10 - 1 Questions to discuss: Describe the sensation when you initially put your fingers in the water. After two minutes describe how the sensation has

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Questions to discuss:

Describe the sensation when you initially put your fingers in the water.

After two minutes describe how the sensation has changed.

Once you submerse your fingers in the third cup of water, discuss any and all sensations.

Determine the neurological pathway for the detection and perception of temperature.

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CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.

*See PowerPoint image slides for all figures and tables pre-inserted into PowerPoint without notes”.

Chapter 10Lecture Outlines*

Hole’s Essentials of HumanAnatomy & Physiology

David ShierJackie ButlerRicki Lewis

Created by Lu Anne Clark Professor of Science, Lansing Community College

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Breakdown Video: How does the video demonstrate the following?

Levels of Organization

Interconnection of Systems

Reasons for disruption of homeostasis

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Chapter 10Somatic and

Special Senses


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Introduction

A. Sensory receptors detect changes in the environment and stimulate neurons to send nerve impulses to the brain. B. A sensation is formed based on the

sensory input.


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Receptors and Sensations

A. Each receptor is more sensitive to a specific kind of environmental change but is less sensitive to others.


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B. Types of ReceptorsFive general types of receptors are

recognized.1. Receptors sensitive to

changes in chemical concentration are called chemoreceptors.

2. Pain receptors detect tissue damage.


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3. Thermoreceptors respond to temperature differences.4. Mechanoreceptors respond to changes in pressure or movement.5. Photoreceptors in the eyes respond to light energy.


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C. Sensations 1. Sensations are feelings that

occur when the brain interprets sensory impulses.

2. At the same time the sensation is being formed, the brain uses projection to send the sensation back to its point of origin so the person can pinpoint the area of stimulation.


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D. Sensory Adaptation 1. During sensory adaptation,

sensory impulses are sent at decreasing rates until receptors fail to send impulses unless there is a

change in strength of the stimulus.


This is one of the focus areas of the lab

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Somatic Senses A. Receptors associated with the skin,

muscles, joints, and viscera make up the somatic senses.

Touch, temperature, pain and pressure (TTPP)

(Q: What is viscera?)


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Viscera = internal organs of thoracic and abdominal cavities

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Somatic Receptors

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B. Touch and Pressure Senses 1. Three types of receptors

detect touch and pressure.2. Free ends of sensory nerve

fibers in the epithelial tissues are associated with touch and pressure.


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3. Meissner's corpuscles are flattened connective tissue sheaths surrounding two or more nerve fibers and are abundant in hairless areas that are very sensitive to touch, like the lips.4. Pacinian corpuscles are large structures of connective tissue and cells that resemble an onion. They function to detect deep pressure.


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C. Temperature Senses 1. Temperature receptors

include two groups of free nerve endings: heat receptors and cold receptors which both work best within a range of

temperatures.


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a. Both heat and cold receptors adapt quickly.

b. Temperatures near 45o C stimulate pain

receptors; temperatures below 10o C also

stimulate pain receptors and produce a freezing

sensation.


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D. Sense of Pain 1. Pain receptors consist of free

nerve endings that are stimulated when tissues are damaged, and adapt little, if at all.

2. Many stimuli affect pain receptors such as chemicals and oxygen deprivation.


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3. Visceral pain receptors are the only receptors in the viscera that produce sensations.

a. Referred pain occurs because of the common nerve pathways leading from skin and internal organs.


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Pain felt in one area of the body does not always represent where the problem is, because the pain may be referred there from another area. For example, pain produced by a heart attack may feel as if it is coming from the arm because sensory information from the heart and the arm converge on the same nerve cells in the spinal

cord.

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4. Pain Nerve Fibersa. Fibers conducting pain

impulses away from their source are either acute pain fibers or chronic pain fibers.

b. Acute pain fibers are thin, myelinated fibers that carry impulses rapidly and cease when the stimulus stops.


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c. Chronic pain fibers are thin, unmyelinated fibers that conduct impulses slowly and continue sending impulses

after the stimulus stops.


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d. Pain impulses are processed in the gray matter of the dorsal horn of the spinal cord.

e. Pain impulses are conducted to the thalamus,

hypothalamus, and cerebral cortex.


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5. Regulation of Pain Impulses a. A person becomes aware of pain when impulses reach the

thalamus, but the cerebral cortex judges the

intensity and location of the pain.


