Vocabulary Terms: Review Stimulus- anything from inside or outside the body that can cause a response in a nerve, muscle, gland, or other tissue. Sensation-

Vocabulary Terms: Review

• Stimulus- anything from inside or outside the body that can cause a response in a nerve, muscle, gland, or other tissue.

• Sensation- conscious awareness of stimuli received by sensory receptors in the nervous system.

Classification of Receptors: Review

1. Mechanoreceptors- activated by mechanical stimuli or deformation of the receptor

2. Chemoreceptor- changing of the chemical concentrations around the body

3. Thermoreceptors- detect hot and cold4. Nociceptors- any stimuli that can

cause tissue damage; sensation of pain

5. Photoreceptors- respond to light

Characteristics of Sensations

• Projection- brain refers a sensation to the point of stimulation

• Adaptation- loss of sensation even though the stimulus is still applied

• Afterimage- persistence of a sensation even though the stimulus is removed

• Referred pain- felt in the skin near or around the organ sending the impulse

• Phantom pain- sensation of pain in a limb that has been amputated

Somatic Sensespain, temperature and touch

• These sensations can be felt throughout the body, yet they are distributed unevenly through the skin.

• Exteroceptors- sense receptors located on body surfaces

• Proprioceptors- found in the muscles and joints

• Visceroceptors- found in internal organs• Nociceptors- pain receptors; free nerve

endings

Review For Touch & Pressure

• Meissner’s corpuscles- touch• Krause’s End Bulbs- touch• Ruffini’s corpuscles- continuous

touch• Pacinian corpuscles- deep pressure

Types of Somatic Senses

• General senses- widely distributed throughout the body– Touch– Pain– Pressure– Temperature– Vibration– Itch– Proprioception

Pain

• Types of pain:– Sharp, localized pain– Diffused, burning, aching pain

• Anesthesia:– Local- one area– General- throughout the body

• Gate control theory- distraction of pain receptors does not allow pain to intensify or continue at a high level

Nose

Olfaction- Smell

• Sense of smell- occurs in response to airborne molecules

• Pathway of smell- nasal cavity, olfactory neurons, olfactory bulb, olfactory tracts, olfactory cortex in brain

Olfaction- Smell

Olfaction: Sense of Smell

• Odorants bind to receptors

• Depolarization occurs

• Nerve impulse is triggered

Cells of the Olfactory Membrane

• Olfactory receptors– neurons with cilia or

olfactory hairs

• Supporting cells – columnar

epithelium

• Basal cells = stem cells– replace receptors

monthly

• Olfactory glands– produce mucus

Olfactory Epithelium

• 1 square inch of membrane holding 10-100 million receptors

• Covers superior nasal cavity

• 3 types of receptor cells

Tongue

Gustation: Taste

• Taste buds- sensory structures that detect stimuli of taste– On papillae, enlargements on surface of

tongue– Taste cells—interior of each taste bud– Taste hairs—on each taste cell that

extends to taste pore– Send signal to brain based on where

they are felt on the tongue

Physiology of Gustation• Complete adaptation in 1 to 5 minutes• Thresholds for tastes vary among the 4

primary tastes– most sensitive to bitter (poisons)– least sensitive to salty and sweet

• Mechanism– dissolved substance contacts gustatory

hairs– receptor potential results in

neurotransmitter release– nerve impulse formed

Anatomy of Taste Buds

• An oval body consisting of 50 receptor cells surrounded by supporting cells

• A single gustatory hair projects upward through the taste pore

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

Gustatory Sensation: Taste

• Taste requires dissolving of substances

• Four classes of stimuli--sour, bitter, sweet, and salty

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

• Found on sides of papillae• Taste and olfaction

combine to give some tastes

More on Gustation

• Four taste sensations:– Sour– Salty– Bitter– Sweet

• Taste and olfaction combine to give some tastes

• All taste buds can sense each sensation, but preferable to one sensation

Taste Buds

Visual Interpretation of Gustation

Eye

Anatomy: Accessory Structures of Eye• Accessory structures:

– Eyebrows—prevent perspiration in eye, shades eye

– Eyelids—protect from foreign objects, blinking reflex; lubrication

– Conjunctiva—mucous membrane that covers the inner surface of eyelids

– Lacrimal apparatus—produces tears

– Extrinsic eye muscles—eye movements

Anatomy: Lacrimal Apparatus

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

Anatomy: Eye

• Hollow, fluid-filled sphere

• Fibrous tunic—outer – Sclera & cornea

• Vascular tunic—middle– Choroid, ciliary

body, & iris• Nervous tunic—

inner– Retina

Anatomy: Tunics and Parts of the Eye

Anatomy: Cavities of the Interior of Eyeball

• Anterior cavity (anterior to lens)– filled with aqueous humor

• produced by ciliary body• continually drained• replaced every 90 minutes

• Posterior cavity (posterior to lens)– filled with vitreous body (jellylike)– formed once during embryonic life

never make more– floaters are debris in vitreous of older

individuals

Anatomy: Fibrous Tunic

• Sclera– “White of the eye”—only small part seen– Maintains the shape of eye, protects

internal structure, provides attachment sites for muscle attachment

• Cornea– Permits light into the eye– Bends or refracts entering light– Transparent, anterior 1/6th of eye

Anatomy:Vascular Tunic

• Choroid-thin structure in back of eye containing melanin cells; helps avoid reflection in the eye

• Ciliary body-contains smooth muscles attaching the lens; in front of choroid

• Iris-colored part of eye• Lens-flexible, biconvex, transparent disc• Pupil-smooth muscle that controls the

amount of light let into the eye

Anatomy: Nervous Tunic

• Retina—back of eye– Rods—20 times more than cones

• Very sensitive to light• Can function in very dim light

– Cones—require a lot of light• Provide color vision• Three types:

– Red, blue, green

Anatomy: Rods & Cones--Photoreceptors

Physiology: Sight

• Night blindness- lack of vitamin A; difficulty seeing in dim light

• Optic nerve- provides stimulus to brainoptic disc- where nerves leave the retina

• Blind spot- part of the optic disc that does not respond to light and contains no photoreceptors

Physiology: Eye

• Light refraction—bending of light – Focal point: crossing point of light

• Focusing images on retina– Depending on how far away the object is

from the retina, the muscles of the eye and lens help to focus and adjust until the object is focused clearly.

