lecture 17, 18, 19, 20, 21: special senses Flashcards
7.4.1.Taste: describe the gustatory receptors
- tastebuds in papillae
3 types:
fungiform: mushroom shaped, all over tongue
vallate: largest, make v shape
foliate: laterally, decrease in age
cells:
- gustatory epithelial cells: have long microvilli gustatory hairs, extend through taste poor, where bathed by salvia containing food chemicals
- gustatory. hairs have receptors for food (tastings) , once activated they activate cranial nerve responsible for taste (dendritic process around gustatory cells)
- turnover is 7-10 days, from basal epithelial cells
taste modalities:
sweet
bitter
umami
-> all release ATP, receptors coupled to G protein
sour (H+ goes in, blocks K+ channels for depolarization)
salty (+ Na to depolarize gustatory epithelial cells)
- threshold most sensitive to bitter (against toxic sensitive)
- 80% of taste experience is due to smell
7.4.1.Taste: the neural pathway for taste
- directed via thalamus, 1st, 2nd, 3rd order neurons to taste cortex
- facial nerve (VII): carries impulses from anterior 2/3 of tongue
- glossopharyngeal (IX) carries impulses from poster 1/3 of tongue and pharynx
- vagus nerve (X) very minor, transmits from epiglottis and lower pharynx
7.4.2.Smell: describe the olfactory receptors
- chemoreceptors
- olfactory epithelium ( in roof of nasal cavity, not best location to catch smells)
- covers superior nasal conchae
- contains olfactory sensory neurons
- bipolar neurons with radiating olfactory cilia
- surrounded and cushioned by columnar supporting cells
- stem cells at base of epithelium: only place to replace neurons
- olfactory neurons have long cilia (increase SA)
- cilia covered in mucus
7.4.2.Smell: the neural pathway for smell
- axons gather into small fascicles to form filaments of olfactory nerve (cranial nerve 1)
- project superiorly through cribriform plate to synapse in olfactory bulb
- axons of mitral cells form olfactory tract
2 destinations of mitral cells:
1) olfactory cortex: smell identified + interpreted info does not travel through thalamus,
2) limbic: link with memory and emotion
7.4.3.1. Describe the structural components of the eye
- eyebrows:
- overlie supraorbital margin, shade eye, protect eye from perspiration - eyelids: (palpebrae)
- separated by palpebral fissure
- lacrimal caruncle: contains sebaceous and sweat glands
- eyelash follicles: innervated, reflex blinking
- tarsal glands: lubricate eyelid and eye with oily secretion - conjunctiva
- transparent mucous membrane, lines eyelid + folds back over eye called bulbar conjuctiva,
- only covers white part of eye
- lubricating mucus to prevent drying of eye - lacrimal gland
- contains mucus, antibodies, lysozyme
- produces tears - fibrous layer
lens: divides eye into anterior + posterior
fibrous: composed of avascular dense CT
- sclera: majority of fibrous layer
- protects+shapes, anchor site for extrinsic eye muscles
- white of the eye
cornea:
- transparent, allows light entry + refraction
- external epithelial sheet: protects + renew cornea, stratified squamous
- corneal endothelium: simple squamous, sodium pumps to maintain corneal clarity
- lots of nerve endings, no blood vessels (no access to immune system for corneal transplant success)
- vascular layer:
choroid: vascularized, nourishes eye layers
pigmented, contains melanin to absorb light, minimize scatter
ciliary body
- encircles lens
- composed of smooth muscles, influence shape of lens, ciliary muscles
iris
- eye colour
- central opening is pupil
- consist of 2 layers of smooth muscles
- allow constriction (circular; PNS) and dilation (radial; SNS)
- only a brown pigment (melanin) , different amounts give different colour (less - more space, diff colour eyes)
- inner layer (retina)
- photo receptors (transduce light)
- 2 layers:
- pigmented layer: absorbs light, cells can be phagocytic, stores vitamin A
- inner neural layer: involved in vision, composed of photoreceptors, bipolar cells, ganglion cells