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Pathway of Pain

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Special Senses

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I. Types of Receptors

A. Chemoreceptors - are stimulated by changes in the chemical concentration of substances.

B. Pain receptors - are stimulated by tissue damage.

C. Thermoreceptors - stimulated by changes in temperature.

D. Mechanoreceptors- are stimulated by changes in movement or pressure.

E. Photoreceptors- are stimulated by light energy.

35

Olfactory Olfactory SystemSystem

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I. General Information

A. Both taste and smell are chemoreceptors, which means that chemicals must dissolve in liquids to stimulate the receptors.

B. Olfaction (smell) and gustation (taste) senses are tied into one another.

C. Sensory adaptation means that as a receptor adapts, the impulses leave them at a decreasing rate, until it stops sending signals.

D. Olfactory adaptation is rapid (doesn’t require many molecules of odorants), but memory is long term.

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II. Olfactory Anatomy

A. Epithelium1. One square inch of

membrane holds 10-100 million receptors

2. Covers superior nasal cavity and cribriform plate.

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B. Olfactory Membrane

1. Olfactory receptors bipolar neurons

w/cilia2. Supporting cells 3. Basal cells = stem

cells replace receptors

monthly4. Olfactory glands

produces mucus

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III. Olfaction: Sense of Smell A. Odorants dissolve in

mucus to bind to receptors.

B. Nerve impulses are sent through the bony cribiform plate to the olfactory bulb of the brain.

C. If each odor stimulates a distinct set of receptor subtypes, it will create a variety of odors.

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Odor Thresholds

1. Strong odors also stimulates the trigeminal nerve which results in stimulation of nasal mucus cells as well as tear cells.

2. Partial or complete loss of smell is called anosmia.

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Gustatory Sensation: Taste

1. Taste requires dissolving of substances

2. Four classes of stimuli--sour, bitter, sweet, and salty

3. 10,000 taste buds found on tongue, soft palate & larynx

4. Found on sides of circumvallate & fungiform papillae

5. 3 cell types: supporting, receptor & basal cells

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Anatomy of Taste Buds

1. An oval body consisting of 50 receptor cells surrounded by supporting cells

2. A single gustatory hair projects upward through the taste pore

3. Basal cells develop into new receptor cells every 10 days.

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Physiology of Taste

1. Complete adaptation in 1 to 5 minutes2. Thresholds for tastes vary among the 4

primary tastesa) most sensitive to bitter (poisons)b) least sensitive to salty and sweet

3. Mechanisma) dissolved substance contacts gustatory

hairsb) receptor potential results in

neurotransmitter releasec) nerve impulse formed in 1st-order neuron

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Taste Nerve Pathway: add to notesTaste receptor in tongueSensory neuron to:

Facial, glossopharyngeal and vagus cranial nerves

To medulla oblongataTo thalamusTo parietal lobe of cerebrum (gustatory cortex)

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Special Sense: VISION

Accessory Structures of Eye

Fibrous Tunic of Eyeball

Vascular Tunic of Eyeball

Nervous Tunic of Eyeball

Physiology of Vision – images

Physiology of Vision - color

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Accessory Structures of Eye

1. Eyelidsa) protect &

lubricate

2. Tarsal glandsa) oily secretions

keep lids from sticking together

3. Conjunctivaa) stops at corneal

edgeb) dilated BV--

bloodshot

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Eyelashes & Eyebrows

1. Eyelashes & eyebrows help protect from foreign objects, perspiration & sunlight

2. Sebaceous glands are found at base of eyelashes (sty) 3. Palpebral fissure is gap between the eyelids

Eyeball = 1 inch diameter

5/6 of Eyeball inside orbit & protected

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Lacrimal Apparatus (pg 278; fig. 10-16)

1. About 1 ml of tears produced per day. Spread over eye by blinking. Contains bactericidal enzyme called lysozyme.

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Tunics (Layers) of Eyeball

1. Fibrous Tunic(outer layer)

2. Vascular Tunic

(middle layer)3. Nervous Tunic

(inner layer)

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1. Transparent 2. Helps focus light(refraction)

a) astigmatism

3. Transplantsa) common & successfulb) no blood vessels so no

antibodies to cause rejection

4. Nourished by tears & aqueous humor

Fibrous Tunic -Cornea

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Fibrous Tunic - Sclera

1. Dense irregular connective tissue layer

2. Provides shape & support

3. Pierced by Optic Nerve (posterior)

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Vascular Tunic -Choroid & Ciliary Body

