Transcript Chapter 12

Chapter 12
Somatic and Special Senses
1
RECEPTORS AND
SENSATIONS
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
3
Receptor Types
• specialized structures at the end of peripheral
nerves that respond to stimuli
– can be classified according to their location in the body,
stimulus type and structure
•Chemoreceptors
respond to changes in
chemical concentrations
•Nociceptors respond to
extreme (harmful) stimuli
by producing
the sensation of pain
(i.e. all types under
extreme stimuli
•Thermoreceptors are
sensitive to temperature
change
•Mechanoreceptors respond
to a change in pressure
(i.e. touch, pressure,
vibrations, stretch)
Photoreceptors (in retina
of eye) respond to
4
changes in light
Sensory Impulse
• All senses work in basically the same fashion
• Special sensory receptors collect information from
the environment and stimulate neurons to send a
message to the brain
• 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
5
they are analyzed and interpreted in the brain
Sensations
• Sensation =the conscious or unconscious
awareness of external or internal stimuli
• Perception =the conscious awareness and
interpretation of 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
6
Sensory Adaptation
• 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
• All sensory receptors, except nociceptors, adapt to
continuous stimuli (i.e. undergo sensory adaptation)
– i.e. when you first put a band-aid on you feel it but soon
don’t notice it at all
7
SOMATIC SENSES
Receptors associated with skin,
muscles, joints, and viscera
provide somatic senses.
8
Three groups
• Exteroceptive Senses:
– detect changes at the body's surface:
– touch
– pressure
– temperature
• Proprioceptive Senses:
– detect changes in muscles, tendons, and body
position
• Visceroceptive Senses:
– detect changes in viscera
– only pain will be discussed here
9
Three types of receptors
• free nerve endings (naked dendritic)
– in epithelium, CT
• Meissner's Corpuscles are encapsulated
dendritic endings
– abundant in hairless portions of skin; lips
– detect fine touch; distinguish between two points
on the skin
• Pacinian Corpuscles are also encapsulated
dendritic endings:
– common in deeper subcutaneous tissues,
tendons, and ligaments
– detect heavy pressure and vibrations
10
11
Temperature Senses
Two types that respond to temperature change:
• Heat receptors
– sensitive to temps above 25oC (77oF)
– unresponsive at temps above 45oC (113oF)
– Pain receptors are also triggered as this temperature
approaches producing a burning sensation
• Cold receptors
– sensitive to temps between 10oC (50oF) and 20oC (68oF)
– below 10oC, pain receptors are triggered producing a
freezing sensation
• Both undergo rapid sensory adaptation
12
Sense of Pain
• Free nerve endings are the receptors that
detect pain
• They are widely distributed throughout the
skin and internal tissues, with the exception
of the nervous tissue of the brain
• Pain Receptors (Nociceptors)
– function is protection against further tissue
damage
– many stimuli may trigger them (i.e. temperature,
pressure, chemicals)
– generally do not adapt to continual stimuli
13
Sense of Pain cont.
• Visceral Pain:
– only visceral receptors that produce sensations
– stretch receptors are stimulated by pressure
and/or a decrease in oxygen levels
• may feel as if its coming from another area of
the body = referred pain
– may occur due to sensory impulses from two
regions following a common nerve pathway to
brain
14
15
Sense of PAIN cont.
Pain Nerve Pathways:
• Acute pain
–
–
–
–
–
occurs rapidly (0.1 sec)
is not felt in deep tissues
sharp, fast, pricking pain
conducted on myelinated fibers
ceases when stimulus is removed
• Chronic pain
– begins slowly and increases in intensity over a period of
several seconds or minutes
– dull, aching, burning, throbbing pain
– can occur anywhere
– conducted on unmyelinated fibers
– may continue after stimulus is removed
16
Stretch Receptors
• Stretch receptors are proprioceptors that
send information to the spinal cord and brain
concerning the length and tension of muscles
17
SPECIAL SENSES
SPECIAL SENSES are senses whose sensory
receptors are located in large, complex organs in
the head.
The five special senses are vision, hearing,
equilibrium, taste, and smell.
18
OLFACTION
Sense of Smell
Organ=epithelial lining of nose
19
Olfactory Receptors
• chemoreceptors that are located in the
upper nasal cavity
– sensitive portion is cilia-like dendrites on bipolar
neurons
– chemicals must be dissolved in solution to be
detected
– undergo rapid sensory adaptation
• Olfactory Code
– hypothesis
– odor that is stimulated by a distinct set of
receptor cells and its associated receptor
proteins
20
21
22
GUSTATION
Sense of Taste
Organ = taste buds on tongue
23
Taste Receptors
• chemoreceptors that are located in taste
buds
– taste cells – modified epithelial cells that function
as receptors
– taste hairs –microvilli that protrude from taste
cells=sensitive parts of taste cells
– Chemicals must be dissolved in saliva to be
detected
– undergo rapid sensory adaptation
24
25
26
Taste Sensations
• most taste buds are far posterior near the
base of the tongue
• Four Primary Taste Sensations
– sweet – stimulated by carbohydrates (tip of
tongue)
– sour – stimulated by acids (lateral tongue)
– salty – stimulated by salts (perimeter of tongue)
– bitter – stimulated by many organic compounds
(posterior tongue)
• Taste varies from person to person
27
28
Sense of Hearing
Organ=Ear (Organ of Corti)
29
Introduction
• The organ of hearing is the Organ of Corti,
which is present in the cochlea of the inner
ear
• The sensory receptors are called
mechanoreceptors
• Once these mechanoreceptors are
stimulated, the impulse travels on the
cochlear branch of the vestibulocochlear
(CN VIII) nerve, which leads to the primary
auditory cortex (temporal cortex) of the
cerebrum
30
EAR STRUCTURE
31
External Ear
• Auricle = outer ear (cartilage)
– Function = collection of sound waves
• External auditory meatus = ear canal
– Function = starts vibrations of sound waves and
directs them toward tympanic membrane
• tympanic membrane
– vibrates in response to sound waves
32
33
Middle Ear
• Function = to amplify and concentrate sound
waves.
