Download The Special Senses : or

The Special Senses : or
Do I Really Have Rocks in My Head?
There are five special senses
•1.
Hearing
(auditory
•2.
Taste
(gustatory)
•3.
Smell
(olfactory)
•4.
Sight
(vision)
5.
Equilibrium
External Anatomy of the Eye
•Eyelids – protect the eye
•Eyelashes – trap foreign
material
•Meibomian glands – oily
secretion that lubricates
the eye
•Ciliary glands –
modified sweat glands –
produce part of the tears
•Lacrimal Apparatus – produce tears
–Lacrimal glands –tears are
produced by these glands
–Lacrimal canals –drain tears
from the eye
–Lacrimal sac and nasolacrimal
duct – drain tears from the eye
and into the nasal passage
Conjunctiva
•Thin membrane that lines the eyelids and covers part of the eyeball
•Secretes mucus that helps keep the eyeball moist
•Conjunctivitis (pinkeye)
– inflammation of the conjunctiva –
usually a bacteria or a virus and is contagious
Eyeball Coverings (Tunics)
•The eye itself is called the eyeball or the “globe”
•Sclera – the outermost tunic
–Thick, white, tough
–Called the fibrous tunic
–The “white of the eye”
– Cornea – the anterior, clear
portion of the sclera
Eyeball Coverings (Tunics)
•Choroid – the middle coat of the eyeball
–Rich blood supply
–Contains a dark pigment
- Anteriorly is modified:
Ciliary body – smooth muscles to which the
lens is attached
•Iris – the “colored part of the eye”
–Contains many small muscles that change
the diameter of the pupil
–This regulates the amount of light entering
the eye
The Retina
Also called the sensory tunic
The innermost tunic
Contains photoreceptors
• Optic disk – the site where the optic nerve exits the eyeball –
no receptors (the blind spot)
• Fovea centralis – lateral to the optic disk – the site of greatest
concentration of photoreceptors
Photoreceptors
1. Rods – allow us to see gray shades in dim
light
–Night blindness – interference with rod
function
2. Cones – respond to colors
–3 types of cones – respond to blue, green
and red light
–Color blindness – interference with
function of cones
Mechanism of Vision
•Light energy causes changes in certain chemicals (called pigments)
–when light strikes rhodopsin protien the retinal changes
the shape –
–this releases the opsin and initiates the impulse to the
nerve
Lens
•The lens focuses light rays onto the retina
Is a flexible, bi-convex crystal – like structure
•Contractions of the ciliary body change the shape of the lens and
allow us to focus on near and far objects
•Produces a real (upside down) image on the retina
Fluids in the Eye
•Anterior chamber filled with a clear watery fluid called
the aqueous humor
Aqueous humor - provides nutrients for the lens and cornea and
helps maintain normal intraocular pressure
Posterior chamber filled with a thick, jelly like material called
the vitreous humor or the vitreous body
Pathway for Light
•Light rays are refracted as they pass from air into the cornea,
through the aqueous humor, lens, and vitreous humor.
Lens changes shape to very the amount of refraction to
allow us to focus our eyes
Accommodation – the ability of the eye to focus on
close objects (less than 20 feet away).