1. Choroida) melanocytes & blood

vesselsb) provides nutrients to

retinac) black pigment in

melanocytes absorb scattered light

2. Ciliary bodya) ciliary processes

1. folds on ciliary body secrete aqueous humor

b) ciliary muscle 1. smooth muscle that

alters shape of lens

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Vascular Tunic- Iris & Pupil

1. Colored portion of eye2. Shape of flat donut

suspended between cornea & lens

3. Hole in center is pupil4. Function is to regulate

amount of light entering eye

5. Autonomic reflexesa) circular muscle fibers contract in bright light to shrink

pupilb) radial muscle fibers contract in dim light to enlarge

pupil

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Muscles of the Iris

1. Constrictor pupillae (circular) are innervated by parasympathetic fibers while Dilator pupillae (radial) are innervated by sympathetic fibers.

2. Response varies with different levels of light

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Vascular Tunic -Lens

1. Avascular2. Crystallin proteins

arranged like layers in onion

3. Clear capsule & perfectly transparent

4. Lens held in place by suspensory ligaments

5. Focuses light on fovea

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Suspensory ligament

1. Suspensory ligaments attach lens to ciliary process2. Ciliary muscle controls tension on ligaments & lens

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Nervous Tunic - Retina

1. Optic disca) optic nerve exiting

back of eyeball

2. Central retina BVa) fan out to supply

nourishment to retina

b) visible for inspection• hypertension &

diabetes

3. Detached retinaa) trauma (boxing)

• fluid between layers• distortion or blindness

View with Ophthalmoscope

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Layers of Retina

1. Pigmented epitheliuma) nonvisual portionb) absorbs stray light &

helps keep image clear

2. Three layers of neuronsa) photoreceptor layerb) bipolar neuron layerc) ganglion neuron layer

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Photoreceptors

1. Rodsa) shades of gray in dim

lightb) 120 million rod cellsc) discriminates shapes &

movementsd) distributed along

periphery

2. Conesa) sharp, color visionb) 6 millionc) Centrally located e.g.

fovea

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Major Processes of Image Formation

1. Refraction of lighta) by cornea & lens b) light rays must fall upon the retina

2. Accommodation of the lensa) changing shape of lens so that light is

focused

3. Constriction of the pupila) less light enters the eye

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Definition of Refraction

1. Bending of light as it passes from one substance (air) into a 2nd substance with a different density(cornea)

2. In the eye, light is refracted by the anterior & posterior surfaces of the cornea and the lens

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Refraction by the Cornea & Lens1. Image focused on retina is inverted & reversed

from left to right2. Brain learns to work with that information3. 75% of Refraction is done by

cornea -- rest is done by the lens4. Light rays from > 20’ are nearly parallel and only

need to be bent enough to focus on retina5. Light rays from < 6’ are more divergent & need

more refraction extra process needed to get additional bending of

light is called accommodation

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Accommodation & the Lens

1. Convex lens refract light rays towards each other

2. Lens of eye is convex on both surfaces

3. View a distant objecta) lens is nearly flat by pulling of

suspensory ligaments

4. View a close objecta) ciliary muscle is contracted &

decreases the pull of the suspensory ligaments on the lens

b) elastic lens thickens as the tension is removed from it

c) increase in curvature of lens is called accommodation

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Correction for Refraction Problems 1. Emmetropic eye (normal)

a) can refract light from 20 ft away

2. Myopia (nearsighted)a) eyeball is too long from front to

backb) glasses concave

3. Hypermetropic (farsighted)a) eyeball is too shortb) glasses convex (coke-bottle)

4. Astigmatisma) corneal surface wavyb) parts of image out of focus

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Convergence of the Eyes

1. Binocular vision in humans has both eyes looking at the same object

2. As you look at an object close to your face, both eyeballs must turn inward.a) convergenceb) required so that light rays from the object will

strike both retinas at the same relative pointc) extrinsic eye muscles must coordinate this

action

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Photoreceptors

1. Named for shape of outer segment2. Transduction of light energy into a

receptor potential in outer segment3. Photopigment is integral membrane

protein of outer segment membrane

4. Photopigments = opsin (protein) + retinal (derivative of vitamin A)a) rods contain rhodopsinb) cone photopigments contain 3 different

opsin proteins permitting the absorption of 3 different wavelengths (colors) of light

