ciliary body
Ciliary zonule
Halo of fine fibrils attached around entire circumference of lens
Iris
Visible colored part of eye; attached to ciliary body and positioned anterior to it; smooth muscle
Pupil
Round, central opening; sphincter pupillae muscle (circularly arranged); dilator pupillae muscle (radially arranged): act to vary size of pupil; pupillary light reflex: protective response of pupil constriction when bright light is flashed in eye
Inner layer
Consists of retina and optic nerve
Retina
Ora serrata retinae: neural layer ends at posterior margin of ciliary body; macula lutea: mostly cones; fovea centralis: only cones and highest visual acuity; optic disc: blind spot
Layers of Retina
Pigmented layer: single outer layer of melanocytes; Neural layer: most inner layer with a sheet of nervous tissue
Neural layer contains:
Photoreceptor cells (rods and cones), bipolar cells, ganglion cells, a 4th cell type interneuron; photoreceptor cells signal bipolar cells which signal ganglion cells which exit at optic nerve
Photoreceptor neurons
Rods: sensitive to light and allow vision in dim light; Cones: operate best in bright light and enable high-acuity, color vision
Visual pathways to cerebral cortex
Optic nerve to optic chiasm into optic tract to lateral geniculate nucleus of thalamus to primary visual cortex
Visual pathways to other parts of brain
Optic tracts to midbrain (superior colliculi controls extrinsic eye muscles and pretectal nuclei mediates pupillary eye reflex); other braches to suprachiasmatic nucleus of hypothalamus which processes biorhythms
Blood supply of retina
Outer third of retinal supplied by capillaries in choroid; inner 2/3 serviced by central artery and vein of retina
Cataracts
Lens becomes opaque; results in blindness
Age-related macular degeneration (AMD)
Buildup of deposits in the retina; loss of vision
Trachoma
Infection from chlamydia of the conjuctiva which causes eyelids to become distorted and inverted scraping against the cornea and lead to corneal scarring
Ear
Receptor organ for hearing
Outer ear
Auricle (pinna) directs sound; external acoustic meatus lined with skin, hairs, sebaceous glands, and ceruminous glands; tympanic membrane forms boundary between external and middle ear
Otitis externa
Infection and inflammation lining external acoustic meatus; “swimmer’s ear” can be cause of problem
Otitis media
Infection of tympanic membrane
Middle ear
Tympanic cavity forms lateral wall within petrous and temporal bone; medial wall penetrated by oval and round windows; pharyngotympanic tube links middle ear and pharynx
Ear ossicles
Smallest bones in body; malleus attaches to eardrum; incus between malleus and stapes; stapes vibrates against oval window
Tensor tympani and stapedius muscles
Two tiny skeletal muscles in middle ear cavity
Internal ear
Labyrinth; within petrous portion of temporal bone
Bony labyrinth consists of
Semicircular canals, vestibule, cochlea
Membranous labyrinth in internal ear
Membrane-walled sacs and ducts; semicircular ducts in semicircular canals; utricle and saccule in vestibule; cochlear duct in cochlea
Endolymph
Clear fluid in membranous labyrinth
Perilymph
CSF in bony labyrinth
Cochlea
Spiral chamber in bony labyrinth; attachment on vestibule around modiolus
Osseous spiral lamina
Spiral of bone in modiolus
Cochlear nerve
Runs through modiolus
