Download Special Senses - Everglades High School

Special Senses
Senses of the body
 General sensory receptors are found all over the body.
 Proprioceptors of muscles and joints.
 Pressure, pain, touch, and temperature receptors
of the skin.
 Special senses include the following with special receptors/organs:
Hearing
Taste
Vision
Smell
Equilibrium
The eye and vision (70% of all sensory receptors are in the eye)

Structures of the eye

Eyelashes – Prevent debris from entering eye

Eyelids – Cover and protect the eye

Conjunctiva – Lines the eyelid and part of the surface of the

Eyeball. Secretes mucus for lubrication.

Lacrimal apparatus – Glands secrete the dilute salt solution with
enzymes and antibodies, wash across the eye to the canals (in the
corner of the eye) then the sac and finally the nasolacrimal duct.

Extrinsic eye muscles – Six muscles attached to the outer eye
surface, responsible for gross motor unit of the eyeball.

Meibomian glands – specialized sebaceous glands to lubricate eye.

Ciliary glands – modified sweat glands between eyelashes for
lubrication.

Eye ball – hollow sphere made from 3 tunics (coats) and is filled with
a liquid (humors). Divided into two chambers by the lens.
Tunics
 Sclera – outermost layer, thick and white with a transparent center
called
the cornea (where light enters the eye).

Choroid – blood rich nutritive tunic with a dark pigment (prevents light from
scattering inside the eye). Forms the ciliary body and the iris (smooth muscles).
Iris has a rounded opening – pupil – which regulates the amount of light entering
the eye.

Ciliary body – attaches to the lens to modify shape

Iris – contracts and relaxes to control pupil size.

Retina – Sensory tunic; location of cones (detects color) and rods (low levels of
light, grays and peripheral vision). These receptor cells lead to sensory neurons
that converge to form the optic nerve.

Blind spot – on the retina where the optic nerve is found (no sensory receptors
so no vision at this point)

Fovea centralis – area lateral to each blind spot where the highest concentration
of sensory receptors is located (area of highest visual acuity)
Humors

Aqueous humor – in the anterior chamber of the eye. Helps
maintain intraocular pressure and provides nutrients for lens and cornea
(they lack blood supply).

Vitreous humor – in the posterior chamber of the eye. Gel like
liquid used to prevent collapse of the eye.
Physiology of vision

Light waves travel towards the eye and enter through the pupil.

The movement of the light waves through the structures of the eye,
bend the light rays (hopefully to focus directly on the retina). This is
called refraction.

Depending on the distance of the object you are looking at, the lens
must change shape (with contraction of ciliary body) to focus light
waves on the retina. The ability to change and focus on objects at
different distances is called accommodation. The image is also
inverted as the light waves travel through the lens.
Notice that the farther the image, the
smaller the image on the retina.

Once the receptors have been stimulated, thereby changing the
shape of pigment proteins in the cell, this change causes electrical
changes creating the nerve impulse.

The optic nerves from both eyes cross at the optic chiasma, which
results in the left side of the brain receiving visual information from the
right eye and vise versa.
Notice the overlap area
which creates binocular
vision – which allows for
depth perception.

Once the impulse has reached the occipital lobe, the visual
information will be interpreted and understood by known visual
information stored in that area of the brain. Ex. recognizing someone
you have met before.
Eye muscle fatique – Internal and External muscles

External muscles- responsible for convergence – reflexive movement
of the eyes medially (toward the center) when you view something
close. Strabismus “crossed “ eyes is caused by unequal pulls by
these muscles. The muscles must be retrained.

Internal muscles – ciliary body constrict focusing lens and iris
contracts reducing the size of the pupil.

Over time these muscles can become fatigued such as when you
read for long periods of time. Take a break and look off in the
distance to relax those muscles.
Hearing and Equilibrium

Mechanoreceptors are used which respond to physical forces (movement of
liquid) to convey information on hearing and equilibrium. There are two
different systems in the ear, one for hearing and one for equilibrium.
Hearing

Anatomy of the ear

External ear
Pinna or Auricle – external auditory meatus, gathers sound waves and
directs them down the canal.

