The Senses The Senses General senses of touch

The Senses

The Senses · General senses of touch · Temperature · Pressure · Pain · Special senses · Smell / Taste · Sight · Hearing / Equilibrium (balance)

The Special Senses Sight – The eye and Vision Smell / Taste – Chemical senses – Nose and Tongue Hearing / Equilibrium (balance) – The Ear

The Eye and Vision

The Eye o Visual organ – the eye o 70% of all sensory receptors are in the eyes. o 40% of the cerebral cortex is involved in processing visual information. o Each eye has over a million nerve fibers. o Protection for the eye n n 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 Eye · Eyelids Designed to protect the eye, and keep moisture distributed over the surface of the eyeball. Slide 8. 3 a

Accessory 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.

Tear ducts or the Lacrimal apparatus • 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.

Eye Muscles · Muscles attach to the outer surface of the eye. · Produce eye movements.

Structure of the Eye The 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 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 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) · 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 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 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 o Visible colored part of the eye o Composed of smooth muscle o 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

Lens · Biconvex crystal-like structure · Held in place by ligaments.

Lens – what it does · 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 Slide 8. 16

Internal Eye Chamber Fluids · Aqueous humor · Vitreous humor · Similar to blood plasma · Keeps the eye from collapsing · Watery fluid found in chamber between the lens and cornea · Gel-like substance behind the lens · Provides nutrients for the lens and cornea · 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 SPOT · 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 Slide 8. 16

The Eye - basic parts review http: //www. bpei. med. miami. edu/site/disease_anatomy. asp

Correcting the Eye o Nearsightedness = myopia n Focus of light in front of retina n Eyeball too long or lens too strong n Distant objects are blurry o Farsightedness = hyperopia n Focus of light beyond the retina n Short eyeball or lazy lens n Near objects are blurry. o Difficulty seeing clase objects = presbyopia n n n Inability of the lens to focus properly at close objects Caused by the aging of the eye. Special reading glasses needed.

Cataracts o The natural lens looses its transparency due o o o 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 Ear · Houses two senses · Hearing · Equilibrium (balance) · Receptors are mechanoreceptors, they react to sound waves.

Anatomy of the Ear · The ear is divided into three areas · Outer (external) ear · Middle ear · Inner ear

The External Ear Involved in hearing only · Structures of the external ear · Pinna (auricle) · External auditory canal

The 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 Cavity · Air-filled cavity within the temporal bone · Only involved in the sense of hearing

The 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 Cavity · Three bones span the cavity (the smallest bones in our bodies!!) · Malleus (hammer) · Incus (anvil) · Stapes (stirrip)

· Vibrations from eardrum move the malleus · These bones transfer sound to the inner ear. Slide

Inner Ear or Bony Labyrinth · Includes sense organs for hearing and balance! · Filled with a fluid called perilymph Slide

Inner Ear or Bony Labyrinth · A maze of bony chambers within the temporal bone · Cochlea · Vestibule · Semicircular canals

Hearing · 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/Orientation · Receptor cells are in two structures: · Vestibule · Semicircular canals

Equilibrium has two functional parts · 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 Think of a snowboarder doing a flip and being able to land on their feet. Figure 8. 16 a, b

Equilibrium 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. Figure 8. 16 a, b

Smell / Taste The Chemical Senses

Chemical 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 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 Smell

Taste · Taste buds house the receptor organs · Location of taste buds · Most are on the tongue Slide 8. 37

The 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 Buds Figure 8. 18 Slide 8. 40

Taste Sensations · Sweet receptors · Sugars · Saccharine · Some amino acids · Sour receptors · Acids · Bitter receptors · Alkaloids · Salty receptors · Metal ions Slide 8. 41

SMELL and TASTE 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 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 Senses · Formed early in embryonic development · Eyes are outgrowths of the brain. · All special senses are functional at birth