Physiology Test #2 Topic 7

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emma.hendrickson
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236880
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Physiology Test #2 Topic 7
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2013-09-25 17:08:37
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nervous system
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Peripheral nervous system: afferent division
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  1. Afferent divisions sends
    info from body to CNS
  2. Visceral affarent
    is subconscious info sent from internal viscera to the CNS.
  3. Sensory afferent
    afferent input that does reach level of conscious awareness is called sensory info, and the pathway is called sensory afferent.
  4. Sensory afferent: two groups
    • Somatosensory system
    • special senses
  5. Somatosensory system
    • body surface sensations
    • skin, muscles, joints, inner ear, limb position
  6. Special senses
    vision, touch, hearing, taste, smell
  7. We can perceive
    sound, color, shape, texture, smells, tastes, temp
  8. we cannot perceive
    magnetic fields (birds can), light polarization (birds can), radio waves, x rays
  9. humans are limited in even perceptions we do have...
    • - we can't hear high frequencies that dogs can
    • - some features of stimuli are accented or ignored during precortical processing
    • - cerebral cortex further manipulates data to "complete the picture"
    • - thus our perceptions of NOT replicate reality
  10. Receptor Physiology
    • a. sensitivity of receptors to stimuli 
    • b. responses of receptors to stimuli
    • c. Adaptation of receptors to simuli
    • d. Fate of information transmitted by receptors
  11. Sensitivity of receptors to stumuli
    • 1. Transduction
    • 2. A receptor is specialized for specific stimuli 
    • 3. Tupes of receptors
    • 4. Compound sensations also occur
  12. Transduction
    a receptor functions by converting stimulus energy to an action potential (AP)
  13. A receptor is specialized for specific stimuli
    • eyes se but do not hear
    • but if you are hit in the eye (hitting is a mechanical stimulus) you "see stars"
  14. types of receptors
    • a)  photoreceptors-vision
    • b)  thermoreceptors
    • (1)  warmth
    • (2)  cold
    • c)  mechanoreceptors
    • (1)  osmoreceptors (ECF osmolarity)
    • (2)  baroreceptors (blood pressure)
    • (3)  hair cells (sound, balance)
    • d)  chemoreceptors
    • (1) taste, smell, blood oxygen, blood pH
    • e) nociceptors (pain)
  15. Compound sensations also occur
    e.g wet= mechano + thermo
  16. Responses of receptors to stimuli
    • receptor structure
    • when receptor stimulates
    • conversion of receptor and generator potentials into APs
  17. Two types of receptor structure
    • a) separate cell, produces a receptor potential, which is a graded potential
    • (1) most special senses are like this

