Chapter 5A - Senses Flashcards
Posterior Cavity
-separated from anterior cavity by the lens
-between lens and retina
-contains vitreous humor
Anterior Cavity
-separated from posterior cavity by the lens
-between cornea and lens
-contains aqueous humor
Lens
-bends light to focus it on the retina
-separates anterior and posterior cavities
Vitreous Humor
-gel-like
-not drained out
-helps maintain the shape of the eyeball
Aqueous Humor
-nutrient rich (provides cornea and lens)
-drained and made fresh
-produced at 5mL/day
-watery, plasma-like fluid
Why don’t the cornea and lens have blood vessels?
It would impede with the passage of light
What structure drains aqueous humor?
Canal of Schlemm
Cornea
-transparent lens
-nutrient fed by aqueous humor
-outer layer where light passes into eye
Sclera
-tough outer layer of connective tissue
-white part of the eye
Choroid
-layer underneath sclera that has blood vessels which nourish retina
-black pigmented layer
Ciliary Body
-formed from choroid layer
-contains ciliary muscle that changes shape of the lens
-contains suspensory ligaments and zonules
-also houses capillary network responsible for aqueous humor
Iris
-formed from choroid layer
-pigmented layer of smooth muscle
-complicated color formation that is more complex than DNA
-mulit-unit
Pupil
-size adjusted by iris muscles to control amount of light that enters the eye
-contains 2 sets of smooth muscle networks
Circular Muscle Network (Pupil)
-muscle fibres run in a ring like fashion
-makes the pupil smaller when they contract in response to bright light
-innervated by parasympathetic nerve endings
Radial Muscle Netwrok (Pupil)
-muscle fibres project outward from pupillary margin
-increases size of pupil in response to dim light
-innervated by sympathetic nerve endings
Conjective
-outermost membrane
-easily infected
Retina
-innermost layer under the choroid
-outer layer and inner nervous tissue layer
-contains photoreceptor: rods and cones
Why are choroid and retina highly pigmented?
To prevent reflection or scattering of light in the eye
Optic Disk
-blind spot (no rods or cones)
-entry/exit point of nerves and blood vessels
Optic Nerve
-CN II
-sends signals to central nervous system
Fovea Centralis
-region of the sharpest vision
-only cones are found here
Macula Lutea
-center of the visual field
-immediately surrounds fovea
-high acuity
CN I
?
CN II
optic nerve
CN III
oculomotor nerve
CN IV
trochlear
CN V
trigeminal
CN VI
abducens
CN VII
facial
CN VIII
ear
Formation and Drainage of Aqueous Humor
-formed by: capillary network in ciliary body
-drains into: canal of Schlemm and eventually enters the blood
Accomodation
-change in strength and shape of the lens
-accomplished by ciliary muscles and suspensory ligaments
-goal=perfect vision by focusing light on the retina
Far Vision
-ciliary muscle is relaxed
-lens is flat
-taut suspensory ligaments
-sympathetic stimulation
Near Vision
-ciliary muscle contracts
-lens is rounded
-slackened suspensory ligaments
-parasympathetic stimulation
Which branch of the nervous system controls the ciliary muscle?
autonomic nervous system (ANS)
Glaucoma
-drainage of aqueous humor is blocked
-pressure build-up of fluid
-if not treated: degenerates optic nerve (blindness)
-treated with: medication or surgery
Macular Degeneration
-“donut vision”
-main concern for blindness in the Western hemisphere
-irreversible
-loss of photo receptors in the macula
-lose middle of visual field and are only left with less distinct peripheral vision
-results from age
Emmetropia
-flattening and rounding of the lens to give perfect vision
-normal eye
Hyperopia
-farsightedness
-focal point falls behind the retina
-corrected with convex lens
Myopia
-nearsightedness
-focal point falls in front of the retina
-corrected with concave lens
Presbyopia
-age related reduction in accommodative ability
-usually occurs middle age (45-55)
-use of reading glasses required
Photoreceptors
-The retina which contains the receptors is an extension of the CNS
-rods and cones transform light energy into electrical signals which are sent to the CNS
-retina contains 3 layers of excitable cells
Outermost Retinal Layer
-closest to the choroid
-contains rods and cones whose light-sensitive ends face the choroid (away from incoming light)
Middle Retinal Layer
-bipolar cells
Inner Retinal Layer
-ganglion cells
-axons join to form the optic nerve
Rods
-more numerous than cones
-used in night vision
-shades of grey vision
-low acuity
-high sensitivity
-more convergence in retinal pathways
-more numerous in peripheral region
Cones
-less numerous
-used in day vision
-colour vision
-high acuity
-less sensitivity
-little convergence in retinal pathways
-concentrated in fovea and macula
Night Blindness
-vitamin A deficiency
-a rod issue
-unable to see well at night or in poor light
-reversible
Color Blindness
-inherited
-cone issue
-more prominent in males than females
How many parts make up a photo receptor?
