Senses

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Senses

• Chapter 49

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Sensory Receptors

• Detect stimuli, but do not interpret the
  information.

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Sensations

• Action potentials that reach the brain via
  sensory neurons.

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Perceptions

• Constructions formed in the brain but do not
  exist outside of it.
• Your eyes do not see, your brain does

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Functions of Sensory Receptors

• Involves four functions

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1. Sensory Transduction

• Conversion of stimulus energy into a change in
  the membrane potential of a sensory receptor
• Change is called receptor potential

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2. Amplification

• The strengthening of stimulus energy by cells in
  sensory pathways.

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3. Transmission

• Passing the receptor potential to neurons in the
  CNS

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4. Integration

• Processing this information within the CNS

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Sensory Adaptation

• Decrease in responsiveness during continued
  stimulation (so you stop feeling your clothes)

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Types of Sensory Receptors

• Mechanoreceptors
• Sense physical change (touch, hearing, stretch,
  equilibrium, etc.)
• Chemoreceptors
• Detect solute concentration (taste and smell)

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Types of Sensory Receptors

• Electromagnetic receptors
• Light, electricity, magnetism
• Thermoreceptors
• Hot and cold
• Pain receptors
• Different groups detect pressure, excessive heat,
  chemicals

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Hearing

• The ear changes the energy of pressure waves
  into nerve impulses which the brain perceives as
  sound.

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Hearing

• Waves cause tympanic membrane (the eardrum) to
  vibrate.
• Vibrations are passed to the three bones of the
  middle ear- malleus (hammer), incus (anvil), and
  stapes (stirrup).
• The stapes vibrates against the oval window.
• Oval window creates pressure waves in the
  cochlear fluid.
• Waves pass through the vestibular canal, around
  to the tympanic canal, and then strike the round
  window.

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Hearing

• Organ of corti in the basilar membrane contains
  hair cells. The hairs of the hair cells are
  moved, generating action potentials.
• Volume Loud Sounds Greater vibration More
  bending of hairs More action potentials
• Pitch more vibrations per second and since
  basilar membrane is uneven, different parts pick
  up different pitches

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Equilibrium

• Fluid filled chambers, lined with hair cells
  respond to movement of ear stones, which the
  brain uses to interpret positioning of head

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Taste and Smell

• Taste- solution
• Smell- air
• Both rely on binding of specific molecules
  binding to specific receptors, which the brain
  uses to form an image

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Taste

• AKA Gustation
• Detects chemicals in solution
• Presence of specific chemicals open certain ion
  channels
• Saltiness- NaCl Na channels
• Sourness- Acids H channels
• Sweetness- Sugars
• Bitterness- K channels
• Umami- glutamate Na channels
• Combination of receptors allows brain to perceive
  stimulus

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Smell

• Odorant binds to odorant receptor (OR), which
  triggers a signal transduction pathway.
• More than 1000 OR genes

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Focusing

• Distance- Lens becomes flatter
• Close- Lens becomes thicker and rounder

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Photoreception

• 70 of all sensory receptors
• Rods Light/Dark
• Cones Color
• Three types- blue, green, red

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Sensory Transduction

• Rhodopsin
• Retinal (light absorbing molecule) bound to
  opsin.

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• Retinal has 2 forms
• In light- cis to trans
• In dark- trans to cis
• Enzymes convert trans back to cis
• Takes a few minutes

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To the brain

• Optic nerve carries info to brain
• Left field- right side of brain
• Right field- left side of brain

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In the Brain

• Corpus callosum- bridge connecting 2 hemispheres
  of the brain.
• Maybe 30 of cerebral cortex dedicated to what we
  see.

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Skeleton

• Serves 3 functions
• Support
• Locomotion
• Movement

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Types

• Hydrostatic
• Fluid held under pressure
• Jellyfish
• Exoskeleton
• Usually made of chitin
• Arthropods
• Must molt
• Endoskeleton
• Bones
• Us

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Muscles

• Move us attach to bones
• Work in antagonistic pairs
• Basic unit- Sarcomere

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Cramps?

• Calcium channels stay open