    • b) modified ending of afferent neuron, produces a generator potential, which is also
    • a graded potential
    • (1) olfactory is only special sense like this
  18. When receptor stimulated (either type), results in
  19. a)  the non-selective opening of all small ion channels
    • b)  usually results in the net influx of Ca++ and/or Na+ ions
    • c)  which causes a membrane depolarization
    • d)  this is a graded potential, not an action potential, so the bigger the stimulus, the bigger the change in potential
  20. Conversion of receptor and generator potentials into APs
  21. a)  modified ending of afferent neuron (Fig 10.2a)
    • (1)  local current flow occurs from end of afferent neuron to axon of same afferent neuron
    • (2)  causes opening of Na+ channels
    • (3)  if threshold is reached in the axon, an AP occurs
  22. b)  separate cell (Fig 10.2b)
    • (1)  separate receptor cell stimulated which opens Ca++ channels
    • (2)  influx of Ca++ causes release of chemical messenger
    • (3)  messenger binds to protein receptor on membrane of afferent axon
    • (4)  causes Na+ channels to open on afferent axon
    • (5)  if enough Na+ channels open, threshold is reached, and an AP occurs
  23. as more receptors are activated...
    more APs are produced
  24. The stronger the stimulus...
    the higher the frequency of AP that occur in afferent neuron
  25. Adaptation of receptors to stimuli
    • Slow adapting receptors
    • fast adapting receports
  26. Slow adapting receptors
    • Do not adapt to stimuli
    • continue to produce APs as stimuli continue 
    • e.g. muscle stretch receptors
  27. Fast adapting receptors
    rapidly adapt to stimuli, stop producing APs even though stimuli continue,
  28. Fate of info transmitted by receptors
    • Receptor causes AP in afferent neuron (the first order neuron)
    • Afferent AP reaching spinal cord either...
  29. Afferent AP reaching spinal cord either...
    • becomes part of a reflex arc
    • or is relayed toward brain by an interneuron (second order neuron)
  30. Taste and smell description
    • receptors are chemoreceptors 
    • stimulation of taste and smell receptors can cause "pleasurable" or "objectionable" sensations
    • important in finding good food, avoiding toxins, finding mates
  31. Taste buds
    • 10,000 buds in mouth.. mostly on tongue
    • each taste bud has a single opening
    • consists of about 50 receptor cells
  32. receptor cells
  33. (1)  each receptor has binding sites that selectively bind chemicals
    • (2)  binding a chemical causes depolarization of receptor membrane
    • (3)  can initiate APs in afferent neurons with which they synapse
    • (4)  taste receptors has lifespan of 10 days
  34. Taste sensations: sour
    • (1)  Caused by acids (H+)
    • (2)  H+ blocks K+ channels, which reduces K+ leaking out of cell, which
    • depolarizes membrane
    • (3)  When membrane depolarizes, Ca++ channels open and Ca++ enters cell
    • (4)  Entry of Ca++ causes release of neurotransmitter which bind to taste afferents and can cause AP in taste afferent.
  35. taste sensations: salt (primarily NaCl)
  36. (1)  Na+ moves through specialized Na+ channels to depolarize membrane
    • (2)  When membrane depolarizes, Ca++ channels open and Ca++ enters cell
    • (3)  Entry of Ca++ causes release of neurotransmitter which bind to taste afferents and can cause AP in taste afferent.
  37. Taste sensations: sweet
    • (1) Glucose or related sugar bind receptor
    • (2)  Activiates a “G protein” system that involves several enzymes
    • (3)  Ultimately results in blocking K+ channels, which reduces K+ leaking out

    of cell, which depolarizes membrane

    (4)  When membrane depolarizes, Ca++ channels open and Ca++ enters cell

    (5)  Entry of Ca++ causes release of neurotransmitter which bind to taste

    afferents and can cause AP in taste afferent.
  38. taste sensations: bitter
    Many chemicals can bind to bitter receptors (caffeine, nicotine, morphine,

    strychnine)



    (2)  Bitter molecule blocks K+ channels, which reduces K+ leaking out of cell,

    which depolarizes membrane



    (3)  When membrane depolarizes, Ca++ channels open and Ca++ enters cell



    (4)  Entry of Ca++ causes release of neurotransmitter



    (5)  Note: Some bitter taste buds apparently use a G protein sytem (as

    described for sweet) which ultimately causes relsease of neurotransmitter

    which bind to taste afferents and can cause AP in taste afferent.
  39. taste sensations: umami
    Amino acids, especially glutamate, bind receptors



    (2)  Causes net influx of Na+ which depolarizes membrane and ultimately

    causes release of neurotransmitter which bind to taste afferents and can

    cause AP in taste afferent.
  40. neural pathway for taste
  41. Taste receptor to afferent neuron (first order neuron) to second order neuron in
    brain stem to third order neuron in thalamus to gustatory cortex
  42. Smell
    • olfactory receptors
    • smell sensations
    • neural pathway
  43. olfactory receptors
    •   Only special sense receptor that is modified endings of afferent neurons (instead
    • of separate cell)

    b)  Axons of olfactory receptors collectively form olfactory nerve (cranial nerve I)

    • c)  Receptor cells constantly replaced; only neurons known that do this
    • d)  5 million receptors of 1000 different kinds (compared to only 3 receptor types for

    • color vision and 4 for taste)
    • e)  each receptor responds to specific components of odors
  44. smell sensations
  45. a) Receptor binds specific odor chemical
    • b) Cascade of intercellular reactions that open Na+ and Ca++ channels
    • c) Can thus generate APs in the afferent axon
    • d) High frequency of binding = high frequency of APs
  46. neural pathway
  47. Olfactory neurons (first order neurons) to mitral cells (second order neurons) in olfactory
    • bulb in forebrain to olfactory tubercle (in cerebrum, not in thalamus) to olfactory cortex
    • and to limbic system (both in cerebral cortex) via third order neurons. This is an
    • evolutionarily ancient pathway. A recently discovered evolutionarily young pathway
    • associated with conscious awareness of smell does seem to utilize the thalamus.

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