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12c properties of sensory receptors (3. Muller's doctrine of …
12c
properties of sensory receptors
1.
specificity of response
or law of adequate stimulus
the receptors respond maximally
only when an appropriate stimulus
is applied
the receptors on each of the sense organs
are thus adapted to
respond to 1 particular form of energy
at a much lower threshold
than other receptor's response to
this form of energy
That particular form of energy
to which a receptor is most sensitive
is called
its adequate stimulus
examples
warm water- stimulates Ruffini's receptor
at low intensity of stimulus
producing a specific response
but
it also stimulates the naked
nerve endingsof pain
at high stimulus
& the response produced is not complete.
the adequate stimuli for the rods & cones
in the eye is light.
-pressure on the eyeball will also
stimulate these receptors
but the threshold of these receptors
to pressure is much higher than
the pressure receptors in the skin
tactile receptors respond to deformation
eg
golgi tendons to stretch
& cochlea to vibrations
of the basement membrane set up by sound
at a much lower threshold of stimulus
2.adaptation
when a stimulus of constant strength
is applied to the receptor,
the frequency of AP in it's sensory nerve
decr over a period of time
-a phenomenon called adaptation
or desensitization
this is due to accommodation of
sensory NF to the generator potential
the degree to which adaptation occurs
varies with type of receptors
the receptors are of 2 types
1.tonic receptors
adapts slowly to stimulus
& continues to produces AP
over the duration of the stimulus
so the generator potential is
prolonged & decays slowly
this is important cos
if these receptors get adapted
it will damage the body
1 more item...
2.phasic/rate receptors
adapts readily to a stimulus
& transmit signals only when
stimulus strength is changed
so impulses transmitted is
directly proportional to the
rate at which the change
takes place
1 more item...
3. Muller's doctrine of
specific nerve energies
the sensation prod by impulses
generated in a receptor depends upon
the specific part of the brain
they ultimately activate
cos the specific pathways to the cortex
are seperate frm the sense organ
when nerve pathways frm a
particular sense organ are stimulated,
sensation produced is
the sensation for which
the receptor is specialized to
-no matter how or where along the pathway
the activity originated
eg: pressing on the eye elicits
sensations of flashes of light
cos the neurons in the retina send
a signal to the occipital lobe.
-despite the sensory input being mechanical,
the experience is visual
Muller 1935
4.law of progection
no matter where
a particular sensory pathway
is stimulated along its course to the cortex,
-the conscious sensation produced
is referred to the
location of the receptor
this principle is called law of projection
eg: -a limb that has been lost by accident/ampu
-the patient usually experiences intolerable pain
& proprioceptive sensations in the limb
that is no longer there
these sensations are due to
-the irritation of the damaged
nociceptive & proprioceptive afferents
at the stump of the removed limb
5.law of intensity discrimination
2 ways in which info abt intensity
of stimuli is transmitted to the brain
1.by variation in the no of the APs generated
by the activity in a given receptor
2.by variation in the no.of receptors activated