lecture 17, 18, 19, 20, 21: special senses Flashcards
(37 cards)
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
7.4.4.2. Explain sound waves
- pressure disturbance (alternating areas of high and low pressure)
- of areas of compression and rarefaction that create sound waves
- frequency: pitch
-most sensitive to 1500-4000 Hz; can distinguish differences of 2-3 Hz in that range and perceive them as differences in pitch
-pitch relates to which area(s) of basilar membrane activated and is perceived by the primary auditory cortex
- high frequency: base
- low frequency: apex
-amplitude: loudness:
-intensity of sound measured in decibels (dB) – a logarithmic scale
- loudness is our perception of sound intensity and, interestingly, an increase of 10 dB is perceived as only about a doubling of loudness
-loudness is perceived at level of brain by:
greater fluid movement leading to greater deflections of hair cells
result is larger graded potentials, more release of NT, more frequent APs in cochlear nerve
7.4.4.4. Explain the major events involved in hearing
-louder sounds cause increased deflection of the tympanic membrane
Outer ear – pinna to acoustic meatus to tympanic membrane
Middle ear – malleus, incus, and stapes to the oval window
Inner ear – scalas vestibuli and tympani to the cochlear duct
- stimulation of spiral organ and generation of impulses in the cochlear nerve
figure 15.3
7.4.4.3. Describe the structure and function of outer and inner hair cells
sound transduction
- movment of basilar membrane -> bend hair - > open cation channels -> receptor potnetial -> release NT glutamate to excite cochlear nerve
- opp direction -> depolarization
- inner hair cells:
- are key in sound transduction
- longest stereocilia are microvilli: embedded in tectorial membrane, connected by fine tip links
movement of basilar membrane:
- bends hairs, tension on tip links
- opens mech gated cation channels
- Ca+, K+ enter, receptor potential
- hair cells release NT glutamate to excite cochlear nerve
- movement in other directions loosens tip link and closes channel, depolarization
- outer hair cells:
- not involved in sound reception
- supportive/protective roles: efferent fibers from brain cause them to stiffen in response to loud noises, dampening motion of basilar membrane and protecting the inner hair cells
- depolarize + repolarize in response to basilar membrane
- move and stretch
- increase responsiveness of inner hair cells by amplifying motion of basilar membrane
7.4.4.5. Describe the auditory pathway
impulses from the cochlea pass through
- the spiral ganglion (in the periphery)
- to the cochlear nuclei (in the brain stem)
-to superior olivary nuclei (localization) and inferior colliculi (auditory reflex center)
- to the auditory cortex
- only some auditory pathways from each ear decussate so that both cortices receive input from both ears
- Localization perceived by superior olivary nuclei that determine relative sound intensity and relative timing reaching the 2 ears
7.4.4.6. Compare static and dynamic equilibrium, and describe the structure and function of receptor organs for equilibrium
- static equilibrium: receptors in vestibule (linear acceleration & position of head with respect to gravity)
- dynamic equilibrium: receptors in semicircular canals monitor head rotation (oriented in 3 planes of space)
Maculae
- one in utricle and saccule
- consists of supporting cells and hair cells
- each hair cell has stereocilia (these are actually microvilli) and one kinocilium (true cilium) embedded in the otolithic membrane (jellylike mass studded with tiny calcium carbonate crystals called otoliths)
- utricular hairs respond to horizontal movement or tilting the head
-saccular hairs respond to vertical movement
-note vestibular nerve fibers wrapped around hair cells
Crista Ampullaris (Crista):
- one in each semicircular canal allowing them to be located in all 3 planes of space
-stimulated primarily by rotational type movements; specifically, changes in velocity
-support cells plus hair cells whose hairs are extend into a gel-like mass, the cupula
- movement bends the hairs of the hair cells → signal
dendrites of vestibular nerve fibers encircle base of each hair cell
-directional bending of the hairs (due to endolymph inertia) increases or decreases the rate at which impulses reach the brain (IS OPPOSITE, 1 DEPOLAR OTHER REPOLAR- INFO ABT DIRECTION OF ROTATION)
7.4.4.7. Describe the equilibrium pathways
need to react quickly (no time to process and decide)
- sensory pathways related to balance go directly to the brainstem
rather than the cerebral cortex, allowing our body to respond reflexively
nuclei integrate information from all 3 types of receptors (vestibular, visual, somatic) and send commands to brain stem motor centers that control extrinsic eye muscles and neck, limb and trunk movements via vestibulospinal tracts
7.5.1.Discuss the levels of motor control
3 levels:
precommand: highest
- cerebellum (no direct access to spinal cord therefore has to coordinate with projection level and motor cortex) + basal nuclei
- start/stop movement
- coordinate movements with posture
- block unwanted movements
- monitor muscle tone
projection level: middle
- primary motor cortex
- brain stem nuclei
- direct + indirect motor pathways
- help control reflex + actions controlled by CPG
segmental level: lowest
- spinal cord
- CPG central pattern generators (excitatory + inhibitory repetitive motor activities)
- automatic movement
sensory vs motor
- descending efferent (motor) instead of ascending afferent ( sensory)
-motor behaviour (motor) instead of perception (sensory)
7.5.2.Describe the direct and indirect pathways of upper motor neurons
descending motor pathways:
- efferent impulse from brain to spinal cord
2 groups:
direct: pyramidal tracts
indirect: all other tracts
involve 2 neurons
upper: in motor cortex
lower: spinal or cranial motor neuron
direct
- axons descent without synapse from primary motor cortex
- synapse at level where neuron exits
- 90% in lateral, 10% in anterior
- crossing over at medulla (pyramid to lateral) or goes straight down
- response happens quickly
indirect:
- includes rubrospinal, vestibulospinal, reticulospinal, tectospinal
- multi-synapse
- axial muscles for balance + posture
- muscles control coarse limb movements
- head, neck and eye movement to follow in visual field
