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Anatomy and Physiology Chapter 16
Sense organ: structure made of nervous tissue and other tissues to enhance response to stimuli
(ex: eyes)
Types of info transmitted by sensory receptors:
1) Modality: type of stimulus (ex: vision, hearing, taste)
2) Location: receptive field; which nerve fibers issue signals to the brain (ex: receptors on fingertips vs.
receptors on large area of skin)
3) Intensity: as stimulus intensity increases, so do the firing frequencies of sensory nerve fibers
4) Duration: how long a stimulus lasts; if stimulus is long-lasting, over time we become less aware of the
stimulus
Classification of Receptors:
Thermoreceptors: respond to heat and cold
Photoreceptors: respond to light
Nociceptors: respond to pain
Chemoreceptors: respond to chemicals (odor, taste, etc.)
Mechanoreceptors: respond to physical stimuli (touch, pressure, etc.)
o Exteroceptors: sense external stimuli (vision, hearing, taste, smell, etc.)
o Interoceptors: sense stimuli from internal organs (nausea, pressure, etc.)
o Proprioceptors: sense position and movement of body parts (occur in muscles, etc.)
General senses: receptors in skin, muscles, viscera, etc. that detect stimuli such as pressure, pain, heat,
etc.
Special Senses: controlled by cranial nerves; include vision, hearing, equilibrium, taste and smell
General Senses
Nerve Endings:
Free nerve endings: found in dermis; detect temperatures (heat and cold)
Merkel discs: found in epidermis; detect light touch (textures, edges, shapes)
Hair receptors: found at hair follicle; respond to hair movement
Meissner corpuscles: found in dermal papillae of skin; detect light touch and texture
End bulbs: found in mucous membranes of lips and tongue; detect light touch
Pacinian corpuscles: found in dermis, bone, joints, some viscera; detect deep pressure
Bulbous corpuscles: found in dermis, joints, and subcutaneous tissue; detects heavy touch, pressure,
stretching of skin, and joint movements
Pain:
Fast (first) pain: sharp pain perceived at time of injury
Slow (second) pain: longer-lasting, dull pain
Visceral pain can result from stretch, ischemia, chemical irritants, etc.
Referred pain: visceral pain that is mistakenly perceived as coming from superficial parts of the body
(ex: heart attack cause pain in the left arm); caused by converging neural pathways in the CNS
Chemical Senses
Taste (gustation):
Lingual papillae: visible bumps on tongue (filiform, foliate, fungiform, vallate)
Taste sensations: salty, sweet, sour, bitter, umami; flavors are influenced by texture, smell,
temperature, appearance, etc.
Cranial nerves VII, IX, and X all play a role in taste sensory perception
Smell (olfaction):
Odorants in nasal cavity detect chemicals
Pathway: Olfactory bulbs Olfactory tracts Primary olfactory cortex
Hearing and Equillibrium:
Sound: any audible vibration of molecules
Pitch: sense of whether a sound is high or low based on frequencies
Loudness: perception of the amplitude of vibrations
Outer ear: funnel for vibrations (includes auricle, auditory canal, guard hairs, and cerumen)
Middle ear: found in tympanic cavity of temporal bone (includes ear drum, auditory tube, auditory
ossicles(malleus, incus, stapes))
Inner ear: made up of bony and membranous systems (includes vestibule, cochlea, scala vestibule,
scala tympani, round window, cochlear duct, spiral organ, and vestibular/basilar membranes)
The cochlear nerve and vestibular nerve form to make the vestibulocochlear nerve (cranial nerve VIII)
Equilibrium: coordination, balance, and orientation
Equilibrium receptors make up vestibular apparatus (semicircular ducts, saccule, utricle)
Static equilibrium: orientation of head when body is still
Dynamic equilibrium: perception of motion or acceleration
Semicircular ducts: detect rotational movements
Vision:
Human vision ranges from 400 to 700 nm (ultraviolet is 400 nm, infared is 700 nm)
Lacrimal apparatus: tear gland and ducts that drain tears
Extrinsic eye muscles:
o Superior, inferior, medial, and lateral rectus muscles move the eye up, down, medially, and
laterally
o Superior, inferior oblique muscles rotate and pull the eyes up or down at the same time
Tunica fibrosa (outer layer of eye): sclera (white of eye) and cornea, which lets light into the eye
Tunica vasculosa (middle layer): choroid, tissue behind retina; ciliary body, muscular ring around lens;
iris and pupil adjust to present light
Tunica interna (inner layer): retina and optic nerve
Blind spot: occurs because the optic disc has no receptor cells
Refraction: bending of light rays to create images
Photoreceptors: rods (process shades of gray), and cones (process colors in short-wavelengths,
medium-wavelengths, and long-wavelengths)
Pathway: Optic nerve optic chiasm optic tracts LGN of thalamus white matter