CH 15 Senses: Vision, Hearing, Olfaction, and Gustation

Special senses

Vision, equilibrium, hearing, olfaction, gustation

Vision

Relies more on vision than any other special sense

Accessory structures of the eye function

Provide protection, lubrication, and support

Eyelids (palpebrae) with conjuctiva

Provide protection and lubrication for the eye

Superficial epithelium of eye

Provides protection for the eye

Lateral apparatus

Provides support for the eye

Conjunctiva

Thin transparent mucous membrane that covers the inner surface of the eyelids and the anterior surface of the eye

Lacrimal gland

Produces tears that bathe the conjunctival surfaces

Tears

Collect at the medial angle of the eye and drain into the nasal cavity

Fibrous tunic

Outer layer of the eye composed of the sclera and cornea

Sclera

White outer layer of the eye that maintains shape, protects internal structures, and provides muscle attachment point

Cornea

Transparent window of the eye that allows light to enter and bends and refracts light (avascular)

Vascular tunic

Middle layer of the eye that provides route for blood vessels and lymphatics, regulates amount of light entering the eye, and controls shapes of lens

Iris

- Colored part of the eye that controls the size of the pupil.

- Controls light entering pupil

- smooth muscle determines size of pupil

Ciliary body

Controls the shape of the lens and produces aqueous humor

Ciliary Muscles

control lens shape; smooth muscle

Ciliary processes attached to the lens by suspensory ligaments; produce __________ humor that fills anterior chamber

aqueous

Choroid

Thin, pigmented layer associated with the sclera that delivers oxygen and nutrients to the retina

Lens

Transparent and biconvex structure that focuses light on the retina

Lens

- Posterior region contains long, columnar epithelial cells called lens _____

- Lose nuclei and other organelles

- Accumulate proteins called _________

- Covered by elastic, transparent capsule

- Supported by suspensory ligaments

fibers, crystallins

Cataracts

loss of transparency in lens

Retina

Inner layer of the eye that contains photoreceptor cells and includes relay neurons

Retina has 2 layers

outer pigmented layer and inner neural layer

outer pigmented layer

Pigment of this layer and choroid help to separate sensory cells and reduce light scattering

Neural layer

- inner layer of rods and cone cells sensitive to light - photoreceptors

- Includes relay neurons

Lens focuses light on

macula and fovea centralis

macula

small yellow spot

Fovea centralis

area of greatest visual acuity; photoreceptor cells (cones) tightly packed

Optic disc

blind spot area through which blood vessels enter eye, where nerve processes from neural layer meet and exit from the eye

Functions of the eye

1. As light passes through the pupil of the iris, it is _______ on the retina by the cornea, lens, and humors.

2. The _____ striking the retina is converted into action potentials.

3. The optic _____ conveys these action potentials to the brain

focused, light, nerve

Electromagnetic spectrum is

the entire range of wavelengths or frequencies of electromagnetic radiation.

Visible light:

portion of Electromagnetic spectrum detected by human eye (380 to 750 nm).

Refraction

the bending of light rays as they pass through materials of different densities

Lens Surface concave =

light ray diver as a result of refraction

Lens Surface convex =

light rays converge as a result of refraction

Focal point

Lens changes shape causing adjustment of focal point on the retina;

Produces an inverted image on the retina

point where light rays converge and cross

Focusing

causing light to converge

Lens changes shape causing __________ of focal point on the retina;

- Produces an inverted image on the retina

adjustment

Accommodation

- Automatic adjustment of eye to provide clear vision

- Lens becomes _______ to focus on nearby objects

- Ciliary muscles _______

- Pulls choroid towards lens reducing tension on suspensory ligaments

- Lens becomes more spherical

- Greater refraction of light

- Lens ______ to see far away

rounder, contract, flatter

Functions of the Eye

Image Formation, Accommodation, Refraction

Retina Neural Layer - 3 layers

- Photoreceptor cells

- Bipolar cells

- Ganglionic cells

- Neurons of adjacent layers synapse w/each other

Photoreceptors

rods and cones

Photoreceptor cells

Detect presence or absence of photons (rods) and provide information about wavelengths of photons (cones)

Both rods and cones have

- Inner segment containing major __________

- Outer segment with membranous discs

- Contain ______ pigments

organelles, visual

Rods

Unusual sensory cells that are depolarized when not stimulated and hyperpolarized by light

When photoreceptor cells are not exposed to light and are in a resting, nonactivated state, Na+ channels are open, so Na+ flows in

- This is the ______ current (resting state)

- causes photoreceptors to continually release the neurotransmitter glutamate

dark

Photoreceptors contain opsins

- Rods have double-layered membranous discs that contain _________

- Found over most of ______, but not in fovea. More sensitive to light than cones.

- Protein rhodopsin changes shape when struck by light; and eventually separates into its two components: opsin and retinal.

