Download Special senses - Human Anatomy

Chapter 16
The Special Senses
1
The Special Senses

Chemical senses




Taste (gustation)
Smell (olfaction)
Vision
The ear


Hearing
Equilibrium
2
Touch
The sense of touch is
part of the General
somatic senses____
This chapter deals with the Special
category of the two left sensory boxes
3
TASTE


Taste buds: mostly on tongue
Two types
 Fungiform papillae (small, on entire surface of tongue)
 Circumvallate papillae (inverted “V” near back of tongue)
4
Taste involves chemicals binding to
microvilli




Taste buds of 50-100
epithelial cells each
Taste receptor cells
(gustatory cells)
Microvilli through pore,
bathed in saliva
Disolved molecules bind
& induce receptor cells
to generate impulses in
sensory nerve fibers
5

Types of taste






Sweet
Sour
Salty
Bitter
Glutamate (MSG)
Gustatory (taste) pathway to brainstem &
cerebral cortex via two cranial nerves:


VII (Facial n.) – anterior 2/3 of tongue
IX (Glossopharyngeal n.) – posterior 1/3 tongue
and pharynx
6
Olfactory epithelium in roof of nasal cavity

Smell
(olfaction)

Pseudostratified columnar epithelium
Has millions of bipolar neurons = olfactory receptor cells
Only neurons undergoing replacement throughout adult life
Olfactory cilia bind odor molecules

Mucus captures & dissolves odor molecules
Each receptor cell has an axon - are bundled into “filaments” of
olfactory nerve

Penetrate cribriform plate of ethmoid bone & enter olfactory bulb
7



Olfactory bulb is in forebrain
In bulb nerve axons branch and synapse with mitral
cells (neurons in clusters of “glomeruli”)
Mitral cells send signals via olfactory tract
Olfactory bulb__
*
___Filaments of Olfactory nerve (CN I)
_______Olfactory tract
*
8
9



1000 types of smell receptors (approx.)
Convergence of many receptor cell signals
onto one glomerulus registers a signature
pattern
Brain recognizes the pattern: sent to unclus
(olfactory center) and limbic area
Anosmia: absence of the sense of smell




Trauma
Colds or allergies producing excessive mucus
Polyps causing blockage
1/3 are from zinc deficiency
10
The Eye and 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




Diameter 2.5 cm (1 inch)
Only anterior 1/6 visible
Lies in bony orbit
Surrounded by a protective cushion of fat
11
Accessory structures of the eye


Eyebrows
Eyelids or palpebrae



Upper & lower separated by palpebral fissure
Corners: medial & lateral canthi
Eyelashes
12

Eyelid tarsal plates give structure


Where orbicularis oculi muscles attach (close eyes)
Levator palpebrae superioris muscle

Lifts upper lid voluntarily (inserts on tarsal plate)
Tears drain into your nose.
13


Tarsal glands –
modified sebaceous (oil)
glands in tarsal plates
Conjunctiva transparent mucus
membrane of stratified
columnar epithelium


Palpebral conjunctiva
Bulbar conjunctiva

Covers white of eye but not
the cornea (transparent
tissue over the iris and
pupil)
14
Lacrimal apparatus

Responsible for tears




The fluid has mucus,
antibodies and lysozyme
Lacrimal gland in orbit
superolateral to eye
Tears pass out through
puncta into canaliculi into
sac into nasolacrimal duct
Empty into nasal cavity
(sniffles)
15

The Eye
16
3 Layers form the external wall of the eye
1.


(outer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea





2.



3.

100s of sheets of collagen fibers between
sheets of epithelium and endothelium
Clear because regular alignment
Role in light bending
Avascular but does have pain receptors
Regenerates
(middle) Vascular: uvea
Choroid – posterior, pigmented
Ciliary body
Iris (colored part: see next slide)
(inner) Sensory
Retina and optic nerve
17
1.


2.


(outer layer) Fibrous: dense
connective tissue
Sclera – white of the eye
Cornea
(middle) Vascular: uvea
Choroid – posterior,
pigmented
Ciliary body




3.

Muscles – control lens
shape
Processes – secrete
aqueous humor
Zonule (attaches lens)
Iris
(inner layer) Sensory
Retina and optic nerve
18
Layers of external wall of eye continued
1.