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Photopigment Physiology

1. Isomerizationa) light causes cis-retinal

to straighten & become trans-retinal shape

2. Bleachinga) enzymes separate the

trans-retinal from the opsin

b) colorless final products

3. Regeneration a) in darkness, an enzyme

converts trans-retinal back to cis-retinal

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Regeneration of Photopigments

1. Pigment epithelium near the photoreceptors contains large amounts of vitamin A and helps the regeneration process

2. After complete bleaching, it takes 5 minutes to regenerate 1/2 of the rhodopsin but only 90 seconds to regenerate the cone photopigments

3. Full regeneration of bleached rhodopsin takes 30 to 40 minutes

4. Rods contribute little to daylight vision, since they are bleached as fast as they regenerate.

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Photopigments for cones

3 Types of opsin protein (different form than opsin in rods)

Retinal + opsin = photopigmentBlue photopigment

Red photopigment

Green photopigment

The length of the wavelength stimulates certain cones (and various combos = various colors)

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Color Blindness & Night Blindness

1. Color blindnessa) inability to distinguish between certain

colorsb)absence of certain cone photopigmentsc) red-green color blind person can not

tell red from green

2. Night blindness (nyctalopia)a)difficulty seeing in low lightb) inability to make normal amount of

rhodopsinc) possibly due to deficiency of vitamin A

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Brain Pathways of Vision

synapse in thalamus & visual cortex

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Synesthesia

is a neurological condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway

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http://en.wikipedia.org/wiki/Stimulation

http://en.wikipedia.org/wiki/File:Synesthesia.svg

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LAB QUIZ1. Explain a taste that also causes the sensation of pain.

2. Name two types of receptors in your tongue.

3. Explain why reaction time is faster with the warning.

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Anatomy of the Ear Region

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External Ear

1. Function = collect sounds2. Structures

a) auricle or pinna elastic cartilage covered with skin

b) external auditory canal curved 1” tube of cartilage & bone leading into temporal bone ceruminous glands produce cerumen = ear wax

c) tympanic membrane or eardrum epidermis, collagen & elastic fibers, simple cuboidal epith.

3. Perforated eardrum (hole is present) 1. at time of injury (pain, ringing, hearing loss, dizziness)2. caused by explosion, scuba diving, or ear infection

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Middle Ear Cavity

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Middle Ear Cavity

1. Air filled cavity in the temporalbone

2. Separated from external ear by eardrum and from internal ear by oval & round window

3. Three ear ossicles connected by synovial jointsa) malleus attached to eardrum, incus & stapes

attached by foot plate to membrane of oval windowb) stapedius and tensor tympani muscles attach to

ossicles

4. Auditory tube leads to nasopharynxa) helps to equalize pressure on both sides of eardrum

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Inner Ear-Bony Labyrinth

ampulla

Vestibule

1. Bony labyrinth = set of tube-like cavities in temporal bonea) semicircular canals, vestibule & cochlea lined with periosteum

& filled with perilymphb) surrounds & protects Membranous Labyrinth

canals

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Cochlear Anatomy

1. 3 fluid filled channels found within the cochleaa) scala vestibuli, scala tympani and cochlear duct

2. Vibration of the stapes upon the oval window sends vibrations into the fluid of the scala vestibuli

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Anatomy of the Organ of Corti

1. Microvilli make contact with tectorial membrane (gelatinous membrane that overlaps the spiral organ of Corti)

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Physiology of Hearing1. Auricle collects sound waves2. Eardrum vibrates

a) slow vibration in response to low-pitched soundsb) rapid vibration in response to high-pitched sounds

3. Ossicles vibrate since malleus attached to eardrum

4. Stapes pushes on oval window producing fluid pressure waves in scala vestibuli & tympani

5. Pressure fluctuations inside cochlear duct move the hair cells against the tectorial membrane

6. Microvilli are bent producing receptor potentials

7. Depolarization of vestibulocochlear cranial nerve to auditory cortex in temporal lobe

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Overview of Physiology of Hearing

