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Somatic and
Special Senses
Communicating with the world
around us
Mrs. S. Taylor
The two major groups
• Somatic senses
– Touch, pressure, temperature and pain
– Found in the skin and the deeper tissues
– Structurally simple
• special senses (sensory)
– Smell, taste, hearing, vision, and equilibrium
– Found in specialized organs for that sense
– Structurally complex
Receptors
• Types of receptors
– Chemoreceptors
• Stimulated by changes in the chemical
concentration of substance
– Pain receptors
• Stimulated by tissue damage
– Thermoreceptors
• Stimulated by changes in temperature
– Mechanoreceptors
• Stimulated by changes in pressure and movement
– Photoreceptors
• Stimulated by light
The sensation
• Sensation occurs when the brain interprets
the sensory impulses.
– Different sections of the brain interpret the
signals, dependent on what type of receptor
they come from
• The cerebral cortex then causes the feeling
to seem to come from the area of the
stimulated receptor.
– This is called projection
• This allows us to know what hurts in most cases
Did you adjust?
• There is noise all around you, things
pressing against you... do you always feel
or hear them?
• The ability for you mind to ignore
unimportant stimuli is called sensory
adaptation
– Receptors become unresponsive – peripheral
adaptation
– Inhibition along the CNS leading to the sensory
regions of the cerebral cortex - central
adaptation
Somatic Sense
• Associated with the skin, muscles, joints,
and the viscera
• Three main types
– Touch and pressure
– Temperature
– Pain
Touch and pressure

Comes from three different types of
receptors
−

They detect mechanical forces that deform or
displace tissue
They are:
−
−
Free nerve endings – extend between the epithelial
cells
Meissner's corpuscles – small oval masses of
flattened connective tissue


−
Abundant in the hairless regions of the body
Respond to light touch
Pacinian corpuscles – large structures in the
deeper subcutaneous fissures and muscles tendons
and ligaments

