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Sensory Physiology
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Nervous System - Senses
General Senses
• receptors that are widely distributed throughout the
body
• skin, various organs and joints
Special Senses
• specialized receptors confied to structures in the
head
• eyes and ears
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Senses
Sensory Receptors
• specialized cells or multicellular structures that collect
information from the environment
• stimulate neurons to send impulses along sensory fibers to
the brain
Sensation
• a feeling that occurs when brain becomes aware of sensory
impulse
Perception
• a person’s view of the stimulus; the way the brain
interprets the information
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Sensory Receptor Types
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Figure 10-1: Sensory receptors
Pathways From Sensation to Perception
(Example of an Apple)
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Receptor Types
Chemoreceptors
• respond to changes in chemical concentrations
Pain receptors (Nociceptors)
• respond to tissue damage
Thermoreceptors
• respond to changes in temperature
Mechanoreceptors
• respond to mechanical forces
Photoreceptors
• respond to light
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Sensory Adaptation
• ability to ignore unimportant stimuli
• involves a decreased response to a particular stimulus
from the receptors (peripheral adaptations) or along
the CNS pathways leading to the cerebral cortex
(central adaptation)
• sensory impulses become less frequent and may cease
• stronger stimulus is required to trigger impulses
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General Senses
• senses associated with skin, muscles, joints, and viscera
• three groups
• exteroceptive senses – senses associated with body surface;
touch, pressure, temperature, pain
• visceroceptive senses – senses associated with changes in
viscera; blood pressure stretching blood vessels, ingesting a
meal
• proprioceptive senses – senses associated with changes in
muscles and tendons
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Touch and Pressure Senses
Free nerve endings
• common in epithelial
tissues
• simplest receptors
• sense itching
•Ex ( nociciptor)
Meissner’s corpuscles
• abundant in hairless portions
of skin; lips
• detect fine touch; distinguish
between two points on the skin
Pacinian corpuscles
• common in deeper subcutaneous
tissues, tendons, and ligaments
• detect heavy pressure and
vibrations
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Touch and Pressure Receptors
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Touch (pressure)
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Figure 10-11: Touch-pressure receptors
Temperature Senses
Warm receptors
• sensitive to temperatures above 25oC (77o F)
• unresponsive to temperature above 45oC (113oF)
Cold receptors
• sensitive to temperature between 10oC (50oF) and 20oC
(68oF)
Pain receptors (nociceptor)
• respond to temperatures below 10oC
• respond to temperatures above 45oC
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Summary of Receptors of the
General Senses
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Special Senses
• sensory receptors are within large, complex sensory
organs in the head
• smell in olfactory organs
• taste in taste buds
• hearing and equilibrium in ears
• sight in eyes
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Sense of Smell
Olfactory Receptors
• chemoreceptors
• respond to chemicals dissolved in liquids
Olfactory Organs
• contain olfactory receptors and supporting epithelial
cells
• cover parts of nasal cavity, superior nasal conchae,
and a portion of the nasal septum
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Olfactor: Sense of Smell
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Figure 10-14a, b: ANATOMY SUMMARY: Olfaction
Olfactory Receptors
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Olfactor: Sense of Smell
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Figure 10-14c: ANATOMY SUMMARY: Olfaction
Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses
travel through
• olfactory nerves
olfactory bulbs
olfactory
tracts
limbic system (for emotions) and
olfactory cortex (for interpretation)
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Figure 10-4: Sensory pathways
Olfactory Stimulation
• olfactory organs located high in the nasal cavity
above the usual pathway of inhaled air
• olfactory receptors undergo sensory adaptation
rapidly
• sense of smell drops by 50% within a second after
stimulation
Olfactory Code
• hypothesis
• odor that is stimulated by a distinct set of receptor cells
and its associated receptor proteins
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Sense of Taste
Taste Buds
• organs of taste
• located on papillae of tongue, roof of mouth, linings of
cheeks and walls of pharynx
Taste Receptors
• chemoreceptors
• taste cells – modified epithelial cells that function
as receptors
• taste hairs –microvilli that protrude from taste
cells; sensitive parts of taste cells
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Taste Receptors
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Taste Sensations
Four Primary Taste Sensations
• sweet – stimulated by carbohydrates
• sour – stimulated by acids
• salty – stimulated by salts
• bitter – stimulated by many organic compounds
Spicy foods activate pain receptors
