Download W5D3H3: Sensory Receptors

W5D3H3: Sensory Receptors
Learning Objectives
1. Outline properties of sensory receptors including how
intensity (strength) and duration are encoded and adaptation to
stimulus.
2. Discuss the importance of the frequency of action potentials
and its relationship to neurotransmitter release and stimulus
coding.
3. Give examples of how sensory receptor properties are utilized
by cutaneous receptors to detect and encode input.
4. Compare and contrast sensory receptor physiology
(photoreceptors, olfactory receptors, gustatory receptors and
hair cells).
Why This Topic?
• Understanding how external signals are detected and
encoded by the nervous system is essential to a bigpicture understanding of how stimuli are detected and
interpreted by the nervous system. Because defects in
this process constrain the well-being and quality of life
for many people and because changes in how stimuli
are detected and integrated can be used to identify more
serious conditions, it is essential to understand this
process. This material also integrates physiology, HFF,
and clinical topics by explaining how nerve damage
from diabetes can alter neuronal signaling.
LO 1. Outline properties of sensory receptors including how intensity (strength) and
duration are encoded and adaptation to stimulus
Primary problem: How do we get information about the outside world and the
inside world? Labeled lines: sensory nerve cells carry information to the
spinal cord and brain about specific types of stimuli.
Abstract
In the somatosensory system, various different sensory receptors capture different stimuli and
convey them to the sensory cortex. Each type of receptor is specialised, that is, receives the
stimulus to which it is predetermined to receive. Immediately as it is stimulated, the receptor
sends a signal to the somatosensory cortex, via nerve fibres, and the area of the cortex that
receives the signal determines the mode of the consequent perception. This mechanism is
called principle of the "labelled" lines. The somatic receptors are the structures designated to
receive stimuli, however, if their afferent fibres are stimulated at any point when approaching
the cortex, the mode of perception by the cortex is the same as when the somatic receptor is
stimulated directly. This occurs after the amputation of a limb, wherein the remaining fibres
transmit to the cortex the mode of sensation for which they were specialised, despite the lack
of somatic receptors at the beginning of the afferent pathway. However, the afferent pathway
ends at the same cortex area as before the deafferentation. Since the somatic receptors and the
integrity of afferent pathways are important to the regulation and modulation of the received
stimuli, after the deafferentation the afferent pathway becomes anatomically and functionally
abnormal. We believe these factors, involved in the pathophysiology of phantom limb (PHL),
might be the explanation for this intriguing phenomenon.
Somatosensory Homunculus
Figure 10-9
LO 1. Outline properties of sensory receptors including how intensity (strength) and
duration are encoded and adaptation to stimulus
Three classes of sensory receptors: (a) free nerve endings, (b) with
accessory structures, and (c) specialized receptor cells.
LO 1 & LO 2. Outline properties of sensory receptors including how intensity (strength) and duration are
encoded and adaptation to stimulus. Discuss the importance of the frequency of action potentials and its
relationship to neurotransmitter release and stimulus coding.
Transmitter release
More
transmitter
release
LO 1 . Outline properties of sensory receptors including how intensity (strength) and duration are encoded
and adaptation to stimulus.
LO 3. Give examples of how sensory receptor properties are utilized by cutaneous (skin) receptors to
detect and encode input.
Area on the skin that receptor responds to
rapidly adapting
slowly adapting
rapidly adapting
slowly adapting
LO 3. Give examples of how sensory receptor properties are utilized by cutaneous (skin) receptors to
detect and encode input.
Area on the skin that receptor responds to
rapidly adapting
Fine touch
< 50 Hz
slowly adapting
rapidly adapting
Light pressure
Vibration
> 50 Hz
slowly adapting
Stretch
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
depolarization
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
Taste buds. Each taste bud is composed of taste cells
joined near the apical surface with tight junctions.
Taste ligands create Ca2 signals that release serotonin or ATP.
Sweet Umami Bitter Sour
(CO2)
Tight junction
Type I support cells
Taste buds are located
on the dorsal surface
of the tongue.
may sense salt when
Na enters through
Na channels.
Taste pore
Salt?
Presynaptic
cell (III)
(Adapted from
Tomchik et al., J
Neurosci 27(40):
10840–10848,
2007.)
ATP
Serotonin
Receptor cells
(type II)
Light micrograph of a taste bud
Primary sensory neurons
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
Panx1
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
HPHY 241
26
Figure 10-16c
LO 4. Compare and contrast sensory receptor physiology (photoreceptors,
olfactory receptors, gustatory receptors and hair cells).
END 
Somatosensory Cortex
4.
5.
It is in the somatosensory cortex that the brain
recognizes where the ascending sensory tracts
originated
i. Each sensory tract has a corresponding region on
the cortex
Within each region, columns
of neurons are devoted to particular
types of receptors
Fig. 9.10
HPHY 241
33
HPHY 241
34
HPHY 241
35
HPHY 241
36
HPHY 241
37
4. The tectoral membrane and hair
cells
HPHY 241
38
HPHY 241
40
HPHY 241
41
HPHY 241
42
HPHY 241
43
HPHY 241
44
HPHY 241
45
HPHY 241
46
HPHY 241
47