Vocabulary Terms: Review
• Stimulus- anything from inside or
outside the body that can cause a
response in a nerve, muscle, gland, or
other tissue.
• Sensation- conscious awareness of
stimuli received by sensory receptors in
the nervous system.
Classification of Receptors: Review
1. Mechanoreceptors- activated by
mechanical stimuli or deformation of the
receptor
2. Chemoreceptor- changing of the chemical
concentrations around the body
3. Thermoreceptors- detect hot and cold
4. Nociceptors- any stimuli that can cause
tissue damage; sensation of pain
5. Photoreceptors- respond to light
Characteristics of Sensations
• Projection- brain refers a sensation to the
point of stimulation
• Adaptation- loss of sensation even though
the stimulus is still applied
• Afterimage- persistence of a sensation
even though the stimulus is removed
• Referred pain- felt in the skin near or
around the organ sending the impulse
• Phantom pain- sensation of pain in a limb
that has been amputated
Somatic Senses
pain, temperature and touch
• These sensations can be felt throughout
the body, yet they are distributed unevenly
through the skin.
• Exteroceptors- sense receptors located on
body surfaces
• Proprioceptors- found in the muscles and
joints
• Visceroceptors- found in internal organs
• Nociceptors- pain receptors; free nerve
endings
Review For Touch & Pressure
•
•
•
•
Meissner’s corpuscles- touch
Krause’s End Bulbs- touch
Ruffini’s corpuscles- continuous touch
Pacinian corpuscles- deep pressure
Types of Somatic Senses
• General senses- widely distributed
throughout the body
– Touch
– Pain
– Pressure
– Temperature
– Vibration
– Itch
– Proprioception
Pain
• Types of pain:
– Sharp, localized pain
– Diffused, burning, aching pain
• Anesthesia:
– Local- one area
– General- throughout the body
• Gate control theory- distraction of
pain receptors does not allow pain to
intensify or continue at a high level
Nose
Olfaction- Smell
• Sense of smelloccurs in response
to airborne
molecules
• Pathway of smellnasal cavity,
olfactory neurons,
olfactory bulb,
olfactory tracts,
olfactory cortex in
brain
Olfaction- Smell
Olfaction: Sense of Smell
• Odorants bind to
receptors
• Depolarization
occurs
• Nerve impulse is
triggered
Cells of the Olfactory Membrane
• Olfactory receptors
– neurons with cilia or
olfactory hairs
• Supporting cells
– columnar epithelium
• Basal cells = stem
cells
– replace receptors
monthly
• Olfactory glands
– produce mucus
Olfactory Epithelium
• 1 square inch of
membrane holding
10-100 million
receptors
• Covers superior
nasal cavity
• 3 types of
receptor cells
Tongue
Gustation: Taste
• Taste buds- sensory structures that
detect stimuli of taste
– On papillae, enlargements on surface of
tongue
– Taste cells—interior of each taste bud
– Taste hairs—on each taste cell that
extends to taste pore
– Send signal to brain based on where they
are felt on the tongue
Physiology of Gustation
• Complete adaptation in 1 to 5 minutes
• Thresholds for tastes vary among the 4
primary tastes
– most sensitive to bitter (poisons)
– least sensitive to salty and sweet
• Mechanism
– dissolved substance contacts gustatory hairs
– receptor potential results in
neurotransmitter release
– nerve impulse formed
Anatomy of Taste Buds
• An oval body consisting
of 50 receptor cells
surrounded by
supporting cells
• A single gustatory hair
projects upward
through the taste pore
• Basal cells develop into
new receptor cells
every 10 days.
