Human Senses

What you will do today . . .

• Name five kinds of sense receptors and explain their functions

• Explain how a sensation arises

• Identify the locations of the receptors of the special senses

• Describe the accessory structures of each of the special senses

Specialized Sensory Neurons

Sensory Regions of the Brain

The Sensations in the Skin

A. The skin is full of receptors that allow us to detect touch, pain, and pressure

1. Touch receptors are concentrated in the fingertips, face, and tongue

2. Body hair also helps to detect touch; the base of the hair follicles are loaded with receptors

The Sensations in the Skin

The Sensations in the Skin

B. Thermoreceptors monitor temperature change

The Sensations in the Skin

C. Pain receptors are sensory receptors that are found throughout the epidermis and interior of the body. They can be stimulated by four types of energy . . .

1. Mechanical

2. Thermal

3. Chemical

4. Electrical

The Sensations in the Skin

5. Pain receptors are most abundant in the hands and mouth

6. Pain receptors generally follow the reflex arc

The Chemical Senses: Taste and Smell

A. Taste buds are the sensory receptor organ for taste; most are on the tongue itself

1. Five general taste groupings

a. Sweet

b. Sour

c. Salty

d. Bitter

e. Umami

A Map of the Tongue

The Chemical Senses: Taste and Smell

2. Different tastes have a purpose

3. Chemicals must be dissolved in saliva to be tasted

4. Three cranial (connected directly to the brain) nerves are involved in the process of gustation

a. Facial

b. Glossopharyngeal

c. Vagus

The Chemical Senses: Taste and Smell

5. Taste triggers digestion

6. Taste is 80% smell

The Chemical Senses: Taste and Smell

The Chemical Senses: Taste and Smell

B. The olfactory epithelium, located in the nasal cavity, allow us to smell odors1. The trigeminal nerves and olfactory nerves send signals to the olfactory bulbs, which lie in the limbic system of the brain2. Smell signals also travel to the amygdala, which trigger emotions, memories, and eating behaviors3. Chemicals must be in a gaseous (volatile) state to be smelled

The Eye and Vision

A. 70% of all sensory receptors are located in the eye

The Eye and Vision

B. Accessory Structures1. Eyebrows

a. Shade eyes from sunlightb. Keep perspiration out of eye

2. Eyelidsa. Closed by orbicularis oculib. Protect the eye and keeps it from drying out

3. Conjunctivaa. Thin, outer layer of eyeballb. Produces mucus to lubricate eyec. Infection is called Pink Eye

The Eye and Vision

B. Accessory Structures

4. Lacrimal Glands

a. Release tears

b. Cleans eye with lysozyme, an antibacterial enzyme

5. Eye Muscles

The Eye

The Eye and Vision

C. Parts of the Eye1. Sclera: the white part that shapes the eyeball2. Cornea: clear structure on surface of eye that bends light3. Choroid layer: blood vessels that provide nutrients to the eye4. Ciliary body: alters the shape of the lens in response to light

The Eye and Vision

C. Parts of the Eye

5. Iris: colored part of eye that regulates the amount of light that enters the eye

6. Pupil: center of eye where light enters

7. Rods: peripheral vision, dark conditions

8. Cones: operate in bright light and allow color vision

The Eye and Vision

C. Parts of the Eye

9. Retina: light-sensitive inner layer of the eye

10. Optic nerves: pathway from eye to brain

The Ear, Hearing, and Balance

The Ear, Hearing, and Balance

A. Sound is transmitted as vibrations, usually of air

B. The external air is connected to the tympanic membrane (eardrum) by the auditory canal

C. Air pressure in the ear can be regulated by the eustachian tube, which is an opening into the throat

D. Vibrations of the tympanic membrane are sent to the hammer, anvil, and stirrup

The Ear, Hearing, and Balance

E. These three bones send vibrations to the cochlea, a coiled tube1. Cochlea contains the Organ of Corti, the organ of hearing2. Organ of Corti contains sensory receptors called hair cells which send sound to the brain via the auditory nerve

F. Semicircular canals of the inner ear contain fluid that regulate balance

References

• http://activity.ntsec.gov.tw/lifeworld/english/content/images/en_brain_c25.jpg

• http://www.sfn.org/skins/main/images/rd/vision/eye.jpg

• http://www.colorado.edu/intphys/Class/IPHY3730/image/figure7-8.jpg

• http://www.health.state.ny.us/nysdoh/antibiotic/ear.gif