- Retinal can be converted to Vitamin A from which it was originally derived. In absence of light, opsin and retinal recombine to form rhodopsin.

rhodopsin, retina

Rhodopsin Cycle

1. In the resting (dark) state, 11-cis-retinal is tightly bound to the internal surface of opsin. Cyclic GMP is attached to the Na+ channel, keeping it open

2. As rod cells absorb light, retinal changes shape from 11-cis-retinal to all-trans-retinal.

- This change causes opsin to also change ______ (dark to light state).

- The changes in opsin activate a G protein called transducin, which activates a cyclic GMP phosphodiesterase

3. The cGMP phosphodiesterase catalyzes the conversion of cGMP to GMP.

- This reaction causes cGMP to diffuse away from Na+ channels, closing them

- What effect will this have on polarization of the cell?

-Hyperpolarization

4. In the all-______ conformation, retinal detaches from the opsin molecule.

- Transducin reassociates with opsin, leading to the deactivation of phosphodiesterase

5. In the absence of ______________ activity, cGMP concentration increases.

- Na+ channels open

6. In a process requiring ATP, all-trans retinal is converted to 11- cis retinal.

11-cis retinal can attach to opsin, returning it to its original (dark) conformation

shape, trans, phosphodiesterase

Adjustment of eyes to changes in light intensity

- Mechanisms:

- Changes in amount of available rhodopsin: In bright light, excess rhodopsin is _______ down

- Conversely, in a dark room more rhodopsin is ________, making the retina more light-sensitive.

- Pupil reflexes: In dim light, the pupil enlarges to allow more light into the eye; in bright light, the pupil constricts to allow less light into the eye.

broken, produced

Night blindness (nyctalopia) Results from

deficiency of vitamin A

Cones

Responsible for color vision and visual acuity

Cones are numerous in

fovea and macula

cones visual pigment

iodopsin

cones have 3 types that

respond to blue, red, and green light

Inner Layers of Retina

- Begin at _________

- End at visual cortex of cerebral hemispheres

- Messages must cross two synapses before moving toward ______

- Photoreceptor to bipolar cell

- Bipolar cell to ganglion cell

photoreceptors, brain

Visual Pathways

1. Each eye has an area from which it collects light - the visual ______.

2. Light stimulates photoreceptors. Action potentials are conducted along the optic _______ (II).

3. The optic nerve leaves the eye through the optic disc

4. Just inside the cranial cavity, the optic nerves are connected to each other at the optic chiasm. At this point, axons from some ganglion cells cross over and project to the opposite side of the brain.

- Both hemispheres receive visual input from both eyes

5. Beyond the optic chiasm, the route of the axons is the optic tract.

- Most of the optic tract axons terminate in the lateral geniculate nucleus of the thalamus.

- However, some axons do not terminate in the thalamus but separate from the optic tract to terminate in the superior colliculi, the center for visual reflexes.

6. Neurons from the ________ form fibers, which project to the visual cortex in the occipital lobe

field, nerve, thalamus

- The projections of ganglion cells from the retina of each eye are related to the visual field for each eye.

- Can be seen by observing with one eye closed.

- Images from the right visual field project to the _____ side of the brain

left

Field of vision is

combined visual images from left and right eyes

__________ _______: visual fields partially overlap yielding depth perception.

- Obtained by comparing relative positions of objects between images received from both eyes

Binocular vision

Circadian rhythm

- Daily pattern of activity tied to day-night cycle

- Established from visual ___________

- Affects metabolic rate, blood pressure, etc.

- Connection to endocrine system

information

Hearing and Balance/Equilibrium

- Divided into external, middle, and inner ear

- External + middle: _________

- Internal: _______ + _________

hearing, hearing, balance

Hearing -

sound waves

Equilibrium/balance -

position and motion

External ear structures

auricle/pinna - elastic cartilage covered w/skin, external acoustic meatus (auditory canal), Tympanic membrane

Tympanic membrane

- ______ membrane of 2 layers of epithelium w/connective tissue between

- Sound waves cause it to ________

- Border between external and middle ear

Thin, vibrate

Middle ear

- Separated from the ______ ear by oval and round windows

- Auditory or eustachian ______: opens into pharynx, equalizes pressure

- _________: malleus, incus stapes: transmit vibrations from eardrum to oval window

- ______ ________: connection between middle and inner ear. Stapes presses here.

inner, tube, Ossicles, Oval window

Inner Ear

- _______ ________: tunnels and chambers in the temporal bone

- Protects the membranous labyrinth:

