The Senses

The SensesThe Senses

The SensesThe Senses General senses of touch

Temperature Pressure Pain

Special senses Smell / Taste Sight Hearing / Equilibrium (balance)

The Special SensesThe Special Senses

Sight – The eye and Vision

Smell / Taste – Chemical senses – Nose and Tongue

Hearing / Equilibrium (balance) – The Ear

The Eye and VisionThe Eye and Vision

The EyeThe Eye Visual organ – the eye 70% of all sensory receptors are in the eyes. 40% of the cerebral cortex is involved in

processing visual information. Each eye has over a million nerve fibers. Protection for the eye

Most of the eye is enclosed in a bony orbit, in other words your eye socket.

A cushion of fat surrounds most of the eye.

Accessory Structures of the EyeAccessory Structures of the Eye

Slide 8.3a

Eyelids

Designed to protect the eye, and keep moisture distributed over the surface of the eyeball.

Accessory Structures of the EyeAccessory Structures of the Eye

Eyelashes

Acts as a dust and particle protector for the eye.

Has modified sebacious glands produce an oily secretion to lubricate the eye.

Ciliary glands

modified sweat glands between the eyelashes.

• Tears contain mucous, antibodies, (anti-bacterial)

• keeps the surface of the eye moist.

• Lacrimal gland – produces the tears.

• Lacrimal sac – fluid empties into nasal cavity.

Tear ducts or the Lacrimal apparatus

Eye MusclesEye Muscles

Muscles attach to the outer surface of the eye.

Produce eye movements.

Structure of the EyeStructure of the EyeThe wall of the eye is composed of three tunics

1. Sclera & Cornea fibrous outside layer

2. Choroid – middle layer

3. Sensory tunic – (retina) inside layer.

1. The Fibrous Tunic1. The Fibrous Tunic Sclera

Tough white connective tissue layer.

The “white of the eye”

Cornea Transparent, central anterior

portion.

Allows for light to pass through.

Repairs itself easily.

The only human tissue that can be transplanted without fear of rejection.

Choroid LayerChoroid Layer

Blood-rich nutritive tunic

Pigment prevents light from scattering.

Modified interiorly into two structures. Cilliary body – smooth muscle

Iris

Pigmented layer that gives eye color

Pupil – rounded opening in the iris

Sensory Tunic (Retina)Sensory Tunic (Retina) Contains receptor cells (photoreceptors)

Rods

Cones

Signals pass from photoreceptors and leave the retina toward the brain through the optic nerve

Neurons of the Retina and VisionNeurons of the Retina and Vision Cones – 3 types

detect different colors

Densest in the center of the retina.

Fovea centralis – area of the retina with only cones.

Lack of one type = color blindness.

Neurons of the Retina and VisionNeurons of the Retina and Vision Rods

Most are found towards the edges of the retina

Allow dim light vision and peripheral vision

Perception is all in gray tones

The Iris

Visible colored part of the eye Composed of smooth muscle Pupil – the round, central opening that is a set

of special muscles which acts to vary the amount of light entering the eye.

Pupil dilation and constriction

LensLens Biconvex crystal-like structure

Held in place by ligaments.

Lens – what it doesLens – what it does

Slide 8.16

Light must be focused to a point on the retina for optimal vision

The eye is set for distance vision (over 20 ft away)

The lens must change shape to focus for closer objects

Internal Eye Chamber FluidsInternal Eye Chamber Fluids

Aqueous humor Similar to blood

plasma

Watery fluid found in chamber between the lens and cornea

Provides nutrients for the lens and cornea

Vitreous humor

Keeps the eye from collapsing

Gel-like substance behind the lens

Lasts a lifetime and is not replaced

Vision Each eye captures its own view

and the two separate images are sent on to the brain for processing.

When the two images arrive simultaneously in the back of the brain, they are united into one picture.

The mind combines the two images by matching up the similarities and adding in the small differences.

The combined image is more than the sum of its parts. It is a three-dimensional stereo picture.

BLIND SPOTBLIND SPOT

Slide 8.16

The area on the retina where the optic nerve enters the eyeball.

This area has no photoreceptors and therefore no visual input.

The cortex appears to fill-in this missing information so we are not conscious of the blind spot.

No photoreceptor cells are at the optic disk, or blind spot.

BLIND SPOT – little test

The Eye - basic parts reviewThe Eye - basic parts review

http://www.bpei.med.miami.edu/site/disease/disease_anatomy.asp

Correcting the Eye Nearsightedness = myopia

Focus of light in front of retina Eyeball too long or lens too strong Distant objects are blurry

Farsightedness = hyperopia Focus of light beyond the retina Short eyeball or lazy lens Near objects are blurry.

