Download Human Senses

Chapter 15
Our Senses
 Vision
 Smell
 Taste
 Hearing
 Balance
 Touch*
Anatomy of an Eyeball
 Accessory structures
 3 tunics (layers)
 Fibrous (blue)
 Vascular (yellow)
 Sensory (red)
 Segments
 Anterior divided into chambers
 Posterior
 Filled with humors (fluid)
 Lens
Accessory Eye Structures
 Eye muscles
 Rectus as named; obliques lateral and opposite
 Diplipia: muscle weakness/alcohol
 Strabismus: eyes not aligned
 Eyebrows
 Eyelids
 Blink to spread secretions
 Eyelashes trigger blinking
 Conjunctiva
 Mucus prevents drying out
 Conjunctivitis
 Lacrimal apparatus
 Tears clean, protect, and moisten
 Excess secretions



Emotional tears unique to humans
Stuffy/runny nose when cry
Watery eyes with cold
Fibrous Tunic
 Avascular CT
 Sclera (white of the eye)
 Protects and shapes
 Muscle attachment
 Continuous with dura mater
 Cornea (transparent)
 Outer stratified squamous, why?
 Inner simple squamous maintain clarity
 Innervated
 Transplants not rejected between people
Vascular Tunic
 Choroid
 Vascularized to supply nutrients
 Melanocytes to absorb light
 Ciliary body
 Smooth muscle ring  ciliary muscles control lens shape
 Ciliary processes secrete aqueous humor
 Suspensory ligaments hold lens in place
 Iris
 Colored portion of ciliary body


Brown pigment only (varies)
Less scatters light = blues/greens/grays (babys)
 Encircles the pupil (2 smooth muscle layers)
Sensory Tunic
 Pigmented layer (outer)
 Prevents light scattering
 Phagocytize damaged photoreceptors
 Neural layer (inner)
 Photoreceptors, bipolar cells, ganglion cells



Rods and cones
Blind spot (optic disc) filled
Macula lutea and fovea centralis
 Rapid eye movement for rapid scene changes
 Vascular supply from choroid and central vein/artery
 Opthalmologist examines
 Retinal detachment when layers separate


Vitreous humor seeps in
Photoreceptors lose nutrients = blindness
Humors
 Anterior segment with aqueous humor
 Similar to blood
 Continual development
 Nutrients & O2 to lens, cornea, & retina
 Blocked drainage = up pressure =
glaucoma
 Posterior segment with vitreous humor
 Transmits light, support lens, &
intraocular pressure
 Embryonic development
The Functioning Eye
 Light enters the pupil, regulated by the iris
 Passes through a convex lens
 Avascular
 Lens fibers added through life

Cataracts = clouding of lens due to loss of nutrients
 Lens is shaped by the ciliary body to focus light on the
retina (accommodation)
 Refraction of light converges to a focal point
 Real image forms upside down and reversed
Visual Pathways
 Visual field
 Overlap to provide depth
perception = 3D vision
 Ganglion cells
 Optic nerve
 Optic chiasm
 Nasal and temporal visual field
 Optic tract
 Thalamus
 LGN
 Primary visual cortex
 Conscious perception of images
Olfactory Receptors
 Ciliated bipolar cells
 Located in olfactory epithelium
(psuedostratified )
 Mucus captures and dissolves odorants
 Pass through cribriform plates
 Synapse in olfactory bulbs
 Odorant detection
 Humans can distinguish 10,000 odors
 Some is pain (ammonia, chili, methanol
 Combinations of different odorant/receptor
binding
Olfactory Neural Pathway
 Olfactory receptors synapse
with mitral cells
 Contained in glomeruli
 Receptor type specific
 Refines smell
 Mitral cells signal via olfactory
tracts
 2 pathways
 Olfactory cortex
 Hypothalmus, limbic system
= emotional connection
Taste
 Taste buds detect molecules in solution
 About 10,000
 Four familiar and 1 other found in papillae
 Sweet: organic substances