- Membranous tunnels and chambers suspended in the bony labyrinth

- __________ flows between the 2 labyrinths

- __________ is within membranous labyrinth

Bony labyrinth, Perilymph, Endolymph

Bony labyrinth subdivided into

- ________: hearing

- ________: balance

- Receptors detect gravity and linear acceleration

- Semicircular canals: ________

- Contain 3 semicircular ducts

- Receptors stimulated by rotation of head

- Start with understanding sound to understand how cochlea functions

Cochlea, Vestibule, balance

The Process of Hearing Overview

- _______ ear

- Collects sound waves, conducts through external auditory canal

- ________ ear

- Tympanic membrane vibrates, ossicles vibrate, vibrations transferred to oval window

- _______ ear

- Vibrations are converted to pressure waves in fluid

- Detected by hair cells in cochlear duct

- Information is sent to auditory cortex of brain

External, Middle, Internal

Auditory Function

- Vibrations produce sound waves

- Pressure waves in ____

- Volume or loudness: function of wave ________

- Pitch: function of wave _________

air, amplitude, frequency

Inner Ear - Cochlea

- ________ ________ communicates w/vestibule, which communicates w/the scala vestibuli (vestibular duct).

- _______ _________ extends from oval window to helicotrema at cochlear apex

- ________ ________ (tympanic duct) extends from helicotrema to round window (exit)

- Scala vestibuli and scala tympani filled w/perilymph

Oval window, Scala vestibuli, Scala tympani

Inner Ear - Cochlea

- _______ ________ extends from oval window to helicotrema at cochlear apex

- _______ _________ (tympanic duct) extends from helicotrema to round window (exit)

Scala vestibuli, Scala tympani

Inner Ear - Cochlea

- Wall of scala vestibuli is vestibular _________

- Wall of scala tympani is _______ membrane

- Cochlear duct: between vestibular and basilar membranes. Filled w/________

- ______ ______ lie in spiral organ (organ of Corti)

- Rests on basilar membrane

- Separates cochlear duct from scala tympani

membrane, basilar, endolymph, Hair cells

Inner Ear - Cochlea

- _____ _________ (sensory cells) have hair-like projections at the apical ends called stereocilia.

- Vibration of perilymph causes vestibular membrane to vibrate, which causes vibrations in ________

- ________ membrane displaced, detected by hair cells.

- Vibrations in scala tympani dissipated by movement of ________ ________

- How many membranes? 3

- Vestibular

- Tectorial

- Basilar

- How many ducts? 3

- Cochlear

- Tympanic

- Vestibular

Hair cells, endolymph., Basilar, round window

How do these all function together?

1. The _______ collects sound waves, which are conducted to the tympanic membrane

2. Sound waves vibrate the tympanic membrane and cause it to vibrate. The three auditory ossicles vibrate

3. The mechanical force of vibration is amplified by the stapes pounding on the ________ _________

4. This produces waves in the perilymph of the scala vestibuli

5. Vibrations go through the vestibular membrane into the endolymph

6. As the basilar membrane distorts, the hair cells resting on it contact the stationary _________ _________ and bend

7. Waves in the _______ __________ pass to the round window and are dissipated

auricle, oval window, tectorial membrane, scala tympani

Effect of Sound Waves on Points Along the -Basilar Membrane

- Different frequency sounds cause maximum vibrations of different regions of basilar membrane

- High pitch near _____

- Low pitch near ______

- What happens w/very high/low pitch sounds?

- Can't hear the sound

- Low sound goes straight to round window without passing through membranes

- High sound doesn't pass through membrane

base, apex

Central Nervous System Pathways for Hearing

- Afferent fibers of sensory ________ neurons in cochlear ganglion form cochlear nerve

- Axons enter medulla oblongata and synapse at cochlear nucleus

- ________ (superior colliculus) coordinates unconscious motor responses

- Ascending auditory sensations synapse in the _________

- Projection fibers deliver information to auditory cortex of ________ lobe

bipolar, Midbrain, thalamus, temporal

Balance/Equilibrium

- State of physical balance

- Sensations provided by receptors of vestibular complex (vestibule and semicircular canals)

- _______ _______

- Sensory receptors of internal ear

- Provide information about direction and strength of mechanical stimuli

Hair cells

Balance/Equilibrium

- Static labyrinth: utricle and saccule

of the vestibule.

- Evaluates position of head relative

to ________

- Detects linear acceleration and deceleration (as in a car).

- Dynamic labyrinth: crista ampullaris of the semicircular canals.

- Evaluates movement of the head in _______ ________ _________

gravity, three dimensional space

State Labyrinth

- Utricular macula senses _________ movement.

- Saccular macula senses ________ movement.

- ________: have many stereocilia (microvilli) and one kinocilium embedded in gelatinous mass weighted by otoliths ("ear stones")

- Densely packed calcium carbonate crystals on surface of "jelly"

horizontal , vertical, Macula

Function of the Vestibule in Maintaining Balance

- __________ mass moves in response to gravity or inertia bending hair cells and initiating action potentials.

