Chapter 29- The Senses• Accommodation• Aqueous humor• Astigmatism• Auditory canal• Basilar membrane• Blind spot• Chemoreceptors• Choroid• Cochlea• Compound eye• Cones• Conjunctiva• Cornea• Eardrum• Electromagnetic receptors• Eustachian tube• Eye cup• Farsightedness• Fovea• Hair cells• Inner ear • Iris• Lens• Mechanoreceptors• Middle ear

• Nearsightedness• Ommatidia• Organ of Corti• Outer ear• Oval window• Pain receptors• Perception• Photopsins• Photoreceptors• Pinna • Pupil• Receptor potential• Retina• Rhodopsin• Rods• Saccule• Sclera• Semicircular canals• Sensation• Sensory adaptation• Sensory transduction• Single-lens eye• Stretch receptors• Thermoreceptors• Utricle• Visual acuity• Vitreous humor

Sensory input

• Sensations- awareness of sensory stimuli• Sensory info moves from receptors via action potentials

to CNS• Body takes sensation and forms perception- meaningful

interpretation of sensory data

Sensory transduction

• Converting stimulus into electrical signal– Change in membrane potential (receptor potential)– Potentials vary- stronger the stimulus- larger the receptor

potential

• Sensory adaptation- tendency of sensory receptors to become less sensitive– Triggers fewer action potentials– Keeps body from reacting to background stimuli

5 types of sensory receptors

• 1- Pain- respond to excess heat, cold, pressure, chemicals– All parts of human body except brain

• 2-Thermoreceptors- detect heat or cold on skin, others deep in body monitor blood temp– Messages get sent to hypothalamus which regulates body temp

• 3-Mechanoreceptors- highly diverse (touch, pressure, stretch, motion, sound)– Stretch receptors in muscle- monitor body position– Hair cells- detect sound waves and movement in air or water

5 types of sensory receptors

• 4- Chemoreceptors- develops potentials in response to chemicals– In nose, mouth and arteries (amount of O2 in blood)

• 5- Electromagnetic- can detect various wavelengths– Ex: fish send out electric current and use receptors to detect

food/obstacles– Some org’s are thought to detect Earth’s magnetic field– Photoreceptors (including eyes)- most common electromagnetic

receptor

3 types of eyes

• Eye cup- (in flat worms)- provide info on intensity and direction of light, brain compares info from each eye and sends signal to move away

• Compound eye- have lens, focus and form images by ommatidia- light detecting units having lens and photoreceptor cells

• Single-lens eye- similar to a camera and vertebrate single lens eye

Vertebrate eye• Detects color, form images, respond to light E

– Sclera- outer surface of eye, whitish CT and clear in front, cornea

– Choroid- underneath sclera, iris in front of eye• Iris- colored part of eye• Pupil- opening- lets in light

– Lens- held in position by ligaments, focuses images onto retina (layer inside choroid)

– Photoreceptors on retina pass action potentials via sensory neurons to optic nerve

– Fovea- retina’s center of focus– Humors- fluid in eye– Conjunctiva- mucous membrane lining eyelid

Focusing

– Fish and squid- rigid lens- muscles move lens back and forth– Mammals- change lens shape- accommodation

Photoreceptor cells

• Rods- sensitive to light, shades of gray- night vision• Cones- stimulated by bright light, distinguish color

– 3 types- blue, green, yellow– Colorblindness- cone deficiency

• When rods and cones absorb light membrane permeability changes

The Ear

• Converts air pressure waves to action potential that’s perceived as sound– To hear and maintain balance – by stimulating cilia like

projections on hair cells

3 regions of the ear• Outer- pinna and auditory canal

– Collect sound waves and channel them to middle ear

• Middle- – Eardrum- separates outer from middle ear– When sound waves strike drum passed to hammer, anvil and

stirrup sending vibrations to inner ear– Eustachian tube- conducts air between inner ear and back of

throat keeps pressure equal on either side of drum

• Inner- fluid-filled channels in bones– Sound waves & movement set fluid in motion– Cochlea- contains hearing organ organ of Corti– Hair cells in Corti ear receptor cells– Regions of basilar membrane in organ can determine types of

sounds

Organs of balance

• Semicircular canals- detect head motion– 3 canals are all perpendicular to each other to detect all directions

• Utricle and saccule- detect head position with respect to gravity

– Motion sickness- conflict between what ear says and eyes say

Smell and Taste

• Dependent on chemoreceptors• Nose receptor can detect up to 50 odors• Some insects have chemoreceptors in feet• * works same way all senses do converting stimuli to

action potentials