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Deafness

1. Nerve deafnessa) damage to hair cells from antibiotics,

high pitched sounds, anticancer drugs the louder the sound the quicker the

hearing loss

b) fail to notice until difficulty with speech

2. Conduction deafnessa) perforated eardrumb) otosclerosis

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Cochlear Implants

1. If deafness is due to destruction of hair cells

2. Microphone, microprocessor & electrodes translate sounds into electric stimulation of the vestibulocochlear nerve

3. Provides only a crude representation of sounds

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Physiology of Equilibrium (Balance)

1. Static equilibriuma)maintain the position of the body

(head) relative to the force of gravityb)macula receptors within saccule &

utricle

2. Dynamic equilibriuma)maintain body position (head) during

sudden movement of any type--rotation, deceleration or acceleration

b)crista receptors within ampulla of semicircular ducts

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Vestibular Apparatus

Notice: semicircular ducts with ampulla, utricle & saccule

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Otolithic Organs: Saccule & Utricle

1. Thickened regions called macula within the saccule & utricle of the vestibular apparatus

2. Cell types in the macula regiona) hair cells with stereocilia (microvilli) & one cilia (kinocilium)b) supporting cells that secrete gelatinous layer

3. Gelatinous otolithic membrane contains calcium carbonate crystals called otoliths that move when you tip your head

macula

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Detection of Position of Head

Movement of stereocilia or kinocilium results in the release of neurotransmitter onto the vestibular branches of the vestibulocochler nerve

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Crista: Ampulla of Semicircular Ducts

1. Small elevation within each of three semicircular ductsa) anterior, posterior & horizontal ducts detect different

movements

2. Hair cells covered with cupula of gelatinous material

3. When you move, fluid in canal bends cupula stimulating hair cells that release neurotransmitter

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Detection of Rotational Movement

1. When head moves, the attached semicircular ducts and hair cells move with ita) endolymph fluid moves and bends the cupula and enclosed hair

cells

2. Nerve signals to the brain are generated indicating which direction the head has been rotated

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Auditory Nerve Pathways 1. Nerve fibers carry

impulses to the auditory cortices of the temporal lobes where they are interpreted.


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Dynamic balance

Cerebellum plays huge role in maintaining balance

What other senses would send information to the cerebellum regarding information for balance?

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THE END

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Design Your Test (partially)

Somatic anatomy and physiology

Hearing anatomy and physiology

Sight anatomy and physiology

Smell and taste anatomy and physiology

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Structure and Process

Goal: as a group design an interactive learning center for students to understand the structures (anatomy) involved in one of the senses studied

Goal: as a group design an interactive learning center for students to understand the process (physiology) involved in one of the senses studied

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Use on exam

If sufficient details are provided by the center, the exact content will be used on the test.

If not, then teacher generated content will be used for the test.

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Details for the center

Group will be assigned one of the senses

Materials such as lab book, textbook and notes should be used.

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Details for the center: Anatomy

Use large paper provided to draw structures involved in the sense. UNLABELEDProvide cards with the names of the structures that go with the unlabeled drawing.Your group decides the necessary content

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Details for the center: Physiology

Design a learning activity to help students to understand the processes involved in the sense.

Examples: • pathway flashcards that students can arrange in a

specific order

• Pathway diagram to be arranged

• Flashcards for match game – need to provide key for student use

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Additional information

Provide page numbers for text and lab manual or state refer to notes to help guide the students

Provide a key to students – ONLY after they attempt the learning themselves

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Sense of HearingA. The ear has external, middle, and inner sections and provides the senses of hearing and equilibrium.B. Outer (External) Ear

1. The external ear consists of the auricle, which collects the sound, which then travels down the external auditory meatus.


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C. Middle Ear 1. The middle ear begins with

the tympanic membrane, and is an air- filled space (tympanic cavity) housing the auditory ossicles.


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a. Three auditory ossicles are the malleus, incus, and stapes.

b. The tympanic membrane vibrates the malleus, whichvibrates

the incus, then the stapes.c. The stapes vibrates the fluid

inside the oval window of the inner ear.

2. Auditory ossicles both transmit and amplify sound waves.


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D. Auditory Tube 1. The auditory, or

eustachian, tube connects the middle ear to the

throat to help maintain equal air pressure on both sides

of the eardrum.


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E. Inner (Internal) Ear 1. The inner ear is made up of a

membranous labyrinth inside an osseous labyrinth.

a. Between the two labyrinths is a fluid called perilymph.

b. Endolymph is inside the membranous labyrinth.


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2. The cochlea houses the organ of hearing; while the semicircular

canals function in equilibrium.3. Within the cochlea, the oval window leads to the upper compartment, called the scala vestibuli.


