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
Extrinsic Eye Muscles
Lateral, medial, superior, and inferior rectus muscles (rectus=straight); superior and inferior oblique muscles
Internal Anatomy of the Eye: Tunics
Tunic: covering (think of clothing)
- Fibrous Tunic: sclera and cornea
- Vascular Tunic: choroid layer
- Sensory Tunic: retina
Internal Anatomy of the Eye
Anterior Segment Contains the Aqueous Humor: iris, ciliary body, suspensory ligament, lens
Posterior Segment contains the vitreous humor
Circulation of the Aqueous Humor
Ciliary process at the base of the iris produces aqueous humor
Scleral venous sinus returns aqueous humor to the blood stream
Glaucoma
any disturbance that increases aqueous humor volume and pressure which causes pain, ultimately the vitreous humor crushes the retina causing blindness
The Optic Disc
Axons of ganglion cells exit to form the optic nerve
Blood vessels enter to serve the retina by running on top of the neural layer
The location of the “blind spot” in our vision
Micrograph of the Retina
Light must cross through the capillaries and the two layers of interneurons to reach the photoreceptors, the rods and the cones
Opthalmoscope Image of the Retina
The Macula Lutea (“yellow spot”) is the center of the visual image
The Fovea Centralis is a central depression where light falls more directly on cones providing for the sharpest image discrimination
Light bouncing off RBC’s hemoglobin causes “red eye” in flash photos
The Two Layers of the Retina
- Outer Pigmented Layer: has a single layer of pigmented cells, attached to the choroid tunic, which absorbs light to prevent light scattering inside
- Inner neural layer: has the photosensory cells and various kinds of interneurons in three layers
Black=absence of light
White=all wavelengths of light are being reflected
Neural Organization in the Retina
- Photoreceptors: rods (for dim light) and cones (3 colors: blue, green and red, for bright light); only graded potential needed
- Bipolar Cells: are connecting interneurons; only graded potential needed
- Ganglion Cells: axons become the optic nerve
- Horizontal Cells: enhance contrast (light v. dark boundaries) and help different colors; Ex: turn off lights in the class and see projector
- Amacrine cells: detect changes in the level of illumination
External Ear
Pinna (auricle): focuses sound waves on the tympanic membrane
Ceruminous glands guard the external auditory canal
Middle Ear and Auditory Tube
Three auditory ossicles (bones) serve as a lever system to transmit sound to the inner ear
Pharyngotympanic (auditory tube): connects to the pharynx, allowing air pressure to equalize on both sides of the tympanic membrane
Middle Ear Ossicles
malleus (hammer)
incus (anvil)
stapes (stirrup)
Act to increase the vibratory force on the oval window
Tensor tympani and stapedius muscles control the tension of this lever system to prevent damage to the delicate tympanic and round window membranes
The Membranous Labyrinth
A series of tiny fluid-filled chambers in the temporal bone
Cochlea transduces sound waves
Semicircular canals and their ampullae transduce balance and equilibrium
The vestibule connects the two portions
The Cochlea: Two Coiled Tubes
Larger outer tube is folded but continuous (like a coiled letter “U”)- the scala vestibule and scala tympani - contains perilymph fluid
Smaller inner tube is the scala media (cochlear duct) contains endolymph fluid
The Spiral Organ of Corti
Between the scala tympani and the scala media/cochlear duct is the complex receptor system: the spiral organ of Corti
Sensory hair cells stand on the basilar membrane and their processes are attached to the tectorial membrane
Wave Pulses in the Cochlea
Stapes moving at the oval window creates pulses of vibration in the perilymph of the scala vesibuli and scala tympani
Harmonic vibrations are created at right angles in the endolymph of the scala media which move the basilar membrane
Movement against the tectorial membrane stimulates the hair cells to send impulses to the auditory cortex
Round window moves to accommodate the vibrations initiated by the stapes
Resonance of Basilar Membrane
High notes are detected at the base of the cochlea
Low notes are detected at the apex
Due to differences in the width and flexibility of the basilar membrane
Auditory Pathway
Afferent impulses for sounds are routed:
Vestibulocochlear Nerve VIII (cochlear branch)
Nuclei in the medulla oblongata where motor responses can turn the head to focus on sound sources
Primary Auditory Cortex in the temporal lobe for conscious interpretation
Macula in the Saccule and Utricle
Chambers near the oval window filled with perilymph
CaCO3 otoliths ("ear stones") slide over the surface lining cells in response to gravity
Static equilibrium tells the CNS "which way is up"Macular Transduction
Hair cells’ stereocilia move in response to the sliding otoliths
To send impulses to the CNS for interpretation
Semicircular Canals
Three endolymph-filled tubes in the bony labyrinth
Each C-shaped loop is in a plane at right angles to the other two
Each has an expanded ampulla containing a sensory structure, the cupola
Ampullar Transduction
Movement in the plane of one of the canals causes endolymph to flow and bends the cupola
Hair cells’ stereocilia move in response to the movement
Dynamic equilibrium tells the CNS “Which way is the head or body moving”
Pathways of Balance and Orientation
Integration of sensory modalities: sight, proprioception, static equilibrium, dynamic equilibrium
Output to skeletal muscles to position: eyes, head and neck, trunk
Wave Pulses at the Cochlea
Stapes moving at the oval window creates pulses of vibration in the perilymph of the scala vestibule and scala tympani
Harmonic vibrations are created at right angles in the endolymph of the scala media which move the basilar membrane
