Transcript Chapter_17_SpecialSensesx

Anatomy and
Physiology I
BIOL 2401
Chapter 17
Special Senses
Special Senses
Special senses
• Smell – Olfactory sense
• Taste – Gustatory sense
• Vision sense
• Hearing (auditory sense) and
equilibrium
Housed in complex sensory organs
Olfactory Sense
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Located in the superior lining of the
nasal cavity.
The receptors are part of the nasal
epithelium.
Threshold of the olfactory receptor
is low - only a few molecules of a
chemical can stimulate the
receptor.
Olfactory receptors are rapidly
adapting (phasic receptors).
Olfactory Sense
Olfactory epithelium is composed of:
• Olfactory receptors
– bipolar neurons with olfactory
hairs embedded in mucus
secretion.
• Supporting cells
– columnar epithelial cells.
• Basal cells (stem cells)
– replace receptors and supporting
cells.
• Olfactory (Bowman’s) glands
– produce mucus to line the nasal
cavity.
Chemicals enter the nasal cavity  stimulate olfactory cilia  Olfactory
receptors generate impulses  nerve impulses travel through the
cribriform plate of the ethmoid bone  to the olfactory bulbs  to the
olfactory tracts  finally to the cerebral cortex and limbic system.
Gustatory Sense
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Located on the tongue,
soft palate & pharynx.
The receptors are on the
lateral walls of the
papillae.
Threshold of the
gustatory receptor is
low - only a few
molecules of a chemical
can stimulate the
receptor.
Gustatory receptors are
rapidly adapting –
phasic.
Gustatory Sense
Taste buds are composed of 3 types of cells:
– Supporting cells
• Epithelial cells, support the receptors.
– Gustatory receptors
• Epithelial cells with gustatory hair
projects into taste pore.
– Basal cells
• Replace receptor and support cells.
Chemicals dissolve in saliva  contact gustatory
hairs  receptors generate impulses 
impulses travel via cranial nerves (V, VII, IX and
X (vagus)  to thalamus & hypothalamus  to
the primary gustatory area on parietal lobe of
the cerebral cortex  conscious perception of
taste.
Vision Sense
Vision sense is to make brain
aware of the environment.
There are several structures
involved:
Eyeballs
Eyelids
Lacrimal glands
Vision Sense
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Eyelashes & eyebrows help protect from foreign objects,
perspiration & sunlight.
Vision Sense – Eyelids (Palpebrae)
Composed of:
• skin covering orbicularis
oculi muscle
– to open and close the
eye
• Eyelashes
- hair lining the eyelids to
protect the eye surface.
• Tarsal glands
– oily secretions
– To keep the eye lids
from adhering to each
other
• Conjunctiva
– palpebral & bulbar
(ocular)
– stops at corneal edge
Palpebral fissure is the gap
between the eyelids.
Vision Sense – Eye Muscles
Six muscles:
• allow the eyeball to move in different directions.
• inserted on the outer surface of the eyeball.
– 4 rectus muscles -- superior, inferior, lateral and medial.
Move the eyeball up, down, laterally or medially.
– 2 oblique muscles -- superior and inferior.
Help in rolling the eyeball around in a circle.
Vision Sense – Lacrimal Apparatus
Lacrimal fluid/tears:
• spread over the eye by blinking.
• Protects, lubricates and cleans the eye surface.
• contains water, mucus, salts and bactericidal enzyme called lysozyme.
• Flow:
Lacrimal gland  secrets lacrimal fluid  fluid is spread over the eye
surface  fluid drained into lacrimal punctum  into lacrimal ducts 
lacrimal sac  nasolacrimal duct  nasal cavity  drained back into
pharynx  into digestive system.
Vision Sense – Eyeball
The wall of the eye is
made of three layers:
– Fibrous Tunic
(outer layer)
– Vascular Tunic
(middle layer)
– Nervous Tunic
(inner layer)
Vision Sense – Eyeball
1. Fibrous tunic is divided into two parts:
– Sclera: “White” of the eye
• Dense irregular connective tissue layer -- collagen & fibroblasts
• Provides shape, support and site for muscle attachment
– Cornea: Transparent
• Helps focus light (refraction)
• Epithelial and connective tissue
• Nourished by tears & aqueous humor
• Transplants - common & successful; no blood vessels - so no antibodies to
cause rejection
Vision Sense – Eyeball
2. Vascular tunic is divided into
three parts:
• Choroid
– blood vessels to provide
nutrients to the eye layers
– pigment in melanocytes
absorb scattered light
• Ciliary body
– Ciliary processes that
secretes aqueous humor
– ciliary muscle
• smooth muscle to change
the shape of the lens
• Iris
– Colored portion of eye
– Hole in center is pupil
– Function is to regulate amount of light entering eye
– Autonomic reflex - circular and radial muscle fibers to regulate
the size of the pupil
Vision Sense – Eyeball
3. Nervous tunic:
• Pigmented epithelium
– Non-visual portion absorbs stray light &
helps keep image clear
• Photoreceptor layer
• Other cell layers (modify the
signal)
– bipolar cells
– ganglion neuron layer
Vision Sense –Photoreceptors
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Rods
•Rod shaped dendrite
•Activated by dim light
•Forms B&W image
•Contain a single type of
photopigment - rhodopsin
Named for shape of outer
segment - dendrite
Receptors transduce light
energy into a receptor
potential in outer segment
Photopigment integrated in
the membrane of outer
segment membrane
Cones
•Cone shaped dendrite
•Activated by brighter light
•Forms sharp & color image
•Contain one of three different kinds
of photopigments (RGB) - photopsins
Vision Sense
Blind Spot and Fovea
Blind Spot
• Place where the optic nerve
exits
• Blood vessels enter/exit
• No rods or cones
• No image is formed
Fovea
• Place with maximum
density of rods or cones
• Sharpest image is formed
• Image formed most often
Vision Sense
Lens
Lens
• Nonvascular
• Located just behind the pupil and iris
• Filled with clear proteins - crystallins
• Focuses light on nervous tunic
Vision Sense
Cavities
Cavities
• Anterior cavity
– Anterior to the lens; divided into:
Anterior chamber - cavity anterior to iris
Posterior chamber - cavity between lens and iris
– Filled with aqueous humor - produced by ciliary body
• Vitreous/posterior cavity
– Posterior to the lens
– Filled with jelly-like vitreous humor
• Formed once during embryonic life
• Maintains shape of the eyeball
Physiology of Vision
Secretion and Reabsorption of Aqueous Humor
Secreted by ciliary body.