Three
Outer Segment
-discs
-detect light stimulus
-holds pigment
Inner Segment
-contains metabolic machinery of the cell
Synaptic Terminal
-transmits signal generated in photoreceptor upon light stimulation to next cells in visual pathways
Photopigments
undergo chemical alterations when activated by light
Opsin
-protein
-integral part of the disc membrane
Retinal (aka retinene)
-vitamin A derivative
-light absorbing part of the photopigment
Rhodopsin
-activated in light
-rod photopigment
-absorbs all visible wavelengths
-shades of grey promote different intensities
3 Types of Cones
-red, green, and blue
-respond selectively to various wavelengths of light
Phototransduction
-process of converting light stimuli into electrical signals
-usually receptors depolarize on stimulation: however, photoreceptors hyperpolarize on light absorption
Sensitivity
varies through light and dark adaptation
Dark Adaptation
-gradually distinguish objects as you enter dark area
-due to the regeneration of rod photopigments that were previously broken down from light exposure
Light Adaptation
-gradually distinguish objects as you enter an area with more light
-due to rapid breakdown of cone photopigments
Photoreceptors in the Dark
-retinol is inactive
-chemically gated channels respond to 2nd messenger cGMP which keeps Na+ channels open
-cGMP is in high concentration
-Na+ channels are open in the absence of stimulation (light)
-cell becomes depolarized
-passive spread of depolarization from outer segment to synapse keeps Ca2+ channels open
-Ca2+ triggers release of inhibitory neurotransmitter
Photoreceptors in Light
-concentration of cGMP is decreased
-photopigment activated, which activated transducin (G-protein), which activates phosphodiesterase enzyme
-the enzyme degrades cGMP, thus decreasing its concentration
-Na+ channels close, causing hyperpolarization
-spreads from the outer segment to synapse
-Ca2+ channels close, and NT release from the synapse is reduced
What inhibits photoreceptors?
-light (their stimulus), which causes them to hyperpolarize
-this process is the reverse of normal: inhibition by adequate stimulus
-brighter the light, the greater the hyperpolarizing response and the greater the reduction of inhibitory NT release
What excites photoreceptors?
-darkness, which causes them to depolarize
-“excited in the absence of stimulation”
Retinal Processing of Light Input
-photoreceptors synapse with bipolar cells (graded potential)
-bipolar cells terminate of the ganglion cells (action potential)
-ganglion cell axons form the optic nerve
-optic chiasm
-optic tract
-thalamus (lateral geniculate)
-optic radiation
-occipital lobe
=IMAGE!
