Transcript Chapter 12

Chapter 12
The Senses
Introduction
• General senses
• Receptors are widely distributed throughout the body
• Skin, various organs and joints
• Touch, pain, temperature, pressure, ect.
• Special senses
• Specialized receptors confined to structures in the head
• Vision, Taste, Smell, Hearing
2
Receptors, Sensation,
and Perception
• 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
3
Receptor Types
• Chemoreceptors
• Respond to changes in chemical concentrations
(smell, taste, pH)
• Pain receptors (nociceptors)
• Respond to tissue damage
• Thermoreceptors
• Respond to changes in temperature
• Mechanoreceptors
• Respond to mechanical forces
• Stretch receptors, proprioceptors, baroreceptors
• Photoreceptors
• Respond to light
5
Sensations and Perception
• Projection
• Process in which the brain projects the sensation back
to the apparent source
• It allows a person to pinpoint the region of
stimulation
Sensory Adaptation
• Ability to ignore unimportant stimuli
• Involves a decreased response to a particular stimulus
from the receptors (peripheral adaptation) 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
12.3: General Senses
• Senses associated with skin, muscles, joints and viscera
• Three (3) groups:
• Exteroceptive senses (exteroceptors)
• Senses associated with body surface such as touch, pressure,
temperature, and pain
• Visceroceptive senses (interoceptors)
• Senses associated with changes in the viscera such as blood
pressure stretching blood vessels and ingestion of a meal
• Proprioceptive senses
• Senses associated with changes in muscles and tendons such
as at joints
8
Touch and Pressure Senses
Free nerve endings
• Common in epithelial
tissues
• Simplest receptors
• Sense itching
Tactile (Meissner’s) corpuscles
• Abundant in hairless portions of
skin and lips
• Detect fine touch; distinguish
between two points on the skin
Lamellated (Pacinian) corpuscles
• Common in deeper subcutaneous
tissues, tendons and ligaments
• Detect heavy pressure and vibrations
9
Touch and Pressure
Receptors
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Free nerve
endings
Section of
skin
Epithelial
cells
Epidermis
(a)
Sensory
nerve fiber
Epithelial
cells
Dermis
Tactile (Meissner’s)
corpuscle
(touch receptor)
(b)
Sensory nerve
fiber
Lamellated
(Pacinian) corpuscle
(pressure receptor)
Connective tissue
cells
Sensory nerve
fiber
(c)
b, c: © Ed Reschke
10
Temperature Senses
• Warm receptors
• Sensitive to temperatures above 25oC (77o F)
• Unresponsive to temperature above 45oC (113oF)
• Cold receptors
• Sensitive to temperatures between 10oC (50oF) and 20oC
(68oF)
• Pain receptors
• Respond to temperatures below 10oC
• Respond to temperatures above 45oC
11
Sense of Pain
• Free nerve endings
• Widely distributed
• Nervous tissue of brain lacks pain receptors
• Stimulated by tissue damage, chemical, mechanical forces, or
extremes in temperature
• Adapt very little, if at all
12
Visceral Pain
• Pain receptors are the only receptors in viscera whose
stimulation produces sensations
• Pain receptors respond differently to stimulation
• Pain receptors are not well localized
• Pain receptors may feel as if coming from some other part of
the body
• Known as referred pain…
13
Referred Pain
• May occur due to sensory impulses from two regions
following a common nerve pathway to brain
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Liver and
gallbladder
Lung and diaphragm
Liver and
gallbladder
Heart
Stomach
Pancreas
Small
intestine
Appendix
Ovary
(female)
Colon
Kidney
Ureter
Urinary bladder
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Pain Nerve Pathways
• Acute pain fibers
• Chronic pain fibers
• A-delta fibers
• C fibers
• Thin, myelinated
• Thin, unmyelinated
• Conduct impulses rapidly
• Conduct impulses more
• Associated with sharp pain
slowly
• Well localized
• Associated with dull,