• Tympanic cavity = air-filled space behind
eardrum; separates outer from inner ear.
• Auditory ossicles = 3 tiny bones in middle
ear:
– Malleus (hammer) is connected to tympanic
membrane
– Incus (anvil) connects malleus to stapes
– Stapes (stirrup) connects incus to the
• Oval window = the entrance to inner ear
34
Middle Ear cont.
• Auditory (Eustachian) tube = passageway
which connects middle ear to nasopharynx
(throat)
• Function = to equalize pressure on both
sides of the tympanic membrane, which is
necessary for proper hearing.
35
36
Inner Ear
• The inner ear consists of a complex system of
intercommunicating chambers and tubes called a
labyrinth. Actually, two labyrinths compose the
inner ear:
• Osseous labyrinth = bony canal in temporal bone
– Perilymph fills the space between the osseous and
membranous labyrinth
• Membranous labyrinth = membrane within
osseous labyrinth.
– Endolymph fills the membranous labyrinth.
37
Inner Ear cont.
• The inner ear labyrinth can further be divided
into three regions (cochlea, vestibule &
semi-circular canals)
• each with a specific function:
– Cochlea = snail shaped portion
• Function = sense of hearing
– Semi-circular canals = three rings
• Function = dynamic equilibrium
– Vestibule = area between cochlea and semicircular canals
• Function = static equilibrium
38
39
The Choclea
• divided into two compartments:
– Scala vestibuli = upper compartment which
extends from oval window to apex
– Scala tympani = lower compartment which
extends from apex to round window
• Both compartments are filled with perilymph
• Between the two bony compartments, we find
the membranous labyrinth = cochlear duct
– The cochlear duct is filled with endolymph
40
41
Cochlea cont.
• There are membranes that separate the
cochlear duct from the bony compartments:
– Vestibular membrane separates the cochlear
duct from the scala vestibuli
– Basilar membrane separates the cochlear duct
from the scala tympani
42
Organ of Corti
• The mechanoreceptors responsible for the
sense of hearing are contained in the Organ
of Corti = 16,000 hearing receptor cells
located on the basilar membrane.
• The receptor cells are called "hair cells"
• The hair cells are covered by the tectorial
membrane, which lies over them like a roof
– different frequencies of vibration move different
parts of basilar membrane
– particular sound frequencies cause hairs of
receptor cells to bend
– nerve impulse generated
43
44
45
46
Sound through the ear
Auditory Nerve Pathways
47
First
• Sound waves arrive at
the tympanic
membrane
48
Second
• Movement of the
tympanic membrane
causes displacement of
the auditory ossicles.
49
Third
• Movement of the
stapes at the oval
window establishes
pressure waves in the
perilymph of the
vestibular duct.
50
Fourth
• The pressure waves
distort the basilar
membrane on their way
to the round window of
the tympanic duct.
51
Fifth
• Vibration of the basilar
membrane causes
vibration of hair cells
against the tectorial
membrane
52
Sixth
• Information about the region and the intensity of
stimulation is relayed to the CNS over the
cochlear branch of cranial nerve VIII.
• thalamus for direction to the
• primary auditory cortex (temporal lobes) of
cerebrum for interpretation
53
SENSE OF EQUILIBRIUM
Organs= vestibule, utricle,
saccule, semi-circular canals
54
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
55
Static Equilibrium
• functions to sense the position of the head
and help us maintain posture while
motionless
• The vestibule of the inner ear contains the
two membranous chambers responsible for
static equilibrium
– The utricle communicates with the semi-circular
canals
– The saccule communicates with the cochlear
duct
56
Static Equilibrium cont.
• Each of these chambers contains a macula =
organ of static equilibrium
• The macula is composed of "hair cells" that
are in contact with a jelly-like fluid containing
calcium carbonate crystals (otolith)
– When the head is moved, the gel sags due to
gravity and the hair cells bend
– This triggers a sensory impulse
57
58
59
Dynamic Equilibrium
• functions to prevent loss of balance during rapid
head or body movement
• The three semi-circular canals contain the organ
responsible for dynamic equilibrium.