- Patterns of stimulation translated by _____ into specific information about head position or acceleration

Gelatinous, brain

Dynamic Labyrinth

- ______ semicircular canals filled with endolymph: transverse, coronal, and sagittal plane.

- Continuous with ________

- Base of each expanded into ampulla with sensory epithelium (crista ampullaris).

- ________ suspended over crista hair cells. Acts as a float displaced by fluid movements within semicircular canals

Three, utricle, Cupula

Function of the Semicircular Canals

- Each hair cell in vestibular complex has

- 80-100 _________ (resemble very long microvilli)

- A single large kinocilium

- Deflection of the hairs toward the kinocilium results in _________ of the hair cells, whereas deflections away from the kinocilium results in hyperpolarization.

- Hair cells have no axons but ________ with neurons of CN VIII.

stereocilia, depolarization, synapse

Central Nervous System Pathways for Balance

1. Sensory neurons in vestibular ganglia

- Monitor hair cells of vestibular complex

- Vestibular nerve of vestibulocochlear nerve (VIII) formed from ganglia fibers

- CN VIII synapse within ________ nuclei

- Integrate sensory information about balance and equilibrium from both sides of head

- Relay information to cerebellum

- Relay information to cerebral cortex

- Providing _______ sense of head position

- Send commands to motor nuclei in brainstem and spinal cord

vestibular, conscious

Central Nervous System Pathways for Balance

- Additionally, ________ nuclei help control reflexive movements of the extrinsic eye muscles.

- Automatic movements of eyes

- Directed by superior _______ of midbrain in response to sensations of motion

- Attempt to keep gaze focused on a specific point

- If spinning rapidly, eyes make _______ movements

- _________

- Trouble controlling eye movements when body is stationary

- Caused by damage to brainstem or internal ear

vestibular, colliculi, jerky, Nystagmus

Central Nervous System Pathways for Balance

- Vestibular neurons also send axons to the posterior ventral nucleus of the _________

- Thalamic neurons project to the vestibular areas of the ________ ________, allowing for conscious awareness of balance

thalamus, cerebral cortex

Olfaction

Sense of smell

Olfactory organs

Located in the nasal cavity and made up of olfactory epithelium and lamina propria

Olfactory epithelium

Contains olfactory neurons that detect odorants

Olfaction

- Olfactory epithelium found in _________ nasal cavity in the olfactory region.

- 10 million olfactory neurons - highly modified nerve cells

- Dendrites of olfactory neurons have enlarged ends called ________ _________

superior, olfactory vesicles

Olfaction

- Olfactory hairs are _____ of olfactory neurons embedded in mucus.

- _______ dissolve in mucus and attach to receptors,

- Cilia depolarize and initiate action potentials in olfactory neurons.

- Olfactory epithelium is replaced as it wears down. Olfactory neurons are replaced by basal cells every _____ months

- Olfactory reception

- Begins with binding of odorant to G protein-coupled receptor

cilia, Odorants, two

How Odorants Bind to Membrane Receptor of Olfactory Hair

1. Each odorant receptor molecule is associated with a __ protein.

2. Binding of an odorant to the receptor molecule activates the G protein.

3. The G protein activates adenylate cyclase.

4. Adenylate cyclase is an enzyme that catalyzes the formation of cyclic _____ (cAMP) from ATP.

5. cAMP in these cells causes Na+ and Ca^2+ channels to ______. The influx of ions into the olfactory hairs results in depolarization and the production of action potentials in the olfactory neurons

G, AMP, open

Olfactory Receptors and Discrimination

- We can distinguish thousands of chemical stimuli

- Dogs have 72 times more olfactory receptor surface area than humans do

- Their sense of smell is more than 10,000 times better than ours!

- Receptor molecules vary in structure to allow for about _______ different odorant receptor molecules that react to odorants of different sizes, shapes, and functional groups.

- Threshold for detecting odors is very _____ and adaptation occurs quickly.

- Replaced about every __ months from basal cells in the olfactory epithelium

1000, low, 2

Olfactory Pathways

- Afferent fibers leave olfactory epithelium

- Collect into 20 or more bundles

- Penetrate _______

- Reach olfactory ______ of cerebrum where first synapse occurs

ethmoid, bulbs

Olfactory Pathways

- Axons leaving _______ _______

- Travel along olfactory ______ to olfactory cortex, hypothalamus, and limbic system

- Olfactory information is the only type of sensory information to reach cerebral cortex _________

- All other sensations are relayed from thalamus

olfactory bulb, tract, directly

Taste

Sense of taste

Taste buds

Contain taste cells that detect tastants

Types of papillae

Filiform, Vallate, Fungiform, Foliate

Filiform papillae

Most numerous papillae on the tongue, but do not contain taste buds

Vallate papillae

Largest and least numerous papillae on the tongue, contain taste buds