2.



(outer) Fibrous: dense connective tissue
Sclera – white of the eye
Cornea
(middle) Vascular: uvea
Choroid – posterior, pigmented
Ciliary body
Iris
Pigmented put incomplete: pupil lets in light
Sphincter of pupil: circularly arranged smooth muscle parasympathetic control
for bright light and/or close vision
Dilator of pupil: radiating smooth muscle – sympathetic
control
for dim light and/or distance vision
(inner) Sensory
3.

Retina
19
Layers of external wall of eye continued
(outer) Fibrous: dense connective tissue
1.


Sclera – white of the eye
Cornea
(middle) Vascular: uvea
2.



Choroid – posterior, pigmented
Ciliary body
Iris
(inner) Sensory
3.

Retina is the only true pigmented structure
of the eye
20
some pictures…
21
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
22
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
23
Cataract (opaque lens)
24
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
25
Know the names of these cells!
Light passes through pupil in iris, through vitreous humor,
through axons, ganglion cells and bipolar cells, to photoreceptors
next to pigmented layer
26
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
27
Photoreceptors: 2 types

Rod cells



More sensitive to light - vision permitted in dim
light but only gray and fuzzy
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
*Know that rods are for B & W and cones are for color
28
One of the Ishihara charts for color blindness
Commonly X-linked recessive: 8% males and 0.4% females
29
30
If you want more
detail, it’s
fascinating…
31
Retina through
ophthalmoscope




Macula: at
posterior pole
Fovea: maximal
visual acuity
(most
concentrated
cones)
Optic disc: optic
nerve exits
Vessels
32
Green is area seen by both eyes, and is
the area of stereoscopic vision
Visual pathways
At optic chiasm, medial fibers from each eye
(which view lateral fields of vision) cross to
opposite side. Optic tracts (of crossed and
uncrossed, sensing opposite side of visual field of
both eyes) synapse with neurons in lateral
geniculate of thalamus. These axons form the optic
radiation and terminate in the primary visual cortex
in the occipital lobe. Left half of visual field
perceived by right cerebral cortex, and vice versa.
33
Visual field defects
print this out and follow from the fields to the visual cortex using 4 colors
remember: fields are reversed and upside down
Visual fields
Location of lesion:
1. Optic nerve
ipsilateral (same side) blind eye
1.
2. Chiasmatic (pituitary tumors
classically)
2.
lateral half of both eyes gone
1.
3. Optic tract
3.
3.
2.
4.
5.
opposite half of visual field gone
4. & 5. Distal to geniculate ganglion
of thalamus:
homonymous superior field (4) or
homonymous inferior field (5)
defect
5.
Visual cortex
4.
34
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
35
The Ear
Parts of the ear



Sound waves enter the EAM through air.
Outer (external)
ear
Middle ear
(ossicles) for
hearing)
Inner ear
(labyrinth) for
hearing &
equilibrium
36
Sound in external acoustic meatus hits tympanic
membrane (eardrum) – it vibrates
The middle ear cavity is
filled with air
Hair cell receptors are
responsible for
equilibrium
Pressure is
equalized by the
pharyngotympanic
tube (AKA
eustachian or
auditory tube)
Receptors (hair cells) for
hearing are in the cochlea
37
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
38
Skeletal muscles of middle ear
When loud, muscles
contract, limiting
vibration and
dampening the noise
39
Inner ear = bony “labyrinth” of 3 parts
1.
2.
3.
Cochlea - hearing
Vestibule - equilibrium
Semicircular canals equilibrium
In petrous part of
the temporal bone
Semicircular canals____
Filled with
perilymph and
endolymph
fluids
Vestibule___________
Cochlea_______________________
40
Spiral organ of Corti in cochlea contains receptors for
hearing (amplifies sound 100 times)



Vibration of
stirrup at oval
window starts
traveling waves
displacing
basilar
membrane
Sensory hair
cells stimulated
Nerve ending of
cochlear nerve
division of VIII
(Vestibulocochlear n.)
41
Auditory pathway
42
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
43
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.)
44
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
45
VIII Vestibulocochlear nerve
46