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4. A lower compartment, the scala tympani, leads to the

round window.5. The cochlear duct lies between these two compartments and is separated from the scala vestibuli by the vestibular membrane, and from the scala tympani by the basilar membrane.


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6. The organ of Corti, with its receptors called hair cells, lies on the basilar membrane.

a. Hair cells possess hairs that extend into the endolymph of the cochlear duct.


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7. Above the hair cells lies the tectorial membrane, which touches the tips of the stereocilia.8. Vibrations in the fluid of the inner ear cause the hair cells to bend resulting in an influx of calcium ions.9. This causes the release of a neurotransmitter from vesicles which stimulate the ends of nearby sensory neurons.


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F. Auditory Nerve Pathways

1. Nerve fibers carry impulses to the auditory cortices of the temporal lobes where they are interpreted.


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Sense of Equilibrium A. The sense of equilibrium consists of

two parts: static and dynamic equilibrium.

1. The organs of static equilibrium help to maintain the position of the head when the head and body are still.

2. The organs of dynamic equilibrium help to maintain balance when the head and body suddenly move and rotate.


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B. Static Equilibrium 1. The organs of static

equilibrium are located within the bony vestibule of the inner ear, inside the utricle and saccule (expansions of the membranous labyrinth).

2. A macula, consisting of hair cells and supporting cells, lies inside the utricle and

saccule.


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3. The hair cells contact gelatinous

material holding otoliths.

4. Gravity causes the gelatin and otoliths to shift, bending hair cells and generating a nervous impulse.


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5. Impulses travel to the brain via the vestibular branch of the vestibulocochlear nerve,

indicating the position of the head.


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C. Dynamic Equilibrium

1. The three semicircular canals detect motion of the head, and they aid in balancing the head and body during sudden movement.


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2. The organs of dynamic equilibrium are called cristae ampullaris, and are located in the ampulla of each semicircular canal of the inner

ear. They are at right angles to each other.


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3. Hair cells extend into a dome- shaped gelatinous cupula.

4. Rapid turning of the head or body generates

impulses as the cupula and hair cells bend.

5. Mechanoreceptors (called propriopceptors)

associated with the joints, and the changes detected by the eyes also help maintain equilibrium.


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Sense of Smell A. Olfactory Receptors

1. Olfactory receptors are chemoreceptors.

2. The senses of smell and taste operate together to aid

in food selection.


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B. Olfactory Organs 1. The olfactory organs contain the olfactory receptors plus epithelial supporting cells and are located in the upper nasal cavity.2. The receptor cells are bipolar neurons with hairlike cilia covering the dendrites. The cilia project into the nasal cavity.


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3. To be detected, chemicals that enter the nasal cavity must first be dissolved in the watery fluid surrounding the cilia.


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C. Olfactory Nerve Pathways1. When olfactory receptors are

stimulated, their fibers synapse with neurons in the olfactory lobes lying

on either side of the crista galli.2. Sensory impulses are first analyzed

in the olfactory lobes, then travel along olfactory tracts to the

limbic system, and lastly to the olfactory cortex within the temporal lobes.


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D. Olfactory Stimulation 1. Scientists are uncertain of how

olfactory reception operates but believe that each odor stimulates a set of specific protein receptors in cell membranes.

2. The brain interprets different receptor combinations as an

olfactory code.3. Olfactory receptors adapt quickly

but selectively.


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Sense of Taste A. Taste buds are the organs of taste and are located within papillae of the tongue and are scattered throughout the mouth and pharynx.


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B. Taste Receptors 1. Taste cells (gustatory cells)

are modified epithelial cells that function as receptors.

2. Taste cells contain the taste hairs that are the portions sensitive to taste. These hairs protrude from openings called taste pores.


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3. Chemicals must be dissolved in water (saliva) in order to be

tasted.4. The sense of taste is not well

understood but probably involves specific membrane protein receptors that bind with specific chemicals in food.

5. There are four types of taste cells.


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C. Taste Sensations 1. Specific taste receptors are

concentrated in different areas of the tongue.

a. Sweet receptors are plentiful near the tip of the tongue.b. Sour receptors occur along the lateral edges of the tongue.


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c. Salt receptors are abundant in the

tip and upper portion of the tongue.

d. Bitter receptors are at the back of

the tongue.


