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Sensory Nervous System
Objectives:
Describe the process of sensory transduction
in general
List the stimuli to which we have receptors
and, for each, identify the general type of
receptor
Distinguish receptor potential from action
potential
Distinguish tonic and phasic receptor function
Somatic senses
fine touch, deep touch, pressure, temp, pain,
joint and muscle position, muscle stretch
Visceral senses
pH, O2, CO2, OsM, glucose, blood pressure, lung
inflation, stomach stretch
Special senses
olfaction, gustation, hearing, equilibrium, vision
Receptors are transducers, neural or non-neural
Types: chemo-, mechano-, photo-, thermo-, nociear (sense organ)
with mechanoreceptors
(transducers)
Vestibulocochlear nerve
graded potentials
action potentials
CNS (decoder)
-medulla to
thalamus to
auditory cortex
non-neural receptors
-receptor potentials
(like graded potentials)
coding: which receptors are activated and AP frequency
General principles of sensory function
1. Each sensory organ and receptor is specialized to
convert one form of stimulus into sensory neuron
action potentials.
2. Each modality has a discrete pathway to the brain.
3. The specific sensation and location of stimulus
perceived is determined by area of brain activated.
4. ‘Intensity’ is coded by frequency of action
potentials and number of receptors activated.
Group the following senses according to whether they
use chemical or mechanical receptors.
-chem
taste (gustation)
-chem and mech
pain (nociception)
-chem
smell (olfaction)
-mech
touch
-mech
vibration
-neither
vision
-chem
oxygen levels
pressure (baroreception) -mech
Which one can be both and which one is neither?
A somatic
sense: touch
• Free nerve
endings
• Meissner’s
corpuscle (light)
• Pacinian
corpuscles (deep)
Example sensory pathway: touch
(receptor cell)
 sensory neuron
 to spinal cord or brainstem
 to thalamus
 to somatosensory cortex
General principles of sensory function
1. Each sensory organ and receptor is specialized to
convert one form of stimulus into sensory neuron
action potentials.
2. Each modality has a discrete pathway to the brain.
3. The specific sensation and location of stimulus
perceived is determined by area of brain activated.
4. ‘Intensity’ is coded by frequency of action potentials
and number of receptors activated.
The specific sensation and location of stimulus perceived
is determined by area of brain activated.
‘Intensity’ is coded by frequency of action potentials
and number
of receptors activated.
FREQUENCY
CODING
LIGHT PRESSURE
LOW
FREQUENCY
MORE PRESSURE
HIGHER
FREQUENCY
POPULATION
CODING
‘Intensity’
is coded by frequency
of action potentials
and number of receptors activated.
LIGHT PRESSURE
MORE PRESSURE
Receptor Types
Chemoreceptors : pH, O2, CO2, glucose, taste, odor,
some pain
Mechanoreceptors : muscle, cell, joint, lung, blood vessel
and stomach stretch, sound, equilibrium
Photoreceptors : light
Thermoreceptors : hot or cold
All receptors are transducers sensitive to a specific
stimulus. Some are neurons, some are not.
General principles of sensory function
Somatic senses -touch, pressure, temp, pain
Objectives: For each sense identify…
• Any specialized structures or sense organs
• Receptor type
• Receptor signal transduction mechanism
• Coding of intensity and duration
• Pathway of conduction to the CNS
• Coding for perceived sensation