Download Introduction to Health Science

Introduction to Health Science
Special Senses
Cranial Nerves
Description of the Special Senses
• Smell
– Occurs when specialized cells in the nose
(chemoreceptors) detect chemicals
– Results in nerve impulses being sent to the brain
for interpretation
Nose
• In the upper part of the nasal cavity are specialized nerve cells
called olfactory receptor cells
• These receptor cells contain hair called cilia to which the dissolved
chemicals attach
• Transmitted from the olfactory receptors cellsolfactory
bulbolfactory nervebrain
• Sense of smell is interpreted then sent back to nasal cavity
• Basic smells include
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Putrid (rotting food)
Pungent (spicy)
Floral (flowers)
Ethereal (medicine smell)
Mint
Taste
• Occurs when specialized cells on the tongue
(chemoreceptors) detect chemicals
– Results in nerve impulses being sent to the brain
for interpretation
Mouth and Tongue
• The sense organs that detect dissolved chemicals for the
sense of taste are the taste buds
– Located in the tongue and throughout the mouth
• When the taste buds are stimulated by chemicals, they
generate nerve impulses which are sent to the brain for
interpretation
• There are five basic tastes, although they are not limited to
specific parts of the tongue:
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Sweet (sugars and carbohydrates)
Sour (acids)
Salt (salt)
Bitter (caffeine)
Umami (protein and amino acids)
Vision
• The sense organs that respond to light are the
eyes
– The light waves travel through the eyes until they
reach the back of the eye called the retina
– Nerve impulses are generated by specialized cells
that are sensitive to light (photoreceptors)
– Nerve impulses travel to the brain
– Interpreted as visual images
– Provide much information about the external
world
– If there is no light, there is no sight!
Eye
• Eyelid
– Structures composed of skin, muscles, and lashes
– Protect the eye from foreign objects by the blink
reflex
– Moves tears along the surface of the eyeball to
keep the eyeball moist
• Conjunctiva
– Membrane lining the insides of the eyelids and
eyeball
– Reduces friction during blinking
Eye
• Sclera
– The white part of the eye
– Provides protection and shape to the eye
• Cornea
– The clear window of the front part of the eye
– Allows light waves to enter the eye
– Helps to bend the light waves on to the back of
the eye (retina)
Eye
• Iris
– The colored portion of the eye which contains two
sets of muscles
– Regulates the size of the pupil to control the amount
of light entering the eye
• Pupil
– An opening in the center of the iris
– Passage for light
• Lens
– Transparent disc shaped structure located behind the
iris and pupil
– Focuses light waves on to the retina
Eye
• Retina
– Most inner layer of the eyeball
– Located under the sclera
– Contains the photoreceptors that when
stimulated by light generate nerve impulses which
are then sent to the brain for interpretation
• Optic Nerve
– Nerve that sends and receives impulses to and
from the brain
Hearing
• Involves the movement of sound vibrations
through the ear
– When they reach a specialized region in the inner
ear nerve impulses are generated by cells that
detect movement (mechanoreceptors)
– Nerve impulses travel to the brain where they are
interpreted as sound
Outer Ear
• Auricle
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The visible portion of the ear on the side of the head
Composed of cartilage
Captures sound waves from environment
Directs them toward the auditory canal
• Auditory Canal
– Tube lined with hair and wax
– Assists in the passage of sound waves to the middle
ear
– Provides protection for the ear as particles, debris and
dust are trapped by the hair and wax
Middle Ear
• Tympanic Membrane
– Known as the eardrum, it is the first structure of the
middle ear
– It vibrates with the sound waves and passes the
vibrations to the middle ear bones
• Auditory Ossicles
– Three tiny bones in the middle ear that continue the
passage of sound vibrations
– They also amplify the vibrations twenty times
• Eustachian Tube (auditory tube)
– Small tube extending from the middle ear into the
throat
– Helps to equalize pressure inside the ear
Inner Ear
• Cochlea
– Snail shaped structure
– Membrane-lined fluid-filled canals that continue
to pass along the sound vibrations
– Reach a specialized structure of the inner ear
called the Organ of Corti where nerve impulses
are generated
– The impulses are transmitted to the brain where
they are interpreted
• Vestibulocochlear Nerve
Touch
• Detection of various amounts of pressure by
the skin
• Nerve impulses are generated by cells that are
sensitive to movement (mechanoreceptors)
and sent to the brain for interpretation
Skin
• The skin contains several different types of nerve
receptors
– Sensitive to deep pressure like poking or light touch
• All regions of the skin are sensitive to touch
– The greatest number of touch receptors are found in the
fingers, toes, and face
• Once the nerve impulses for touch are generated,
they are sent to the brain for interpretation
• Learning Log
– What problems could we have with our
senses?
– What would cause those problems?
Disorders of the Special Senses
• Conjunctivitis
– Conjunctivitis is the
inflammation of the
conjunctiva
– Can be caused by viruses,
bacteria, fungi, and
allergies
– The most common cause is
viral
– ”Pinkeye” is the common
term for conjunctivitis
Middle Ear Infection (Otitis Media)
• Causes include anything that
causes the Eustachian (auditory)
tubes to become blocked,
inflamed or irritated
– Examples include colds, sinus
infections, allergies, tobacco smoke
– Babies who spend a lot of time
drinking in the supine position
• Most common symptom is
earache
• Treatment includes
– Antibiotics for bacterial infections
– Use of warm cloths and analgesics
to relieve pain
– Possible surgery if ear infections
recur frequently
Deafness
• Complete or partial loss of hearing in one
or both ears
• May be caused by a blockage of the
sound waves through the middle ear
– Wax build up, foreign objects, tumors or
other matter
– Generally improves once the blockage is
removed
• May also result from damage to the
nerves or to the Organ of Corti
– Usually irreversible and may progressively
get worse
• Treatment may include removal of the
blockage, hearing aids, or cochlear
implants
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Myopia
• Nearsightedness
– When a person sees near
objects clearly and distant
objects are blurred
• Physical length of the eye is
greater than the optical
length
• Symptoms include blurred
vision of distant objects,
squinting, eyestrain, and
sometimes headaches
• Treated with concave lenses
or LASIK surgery
Hyperopia
• Farsightedness
– A person sees far objects clearly
and near objects are blurred
• Physical length of the eyeball is
too small or the focusing
power of the lens is too weak
• Symptoms include blurred
vision of close objects, eye
strain, aching eyes, and
headaches while reading
• Treated with convex lenses
• Surgical options also available
Presbyopia
• Normal loss of power of the eye which
occurs as a consequence of aging
• Lens becomes less flexible and less able
to bulge or accommodate for near vision
• Symptoms are similar to those of
farsightedness and include:
– blurring of close objects
– eye strain
– holding objects further from the face to
focus
– headaches or fatigue from focusing on
close objects
• Treatments may include the use of
reading glasses or bifocals