Transcript P215 - Basic Human Physiology

Sensory Physiology
Chapter 13
Sensors
• Detect changes in environmental conditions
• Primary Sensors
– neurons modified to undergo action potentials
in response to specific stimuli (e.g. chemical,
mechanical)
• Secondary Sensors
– Cells that respond to environmental change by
releasing neurotransmitters to neurons
Transduction
• Conversion of environmental change
into an electrical signal
• Receptor responds to stimulus by
– opening ion channels (primary sensors)
– releasing neurotransmitter to a neuron
(secondary sensors)
– receptor potential (graded)
• Lead to action potential formation in
sensory neurons
– Rate of AP generation is proportional to
stimulus strength
Types of Environmental Stimuli
• Chemoreception
• Mechanoreception
• Electromagnetic Reception
Chemoreception
• Detection of chemical types and
concentrations
• Gustation (Taste)
– chemicals in contact with the animal
• Olfaction (Smell)
– chemicals concentrated at a distance
• Internal Chemoreceptors (PO2, PCO2, pH)
Taste Buds
(Contact Chemoreceptors)
• Detect chemicals from sources in contact with animal
• Contain microvilli that project to the external surface
• Chemicals come into contact with these hairs
– Release neurotransmitter to sensory neurons
– Action potentials are generated in neuron
Olfactory Receptors
(Distance Receptors)
• Detection chemicals from
distant sources
• Modified neurons
– receptors located in nasal
epithelium in the nasal cavity
– Have hair-like projections that
respond to chemicals in air
Squamate Tongues
• Tongue collects
chemicals then retracts
• swab chemicals over
vomeronasal organ
(Jacobson’s organ)
• chemical perception
• forked tongue gives
directional perception
Insect Antennae
• Pheromonal Reception
Mechanoreception
• Detection of Mechanical Energy and Force
–
–
–
–
Tactile (touch and pressure)
Proprioception (movement, body position)
Equilibrium (gravity and acceleration)
Vibrations (sound)
Tactile Receptors
• Insect cuticular receptors
– Bristle/hair receptors
• Vertebrate cutaneous receptors
– Expanded dendritic endings
• Ruffini endings and Merkel's disks
• Touch
– Encapsulated endings
• Meissner's corpuscles, Krause's
corpuscles, Pacinian corpusles
• Pressure
Proprioceptors
• Detect changes in
length and tension
of the muscles
Equilibrium:
Hair Cells
• located deep inside the ear
• vibrations bend “hairs”
(stereocilia)
– opens/closes physically gated ion
channels
• alters release of neurotransmitter
to sensory neurons
Equilibrium:
Invertebrate Statocysts
• Central statolith
stimulates different
hair cells based on
orientation to gravity
Equilibrium:
Vertebrate Vestibular Organs
• Fluid-filled compartments
in the inner ear
• Semi-circular canals
– Rotation of the head
• Otolith organs
– linear movement of head and
orientation relative to gravity
Vibration
• Vertebrate Cochlea
– Elongate structure containing hair cells
– Fluid pressure waves induce vibration of the
basilar membrane
– Stimulates hair cells
Vibrations:
Insect “Ears”
• Tympanic Organs
• Terminal Cerci
• Johnston’s organ
– Wind receptor
– May be tuned to specific
frequencies
Vibrations:
Lateral Lines
• Fish and aquatic
amphibians
• Hair cells distributed
along lateral line
• Detect vibrations in
water and flow of
water
Animation:
http://www.blackwellpublishing.co
m/matthews/haircell.html
Electromagnetic and Thermal
Perception
•
•
•
•
Vision
Temperature
Electric
Magnetism
Vision
• Perception of
electromagnetic radiation
– portion of the EM spectrum
Advanced Eyes:
Refraction of Light
• Light refracted by
transparent/translucent
structures
• bending of light leads to
projection of focused
image on the retina
Vertebrate Photoreceptors
•
•
•
•
rods - light intensity
cones - color
Each photoreceptor has two segments
Inner segment
– metabolic machinery
– synaptic endings
• Outer segment
– contains layers of internal membranes
containing photopigments
Transduction of Light
• Cells change metabolic
activity with activation
of photopigments
• Stimulate sensory
neurons
Compound Eyes (Arthropods)
• Consist of many ommotadia
– Each with lens and
photoreceptor cells
• E.g., Green, Blue, Ultraviolet in
honeybees
• Images from many
ommotadia processed into a
single visual picture
Thermal Perception
• Modified neurons
– E.g. cutaneous heat and cold
receptors
• Thermosensory pits (snakes)
– Detect heat from warm prey,
thermal conditions in habitat
Electroreception
• Marine elasmobranchs
– ampullae of Lorenzini
• detect electrical fields generated by
other fish
• Freshwater teleosts
– caudal electric organs
• generates electrical field around animal
• objects near animal alter electric field
• detected by cells in lateral line
• Platypus
– Mucous/serous gland electroreceptor
• Neurons surround pores of mucous and
serous glands
Magnetic Field Perception
• Long distance orientation
– Follow the earth’s magnetic
field
• Mechanism (?)
– Magnetite (Fe3O4) present in
various receptor cell types
• Photoreceptors – birds,
salamanders
• Electroreceptors –
elasmobranchs
• Olfactor receptors - trout