Transcript Notes - 8 Special Senses

The Special Senses
1.
Taste (gustation)
parietal lobe (sensory
area) & temporal lobe
(limbic system)
tongue
chemical
senses
2.
3.
4.
5.
Smell (olfaction)
Vision
Hearing & Equilibrium
What about Touch?......
temporal lobe (limbic
system)
nose
eye
occipital lobe
hearing
temporal lobe
equilibrium
cerebellum
ear
skin
parietal lobe
What about Touch.....?
(Not really a SPECIAL sense)
The sense of touch is
part of the General
somatic senses____
This topic deals with the Special
category of the two left sensory boxes
TASTE (gustation)
Smell (olfaction)
 Olfactory bulb (contains receptors) is in forebrain (just
under the frontal lobe)
 Receptor cells send signals via olfactory tract (or nerve)
to the parietal lobe to interpret smell
Olfactory bulb__
_______Olfactory tract
Vision
 Vision is the dominant sense in humans
 70% of sensory receptors in humans are
in the eyes
 40% of the cerebral cortex is involved in
processing visual information
 The eye (or eyeball) is the visual organ
 Lies in bony orbit
 Surrounded by a protective cushion of fat
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8
some pictures…
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Chambers and fluids
(see previous pics)
 Vitreous humor in posterior segment
 Jellylike
 Forms in embryo and lasts life-time
 Anterior segment filled with aqueous
humor – liquid, replaced continuously
 Anterior chamber between cornea and iris
 Posterior chamber between iris and lens
 Glaucoma when problem with drainage
resulting in increased intraocular pressure
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Lens: thick, transparent biconvex disc
 Changes shape for precise focusing of light on retina
 Onion-like avascular fibers, increase through life
 Cataract if becomes clouded
Note lens below,
but in life it is clear
Cataract below: the lens is milky
and opaque, not the cornea
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Cataract (opaque lens)
The eye is an optical
device: predominantly
the lens
(to a lesser degree, not
shown here, the cornea also)
Note: images are
upside down and
reversed from left to
right, like a camera
a.
Resting eye set for distance vision: parallel light focused on retina
b.
Resting eye doesn’t see near objects because divergent rays are
focused behind retina
Lens accommodates (becomes rounder) so as to bend divergent rays
more sharply, thereby allowing convergence on the retina
c.
Retina: develops as part of the brain
Remember
the 3 layers of
the external
eye?
1. (outer layer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
2. (middle layer) Vascular: uvea
Choroid – posterior, pigmented
Ciliary body
Iris
3. (inner layer) Sensory
Retina and optic nerve
Retina is 2 layers
 Outer thin pigmented layer:
 Melanocytes (prevent light scattering)
 Inner thicker neural layer
 Plays a direct role in vision
 Three type of neurons: 1. Photoreceptors
2. Bipolor cells
3. Ganglion cells
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Light passes through pupil in iris, through vitreous
humor, through axons, ganglion cells and bipolar cells, to
photoreceptors next to pigmented layer
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Photoreceptor neurons signal bipolar cells, which signal
ganglion cells to generate (or not) action potentials: axons
run on internal surface to optic nerve which runs to brain
*Know that axons from the retina form the optic nerve, CN II
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Photoreceptors: 2 types
 Rod cells
 Only black and white and not sharp
 Cone cells
 High acuity in bright light
 Color vision
 3 sub-types: blue, red and green light cones
One of the Ishihara charts for color blindness
Commonly X-linked recessive: 8% males and 0.4% females
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If you want more
detail, it’s
fascinating…
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Retina through ophthalmoscope
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Green is area seen by both eyes, and is
the area of stereoscopic vision
Visual pathways
At the optic chiasm, nerve fibers from each
eye cross to the opposite side. Optic tracts
travel to and terminate in the primary
visual cortex in the occipital lobe. Left half
of visual field perceived by right cerebral
cortex, and vice versa.
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Terminology, remember…
 Optic – refers to the eye
 Otic – refers to the ear
 Getting eyedrops and ear drops mixed up
is probably not a good idea
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The Ear
Parts of the ear
 Outer (external)
ear
 Middle ear
(ossicles) for
hearing)
 Inner ear
(labyrinth) for
hearing &
equilibrium
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Sound in external acoustic meatus hits
tympanic membrane (eardrum) – it vibrates
Pressure is
equalized by the
pharyngotympanic
tube (AKA
eustachian or
auditory tube)
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TM causes ossicles in air filled middle ear to move:
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrup)
These are 3 of the
smallest bones of the body
Ossicles articulate to
form a lever system
that amplifies and
transmits the vibratory
motion of the TM to
fluids of inner ear
cochlea via oval
window
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Inner ear = bony “labyrinth” of 3 parts
1. Cochlea - hearing
2. Vestibule - equilibrium
3. Semicircular canals equilibrium
In petrous part of
the temporal bone
Semicircular canals____
Filled with
perilymph and
endolymph
fluids
Vestibule___________
Cochlea_______________________
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Equilibrium pathway
 Via vestibular nerve branch of VIII
(Vestibulocochlear n.) to the brain
stem
 Only special sense for which most of
the information goes to lower brain
centers
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Vestibule contains
utricle and saccule
 Each contains a macula
 Senses static equilibrium
and linear acceleration of
the head
(not rotational movements)
 Tips of hairs imbedded in
otolithic membrane (calcium
carbonate “stones”)
 Vestibular nerve branches of
VIII (Vestibulocochlear n.)
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Semicircular canals




Each of the 3 lies in one of the 3 planes of space
Sense rotational acceleration of the head
Duct with ampulla housing a small crest: crista ampulla
Hairs project into jellylike cupula & basilar cells synapse
with fibers of vestibular nerve
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VIII Vestibulocochlear nerve
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