Sensation- a feeling resulting from a sensory impulse

2 Major Categories 1) Special Senses - smell, taste, sight, hearing and balance2) General Senses - touch, pressure, pain, temp, vibration,

itch and proprioception (sense of movement and position of the body and limbs)

Sensory adaptation - when receptors adapt and fail to send

signals.

Receptor - sensory nerve ending in the skin and other tissues capable of responding to stimuli by developing action potentials

Types of Receptors1. Mechanoreceptors - respond to mechanical stimuli

(bending or stretching)2. Chemoreceptors - respond to chemicals 3. Photoreceptors - respond to light 4. Thermoreceptors - respond to temp changes 5. Nociceptors - respond to pain sensations

1. Sensory Nerve Fibers - free nerve endings found in epithelial tissue and are associated with touch and pressure.

2. Meissner’s Corpuscles - loose fibers surrounded by flattened connective tissue related to the sensation of light touch. Numerous in hairless portions of skin(lips, soles, fingertips, palm, genitals, etc)p451 Fig15-1

3. Pacinian Corpuscles - bigger and found deep in tissues(tendons, muscles, ligaments in joints etc)Associated with heavy or deep pressure

pacinian

Sensory Meissner

Heat receptors (free nerve endings) Cold receptors

(free nerve endings)

1) acute pain fibers - sharp, well-localized, pricking, or cutting pain resulting from rapidly conductingaction potentials

2) chronic pain fibers - diffuse, burning, or dull aching pain resulting from slow conducting action

potentials (visceral pain stimuli are normally perceived as diffuse pain)

Referred pain - a painful sensation perceived to originate in a region of the body that is not the source of the pain stimulus p450 Box 15-1

exp: heart …….. Referred to the left shoulder or left arm

-smell and taste, hearing and balance, vision and light

I. Olfaction - sense of smell

*The olfactory receptor cells (bipolar neurons) are equipped with olfactory hairs, long cilia that protrudes out from the nasal epithelium and are layered by mucus. When stimulated by chemicals dissolved in the mucus, they transmit impulses along the olfactory nerve.

*closely tied to the limbic system “emotional brain” thus smells are long lasting and very much a part of our memories and emotions

Undergo sensory adaptation

P454 Fig 15-2

II. Taste

Taste bud - specific receptors for the sense of tastepapillae - small peg-like projections that cover the dorsal tongue surface p455 Fig 15-4

II. Taste

Taste cell - modified epithelial cells that function as receptors

*taste pore on the surface and projecting out of the pore are taste hairs

4 Basic Types 1. Sour2. Salty3. Sweet4. Bitter5. Umani (MSG)

Humans have almost 10,000 taste buds, some of them are on the roof of your mouth.

Girls usually have more taste buds than boys

The older you get the fewer taste buds you have

Insects are better at tasting than animals

III. Hearing

External Ear 1. Auricle - funnel like structure that helps collect sound waves and

direct them to the external auditorymeatus

2. External Auditory Meatus - s-shapedtube that leads to the temporal bone.

P457 Fig 15-5

III. Hearing

Middle Ear 1. Tympanic membrane (eardrum): cone-

shaped semitransparent membrane covered by a thin layer of skin.

2. Auditory Ossicles - 3 bones that connectthe eardrum to the inner ear and function in transmitting vibrations

The 3 bones (based on shape) 1. Malleus or hammer 2. Incus or anvil3. Stapes or stirrup

P457 15-5

III. Hearing

Oval window - an opening that leads to the inner ear. Transmits vibrations from the stapes to the fluid within the inner ear, which is responsible for stimulating hearing receptors.

Auditory Tube (eustachian tube) - connects middle ear to throat. It helps maintain equal air pressure on eachside of the eardrum

P457 15-5

III. Hearing

*Inflamation of the middle ear otitis media - result of sore throat in children whose auditory tubes are more horizontal.

III. Hearing

Inner Ear - a maze of bony chambers called osseous or bony labyrinth

3 Divisions of the Bony Labyrinth

1. 3 semicircular canals - involved in kinetic equilibrium/balance

2. Cochlea - (resembles a small snail) contains receptors for hearing

3. Vestibule - between semicircular canals and cochlea, sense of movement and static eq

p457 Fig 15-5, p458 Fig 15-6

III. Hearing

* The bony labyrinth is filled with plasma like fluidcalled perilymph. The system of membranes that followthe shape of the bony labyrinth is the membraneous labyrinth. The thicker fluid inside the membraneous labyrinth is called endolymph.

P458 Fig 15-6

III. Hearing

Static Equilibrium - sense the position of the head with respect to the pull of gravity when the body is not moving found in the vestibule.

