Senses: Touch/Hot and Cold/Pain/Smell/Taste/Hearing

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SensesTouch/Hot and Cold/Pain/Smell/Taste/Hearin
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Introduction

• Our body is full of sensory receptor cells.
  Sensory receptor cells are nerve cells that
  detect a particular stimulus and trigger a nerve
  impulse in response, which is transmitted to the
  central nervous system.

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Types of Receptors

• There are five types of sensory receptors
• Chemoreceptors--sensory receptors that are
  stimulated by changes in the chemical
  concentration of substances
• Pain receptors--stimulated by tissue damage
• Thermoreceptors--stimulated by changes in
  temperature
• Mechanoreceptors--stimulated by changes in
  pressure or movement
• Photoreceptors--stimulated by light energy

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Sensation

• A sensation is a feeling that occurs when the
  brain interprets sensory impulses. All sensory
  impulses that travel away from sensory receptors
  are the same regardless of the kind of stimulus
  how a sensation is interpreted is determined by
  which region of the brain receives the impulse.
  When the brain receives the impulse, the brain
  then projects the sensation back to its apparent
  source.

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Sensory Adaptation

• Sometimes, when sensory receptors are
  continuously stimulated, the receptors adapt and
  start to send impulses more slowly until
  eventually, the receptors may stop sending
  signals. This is called sensory adaptation.

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Touch and Pressure

• The sense of touch involves three kinds of
  mechanoreceptors
• Sensory nerve fibers--found in skin, the ends of
  these nerve fibers are found in between skin
  cells. They detect sensations of touch and
  pressure.
• Meissners corpuscles--these sensory receptors
  are abundant in the hairless portions of the
  skin, such as the lips, fingertips, palms, soles,
  nipples, and external genital organs. They
  respond to the motion of objects that barely
  touch the skin, sense light touch
• Pacinian corpuscles--found in deeper portions of
  the skin, tendons, and ligaments. They are only
  stimulated by heavy pressure and are associated
  with the sensation of deep pressure.

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Hot and Cold

• There are two types of thermoreceptors
• heat receptors
• respond to warmer temps, most sensitive to
  temperatures above 77 degrees Fahrenheit and
  become unresponsive to temperatures above 113
  degrees Fahrenheit. Temperatures above 113
  degrees Fahrenheit stimulate pain receptors.
• cold receptors
• respond to colder temps, most sensitive to
  temperatures between 50 degrees Fahrenheit and 68
  degrees Fahrenheit. Temperatures below 50 degrees
  Fahrenheit stimulate pain receptors.

Both heat and cold receptors easily
undergo sensory adaptation.
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Pain

• Pain Receptors
• stimulated by tissue damage
• found in all skin and tissues except for nervous
  tissue in the brain. Headaches are caused by
  prolonged contraction of the muscles in the
  forehead, sides of the head, or back of the neck.
  They are also caused by the constriction or
  dilation of the cranial blood vessels. Both the
  muscles surrounding the brain tissue and also the
  blood vessels traveling in the brain contain
  nerves.

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Referred Pain

• Sometimes, pain may feel as if it is coming from
  some part of the body other than the part being
  stimulated. This is called referred pain.
  Referred pain often arises in nerve pathways that
  carry impulses from skin areas that are
  stimulated often and organs that are not
  stimulated very often. For example, when pain
  receptors in the heart are stimulated, the brain
  projects them as coming from the left shoulder
  and left upper limb because pain impulses from
  the heart and the left shoulder and left upper
  limb travel over the same nerve pathways. Since
  the brain is not accustomed to receiving pain
  impulses from the heart, the brain projects them
  as coming from the left shoulder or arm.

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Smell

• Smell receptor cells
• are ciliated chemoreceptors
• Chemicals dissolved in liquids stimulate smell
  receptor cells.
• are also called olfactory receptor cells
• Receptors are found in the upper region of the
  nasal cavity in yellowish-brown olfactory organs.
  

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Smell

• The science of smell
• Odor molecules enter the nose and dissolve in the
  mucus that surround the ciliated olfactory
  receptor cells before the receptors can detect
  them.
• Once dissolved, odor molecules bind to some of
  the 500 types of receptor proteins located on the
  surface of the cilia. Odor molecules bind to
  specific receptor proteins in patterns.
• Sauerkraut may stimulate receptors 2,44, 11, and
  70
• Chocolate may stimulate receptors 1, 5, and 250.

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Smell

• Olfactory receptor cells, if stimulated by the
  same concentration of odor molecules
  continuously, will undergo sensory adaptation
  very rapidly.
• Anosmia--partial or complete loss of smell. May
  be caused by inflammation of the nasal cavity due
  to a respiratory infection, cigarette smoking, or
  use of certain drugs.
• Humans have about 12 million olfactory receptor
  cells. In contrast, a bloodhound has about 4
  billion.
• Smell is tied to taste and memory.

