Bio Notes February 12 - Bio Notes CHAPTER 42 Sensory...

Bio Notes February 12, 2009
CHAPTER 42
Sensory Receptors Classified by Location of Stimuli
o Exteroceptors
o Receive stimuli from outside environment
 How to determine the type of food source, friendly associations (pleasant
or painful), hot or cold etc…
o Interoceptors
o Detect changes within the body
o Changes in pH, body temp, chemical composition of blood, osmotic pressure
o The person is unaware of messages sent to CNS until signal internal conditions
 E.g. thirst in diabetes insipidus
• Hyperglycemia- higher level of glucose in the blood- that changes
the osmotic pressure in the body and the body has to rectify that
Sensory Receptors Classified by Type of Energy
• Thermoreceptors : respond to heat and cold-
o Receptors in antennae locate prey, or ticks identifying an endothermic prey
o Mammals
 External: skin, tongue, ear, eye
 Changes in temp via receptors/nerve endings on body surface signal
internal thermorecptors in hypothalamus
• Homeostatic mechanisms ensure constant internal body
temperature
• Electroreceptors
o Used by predatory fishes to detect prey
 Respond to electrical potential
• Electric fields from muscle activity of prey
• Feedback signals from electric organs (other animals)
o Electromagnetic receptors
 Detect Earth’s magnetic field
• Some animals orient by magnetic fields
• Migratory animals (birds) navigate via magnetic fields
• Nociceptors
o Pain receptors
 Free nerve endings (dendrites) of certain sensory neurons transmit signal
• Three types respond to extreme conditions
o Strong tactile stimuli (1. mechanical)
o Temperature extremes (2. thermal)
o Certain chemicals (3. others)
• The release of neurotransmitters glutamate and substance P
(enhances signal of glutamate ) enhances the signal via interneuron
to the spinal cord, hypothalamus and finally the brain centers (pain

awareness)
• Mechanoreceptors
o Transduce mechanical energy
 Activated when they change shape (mechanical push or pull)
 Allow animals to feel, hear, maintain balance (head up, feet down)
 Operation of internal organs (presence food in stomach etc)
o Include:
 Gravity (statocysts)
• In invertebrates:
o Statocysts tilts in response to movement; correct abnormal
orientation
o Sensory hair cells bend one or more statoliths (granules of
sand or calcium carbonate that change position as animal
moves)
o Receptor potentials and action potentials inform CNS of
change in position
 Sensory (touch)
 Movement and tension (propriorectors, hair cells, and lateral line
organs)
• In mammals:
o Receptors in the skin (hair in a hair follicle)
o Displacement of hair (motion) leads to movement of
receptor in deeper hair follicle and receptor potential
o Encapsulated endings- Merkel Discs (adapt slowly),
Meissner (adapts quickly (action to impulse is quick but
not sustained)), and Ruffini corpuscles (adapt slowly
(helps adapt to pain))
o Pacinian Corpuscle responds to very deep touch and
pressure caused by rapid movement of tissue; Action
Potential ceases (e.g. surgery)
• Propriorectors