- optic disc: no photoreceptors, blind spot of eye
-photoreceptors:
rods: more present, dim light and peripheral vision, no sharp image
cones: less present, bright light, high resolution, colour vision, in centre of eye (fovea + macula)
macula lutea:
- high concentration of cones for visual acuity, fine details
- mostly cones
fovea:
- centre of macula
- other cells off to the side
- light has direct access to photoreceptors (only cones)
aqueous humor
- in anterior segment (anterior + posterior segments)
- supplies nutrients and O2 to lens + cornea
- carries away metabolic waste
- turns over, we can lose this
vitreous humor
- in posterior segment
- forms in the embryo + lasts lifetime
- transmits light
- holds 2 retinal layers together
- maintains intraocular pressure (layers stay in place)
7.4.3.2. Explain the concepts of refraction, image formation, accommodation
- cornea + lens focus light on retina
- mixture of RBG wavelengths
- objects have colour as they absorb + reflect wavelengths
- light passes from one transparent medium to another that has a different density, speed changes
- if light changes density, when approaching on an angle it is refracted; convex lens of the eye, image is upside down and flipped left to right, flipped again in primary visual cortex
near vision:
accommodation of lens: bulge more, 10 cm from eye, furthers while aging
- presbyopia: after 50, need reading glasses
- constrict pupils: PNS
- convergence of eye: keep object focused on retinal fovea, medial rectus muscle + oculomotor cranial nerve
7.4.3.5. Describe the neural pathway for vision
cornea -> aqueous humor -> lens -> vitreous humor -> neural layer -> photoreceptors
refracted 3 times
cornea, entering lens, leaving lens
- refraction is constant in retina, can be adjusted for distance in lens
- eyes best adapted for distant vision
- emmetropic point: vision far point, distance at which no change in lens is required
- distant vision: parallel rays, precise focus on retina, ciliary muscles are relaxed (SNS) and lens is flat
- close vision: light diverges so needs to be focused by lens, ciliary muscles contract (PNS - rest/digest) and lens bulges
7.4.3.3. Describe the principal refraction abnormalities
- problems related to shape:
myopia: nearsightedness, eyeball is longer, object focus in front of retina instead of on it
- concave lens to move focal point further back
hyperopia: farsightedness, eyeball is short, distant objects focus behind retina
- convex lens to move focal point forward
7.4.3.4. Briefly describe the processing of visual signals in the retina
photoreceptors:
- receptive region in pigmented layer of retina
- cilium connects outer to inner segment
- outer segments: contain visual pigments (rhodopsins) change shape as light is absorbed, embedded in disc membranes
- rods and cones very vulnerable to damage,
- renew segment every 24 hrs with new discs
- old discs detach at the other end and are phagocytize by pigment cells
- in dark we synthesize pigment
- cis to trans, rhodopsin to opsin
- cones are stronger therefore require stronger light
- photoreceptors hyper polarize when exposed to light and acts as a signal (channels closed, no Ca+ or Na+)
- photoreceptors remain depolarized in the dark
- no release of NT
- light takes away inhibitory action potentials, at level of bipolar cells allowing ganglion cells to be activated, ESPS occurs in ganglion cells, action potential occurs
- allows us to see by taking aways ISPS at bipolar cells
(DIAGRAM)
7.4.3.4. Briefly describe the processing of visual signals in the retina (light + dark adaptation)
- dark to light
- both stimulated, only see white light
- rods become non functional as rhodopsin bleaches
- cones take over (5-10 min)
- closes pupil
- light to dark
- initially everything looks dark,
- cones no longer stimulated
- rhodopsin accumulates and rods and tranducin moves back onto disc membranes
- opens pupils
7.4.3.5. Describe the neural pathway for vision
DIAGRAM
ganglion-> optic nerve -> lateral geniculate (thalamus) -> primary visual cortex