External canal – (about 1 inch), conduct waves through the temporal bone.

Ceruminous glands – secrete wax, contains antibodies and filters debris,
also a deterrent for mosquitoes

Tympanic membrane – vibrates when sound waves strike it and transmit
vibrations to middle ear.
Middle ear (about the size of a dime)

Auditory tube – links middle ear with throat and helps to equalize pressure in
middle ear. Typically is closed.

Oval window – connects the stirrup (stapes) to the inner ear on cochlea.
Ossicles

Hammer / malleus – transmits vibrations of the eardrum to the next ossicle.

Anvil / incus – second ossicle, transmits vibrations.

Sirrup / stapes – transmits vibrations to cochlea.

Inner ear (bony chamber/labyrinth) – just behind eye orb.

Cochlea (contains the organ or corti) – location of hair cells (hearing
receptors). Receives vibrations from oval window. Made up of vestibule and
semicircular canals. Contains a fluid that transmits vibrations to auditory
nerves
Pathway and mechanism of hearing – the journey of the vibration
Hearing Deficit Causes
 Conduction deafness – There is an obstruction to the conduction of vibrations
on the way to the organ of corti. Causes include ear infection, build up of wax
in canal, fusion of ossicles, and ruptured eardrum. Hearing aids can help by
sending the vibrations via the bone.
 Sensorineural deafness – Degeneration or damage to the receptor cells.
Causes include over exposure to very loud sounds. No treatment.
 Equilibrium
 Monitored by the vestibular apparatus (includes the vestibule and semicircular
canals of inner ear). Help control balance with the cerebellum! Where are you
in space or deep in the water?
Two different functions
 Static equilibrium – receptors in vestibule monitor the position of the head with
respect to gravity when you are not moving. (i.e. – sitting in your chair and you
turn your head to the side). When your head moves, the gel moves and
triggers the hair cells sending the message to the brain via the 8th cranial nerve
(vestibular).

Dynamic equilibrium – Receptors are in semicircular canals and
respond to the circular movements of the head (ex. twirling on
the dance floor, the movements of your body while on a boat in
rough seas). The endolymph within the semicircular canals
moves opposite the direction that your body is moving, this
motion shifts the cupula (gel like material) thereby stimulating
the receptor hairs. Once stimulated the information about the
movement of the head and body is transmitted to the brain via
the vestibular nerve.
Chemical Senses – These receptors respond to specific chemicals in solution
 Olfactory (smell)
 Olfactory receptors are located in the roof of each nasal cavity, there are 1000’s
that each detect a different chemical odor. These receptors are at the top of
the nasal cavity, which is why “sniffing” intensified the smell, because more air
is forced to the top of the cavity, stimulating the receptors.

The receptor cells have hairs on them (similar to equilibrium and
hearing). They are bathed in a thick layer of mucus. As the
olfactory chemicals diffuse through the mucus, they stimulate
the receptors which send the message via the olfactory
filaments to the olfactory nerve (CN I).

This pathway goes directly through the limbic system (emotional center),
therefore there tends to be strong emotional ties to smells.
These receptors, like others, can adapt to stimuli that are
constant, which is why women or men don’t smell their own
cologne or perfume after a period of time.
Sense of Taste
 Receptors are called taste buds and there are over 10,000 located on the
tongue. Very few are located on your soft palate and the inside of your
cheek.
 There are 4 basic taste sensations:
 Sweet – respond to sugar, saccharine, and some amino acids.
 Sour – respond to H+ ions (acids)
 Bitter – respond to alkaloids (basic)
 Salty – respond to metal ions
 The regions of the tongue don’t truly hold true, because the
receptors are pretty well evenly distributed over the surface of the tongue.
 Sense of taste and certain cravings help to satisfy homeostatic
imbalances. When you crave carbohydrates or orange juice it can be
your
body’s way of communicating to your consciousness to fulfill these deficiencies.