Inhibitory Action on Bipolar Cells
-the reduction inhibitory NTs release decreases inhibitory action on bipolar cells
-and removal has the same effect as direct excitation
Visual Field
what can be seen without moving the head
Upside Down Image
-the image detected on the retina at the onset of visual processing is upside down and backwards because of the bending of the rays at the lens
-brain must correct the orientation of the image
On-center Ganglion Cell (donut hole)
increases the rate of firing when light is most intense at the center of its receptive field
Off-center Ganglion Cell (donut)
increases the rate of firing when the periphery of the field is most intensely illuminated
Optic Chiasm
-met by optic nerves
-underneath hypothalamus
Optic Tracts
-reorganized fibers that cross in the chiasm
-each tract carries info from the lateral half of one retina and the medial half of another
Hearing
neural perception of sound energy
External Ear
-pinna, ear canal, tympanic membrane
-transmits sound waves to inner ear
-amplifies sound energy
Pinna
outer piece of cartilage that is used to colect sound waves
Ear Canal
-most prone to infection
-contains hairs and glands that produce earwax
-prevent airborne particles from interfering with hearing
Tympanic Membrane (aka ear drum)
-vibrates when struck by waves
-resting air pressure on both sides must be equal
Middle Ear
-contains ossicles and eustachian tube
-transmits sound waves to inner ear
-amplifies sound energy
Ossicles
-malleus, incus, stapes
transmits movement from tympanic membrane to oval window
Eustachian Tube
-connects middle ear to pharynx (back of the throat)
-regulates pressure in the ear (ie. yawning, chewing)
Otitis Media
-infection of the middle ear
-redness and swelling interfere with sound conduction
-treated with antibiotics
Oval Window
-the entrance to the cochlea
-seals scala vestibuli from middle ear
Inner Ear
-houses cochlea and vestibular apparatus
Cochlea
-contains receptors for conversion of sound waves into nerve impulses which make hearing possible
-fluid filled portion used in hearing
-divided into 3 fluid filled compartments
Vestibular Apparatus
-necessary for sense of equilibrium
-balance
Round Window
-membrane covered opening
-seals the scala tympani from the middle ear
Cochlear Duct (scala media)
-the middle compartment
-houses endolymph (ICF)
Vestibular Duct (scala vestibuli)
-upper compartment
Tympanic Duct (scala tympani)
-lower compartment
Perilymph
-housed in the vestibular and tympanic ducts
-ECF
Helicotremma
-tip of the cochlear duct where the two outer regions meet
Tectorial (vestibular) Membrane
-forms the ceiling of the cochlear duct and separates it from scala vestibuli
Basilar Membrane
-forms the floor of the cochlear duct and separates it from scala tympani
-holds the Organ of Corti
Organ of Corti
-the sense organ for hearing
-hair cells transduce sound waves
-hair cells arranged in 4 parallel rows: 1 row of inner hair cells and 3 rows of outer hair cells
Stereocilia
-protrude from the surface of each hair cell
-actin-stiffened microvilli
-contact the tectorial membrane
Role of Hair Cells
-generate neural signals when their surface hairs are mechanically deformed by fluid movements in the inner ear
Kinocilium
tallest hair cells
-bending stereocilia towards kinocilium = DEPOLARIZATION
-kinocilium towards stereocilia = REPOLARIZATION
Step 1
tympanic membrane vibrates when struck by sound waves
Step 2
middle ear transfers vibrations through ossicles to the oval window
Step 3
waves in cochlear fluid set the basilar membrane in motion
Step 4
receptive hair cells are bent as basilar membrane is deflected up and down
Step 5
mechanical deformation of hair cells is transduced into neural signals that are transmitted to the auditory cortex in the temporal lobe of the brain for sound perception
Frequency
-measure in Hertz
-1000 to 3000Hz
Amplitude
-measured in Decibels
-60dB
-rock concert is about 120dB
Conductive Hearing Loss
-sound waves are not adequately conducted to set the fluid in motion
-could be from: blockage, earwax, infection, ear drum damage
-reversible
Central Hearing Loss
-neural pathways are damaged
-functioning of auditory cortex is impaired
-could result from a stroke
Sensorineural Hearing Loss
-sound waves transmitted but not not translated into neural signals
-defect can lie in: organ of corti, auditory nerve, ascending auditory pathway, or the auditory cortex
-best fixed with cochlear implant
-not reversible
Vestibular Apparatus…
-Provides essential info for the sense of equilibrium
-head and eye coordinated movement
-posture
-balance
Similarities of Vestibular Apparatus with Cochlea and organ of Corti
-cochlea: VA contains endolymph and are surrounded with perilymph
-Corti: hair cells that respond to mechanical deformation
Differences between VA and auditory system
-VA info doesn’t usually reach conscious awareness
Semicircular Canals
-detect rotational acceleration or deceleration in any direction
-houses ICF
-3 canal divisions
-CN VIII
Superior Canal
head nodding “YES”
Horizontal Canal
head shaking “NO”
Posterior Canal
L and R head tilt
Ampulla
-swelling at the base of each canal
-receptive hair cells sit on top of a ridge here
-fluid filled, moves when head does
Capula
-gelatinous layer where the hairs are embedded
-protrude into the endolymph within the ampulla
-sways in direction of fluid movement like sea weed
Vestibulocochlear Nerve CN VIII
-vestibular nerve and auditory nerve unite
Action Potentials in VA
-depolarization increases the release of NT from the hair cell, decreasing the frequency of action potentials in afferent fibers
When do semicircular canals not respond?
