Bell Work 4/25/11

Identify the special senses

A: Smell, Taste, Hearing, Vision, Balance

Somatic and Special Senses

Chapter 12

Types of Senses

• Somatic Senses include: Tactile (touch, pressure, and vibration), thermal (hot and cold), pain and proprioceptive sensations (joint and muscle position sense, and movements of limbs and head).

• Visceral Senses provide information about conditions within the body fluids and internal organs.

What is a Sensation?

• The conscious or subconscious awareness of internal or external conditions of the body.

Sensation Conditions• For a sensation to occur 4 conditions must be

met:1. A stimulus or change in the environment that

is capable of activating certain sensory neurons. (may be in the form of light, heat, pressure, mechanical energy or chemical energy)

2. A sensory receptor must convert the stimulus to an electrical signal-producing 1 or more nerve impulses.

Sensation Conditions

3. Nerve impulses must be conducted along a neural pathway from the sensory receptor to the brain.

4. A region of the brain must receive and integrate the nerve impulses into a sensation.

Sensation Characteristics

• Perceptions are conscious sensations that are integrated in the cerebral cortex. (sight, pain, and hearing)

• Sensory impulses from each part of the body arrive in a specific region of the cerebral cortex interpreting the sensation as it comes from the stimulated receptors.

• A given sensory neuron carries info for one type of sensation only.

Sensation Characteristics • Adaptation is a characteristic of most sensory

receptors that decrease sensation strength during a prolonged stimulus.

• Caused in part by a decrease in responsiveness to sensory receptors.

• As a result of adaptation, perception of sensation may fade or disappear.

• Receptors vary in how fast they adapt; pressure, touch, and smell adapt rapidly.

Types of Sensory Receptors

• Free nerve endings include receptors for pain, thermal, tickle, itch and some touch sensations.

• Encapsulated nerve endings include receptors for other somatic and visceral sensations such as touch, pressure and vibrations.

Homework

Complete checkpoints 1-5

Bell Work 4/26/11

Which receptors are especially abundant in the

fingertips, palms and soles?A: Corpuscles of touch

(Meissner corpuscles) are abundant in the fingertips, palms and soles.

Somatic Senses

Objectives: – Describe the location and fxn of the receptors for

tactile, thermal, and pain sensations. – Identify the receptors for proprioception and

describe their functions

Somatic Senses

• Arise from stimulation of sensory receptors in the skin, mucous membranes, muscles, tendons, and joints.

• Distributed unevenly• Largest amount of sensory receptors includes:

tip of the tongue, lips and fingertips.

Tactile Sensations

• Touch, pressure, vibration, itch, and tickle• Tactile receptors in the skin include corpsucles

of touch, hair root plexuses, type I and II cutaneous mechanoreceptors, laminated corpuscles and free nerve endings.

Touch• Result of stimulation of tactile receptors in the

skin. • Corpuscles of touch (Meissner corpuscles) are

located in the dermal papillae of hairless skin.• Each corpuscle is an egg shaped mass of

dendrites enclosed by a capsule of connective tissue-abundant in hands, eyelids, tip of the tongue, lips, nipples, soles, clitoris, and tip of the penis.

Touch

• Hair root plexuses consist of free nerve endings wrapped around hair follicles in hairy skin.

• Detect movement on the skin surface that disturb hairs.

• 2 types of slowly adapting touch receptors:– Type I cutaneous mechanoreceptors aka merkel

disks

Touch• Type I cutaneous mechanoreceptors are saucer

shaped, flattened nerve nedings that contact Merkel cells of the stratum basale (plentiful in fingertips, hands, lips and external genetalia)

• Type II cutaneous mechanoreceptors or ruffini corpuscles are elongated, encapsulated receptors located deep in the dermis, ligaments, and tendons. Present in the hands, and abundant in the soles, they are the most sensitive to stretching that occurs as digits or limbs are moved.

Pressure and Vibration

• Pressure is a sustained sensation that is felt over a larger area than touch.

• Receptors that contribute to sensations of pressure include corpuscles of touch, type I mechanoreceptors, and lamellated corpscles.

• Lamellated or pacinian corpuscles are large oval structures composed of a multi layered connective tissue capsule that encloses a nerve ending.

Pressure and Vibration

• Adapt rapidly• Widely distributed thru the body• Vibration results from rapidly repetitive

sensory signals from tactile receptors• Corpuscles of touch detect low frequency

vibrations• Lamellated corpuscles detect higher

frequencies

Itch and Tickle

• Itch results from stimulation of free nerve endings by certain chemicals: bradykinin, often as a result of an inflammatory response.