aching pain
• Difficult to pinpoint
15
Regulation of Pain Impulses
• Thalamus
• Allows person to be aware of pain
• Cerebral cortex
• Judges intensity of pain
• Locates source of pain
• Produces emotional and motor responses to pain
• Pain inhibiting substances:
• Enkephalins
• Serotonin
• Endorphins
16
Proprioception
• Mechanoreceptors
• Send information to spinal cord and CNS about body
position and length, and tension of muscles
• Main kinds of proprioceptors:
• Pacinian corpuscles – in joints
• Muscle spindles – in skeletal muscles*
• Golgi tendon organs – in tendons*
*considered to be stretch receptors
17
Stretch Receptors
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Sensory
nerve fiber
Sensory
nerve endings
Golgi tendon organ
Sensory
nerve fiber
Tendon
Intrafusal
fiber
Skeletal muscle
fiber
Muscle spindle
Skeletal muscle fiber
Connective
tissue sheath
(a)
(b)
1818
Visceral Senses
• Receptors in internal organs
• Convey information that includes the sense of fullness
after eating a meal as well as the discomfort of intestinal
gas and the pain that signals a heart attack
19
Summary of Receptors of the
General Senses
End of Section 1, chapter 12
section 2, chapter 12
Smell, Taste, and Hearing
• 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
21
Sense of Smell
• Olfactory receptors
• Bipolar Chemoreceptors
• Respond to chemicals (called odorants) dissolved in liquids
• Olfactory organs
• Olfactory epithelium - contain olfactory receptors and
supporting epithelial cells
• Cover parts of nasal cavity, superior nasal conchae, and a
portion of the nasal septum
22
Olfactory Receptors
Figure 12.5 Olfactory receptors. (a) columnar epithelial cells support olfactory
receptor cells, which have cilia at their distal ends. The olfactory receptors pass
through olfactory foramina in the cribriform plate and synapse with the olfactory
bulb in the brain.
(b) Olfactory epithelium cover the upper nasal cavity and superior nasal conchae.
Olfactory Nerve Pathways
• Once olfactory receptors are stimulated, nerve impulses travel through
•
•Olfactory nerves
olfactory bulbs
olfactory tracts
limbic system (for emotions) & olfactory cortex (for interpretation)
The limbic system, which is involved with emotions and
memory is strongly effected by smell.
24
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
25
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
26
Taste Receptors
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Papillae
Taste buds
Epithelium
of tongue
Taste cell
(a)
Taste hair
Supporting
cell
Taste
pore
Connective
tissue
Sensory
nerve fibers
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(b)
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
28
Taste Nerve Pathways
• Sensory impulses from taste receptors travel along:
• Cranial nerves to…
• Medulla oblongata to…
• Thalamus to…
• Gustatory cortex (for interpretation)
29
Sense of Hearing
• Ear
• Organ of hearing
• Three (3) sections:
• External ear
• Middle ear
• Inner ear
30
External Ear
• Auricle
• Collects sounds waves
• External auditory meatus
• Lined with ceruminous
glands
• Carries sound to
tympanic membrane
• Terminates with
tympanic membrane
• Tympanic membrane
• Vibrates in response to
sound waves
Auricle
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Semicircular
canals
Incus
Stapes
Malleus
Cochlea
Vestibulocochlear
nerve
Oval window (under stapes)
Round window
Tympanic cavity
Tympanic
membrane
External acoustic
meatus
Auditory tube
Pharynx
31
Middle Ear
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• Tympanic cavity
• Air-filled space in
temporal bone
• Auditory ossicles
• Vibrate in response to
tympanic membrane
• Malleus, incus and stapes
• Hammer, anvil and stirrup
• Oval window
• Opening in wall of
tympanic cavity
• Stapes vibrates against it to
move fluids in inner ear
Auricle
Semicircular
canals
Incus
