Transcript Olfactory Receptors

PowerPoint Lecture Outlines
to accompany
Hole’s Human
Anatomy and Physiology
Eleventh Edition
Shier w Butler w Lewis
Chapter
12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
Chapter 12
Nervous System III - 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
2
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
3
SENSORY RECEPTION
• Sensory receptors convert stimulus energy to
action potentials
– Sensory receptors
•
Are specialized cells or neurons that detect
stimuli
4
– Sensory transduction converts stimulus energy
into receptor potentials
•
Which trigger action potentials that are
transmitted to the brain
Sugar
molecule
Taste
pore
Tongue
Taste
bud
1
Sugar
molecule
(stimulus)
Membrane
of sensory
receptor cell
2
Sensory
receptor
cells
Signal
transduction
pathway
Ion
channels
Sensory
receptor
cell
3


Ion
Sensory neuron
Receptor
potential
4
Neurotransmitter
Sensory neuron
mV
Action potential
No sugar
Figure 29.2A
5 Action potentials
Sugar present
5
– Action potential frequency
•
Reflects stimulus strength
Sugar
receptor
“Sugar” interneuron
“Salt” interneuron
Salt
receptor
Brain
Sensory
neurons
Taste
bud
No sugar
Figure 29.2B
Taste
bud
No salt
Increasing sweetness
Increasing saltiness
6
• Mechanoreceptors
– Mechanoreceptors
•
Respond to mechanical energy such as touch,
pressure, and sound
“Hairs” of
receptor cell
Neurotransmitter
at synapse
More
neurotransmitter
Less
neurotransmitter
Sensory
neuron
Action
potentials
Action
potentials
1 Receptor cell at rest
Figure 29.3B
2 Fluid moving in one direction
3 Fluid moving in other direction
7
– Repeated stimulus
•
May lead to adaptation, a decrease in
sensitivity
8
• Specialized sensory receptors detect five
categories of stimuli
– A section of human skin
•
Reveals many types of sensory receptors
Light
Heat touch
Pain
Cold Hair
Light
touch
Epidermis
Dermis
Figure 29.3A
Hair
Nerve Connective
movement
tissue
Strong
pressure
9
Pathways From Sensation to Perception
(Example of an Apple)
10
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
11
Sensory Impulses
• stimulation of receptor causes local change in its receptor potential
• a graded electrical current is generated that reflects intensity of stimulation
• if receptor is part of a neuron, the membrane potential may generate an
action potential
• if receptor is not part of a neuron, the receptor potential must be
transferred to a neuron to trigger an action potential
• peripheral nerves transmit impulses to CNS where they are analyzed and
interpreted in the brain
12
Sensations
Projection
process in which the brain projects the sensation
back to the apparent source
it allows a person to pinpoint the region of
stimulation
13
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
14
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
15
Touch and Pressure Senses
Free nerve endings
• common in epithelial
tissues
• simplest receptors
• sense itching
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
16
Touch and Pressure Receptors
17
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
• respond to temperatures below 10oC
• respond to temperatures above 45oC
18
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
19
Visceral Pain
• pain receptors are the only receptors in viscera whose
stimulation produces sensations
• pain receptors respond differently to stimulation
• not well localized
• may feel as if coming from some other part of the body
• known as referred pain
20
Referred Pain
• may occur due to sensory impulses from two regions
following a common nerve pathway to brain
21
Pain Nerve Pathways
Acute pain fibers
• A-delta fibers
•thin, myelinated
• conduct impulses
rapidly
• associated with
sharp pain
• well localized
Chronic pain fibers
• C fibers
•thin, unmyelinated
• conduct impulses more
slowly
• associated with dull,
aching pain
• difficult to pinpoint
22
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
23
Proprioceptors
• mechanoreceptors
• send information to spinal cord and CNS about body
position and length and tension of muscles
• Main kinds of proprioreceptors
• Pacinian corpuscles – in joints
• muscle spindles – in skeletal muscles*
• Golgi tendon organs – in tendons*
*stretch receptors
24
Stretch Receptors
25
Summary of Receptors of the
General Senses
26
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
27
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
28
Olfactory Receptors
29
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)
30
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
31
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
32
Taste Receptors
33
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
34
Taste Nerve Pathways
Sensory impulses from taste receptors travel along
• cranial nerves to
• medulla oblongata to
• thalamus to
• gustatory cortex (for interpretation)
35
Hearing