-when head is motionless
-when head is moving in a circle at a constant speed
Otolith Organs
-provide info about the position of the head relative to gravity
-detect changes in the rate of linear motion
-houses saccule and utricle in a bony chamber between canals and cochlea
Saccule
-vertical movement
-ie. trampoline, elevator
Utricle
-horizontal movement
Otolith Crystals
-calcium carbonate + protein
-suspending in the gelatinous layer
Meniere’s Disease
-fluid imbalances in the inner ear that lead to dizziness and nausea
-both vestibular and auditory symptoms occur
-vertigo
-tinnitus
Inner Hair Cells
-transform the mechanical forces of sound (cochlear fluid vibration) into electrical impulses (action potentials)
Outer Hair Cells
-enhance the response/sensitivity of the inner hair cells
-electromotility: change length in response to changes in membrane potential
-hair cells shorten on depolarization and lengthen on hyperpolarization
Auditory Action Potentials
-depolarization of hair cells (basilar memb. is deflected upward) increases rate of NT release which increases rate of firing in afferent fibres
-firing rate decreases as less NTs are released when hyperpolarized upon displacement in the opposite direction
How do hair cells form action potentials?
-shifting mechanical deformation opens and closes receptor cell channels, bringing about graded potentials that lead to action potentials which are propogated to the brain
Taste (aka gustation)
-chemoreceptors are housed in taste buds in mouth and throat
-taste receptors have a 10 day lifespan
Taste Pore
-opening where fluids come into contact with the surface of receptor cells
Taste Receptor Cells
-modified epithelial cells with surface folds (microvilli)
-plasma membrane of microvilli contain receptor sites that selectively bind with chemical molecules
Tastant
-taste-provoking chemical
-binds too receptor cell and depolarizes the cell
Cortical Gustatory Area
-region in the parietal lobe adjacent to the tongue area of the somatosensory cortex
-gustatory pathways are uncrossed
Salty
-stimulated by chemical salts
-NaCl
Sour
-acids which contain a free hydrogen ion, H+, that blocks K+ channels
-citrus fruits
Sweet
-evoked by particular configuration of glucose
-binding of glucose with receptor activated cGMP (G-protein), the second messenger pathways blocks K+ channels
Bitter
-chemically diverse group of tastants
-ie. alkaloids, toxic plant derivatives, poisonous substances
-G-protein, Gustducin, sets off 2nd messenger pathway
Umami
-meaty/savoury
-triggered by amino acids, esp. glutamate (MSG)
-gluatmate binds to a G-protein coupled receptor to start a 2nd messenger pathway
Cranial Nerves of Taste
??
Olfactory Receptor Cells
-renewable afferent neurons
-receptor portion lie in olfactory mucosa
-axons form olfactory nerve
Olfactory Mucosa
-3cm^2 path of mucosa in the ceiling of the nasal cavity
-contains the 3 cell types
Supporting Cells
secrete mucus which coats nasal passages
Basal Cells
precursors for new olfactory receptor cells which get replaced every 2 months
How many different types of olfactory receptors exist?
1000
Odorants
-molecules that can be smelled
-receptor sites on cilia
Olfaction
-binding to receptor cell activates G-protein, triggering cAMP 2nd messenger system to open Na+ channels
-action potential triggered in afferent fibre
Frequency of APs
depends on concentration of stimulating chemical molecules
Olfactory Bulbs
-where afferent fibres synapse
-contains several layers of cells (functionally similar to retinal layers)
Glomeruli
-small ball-like neural junctions that line the olfactory bulbs
-synapse with mitral cells
-“smell files”: forst relay/sorting station for processing olfaction
Mitral Cells
-where olfactory receptors terminate in the glomeruli
-refine smell signals and relay them to the brain (2 possible routes)
Subcortical Route
-goes to limbic system: primary olfactory cortex in lower medial sides of temporal lobes
-hypothalamic involvement: coordination between smell and behavioural reaction
Cortical Route
-from thalamus to cortex
-important for perception and fine discrimination of smell
Adaptability
-sensitivity of an odour diminishes after a short period of time
-highly adaptive
-odour-eating enzymes
Vomeronasal Organ
-detects pheromones
-nonvolatile chemical signals passed subconsciously between individuals
-triggers sociosexual behaviours
