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Sensory ReceptorsSensory Receptors
Sensory Receptors
(some basic properties)
Sensory Receptors
(some basic properties)
Organs which
receive information
from outside or
Organs which
receive information
from outside or
within the body and
send it to the
central nervous
system for
processing
within the body and
send it to the
central nervous
system for
processing
Activated by various forms of energy:
light heat
Activated by various forms of energy:
light heat
Sensory Receptors
(some basic properties)
Sensory Receptors
(some basic properties)
Specialised nerve ending
light, heat, mechanical chemical etc.
light, heat, mechanical chemical etc.
Sensory receptors are either specialized endings of afferent neurones or separate cells that signal to the afferent neurone
Sensory receptors are either specialized endings of afferent neurones or separate cells that signal to the afferent neurone
Specialised cells
Definition of a Transducer or Transduction
Conversion of one form of energy (e.g. heat,
pressure, chemical) into another form: e.g. electrical
energy or depolarisation
Definition of a Transducer or Transduction
Conversion of one form of energy (e.g. heat,
pressure, chemical) into another form: e.g. electrical
energy or depolarisation
Sensory Receptors Are TransducersSensory Receptors Are Transducers
The depolarisation occurring at the sensory terminal is
a). Graded – Non-propagating, confined to terminal
b). Called the Receptor Potential (R.P.)
The depolarisation occurring at the sensory terminal is
a). Graded – Non-propagating, confined to terminal
b). Called the Receptor Potential (R.P.)
The Receptor Potential:
If large enough will evoke all or nothing action
potentials that propagate along the nerve fibre
The Receptor Potential:
If large enough will evoke all or nothing action
potentials that propagate along the nerve fibre
Variable stimulus intensity
Produces graded receptor potentials
The Receptor PotentialThe Receptor Potential
Adequate stimulus
10mV
Produces variable patterns of action potentials in the CNS
More Stimulus = More Transmitter Released
Intensity of Stimulus is Linearly EncodedIntensity of Stimulus is Linearly Encoded
The number of action potentials generated by a pressure- sensitive sensory afferent neuron is directly proportional to the stimulus intensity.
The number of action potentials generated by a pressure- sensitive sensory afferent neuron is directly proportional to the stimulus intensity.
Receptor Potential:
more or less proportional to stimulus
Receptor Potential:
more or less proportional to stimulus
stimulusstimulus receptor potentialreceptor potential
adaptation
mV
Adaptation to stimulus depends on receptor typeAdaptation to stimulus depends on receptor type
adaptation
Who can guess how a membrane
of a neurone could react to
pressure or temperature by a
change in membrane potential?
The off response
Adaptation: A Mechanism Preventing
Sensory Information Overload
Adaptation: A Mechanism Preventing
Sensory Information Overload
Skin: Paccinian Corpuscles pressure/touch
Skin: Paccinian Corpuscles pressure/touch
Different receptors vary in their speed of adaptation to stimuliDifferent receptors vary in their speed of adaptation to stimuli
Muscle: stretch receptors
Muscle: stretch receptors
Specific types of sensory receptors for
different mechanosensory stimulation
Specific types of sensory receptors for
different mechanosensory stimulation
Receptor SpecificityReceptor Specificity
Mechanoreceptors PhotoreceptorsPhotoreceptors ChemoreceptorsChemoreceptors
Receptors have a differential sensitivity to
different energies or stimuli
Receptors have a differential sensitivity to
different energies or stimuli
nerve ending
A receptor is specific to one energy (or stimulus), because it is most sensitive to that energy. Other energies may stimulate but only at high intensities.
A receptor is specific to one energy (or stimulus), because it is most sensitive to that energy. Other energies may stimulate but only at high intensities.
Sensory afferent (A) has a more spatially limited receptive field than sensory afferent
Sensory afferent (A) has a more spatially limited receptive field than sensory afferent
Sensory Processing:
spatial discrimination
Sensory Processing:
spatial discrimination
neuron (B).neuron (B).
Convergence of sensory pathways is one of the reasons for “referred” pain from visceral organs
Sensory Modality Representation is Location
Specific in the Cerebral Cortex
Sensory Modality Representation is Location
Specific in the Cerebral Cortex
Fine discrimination
is highly represented
Fine discrimination
is highly represented
Sensory Representation is CortexSensory Representation is Cortex
cortical homunculus
Summary:
- Sensory receptors allow our body to interact with the external environment
- Sensory receptors in internal organs are essential for homeostasis and also alert the body in case of some anomaly
- Some receptors adapt fast, others slow and some – almost not at all.
- The intensity of the stimulus is encoded by the frequency of the action potentials.
- Most receptors detect the stimulus via a subset of highly specialised ion channels which open (Na+) or close (K+) to evoke depolarisation of the membrane of the sensory ending in response to the stimulus.
- Information sent from the receptors is called AFFERENT information. In the CNS it is usual that several afferent neurones contact the same postsynaptic cell. This is the convergence, which is also a reason for referred pain.
- The organs with the highest tactile sensitivity have the largest representations in the “sensory homunculus”