Reabsorbed by scleral venous sinus.
Physiology of Vision
Regulation of Pupil Size
Pupil - regulate light entering the eye.
Pupillary radial muscle  dilation the pupil.
Pupillary sphincter muscle  constriction of pupil.
Physiology of Vision
Refraction and Image Formation
Image is formed on retina (nervous tunic).
The image is upside down and reversed.
Physiology of Vision
Shape of the Lens and Image Formation
Ciliary muscles help change the shape of the lens.
Changing the shape of the lens  Image is focused on the retina.
Physiology of Vision – Optic Pathway
• Absorption of light by photopigments in
rods and cones (photoreceptors).
• Impulses are conveyed through the retina
to the optic nerve.
• Optic nerves cross (optic chiasm).
• Optic tract passes through the thalamus.
• Tracts eventually reach the occipital
lobes of the cerebral cortex.
• Brain learns to work with that information
Physiology of Vision – Optic Chiasm
Left occipital lobe sees right side of the world.
Right occipital lobe sees left side of the world.
Physiology of Vision – Eyesight Disorders
Other Disorders of the Eye
The following are the common disorders of the eye:
Conjunctivitis: inflammation of conjunctiva due to bacterial or viral infection.
Cataract: where the lens becomes cloudy due to age related denaturation of
proteins.
Glaucoma: increased pressure due to accumulation of aqueous humor in
the anterior cavity; may affect vision.
Colorblindness: inability to see colors due to absence of specific cone cells;
sex-linked disorder.
Macular degeneration: loss of acute vision due to degeneration of retina;
heredity, infection, trauma or aging.
Retinal detachment: separation of retina from choroid that causes
disconnection of blood and nerve supply to retina; loss of eyesight.
Auditory Sense and Sense of Equilibrium
The external (outer) ear.
The middle (tympanic cavity) ear.
The internal (inner) ear.
Auditory Sense and Sense of Equilibrium
External Ear
Collects and directs sound waves
inwards
Composed of
– auricle or pinna
• cartilage covered with skin
– external auditory canal
• passage through the temporal
bone
• ceruminous glands produce
cerumen (ear wax)
– tympanic membrane/eardrum
• thin membrane
Auditory Sense and Sense of Equilibrium
Middle Ear
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Air filled cavity
Connects external ear with internal ear
Has 3 ossicles
– malleus (attached to eardrum), incus, & stapes (attached to the
membrane on inner ear (oval window)
– Amplify vibration sound stimulus
Eustachian (Auditory) tube leads to nasopharynx
– helps to equalize pressure on both sides of eardrum
Auditory Sense and Sense of Equilibrium
Inner Ear
Labyrinth is divided into three
parts:
• Cochlea
– contains receptors for
hearing
• Vestibule
– contain receptors for
static equilibrium
• Semicircular canals
– contain receptors for
dynamic equilibrium
Auditory Sense - Cochlea
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Shell shaped region of the labyrinth
Has fluid canals (scala tympani and scala vestibuli) extending
from oval window to round window
Located between the canals is the spiral organ or organ of Corti
Has mechanoreceptors (hair cells) that are stimulated by the
movement of the fluid in the canals
Impulses from cochlea  cochlear nerve  vestibulocochlear
nerve auditory area in the temporal lobe of the cerebrum
Internal Structure of Cochlea
Auditory Sense Pathway
Sense of Static Equilibrium - Vestibule
Static equilibrium:
• maintain the position of the
body (head) relative to the
force of gravity
• receptors (hair cells with
cilia) within the vestibule
(saccule & utricle)
• supporting cells secrete
gelatinous layer
• gelatinous layer contains
calcium carbonate crystals
(otoliths) that move when you tip
your head.
Sense of Static Equilibrium - Vestibule
Movement of cilia
 release of neurotransmitter
 impulse is generated on the
vestibular nerve
 vestibulocochlear nerve
 medulla and cerebellum of brain
 cerebellum updates sensory
information going to the motor areas
of the cerebral cortex
 motor cortex can then adjust its
signals to maintain balance
Sense of Dynamic Equilibrium – Semicircular Canals
Dynamic equilibrium:
• maintain the balance during
movement of the body or
body part
• composed of three canals
attached to the vestibule
• receptors (hair cells with
cilia) within the ampullae at
the base of the canals
• supporting cells secrete
gelatinous layer
• when the body moves, fluid
movement in the canals
stimulates hair cells
Sense of Dynamic Equilibrium – Semicircular Canals
Movement of cilia  release of neurotransmitter  impulse is generated on
the ampullary nerve  vestibulocochlear nerve  medulla and
cerebellum of the brain  cerebellum updates sensory information
going to the motor areas of the cerebral cortex  motor cortex can then
adjust its signals to maintain balance
Ear Disorders
• Motion sickness
– Dysfunctions caused by stimulation of semicircular
canals during motion
• Otitis Media
– Infections in the middle ear
• Deafness: Significant or total hearing loss.
– Sensorineural Deafness
– Conduction deafness