© 2014 Pearson Education, Inc. Human Biology Concepts and Current Issues Seventh Edition Michael D. Johnson Lecture Presentations by Robert J. Sullivan Marist College 12 Sensory Mechanisms

© 2014 Pearson Education, Inc. Receptors Receive and Convert Stimuli  Stimulus:  A change in the environment –Heat, pressure, pain, touch, sound, light, chemical  Receptor: a structure sensitive to a specific stimulus and converts its energy into electric signals

© 2014 Pearson Education, Inc. Receptors Are Classified According to Stimulus  Mechanoreceptors –Respond to mechanical stimuli –Example; respond to touch, pressure  Thermoreceptors –Respond to heat or cold  Pain receptors –Respond to tissue damage or excessive heat or pressure  Chemoreceptors –Respond to presence of chemicals example, taste receptors  Photoreceptors –Respond to light

© 2014 Pearson Education, Inc. CNS Interprets Nerve Impulses  Nerve impulses are transmitted from receptors to specific portions of brain  Sensations are perceived in the brain, example sensation of pain, heat, cold, vision

© 2014 Pearson Education, Inc. General (somatic) Sensations and Special Senses Provide Sensory Information  General (somatic) sensations –Arise from sensory receptors located throughout the body –Temperature, pressure, touch, vibration, pain, of body position  Special senses –Arise from sensory receptors restricted to specific areas of the body –Taste, smell, hearing, balance, vision

© 2014 Pearson Education, Inc. General (somatic)Sensations Arise from Receptors Throughout the Body  Somatic receptors include sensory receptors in skin, muscle, joints, ligaments  Nerve impulses from general (somatic) receptors sent to the primary somatosensory area of parietal lobe of cerebral cortex  Somatosensory area processes the information and perception of sensation happens here

© 2014 Pearson Education, Inc. Figure 12.1 Hair Epidermis Dermis Subcutaneous layer Modified and encapsulated nerve endings Unencapsulated dendritic endings Receptors that sense changing position of hairs Thermo- light touch, and pain receptors Merkel disks: light touch Meissner’s corpuscle: light touch Ruffini endings: pressure Pacinian corpuscle: deep pressure and high- frequency vibration Skin receptors

© 2014 Pearson Education, Inc. Special Senses: Taste  Taste buds –Chemoreceptors bind with dissolved substances –Most are distributed around edge, front, back of tongue  Taste categories –Sweet –Salty –Sour –Bitter

© 2014 Pearson Education, Inc. Special Senses: Smell  Olfactory receptor cells –Chemoreceptors that bind with odorants –Detect  1,000 different odorants Sense of smell is perceived in the temporal lobe of the brain Olfactory epithelium Olfactory bulb

© 2014 Pearson Education, Inc. Figure 12.9 Outer earMiddle earInner ear Incus (anvil) Pinna Malleus (hammer) Auditory canal Tympanic membrane Auditory tube Round window Cochlea Stapes (stirrup) Oval window (behind stirrup) Vestibule Cochlear nerve Vestibular nerve Vestibulocochlear nerve ( VIII) Nerve Semicircular canals Special Senses- Hearing: receptors detect sound waves

© 2014 Pearson Education, Inc. The Outer Ear  Pinna: visible portion of ear, directs sound waves to auditory canal  Auditory canal: directs sound waves to the tympanic membrane  Tympanic membrane (ear drum): separates outer ear from middle ear, vibrates in response to sound waves and passes along vibrations to the ear bones

© 2014 Pearson Education, Inc. The Middle Ear  Air-filled space with three small bones  vibrations of tympanic membrane, passed to these three bones in sequence  vibrations passed to inner ear  Auditory tube (eustachian tube) –Connects to throat –Equalizes pressure

© 2014 Pearson Education, Inc. The Inner Ear & hearing  Bony cochlea (looks like a snail),contains a cochlear duct- has receptors for hearing which get stimulated  Sound waves converted to action potentials (nerve impulses)  Nerve impulses carried by VIII cranial nerve (vestibulocochlear nerve) to auditory area in the temporal lobe of the brain

© 2014 Pearson Education, Inc. Inner Ear also plays an essential role in balance  Vestibular apparatus  Helps maintain equilibrium –Three semicircular canals and vestibule –Contain receptors for detecting changes in position of head  Sensing rotational movement –Detected by receptors in semicircular canals  linear movement –Detected by receptors in vestibule

© 2014 Pearson Education, Inc. Cochlea (for hearing) Semicircular canals Vestibule Inner Ear for balance

© 2014 Pearson Education, Inc. Eye & Vision  Vision involves converting light energy to nerve impulses and transmitting them to the occipital lobe of the brain  Eye ball structures –Sclera (white of the eye) and cornea –Iris, choroid –lens –Aqueous humor & vitreous humor –Retina, macula – optic nerve, optic disc

© 2014 Pearson Education, Inc. Figure Macula Fovea centralis Optic nerve Optic disk Retina Choroid Ciliary muscle Vitreous humor Lens Pupil Iris Aqueous humor Cornea Canal of Schlemm Sclera

© 2014 Pearson Education, Inc. Table 12.4

© 2014 Pearson Education, Inc. Figure Blind spot Retina Artery Vein Optic nerve Rod Cone Photo- receptor cells Pigmented cell layer Rod cell and cone cell layer Bipolar cell layer Ganglion cell layer To optic nerve Axons of ganglion cells Light Retina- contains photoreceptors: rods and cones

© 2014 Pearson Education, Inc. Photoreceptors  Photoreceptors contain photo pigments  Rods- provide vision in dim light  Contain single type of photo pigment  In dim light, vision primarily dependent on rods  Cones- provide color vision and accurate images  Three types of cones, according to three types of photopigments- red, green, blue

© 2014 Pearson Education, Inc. Disorders Otitis media Deafness Retinal detachment Cataract Glaucoma Color blindness