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Taste Nerve Pathways
Sensory impulses from taste receptors travel along
• cranial nerves to
• medulla oblongata to
• thalamus to
• gustatory cortex (for interpretation)
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Figure 10-4: Sensory pathways
Taste: Chemoreceptors
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Taste: Chemoreceptors
• Salt --- Na passive
• Acids– H block k channels
• Sweet – Gs anhydrate cyclase – protein kinase(A) –
Phosphorylation of k channels so it will close
• Bitter – Gb – phospholipasec – release of ca from ER
• Depolarization –activate neurotransmitter vesicle to
diffues to membrane and release neurotransmitter
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The Ear: Hearing and
Equilibrium
• The ear – receptor organ for hearing and
equilibrium
• Composed of three main regions
– Outer ear – functions in hearing
– Middle ear – functions in hearing
– Inner ear – functions in both hearing and
equilibrium
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The Outer (External) Ear
• Composed of:
– The auricle (pinna)
• Helps direct sounds
– External acoustic meatus
• Lined with skin
– Contains hairs, sebaceous glands, and
ceruminous glands
– Tympanic membrane
• Forms the boundary between the external and
middle ear
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The Outer (External) Ear
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Figure 16.17a
The Middle Ear
• The tympanic cavity
– A small, air-filled space
– Located within the petrous portion of the temporal bone
• Medial wall is penetrated by:
– Oval window
– Round window
• Pharyngotympanic tube (auditory or eustachian
tube)
– Links the middle ear and pharynx
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Structures of the Middle Ear
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Figure 16.17b
The Middle Ear
• Ear ossicles –
smallest bones in
the body
– Malleus – attaches
to the eardrum
– Incus – between the
malleus and stapes
– Stapes – vibrates
against the oval
window
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Figure 16.19
The Inner (Internal) Ear
• Inner ear – also called the labyrinth
• Lies within the petrous portion of the
temporal bone
• Bony labyrinth – a cavity consisting of three
parts
– Semicircular canals
– Vestibule
– Cochlea
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The Inner (Internal) Ear
• Membranous labyrinth
– Series of membrane-walled sacs and ducts
– Fit within the bony labyrinth
– Consists of three main parts
• Semicircular ducts
• Utricle and saccule
• Cochlear duct
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The Inner (Internal) Ear
• Membranous labyrinth (continued)
– Filled with a clear fluid – endolymph
• Confined to the membranous labyrinth
– Bony labyrinth is filled with perilymph
• Continuous with cerebrospinal fluid
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The Membranous Labyrinth
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Figure 16.20
The Inner (Internal) Ear
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Figure 16.17b
Cochlea
Cochlear duct
• portion of membranous
labyrinth in cochlea
Vestibular membrane
• separates cochlear duct
from scala vestibuli
Basilar membrane
• separates cochlear duct
from scala tympani
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The Cochlea
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Figure 16.23a–c
Organ of Corti
• group of hearing receptor cells
(hair cells)
• on upper surface of basilar
membrane
• different frequencies of vibration
move different parts of basilar
membrane
• particular sound frequencies cause
hairs of receptor cells to bend
• nerve impulse generated
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Hearing: Mechanoreceptors
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Figure 10-19: Sound transmission through the ear
Hearing: Hair Cell Transduction
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Figure 10-20: The cochlea
Hearing: Hair Cell Transduction
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Figure 10-21: Signal transduction in hair cells
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Summary of the Generation of
Sensory Impulses from the Ear
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Equilibrium
Static Equilibrium
• vestibule
• sense position of
head when body is
not moving
Dynamic Equilibrium
• semicircular canals
• sense rotation and
movement of head and
body
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Vestibule
• Utricle
• communicates with
saccule and
membranous portion of
semicircular canals
• Saccule
• communicates with
cochlear duct
• Mucula
• hair cells of utricle and
saccule
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Macula
• responds to
changes in head
position
• bending of hairs
results in generation
of nerve impulse
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Anatomy and Function of the Maculae
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Figure 16.21a
Semicircular Canals
• three canals at right angles
• ampulla
• swelling of membranous
labyrinth that communicates
with the vestibule
• crista ampullaris
• sensory organ of ampulla
• hair cells and supporting
cells
• rapid turns of head or body
stimulate hair cells
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Crista Ampullaris
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Vestibular System & Balance
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Rotation & Gravity