– Each semi-circular canal ends in an enlargement called
the ampulla
– Each ampulla houses a sensory organ for dynamic
equilibrium called the crista ampullaris, which contains a
patch of "hair cells" in a mass of gelatin
– When the head is moved, the gelatin stays put due to
inertia causing the hair cells to bend.
– This triggers a sensory impulse
60
61
Vision
Organ=the eye
Visual Accessory Organs=
eyelids, lacrimal apparatus, extrinsic
eye muscles
62
Introduction
• The organ of vision is the retina of the eye
• The sensory receptors are called
photoreceptor
• When photoreceptors are stimulated,
impulses travel within the optic nerve (CN II)
to the visual (occipital) cortex for
interpretation
63
Visual Accessory Organs
• Eyelids = protective
shield for the eyeball.
• Conjunctiva= inner
lining of eyelid; = red
portion around eye.
• Lacrimal apparatus =
tear secretion &
distribution
• Lacrimal gland = tear
secretion; located on
upper lateral surface
– Tears contain an
enzyme called
lysozyme, which
functions as an antibacterial agent.
• Nasolacrimal duct =
duct which carries tears
into nasal cavity
(drainage)
64
65
Extrinsic Eye Muscles
66
Structure of the Eye
The eye is composed of three distinct layers
or tunics:
• The Outer Tunic (fibrous tunic)
• The Middle (vascular tunic)
• The inner (nervous tunic)
67
The Outer Tunic
• Function= protection
• Cornea = transparent anterior portion
– Function: helps focus (75%) incoming light rays
• Sclera = white posterior portion, which is
continuous with eyeball except where the
optic nerve and blood vessels pierce through
it in the back of eye
– Functions:
• protection
• attachment (of eye muscles)
68
69
The Middle tunic (vascular)
• Function= nourishment
• Choroid coat = membrane joined loosely to sclera
containing many blood vessels to nourish the
tissues of the eye
– pigments absorb extra light
• Ciliary body = anterior extension from choroid coat,
which is composed of 2 parts:
– Ciliary muscles which control the shape of the lens (i.e.
Accommodation)
– Ciliary processes which are located on the periphery of
the lens
– Suspensory ligaments extend from the ciliary processes
on the lens to the ciliary muscles and function to hold the
lens in place
70
71
The Middle tunic cont.
• Iris = colored ring around pupil
– thin diaphragm muscle
– lies between cornea and lens
– The iris separates the anterior cavity of the eye
into an anterior chamber and posterior
chamber
– The entire anterior cavity is filled with aqueous
humor, which helps nourish the anterior portions
of the eye, and maintains the shape of the
anterior eye
72
73
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
74
The Inner tunic (nervous, sensory)
• Retina = inner lining of the eyeball; site of
photoreceptors
– A picture of the retina can be taken with a camera
attached to an ophthalmoscope
• The optic disc is the location on the retina where
nerve fibers leave the eye & join with the optic nerve
• the central artery & vein also pass through this disk
– No photoreceptors are present in the area of the optic
disk = blind spot.
• The posterior cavity of the eye is occupied by the
lens, ciliary body, and the retina
– The posterior cavity is filled with vitreous humor, which
is a jelly-like fluid, which maintains the spherical shape of
the eyeball
75
76
Accommodation
• the process by which the lenschanges shape
to focus on close objects
– The lens is responsible (with cornea) for focusing
incoming light rays.
– If light rays are entering the eye from a distant
object, the lens is flat.
– When we focus on a close object, the ciliary
muscles contract, relaxing the suspensory
ligaments. Accordingly, the lens thickens
allowing us to focus.
77
Figure 12.29
78
Light Refraction
• Incoming light rays are refracted (bent) onto
the retina due to the convex surface of both
the cornea and the lens.
• Pathway of Light Through Eye:
1. cornea
2. aqueous humor
3. lens
4. vitreous humor
5. photoreceptors in retina.
• Once the rods and/or cones are stimulated, a
sensory impulse is carried
79
80
Light Through the Eye
• 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
81
Macula lutea –yellow spot
of mostly cones
Fovea centralis –
depression of ALL cones,
sharpest vision
82
Visual Receptors
Rods= long, thin projections Cones=short/blunt
• contain light sensitive
projections
pigment called rhodopsin
• contain light sensitive
• hundred times more
pigments called
sensitive to light than
erythrolabe, chlorolabe,
cones
and cyanolabe
• provide vision in dim light • provide vision in bright
• produce colorless vision
light
and outlines
• produce sharp images
• produce color vision
•dark adapted – all opsin
•light adapted – most
and retinal is together,
opsin and retinal
therefore rods are VERY
decomposes
sensitive, vision possible
83
even in dark
84
Visual Pigments
Rhodopsin
Pigments on Cones
• light-sensitive
• each set contains different
pigment in rods
light-sensitive pigment
• decomposes in
• each set is sensitive to
presence of light
different wavelengths
• triggers a complex
• color perceived depends on
series of reactions
which sets of cones are
that initiate nerve
stimulated
impulses
• red, green, or blue
• impulses travel
along optic nerve
85
Stereoscopic Vision
• provides perception of distance and depth
• results from formation of two slightly different
retinal images
86