• Tickle thought to be free nerve endings and lamellated corpuscles.

• Arises when someone else touches you rather than when you touch yourself.

Thermal Sensations

• Thermal receptors are free nerve endings• 2 distinct sensations are cold and warmth• Cold are located in the epidermis, warm are

located in the dermis• Cold receptors are activated 50*-105*F• Warm receptors are activated 90*-118*F• Both adapt rapidly at the onset of the stimulus

Bell Work 4/27/11

Which visceral organ has the broadest area for referred

pain?

A: Kidneys

Pain Sensations

• Nociceptors are the sensory receptors for pain; found in almost every tissue of the body except the brain and respond to several types of stimuli.

• Sensation of pain is caused by excessive stimulation of sensory receptors, excessive stretching of structure, prolonged muscular contractions, inadequate blood flow, or presence of certain chemicals.

Pain Sensations

• Pain may persist even after the pain-producing stimulus is removed b/c the pain causing chem remain longer and b/c nociceptors do not exhibit little adaptation.

• If adaptation to painful stimuli could occur, irreparable tissue damage could result.

Pain Sensations

• Cerebral cortex is responsible for pain recognition type, and intensity

• Somatic pain is projected from the cerebral cortex back to the location of the pain.

• Visceral pain is felt in the skin overlaying the stimulated organ known as referral pain.

Types of Pain Sensations• Fast: occurs rapidly- w/in .1 sec after a stimulus is

applied. (needle prick or knife cut)– Aka acute, sharp, or pricking pain.– Precise and localized to the stimulated area– Not felt in deeper tissues of body

• Slow: begins a second or more after a stimulus occurs, gradually increasing over time. – Excruciating pain– Referred to as chronic, burning, aching, or throbbing

pain– Can occur in skin and deeper tissues and organs

(toothache)

Proprioceptive Sensations

• Inform you consciously and subconsciously of the degree to which your muscles are contracted, amount of tension present in your tendons, position of your joints, and the orientation of your head.

• Proprioceptors adapt slowly –beneficial so the brain can be aware of what is occurring at different parts of your body at all times.

Proprioceptive Sensations

• Kinesthesia allows you to walk, type or dress w/o using your eyes.

• Proprioceptors allow you to estimate the weight of an object, and the effort necessary to perform the task (bag of books vs bag of feathers)

• Proprioceptors are located in skeletal muscles, tendons around synovial joints and the inner ear.

Olfaction: Sense of Smell

• The nose contains 10mill-100mill receptors for smell-aka olfaction

• b/c some nerve impulses for smell and taste return to the limbic system, certain odors and tastes can bring back a flood of memories.

Bell Work 4/28/11

What is the function of basal stem cells

A: Basal stem cells undergo cell division to produce new olfactory receptors.

Structure of the Olfactory Epithelium

• Olfactory receptors are the first order neurons of the olfactory pathway.

• Olfactory hairs are cilia that project from a knob shaped tip on the olfactory receptor-respond to inhaled chemicals which in turn stimulates he olfactory hairs initiating olfactory receptors by odorants.

Structure of the Olfactory Epithelium• Supporting cells provide physical support,

nourishment, and electrical insulation for the olfactory receptors, and help to detoxify chemicals that come in contact w/ olfactory epithelium.

• Basal stem cells produce new olfactory receptors; live for a month before they are replaced.(these are neurons)

• Olfactory Glands produce mucus that moistens the surface of olfactory epithelium & acts as a solvent for inhaled odorants.

Stimulation of Olfactory Receptors• Our ability to recognize ~10,000 diff odors

probably depends on brain activity that arise from activation of many different combinations of olfactory receptors.

• Olfactory receptors adapt by 50% in the first second after stimulation, and very slowly thereafter.

• Olfactory receptors react to odorants by producing an electrical molecule that triggers the nerve impulse.

Olfactory Pathway

• Olfactory nerves form the right and left cranial nerve consisting of ~40 bundles of axons.

• Olfactory bulbs contain axons terminals of olfactory nerves that form synapses w/dendrites of neurons in the olfactory pathway.

Sense of Smell

Olfactory Pathway• The axons of the neurons from the olfactory

bulb form the olfactory tract.• Primary olfactory area is where the conscious

awareness of smell begins .

Gustation: Sense of Taste• 5 primary tastes: sweet, sour, bitter, salty, and

umami (meaty/savory)• All other flavors are a combination of tastes in

conjunction w/touch and smell. • Odors from food an pass upward from the mouth

into the nasal cavity, stimulating olfactory receptors.

