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• Chemosensory Systems


  Taste and smell (detect chemicals)
• Mechanoreceptor systems


  Touch, hearing, and balance (detect pressure)
• Electromagnetic receptor systems


  Sight
• Sensory Receptor cells


  -Rely on membrane receptors that are embedded in cells that communicate with neurons (taste and sight) or embedded directly in neuron membranes (smell)

  -Organized into sensory organs
• Sensory Transduction


  -Conversion of physical or chemical stimuli into nerve impulse

  -Stimulated membrane sensory receptor causes ion channels in plasma membrane to open

  -Then receptors fire action potentials or synapse with neurons that will fire

  -Signals interpreted in central nervous system
• Chemoreceptors

  -Provide sense of smell and taste

  -Respond to molecules in environment (or mouth) that bind to receptors in the cell membrane
• Chemoreceptors (smell)


  Projections of neurons that extend into the mucus on the upper part of the nasal passage
• Chemoreceptors (taste)


  Taste buds on our tongue synapse with sensory neurons
• Mechanoreceptors


  -Respond to physical deformation of the plasma membrane

  -Opens a Na+ ion channel, which causes an action potential to fire

  -Responsible for sense of touch
• Hair cells

  -Help with sense of hearing & balance

  -Are mechanoreceptors that sense mechanical vibration using stereocilia on their surface

  -They don’t fire action potentials, they synapse with neurons and the rate the neurons fire can be altered by stimulation of hair cells
• Cochlea 


  Contains hair cells that are responsible for hearing
• Mechanoreceptors for hearing


  -Sound vibrations enter the outer ear and vibrate the tympanic membrane (eardrum).

  -The eardrum will then move the bones in the middle ear (incus, malleus, & stapes)

  -Middle ear bones will vibrate the oval window in the cochlea
• Vestibular system


  Detects gravity, acceleration, and deceleration with 3 semicircular canals in the inner ear
• Semicircular canal

  Detects angular momentum that the head can turn.

  -Utricle detects head can move side to side

  -Saccule detects head can move up & down and forward & back

  -When the body moves, fluid in the canals move hair cells and that movement is converted into nerve impulses
• Electromagnetic receptors

  Respond to electrical, magnetic, and light stimuli

  -Photoreceptors are the most common
• Opsin

  Light-sensitive protein relating to electromagnetic receptors that converts light energy into electrical signals
• Retinal


  A pigment contained by each opsin protein

  -When light energy strikes it, it shifts from a cis to trans isomer configuration that opens Na+ channels (depolarize cell)
• Eyecup


  Eye that worms have. Simple photoreceptors to only detect direction and intensity of light
• Compound eye 


  Eye that flies have. Composed of hundreds of lens called ommatidia each individually sensing light. More ommatidia means greater visual resolution
• Single-lens eye


  Eye that humans have.

  -Retina is a thin, photoreactive tissue in the back of the eye that light is focused on. -Rod cells are blue-green sensitive and brain interprets this as black and white vision. -Cone cells provide color vision