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2. Taste buds may be responsive to at least 2 taste sensations but one is likely to dominate.

3. Taste receptors rapidly undergo adaptation.


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D. Taste Nerve Pathways1. Taste impulses travel

on the facial, glossopharyngeal, and vagus nerves to the medulla

oblongata and then to the gustatory cortex

of the cerebrum.


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Click here to playEffect of Sound Waves

on the CochlearFlash Animation

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Sense of SightA. Accessory organs, namely the lacrimal apparatus, eyelids, and extrinsic muscles, aid the eye in its function.


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B. Visual Accessory Organs

1. The eyelid protects the eye from foreign objects and is made up of the thinnest skin of the body lined with

conjunctiva.


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2. The lacrimal apparatus produces tears that lubricate and cleanse the eye.

a. Two small ducts drain tears into the nasal cavity.

b. Tears also contain an antibacterial

enzyme.3. The extrinsic muscles of the eye attach to the sclera and move the eye in all directions.


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C. Structure of the Eye 1. The eye is a fluid-

filled hollow sphere with three distinct layers, or tunics.


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2. Outer Layer a. The outer (fibrous) tunic

is the transparent cornea at the front of the eye, and the

white sclera of the anterior eye.b. The optic nerve and

blood vessels pierce the sclera at the posterior of the eye.


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3. Middle Layer a. The middle, vascular

tunic includes the choroid coat, ciliary body, and iris.

b. The choroid coat is vascular and darkly pigmented and performs two functions: to nourish other tissues of the eye and to keep the inside of the eye dark.


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c. The ciliary body forms a ring around the front of the eye and contains ciliary muscles and suspensory ligaments that hold the lens in position and change its shape (focus).d. The ability of the lens to adjust shape to facilitate focusing is called accommodation.


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e. The iris is a thin, smooth muscle that adjusts the amount of light entering the pupil, a hole in its center.

i. The iris has a circular set of and a radial set of

muscle fibers.f. The anterior chamber (between the cornea and iris) and the posterior chamber (between the iris and vitreous body and housing the lens) make up the anterior cavity, which is filled with aqueous humor.


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g. The aqueous humor circulates from one chamber to the other through the pupil.


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4. Inner Layera. The inner tunic consists of the retina, which contains

photoreceptors; the inner tunic covers the back side of the eye to the ciliary body.b. In the center of the retina is the macula lutea with the fovea centralis in its center, the point of sharpest vision in the retina.


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c. Medial to the fovea centralis is the optic disk, where nerve fibers leave the eye and where there is a blind spot.

d. The large cavity of the eye is filled with vitreous humor.


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D. Light Refraction1. Light waves must bend to

be focused, a phenomenon called refraction.

2. Both the cornea and lens bend light waves that are focused on the retina, as do the two humors to a lesser degree.


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E. Visual Receptors 1. Two kinds of modified

neurons comprise the visual receptors; elongated rods and blunt-shaped cones.

2. Rods are more sensitive to light and function in dim light; they produce colorless vision.


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3. Cones provide sharp images in bright light and enable us to see in color.

a. To see something in detail, a person moves the eyes

so the image falls on the fovea centralis, which contains the highest concentration of cones.

b. The proportion of cones decreases with distance from the fovea centralis.


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F. Visual Pigments 1. The light-sensitive

pigment in rods is rhodopsin, which breaks down into a protein, opsin, and retinal

(from vitamin A) in the presence of light.


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a. Decomposition of rhodopsin activates an enzyme that initiates changes in the rod cell membrane, generating a nerve impulse.b. Nerve impulses travel away from the retina and are interpreted as vision.


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2. The light-sensitive pigments in cones are also proteins; there are three sets of cones, each containing a different visual pigment.


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a. The wavelength of light determines the color perceived from it; each of the three pigments is sensitive to different wavelengths of light.

b. The color perceived depends upon which sets of cones the light stimulates: if all three sets are stimulated, the color is white; if none are stimulated, the color is black.


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G. Visual Nerve Pathways1. The axons of ganglion cells

leave the eyes to form the optic nerves.

2. Fibers from the medial half of the retina cross over in the optic chiasma.

3. Impulses are transmitted to the thalamus and then to the visual cortex of the occipital lobe.


Documents

10 - 1 Questions to discuss: Describe the sensation when you initially put your fingers in the water. After two minutes describe how the sensation has