Difficulty seeing clase objects = presbyopia Inability of the lens to focus properly at close objects Caused by the aging of the eye. Special reading glasses needed.

Cataracts The natural lens looses its transparency due

to damage to its fibers over time. Lens fibers are not replaced. When the lens of the eye turns cloudy enough

to impair vision, it is considered a cataract. They are the main cause of blindness

worldwide. Most individuals over 60 years old develop

some degree of cataract. Treatment consists of a safe and precise

surgical procedure.

The Ear – Hearing and Equilibrium

The EarThe Ear

Houses two senses

Hearing

Equilibrium (balance)

Receptors are mechanoreceptors, they react to sound waves.

Anatomy of the EarAnatomy of the Ear

The ear is divided into three areas Outer (external) ear

Middle ear

Inner ear

The External EarThe External Ear

Structures of the external ear Pinna (auricle)

External auditory canal

Involved in hearing only

The External Auditory CanalThe External Auditory Canal

Narrow chamber in the temporal bone

Lined with skin

Ceruminous (wax) glands are present

Ends at the tympanic membrane or ear drum.

The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity

Air-filled cavity within the temporal bone

Only involved in the sense of hearing

The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity Two tubes are

associated with the inner ear The opening from the

auditory canal is covered by the tympanic membrane (Ear drum)

The auditory tube connecting the middle ear with the throat

Allows for equalizing pressure during yawning or swallowing

This tube is otherwise collapsed

Bones of the Tympanic CavityBones of the Tympanic Cavity

Three bones span the cavity (the smallest bones in our bodies!!)

Malleus (hammer)

Incus (anvil)

Stapes (stirrip)

Slide 8.25b

Vibrations from eardrum move the malleus

These bones transfer sound to the inner ear.

Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth

Slide 8.26a

Includes sense organs for hearing and balance!

Filled with a fluid called perilymph

Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth

A maze of bony chambers within the temporal bone

Cochlea

Vestibule

Semicircular canals

HearingHearing

Located within the cochlea

Receptors = hair cells a membrane on it’s inner surface.

Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe of the brain.

Equilibrium – Balance/OrientationEquilibrium – Balance/Orientation

Receptor cells are in two structures:

Vestibule

Semicircular canals

EquilibriumEquilibrium Static equilibrium

– sense of gravity at rest. Ability to stay still in one place.

Dynamic equilibrium

– angular and rotary head movements. Keeping a sense of where you are at all times

Figure 8.16a, b

Equilibrium has two functional parts

Think of a snowboarder doing a flip and being able to land on their feet.

EquilibriumEquilibrium

Figure 8.16a, b

This balance is achieved by vestibular nerve endings in side the Vestibule and the Semicircular canals, sensing the subtle changes in the fluid (endolymph) inside these structures.

Smell / Taste The Chemical Senses

Chemical Senses – Taste and SmellChemical Senses – Taste and Smell

Both senses use chemoreceptors

Stimulated by chemicals in solution.

Taste has four types of receptors.

Smell can differentiate a very large range of chemicals.

**Both senses complement each other and respond to many of the same stimuli**

Olfaction – The Sense of SmellOlfaction – The Sense of Smell

Olfactory receptors are in the roof of the nasal cavity.

Neurons with long cilia

Chemicals must be dissolved in mucus for detection

Impulses are transmitted via the olfactory nerve

Interpretation of smells is made in the cortex of the Brain

The Sense of SmellThe Sense of Smell

TasteTaste

Slide 8.37

Taste buds house the receptor organs

Location of taste buds Most are on

the tongue

The Tongue and TasteThe Tongue and Taste The tongue is covered

with projections called papillae

Filiform papillae – sharp with no taste buds

Fungifiorm papillae – rounded with taste buds

Circumvallate papillae – large papillae with taste buds

Taste buds are found on the sides of papillae

Anatomy of Taste BudsAnatomy of Taste Buds

Slide 8.40

Figure 8.18

Taste SensationsTaste Sensations

Slide 8.41

Sweet receptors Sugars Saccharine Some amino acids

Sour receptors Acids

Bitter receptors Alkaloids

Salty receptors Metal ions

To distinguish most flavours, the brain needs information about both smell and taste.

These sensations are communicated to the brain from the nose and mouth.

Several areas of the brain integrate the information, enabling people to recognize and appreciate flavours.

.

SMELL and TASTE

SMELL and TASTE

So … our senses of Smell and Taste are Complementary, they are partners in interpreting chemical stimuli.

When you have a cold and your nose is blocked, then you will notice that your ability to taste is greatly reduced.

Development of the Special Development of the Special SensesSenses

Formed early in embryonic development

Eyes are outgrowths of the brain.

All special senses are functional at birth