- axons of retinal ganglion form optic nerve
- most fibres of optic tracts continue to lateral geniculate body of thalamus
- other optic tract fibres end in superior (visual reflex) and pretectal nuclei (pupil reflex)
- optic radiations travel from thalamus to primary visual cortex
more detail:
- medial retina receives light from lateral field of view
- lateral retina revives light from central field of view (overlap here)
- medial fibers of optic nerve decussate at optic chasm
- each optic tract leaving optic chiasm contains fibres from lateral part of eye on same side and medial of opp eye
- each optic tract carries info for same half of visual field
depth perception:
- overlap in middle area, each eye sees on diff angle
- PVC fuses images from both eyes to give depth perception
- lost if only looking with one eye
7.4.4.1. Describe the anatomy of the three main regions of the ear
(external ear)
external ear: hearing only
auricle: elastic cartilage, funnels sound waves into external acoustic meatus
lobule: lacks cartilage
external acoustic meatus:
-elastic cartilage to canal in temporal bone
- lined with hair, skin, sebaceous + ceruminous glands (secrete earwax to trap foreign bodies + repel insects)
tympanic membrane: ear drum
- vibrated by sound waves, energy transferred to ossicles
-tympanic membrane is the boundary between middle and outer ear
- thin connective tissue
7.4.4.1. Describe the anatomy of the three main regions of the ear
(middle ear)
middle ear: hearing
- air filled cavity with eardrum laterally and a bony wall with 2 openings: oval window and round window
pharyngotympanic tube:
- links middle ear with nasopharynx
- eardrum vibrates only if pressure on both sides is equal, other wise sounds are distorted (ear popping on air plane)
ossicles:
- 3 smallest bones in body
- handle of malleus links to ear drum
- stapes fits into oval window
- transmit vibration of eardrum to oral window
tensor typmani and stapedius:
- 2 tiny muscles that contract to protect hearing receptors by limiting ossicle vibrations under loud noises
7.4.4.1. Describe the anatomy of the three main regions
of the ear
(internal ear: 2 labyrinths, 4 parts)
internal ear: hearing + balance
a) bony labyrinth:
- system of tortuous canals through temporal bone
- contains vestibulae, cochlea, semicircular canals
- filled with perilymph (like CSF)
b) membranous labyrinth:
- membranous sacs within bony labyrinth
- filled with endolymph (K+ rich intracellular fluid)
- these fluids conduct sound vibrations + respond to mechanical forces linked to changes in body position + acceleration
bony labyrinth:
1. vestibule:
- central cavity in bony labyrinth
- contains 2 sacs in perilymph
- utricle: leads to semicircular canals
- saccule: leads to cochlea
- monitor head position, contain equilibrium receptors called: maculae that respond to gravity
- semicircular canals:
- 3 canals that lie on 1/3 planes of space
- lined with membranous semicircular ducts, that link to utricle
- ampulla: swollen end of canal, houses equilibrium receptors in region called: cristae ampullares
- respond to angular movements of head - cochlea:
- extend from anterior vestibule (saccule)
- coils (2.5 turns) around a bony pillar: modiolus
- contains cochlear duct, which ends at cochlear apex
- contains spiral organ of corti: hearing receptor
- central cochlear
duct: 3 chambers - scala vestibuli: perilymph,
continuous with vestibule, begins at oval window - scala media: endolymph, cochlear duct itself
- scala tympani:
perilymph, links to round window - helicotrema: allows 2 perilymph champers to be continuous
- spiral organ:
- sits on basilar membrane (important for sound reception)
- basilar membrane is narrow and thick near oval windows and widens and thins as it approaches apex
- consists of supporting cells + cochlear hair cells (hearing receptors)
-1 row of inner cells + 3 rows of outer hair cells sandwiched between tectorial and basilar membrane
Note cochlear branch of vestibulocochlear nerve