• Aromas from food can stimulate the olfactory system 1,000’s of times stronger than the gustatory system.

• Lack of taste during illness is due to blockage of olfaction.

Structure of Taste Buds

• The receptors for taste sensations are located in the taste buds

• w/age, taste bud # declines dramatically• Found in elevations on tongue called papillae

Structure of Taste Buds

• Vallate papillae form an inverted v shape row at the back of the tongue

• Fungi papillae mushroom shaped elevations over the entire surface of the tongue

• Filliform papillae contain touch receptors, but no taste buds

• Each taste bud is an oval body w/epithelial cells-supporting, gustatory receptors, basal cells

Structure of Taste Buds

• Supporting cells surround 50 gustatory receptor cells

• Single long gustatory hair projects from gustatory receptor cell to the external surface thru the taste pore-opening in the taste bud

• Basal cells produce supporting cells that develop into gustatory receptor cells that have a life span of ~10 days

Stimulation of Gustatory Receptors

• Tastants are chemicals that stimulate gustatory receptor cells.

• Once the chemical is dissolved in the saliva, taste pores make contact with plasma membrane of the gustatory hair=electrical signal that stimulates neurotransmitter release.

• Indiv gustatory receptor cells may respond more than one of five primary tastes

Stimulation of Gustatory Receptors

• Complete adaptation (loss of sensitivity) to a specific taste can occur w/in 1-5min

• Different tastes arise from activation of different groups of taste neurons; some responding stronger to certain tastants that others.

Gustatory Pathway

• From taste buds, impulses propigate along cranial nerve VII, IX and X to the medulla oblongata

• Taste signals that project from the hypothalamus to the primary gustatory area give rise to the conscious perception of taste.

Bell Work 5/3/11

In order from the tongue to the brain, what structures form the

gustatory pathway.

A: gustatory receptor cells-> cranial nerves VII, IX, and X -> medulla oblongata

-> thalamus ->primary gustatory area in the parietal lobe of the cerebral cortex.

Vision

• Objectives: – Describe the accessory structures of the eye,

layers of the eyeball, the lens, interior of the eyeball, image formation and binocular vision.

– Describe the receptors for vision and the visual pathway to the brain.

Vision

• More than ½ the sensory receptors in the human body are located in the eyes, and a large part of the cerebral cortex is devoted to processing visual information.

Accessory Structures of the Eye

• Eyebrow, eyelashes, eyelids, muscles that move the eyeballs and lacrimal (tear-producing) apparatus.

• The eyebrows and eyelashes protect the eyeballs from foreign object such as perspiration (sweat), and direct rays of the sun.

• Upper and lower eyelids shade the eyes during sleep, protect from excessive light and spread lubricating secretions over the eyeball by blinking.

Accessory Structures of the Eye

• Six eye muscles work together to move the eyeball each direction.

• Neurons in the brain stem and cerebellum coordinate and synchronize the movements of the eyes.

Accessory Structures of the Eye

• Lacrimal apparatus is a group of glands, ducts, canals and sacs that produce and drain lacrimal fluid of tears.

Cornea - the clear, dome-shaped tissue covering the front of the eye. Iris - the colored part of the eye - it controls the amount of light that enters the eye by changing the size of the pupil Lens - a crystalline structure located just behind the iris - it focuses light onto the retina Optic nerve - the nerve that transmits electrical impulses from the retina to the brain

Pupil - the opening in the center of the iris- it changes size as the amount of light changes (the more light, the smaller the hole) Retina - sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve Vitreous - a thick, transparent liquid that fills the center of the eye - it is mostly water and gives the eye its form and shape (also called the vitreous humor)

Accessory Structures of the Eye

• Lacrimal glands are each about the size and shape of an almond.

• Secrete tears thru lacrimal ducts• Tears pas over the surface of the eyeball to the

nose into 2 lacrimal canals and nasolacrimal ducts which allow tears to drain into the nasal cavity-> runny nose while crying.

Accessory Structures of the Eye

• Tears are a watery solution containing salts, mucus, and a bacteria killing enzyme called lysozyme.

• Tears are cleared away by evaporation or by passing into the nasal cavity as fast as they are produced.

Layers of the Eye Ball

• 1 in or 2.5 cm• 3 layers: fibrous tunic, vascular tunic and

retina.• Fibrous tunic: outer coating of the eyeball;

cornea is a transparent fibrous coat that covers the colored part of the eyeball, the iris -> helps to focus light rays into the retina.

