Human Anatomy and
Physiology II
Special Senses
All senses work the same way:
Receptors collect information
stimulate neurons
information is sent to the brain
the cerebral cortex integrates the
information with that from other senses
forms a perception (a person’s particular
view of the stimulus)
Receptor types:
 Pain receptors or nociceptors – respond to
tissue damage due to mechanical, electrical,
thermal or chemical energy
 Thermoreceptors
– respond to temperature change
Receptor types:
 Mechanoreceptors – respond to mechanical forces,
such as pressure or fluid movement; changes
usually deform the receptor
 Proprioceptors – sense changes in muscles and
tendons
 Baroreceptors – in blood vessels – detect changes in
pressure
 Stretch receptors – in lungs – sense degree of
inflation
Receptor types:
 Photoreceptors -respond to light – as little as
one photon
 Chemoreceptors – sensitive to chemical
concentration of various substances
Receptors are structured in two basic ways:
• receptors can be nerve endings
• other kinds of cells which are associated with nerve
endings
•When these are stimulated, they produce graded
potentials. If hit threshold, nerve fires.
A sensation or perception occurs when the brain
interprets the incoming nerve impulses.
All impulses coming into the brain are alike.
The sensation depends on which part of the brain
is stimulated.
Synesthesia – tasting, colors, etc.
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Involuntary: synesthetes do not actively think about their
perceptions; they just happen.
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Projected: rather than experiencing something in the "mind's eye," as
might happen when you are asked to imagine a color, a synesthete
often actually sees a color projected outside of the body.
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Durable and generic: the perception must be the same every time; for
example, if you taste chocolate when you hear Beethoven's Violin
Concerto, you must always taste chocolate when you hear it; also, the
perception must be generic -- that is, you may see colors or lines or
shapes in response to a certain smell, but you would not see
something complex such as a room with people and furniture and
pictures on the wall.
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Memorable: often, the secondary synesthetic perception is
remembered better than the primary perception; for example, a
synesthete who always associates the color purple with the name
"Laura" will often remember that a woman's name is purple rather
than actually remembering "Laura."
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Emotional: the perceptions may cause emotional reactions such as
pleasurable feelings.
Who has synethesia
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Women: in the U.S., studies show that three times as many
women as men have synesthesia; in the U.K., eight times as
many women have been reported to have it. The reason for this
difference is not known.
Left-handed: synesthetes are more likely to be left-handed
than the general population.
Neurologically normal: synesthetes are of normal (or
possibly above average) intelligence, and standard neurological
exams are normal.
In the same family: synesthesia appears to be inherited in
some fashion; it seems to be a dominant trait and it may be on
the X-chromosome.
7, 9, 4, 0, 3, 8, 2, 5, 1,
6.
Developmental Aspects of
the Special Senses
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Special sense organs are formed early in embryonic development. Maternal infections
during the first five or six weeks of pregnancy may cause visual abnormalities as well as
sensorineural deafness in the developing child. An important congenital eye problem is
strabismus. The most important congenital ear problem is lack of the external auditory
canal.
Vision requires the most learning. The infant has poor visual acuity (is farsighted) and
lacks color vision and depth perception at birth. The eye continues to grow and mature
until the eighth or ninth year of life,
Problems of aging associated with vision include presbyopia, glaucoma (the most
common cause of blindness in the U.S.), cataracts, and arteriosclerosis of the eye's
blood vessels.
The newborn infant can hear sounds, but initial responses are reflexive. By the toddler
stage, the child is listening critically and beginning to imitate sounds as language
development begins.
Sensorineural deafness (presbycusis) is a normal consequence of aging.
Taste and smell are most acute at birth and decrease in sensitivity after the age of 40 as
the number of olfactory and gustatory receptors decreases.
Sensory adaptation
The only receptors that don’t adapt are:
pain receptors
Somatic Senses:
Exteroceptive senses – changes at
body surface
Proprioceptive senses – changes in
muscles and tendons and body
position
Visceroceptive senses – changes in
viscera(The internal organs of the
abdomen and thorax; specifically, the hollow
Organs such as intestines, bladder, etc.)
