A&P Chp. 15: The Special Senses Flashcards
The Five Special Senses
Smell and Taste: chemical senses (chemical transduction)
Sight: light sensation (light transduction)
Hearing: sound perception (mechanical transduction)
Equilibrium: static and dynamic balance (mechanical transduction)
Special Sensory Receptors
Distinct types of receptor cells are confined to the head region
Located within complex and discrete sensory organs (eyes and ears) or in distinct epithelial structures (taste buds and the olfactory epithelium)
The Chemical Senses: Taste and Smell
The receptors for taste (gustation) and smell (olfaction) are chemoreceptors (respond to chemicals in an aqueous solution)
Chemoreception involves chemically gated ion channels that bind to odorant or food molecules
Location of Taste Buds
Located mostly on papillae of tongue
Two of the types of papillae: fungiform and circumvallate
Taste Buds
Each papilla contains numerous taste buds
Each taste bud contains many gustatory cells
The microvilli of gustatory cells have chemoreceptors for tastes
The Five Basic Tastes
- Sweet: sugars, alcohols, some amino acids, lead salts
- Sour: H+ ions in acids
- Salty: Na+ and other metal ions
- Bitter: many substances including quinine, nicotine, caffeine, morphine, strychnine, aspirin
- Umami: the amino acid glutamate (“beef” taste)
Taste Transduction
A direct influx of various ions (Na+, H+) or the binding of other molecules which leads to depolarization of the receptor cells
Depolarization of the receptor cell causes it to release neurotransmitter that stimulates nerve impulses in the sensory neurons of gustatory nerves
Sensory Pathways for Taste
Afferent impulses of taste stimulate many reflexes which promote digestion (increased salivation, and gastrointestinal motility and secretion)
“Bad” taste sensations can elicit gagging or vomiting reflexes
Odor Receptors
Bipolar Neurons
Collectively constitute cranial nerve 1
Unusual in that they regenerate (on a roughly 60 day replacement cycle)
Odors
Very complicated
Humans can distinguish thousands
More than a thousand different odorant-binding receptor molecules have been identified
Different combinations of specific molecule-receptor interactions produce different odor perceptions
Transduction of Smell
Binding of an odorant molecule to a specific receptor activates a G-protein and then a second messenger (cAMP)
cAMP causes gated Na+ and Ca2+ channels to open, leading to depolarization
Olfactory Pathway
One path leads from the olfactory bulbs via the olfactory tracts to the olfactory cortex where smells are consciously interpreted and identified
Another path leads from the olfactory bulbs via the olfactory tracts to the thalamus and limbic system where smells elicit emotional responses
Smells can also trigger sympathetic nervous system activation or stimulate digestive processes
Surface Anatomy of the Eye
Eyebrows divert sweat from the eyes and contribute to the facial expressions (eccrine glands)
Eyelids (palpebrae) blink to protect the eye from foreign objects and lubricate their surface
Eyelashes detect and deter foreign objects
People in front of the computer who don’t blink for a while may experience pain because they are not lubricating the surface of their eyes
Conjunctiva
A mucous membrane lining the inside of the eyelids and the anterior surface of the eyes
Forms the conjunctival sac between the eye and eyelid
Forms a closed space when the eyelids are closed
Conjunctivitis
inflammation of the conjuncitval sac
“pinkeye”
The Lacrimal Apparatus
Lacrimal Apparatus: lacrimal gland, lacrimal sac, nasolacrimal duct
Rinses and lubricates the conjunctival sac
Drains to the nasal cavity where excess moisture is evaporated
Lacrimal gland is always on the lateral side of the eye