Fibrous Tunic

• Sclera “white” of the eye• Coat of dense connective tissues that covers

all of the eye except the cornea.• Gives eye shape, protects inner parts, makes it

rigid.• Conjunctiva covers the anterior surface of the

eyeball, and lines inner surface of the eyelids.

Vascular Tunic• Middle layer of eyeball and is composed of choroid

cilliary body and iris. • Choroid is a thin membrane that lines most of the

internal surface of sclera.• Contains many blood vessels that help nourish the

retina. • Lens transparent and focuses light rays onto the

retina. • Iris is colored part of eyeball• Pupil is a hole at the center of the iris in which light

enters

Bell Work 5/4/11

What are the components of the fibrous and vascular tunic.

A: fibrous tunic consists of the cornea & sclera, vascular tunic consists of choroid,

cilliary body and lens.

Retina

• Third and inner coat of the eyeball-lies posterior ¾ of the eyeball and is the beginning of the visual pathway.

• 2 layers: neural layer & pigmented layer.• Neural layer is multilayered outgrowth of the

brain.

Pigmented Layer of the Retina

• Sheet of melanin-containing epithelial cells located btw the choriod and neural part of the retina.

• Melanin in the choroid & pigmented layer absorbs stray light rays, preventing reflection and scattering of light w/in the eyeball.

• As a result of ^, the image is cast on the retina by the cornea and lens remains sharp & clear.

Page 301

Photoreceptors

• 2 types: Rod & Cone• Rod allow us to see shades of gray in dim light,

such as moonlight.• Cones are stimulated by brighter light, giving

rise to color vision. • ~6mill cones & ~ 20mill rods

Flow of Information

• From photoreceptors -> through the outer synaptic layer -> bipolar cells of the bipolar layer-> bipolar cells-> inner synaptic layer -> ganglion cells of the ganglion cell layer.

Blind Spot

• Blind spot (optic disc) is a small area of the retina where axons of the gangilon cells exit as the optic nerve.

• We are unaware of this blind spot, but on page 302 examine the figures and cover your left eye, and increase the distance btw the book and your eye- at some point one of the images will disappear into your blind spot.

Interior of the Eyeball• Divided into 2 cavities: anterior cavity &

vitreous chamber.• Anterior cavity is filled w/ aqueous humor->

watery fluid similar to cerebral spinal fluid. • Aqueous humor is secreted by blood capillaries

to fill the anterior cavity, and drains into the scleral venous sinus (canal of Schlemm) where it re enters the blood.

• Aqueous humor helps to maintain the shape of the eye & nourishes the lens and cornea.

Interior of the Eyeball

• Vitreous chamber contains a clear, jelly-like substance called the vitreous body-forms during embryonic life and is there forever.

• Vitreous body helps prevent the eyeball from collapsing and holds the retina flush against the choroid.

Refraction of Light Rays

• ~75% of total refraction (bending of light rays) occurs at the cornea.

• Light further refracts through the lens so they can come into focus on the retina.

• Images are inverted at the retina, and undergo right-left reversal-brain must decipher the images and store them to be recalled later.

Bell Work 5/5/11

What is presbyopia?

A: Loss of elasticity in the lens that occurs w/age

Accommodation• The increase in curvature of the lens for near

vision• While viewing distant objects, the ciliary

muscle is relaxed and nearly flat.• While viewing a close object, the ciliary

muscle contracts pulling the ciliary process and choroid close to the lens allowing it to be come rounder-increasing focusing power and greater convergence of light rays.

Accommodation

• Normal eye aka emmetrophic eye, can sufficiently refract light rays from an object 20ft away so a clear image is focused on the retina.

• Many people lack this ability b/c refraction abnormalities.

Abnormalities of the Eye

• Myopia (nearsightedness) occurs when the eyeball is too long relative to the focusing power of the cornea and lens.

• Hypermetropia (farsightedness) eyeball length is short relative to the focusing power or the cornea and lens. (see figure 12.10 pg 304)

• Astigmatism is which either the cornea or lens has an irregular curvature.

Constriction of the Pupil• Is a narrowing of the diameter of the hole

through which light enters the eye. • Occurs due to contraction of the circular

muscles of the iris. • Pupil constricts in bright light to limit the

amount of light that strikes the retina.

Convergence• Both eyes focus on a single object or set of objects-

binocular vision.• Binocular vision allows us to perceive depth and 3D

objects. • As you come closer to an object, your eyes must rotate

toward your nose for light rays to be reflected to the retinas.