Stapes
Malleus
Cochlea
Vestibulocochlear
nerve
Oval window (under stapes)
Round window
Tympanic cavity
Tympanic
membrane
External acoustic
meatus
Auditory tube
Pharynx
32
Auditory Tube
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• Also known as the
Eustachian tube
• Connects middle ear to
throat
• Helps maintain equal
pressure on both sides of
tympanic membrane
• Usually closed by valvelike flaps in throat
Auricle
Semicircular
canals
Incus
Stapes
Malleus
Cochlea
Vestibulocochlear
nerve
Oval window (under stapes)
Round window
Tympanic cavity
Tympanic
membrane
External acoustic
meatus
Auditory tube
Pharynx
33
Inner Ear
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• Complex system of labyrinths
• Osseous labyrinth
• Bony canal in temporal
bone
• Filled with perilymph
• Membranous labyrinth
• Tube within osseous
labyrinth
• Filled with endolymph
Bony labyrinth
Perilymph
Membranous
labyrinth
Endolymph
Bony labyrinth
(contains perilymph)
Membranous labyrinth
(contains endolymph)
Semicircular
canals
Utricle
Saccule
Vestibular nerve
Cochlear nerve
Scala
vestibuli (cut)
Scala
tympani (cut)
Cochlear
duct (cut)
containing
endolymph
Ampullae Oval Vestibule Round Maculae
window
window
Cochlea
(a)
34
Inner Ear
• Three (3) parts of labyrinths:
• Cochlea
• Functions in hearing
• Semicircular canals
• Functions in
equilibrium
• Vestibule
• Functions in
equilibrium
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Bony labyrinth
Perilymph
Membranous
labyrinth
Endolymph
Bony labyrinth
(contains perilymph)
Membranous labyrinth
(contains endolymph)
Semicircular
canals
Utricle
Saccule
Vestibular nerve
Cochlear nerve
Scala
vestibuli (cut)
Scala
tympani (cut)
Cochlear
duct (cut)
containing
endolymph
Ampullae Oval Vestibule Round Maculae
window
window
Cochlea
(a)
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Cochlea
• Scala vestibuli
• Upper compartment
• Leads from oval
window to apex of
spiral
• Part of bony labyrinth
• Scala tympani
• Lower compartment
• Extends from apex of
the cochlea to round
window
• Part of bony labyrinth
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Stapes vibrating in
oval window
Helicotrema
Scala vestibuli
filled with perilymph
Vestibular
membrane
Basilar
membrane
Scala tympani
filled with
perilymph
Round window
Membranous
labyrinth
Cochlear duct
filled with endolymph
36
Cochlea
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• Cochlear duct
• Portion of
membranous labyrinth
in cochlea
• Vestibular membrane
• Separates cochlear
duct from scala
vestibuli
• Basilar membrane
• Separates cochlear
duct from scala
tympani
Scala vestibuli
(contains perilymph)
Vestibular membrane
Branch of
cochlear
nerve
Cochlear duct
(contains endolymph)
Spiral organ (organ of Corti)
Basilar membrane
Scala tympani
(contains perilymph)
(a)
37
Organ of Corti
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• 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
Scala vestibuli
(contains perilymph)
Vestibular membrane
Cochlear duct
(contains endolymph)
Spiral organ (organ of Corti)
Branch of
cochlear
nerve
Basilar membrane
Scala tympani
(contains perilymph)
(a)
Tectorial
membrane
Hair cells
(b)
Branch of
cochlear nerve
Nerve
fibers
Supporting
cells
Basilar
membrane
38
Organ of Corti
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Cochlear duct
Tectorial membrane
Scala tympani
Hair cells
Basilar
membrane
(a)
(b)
a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited
39
Auditory Nerve Pathways
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Auditory cortex
(temporal lobe)
Thalamus
Medial geniculate
body of thalamus
Midbrain
Pons
Cochlear
nuclei
Superior
olivary
nucleus
Medulla
oblongata
Vestibulocochlear
nerve
40
Summary of the Generation of
Sensory Impulses from the Ear
41
Sense of Equilibrium
• Static equilibrium
• Vestibule
• Senses position of
head when body is not
moving
