Chapter 15

 

Chapter 15: The Senses

 

15.1 Sensing and Perceiving

  • Survival often depends on the ability to sense and respond appropriately to environmental changes
  • Information we have about the world comes to us through specialized cells called __________________________________
  • _________________________ are the structures and processes that receive and interpret environmental conditions (____________________________)

 

  • The five senses are:
    • Sight
    • Hearing
    • Taste
    • Smell
    • Touch
    • Propriorecetoption
  • Senses are based on the stimuli they respond to

Humans have five types of sensory receptors:

  • ______________________________________ respond to a shape change in the receptor or nearby cells
  • _______________________________________ sense temperature change
  • _______________________________________ respond to light
  • _______________________________________ react to chemical stimuli
  • _______________________________________ respond to tissue damage or extreme temperatures

 

  • Sensory receptors have different focal points
    • ________________________________________ sense external conditions, allowing us to respond to the environment
    • ________________________________________ sense internal conditions reflected in homeostasis

 

  • Sensory input can be classified by receptor specialization
    • Receptors for touch, pressure, vibration, temperature, pain, and body and limb position are found all over the body
      • The information they report is termed the ________________________ or somatic senses
    • Sight, hearing, taste, smell, and equilibrium are __________________________
      • They are reported by specialized __________________________________ located in the head

 

  • The only known pathways for stimuli to enter our consciousness are the special and general senses
  • Our sensory receptors respond to just a fraction of all possible stimuli
    • Those that are important for survival
  • Other organisms can detect other sets of stimuli

 

  • A stimulus causes an electrical change in the receptor’s membrane causing it to ________________________
  • The change must be large enough to stimulate a sensory neuron carrying the information to the central nervous system

 

  • The spinal cord receives the signals from the sensory neurons, and then the brain processes them
  • The processing is unconscious, such as the information that regulates posture or blood pressure
  • Some of the input impacts our consciousness, producing a _____________________

 

  • A ______________________________ is our interpretation of a sensation
  • The brain interprets a signal from a sensory neuron
    • For example, a punch in the eye causes you to see bright colored lights because the sensory neurons that trigger light and color have been mechanically disrupted enough to send a signal

 

  • If a stimulus continues over a regular span of time, perception is reduced, a process called ________________________________
    • Neural adaptation occurs when a receptor stops sending a signal
    • Habituation occurs when a signal stops being sent from the subconscious to the conscious brain

 

15.2 The General Senses

  • Large numbers of sensory receptors on the body surface sense pain, heat, air movement, pressure on the skin, and vibration
  • Receptors in muscles and tendons monitor posture and the position of body parts
  • These general senses pick up information about our environment that may not be obvious to the eyes, ears, and nose

 

  • ___________________________ transmit signals when they are deformed
    • Touch receptors are not distributed equally; most are found where sensitivity is important for survival and reproduction – hands and mouth
    • Less abundant on the back and abdomen

 

  • __________________________________ in the skin detect moderate temperature change
    • Some of the receptors respond to cool temperatures (50-68F) and to higher temperatures (77-113)
  • Chemicals in food can activate thermoreceptors giving a sense of hot/cold while eating
  • Skin thermoreceptors respond to temperature changes but adapt to stable temperatures quickly

 

  • Extreme temperatures are sensed by ________________________, which are free nerve endings found in skin, joints, bones, and blood vessels
  • Internal organs have few pain receptors
    • Share nerve pathways with surface pain receptors

 

  • Damage to internal organs often manifests itself as pain in a different area of the body; called _______________________________
  • There are characteristic patterns of referred pain
    • For example, heart damage is often felt as arm or shoulder pain

 

  • _______________________ transmits signals from deep cuts or burns triggering an immediate withdrawl reflex
  • _______________________ replaces fast pain; slow receptors have large receptor fields, so it is difficult to localize the exact origin of pain
    • Slow pain receptors take a long time to adapt, so the pain lingers beyond the time when anything can be done to change the damage that has occurred

 

  • ______________________________ is generally slow pain
    • Might be resolved by blocking the pain receptors
      • Aspirin and other anti-inflammatory drugs
    • Morphine and codeine mimic endorphins, natural pain relieves
      • The chemicals bloc pain perception rather than sensory reception

 