Gustatory Sensation: Taste
• Taste requires dissolving
of substances
• Four classes of stimuli-sour, bitter, sweet, and
salty
• 10,000 taste buds found
on tongue, soft palate &
larynx
• Found on sides of papillae
• Taste and olfaction
combine to give some
tastes
More on Gustation
• Four taste sensations:
– Sour
– Salty
– Bitter
– Sweet
• Taste and olfaction combine to give
some tastes
• All taste buds can sense each sensation,
but preferable to one sensation
Visual Interpretation of
Taste
Buds
Gustation
Eye
Anatomy:
Accessory Structures of Eye
• Accessory structures:
– Eyebrows—prevent
perspiration in eye, shades
eye
– Eyelids—protect from
foreign objects, blinking
reflex; lubrication
– Conjunctiva—mucous
membrane that covers the
inner surface of eyelids
– Lacrimal apparatus—
produces tears
– Extrinsic eye muscles—
eye movements
Anatomy: Lacrimal Apparatus
• About 1 ml of tears produced per day. Spread over eye by
blinking. Contains bactericidal enzyme called lysozyme.
Anatomy: Eye
• Hollow, fluid-filled
sphere
• Fibrous tunic—outer
– Sclera & cornea
• Vascular tunic—
middle
– Choroid, ciliary body,
& iris
• Nervous tunic—inner
– Retina
Anatomy: Tunics and Parts of the Eye
Anatomy:
Cavities of the Interior of Eyeball
• Anterior cavity (anterior to lens)
– filled with aqueous humor
• produced by ciliary body
• continually drained
• replaced every 90 minutes
• Posterior cavity (posterior to lens)
– filled with vitreous body (jellylike)
– formed once during embryonic life
never make more
– floaters are debris in vitreous of older
individuals
Anatomy: Fibrous Tunic
• Sclera
– “White of the eye”—only small part seen
– Maintains the shape of eye, protects
internal structure, provides attachment
sites for muscle attachment
• Cornea
– Permits light into the eye
– Bends or refracts entering light
– Transparent, anterior 1/6th of eye
Anatomy:Vascular Tunic
• Choroid-thin structure in back of eye
containing melanin cells; helps avoid reflection
in the eye
• Ciliary body-contains smooth muscles
attaching the lens; in front of choroid
• Iris-colored part of eye
• Lens-flexible, biconvex, transparent disc
• Pupil-smooth muscle that controls the amount
of light let into the eye
Anatomy: Nervous Tunic
• Retina—back of eye
– Rods—20 times more than cones
• Very sensitive to light
• Can function in very dim light
– Cones—require a lot of light
• Provide color vision
• Three types:
– Red, blue, green
Anatomy: Rods & Cones--Photoreceptors
Physiology: Sight
• Night blindness- lack of
vitamin A; difficulty
seeing in dim light
• Optic nerve- provides
stimulus to brain
optic disc- where
nerves leave the retina
• Blind spot- part of the
optic disc that does not
respond to light and
contains no
photoreceptors
Physiology: Eye
• Light refraction—bending of light
– Focal point: crossing point of light
• Focusing images on retina
– Depending on how far away the object is
from the retina, the muscles of the eye and
lens help to focus and adjust until the
object is focused clearly.
Physiology: Major Processes of Image Formation
• Refraction of light
– by cornea & lens
– light rays must fall upon the retina
• Accommodation of the lens
– changing shape of lens so that light is focused
• Constriction of the pupil
-less light enters the eye
• Convergance- both eyes focusing on one
object so we only see one imageSingle Binocular Vision
Physiology: Accommodation & the Lens
• Convex lens refract light rays towards each
other
• Lens of eye is convex on both surfaces
• View a distant object
– lens is nearly flat by pulling of suspensory
ligaments
• View a close object
– elastic lens thickens as the tension is removed
from it
– increase in curvature of lens is called
accommodation
Eye Disorders
•
•
•
•
•
•
•
•
•
Conjunctivitis
Myopia
Presbyopia
Hyperopia
Astigmatism
Strabismus
Color blindness
Cataract
Retinal detachment
Normal, nearsightedness,
and farsightedness
•
Nearsightedness results in blurred vision
when the visual image is focused in front
of the retina, rather than directly on it.
It occurs when the physical length of the
eye is greater than the optical length.
For this reason, nearsightedness often
develops in the rapidly growing schoolaged child or teenager, and progresses
during the growth years, requiring
frequent changes in glasses or contact
lenses. A nearsighted person sees near
objects clearly, while objects in the
distance are blurred.
