A&P Chp. 15: The Special Senses

Question 1

The Five Special Senses

Answer 1

Smell and Taste: chemical senses (chemical transduction)
Sight: light sensation (light transduction)
Hearing: sound perception (mechanical transduction)
Equilibrium: static and dynamic balance (mechanical transduction)

Question 2

Special Sensory Receptors

Answer 2

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)

Question 3

The Chemical Senses: Taste and Smell

Answer 3

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

Question 4

Location of Taste Buds

Answer 4

Located mostly on papillae of tongue

Two of the types of papillae: fungiform and circumvallate

Question 5

Taste Buds

Answer 5

Each papilla contains numerous taste buds
Each taste bud contains many gustatory cells
The microvilli of gustatory cells have chemoreceptors for tastes

Question 6

The Five Basic Tastes

Answer 6

1. Sweet: sugars, alcohols, some amino acids, lead salts
2. Sour: H+ ions in acids
3. Salty: Na+ and other metal ions
4. Bitter: many substances including quinine, nicotine, caffeine, morphine, strychnine, aspirin
5. Umami: the amino acid glutamate (“beef” taste)

Question 7

Taste Transduction

Answer 7

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

Question 8

Sensory Pathways for Taste

Answer 8

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

Question 9

Odor Receptors

Answer 9

Bipolar Neurons
Collectively constitute cranial nerve 1
Unusual in that they regenerate (on a roughly 60 day replacement cycle)

Question 10

Odors

Answer 10

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

Question 11

Transduction of Smell

Answer 11

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

Question 12

Olfactory Pathway

Answer 12

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

Question 13

Surface Anatomy of the Eye

Answer 13

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

Question 14

Conjunctiva

Answer 14

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

Question 15

Conjunctivitis

Answer 15

inflammation of the conjuncitval sac

“pinkeye”

Question 16

The Lacrimal Apparatus

Answer 16

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

Question 17

Extrinsic Eye Muscles

Answer 17

Lateral, medial, superior, and inferior rectus muscles (rectus=straight); superior and inferior oblique muscles

Question 18

Internal Anatomy of the Eye: Tunics

Answer 18

Tunic: covering (think of clothing)

1. Fibrous Tunic: sclera and cornea
2. Vascular Tunic: choroid layer
3. Sensory Tunic: retina

Question 19

Internal Anatomy of the Eye

Answer 19

Anterior Segment Contains the Aqueous Humor: iris, ciliary body, suspensory ligament, lens
Posterior Segment contains the vitreous humor

Question 20

Circulation of the Aqueous Humor

Answer 20

Ciliary process at the base of the iris produces aqueous humor
Scleral venous sinus returns aqueous humor to the blood stream

Question 21

Glaucoma

Answer 21

any disturbance that increases aqueous humor volume and pressure which causes pain, ultimately the vitreous humor crushes the retina causing blindness

Question 22

The Optic Disc

Answer 22

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

Question 23

Micrograph of the Retina

Answer 23

Light must cross through the capillaries and the two layers of interneurons to reach the photoreceptors, the rods and the cones

Question 24

Opthalmoscope Image of the Retina

Answer 24

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

Question 25

The Two Layers of the Retina

Answer 25

1. Outer Pigmented Layer: has a single layer of pigmented cells, attached to the choroid tunic, which absorbs light to prevent light scattering inside
2. 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

Question 26

Neural Organization in the Retina

Answer 26

1. Photoreceptors: rods (for dim light) and cones (3 colors: blue, green and red, for bright light); only graded potential needed
2. Bipolar Cells: are connecting interneurons; only graded potential needed
3. Ganglion Cells: axons become the optic nerve
4. Horizontal Cells: enhance contrast (light v. dark boundaries) and help different colors; Ex: turn off lights in the class and see projector
5. Amacrine cells: detect changes in the level of illumination

Question 27

External Ear

Answer 27

Pinna (auricle): focuses sound waves on the tympanic membrane
Ceruminous glands guard the external auditory canal

Question 28

Middle Ear and Auditory Tube

Answer 28

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

Question 29

Middle Ear Ossicles

Answer 29

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

Question 30

The Membranous Labyrinth

Answer 30

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

Question 31

The Cochlea: Two Coiled Tubes

Answer 31

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

Question 32

The Spiral Organ of Corti

Answer 32

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

Question 33

Wave Pulses in the Cochlea

Answer 33

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

Question 34

Resonance of Basilar Membrane

Answer 34

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

Question 35

Auditory Pathway

Answer 35

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

Question 36

Macula in the Saccule and Utricle

Answer 36

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"

Question 37

Macular Transduction

Answer 37

Hair cells’ stereocilia move in response to the sliding otoliths
To send impulses to the CNS for interpretation

Question 38

Semicircular Canals

Answer 38

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

Question 39

Ampullar Transduction

Answer 39

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”

Question 40

Pathways of Balance and Orientation

Answer 40

Integration of sensory modalities: sight, proprioception, static equilibrium, dynamic equilibrium
Output to skeletal muscles to position: eyes, head and neck, trunk

Question 41

Wave Pulses at the Cochlea

Answer 41

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