Ch 15 - The Special Senses Flashcards
Accessory Structures of the Eye
1) Conjunctiva: transparent mucous membrane (produce lubricating mucus)
2) Papebrae: eyelids (orbicularis oculi & levator papebrae superioris)
3) Lacrimal Apparatus: produce & drain tears, protect eye
4) Extrinsic Eye Muscles: 4 rectus & 2 oblique
Five Special Senses
1) Vision
2) Olfaction (smell)
3) Gustation (taste)
4) Hearing
5) Equilibrium
Muscles that allow the eyelids to open or close
1) Orbicularis oculi muscle: encirces the eye, sphincter-like muscle that closes/lowers lids
2) Levator palpebrae superioris: opens eyelids
Components of the Lacrimal Apparatus
1) Lacrimal glands: produce/release dilute saline solution (tears)
2) Lacrimal canaliculi: drains tears from eye surface at medial portion of eye
3) Nasolacrimal duct: drains tears from lacrimal canaliculi into nasal cavity
Extrinsic Eye Muscles and their Movements
1) Lateral Rectus - moves eye laterally (directly lateral to eye)
2) Medial Rectus - moves eye medially (directly medial to eye)
3) Superior Rectus - elevates eye and turns it medially (directly superior, pulls slightly medially)
4) Inferior Rectus - depresses eye and turns it medially (directly inferior, pulls slightly medially)
5) Inferior Oblique - elevates eye and turns it laterally (attaches inferiorally and laterally)
6) Superior Oblique - depresses eye and turns it laterally (attaches superiorally, underneath superior recutus)
Purpose of the Oblique Eye Muscles
Move the eye in the vertical plane when the eyeball is already turned medially - allows for focusing on things closer/further
Gross Anatomy of the Eyeball
Fibrous Layer: outermost layer (2)
Vascular Layer: middle coat of the eye (3)
Retina: innermost layer, contains photoreceptors
Anatomy of the Fibrous Layer of the Eyeball
Fibrous Layer: outermost layer (2)
1) Sclera: the “whites of the eyes” - gives eyeball shape and provides anchor
2) Cornea: transparent layer at the most anterior region of the eye
Anatomy of the Vascular Layer of the Eyeball
Vascular Layer: middle coat of the eye (3)
1) Choroid: well-vascularized layer - dark, absorbs light
2) Ciliary body: (continuous with choroid) encircles the lens
3) Iris: colored portion of the eye (center is pupil)
Anatomy of the Retina of the Eyeball
Retina: innermost layer, contains photoreceptors
1) Pigmented layer: (superficial layer) absorbs light, stores vitamin A
2) Neural layer: (deepest layer) contains photoreceptor cells (rods/cones) - also bipolar and ganglion cells
Transparent layer of fibrous tissue at most anterior region of the eye
Cornea
Has many pain receptors, high regenerative capacity
but: no blood vessels, no immune system supply
Structures that Compose the Ciliary Body
1) Ciliary muscle: smooth muscle bundles that control lens shape
2) Ciliary processes: secrete aqueous humor
3) Suspensory ligaments: extend from ciliary body to lens: holds lens in place & transmits tension from ciliary muscle to lens
Smooth muscle layers of Iris that allows for constriction or dilation of pupil
1) Sphincter pupillae: contracts = twists, pupil size decreases
2) Dilator pipillae: contracts = pulls outwards, pupil size increases
Structures Associated with the Retina
1) Optic disc: point at which the optic nerve exiys the back of the eye (blind spot)
2) Macula lutea: area where other structures are displaced - photoreceptors recieve direct light - most detailed vision center
3) Foeva centralis: center of macula lutea - contains only cones, very detailed color vision - only 1/1000th of total visual field
Chambers & Fluids of the Eye
1) Anterior segment: contains aqueous humor - watery fluid. functions: supplies nutrients and oxygen to structures in the front of the eye & removes waste - continuously drained and produced
