Transcript CHAPTER 8 NOTES A

Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 8
Special Senses
Slides 8.1 – 8.19
Lecture Slides in PowerPoint by Jerry L. Cook
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The Senses
 General senses of touch
 Temperature
 Pressure
 Pain
 Special senses
 Smell
 Taste
 Sight
 Hearing
 Equilibrium
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Slide 8.1
The Eye and Vision
 70 percent of all sensory receptors are
in the eyes
 Each eye has over a million nerve fibers
 Protection for the eye
 Most of the eye is enclosed in a bony orbit
 A cushion of fat surrounds most of the eye
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Slide 8.2
Some things you may not know about your eyes .
..
•
The average blink lasts for about 1/10th of a second.
•
While it takes some time for most parts of your body to warm up to their full
potential, your eyes are on their “A game” 24/7.
•
Eyes heal quickly. With proper care, it only takes about 48 hours for the eye
to repair a corneal scratch.
•
Seeing is such a big part of everyday life that it requires about half of the
brain to get involved.
•
Newborns don’t produce tears. They make crying sounds, but the tears don’t
start flowing until they are about 4-13 weeks old.
•
Around the world, about 39 million people are blind and roughly 6 times that
many have some kind of vision impairment.
•
Doctors have yet to find a way to transplant an eyeball. The optic nerve that
connects the eye to the brain is too sensitive to reconstruct successfully.
1. You blink about 12 times every minute.
2. Some people are born with two differently colored eyes.
This condition is heterochromia.
•
Your eyes are composed of more than 2 million working
parts.
•
We all have microscopic creatures lurking in our
eyelashes.
•
Only 1/6 of your eye is exposed to the outside world. It is
2.5 cm in length and weighs about 7 grams.
•
Your eyes begin to develop 2 weeks after conception.
•
The entire length of all the eyelashes shed by a human in
their life is over 98 feet.
•
When you blink, you shut your eyes for 0.3 seconds.
That’s a total of 30 minutes each day!
• Myth: Reading in dim light is
harmful to your eyes.
Accessory Structures of the Eye
 Eyelids
 Eyelashes
Figure 8.1b
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Slide 8.3a
Accessory Structures of the Eye
 Meibomian glands –
modified
sebacious
glands
produce an
oily secretion
to lubricate
the eye
Figure 8.1b
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Slide 8.3b
Accessory Structures of the Eye
 Ciliary glands –
modified
sweat glands
between the
eyelashes
Figure 8.1b
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Slide 8.3c
Accessory Structures of the Eye
 Conjunctiva
 Membrane that lines the eyelids
 Connects to the surface of the eye
 Secretes mucus to lubricate the eye
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Slide 8.4a
Accessory Structures of the Eye
 Lacrimal
apparatus
 Lacrimal gland –
produces lacrimal
fluid
 Lacrimal canals –
drains lacrimal
fluid from eyes
Figure 8.1a
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Slide 8.4b
Accessory Structures of the Eye
 Lacrimal sac –
provides
passage of
lacrimal fluid
towards nasal
cavity
Figure 8.1a
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Slide 8.4c
Accessory Structures of the Eye
 Nasolacrimal
duct – empties
lacrimal fluid into
the nasal cavity
Figure 8.1a
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Slide 8.4d
Function of the Lacrimal Apparatus
 Properties of lacrimal fluid
 Dilute salt solution (tears)
 Contains antibodies and lysozyme
 Protects, moistens, and lubricates the
eye
 Empties into the nasal cavity
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Slide 8.5
Extrinsic Eye Muscles
 Muscles attach to the outer surface of
the eye
 Produce eye movements
Figure 8.2
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Slide 8.6
Structure of the Eye
 The wall is composed of three tunics
 Fibrous tunic –
outside layer
 Choroid –
middle
layer
 Sensory
tunic –
inside
layer
Figure 8.3a
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Slide 8.7
The Fibrous Tunic
 Sclera
 White connective tissue layer
 Seen anteriorly as the “white of the eye”
 Cornea
 Transparent, central anterior portion
 Allows for light to pass through
 Repairs itself easily
 The only human tissue that can be
transplanted without fear of rejection
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Slide 8.8
Choroid Layer
 Blood-rich nutritive tunic
 Pigment prevents light from scattering
 Modified interiorly into two structures
 Cilliary body – smooth muscle
 Iris
 Pigmented layer that gives eye color
 Pupil – rounded opening in the iris
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Slide 8.9
Sensory Tunic (Retina)
 Contains receptor cells (photoreceptors)
 Rods
 Cones
 Signals pass from photoreceptors via a
two-neuron chain
 Bipolar neurons
 Ganglion cells
 Signals leave the retina toward the brain
through the optic nerve
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Slide 8.10
Neurons of the Retina
Figure 8.4
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Slide 8.11
Neurons of the Retina and Vision
 Rods
 Most are found towards the edges of the
retina
 Allow dim light vision and peripheral vision
 Perception is all in gray tones
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Slide 8.12a
Neurons of the Retina and Vision
 Cones
 Allow for detailed color vision
 Densest in the center of the retina
 Fovea centralis – area of the retina with
only cones
 No photoreceptor cells are at the
optic disk, or blind spot
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Slide 8.12b
Cone Sensitivity
 There are three
types of cones
 Different cones
are sensitive to
different
wavelengths
 Color blindness is
the result of lack
of one cone type
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Figure 8.6
Slide 8.13
Lens
 Biconvex crystal-like structure
 Held in place by a suspensory ligament
attached to the ciliary body
Figure 8.3a
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Slide 8.14
Internal Eye Chamber Fluids
 Aqueous humor
 Watery fluid found in chamber between the
lens and cornea
 Similar to blood plasma
 Helps maintain intraocular pressure
 Provides nutrients for the lens and cornea
 Reabsorbed into venous blood through the
canal of Schlemm
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Slide 8.15a
Internal Eye Chamber Fluids
 Vitreous humor
 Gel-like substance behind the lens
 Keeps the eye from collapsing
 Lasts a lifetime and is not replaced
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Slide 8.15b
Lens Accommodation
 Light must be
focused to a point
on the retina for
optimal vision
 The eye is set for
distance vision
(over 20 ft away)
 The lens must
change shape to
focus for closer
objects
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Figure 8.9
Slide 8.16
Images Formed on the Retina
Figure 8.10
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Slide 8.17
Visual Pathway
 Photoreceptors of
the retina
 Optic nerve
 Optic nerve crosses
at the optic chiasma
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Figure 8.11
Slide 8.18a
Visual Pathway
 Optic tracts
 Thalamus (axons
form optic radiation)
 Visula cortex of the
occipital lobe
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Figure 8.11
Slide 8.18b
Eye Reflexes
 Internal muscles are controlled by the
autonomic nervous system
 Bright light causes pupils to constrict
through action of radial and ciliary muscles
 Viewing close objects causes
accommodation
 External muscles control eye movement
to follow objects
 Viewing close objects causes
convergence (eyes moving medially)
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Slide 8.19