15.3 The Chemical Senses

  • Taste
    • ___________________________________________ are found on the top of the tongue and around the mouth and throat
      • The rough tongue surface is made up of small protrusions, the ______________________________
      • Each papilla has 100-200 taste receptors called __________________
    • The mouth has about 10,000 taste buds, each made up of about 25 ________________________ and about the same numbers of support cells

 

  • Each taste cell has a number of _________________________ on its surface
  • Cells within the taste buds are replaced every 10 days

 

  • The taste hair surfaces have receptors that bind to the chemicals found in foods
  • This stimulates neurotransmitter release from the taste cell, triggering a sensory neuron
  • Activation of a particular receptor signals one of five possible taste qualities
  • Several types can be triggered at the same time
  • These sensations, along with odor sensations, produce the perception of a flavor

 

  • Taste buds are unevenly distributed on the tongue surface
  • There is a higher concentration of sweet receptors in the front of the tongue and bitter receptors in the back
  • Evolution has shaped our reaction to different tastes
  • Sweet, salty, and meaty foods prompt us to swallow
  • Bitter prompts a gag reflex – bitter may mean poisonous or spoiled food
  • Receptors are 100,000 times more sensitive to bitter than sweet receptors are to sweet

 

  • Smell
    • _________________________________________ are found in two patches on the roof of the nasal passage
    • The receptor surface is a hair-covered section of a sensory nerve dendrites
  • The hairs project into the nasal cavity and bind with _________________________ that become dissolved in the nasal mucus
  • Olfactory receptors are replaced every 60 days and can be regenerated, which is rare among nerve cells
  • Odors may trigger profound emotional responses
  • Odor perception is “hard-wired” – meaning we have instinctive positive and negative responses to some odors from our past

 

  • Most mammals are much more sensitive to odors than humans
  • Hounds are nearly a hundred million times more sensitive than a human

 

  • __________________________________ are species-specific scents used as a form of communication
    • They can be used to advertise sexual readiness, danger, and the location of food or territory
  • Rodents have a vomeronasal organ to detect pheromones, but humans lack such a structure
  • Whether humans produce pheromones is unclear

 

15.4 Senses of the Ear

  • Hearing
    • The ____________ has two separate sets of mechanoreceptors
    • One set of senses, ___________________________________ generate our sense of hearing
    • The other set provides information on the position of the head, helping us to maintain balance     

 

  • Sound is compressed waves of air
  • All sound is a pulse of air followed by some low pressure – the waves generated by the vibration of some materials
  • Mechanoreceptors in the ear sense the waves and the nervous system translates them into sound perception

 

  • The inner ear senses both sound and head position
  • The fluid filled ___________________________ senses sound
  • There are two fluid-filled tubes, one inside the other
  • Vibrations from the oval window are transferred to the fluid in the outer tube and pass over the top of the inner tube, the cochlear duct, then around its end and along its bottom to reach the round window
  • The round window acts as a damper to dissipate the energy from the sound wave back to the middle ear and eventually into the mouth via the _______________________________________

 

  • __________________________, each with about 100 hair-like extensions, are the ___________________________________ in the cochlear duct

 

  • Contact with the hair cells causes it to bend, which triggers the release of a neurotransmitter from the hair cells
  • The neurotransmitter stimulates a sensory nerve, which sends a signal to the __________________________
  • Hair cell location gives information on the frequency or pitch of a sound
  • The number of responding hair cells indicate sound amplitude perceived as loudness

 

  • Human ears are especially good at tuning in on human speech, leaving us with limitations in other sound frequencies
  • Sound wave frequency is measured in hertz (Hz)
  • Human range is 20-20,000 Hz
  • Infrasounds are very low frequency sounds, outside our range, which accompany earthquakes and volcanoes
  • Experiencing infrasounds may evoke a feeling of fear and discomfort

 

  • Inner ear mechanoreceptors located in the _______________________________ sense head movement and position in space
  • The vestibular apparatus consists of a basal sac and three ___________________________________________

 

  • Each of the three canals projects into one of the three dimensions of movement (up-down, sided-to-side, back-forth)
  • When the head is moved, fluid in the canals moves in the opposite direction, impacting the cupula at the base of each canal
  • Fluid in the cupula deforms hair cells that send signals to the brain about movement

 