2) Posterior segment: contains vitreous humor - jelly-like fluid. functions: transmits light, stabilizes the lens from the posterior side, holds the retina in place, contributes to intraocular pressure - lasts a lifetime
Visible light spectrum
400-700 nm
Where light is refracted to focus on the retina
1) Cornea - mostly responsible for bending light BUT - cannot change shape
2) Anterior surface of lens
3) Posterior surface of lens
Lens used to fine-tune refraction
How is lens shape changed
Use of ciliary muscles around lens and suspensory ligaments
1) Relaxation of ciliary muscle = increased tensuon in suspensory ligaments = lens flattens
2) Contraction of ciliary muscle = decreased tension in suspensory ligaments = lens bulges
Focusing light for distant vision
Ciliary muscles are relaxed when we look at objects that are far away - flattened
Focusing light for close vision
3 Processes:
1) Accommodation of the lens - contraction of ciliary muscles (bulge)
2) Constriction of pupils - prevents divergent rays from entering eye
3) Convergence of eyes - medial rotation of the eyeballs; keeps object focused on foveae
Near point of vision
normal - 4 inches
Functional Anatomy of Photoreceptors
Rods and Cones (in both):
1) Outer segment - embedded in pigmented layer of retina (contain photopigments/visual pigments, folded into discs)
2) Inner segment - embedded in the neural layer of retina (metabolic processes)
Differences between Rods and Cones
Rods: brightness
1) Sensitive to light
2) Only one visual pigment in rods
3) Converging pathways - all synapse with a single ganglion cell
Cones: color
1) Low sensitivity to light
2) Single cone has 1 of 3 visual pigments
3) Each cone synapses on it own ganglion cell
How is light stimuli converted into an electrical signal?
1) Photoreceptor cells (Rods+cones): create graded receptor potential in response to incoming light stimuli
2) Bipolar cells: create either IPSP or EPSP
3) Ganglion cell: generate action potential that is propagated along the optic nerve
How the retina processes light in the dark
Photoreceptor ion channels are open - depolarized to -40mV
How the retina processes light in the light
Photoreceptor ion channels close - hyperpolarized to -70mV
Uses a G-protein (transducin) signaling system - 11-cis-retinol absorbs light and converts to all-trans retinol
How long does it take to adapt to light v dark
Light: ~60 secs, peak @ 5mins
Dark: up to 30 mins
Pathway to the Visual Cortex
1) Optic nerve exits the back of the eye
2) Optic chiasm: location where medial fibers from each optic nerve cross over to other hemisphere (lateral fibers do not cross over)
3) Optic tracts: continue to visual cortex
Each optic tract:
1) Carries fibers from the lateral portion of the eye on the same side and
2) Carries fibers from the medial portion of the eye to the opposite side
Where do fibers end up from optic tracts?
1) Most end up in occipital lobe, others:
2) Superior colliculi - visual reflex center
3) Pretectal nuclei - mediates pupillary response to light
4) Suprachiasmatic nucleus - sets biorhythms
Visual field
Each eye has a visual field of ~170 degrees, which overlap. The differences in what each eye sees creates depth.
What and Where are Olfaction Receptors
Chemoreceptors (only respond to stimuli dissolved in solution) that are found in the olfactory epithelium.
Olfaction continue from pg 46
Cell types of olfactory epithelium
1) Olfactory sensory neurons
2) Supporting cells
3) Olfactory stem cells
Name and purpose of hair-like projections in olfactory epithelium
Olfactory cilia, increases receptive surface area of neuron.