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Auditory Pathway from the
Organ of Corti
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Figure 16.25
Sight
Visual Accessory Organs
• eyelids
• lacrimal apparatus
• extrinsic eye muscles
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Lacrimal Apparatus
• lacrimal gland
• lateral to eye
• secretes tears
• canaliculi
• collect tears
• lacrimal sac
• collects from canaliculi
• nasolacrimal duct
• collects from lacrimal
sac
• empties tears into nasal
cavity
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Extrinsic Eye Muscles
Superior rectus
• rotates eye up and
medially
Inferior rectus
• rotates eye down
and medially
Medial rectus
• rotates eye
medially
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Extrinsic Eye Muscles
Lateral rectus
• rotates eye
laterally
Superior oblique
• rotates eye down and
laterally
Inferior oblique
• rotates eye up and
laterally
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Structure of the Eye
• hollow
• spherical
• wall has 3 layers
• outer fibrous tunic
• middle vascular tunic
• inner nervous tunic
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Outer Tunic
Cornea
• anterior portion
• transparent
• light transmission
• light refraction
Sclera
• posterior portion
• opaque
• protection
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Middle Tunic
Iris
• anterior portion
• pigmented
• controls light intensity
Ciliary body
• anterior portion
• pigmented
• holds lens
• moves lens for focusing
Choroid coat
• provides blood supply
• pigments absorb extra light
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Anterior Portion of Eye
• filled with aqueous humor
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Lens
• transparent
• biconvex
• lies behind iris
• largely composed of
lens fibers
• elastic
• held in place by
suspensory ligaments
of ciliary body
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Ciliary Body
• forms internal ring around front of eye
• ciliary processes – radiating folds
• ciliary muscles – contract and relax to move lens
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Accommodation
• changing of lens shape to view objects
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Iris
• composed of connective
tissue and smooth muscle
• pupil is hole in iris
• dim light stimulates
radial muscles and pupil
dilates
• bright light stimulates
circular muscles and
pupil constricts
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Aqueous Humor
• fluid in anterior cavity of eye
• secreted by epithelium on inner surface of the ciliary body
• provides nutrients
• maintains shape of anterior portion of eye
• leaves cavity through canal of Schlemm
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Inner Tunic
• retina
• contains visual receptors
• continuous with optic nerve
• ends just behind margin of the ciliary body
• composed of several layers
• macula lutea – yellowish spot in retina
• fovea centralis – center of macula lutea; produces
sharpest vision
• optic disc – blind spot; contains no visual receptors
• vitreous humor – thick gel that holds retina flat against
choroid coat
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Posterior Cavity
• contains vitreous humor – thick gel that holds retina
flat against choroid coat
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Major Groups of Retinal Neurons
• receptor cells, bipolar cells, and ganglion cells - provide
pathway for impulses triggered by photoreceptors to reach the
optic nerve
• horizontal cells and amacrine cells – modify impulses
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Layers of the Eye
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Light Refraction
Refraction
• bending of light
• occurs when light waves pass at an oblique angle into
mediums of different densities
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Types of Lenses
Convex lenses cause
light waves to converge
Concave lenses cause
light waves to diverge
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Focusing On Retina
• as light enters eye, it is refracted by
• convex surface of cornea
• convex surface of lens
• image focused on retina is upside down and reversed from
left to right
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Visual Receptors
Rods
• long, thin projections
• contain light sensitive
pigment called rhodopsin
• hundred times more
sensitive to light than cones
• provide vision in dim light
• produce colorless vision
• produce outlines of objects
Cones
• short, blunt projections
• contain light sensitive
pigments called
erythrolabe, chlorolabe,
and cyanolabe
• provide vision in bright
light
• produce sharp images
• produce color vision
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Rods and Cones
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Visual Pigments
Rhodopsin
• light-sensitive pigment in rods
• decomposes in presence of
light
• triggers a complex series of
reactions that initiate nerve
impulses
• impulses travel along optic
nerve
Pigments on Cones
• each set contains different lightsensitive pigment
• each set is sensitive to different
wavelengths
• color perceived depends on
which sets of cones are stimulated
• erythrolabe – responds to red
• chlorolabe – responds to green
• cyanolabe – responds to blue
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Rod Cells
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Visual Nerve Pathway
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