• Dynamic Equilibrium
• Semicircular canals
• Senses rotation and
movement of head and
body
42
Vestibule
• Utricle
• Communicates with
saccule and membranous
portion of semicircular
canals
• Saccule
• Communicates with
cochlear duct
• Macula
• Hair cells of utricle and
saccule
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Ampullae of
semicircular
canals
Vestibulocochlear
nerve
Cochlea
Utricle
Cochlear
duct
Maculae Saccule Vestibule
43
Macula
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• Responds to changes
in head position
• Bending of hairs
results in generation of
nerve impulse
Hairs of
hair cells bend
Gelatinous
material sags
Otoliths
Macula
of utricle
Hair cells
Sensory nerve fiber
Gravitational
force
Supporting cells
(a) Head upright
(b) Head bent forward
44
Semicircular Canals
• Three (3) canals at right angles
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• Ampulla
• Swelling of membranous
Vestibulocochlear
labyrinth that communicates
nerve
Ampullae of
Cochlea
semicircular
Utricle
with the vestibule
canals
Cochlear
duct
• Crista ampullaris
• Sensory organ of ampulla
• Hair cells and supporting cells
• Rapid turns of head or body
stimulate hair cells
Maculae Saccule Vestibule
45
Crista Ampullaris
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Endolymph
Semicircular canal
Cupula
Crista
ampullaris
(a) Head in still position
Ampulla
Crista ampullaris
Hairs
Hair cell
Supporting cells
Sensory nerve fibers
(b) Head rotating
(c)
End of section 2, chapter 12
46
ivyanatomy.com
section 3, chapter 12
vision
Sense of Sight
• Visual accessory organs
• Eyelids
• Lacrimal apparatus
• Extrinsic eye muscles
48
Eyelid
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• Palpebra
• Composed of four (4) layers:
• Skin
• Muscle
• Connective tissue
• Conjunctiva
• Orbicularis oculi – closes eyelid
• Levator palpebrae superioris –
opens eyelid
• Tarsal glands – secrete oil onto
eyelashes
• Conjunctiva – mucous
membrane; lines eyelid and covers
portion of eyeball
Tendon of levator
palpebrae superioris
Superior
rectus
Orbicularis
oculi
Eyelid
Tarsal glands
Eyelash
Cornea
Conjunctiva
Inferior
rectus
49
Lacrimal Apparatus
• Lacrimal gland
• Lateral to eye
• Secretes tears
Lacrimal gland
• Canaliculi
• Collect tears
Superior and
inferior canaliculi
• Lacrimal sac
Lacrimal sac
• Collects from
canaliculi
Nasolacrimal
• Nasolacrimal duct
duct
• Collects from lacrimal
sac
• Empties tears into nasal
cavity
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50
Extrinsic Eye Muscles
• Superior rectus
• Rotates eye up and
medially
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Medial Superior
rectus rectus
Superior
oblique
• Inferior rectus
• Rotates eye down
and medially
• Medial rectus
• Rotates eye
medially
Lateral
rectus
(cut)
Inferior rectus
Inferior oblique
51
Extrinsic Eye Muscles
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• Lateral rectus
• Rotates eye
laterally
Medial Superior
rectus rectus
Superior
oblique
• Superior oblique
• Rotates eye down
and laterally
• Inferior oblique
• Rotates eye up and
laterally
Lateral
rectus
(cut)
Inferior rectus
Inferior oblique
52
Structure of the Eye
The eye has three distinct layers “tunics”
1. Fibrous tunic
2. Vascular tunic
3. Nervous tunic
Outer Tunic
• Cornea
• Anterior 1/6th of eye
• “window of the eye”
• Transparent
• Light transmission
• Sclera
• Posterior portion
• Opaque
• Protection
Middle Tunic
• Choroid coat
• Provides blood supply
• Pigments absorb extra light
• Iris “rainbow”
• Anterior portion
• Pigmented
• Controls light intensity
• Ciliary body
• Anterior portion
• Pigmented
• Suspensory ligaments
holds lens
• Ciliary muscles moves
lens for focusing
Anterior Portion of Eye
• Filled with aqueous humor
Lens
• The lens is an elastic, biconvex, and transparent structure largely
composed of epithelial cells, called lens fibers.
