Introduction to Health Science

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Introduction to Health Science

• Special Senses

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Cranial Nerves
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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

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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
• Putrid (rotting food)
• Pungent (spicy)
• Floral (flowers)
• Ethereal (medicine smell)
• Mint

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Taste

• Occurs when specialized cells on the tongue
  (chemoreceptors) detect chemicals
• Results in nerve impulses being sent to the brain
  for interpretation

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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
• Sweet (sugars and carbohydrates)
• Sour (acids)
• Salt (salt)
• Bitter (caffeine)
• Umami (protein and amino acids)

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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!

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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

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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)

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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

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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

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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

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Outer Ear

• Auricle
• 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

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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

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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

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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

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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

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• Learning Log
• What problems could we have with our senses?
• What would cause those problems?

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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

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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

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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

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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

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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