FNH 160:
Integrated Physiology for Human Nutrition
LECTURE 8:
Peripheral Nervous System:
Somatosensation &
Special Senses Part 1
Dr. Elizabeth Novak
University of British Columbia
Oct 3, 2023
October Update & Check In
Upcoming schedule:
Oct 3, 5 & 10: Peripheral nervous system
Oct 12: No Class- Makeup Monday
Oct 17: Open class for review and finishing nervous system assignment
Oct 19: MIDTERM EXAM
• Midterm will cover all material from the start of the course to the
end of nervous system
• Key terms, practice exams, and more info on exam will be posted
next week
CLICKER CHECK IN
If I could make one suggestion for this course that would enhance
my learning (or preparation for the midterm), it would be:
Learning Objectives
1. Differentiate between visceral and sensory stimuli
2. Discuss the concept of sensory perception
3. List the types of sensory receptors and describe how sensations are
coded/differentiated by the nervous system
4. Define somatosensation and describe the types of somatosensation
5. Describe pain transmission and explain the effect of opioids
6. Describe the ascending pathway for sensory information
7. Identify key structures of the eye including: pupil, iris, sclera, lens,
cornea, aqueous and vitreous humour, retina, optic nerves
8. Describe the roles of the iris and accommodation in focusing light
9. Differentiate between rods and cones
10.Describe the process of transducing visual information and sending it
to the brain
11.Describe how visual fields cross in the cortex and the implications for
binocular vision
Organization of the Nervous System
Figure 4-1, p. 96
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Visceral vs Sensory Stimuli
• Visceral = Internal
– Blood pressure, CO2 concentration, acidity…
– Usually subconscious
things that we detect.
Internal things
I am not aware my body is detecting them
• Sensory = External
– Somatic sensation: Touch, pain, hot/cold, propioception
– Special senses: visual, auditory, olfactory, taste,
equilibrium
– Conscious awareness
I am aware what I am hearing...
Comes from all around the bosy. Special
sense comes from specific part.
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Perception
. Sensory stimuli
. Evolves makeing a meaning of a stimuly
. Let us detect only certain parts of stimuli. Not all
of it.
.
• Perception
– Conscious interpretation of external world derived
from sensory input
– Our sensory perception does not give the true reality.
like optical illutions
• The cerebral cortex manipulates incoming information.
• Humans have receptors that detect only a limited
number of existing energy forms
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Our World is What We Perceive It To Be
my body interprete this images
getting something familiar to
them.
Figure 5-1, p. 147
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Receptors & Their Stimuli
Perception can detect:
• Mechanoreceptors
– Sensitive to mechanical energy (touch, pressure, vibration, stretch)
• Thermoreceptors
– Sensitive to warmth and cold
• Photoreceptors
– Responsive to visible wavelengths of light
vision
• Osmoreceptors
– Detect changes in concentration of solutes in body fluids and
resultant changes in osmotic activity
hosmolarity
• Chemoreceptors
certain chemicals
– Sensitive to specific chemicals; Include receptors for smell and
taste, O2 and CO2 concentrations in blood, and contents of
digestive tract
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Receptor Physiology
• Receptors of the nervous system are structures at the peripheral
endings of afferent neurons
• Detect various stimuli
• Convert stimuli into electrical signals (graded & action potentials)
• Process is called transduction
one of the 4 types of neurones.
smell, light. When they detect that they open ion channels to initiate action
potential. Thet detect an stimuli and convert oit into an action potential. This
is call trasduction.
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Conversion of Receptor Potential into
Action Potentials
Sensors detect the stimulios. Then open ion channels and Na comes in. It goes
when there are more - charges. We reach trashole and continue going through the
cell
Figure 5-2, p. 149
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Coding sensory info:
the way in which the
body is able to
distinguish different
types of stimuli.
detected by the location
of the location and how
the stimuli goues unto
the CNS nad how the
brain reacts.
detected by how many
detector are activated
and how intsne the
stimuli is.
Table 5-1, p. 151
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CLICKER QUESTION
A loud sound would be differentiated from a soft sound by:
A.
B.
C.
D.
E.
The type of stimulus/receptor activated
The location of the stimulus
The size of action potential generated
The frequency of action potentials generated
Two or more of the above
more action potentials,
more receptors.
CLICKER QUESTION
A tap on your right arm would be differentiated from a tap on
your left leg by:
A.
B.
C.
D.
E.
The type of stimulus/receptor activated
The location of the stimulus and and the spinal nerve
The size of action potential generated
The frequency of action potentials generated
Two or more of the above
there is only 1 size of
depends on whether the stimuli goes.
ion Potential.
Somato: body
Somatosensation
sesations that are
interpretate in the SSA.
