Senses and Perception

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Senses and Perception

• Lab 17

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Organization of the Vertebrate Nervous System

• Central nervous system (CNS) brain spinal
  cord.
• Responsible for more complex reflexes and higher
  associative functions like learning memory.
• Peripheral nervous system (PNS) motor and
  sensory neurons.

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Organization of the Vertebrate Nervous System

• Motor neurons carry impulses away from the CNS to
  effectors (muscles and glands).
• Sensory neurons carry impulses from sensory
  receptors to the CNS.

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Reflexes

• A reflex produces a very fast motor response to a
  stimulus because the sensory neuron bringing
  information about the threat passes the
  information directly to the motor neuron.

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Sensory Receptors

• The sensory nervous system carries impulses to
  the CNS.
• Sensory receptors are specialized sensory cells
  that detect changes in blood pressure, strain on
  ligaments, and smells in the air, among other
  things.
• Complex sensory receptors made of many cell
  tissue types are called sensory organs.
• Eyes, ears, taste buds.

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Sensory Receptors

• The brain can tell what kind of impulse is coming
  (light, sound, pain, etc) because the signal came
  from a particular type of receptor.
• Light signals come from light receptors.

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The Path of Sensory Information

• There are many different kinds of sensory
  receptors.
• Exteroceptors are receptors that sense stimuli
  that come from the external environment.
• Interoceptors sense stimuli that come from inside
  the body.

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Sensing Chemicals Taste

• Taste taste buds embedded in the surface of the
  tongue contain taste receptor cells.
• Chemicals from food dissolve in saliva and
  contact the taste cells.
• Salty, sour, sweet, bitter chemicals are
  detected in different ways.

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Sensing Chemicals Smell

• Smell chemically sensitive neurons in the nose
  detect chemicals and transmit the information to
  the brain where smell information is processed
  analyzed.

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Sensing Sounds Hearing

• Hearing a sound involves detecting the vibrations
  of the air.
• Waves of pressure in the air beat against the ear
  push the eardrum in out.
• Three small bones on the other side of the
  eardrum increase the force of the vibration.

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Sensing Sounds Hearing

• The vibration crosses a second membrane to the
  fluid of the inner ear the cochlea.
• The inner ear is connected to the throat by the
  eustachian tube to equalize pressure.

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Sensing Sounds Hearing

• The sound receptors occur in the cochlea.
• When sound vibrations enter the cochlea, they
  send nerve impulses to the sensory neurons that
  travel to the brain.

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Sensing Sounds Hearing

• Sounds of different frequencies cause different
  parts of the membrane inside the cochlea to
  vibrate and fire different neurons.
• Intensity is determined by how often the neurons
  fire.

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Sensing Light Vision

• Vision is the perception of light.
• The eye is a special sensory organ that uses
  pigments in structures called rods and cones to
  absorb photons of light.

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Structure of the Vertebrate Eye

• Light passes through the transparent cornea which
  begins to focus light on the rear of the eye,
  then through the lens which completes the
  focusing.
• The lens is suspended by ciliary muscles.

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Structure of the Vertebrate Eye

• The iris is a shutter that controls the amount of
  light entering the eye.
• The pupil is the transparent zone in the center
  of the iris that gets larger in dim light and
  smaller in bright light.

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Structure of the Vertebrate Eye

• The light is focused by the lens onto the back of
  the eye.
• An array of light sensitive receptor cells called
  the retina line the back of the eye.
• Rods cones two types of receptor cells
  generate nerve impulses that pass along the optic
  nerve.

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Structure of the Vertebrate Eye

• Rods are very sensitive to light and can detect
  shades of gray in very dim light, but they do not
  detect color and the images are not sharp.
• Cones detect colors and produce sharp images.

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Color Vision

• Three kinds of cone cells allow color vision.
• Each has a different version of the opsin protein
  and so absorbs different wavelengths of light.
• The brain compares relative intensities of the
  signals from the three types of cones.

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Binocular Vision

• Primates and most predators have two eyes facing
  forward, so the field of view overlaps.
• This binocular vision allows perception of 3D
  images and depth.
• Animals with eyes on the sides can detect motion
  in a wider field good for prey animals.