Emmetropia – images focused correctly on the retina
Pathway for Light #2
Myopia – nearsightedness - light from far away objects in focused
in front of the retina – image is then blurred
Hyperopia – farsightedness – light from close objects is focused
behind the retina – image is blurred
Visual Fields and Pathways
Axons from rods and cones are bundled together ans leave
the eyeball as the optic nerve
•Optic chiasma – fibers from the medial side of each
optic nerve cross over to the opposite side
The resulting fiber tracts are called the optic tracts and
contain lateral fibers fromthe same side of the body and
medial fibers from the opposite side of the body
These tracts continue into the thalamus
Visual Fields and Pathways #2
•Each side of the brain receives visual input from both eyes
The visual fields from each eye overlap
These two facts produce our binocular vision
Eye Reflexes
•Photopupillary reflex – pupil responds to bright or dim light
•by contracting or widening
•Accommodation pupillary reflex – pupils constrict when
•we view close objects
The Ear: Hearing and Balance
The structures of our ear allow us to detect sound vibrations
form a frequency range of 20 – 20,000 Hertz
Structures in our ear also provide information
concerning position of our head with respect to
gravity as well as information concerning motion of our head
Anatomy of the Ear
External Ear
•3 regions – external, middle, inner ear
Pinna – the cartiledge structure that surrounds the auditory opening
External auditory canal – leads to the eardrum
Tympanic membrane – the eardrum
Anatomy of the Ear
Middle Ear
–Air filled cavity within the temporal bone
The bony wall has two openings –
the oval window and the round window
–The auditory tube (eustation tube)
–Contains 3 small bones called
ossicles
•Malleus (hammer),
•incus (anvil),
•stapes (stirrup)
Inner Ear
•Consists of a group of bony chambers called the bony labyrinth
•3 divisions of the labyrinth
–Cochlea,
–vestibule,
–semicircular canals
Mechanism of Hearing
•Sound waves reach the cochlea through vibrations of
the tympanic membrane, ossicles, and oval window
The cochlea contains the organ of Corti which
contains hearing receptors.
•Hearing receptors (called hair cells) are embedded
•in the basilar membrane
•A thick, gel – like membrane called the tectorial membrane
•lies over the hair cells
High pitch sounds stimulate receptors near the oval window
and low pitched sounds are detected further along the cochlea.
Mechanism of Hearing #2
•Sound vibrations that reach the oval window sets the fluids
•of the inner ear into motion
•Fluid motion causes the tectorial membrane to move
•Movement of the tectorial membrane stimulates the hearing receptors.
•The sound impulses are transmitted via the cochlear nerve to the brain
Mechanism of Equilibrium
•Equilibrium receptors are called the vestibular apparatus
Two types of equilibrium – static and dynamic
Static – the position of our head with respect to gravity
–Dynamic – movements of our head
Static Equilibrium #2
•As the head moves, the otoliths roll in response to changes
•in the pull of gravity.
•This movement pulls on the gel (otolithic membrane)
•Movements of the otolithic membrane pull on receptors that are
•embedded in the membrane
Movement of the receptors provide information on the position of
the head with respect to gravity
The receptors send their nerve impulses along the vestibular nerve
Dynamic Equilibrium
Receptors for dynamic equilibrium are found in the semicircular canals
•3 semicircularcanals postioned at right angles to each other (x, y z axes)
•Each semicircular canal contains a receptor region called
•the crista ampullaris
•Each crista ampullaris contains a tuft of receptor hair cells covered
•by a cap of gelatinous material called the cupula
Dynamic Equilibrium #2
•When your head moves, the thick fluid in the semicircular canals
(endolymph) lags behind because of greater inertia.
•The fluid moves in the opposite direction and drags
the cupula in the opposite direction along with it.
•These impulses provide information on changes in motion of your head
These receptors respond to changes in velocity (acceleration) and
not constant motion
Chemical Senses: Taste and Smell
•Receptors for taste and smell are called chemoreceptors because they
•respond to chemicals in solution
There are four types of taste receptors and one type of olfactory receptor
•These senses complement each other and respond to
•many of the same stimuli
Sense of Smell
•There are thousands of olfactory receptors located in a
postage stamp sized area in the roof of each nasal passage
•Sniffing causes more air to flow in the upper regions of
the nasal passages and thereby intensifies the sense of smell
Olfactory receptor cells have long clia called olfactory hairs that
protrude from the nasal epithelium and are constantly bathed in mucus.
Sense of Smell #2
They are stimulated by chemicals dissolved in the mucus
These receptors are very sensitive – just a few molecules can
activate them.
•They adapt quickly to unchanging odors – we can no longer smell them
•Olfaction is tied closely to the emotional – visceral parts of the brain
•Olfaction is tied closely to memory