The Senses

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Sensory Receptors Changes environmental stimuli into nerve impulses

Generalized Sensory Pathway

Impulses are conducted to sensory areas of the cerebral cortex

Sensing the Internal Environment Neurons send messages to homeostasis centers in the brain Sensor types Temperature Carbon dioxide levels Oxygen levels pH Stretch Pain

Proprioceptors Position receptors Sense position in space Within skeletal muscle Within tendons In the inner ear Sense position in space Example: stretch receptor in muscle

Mechanoreceptors Detect touch, movement & pressure Example: lateral line system

Touch Receptors in Human Skin Merkel’s discs, Meissner’s corpuscles & Pacinian corpuscles

Thermoreceptors Sensitive to temperature change

Detecting Infrared Heat is sensed as infrared radiation Pit organs of some snakes

Detecting UV light Insects have receptors to detect UV UV light transmitted by flowers Insects are pollinators of flowers Normal Light UV Light

Electroreceptors Detect electric fields Found in some fish, salamanders & platypus

Detection of Magnetic Fields Found in variety of migratory animals Used for orientation to return to certain areas

Chemoreception Widespread in animal kingdom May be found on many parts of the body Includes senses of taste & smell

Taste Receptor = taste buds Detect chemicals in food Primary tastes Salty Sweet Sour Bitter

Taste Buds Within tongue papillae Microvilli extend through taste pore Nerves attached to receptor cells

Smell Olfactory receptors Can distinguish several thousand odors In nasal epithelium Can distinguish several thousand odors

Photoreception Sensing light Different organisms sense different wavelengths Not all eyes are image forming

Multifaceted Eyes Each facet sees part of image Image is summed by brain to form single image

Phototaxis Detection of light can change behavior Positive phototaxis Organism moves toward light Negative phototaxis Organism moves away from light

Human Eye Camera-like eye also found in cephalopods Single lens Receptors sensitive to various wavelengths Light is focused onto receptors

Structure of the Human Eye

Outer Layer of Eye Sclera Cornea Aqueous humor Tough connective tissue layer White region of the eye Cornea Transparent front of eye Allows light to enter Aqueous humor Liquid behind cornea Fills anterior chamber

Lens Just behind aqueous humor Suspended by ligaments Ligaments attached to cilliary muscles Cilliary muscles are able to change lens shape for focusing

Focusing the Eye

Iris Lies between cornea & lens Colored part of eye Controls size of opening Opening = pupil

Choroid Layer Dark brown membrane Lines sclera Contains blood vessels Nourishes eye

Retina Contains sensory receptors Fovea Rods Cones Low levels of light Cones Three types Stimulated by different wavelengths Allows for color vision Fovea Central area with many cones

Structure of the Retina

Optic Nerve Creates blind spot in retina Carries impulses to brain

Depth Perception Possible because of two eyes in different positions Provides two images summed by brain Results in three dimensional quality image

Sound Type of mechanical energy Many different types of sound receptors Some animals hear different wavelengths Bats use echolocation or animal sonar

Human Hearing Human ear has three parts Inner ear has sound receptors

Outer Ear Pinna External auditory canal Funnels sound waves Leads to tympanic membrane

Tympanic Membrane Eardrum Stretches over middle ear opening Amplifies & increases vibrations Transfers vibrations to bones of middle ear

Bones of Middle Ear Malleus, Incus & Stapes Transfer vibrations to opening of Cochlea

Eustachian Tube Connects middle ear to nasopharynx Equalizes air pressure

Inner Ear Membrane covers oval window Fluid filled cochlea Contains organ of Corti Hair cells are receptors

Transmission of Pressure Waves in Inner Ear

Sound Perception Different frequencies set up differing wave patterns Loud sound increases wave magnitude

Vestibule & Semicircular Canals Detect position and movement Both found in inner ear

Vestibule Senses if you are upside down Detects effects of gravity Includes two areas Utricle Saccule Jelly filled chambers

Movement Detection in Vestibule Otoliths – small pebbles Movement can cause otoliths to stimulate receptor cells Brain makes sense of sensory input

Semicircular Canals Three fluid filled canals Canals oriented at right angles Contain ciliated sensory cells Jelly like material lies above cells Movement initiates depolarization Complex movements analyzed by brain