Somatic and Special Senses

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Somatic and Special Senses

• Anatomy and Physiology

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The Pathway

• Sensory receptor gets stimulated
• Triggers a nerve impulse (wave of depolarization)
• Impulse sent to the brain
• You feel a sensation
• Sensation a feeling that occurs when brain
  interprets electrical impulses

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Sensory receptors stimulated by different and
specific things

• Chemoreceptors chemicals
• Pain receptors tissue damage
• Thermoreceptors temperature change
• Mechanoreceptors pressure or movement
• Photoreceptors light

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Chemoreceptors

• Taste
• Smell
• CO2 and O2 levels in the blood

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Pain Receptors

• Consist of free nerve endings
• Widely distributed in the skin
• Not so accurate in the viscera
• No pain receptors in the brain

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Referred Pain

• Feels as though the pain is coming from somewhere
  else
• Example a person might feel pain in the left
  arm during a heart attack
• Several body parts use the same nerve pathways

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Thermoreceptors

• Two kinds
• Heat receptors
• Cold receptors
• Hot and cold extremes also stimulate pain
  receptors

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Mechanoreceptors

• Pressure or movement
• Free nerve endings
• Meissners corpuscles are sensitive to light
  touch
• Pacinian corpuscles are sensitive to heavy
  pressure

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Meissners corpuscle
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Pacinian corpuscle
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Photoreceptors

• Sensitive to light
• Only found in the eye
• Rods and Cones

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Sensory Adaptation

• When receptors continue to be stimulated, they
  stop sending the nerve impulse
• Particularly noticeable with smell
• Pain receptors adapt poorly, if at all

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What makes one sensation different from another?

• All nerve impulses are the same
• They are simply waves of depolarizationelectrical
  signals
• Depends on which area of the brain receives the
  impulse

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Sense of Smell

• Chemoreceptors
• Chemicals dissolved in liquid stimulate them
• Olfactory is associated with smell
• Smell and taste function together

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Olfactory Receptors

• Olfactory organs in the upper part of the nasal
  cavity contain the olfactory receptors
• The receptors are surrounded by columnar
  epithelial cells
• Cilia cover the dendrite ends

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Olfactory Receptors
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Olfactory Receptors
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The nerve pathway

• Receptors send impulses to neurons in the
  olfactory bulb
• Olfactory nerve tracts take the impulse from the
  bulb to temporal and frontal lobes
• Brain interprets the receptor combinations as an
  odor

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The Brain Areas
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Not everyone can smell!

• 2 million people in the U.S. have no sense of
  smell
• This condition is called anosmia
• Usually due to damage in the olfactory nerves,
  but could also be frontal lobe damage

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Sense of Taste

• Chemoreceptors
• Receptors are in the taste buds
• Taste buds are part of tiny elevations (bumps) on
  the tongue called papillae

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Taste buds are in the folds of the papillae
papilla
Taste bud
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Taste Buds
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The Four Taste Sensations

• Sweet
• Sour
• Salty
• Bitter
• Taste can be a
• combination of
• these

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The Pathway

• Taste receptors send nerve impulses along three
  cranial nerves into the medulla oblongata
• From there it goes to the thalamus (relay center)
  to the parietal lobe

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Hearing

• Involves mechanoreceptors
• Vibration stimulates the tiny hairs mechanically
• Chain reaction sends the vibrations to the inner
  ear

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Hearing

• Ear is divided into three sections outer,
  middle, and inner
• Outer ear consists of auricle (pinna), external
  auditory canal (meatus), up to the eardrum
  (tympanic membrane)

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Hearing

• Function of the auricle is to gather sound waves
  into the ear
• Sound waves travel through the external auditory
  canal
• Sound waves vibrate the eardrum

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Hearing

• In the middle ear, there are three bones called
  ossicles.
• They are lined up end to end.
• The vibrating eardrum causes the first bone to
  vibrate, then the second, then the third.

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Hearing

• The first bone is the malleus (hammer), then the
  incus (anvil), then the stapes (stirrup)

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Hearing

• The stirrup pushes on another membrane called the
  oval window
• This is the entrance into the inner ear
• Real hearing takes place in the inner ear

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Hearing

• The oval window is smaller than the tympanic
  eardrum (eardrum)
• So there is more force per unit area, resulting
  in amplification of the vibrations

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Hearing

• Oval window is touching the cochlea, the real
  organ of hearing
• Chochlea is snail shaped
• Inside the cochlea is the Organ of Corti, which
  contains the actual hearing receptors

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Hearing

• The actual hearing receptors are hair cells
  inside the cochlea
• The hair cells are attached to membranes. When
  the membranes vibrate, the hair cells are bent.
• This triggers the attached neuron to depolarize,
  sending the impulse to the temporal lobe of the
  brain

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Hearing

• Different frequencies of sound waves vibrate
  different parts of the membrane.
• This causes different neurons to be stimulated,
  allowing us to hear different sounds

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Loss of Hearing

• In older people, the membranes become less
  flexible
• Could be damage to the auditory nerve or the
  cochlea
• Loud noises or music can speed up the loss of
  hearing

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Ear Infections

• Common in young children
• Auditory tube connects the throat with the middle
  ear
• Cold, sore throat, infection may spread into ear

Normal eardrum
Infected eardrum
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Balance and Equilibrium

• Inner ear also controls balance and equilibrium
• Static equilibrium senses the position of the
  head and posture when the body is still
• Dynamic equilibrium involves moving

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Balance and Equilibrium

• Static equilibrium is controlled by the
  vestibule, a structure located between the
  cochlea and the semicircular canals.

Vestibule
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Balance and Equilibrium

• In the vestibule, hairs of sensory neurons stick
  up into a gel material. Moving the head forward,
  backward, or to one side stimulates the hair
  cells. They send a nerve impulse to the brain.
  The brain controls muscles to maintain balance.

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Balance and Equilibrium
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Balance and Equilibrium

• Dynamic equilibrium is controlled by the
  semicircular canals
• The three semicircular canals are at right angles
  to each other, making them in different planes
• Contain hair cells (receptors) and fluid
• When body moves, the canals move, but the fluid
  stays stationary, bending the hairs

The hair cells (sensory neurons, send impulses to
the brain. The brain interprets and adjusts to
maintain balance.
Seasick
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Balance and Equilibrium
Vertigo a sensation of dizziness You are not
moving, but your eyes send a message that you are.
Causes inner ear infection, or in roller
coasters, motion sickness, receptors and brain
cannot compensate for abnormal movements
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Balance and Equilibrium

• Other structures help in maintaining equilibrium.
  Special mechanorecptors called proprioceptors
  detect body position. The eyes also send
  information about body position.