Physiology: Major Processes of Image Formation

• Refraction of light– by cornea & lens – light rays must fall upon the retina

• Accommodation of the lens– changing shape of lens so that light is focused

• Constriction of the pupil-less light enters the eye

• Convergance- both eyes focusing on one object so we only see one image- Single Binocular Vision

Physiology: Accommodation & the Lens

• Convex lens refract light rays towards each other

• Lens of eye is convex on both surfaces• View a distant object

– lens is nearly flat by pulling of suspensory ligaments

• View a close object– elastic lens thickens as the tension is

removed from it– increase in curvature of lens is called

accommodation

Eye Disorders

• Conjunctivitis• Myopia• Presbyopia• Hyperopia• Astigmatism• Strabismus• Color blindness• Cataract• Retinal detachment

Normal, nearsightedness, and

farsightedness

• Nearsightedness results in blurred vision when the visual image is focused in front of the retina, rather than directly on it. It occurs when the physical length of the eye is greater than the optical length. For this reason, nearsightedness often develops in the rapidly growing school-aged child or teenager, and progresses during the growth years, requiring frequent changes in glasses or contact lenses. A nearsighted person sees near objects clearly, while objects in the distance are blurred.

• Normal vision occurs when light is focused directly on the retina rather than in front or behind it. A person with normal vision can see objects clearly near and faraway.

• Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak. Farsightedness is often present from birth, but children can often tolerate moderate amounts without difficulty and most outgrow the condition. A farsighted person sees faraway objects clearly, while objects that are near are blurred

Near Point of Vision

• Near point is the closest distance from the eye an object can be & still be in clear focus– 4 inches in a young adult– 8 inches in a 40 year old

• lens has become less elastic– 31 inches in a 60 to 80 year old

• Reading glasses may be needed by age 40– presbyopia– glasses replace refraction previously provided

by increased curvature of the relaxed, youthful lens

Ear

Introduction to the Ear:Basic AnatomicalTerms

• Pinna— Elastic cartilage; funnel sound waves• Auditory canal – tunnel• Tympanic membrane— eardrum; vibrates ossicles• Ear ossicles— malleus, incus, stapes; which amplify sound

waves• Two membranes in inner ear— oval window, round window• Cochlea- “houses organ for hearing”• Semi-circular canals – “center” for balance• Eustachian tube— connects ear to throat; “equalization of

pressure”

Anatomy: Outer Ear

• External ear– Auricle-fleshy part

of ear– External auditory

meatus-passageway to eardurm

– Eardrum-sound waves cause it to vibrate

Anatomy: Middle Ear

• Middle ear-medial – Malleus-attached to

eardrum– Incus-between

malleus & stapes– Stapes-after incus;

vibrations amplified 20x

– Auditory tube- opens to pharynx & enables air pressure to be equalized outside & in

Middle ear

Auditory tube

Anatomy: Middle Ear Cavity

Anatomy: Inner Ear

• Inner ear- tunnels & chambers called bony labyrinth– Membranous labyrinth- filled with clear

fluid– Bony labyrinth:

• Cochlea- involved in hearing• Vestibule- involved in primary balance• Semicircular canals- involved in primary

balance

Anatomy: Inner Ear

Physiology: Auscultation

• Sound waves are collected by auricle and conducted through the external auditory meatus to the eardrum causing it to vibrate

• Eardrum vibrations cause the malleus, incus, & stapes to vibrate

• Vibration causes cochlear membrane to vibrate

• Microvilli in cochlear membrane bend

Physiology: Auscultation

• Microvilli bending causes depolarization of hair cells

• Hair cells send impulse in cochlear neurons

• Cochlear neurons send impulse to CNS

• Impulse is translated in cerebral cortex as sound

Physiology of Auscultation:Tubular Structures of the Cochlea

Distinguishing Different Sounds?

• Sounds at different frequencies vibrate different portions of the basilar membrane– high pitched sounds vibrate the stiffer more

basal portion of the cochlea– low pitched sounds vibrate the upper cochlea

which is wider and more flexible• Loud sounds vibrate cause a greater vibration of

the basilar membrane & stimulate more hair cells which our brain interprets as “louder”

Deafness

• Nerve deafness– damage to hair cells from antibiotics,

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

loss

– fail to notice until difficulty with speech

• Conduction deafness– perforated eardrum– otosclerosis

Equilibrium

• AKA balance• Static equilibrium- vestibule evaluating

position of head due to gravity• Kinetic equilibrium- semicircular canals

evaluating the change in rate of head movements

• Movement of fluid in the ears and hair cells tries to “catch up” with actual movements. When it does, we are equilized.

Detection of Rotational Movement

• When head moves, the attached semicircular ducts and hair cells move with it– endolymph fluid does not and bends the cupula and enclosed

hair cells

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