Respond toe heavy pressure and deep pressure
Temperature Senses
•
Depends on two types of free nerve
endings in the skin
–
Warm receptors
• Sensitive to temps above 25˚C (77˚F)
and are unresponsive with temps more
than 45˚C (113˚ F)
–
–
Then the pain receptors kick in and you feel
a burning sensation
Cold receptors
• Sensitive to temps between 10˚C(50˚ F)
and 20˚ C (68˚ F)
–
Below 10˚ C produces a freezing sensation
and pain
Pain
•
Free nerve endings
–
Spread through the skin and internal
tissues
•
•
Exception – the brain, it has none
Protect the body
–
Is stimulated by tissue damage
•
–
How this does it is not well understood
Don't adapt well, so pain can be persistent
Visceral Pain
•
In the vicera, you typically need a
widespread stimulation to get a response.
–
–
•
So, a small cut in a region of the intestines
= no pain
Intestinal cramping = pain
Visceral pain feel like it is coming from
some other part of the body
–
–
Called referred pain
Tends to be caused by the sharing of
neural pathways that go to the skin as well
as the viscera
Pain nerve fibers
•
Two main types
–
Acute
•
•
•
–
Thin and myelinated , fast impulses
Sensation of sharp pain that seldom
continues after the stimuli has gone. Easy
to pin point location
Typically only from skin
Chronic
•
•
•
Thin and unmyelinated, slow impulses
Dull aching sensation, difficult to pinpoint,
continuous
From both skin and deeper tissues
Special Senses
•
•
•
•
•
•
Have large complex sensory organs in
the head
Smell – olfactory organs
Taste – taste buds
Hearing – ears
Equilibrium – ears
Sight – eyes
•
Sense of smell
Olfactory organs
–
Are located in small patches
•
•
–
Covers the upper nasal cavity, nasal
conchea, and portions of the nasal septum
Yellowish brown masses of epithelium
Composed of olfactory receptors
•
a type of chemoreceptors
–
•
Neurons surrounded by columnar epithelial
cells
–
•
Chemicals dissolved in liquids stimulate
them
Have cilia like ending that harbor 400 types
of protein receptors
» Detects odorant molecules
Smell and taste are closely related
Sense of taste
•
Taste buds - chemoreceptors
–
Where are they
•
Approx 10,000 are located on the tongue
–
•
–
Located on papillae
1,000 are scattered about the roof of the
mouth and the walls of the throat.
Composed of
•
modified epithelial cells called taste cells
(gustatory cells)- the receptors
–
•
•
•
50-150 of these/ taste bud
Taste pore – hole at the top of the spherical
shaped bud
Taste hair – protrude from taste cell into the
the taste pore
Nerve fibers woven about the cells
•
Taste sensations
The tastes
–
4 primary
•
•
Sweet, Sour, Salty, Bitter
All taste all of these, but at different levels
–
–
Others sometimes recognized
•
–
Alkaline, metallic, umami (MSG)
Some taste stimulate other nerves
•
•
–
Therefore there are areas of concentration
of the flavors
Chile peppers and ginger – pain receptors
Chile peppers (capsaicin)– warm receptors
Taste is a combination of the different
nerves stimulated, texture, temperature,
and smell
Sense of hearing
•
Three zones
–
–
–
Outer ear
Middle ear
Inner ear
•
Outer
ear
Three parts
–
Auricle (pinna)– outer funnel-like structure
•
–
External ascoustic meatus (external
auditory canal) – s-shaped tube that leads
inwards for about 2.5 cm
•
–
Collects sound waves
Tunnels/ directs to the eardrum
Tympanic membrane (eardrum) –
semitransparent membrane covered by a
thin layer of skin on the outside and a
mucous membrane on the inside.
•
•
Oval margin and cone-shaped that attaches to
the malleus (mallet)
Vibrates when sound waves hit it causing the
malleus to move
Middle Ear
•
AKA Tympanic Caviry
–
–
Air filled space in the temporal bone
Contains 3 small bones (auditory ossicles)
•
•
•
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Malleus (mallet), Incus(anvil) ,Stapes
(stirup)
Attached to the cavity by small ligaments
and the oval window (stapes)
Covered by a mucous membrane
The bones transmits the sound waves from
the eardrum to the oval window
–
Also help to amplify the sound waves
because the size of the eardrum (larger) and
the oval window (smaller)
Middle Ear connection
•
Auditory tube (Eustachian tube)
–
–
Connects the middle ear with the
nasopharynx
Helps to regulate the air pressure in the
middle ear.
•
•
Must be the same as on the outside of the
eardrum
If a sudden change happens in external
pressure, the adjustment will sound like a
pop
Inner ear
•
Entire region is called the Labyrinth
–
Divided into two main areas
•
•
–
3 semicircular canals – used in equilbrium
Cochlea – used to hear
Two main parts
•
Osseous labyrinth – tunnel through the
temporal bone
–
•
Secrets a fluid called perilymph
Membranous labyrinth – membrane inside
of the bone tunnel
–
Secrets endolymph
Cochlea
•
The oval window allows sound vibrations
into the cochlea. The stapes pulls and
pushes on the oval causing the lymphs to
move
–
•
•
This movement causes waves through out the cochlea
Has a bony core with the bony shelf that
winds about the core in a spiral
The organ of Corti – where the hearing
receptors stretches from the apex to the
base of the cochlea
–
–
Hair like cells detect the changes in the lymph
Two levels of sensitivity
Equilibrium
•
2 types
–
Static equilibrium
•
–
Sense the head and maintain stability and
posture when head and body are still
Dynamic equilibrium
•
Detects motion and aids in maintaining
balance when head and/or body moves or
rotates
Static Equilibrium
•
Organs are located in the vestibule
–
A bony chamber in between the cochlea
and the semicircular canals has two
chambers
•
•
–
Utricle and saccule
Macule – structures in the chambers that
contain the sensory receptors (hairs) and
gelatinous material, and otoliths (CaCO4)
Hairs project into a mass of gelatinous
material. When the gelatinous material
moves and bends the hairs, the brain is
told of the change of position of the head
Dynamic Equilibrium
•
Organs are in the semicircular canals
–
•
Lie at right angles to each other,
corresponding to a different anatomical
plane
Crista ampullaris
–
Contains sensory hair cells and supporting
cells
•
–
–
Inside a gelatinous mass called cupula
Responds to rapid turns of head or body
Gelatinous material doesn't move, but hair
cells do.
Sense of sight
•
Organs
–
–
Eyes – has the visual receptors
Accessory organs to help out
The Accessories
•
The orbital cavity
–
–
•
Pear shaped cavity in the skull
Has fat, blood vessels, nerves, and
connective tissues
Eyelid
–
4 layers
•
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Skin, Muscle, Connective tissue, conjuntiva
The conjunctive is a mucous membrane
that lines the inner surface of the eyelid and
the fold to cover the anterior surface of the
eyeball, except the center section
Another accessory
•
Lacrimal apparatus
–
Lacrimal gland - produces tears
•
•
–
Located in the orbit (eye socket)
Contains lysozyme – an antibacterial agent
Series of ducts•
Lateral and medial ducts empty into the
lacrimal sac which then goes to the
nasolacrimal duct
Last one
•
Extrinsic Muscles
– 6 of them, moves the eyes in specific
directions
•
•
•
•
•
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Superior rectus – upward, towards midline
Inferior rectus- downward, towards midline
Medial rectus- towards midline
Lateral rectus- away from midline
Superior oblique- downwards, away from
midline
Inferior oblique – upward, away from
midline
•
Three layers
–
Outer layer
•
•
•
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The eye
Sclera – white of the eye
Optic nerve – attached to the back of eye
Cornea – clear window
Middle layer
•
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•
•
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Choroid coat -honeycombed, lots of blood
vessels, melanocytes to absorb excess light
Ciliary body – extends from choroid coat to the
front of the eye, forming an internal ring
Lens – transparent, focus light on retina
Iris – extends form ciliary body to the pupil,
muscle
Aqueous humor – liquid from the ciliary body to
the cornea
Pupil – hole in the eye that lets light in.
•
Inner layer
–
Retina – contains the visual receptors
•
•
•
–
Macual is the central region of the retina
Fovea – depression in the middle that provides
the clearest images
Optic Disc
•
•
–
Coats inner surface of the eye, end just behind
the ciliary body
Rods- see in greyscale
Cones – see color; three types – red, green ,
blue
Fovea centralis and Macula Lutea
•
•
–
Last layer
Where the nerve fibers go in the optic nerve
The blind spot in the eye
Vitreous humor
•
Jelly like fluid inside the eye