•
Normal vision occurs when light
is focused directly on the
retina rather than in front or
behind it. A person with normal
vision can see objects clearly
near and faraway.
•
Farsightedness is the result of
the visual image being focused
behind the retina rather than
directly on it. It may be caused
by the eyeball being too small or
the focusing power being too
weak. Farsightedness is often
present from birth, but children
can often tolerate moderate
amounts without difficulty and
most outgrow the condition. A
farsighted person sees faraway
objects clearly, while objects
that are near are blurred
Near Point of Vision
• Near point is the closest distance from the eye an
object can be & still be in clear focus
– 4 inches in a young adult
– 8 inches in a 40 year old
• lens has become less elastic
– 31 inches in a 60 to 80 year old
• Reading glasses may be needed by age 40
– presbyopia
– glasses replace refraction previously provided by
increased curvature of the relaxed, youthful lens
Ear
Introduction to the Ear:
Basic AnatomicalTerms
•
•
•
•
•
•
•
•
Pinna— Elastic cartilage; funnel sound waves
Auditory canal – tunnel
Tympanic membrane— eardrum; vibrates ossicles
Ear ossicles— malleus, incus, stapes; which amplify sound waves
Two membranes in inner ear— oval window, round window
Cochlea- “houses organ for hearing”
Semi-circular canals – “center” for balance
Eustachian tube— connects ear to throat; “equalization of pressure”
Anatomy: Outer Ear
• External ear
– Auricle-fleshy part
of ear
– External auditory
meatus-passageway
to eardurm
– Eardrum-sound waves
cause it to vibrate
Anatomy: Middle Ear
• Middle ear-medial
– Malleus-attached to
eardrum
– Incus-between
malleus & stapes
– Stapes-after incus;
vibrations amplified
20x
– Auditory tube- opens
to pharynx & enables
air pressure to be
equalized outside & in
Middle ear
Auditory tube
Anatomy: Middle Ear Cavity
Anatomy: Inner Ear
• Inner ear- tunnels & chambers called
bony labyrinth
– Membranous labyrinth- filled with clear
fluid
– Bony labyrinth:
• Cochlea- involved in hearing
• Vestibule- involved in primary balance
• Semicircular canals- involved in primary balance
Anatomy: Inner Ear
Physiology: Auscultation
• Sound waves are collected by auricle
and conducted through the external
auditory meatus to the eardrum causing
it to vibrate
• Eardrum vibrations cause the malleus,
incus, & stapes to vibrate
• Vibration causes cochlear membrane to
vibrate
• Microvilli in cochlear membrane bend
Physiology: Auscultation
• Microvilli bending causes depolarization
of hair cells
• Hair cells send impulse in cochlear
neurons
• Cochlear neurons send impulse to CNS
• Impulse is translated in cerebral cortex
as sound
Physiology of Auscultation:
Tubular Structures of the Cochlea
Distinguishing Different Sounds?
• Sounds at different frequencies vibrate different
portions of the basilar membrane
– high pitched sounds vibrate the stiffer more basal
portion of the cochlea
– low pitched sounds vibrate the upper cochlea which
is wider and more flexible
• Loud sounds vibrate cause a greater vibration of the
basilar membrane & stimulate more hair cells which
our brain interprets as “louder”
Deafness
• Nerve deafness
– damage to hair cells from antibiotics, high
pitched sounds, anticancer drugs
• the louder the sound the quicker the hearing
loss
– fail to notice until difficulty with speech
• Conduction deafness
– perforated eardrum
– otosclerosis
Equilibrium
• AKA balance
• Static equilibrium- vestibule evaluating
position of head due to gravity
• Kinetic equilibrium- semicircular canals
evaluating the change in rate of head
movements
• Movement of fluid in the ears and hair cells
tries to “catch up” with actual movements.
When it does, we are equilized.
Detection of Rotational Movement
• When head moves, the attached semicircular ducts and hair
cells move with it
– endolymph fluid does not and bends the cupula and enclosed hair
cells
• Nerve signals to the brain are generated indicating which
direction the head has been rotated