Ear – organ of hearing
Three Sections
• External
• Middle
• Inner
36
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
37
Middle Ear
• tympanic cavity
• air-filled space in temporal
bone
• auditory ossicles
• vibrate in response to tympanic
membrane
• malleus, incus, and stapes
• oval window
• opening in wall of tympanic
cavity
• stapes vibrates against it to
move fluids in inner ear
38
Auditory Tube
• eustachian tube
• connects middle ear to
throat
• helps maintain equal
pressure on both sides
of tympanic membrane
• usually closed by
valve-like flaps in throat
39
Inner Ear
• complex system of labyrinths
• osseous labyrinth
• bony canal in temporal
bone
• filled with perilymph
• membranous labyrinth
• tube within osseous
labyrinth
• filled with endolymph
40
Inner Ear
Three Parts of Labyrinths
• cochlea
• functions in hearing
• semicircular canals
• functions in
equilibrium
• vestibule
• functions in
equilibrium
41
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
42
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
43
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
44
Organ of Corti
45
Auditory Nerve Pathways
46
Summary of the Generation of
Sensory Impulses from the Ear
47
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
48
Vestibule
• Utricle
• communicates with
saccule and
membranous portion of
semicircular canals
• Saccule
• communicates with
cochlear duct
• Mucula
• hair cells of utricle and
saccule
49
Macula
• responds to
changes in head
position
• bending of hairs
results in generation
of nerve impulse
50
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
51
Crista Ampullaris
52
Sight
Visual Accessory Organs
• eyelids
• lacrimal apparatus
• extrinsic eye muscles
53
Eyelid
• palpebra
• composed of four layers
• skin
• muscle
• connective tissue
• conjunctiva
• orbicularis oculi - closes
• levator palperbrae superioris –
opens
• tarsal glands – secrete oil onto
eyelashes
• conjunctiva – mucous
membrane; lines eyelid and
covers portion of eyeball
54
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
55
Extrinsic Eye Muscles
Superior rectus
• rotates eye up and
medially
Inferior rectus
• rotates eye down
and medially
Medial rectus
• rotates eye
medially
56
Extrinsic Eye Muscles
Lateral rectus
• rotates eye
laterally
Superior oblique
• rotates eye down and
laterally
Inferior oblique
• rotates eye up and
laterally
57
58
Structure of the Eye
• hollow
• spherical
• wall has 3 layers
• outer fibrous tunic
• middle vascular tunic
• inner nervous tunic
59
Outer Tunic
Cornea
• anterior portion
• transparent
• light transmission
• light refraction
Sclera
• posterior portion
• opaque
• protection
60
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
61
62
Anterior Portion of Eye
• filled with aqueous humor
63
Lens
• transparent
• biconvex
• lies behind iris
• largely composed of
lens fibers
• elastic
• held in place by
suspensory ligaments
of ciliary body
64
Ciliary Body
• forms internal ring around front of eye
• ciliary processes – radiating folds
• ciliary muscles – contract and relax to move lens
65
Accommodation
• changing of lens shape to view objects
66
• To focus, a lens changes position or shape
– Focusing
•
Involves changing the shape of the lens
Choroid
Ciliary muscle contracted
Ligaments slacken
Retina
Light from a near object
(diverging rays)
Lens
Near vision (accommodation)
Ciliary muscle relaxed
Ligaments pull on lens
Light from a distant object
(parallel rays)
Figure 29.6
Distance vision
67
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
68
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
69
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
70
Posterior Cavity
• contains vitreous humor – thick gel that holds retina
flat against choroid coat
71
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
72
Layers of the Eye
73
Light Refraction
Refraction
• bending of light
• occurs when light waves pass at an oblique angle into
mediums of different densities
74
Types of Lenses
Convex lenses cause
light waves to converge
Concave lenses cause
light waves to diverge
75
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
76
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
77
Rods and Cones
78
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
79
Rod Cells
80
Stereoscopic Vision
• provides perception of distance and depth
• results from formation of two slightly different retinal
images
81
Visual Nerve Pathway
82
Life-Span Changes
Age related hearing loss due to
• damage of hair cells in organ of Corti
• degeneration of nerve pathways to the brain
• tinnitus
Age-related visual problems include
• dry eyes
• floaters (crystals in vitreous humor)
• loss of elasticity of lens
• glaucoma
• cataracts
• macular degeneration
83
Clinical Application
Refraction Disorders
• concave lens corrects
nearsightedness
• convex lens corrects
farsightedness
84