Touch and pressure senses:
1. Free nerve endings – touch and pressure
2. Meissner’s corpuscles – light touch
receptors are connective tissue
3. Pacinian corpuscles – heavy pressure
and vibrations receptors are connective tissue
Itch and Tickle:
Receptors are free nerve endings
Temperature senses:
Free nerve endings in skin
 Heat receptors –
respond primarily between 25 – 45 o C or 77 – 113 o F
unresponsive above, but pain receptors
fire = burning
 Cold receptors –
respond primarily between 10 – 20 o C or 50 - 68 o F
unresponsive below, but pain receptors
fire = burning
Pain
 Also free nerve endings
 Most pain receptors can be stimulated by more than
one stimulus, although some are more sensitive to
mechanical damage, and others to extreme
temperature, or chemicals.
 Deficiency of blood flow (ischemia) and thus a deficiency
of oxygen (hypoxia) can stimulate pain receptors.
Visceral pain:
Pain receptors are the only receptors in the
viscera that produce sensations.
Tends to be referred pain – feels as though it
comes from elsewhere – due to common nerve
pathways
Phantom pain – comes from a limb that has been amputated.
Pain fibers are of two types:
Acute pain fibers ( A or delta fibers) – thin, myelinated fibers
(Conducts up to 30 meters/sec)
Sharp, localized pain
Seldom continues after stimulus stops
Chronic pain fibers (C fibers) – thin, unmyelinated fibers
(conduct up to 2 meters per second)
Dull, aching and widespread pain
May continue for some time after stimulus
Stretch receptors:
•We know how our body parts are moving
through our proprioceptive or kinesthetic sense.
•These receptors adapt only slightly
•Keep brain informed of the status of body
parts to insure coordination.
•Use specialized receptors that sense tension in
tendons and muscles.
•No sensation occurs when these are stimulated.
Muscle spindles sense stretching
of muscle, and cause contraction
Of the muscle to maintain position.
Golgi tendon organs sense stretching of
tendons and cause the muscle to relax
to prevent damage to the tendon.
Special Senses
Olfactory sense –
The sense of smell
Both smell and taste use chemoreceptors.
Of all the senses, only smell and taste have
fibers that run to both cortical areas
And the limbic system.
Olfactory receptors are bipolar neurons.
•Are replaced throughout lifetime, but lost at the
rate of about 1 % per year.
•The cilia, or olfactory hairs are the sensitive portions
•Chemical must be dissolved in watery mucus to
stimulate the receptor.
•Combinations of primary scents allow us to recognize
thousands of different odors.
Gustatory sensations : Taste
Uses chemoreceptors
Substance must be dissolved before can be detected
Detects 4 basic sensations:
salty, sour, sweet and bitter
Also may have receptors for alkaline, metallic,
umami (Savoriness found in fermented and aged foods )
and water!
3, 6, 5, 9, 4, 1, 7, 0, 5,
2, 8.
Auditory sensations and Equilibrium
Hearing and equilibrium rely on mechanoreceptors
The ear is divided into three parts:
• Outer ear
• Middle ear
• Inner ear
Outer ear:
• Ceruminous glands – Cerumen
- ear wax in external auditory meatus
•Outer ear structures are the pinna (auricle), external auditory canal, and
tympanic membrane (eardrum). Sound entering the external auditory
canal sets the eardrum into vibration. These structures are involved
with sound transmission only.
Middle ear:
•Tympanic antrum – opening into mastoid process
•Auditory (Eustachian) Tube
•Otitis media – inflammation of the MIDDLE ear
•Auditory ossicles or ear bones
•Tensor tympani muscle
•Stapedius muscle
•Tympanic reflex
•The ossicles (malleus, incus, and stapes)transmit the vibratory
motion from the eardrum to the oval window. The auditory tube allows
pressure to be equalized on both sides of the eardrum. These
structures are also involved with sound transmission only.
INNER EAR : Bony chambers
• Cochlea – hearing
• Vestibule – static equilibrium
• Semicircular canals – dynamic equilibrium
•The bony labyrinth contains perilymph and membranous sacs filled
with endolymph. Within the membranous sacs of the vestibule and
semicircular canals are equilibrium receptors. Hearing receptors are
found within the membranes of the cochlea.
 Hair cells of the organ of Corti (the receptor for hearing within the
cochlea) are stimulated by sound vibrations transmitted through air,
membranes, and fluids
 Deafness is any degree of hearing loss. Conduction deafness results
when the transmission of sound vibrations through the external and
middle ears is hindered. Sensorineural deafness occurs when there is
damage to the nervous system structures involved in hearing.
 Receptors of the semicircular canals (cristae) are dynamic equilibrium
receptors, which respond to angular or rotational body movements.
Receptors of the vestibule (maculae) are static equilibrium receptors,
which respond to the pull of gravity and report on head position.
