Transcript The Special Senses

The Special
Senses
CHAPTER 15
Unit Objectives

Classify Sense organs as special or general and explain
the basic differences between the two groups.
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Discuss how a stimulus is converted into a sensation.
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Discuss the general sense organs and their functions.
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List the major senses.
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Describe the structure of the eye and the functions of
its components.

Discuss the anatomy of the ear and its sensory function
in hearing and equilibrium.
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Discuss the chemical receptors and their functions.
Classification of Sense
Organs
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General Sense Organs:
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Exist as individual cells or receptor units
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Widely distributed throughout the body
Special Sense Organs
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Large & Complex
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Localized grouping of specialized
receptors
Presence or absence of covering
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Encapsulated
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Unencapsulated
General Sense Organs
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Free Nerve Endings
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Location: Skin, Epithelial & mucosa
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General Senses: Pain, crude touch, temperature,
itch, tickle
General Sense Organs
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Encapsulated Nerve Endings
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Meissner’s Corpuscles
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Location: Skin, fingertips & lips
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General Senses: Fine touch and low-frequency
vibration
Ruffini’s Corpuscles
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Location: Skin & subcutaneous tissue of fingers
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Touch & Pressure
Pacinian Corpuscles
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Around joints, in mammary glands & external
genitals of both sexes
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General Senses: pressure & high frequency
vibration
General Sense Organs
Encapsulated Nerve Endings
Cont
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Krause’s end-bulbs
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Location : Skin dermal; mucosa of lips, eyelids,
& external genitals
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General Sense: Touch & cold
Golgi Tendon Receptors
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Location: Near Junction of Tendons & Muscles
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General Sense: Muscle tension
(proprioception: individual perception)
Muscle spindles
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Skeletal muscles
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General Sense: Muscle length (proprioception)
Special Sense Organs
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Eye
 Specific Receptor: Rods & Cones
 Type of Receptor: Photoreceptor
 Sense:

Vision
Ear
 Specific Receptor: Organ of Corti &
Cristae ampullares
 Type
of Receptor: Mechanoreceptor
 Sense: Hearing & Balance
Special Sense Organs
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Nose
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Specific Receptor: Olfactory cells
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Type of Receptor: Chemoreceptor
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Sense: Smell
Taste Buds
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Specific Receptor: Gustatory cells
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Type of Receptor: Chemoreceptor
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Sense: Taste
Type of
Stimuli Defined
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Photoreceptors (light)
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Chemoreceptors (chemicals)
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Pain receptors (injury)
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Thermoreceptors (temperature change)
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Mechanoreceptors (movement or deforming of
capsule)
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Proprioceptors (position of body parts or changes
in muscle length or tension)
Converting Stimulus to
Sensation
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All sense organs have 3 common functional
characteristics:
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Can detect a particular stimulus
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Stimulus is converted into a nerve impulse
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Nerve impulses is perceived as a sensation
The Eye
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Layers of eyeball
Sclera: tough outer coat; white of eye;
cornea is the transparent part of sclera
over iris
 Choroid: pigmented vascular layer
prevents scattering of light; front part of
this layer is made of ciliary muscle & iris,
the colored part of the eye; the pupil is
the hole in the center of the iris;
contraction of iris muscle dilates or
constricts pupil
 Retina: inner most layer of the eye;
contains rods (receptors for night vision) &
cones (reception for day & color vision)
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The Eye
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Conjuctiva: mucous membrane covering the
front surface of the sclera and lining the eyelid
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Lens: transparent body behind the pupil; focuses
light rays on the retina
Suspensory
2
ligaments
1
9
3
10
4
8
humor
11
5
6
humor
7
Optic
12 Disk
Eye Fluids
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Aqueous humor: in the anterior chamber in front
of the lens
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Vitreous humor: in the posterior chamber behind
the lens
Visual pathway
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Innermost layer of retina contains rods
& cones
Impulse travels from the rods and
cones through the layers of the retina
Nerve impulse leaves the eye through
the optic nerve; the point of exit is free
of receptors and is therefore called a
blind spot
Visual interpretation occurs in the
visual cortex of the cerebrum
The Ear
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Functions in hearing, equilibrium, & balance
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Receptors for hearing & equilibrium:
mechanoreceptors
Divisions of Ear
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External
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Auricle (pinna)
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External auditory canal
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Curves approx. 2.5 cm in length
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Contains ceruminous glands (produce a waxy
substance)
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Ends at tympanic membrane
Divisions of Ear
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Middle Ear
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Ear ossicles: malleus, incus, & stapes
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Ends in the oval window
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Eustacian tube connects the middle ear to the
throat
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Inflammation called otitis media
Divisions of Ear
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Inner Ear
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Bony labyrinth filled with perilymph
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Subdivided into the vestibule, semicircular
canals, and cochlea
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Membranous labyrinth filled with endolymph
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Receptors for balance in the semi-circular
canals: cristae ampullairs
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Specialized hair cells on the organ of Corti
respond when bent by the movement of
surrounding endolymph set in motion by sound
waves
Semi-Circular Canals
Incus
Oval Window
Eustachian
Tube
Vestibulocochlear
nerve
Malleu
Vestibule TympanicsMembrane
Cochlea
Pinna
External Auditory Meatus
Stapes
Taste Receptors
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Chemoreceptors called taste buds
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Cranial nerves carry gustatory (respond to
chemicals dissolved in saliva) impulses
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4 primary taste sensations
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Sweet
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Sour
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Bitter
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Salty
Gustatory & Olfactory senses work together
Smell Receptors
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Receptors for fibers of olfactory/cranial nerve lie in
olfactory mucosa of nasal cavity
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Olfactory receptors are extremely sensitive but
easily fatigued
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Odor-causing chemicals initiate a nervous signal
that is interpreted as a specific odor by the brain