Chapter 10- Sensory System

Question 1

Compare phasic to tonic receptors

Answer 1

• Tonic receptors
  ○ Do not adapt at all or adapt slowly: pain receptor
  § CNS must continually get info about degree of muscle length and joint position (bath)
  
  • Phasic receptors
    ○ Rapidly adapting receptors
    § No longer responds to maintained stimulus
    § Important to signal a change in stimulus
    § Tactile (touch) receptors in skin

Question 2

Describe the nature and significance of the receptor potential

Answer 2

• Environmental stimulus opens ion channel
  
  • Change in membrane permeability leads to influx of Na+ producing receptor potentials
  • Magnitude of receptor potential represents opens more ion channels
  • A receptor potential of sufficient magnitude can produce an action potential
    ○ Action potential is propagated along an afferent fiber to the CNS
    § Just sends more AP, doesn’t change magnitude

Question 3

Differentiates between sensation and perception

Answer 3

• Perception
  ○ Conscious interpretation of external world derived from sensory input, interpretation of what is sensed.
  § Pattern of nerve impulses delivered to brain
  ○ Why sensory input does not give true reality perception
  § Humans have receptors that detect only a limited number of existing energy forms
  § Information channels in our brains are not high-fidelity recorders
  § Cerebral cortex further manipulates the data
  ○ Four steps to perception
  1. Stimulus
  2. Transduction
  3. Conduction
  4. Perception
  
  • Sensation
    ○ Collection of information, ability to detect the environment in the world

Question 4

define sensory acuity and explain factors that affect acuity

Answer 4

• Refers to discriminative ability
  
  • Influenced by
    ○ Receptive field size
    ○ # of receptors
    ○ Area of somatosensory cortex
    § More sensitivity= more receptors

Question 5

describe the different types of sensory receptors

Answer 5

• Photoreceptors
  ○ Visible wavelengths of light
  § Responsive to visible wavelengths of light
  
  • Mechanoreceptors
    ○ Mechanical energy
    § Important in blood vessels
  • Thermoreceptors
    ○ Temperature
  • Osmoreceptors
    ○ Solute concentration
    § ADH
  • Chemoreceptors
    ○ Specific chemicals
    § Smell, taste
    § O2, CO2
    □ Not enough CO2, heart rate decreases
  • Nociceptors
    ○ Pain, detects damage to tissue
  • Proprioceptors ??
  • Location
    ○ Exteroceptors
    § Outside the body
    ○ Interoreceptor
    § Detects things inside the body

Question 6

describe pain and receptors involved in sensing pain

Answer 6

• Primarily a protective mechanism meant to bring a conscious awareness that tissue damage is occurring or about to occur
  
  • Storage of painful experiences in memory helps avoid harmful events in the future
  • Stimulation of nociceptors elicits perception of pain
    ○ Memory: limbic system
    § Amygdala
    § hippocampus

Question 7

Taste receptors and function

Answer 7

• Chemo receptors
  ○ Receptors sensitive to dissolved molecules
  § Exteroreceptors: even though the receptors are inside
  § Smell influences taste
  ○ Function
  § Influence flow of digestive juices and affect appetite
  § Stimulation of receptors induces pleasurable or objectionable sensations and signals presence of something to seek or avoid

Question 8

taste

Answer 8

• Taste
  ○ Gustation
  ○ Chemoreceptors housed in taste buds
  § Long microvilli
  ○ Taste receptors have life span of about 10 days
  ○ Taste buds consist of taste pores and taste receptor cells
  ○ Tastant= taste-provoking chemical
  ○ All tastes are variance of 5 primary tastes
  § Salty: stimulated by chemical salts, especially NaCl
  § Sour: caused by acids which contain a free hydrogen ion, H+
  § Sweet: evoked by configuration of glucose
  § Bitter: brought about by more chemically diverse group of tastants
  § Umami: meaty or savory taste

Question 9

Primary tastes

Answer 9

○ Primary tastes
§ Binding of tastant with receptor cell, produce receptor potential
□ Each taste has different receptor
§ Receptor potential initiates action potentials of afferent nerve fibers
§ Signals conveyed to medulla via cranial nerves, to thalamus to brain
□ Primary gustatory cortex= insula: deep to lobes
□ Somatosensory cortex= tongue: parietal

Question 10

Odorants and how they stimulate receptors and how information is conveyed to brain

Answer 10

• Olfaction
  
  • Odorants
    ○ Molecules that can be smelled
  • To be smelled, a substance must be
    ○ Sufficiently volatile (enough concentration) that some of its molecules can enter nose in inspired air
    ○ Sufficiently water soluble that it can dissolve in mucus coating the olfactory muscosa
  • Olfactory receptors in nose are specialized endings of afferent neurons
  • Olfactory mucosa
    ○ Ceiling of nasal cavity
    ○ Cell types
    § Olfactory receptor cell
    § Basal stem cells
    § Supporting cells
  • 1000 different types of olfactory receptors
    ○ Each receptor responds to one component of an odor
    ○ Odorant has characteristic chemical groups, activating receptor
    ○ Identity of odorant determined by combination of receptors
  • Different odorants act through second-messenger systems
  • Axons of neurons form olfactory nerve
  • Olfactory nerve terminates in
    ○ Limbic system
    § Smell and behavioral reactions
    □ Feeding
    □ Mating
    □ Direction orienting
    ® Used to have in humans
    ○ Olfactory cortex
    § Conscious perception
    § Fine discrimination of smell