Visual and proprioceptor input are also necessary for normal balance.
 Symptoms of equilibrium apparatus problems include involuntary
rolling of the eyes, nausea, vertigo, and an inability to stand erect.
Organ of Corti
•Vestibulocochlear nerve – cranial nerve VIII
•Audible range: 20 -- 20,000 hertz
•Ossicles amplify sound 22 X
•Some nerve fibers cross over to opposite
side of brain; some don’t. Why?
Equilibrium – Balance
Static equilibrium – maintenance of body
posture relative to gravity while the body is
still.
Dynamic equilibrium – maintenance of
the body posture (mainly the head) in
response to sudden movements. Tracking
a moving object.
Static Equilibrium
•Inside the vestibule are two chambers :
utricle and saccule.
•Regions of hair cells and supporting
cells called maculae.
•Otoliths – “ear rocks”
Dynamic Equilibrium
•Semicircular canals
•In ampulla is the crista ampullaris –
contains hair cells and supporting cells
covered by a gelatinous mass called the
cupula.
•Neurological connections between eyes
and semicircular canals – for tracking
•Nystagmus
The Eye
Accessory structures or Adnexa
4 layers:
1. Skin – thinnest in the body
2. muscle – orbicularis oculi and
levator palpebrae superioris
3. Connective tissue – tarsal plate
contains tarsal or Meibomian glands Chalazion
4. Conjunctiva – mucous
membranpalpebral conjunctiva, bulbar
conjunctiva
Eyelashes
sebaceous ciliary glands at base of hair
follicles – hordeolum or stye
Lacrimal apparatus – forming and draining
tears.
Strabismus – turned eye
Phoria – weakness of eye muscles
Eyeball – 3 layers or tunics:
1. Fibrous tunic (outer tunic)
Cornea – clear - avascular
Scleara – white –means “hard”
2. Vascular tunic : Uvea
Choroid – blood vessels and pigment
Ciliary body :
ciliary processes make aqueous humor
ciliary muscle - accomodation
Accommodation:
Focusing the eye to see close objects
Lens is thin when stretched by suspensory
ligaments (low power)
When round ciliary muscle contracts, tension is
released from lens and it becomes thicker
(higher power lens).
Lens – avascular, clear, elastic
contains proteins called crystallins
becomes opaque = cataract
Iris – pigmented, divides anterior and
posterior chamber
Aqueous humor – drains into scleral
venous sinus (Schlemm’s canal)
intraocular pressure - glaucoma
3. Nervous Tunic – Retina several layers
“inside out”
•Pigmented epithelium
•Rods and Cones (photoreceptors)
•Bipolar cells
•Ganglion cells
(vitreous humor)
•Light is focused by cornea and lens on
the Fovea centralis (“central pit”)which is in the
center of the Macula lutea (“yellow spot”)
The third refractive component is the
length of the eyeball.
Refractive Disorders
Emmetropia – good vision 20/20
Myopia – nearsightedness
Hyperopia – farsightedness
Astigmatism – light does not focus to a single
point on the retina
Presbyopia – “old sight” – loss of ability to
accommodate or see up close
Physiology of vision
In the dark, Na+ channels are held open by a
nucleotide called cyclic GMP (guanosine
monophosphate)
Inflow of sodium (“dark current”) triggers the
continual release of neurotransmitter .
This neurotransmitter is inhibitory- it prevents
bipolar cells from firing by hyperpolarizing
them.
When light strikes the retina, retinal (from
vitamin A) which is bent, straightens out,
and no longer fits into the opsin.
The two separate – this is called bleaching.
The opsin becomes an active enzyme, that
activates other enzymes that break down
cyclic GMP.
Without cyclic GMP, the Na+ channels
close.
The receptor hyperpolarizes, stopping the
release of inhibitory neurotransmitter.
This decrease in inhibition allows the bipolar
cells to fire, and information is sent to the
visual cortex.
Differentiation of color is assisted by
horizontal cells.
In darkness, retinal isomerase converts transretinal back to cis-retinal, which binds with
opsin forming a functional photopigment.
Color vision
Uses three different photopigments :
blue, green and red
Wavelength of pigments may be shifted, causing
color blindness
Red – green color blindness most common
Sex-linked trait carried on X chromosome
(Males only have one gene for color vision)
Stereopsis
Use both eyes to perceive depth – “depth
perception”
Nasal fibers cross at the optic chiasm
Temporal fibers do not cross over
Each visual cortex (R &L) receives
information from both eyes so it can compare
what each eye sees.