The Senses

Learning ObjectivesLearning Objectives

• Classify sense organs as special or general and explain the basic differences between the two groups

• Discuss how a stimulus is converted into a sensation

• Discuss the general sense organs and their functions

Learning Objectives (cont’d.)Learning Objectives (cont’d.)

• Describe the structure of the eye and the functions of its components

• Discuss the anatomy of the ear and its sensory function in hearing and equilibrium

• Discuss the chemical receptors and their functions

SENSES Sensory Receptors - detect environmental changes and trigger nerve impulses - somatic senses (touch, pressure, temp, pain)- special senses (smell, taste, vision, equilibrium)

CLASSSIFICATION

• Encapsulated –– Free nerve endings (pain, crude touch, temperature,

itch, tickle

• Unencapsulated - free or naked – Dermis, and deeper

Receptors 1. Chemoreceptors = _____________________

2. Pain receptors = ____________________ 3. Thermoreceptors = _____________________

4. Mechanoreceptors =_____________________

5. Photoreceptors = _____________________

6. Proprioceptors – _____________________

SensationsSensation = feeling that occurs when a brain interprets a sensory impulse

Projection = process where the cerebral cortex causes a feeling to stem from a source (eyes, ears)

Sensory adaptation = sensory receptors stop sending signals when they are repeatedly stimulated

What do you think is going on in this picture?

 

Sensory Deprivation is a technique initially used by neuro-psychiatrists designed to deliberately reduce or completely remove stimuli from one or all of the senses.

CONVERTING A STIMULUS INTO A SENSATION• All sense organs are able to detect a particular

stimulus

• A stimulus is converted into a nerve impulse

• A nerve is perceived as a sensation in the CNS

Somatic Senses1. Sensory Nerve Fibers - epithelial tissue, pain and pressure2. Meissner's corpuscles - hairless areas of skin (lips, fingertips)3. Pacinian corpuscles - deep pressure (tendons, joints)

Temperature Senses (warm and cold receptors)

10.4  Special Senses

Olfactory (smell)Gustatory (taste)Hearing & EquilibriumSight

Sense of Smell (Olfactory)

Odor --> Receptor Cell  -->  Olfactory bulb --> Olfactory Tract 

--> LIMBIC SYSTEM

Aromatherapy....

Real or Bunk?

Sense of Taste (Gustatory)

SweetSourBitterSalty

•What did the right eye say to the left eye?

• Between you and me, something smells!

Sense of Hearing

External EarAuricle (pinna) - outer earExternal Auditory Meatus

Middle Ear (tympanic cavity)• Eardrum (tympanum)• Auditory Ossicles - malleus, incus, stapes -

transmit vibrations and amplify the signal• Auditory Tube (eustachian tube) -

connects the middle ear to the throat - helps maintain air pressure

Inner Ear

• Labyrinth - communicating chambers and tubesOsseous Labyrinth and Membranous LabyrinthPerilymph and Endolymph (fluids within the labyrinth)

• Semicircular Canals - sense of equilibrium • Cochlea - sense or hearing• Organ of Corti - contains hearing receptors,

hair cells detect vibrations Organ of hearing

Why do children get tubes put in their ears?

Inner Ear: Cochlea• Inside the cochlea are special neurons

called HAIR CELLS• The stapes is attached to the OVAL

WINDOW, and vibrations cause the perilymph to vibrate; the hair cells here transmit this vibration.

• Therefore the HAIR CELLS in this region are receptors for HEARING. As you age, hair cells become damaged (loud music can speed this process along). Older people usually can’t hear frequencies that younger people can hear. Try the hearing test!

Steps in Hearing

1. Sound waves enter external auditory meatus2. Eardrum vibrates3. Auditory ossicles (malleus, incus, stapes) amplify vibrations4. Stapes hits oval window and transmits vibrations to cochlea5. Organs of corti contain receptor cells (hair cells) that deform from vibrations6. Impulses sent to the vestibulocochlear nerve7. Auditory cortex of the temporal lobe interprets sensory impulses8. (Round window dissipates vibrations within the cochlea)

Decibel Level Example of Noise Dangerous Time

0 Lowest audible sound

30 Quiet library

50 Refrigerator noise

70 Noisy restaurant Critical level

80 Factory noise 8 + hours

90 Shop tools Impairment

100 Chain saws < 2 hours

120 Rock concert Immediate harm

140 Gunshot blast Damage probable

180 Rocket launchpad Permanent loss

Sense of EquilibriumStatic Equilibrium - sense the position of the head, maintain stability and posture Dynamic Equilibrium (semicircular canals) - balance the head during sudden movement Cerebellum - interprets impulses from the semicircular canals and maintains overall balance and stability

• The eye is in the orbit of the skull for protection.• Within the orbit are 6 extrinsic eye muscles, which move

the eye. • There are 4 cranial nerves: Optic (II),

Occulomotor (III), Trochlear (IV), and Abducens (VI).