  • The vestibule part of the vestibular apparatus is divided into a larger _____________________ and a smaller ___________________________
    • They measure head position changes relative to gravity, acceleration and deceleration
  • Both regions contain an ___________________________,hair cells embedded in a gelatin-like substance
  • Calcium carbonate stones in the substance move as the head moves, and they distort the hair cells

 

  • The vestibular apparatus and vision are integrated to help you maintain ____________________________
  • Signal discrepancy often results in motion sickness or __________________, an inappropriate sense of motion
  • When you read in a car your vestibular system is recording motion but the page you are reading is at rest

 

15.5 Vision

  • Vision
    • ________________________________ in eyes respond to light energy between certain wavelengths, called visible light
    • The ______________ is adapted to sensing and focusing visible light
  • Much of the eyeball is a cavity surrounded by connective tissue

 

  • The sclera is white and opaque with a small clear opening in front, the _____________________, which allows light to pass
  • The cornea is very sensitive to pain
  • Just behind the cornea is the anterior chamber filled with ______________________________________
  • The chamber s continuously drained, but if draining channels fail, an increase in pressure occurs (glaucoma)
    • Glaucoma can cause blindness due to compressed ocular blood vessels, so drug therapy or surgery is imperative

 

  • Light entering the eye is screened by the _____________, a muscle that adjusts the _______________________
  • In dim light, the iris dilates to allow as much light as possible into the eye
  • Light that passes through the pupil is focused by the ________________ through a cavity filled with _______________________ onto the ____________

 

  • To focus on close items, the muscle connected to the lens contracts and the lens bulges, shortening the focal length
  • When the muscle relaxes, the lens is pulled taut and the focal distance increases
  • If the relaxed lens focuses the image in front of the retina, ______________ or nearsighteness occurs

 

  • _____________________________ is when the focal point falls behind the retina
  • As we age, the lens becomes less flexible and doesn’t relax adequately, causing age-related farsightedness
  • Clear focus may also be impaired if the cornea is misshaped, causing light to scatter, a condition called _______________________
  • Glasses, contact lenses, and surgery to reshape the cornea change the light path to put the image back on the retina

 

  • The lens may become cloudy because proteins become malformed, producing ____________________________
  • Cataracts are caused by diabetes or as a result of aging
  • An artificial lens can be inserted to replace cloudy lenses

 

  • The retina contains rods and cones that sit on top of the ________________
  • The choroid contains capillaries that bring nutrients and oxygen to the photoreceptors
  • The connection of the retina to the choroid is weak, and a tear or hole allows vitreous humor to enter and pull the retina away
  • This causes retinal detachment than can be treated by laser treatment

 

  • ___________________________________ in the eye respond to light by changing shape
  • ______________________ function in night vision and peripheral vision
    • 120 million rods
  • _____________________ record color and detain
    • 6 million cones
  • Rods and cones, once lost, cannot be replaced

 

  • What we see is a subset of surrounding conditions and the brain’s tendency to see patterns
  • Green, red, and blue photoreceptors are found in unequal numbers, with green outnumbering the others
  • The colors we see aren’t perfect representations of the source
  • A candle flame gives yellow to red light, but we are more sensitive to yellow, so the flame looks yellow

 

  • Mutations in photoreceptor genes cause __________________________________
  • The most common form is the loss of either the red or green photoreceptor, where red or green appears gray
  • There is a range of wavelengths, including x-rays, microwaves, and infrared that we can’t see
  • They can be detected by special cameras, films, and detectors

 

  • Visual processing by the brain is a complex process

 

  • Information on color, light intensity, and movement is integrated by ganglion cells (bunch of nerve cell bodies) and passed via the ____________________________ nerves to the _____________________________
  • Information from each eye is shared at the optic chiasm so that signals from both eyes are sent to each brain hemisphere
  • The shared signals provide for binocular vision and depth perception

 

  • Signals from the optic chiasm travel to the brain, where the information is broken down and then moved to the _____________________ for reassembly and perception
  • Since visual processing takes nanoseconds, the brain has shortcuts to “fill in” information
  • The exit point of the optic nerve through the retina leaves a _________________________ that is filled in by the visual cortex

 

  • The ability to perceive patterns in the environment has survival values but also causes us to identify a pattern when none exists
  • Seeing a face in a photo of the surface of Mars