Alcohol, sugar, amino acids
 Sour : acids, H+ in solution
 Salty: inorganic salts
 Bitter: alkaloids
 Aspirin, nicotine, caffeine
 Umami: glutamate & aspartate
 meats, cheeses, and protein-rich foods (MSG)
 Each receptor responsive to a particular type of substance
 Often mixes
 Many ‘tastes’ (80%) are really smell (head colds)
Papillae
 Fungiform
 Mushroom shaped
 Tops of, all over tongue
 Foliate
 Fold is side walls
 Circumvallate
 Largets, fewest, back of tongue
 Filiform
 Hair like projections all over tongue
 Do not have taste buds
Gustatory Neural Pathway
 Cranial nerves carry
sensations to medulla
 Relay through the
thalamus into primary
gustatory cortex
 Pathway initiates
digestive process too
Regions of the Ear
 Outer ear
 Pinna, external auditory canal, and
tympanic membrane (separates)
 Middle ear
 Pharyngotympanic tube equalizes
pressure b/w middle ear and atmosphere
(‘pop’)
 Function of tympanic membrane
 Ossicles (malleus, incus, & stapes)
amplify signal
 Inner ear
 Bony and membranous labyrinths
 Semicircular canals for rotation of head
 Vestibule report on changes of head
position

Saccule and utricle with equilibrium sensors
called maculae
 Cochlea houses the hearing organ
The Cochlea
 Scala vestibuli
 Perilymph: like CSF
 Oval window
 Scala Tympani
 Perilymph
 Round window
 Scala media (Cochlear duct)
 Endolymph: K+ rich intercellular fluid
 Organ of Corti

Contains hair cells embedded in a basilar membrane
 Vestibular membrane
 Tectorial membrane bends cells as basilar membrane
moves

Signal to auditory nerve
Frequency and Amplitude
 Pitch depends on frequency
 High pitch = higher
frequency
 Basilar membrane responsive
to certain frequencies
 Sounds detected as increase
in AP’s by the brain
 Greater volume = higher amp
of generated wave
 Vigorous vibrations in
cochlea = more bending =
more AP’s
 Hair cells easily damaged due
to prolonged exposure to
certain frequencies
Physiology of Hearing
 Pinna collects sound waves
 Travel down auditory canal to tympanic membrane

Moves ossicles as it vibrates
 Stapes pushes on oval window, in and out
 Creates fluid pressure waves in scala vestibuli perilymph
 Pressure waves deform scala tympani to push round
window in and out
 Pressure changes move endolymph
 Pressure changes in endolymph, from perilymph changes,
moves the basilar membrane
 Hair cells on Organ of Corti bend as they move against the
tectorial membrane
 Generates nerve impulses that leave via the cochlear nerve
Auditory Pathway
 AP signals from cochlea to
medulla
 Cochlear nuclei
 Some fibers cross, all ascend,
from olives into MGN in the
thalamus
 Pass through inferior colliculi
(reflex area)

Interactions with superior colliculi
to turn toward sound
 Synapse in primary auditory
cortex
 Localization utilizes relative
intensity and timing
http://openlearn.open.ac.uk/file.php/3373/SD329_1_027i.jpg
Equilibrium
 Static
 Respond to changes only, keeps
head still and balanced
 Maculae embedded in otolithic
membranes in saccule/utricle
 Dynamic
 Maintenance of body position after
sudden movement
 Crista in ampullae of semicircular
canals
 Both operate by bending hair cells
 Head movements cause fluid
movement (slower)
 Changes action potentials
 Sudden stop, but fluid still moving
= dizzy
 Brain interprets and commands
skeletal muscles
Motion Sickness
 Results from conflict between eyes and equilibrium
sensors in the inner ear
 Feeling motion, but not seeing it (inside car)
 One system is hallucinating, implying toxins in system =
vomiting
 Dramamine inhibits input from equilibrium sensors
 Astronauts learn to control