People of Asian descent have an EPICANTHIC FOLD in the upper eyelid; no functional difference.

THE EYE

THE EYEBALL

Three layers of the eyeball

Sclera

Choroid

Retina

Eyelid

Covers and protects the eye, thin skin Skin will not protect you from intense radiation, that’s why we use special goggles in a tanning bed

CONJUNCTIVA is like a covering around the eye and under the eyelids.  PINK EYE - also known as CONJUNCTIVITIS  (from bacteria, very contagious) Pink Eye Slide Show f

rom Web MD

Lens

• Transparent body behind the pupil focuses the light rays on the retina

Eye Fluids

• Aqueous humor – watery fluid in the anterior chamber of the eye

• Vitreous humor – jelly like fluid in the posterior chamber of the eye

• LACRIMAL GLANDS are the largest set. They are on the superior lateral eyelid and they produce tears, which drain into the nasal cavity via the LACRIMAL DUCT.

• The function is to moisten and lubricate the eye surface, and it has enzymes to kill bacteria (which thrive in warm, moist conditions).

Figure 16.5b

Outer Tunic

•Cornea - transparent, focuses light rays

•Sclera – continuation of cornea, going toward the back of the eye (white of the eye)

Middle TunicChoroid Coat – contains blood vessels

Ciliary Body – holds the lens in place

Lens – focusing

Iris – colored portion of the eye

Aqueous humor – liquid surrounding the lens

Pupil – opening for light to enter

Inner TunicRetina - visual receptor cells Fovea Centralis - region of the sharpest vision (aka, macula) Optic Disc – where nerve fibers leave the eye, creating the blind spot Vitreous Humor – supports internal parts, fluid

Figure 16.7a

Retina

The retina is made up of PHOTORECEPTORS, which are sensors for light.

Rods = monochromatic (b&w)Cones  = color vision

https://www.youtube.com/watch?v=JadaWSDxBYk

We have difficult interpreting images that are upside down

Which one is the real mona lisa?

• Fun Fact: -When you are looking at someone you love, your pupils dilate, and they do the same when you are looking at someone you hate.

What causes red-eye?

The flash on a camera is bright enough to cause a reflection off of the retina -- what you see is the red color from the blood vessels.

Many cameras have a "red eye reduction" feature. In these cameras, the flash goes off twice -- once right before the picture is taken, and then again to actually take the picture. The first flash causes people's pupils to contract, reducing "red eye" 

Problems with the Eyes

CataractsClouding of the lens leads to a clinical condition known as CATARACTS.

 

Treatment is to remove the lens and replace it with a plastic one (which is not flexible either).

Why are all babies born with blue eyes? Melanin is a brownish pigment that adds color to your hair, eyes, and skin. At the time babies are born, melanin hasn't yet been "deposited" in the eyes' iris. Hence, they appear blue.   After about six months, eyes change color depending on the amount of melanin. If you have a lot of it, your eyes will turn dark brown.  If you have little, they'll stay blue. And if you have no melanin, your eyes may appear pink (albino). .

ColorblindnessA genetic trait that affects boys more than girls. The location of the gene is on the X chromosome

• The region where the optic nerve and blood vessels goes in and out of the eye has no photoreceptors = BLIND SPOT.

• Hold your hands out at 45° and that’s the location of the blind spot.

• You can still see your hands because the other eye sees it. Close your right eye and look for your right hand and you’ll find the blind spot.

FLOATERS are when a capillary breaks and cells break off.  Floaters don’t actually move, the eye just tries to track them.

HYPEROPIA (far-sighted) eyes are too short MYOPIA (nearsighted)eyes are too long

ASTIGMATISMASTIGMATISM is when the cornea has an irregular shape. Part of the field of view is out of focus. They eyeball changes shape until age 24.

Lasik Surgery

See a real LASIK surgery (not for the squeamish)