Chapter 25 Section 2

List four sensations that are detected by receptors in the skin

Describe how a feedback mechanism works

Describe how the senses of hearing, taste, and smell work

Sensory receptors in the skin are stimulated = touch

Skin has receptors that respond to a kind of stimulus: Pressure Temperature (ex: thermoreceptors) Pain Vibration

An immediate involuntary reaction = reflex

Pain – leads to – impulse to spinal cord – leads to – reflex action

Brain processes info from skin receptors

Example: hot day – heat receptors tell sweat glands to make sweat – blood vessels dilate – body cools – new message is sent to reduce this activity

A cycle of events in which information from one step controls or affects a previous step

Allows you to see the size, shape, motion, and color of objects around you

You see an object when it sends of reflects visible light toward your eyes

Your eyes detect light, your brain processes it to form a visual image

Cornea: thin membrane that covers the front of the eye; protects the eye allows light to enter

Pupil: light enters through this opening in the front of the eye

Retina: light-sensitive inner layer of the eye; it receives images formed by the lens which are transmitted through the optic nerve to the brain

http://www.mycompleteeyecare.com/style-inc/gfx/eye_anatomy.gif

Packed with photoreceptors (special neurons that change light into electrical impulses)

2 kinds of photoreceptors: Rods: very sensitive to dim light

Important for night vision Interpreted as black & white images

Cones: very sensitive to bright light Allows you to see details & colors

Impulses travel along axons to optic nerve to the brain

http://starizona.com/acb/basics/images/rods_cones.jpg

Iris: a ring of muscle; the opening is called the pupil; controls the amount of light that enters the eye; gives the eye its color

Iris contracts in bright light; opens in dim light

http://fc02.deviantart.net/fs27/f/2008/042/0/0/Iris_Eye_Macro_Stock_by_zpyder.jpg

Light travels in straight lines until it reaches the cornea & lens

Lens: the oval shaped piece of clear, curved material behind the iris

Muscles in the eye change the shape of the lens in order to focus light on the retina

Objects close to the eye: lens curves Objects far away: lens gets flatter

http://www.uniteforsight.org/course/image/m_eye.jpg http://www.uniteforsight.org/course/image/h_eye.jpg

A concave lens bends light rays outward to correct nearsightedness

A convex lens bends light rays inward to correct farsightedness

http://thumbs.dreamstime.com/thumb_404/12436315187ijB2I.jpg

http://static-p3.fotolia.com/jpg/00/11/88/46/400_F_11884612_edQtgjQhcRti1fFJLnxN4eHzvUfuTMQy.jpg

Vibration of particles produces sound

Outer, middle, inner portions of the ear Outer: funnels sound waves to middle ear Middle: waves make eardrum (thin

membrane) vibrate tiny bones in the ear Inner: tiny bones vibrate against the cochlea

(fluid filled organ – neurons change waves to electrical impulses) – auditory nerve- to brain

http://www.daviddarling.info/images/ear_diagram.jpg

Detects chemicals & distinguishes flavors

Tongue is covered with tiny bumps (papillae)

Most papillae contain taste buds (clusters of taste cells) – receptors for taste

4 basic tastes: sweetness, sourness, saltiness, and bitterness

http://www.understandingfoodadditives.org/assets/taste_map.jpg

Olfactory cells: receptors for smell (upper part of nasal cavity)

Respond to chemical molecules in the air

Trigger impulses that are sent to the brain

Senses from taste and smell are combined to give information about flavor

http://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Head_olfactory_nerve.jpg/250px-Head_olfactory_nerve.jpg