Chapter 24 Notes: Taste & Smell, Hearing & Balance, Vision (A&P II)

I. Taste and Smell

  • A. Anosmia – inability to smell
    • 1. May be the result of head trauma, respiratory infections, aging, etc.
    • 2. May cause serious depression.
  • B. In special senses there are sensory cells that translate different sources into action potentials that the nervous system can make sense of which is transduction
    • A. Chemical
    • B. Electromagnetic
    • C. Mechanical
  • C. Taste and smell rely on chemical receptors
    • 1. Molecules inhaled
    • a. Transported to olfactory epithelium which has olfactory neurons which have receptors for one specific kind of smell
    • b. Bind to olfactory neurons
    • c. If enough stimulation, trigger action potential which goes to the olfactory bulb in the brain
    • d. 40{,}000{,}000 different olfactory receptor neurons help us identify about 10{,}000 different smells
    • e. From the olfactory tract to the olfactory cortex to the frontal cortex and limbic system
      • i. Memory of smells is triggered from limbic system
      • ii. Emotions associated with smells are also triggered
    • f. Smell and taste simultaneously.
  • IV. Taste buds
    • A. Five basic tastes
    • 1. Salty
    • 2. Sweet
    • 3. Sour
    • 4. Bitter
    • 5. Umami – Savoriness. Found especially in mushrooms and anchovies
    • B. All tastes register in all parts of the tongue
    • 1. There are specialized epithelial cells which need neurons to send information to the brain.
  • C. Salty taste has sodium channels in gustatory cells which open and generate a graded potential which sparks an action potential.
  • D. Sour taste has a different route to activate a proton channel.
  • E. 7^{th}, 9^{th}, and 10^{th} cranial nerves are involved.
  • F. Impulses go to cerebral cortex which stimulates release of digestive enzymes to break food down.

II. Hearing and Balance

  • A. Sound is vibrations in the environment – waves of vibrations
    • 1. Vibrations move the tympanic membrane
    • 2. Auditory ossicles are vibrated which causes fluid to move
    • 3. Hair cells in organ of Corti are triggered
    • 4. Neurons are stimulated which sends an action potential to the brain which interprets it as sound and uses it in equilibrium.
  • B. Sounds
    • 1. Frequency is the number of sound waves that pass a certain point in a given time frame
    • a. High pitch is made of short waves moving quickly
    • b. Low pitch is made of few and slower waves
    • 2. Amplitude of waves determines loudness
    • 3. Sound waves need to be changed into signals so the brain can understand and make sense of it.

III. Ear

  • A. Three areas
    • 1. External – only involved in hearing
    • a. Pinna is made of elastic cartilage and skin and catches sound waves which are passed deeper into ear.
    • b. Sound funneled into the external acoustic meatus
    • c. From the auditory canal sound is transmitted to the tympanic membrane
    • d. Tympanic membrane vibrates and passes vibrations to the bones of the middle ear.
    • 2. Middle – only involved in hearing
    • a. Auditory ossicles amplify sound waves which are sent to the inner ear at the oval window
      • i. Malleus – hammer
      • ii. Incus – anvil
      • iii. Stapes – stirrups
    • 3. Inner ear – involved in hearing and equilibrium
    • a. Inner ear is also the labyrinth
    • b. Turns physical vibrations into electrical impulses that the brain can identify as sounds and helps to maintain equilibrium
    • c. Hearing part of inner ear is in the cochlea which looks like a seashell
      • i. Scala vestibule
      • ii. Scala media
      • iii. Scala tympani
    • d. Fibers resonate at different frequencies on the basilar membrane
    • e. Basilar membrane moves and stimulates hair cells of organ of Corti
    • f. Sodium channels open and stimulate action potentials which go to brain which can interpret them as sound.
    • g. Travel along cochlear nerve to the auditory cortex in the brain.
  • B. Equilibrium
    • 1. Uses vestibular apparatus.
    • 2. Fluid controlled by movement of head
    • 3. Three semicircular canals at right angles to each other
    • 4. Connected to utricle and saccule which are full of hair cells that sense motion of fluid
    • 5. Sensory conflict occurs when movement of fluid contradicts what is happening in the rest of the body. Motion sickness.

IV. Vision

  • A. Nearly 70% of all sensory receptors in the body are in the eyes
  • B. Nearly half of the cerebral cortex is involved in vision
  • C. Light
    • 1. Electromagnetic radiation traveling in waves
    • a. Frequency of light waves determines its hue
    • i. Short waves at high frequency are blue
    • ii. Long low frequency waves are red
    • b. Amplitude of the waves relates to its brightness
    • D. Eye photoreceptors convert light energy into nerve impulses that the brain receives and interprets
  • E. Anatomy of eye
    • 1. Eyebrows keep sweat away from the eyeball
    • 2. Eyelashes trigger reflexive blinking
    • 3. Eyelids and tear producing structures help protect the eyeball
    • 4. Eyeball
    • i. Six muscles connect to eyeball for motion up, down, side to side, and angled
    • ii. Sclera – the white of the eye
    • iii. Cornea – transparent covering of eyeball
    • iv. Choroid – vascular layer which supplies blood to eyeball
    • v. Ciliary body surrounds lens to change its shape in response to light
    • vi. Iris is the colored part of the eye which has smooth muscle tissue between the cornea and lens which changes the size of the area surrounding the pupil.
  • F. Light comes in through cornea and pupil and hits lens
  • G. Lens focuses light and projects it to the retina
  • H. Retina has millions of photoreceptors which convert light energy into electrical signals that brain receives and interprets
  • I. Rods – more numerous and light sensitive – register gray scale of black and white. Gives peripheral vision and general shape of an object
  • J. Cones – involved in fine detail and color. Has red, green, and blue cell types. Individual ganglionic cell allows for detailed color vision if conditions are bright enough
  • K. Bipolar neurons synapse on both ends
    • 1. One side synapses with photoreceptor
    • 2. Other side synapses with ganglionic neuron
    • 3. Signal goes to optic nerve and to thalamus and then visual cortex
  • L. Rods and cones can get “tired” and stop responding
  • M. Summary
    • 1. Fibrous layer
    • 2. Vascular layer
    • 3. Inner layer
    • a. Retina
    • b. Three kinds of neurons
      • i. Photoreceptor
      • ii. Bipolar
      • iii. Ganglionic neurons