•The lens lies behind the iris and is held in place by
suspensory ligaments of ciliary body
Accommodation
• Changing of lens shape to view objects
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Ciliary muscle
fibers contracted
Suspensory
ligaments relaxed
Lens thick
(a)
Ciliary muscle
fibers relaxed
Suspensory
ligaments taut
Lens thin
58
(b)
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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Cornea
Aqueous humor
Anterior
chamber
Iris
Scleral venous sinus
(canal of Schlemm)
Lens
Sclera
Ciliary process
Ciliary
body
Ciliary muscles
Vitreous humor
Posterior
chamber
59
Ciliary Body
• Forms internal ring around the front
of the eye
• Ciliary processes – radiating folds
• Ciliary muscles – contract and relax to
move lens
Figure 12.28 Lens and ciliary
body viewed from behind.
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
Inner Tunic
• Retina
• Contains visual receptors
• Continuous with optic nerve
• Fovea centralis – center of macula lutea; produces sharpest vision
•Macula lutea – yellowish spot in retina
• Optic disc – blind spot; contains no visual receptors
• Vitreous humor – thick gel that holds retina flat against choroid coat
Posterior Cavity
• Contains vitreous humor – thick gel that holds retina flat
against choroid coat
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Lateral rectus
Retina
Ciliary body
Suspensory
ligaments
Choroid coat
Sclera
Vitreous humor
Iris
Lens
Fovea centralis
Pupil
Cornea
Aqueous
humor
Anterior
cavity
Anterior
chamber
Posterior
chamber
Optic nerve
Optic disc
Posterior cavity
Medial rectus
63
Layers of the Eye
64
Light Refraction
• Refraction
• Bending of light
• Occurs when light waves pass at an oblique angle into
mediums of different densities
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Perpendicular line
Air
Light wave
Glass
Refracted
light wave
65
Types of Lenses
• Convex lenses cause
light waves to converge
• Concave lenses cause
light waves to diverge
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Light
wave
Air
Convex
surface
Concave
surface
Glass
Converging
light waves
(a)
Diverging
light waves
(b)
66
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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Light waves
Image
Retina
Object
Cornea
67
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
Figure 12. Notice that
photoreceptors (rods and cones) are
the posterior most cells in this circuit.
Light waves stimulate the
photoreceptors, which send impulses
forward to horizontal cells and
ganglion cells before leaving the eye
through the optic disc.
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 outlines of objects
• Cones
• Short, blunt projections
• Provide vision in bright light
• Produce sharp images
• Produce color vision
• Pigments include:
• Erythrolabe – responds to red
• Chlorolabe – responds to green
• Cyanolabe – responds to blue
Color perceived depends on
which sets of cones are
stimulated
Figure 12.38 Rods and cones. (a) Several
rods converge onto a single sensory nerve
fiber to the brain (b) separate sensory nerve
fibers transmits impulses from the cones to
the brain. (c) Scanning electron micrograph of
rods and cones.
12.6 Clinical Application
Refraction Disorders
• Concave lens corrects
nearsightedness
• Convex lens corrects
farsightedness
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Lens
Point
of focus
Uncorrected
point of focus
Cornea
Light waves
Light waves
(a) Eye too long (myopia)
Point
of focus
Concave lens
(a)
Corrected
point of focus
Light waves
Retina
Uncorrected
point of focus
(b) Normal eye
Point
of focus
Light waves
Convex lens
(c) Eye too short (hyperopia)
(b)
Corrected
point of focus
71
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
72
Stereoscopic Vision
• Provides perception of distance and depth
• Results from formation of two slightly different retinal images
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Light
waves
Left eye
Right eye
73
Visual Nerve Pathways
Axons from ganglion cells in retina leave the eyes to form the optic nerves.
Some of the fibers decussate at the optic chiasm.
• Fibers from the nasal (medial) half of retina cross over
• Fibers from temporal half (lateral) of retina do not cross over
Most fibers of the optic tract continue to the lateral
geniculate nucleus of the thalamus, which relays
impulses towards the visual cortex.
Figure 12.41 The visual pathway
includes the optic nerve, optic
chiasma, optic tract, and optic
radiations.
End of Chapter 12