THE SPECIAL SENSES: Sight, Sound, Smell, Taste, Touch
I. SIGHT: The Eye
Rods and Cones:
II. SOUND AND BALANCE: The Ear
The Eardrum (Tympanic Membrane):
Ear Infections (Otitis), Fluid in Ear, Ear Tubes:
Otitis externa (outer ear infection): Swimmer's Ear
- Involves the outer ear and ear canal
- Usually bacterial or fungal (Pseudomonas aeruginosa is a common cause)
- The ear is painful to touch and is often red, swollen, peeling, and has drainage or exudate
- Often caused by bacteria or fungi-infested water in the external auditory canal
Otitis media (middle ear infection):
- The ear is infected around or behind the eardrum
- There may be fluid buildup behind the eardrum
- Chronic middle ear infections in childhood often result in myringotomy, a surgical procedure in which tiny tubes are put in the ears through the eardrums to relieve pressure and help the fluid drain. These typically fall out on their own.
- Bacteria and viruses are often the cause
Fluid in Middle Ear and Tympanic Eardrum Membrane Perforation:
Tubes in Ears:
Otitis interna (inner ear infection):
Hearing Loss/Hearing Aids:
III. Smell
IV. TASTE:
V. TOUCH, PRESSURE, PAIN, HOT, COLD, ITCHING, TICKLING:
A. Meissner's (Lamellar/Tactile) Corpuscles:
B. Pacinian (Lamellated) Corpuscles:
C. Merkel (Tactile) Discs:
D. Ruffini Corpuscles:
E. Root Hair Plexus:
F. Free Nerve Endings:
- Mechanoreceptor
- A nerve ending in the skin that is responsible for the sensitivity to light touch
- Highest sensitivity
- Lowest threshhold
- Sense vibrations at 10-50 Hz
- Quickly adapt, which is why we grow used to the feeling of clothes against our skin
- Concentrated in thick, hairless skin, such as found on the soles of the feet and palms of the hands and fingerpads and the lips
- Distributed on various areas of the skin
- Found within the dermal papillae in the skin
- Encapsulated (connective tissue)
- Unmyelinated
- Useful in reading Braille
B. Pacinian (Lamellated) Corpuscles:
- Nerve endings in the skin that are specialized for vibration and pressure
- Respond to sudden disturbances
- Used to detect pressure: rough, smooth, bumpy, sharp, soft, hard, etc...
- Adapt very quickly
- Encapsulated by connective tissue
C. Merkel (Tactile) Discs:
- Responsible for light touch
- Abundant in highly sensitive areas like the fingertips and lips
- Found in the stratum basale of the epidermis layer of skin
- Slow to adapt
D. Ruffini Corpuscles:
- Slowly adapting
- Mechanoreceptor
- Located in the cutaneous tissue in the deep layers
- Sensitive to skin stretch
- Senses finger control and movement
- Highest density around fingernails
- Sense grip and slippage of objects
- Sense sustained pressure
- Found around joints and aid in the sense of different angles
- Thermoreceptors (if a person has a deep burn, these burn off so there is no pain)
E. Root Hair Plexus:
- Special group of nerve fiber endings
- Very sensitive to touch
- Mechanoreceptor
- Network around hair follicle (which is why it hurts so bad when our hair is pulled)
- Receptor (sends and receives nerve impulses to and from the brain)
F. Free Nerve Endings:
- Unspecialized
- Afferent nerve fibers
- Unmyelinated nerve fibers originate in the skin and detect itching and cause itching reflex or tickling (light touch)
- Information goes through the spinothalamic tract
- Information goes through the spinothalamic tract
- Ending of sensory neurons
- Sends information to the brain
- Cutaneous nociceptor
- Detects pain
- Unencapsulated
- Most common receptor type
- Found in the skin
- Penetrate the dermis and the stratum granulosum of the epidermis
- Found in middle of dermis and network around hair follicles
- Different rates of adaptation
- Different stimulus modalities
- Different fiber types
- Can detect temperature
- Can detect touch, pressure, stretch
- Can detect danger (nociception)
- Polymodality