The mucous surrounding cilia dissolves airborne odorants
Part of olfactory sensory neuron
2 things necessary for sensation of smell
1) Activation of sensory neurons - odorant must dissolve in mucous and bind to receptor protein in olfactory cilium membrane]
2) Transduction of smell
Steps of Smell Transduction
1) Odorant binding creates graded potential
2) Axon of sensory neuron carries graded potential through ethmoid bone into the brain via olfactory tract
3) Synapses with mitral cells in olfactory bulb at glomeruli
4) If Ca2+ influx continues in mitral cell, adaptation will occur - decreased response to sustained odorant stimulus
Longevity of Olfactory Sensory Neurons
Superficial - prone to destruction
Life span = 30-60 dyas
Olfactory stem cells replace damaged/destoryed neurons
Where do impulses from the olfactory bulb end
1) Olfactory cortex - smell is consciously interpreted/identified
2) Limbic system - smell elicits an emotional response (activates sympathetic or parasympathetic systems)
Where are tastebuds found
3 types of Papillae
1) Fungiform papillae: 1-5 tastebuds each (most of tongue)
2) Vallate papillae: each papillae has many tastebuds (single line of large papillae)
3) Foliate papillae: varies with age (on sides of tongue)
Epithelial cells on taste bud
1) Gustatory epithelial cells: receptors for taste
2) Basal epithelial cells: stem cells (replace gustatory epithelial cells ebery 7-10 days)
Receptor cells for taste
Gustatory epithelail cells
Gustatory hairs that project from cell bind to tastant to produce graded potential by gustatory epithelial cell
Sensory dendrites wrap around gustatory cells
6 Basic Modalities of Taste
1) Sweet - most sugars, alcohols, some amino acids
2) Sour - acids
3) Salty - metal ions (inorganic salts)
4) Bitter - mostly alkaloids
5) Umami - amino acids glutamate & aspartate
6) Long-chain fatty acids - lipids
Taste cell responsds to only 1 modality each
Which tastant binds
Na+ influx through Na+ channels directly depolarizes gustatory epithelail cell
Salty
Which tastant binds
H+ acts intracellularly to open ion channels
Sour
Which tastant binds
G-protein gustducin activation leads to opening of ion channels to depolarize membrane
Bitter/sweet/umami
Pathway to Gustatory Cortex
Facial Nerve (VII) - carries information from anterior 2/3 of tongue
Glossopharyngeal nerve (VIII) - carries information from posterior 1/3 of tongue
Most fibers travel to primary gustatory cortex, but others travel to limbic system and hypothalamus
Major Regions of the Ear
1) External Ear (external acoustic meatus, pinna)
2) Middle Ear (tympanic membrane, malleus, incus, stapes, oval window, round window, pharyngotympanic tube)
3) Inner Ear (WAY more - vestibule, semicircular canals, scalae, membranous/bony labyrinth)
Parts of the External Ear
1) External acoustic meatus: tube extending from auricle/pinna to tympanum
2) Tympanic membrane (tympanum): thin membrane that divides outer ear from middle ear (vibrates in response to sound)
Parts of Middle Ear
1) 3 ossicles (malleus, incus, stapes)
2) Oval window - attached to the base of the stapes, allows sound to be transmitted into inner ear
3) Round window - allows for pressure equalization between middle and inner ear
4) Pharyngotympanic tube - runs from middle ear to throat, equalizes pressure in middle ear (mismatched pressure = no hearing)
Muscles associated with ossicles
Tensor tympani & stapedius: contract in response to extreme sound vibrations
Divisions of the Inner Ear
(and the senses they command)
1) Cochlea: fluid-filled structure that converts sound waves to action potentials for hearing
2) Vestibule & semicircular canals: fluid-filled regions of inner ear containing receptors responsible for equilibrium and balance
Compartments of all Divisions of Inner Ear and the fluid within
1) Bony Labyrinth - cavity within the bone filled with perilymph (fluid similar in comp. to CSF) that surrounds and supports the:
2) Membranous Labyrinth - membranous sacs and ducts found within bony labyrinth filled with endolymph (fluid similar in comp. to intracellular fluid) that contains
Chambers of the Cochlea:
1) Scala vestibuli - part of bony labyrinth that begins at oval window
2) Scala tympani - part bony labyrinth that ends at round window
3) Scala media - part of membranous labyrinth with: Stria vascularis (produces & secretes endolymph) and Basilar membrane (forms floor of scale media - responds to sound)
Vestibuli and tympani are cont. - meet at helicotrema (end of spiral)
Receptor Organ for Hearing
& its two cell types
Cochlea
1) Cochlear hair cells - inner and outer hair cells, cochlear nerve fibers wrap around base of hair cells
2) Supporting cells - support hair cells
Human hearing ranges
20-20,000 Hz
0-120 dB (above painful)
Sound transmission paths within perilymph of scala vestibili
1) Basilar membrane path - sound waves transmitted through scala media - stimulates hair cells in spiral organ (generates action potential)
2) Helicotrema path - low frequency (<20 Hz) pass completely around helicotrema (does not vibrate)
