Sensory Receptors

1
Sensory Receptors

• specialized cells or processes that detect
  stimuli and translates it into an action
  potential
• conducted to the CNS
• translation ____________________
• types of sensations
• 1. General senses
• pain, temperature, touch, pressure, vibration and
  proprioception
• 2. Special senses
• olfaction, vision, gustation, equilibrium, and
  hearing

2
Sensory Receptors

• receptor specificity
• each receptor is receptive to a specific
  sensation
• receptive field
• the area monitored by a single receptor cell
• the larger the area, the _____________ your
  ability to localize a stimulus
• receptor potential
• stimulus causes a change in the membrane
  potential of the receptor cell

3
Sensory Receptors

• typical receptor for general senses
• modified _____________ of a sensory neuron
• any receptor potential that depolarizes the cell
  membrane will bring the membrane closer to
  threshold
• a receptor potential large enough to produce an
  action potential is called a _______________
  potential
• typical receptor for special senses
• specialized receptor cells that communicate with
  sensory neurons across a chemical synapse

4
Sensory Receptors

• tonic receptors
• always active
• frequency of action potentials they generate
  indicates background level of stimulation
• when stimulus increases or decreases, rate of
  action potential changes
• phasic receptors
• normally inactive but become active in a short
  time

5
Adaptation

• reduction in sensitivity in presence of constant
  stimulus
• peripheral adaptation -- receptor responds
  strongly at first, then activity declines
• reduces the amount of information that reaches
  the CNS
• fast -adapting receptors
• thermoreceptors
• slow-adapting receptors
• nociceptors (pain)

6
Adaptation

• central adaptation
• sensory neurons still active but adaptation
  occurs within the _______________
• restricts the detail that arrives at the cerebral
  cortex
• only about 1 of the information provided by
  sensory neurons reaches the cerebral cortex

7
Nociceptors

• pain receptors
• found
• superficial portions of skin
• in joint capsules
• within periostea of bones
• around walls of blood vessels
• __________________ with large receptive fields
• three sensitivities
• a. extremes of temperature
• b. dissolved chemicals such as released by
  injured cells
• c. mechanical damage

8
Nociceptors

• stimulation
• use _____________ and ______________ as
  neurotransmitters
• axons carrying pain
• type A fibers
• fast pain or prickling pain
• type C fibers
• slow pain or aching pain

9
Thermoreceptors

• free nerve endings in dermis, skeletal muscles,
  liver, and hypothalamus
• cold receptors
• 3 - 4 times more common than warm receptors
• carried along same pathway as pain
• _____________ receptors

10
Mechanoreceptors

• sensitive to stimuli that distorts membrane
• contain mechanically regulated channels
• classes
• 1. tactile receptors
• touch, pressure and vibration
• 2. baroreceptors
• pressure within walls of blood vessels in and
  part of digestive, reproductive and urinary
  tracts
• 3. proprioreceptors
• monitor position of joints and muscles

11
Chemoreceptors

• detect small changes in concentrations of
  specific chemicals
• show peripheral adaptation over a period of
  seconds and central adaptation may also occur
• not consciously aware of these sensations
• sensory information is routed to the brain stem
• examples where they are found
• a. surface of medulla oblongata monitoring CSF
• pH and CO2
• b. carotid artery and aortic arch
• pH, CO2 and O2

12
Olfaction

• pair of olfactory organs
• location- nasal cavity above superior turbinate
• two layers
• 1. olfactory epithelium
• olfactory receptors, supporting cells and basal
  cells
• 2. lamina propria
• olfactory glands - form a thick , pigmented mucus
• 2 of inhaled air reaches organ
• __________ soluble and __________ soluble
  materials diffuse into the mucus before can
  stimulate olfactory receptors

13
Olfactory Receptors

• highly modified neurons with up to ___________
  that extend into surrounding mucus
• olfactory reception occurs on the surfaces of
  olfactory cilia
• dissolved chemicals interact with receptors
  called ____________________ on membrane surface
• odorants
• small organic molecules
• strongest are highly soluble in lipids and in
  water
• open ___________ channels in membrane which
  begins depolarization
• 10 - 20 million olfactory receptors

14
Olfaction

• discrimination
• can make subtle distinction among 2000 - 4000
  chemicals
• at least 50 primary smells are known
• aging
• high turnover of olfactory receptors but have
  ________________________
• elderly have difficulty detecting odors in low
  concentrations

15
Taste or Gustation

• taste receptors
• over superior surface of tongue
• portions of pharynx and larynx
• with specialized cells form taste buds
• have about 3000 taste buds
• tongue papillae
• filiform papillae
• fungiform papillae
• circumvallate papillae

16
Taste Receptors

• each taste bud contains about 40 slender
  receptors called gustatory cells and many
  supporting cells
• taste buds are recessed into surrounding
  epithelium
• each gustatory cell extends slender
  ________________ called taste hairs into the
  surrounding fluids thru the taste pore
• gustatory cells survive for only about 10 days

17
Gustatory Discrimination

• dissolved chemicals contacting taste hairs bind
  to receptor proteins
• taste sensations
• A. sweet
• B. salt
• C. sour
• D. bitter
• E. umami
• beef and chicken broth
• F. water