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Taste

• Taste Receptor Cells
• are chemoreceptors
• Chemicals dissolved in liquids (saliva) stimulate
  them
• are also called gustatory cells
• Taste Buds
• There are 50 to 150 taste receptor cells in each
  taste bud.
• Taste receptors cells are replaced every 3 days.
• Each taste receptor cell have highly sensitive
  taste hairs that protrude from the outer ends of
  the cells and extend into the taste pore.
• Taste buds are found primarily on the surface of
  the tongue but are also found in smaller numbers
  on the roof of the mouth and on the walls of the
  pharynx.

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Taste

• There are four different types of gustatory
  (taste) receptor cells. Each type is MOST
  sensitive to a particular kind of chemical
  stimulus.
• Sweet
• Sour
• Salty
• Bitter
• Experiencing flavors involves taste, odors,
  texture, and temperature.
• Some foods like chili peppers, stimulate pain
  receptors instead of taste receptors.
• Taste receptors undergo sensory adaptation
  rapidly. Moving bits of food over the surface of
  the tongue to stimulate different receptors at
  different moments avoids the resulting loss of
  taste.

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Hearing

• The Ear
• It is divided into three main parts
• the outer ear
• the middle ear
• the inner ear
• Function
• to hear
• to maintain equilibrium.

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Hearing

• The External (Outer) Ear
• Consists of 2 parts
• The auricle
• outer, funnel like structure
• funnels sound waves that travel through the air
  into the ear
• The External Auditory Meatus
• tube that leads inward through the temporal bone
  for about 2.5 cm
• at its end is the tympanic membrane (eardrum)

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Hearing

• The Middle Ear
• Consists of three parts
• The Tympanic Membrane (Eardrum)
• 3 Auditory Ossicles
• The Eustachian tubes
• The Tympanic Membrane
• semitransparent membrane that is covered by a
  thin layer of skin on the outside surface and a
  mucous membrane on the inside
• sort of cone shaped, with the top of the cone
  directed inward
• vibrates in response to the sound waves that
  cause it to vibrate

A ruptured eardrum is a perforation of the thin
membrane that separates the outer ear from the
inner ear. Symptoms of a ruptured eardrum include
severe pain, hearing loss, discharge from the
ear, or ringing in the ear. A ruptured eardrum
may be uncomfortable but will usually heal on its
own within a couple of months.
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Hearing

• 3 auditory ossicles
• malleus, incus, stapes
• responsible for transmitting vibrations from the
  eardrum to the inner ear.
• The malleus is attached to the eardrum. When the
  eardrum vibrates, it vibrates the malleus. Next,
  the malleus causes the incus to vibrate, and then
  the incus causes the stapes to vibrate. The
  stapes is attached (via ligaments) to a structure
  called the oval window. The oval window leads
  into the inner ear. The vibration of the stapes
  at the oval window moves a fluid within the inner
  ear, which stimulates the hearing receptor cells
  in the cochlea.

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Hearing

• The Eustachian Tube (Auditory Tube)
• a tube that leads from each middle ear to the
  throat.
• these tubes conduct air between the tympanic
  cavity and the outside of the body by way of the
  throat and mouth helping to maintain equal
  pressure on both sides of the eardrum
• Sometimes, when you move from a high altitude
  (low pressure) to a lower altitude (high
  pressure) rapidly, the increased pressure outside
  of the ear will push on the eardrum, causing
  hearing loss. However, air movement through the
  auditory tube will equalize the pressure on both
  sides of the membrane. When this happens, the
  person will hear a popping sound.
• It is not a good idea to pinch a nostril when
  blowing your nose because pressure in the nasal
  cavity may force infection from the throat up the
  auditory tube and into the middle ear, causing a
  middle ear infection.

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Hearing

• The Inner Ear
• Consists of two labyrinths.
• Outer labyrinth-Osseous labyrinth
• Bony
• Inner labyrinth-Membranous labyrinth
• Located inside of the Osseous labyrinth
• Is a tube
• Both labyrinths are filled with lymph fluid.

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Hearing

• The labyrinth is made up of three semicircular
  canals, a vestibule, and a cochlea.
• Semicircular canals and vestibule
• provide a sense of equilibrium
• Cochlea
• functions in hearing
• contains hearing receptor cells
  (mechanoreceptors) that vibrations in the fluids
  of the inner ear stimulate.

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Equilibrium

• Semicircular Canals
• Ampullae
• Organs of dynamic equilibrium
• Swollen ends of semicircular canals that contain
  receptor cells that help maintain equilibrium
  when the head and body are in motion
• Vestibule
• Utricle and Saccule
• Organs of static equilibrium
• Contain receptor cells that help maintain
  equilibrium when the head and body are still

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Equilibrium

• Hair cells, which serve as sensory receptor cells
  (mechanoreceptors) are found within the two
  chambers inside the vestibule (the utricule and
  the saccule) and the ampullae of the semicircular
  canals. Gelatinous material inside of these
  chambers pass over the hair cells and cause the
  hair to bend thus sending nerve signals to the
  brain informing the brain of head and body
  position. The brain then responds by sending
  impulses to muscles which cause them to contract
  and relax to maintain balance.