Maculae - a patch of receptor cells with their “hairs” embedded in a gel-like material containing otoliths (tiny stones made up of calcium salts).

As the head moves otoliths respond to the pull of gravity and creates a pull on the gel and bends the hairs.

p462 Fig 15-8

III. Hearing

Dynamic Equilibrium - responds to angular or rotary movements of the head, the receptorsare found in the semicircular canals.

Crista ampullaris - a receptor site within each semi-circular canal that contains a tuft of hair covered with a gelatinous cap or cupula

p463 Fig 15-8

When head moves in a circular motion the endolymph pushes the cupula in the opposite direction of the body’s motion. When the motion stops the endolymph flows in the opposite direction causing that reversed motion feeling you get when you suddenly stop.

III. Hearing

Mechanisms of Hearing

Organ of Corti - contains hearing receptors withhair cells and when stimulated the hairs transmit impulses along the cochlear nerveto the temporal lobe where the sound is interpreted.

P458 Fig 15-6

http://www.youtube.com/watch?v=qgdqp-oPb1Q&safe=active

http://www.sumanasinc.com/webcontent/animations/content/soundtransduction.html

*Hearing is the last sense to leave our awarenesswhen we fall asleep and die and the first to return when we awaken

External and Accessory Structures

*6 extrinsic or external eye muscles attached to outersurface of eye and make it possible for eyes to followmoving objects.

External and Accessory Structures

Eyelids - thin skin that covers the outer surface of the eye and fuses with the margin of the lid

Composed of 4 layers 1) skin 2) muscle 3) connective tissue 4) conjunctiva - lines the eyelids and secretes mucus to

lubricate and keep eyeball moist

External and Accessory Structures

Lacrimal Apparatus - *lacrimal glands - secrete tears and the tears then flush across the eyeball into the lacrimal canals then into the lacrimal sac and finally into the nasolacrimal duct which empties into the nasal cavity

p468 Fig 15-18

*If you very gently pull down the inside corner of your eye. When you see a tiny little hole, you've found the tear duct/lacrimal canal.

Internal Eye Structures

Eyeball - the eye, its wall is composed of 3 layers or tunics and its interior is filled with fluids that helpmaintain its shape.

Internal Eye Structures

The Tunics

1. Outermost tunic - (fibrous tunic)sclera - or fibrous tunic “white of eye” the thick,

white, connective tissue that supports and protects the eye.

cornea - the transparent “window” where light enters the eye. It helps focus light rays.

The cornea is the only tissue that can be transplanted w/out the worry of rejection b/c it has no blood vessels

p464 Fig 15-10

Internal Eye Structures

II. Middle Tunic – (vascular tunic)

Choroid - blood-rich nutritive tunic that contains a dark pigment that prevents light from scattering inside the eye

Ciliary body - thickest part of the middle tunic to which the lens and iris attach,

muscular structure that manipulates the lens.

p464, p465

Internal Eye Structures

Lens - the elastic, double convex structure in the eye that focuses the light on the retina.

Iris - the pigmented, involuntary muscle that acts as the diaphragm of the eye (colored portion).

Pupil - rounded opening through which light passes

p464, 465, and 467

bright light - circular fibers contract and pupils constrict to decrease the amt of light entering eye

dim light - radial fibers contract and pupils dialate to allow more light to enter the eye. Fig 10.21

Internal Eye Structures

III. Innermost Tunic

Retina - the innermost tunic which contains photo-receptors (rods and cones) that respond to light.

Fovea centralis - the region of sharpest vision inside the retina

Optic disk or blind spot - is where nerve fibers fromthe retina leave the eye and become partof the optic nerve. P464, p466

*The lens divides the eye into two chambers the aqueous chamber, anterior to the lens, contains a clearwatery fluid called aqueous humor. The vitreous chamber,posterior to the the lens, is filled with a gel-like substance,vitreous humor.

As light passes through the eye it passes through the corneathen past the aqueous humor, the lens, and then the vitreous humor and retina.

http://www.youtube.com/watch?v=gvozcv8pS3c&safe=active

Common correctable vision problems

Myopia (near sighted) light focuses in front of the retina

Hyperopia (far-sighted) light focuses behind the retina

Astigmatism

irregular curvature of the cornea, causes light to focus on more than one point = blurriness

Glaucoma

a result of excessive accumulation of aqueous humor, increased pressure in the eye

Cataract Cloudy lens that obstructs the light before it hits the retina

http://www.youtube.com/watch?v=6YxffFmi4Eo&safe=active