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