• Convergence is the name for this automatic movement of the 2 eyeballs toward the midline-caused by the coordinated action of extrinsic eye muscles.

• The nearer the object, the greater convergence needed to maintain binocular vision.

Stimulation of Photoreceptors

• Photopigment is a substance that can absorb light and undergo change in its structure.

• Rhodopsin are the rods in photo pigment and composed of protein called opsin and a derivative of vitamin A called retinal.

• When the light level is dim opsin and retinal recombine into rhodopsin as fast as rhodopsin is split apart.

• Cones fxn in bright light to provide color vision• Photopigments in cones also contain retinal

but there are 3 diff opsin proteins• One type of cone pigment responds to

yellow/orange light, second to green, third to blue.

• The cone photopigments reform much more quickly than the rod photopigment.

Visual Pathway• Bipolar cells transmit both excitatory

inhibitory signals to ganglion cells.• Ganglion cells become polarized and generate

nerve impulses.• Axons of ganglion cells exit the eyeball as the

optic nerve, cranial nerve and extend posterior to the optic chiasm.

• After passing the optic chaism, the axons are now part of the optic tract.

Bell Work 5/6/11

Where are the receptors for hearing and equilibrium

located?

A: Inner ear, cochlea (hearing) and semicircular ducts (equilibrium)

Hearing and Equilibrium

• Objective: Describe the structures of the outer, middle and inner ear.

• Describe the receptors for hearing and equilibrium and their pathways of the brain.

Structure of the Ear

• Sensory receptors can convert sound vibrations into electrical signals 1000x faster than photoreceptors can respond to light.

• Divided into 3 main regions: outer, inner and middle ear.

Outer Ear• Collects sound waves and passes them inward. • Consists of an auricle-outer “shell” of the ear composed

of cartilage.• Directs sound waves toward the external auditory

canal-curved tube from the auricle directing sound to the eardrum.

• Canal contains hairs and ceruminous glands which produce earwax (cerumen).

• Hair and wax help to prevent foreign objects from entering the ear.

• The eardrum (tympanic membrane) is a thin, semi transparent partition-sound waves cause its vibration.

Middle Ear

• Small, air filled cavity. An opening in the anterior wall of the middle ear leads directly to the auditory tube (eustatian tube) which connects to he middle ear w. up part of the throat.

• When the auditory tube is open, air pressure can =ize on both sides of the eardrum; changes in pressure on one side can cause rupture.

• During yawning and swallowing, the tube opens which is why yawning can help =ize pressure changes while flying.

Middle Ear

• Auditory ossicles= malleus, incus, and stapes aka hammer, anvil stirrup.

• Tiny skeletal muscles control the amount of movement of these bones to prevent damage by extremely loud noises. The stapes fits into a small opening in the thin bony partition btw the middle & inner ear-oval window.

Inner Ear

• Divided into outer bony labyrinth and inner membranous labyrinth.

• Bony labyrinth is a series of cavities in the temporal bone including the cochlea, vestibule and semicircular canals.

• Cochlea is the sense organ for hearing; vestibule and semicircular canals are for equilibrium and balance.

Inner Ear

• Consists of a fluid called perilymph w/in the bony labyrinth.

• This fluid surrounds inner membraneous labyrinth (a series of sacs and tubes w/ the same shape as the bony labyrinth.)

• The membranous labyrinth contains a fluid called endolymph.

Hearing Assistive Devices

Physiology of Hearing

1. Auricle directs sound into external auditory canal

2. Sound waves strike the eardrum causing it to vibrate (distance and speed depend on the intensity and frequency of sound waves.)

3. Malleus starts to vibrate and is transmitted to the incus and stapes.

4. Stapes moves back and fourth, pushing the oval window in & out.

Physiology of Hearing

5. Movement of the oval window sets up fluid pressure waves in the perilymph of the cochlea.

6. The fluid pressure waves are transmitted from the scala vestibuli to the scala tympani and eventually to the membrane covering the round window causing it to bulge into the middle ear.

Physiology of Hearing7. As the pressure waves deform the walls of the

scala vesstibuli and scala tympani they also push the vestibular membrane back and forth creating pressure waves in the endolymph inside the cochlear duct.

8. Pressure waves in the endolymph cause basalar membrane to vibrate which moves the hair cells of the spiral organ against tectorial membrane. Bending of the hairs stimulates the release of neurotransmitters to part of the vestibular nerve.