Transcript PowerPoint to accompany

Sensory Physiology
1
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
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 Receptor Types
4
Figure 10-1: Sensory receptors
Pathways From Sensation to Perception
(Example of an Apple)
5
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
6
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
7
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
8
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
9
Touch and Pressure Receptors
10
Touch (pressure)
11
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
12
Summary of Receptors of the
General Senses
13
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
14
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
15
Olfactor: Sense of Smell
16
Figure 10-14a, b: ANATOMY SUMMARY: Olfaction
Olfactory Receptors
17
Olfactor: Sense of Smell
18
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)
19
20
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
21
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
22
Taste Receptors
23
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
24
Taste Nerve Pathways
Sensory impulses from taste receptors travel along
• cranial nerves to
• medulla oblongata to
• thalamus to
• gustatory cortex (for interpretation)
25
26
Figure 10-4: Sensory pathways
Taste: Chemoreceptors
27
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
28
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
29
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
30
The Outer (External) Ear
31
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
32
Structures of the Middle Ear
33
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
34
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
35
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
36
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
37
The Membranous Labyrinth
38
Figure 16.20
The Inner (Internal) Ear
39
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
40
The Cochlea
41
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
42
Hearing: Mechanoreceptors
43
Figure 10-19: Sound transmission through the ear
Hearing: Hair Cell Transduction
44
Figure 10-20: The cochlea
Hearing: Hair Cell Transduction
45
Figure 10-21: Signal transduction in hair cells
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
Anatomy and Function of the Maculae
51
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
52
Crista Ampullaris
53
Vestibular System & Balance
54
Rotation & Gravity
55
Auditory Pathway from the
Organ of Corti
56
Figure 16.25
Sight
Visual Accessory Organs
• eyelids
• lacrimal apparatus
• extrinsic eye muscles
57
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
58
Extrinsic Eye Muscles
Superior rectus
• rotates eye up and
medially
Inferior rectus
• rotates eye down
and medially
Medial rectus
• rotates eye
medially
59
Extrinsic Eye Muscles
Lateral rectus
• rotates eye
laterally
Superior oblique
• rotates eye down and
laterally
Inferior oblique
• rotates eye up and
laterally
60
Structure of the Eye
• hollow
• spherical
• wall has 3 layers
• outer fibrous tunic
• middle vascular tunic
• inner nervous tunic
61
Outer Tunic
Cornea
• anterior portion
• transparent
• light transmission
• light refraction
Sclera
• posterior portion
• opaque
• protection
62
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
63
Anterior Portion of Eye
• filled with aqueous humor
64
Lens
• transparent
• biconvex
• lies behind iris
• largely composed of
lens fibers
• elastic
• held in place by
suspensory ligaments
of ciliary body
65
Ciliary Body
• forms internal ring around front of eye
• ciliary processes – radiating folds
• ciliary muscles – contract and relax to move lens
66
Accommodation
• changing of lens shape to view objects
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
Visual Nerve Pathway
81
82