• Sensations arising from the body/skin: touch, pressure, cold,
warmth, and pain
• Primary somatosensory area is located in the parietal lobes of
the cerebral cortex
whe detect them trough
receptor
• Also includes sensations from
the muscles, tendons, and
joints = position of the limbs
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somato sensitive are
(SSA) THE AREA IN
BLUE: mand the body
through that area
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Mechanoreceptors: Touch & Pressure
sensed through mechanicreceptor.
• Respond to physical contact and movement
• Five types
– Pacinian corpuscles
– Meissner’s corpuscles
– Merkel’s discs
– Ruffini corpuscles
– Free nerve endings – most abundant - touch,
tickling, itch
of receptors:
Types of mechanoreceptors NOT examinable
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Thermoreceptors: Warmth & Cold
respond to deeper presures
when temperature goes down
when temperature goes off
Free Nerve Endings:
Touch, temperature,
pain
Pain
alests when somth goes
wrong in the body so
that we fix it.
• Protective mechanism meant to bring a conscious awareness
that tissue damage is occurring or is about to occur
• Helps us avoid potentially harmful events in future
• Detected by nociceptors:
– Mechanical nociceptors
• Respond to mechanical damage such as cutting,
crushing, or pinching
– Thermal nociceptors
• Respond to temperature extremes
– Chemical nociceptors
• Respond to many kinds of irritating chemicals
noxious
respond to mechanical damage
in the body
repoind to extremes
chemicals can be reales
inside of body too.
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Pain Transmission
Pain is transmitted from
nociceptors to the cortex and
limbic system
to the spinal cored and
brain and to the limbic
system
Figure 5-6a, p. 155
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Opioids Modulate Pain Transmission
Endogenous opiates (endorphins) block
pain transmission to the brain
Exogenous opioids (morphine, heroin,
Brein send down opiate receptor to
neurones. These are ment to reduce pain.
Our body makes them.
we administrate them in the body.
Hace the same effect. They block
pein trasmition too.
codeine, oxycodone, hydrocodone and
fentanyl) also block pain transmission by
binding to opioid receptors
Figure 5-6b, p. 155
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Opioids Modulate Pain Transmission
Endogenous and exogenous
opioids also block GABA
release in the brain and
stimulate the release of
dopamine
Opiodis block GABA (INHIBITORY neurone
trasmitor) in the brein.
Opiods block the GABA and they reaease
dopamine. We gat sense of euphorya and
plesure.
the more you take opiods, the more you
become tolerant to them and you have to
take more each time.
If you stop takin them you start to feel
pain. The only way to avercome this pain
is to take opio again. This in an
addiction
In overdose the part of the bain that
tell us to breath stop working and we
get axficied and we doie.
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SOMATOSENSATION LAST PART:
Transmission of Information Via
Ascending Pathways
First-order sensory neuron
Afferent neuron that detects
stimulus and sends
information into the CNS
Second-order sensory neuron
Origin in either the spinal
cord or brain stem.
Synapses with third-order
neuron in thalamus
Third-order sensory neuron
Thalamus to cerebral cortex
AFFERENT NEURONE THAT
DETECT THE STIMULI
AND BRONIG IT INTO
THE CNS (brain)
STARTS in the
CNS and takes
it to the
thalamous
(centre of the
brain)
From the thalamous to the conrtex
where we process the info.
If I felt the stimuli form my
left, it goes to the right part
of the cerebrum.
Figure 4-11, p. 109
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CLICKER QUESTION
Gently tap your right finger on your desk.
In transmitting the sensation from your finger to your
brain, which of the following represents the correct first
order neuron path?
A.
B.
C.
D.
E.
Mechanoreceptor to thalamus
Mechanoreceptor to parietal cortex
Mechanoreceptor to medulla (brain stem)
Chemical receptor to thalamus
Nociceptor to medulla
CLICKER QUESTION
Gently tap your right finger on your desk.
In transmitting the sensation from your finger to your
brain, which of the following represents the correct
SECOND order neuron path?
A.
B.
C.
D.
E.
Medulla to hypothalamus
Medulla to thalamus
Medulla to spinal cord
Medulla to right parietal cortex
Medulla to left parietal cortex
CLICKER QUESTION
Gently tap your right finger on your desk.
In transmitting the sensation from your finger to your
brain, which of the following represents the correct THIRD
order neuron path?
A.
B.
C.
D.
E.
Thalamus to right parietal cortex
Thalamus to left parietal cortex
Thalamus to spinal cord
Left parietal cortex to motor neuron
Right parietal cortex to motor neuron
Vision
Special senses
blood vessels
where fotoreceptors
are. Detect light
protective coding
focal point of
the eye. Where
the image in more
clear.
focusing lihjt
instead of the
sclera
provide oxgen
keeps the shape
of the eye
blind spot o el
chroid
know all this
funtions
Figure 5-7, p. 158
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View of the Retina Seen through an
Ophthalmoscope
Figure 5-17, p. 164
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The Iris
make pupil smaller.
make pupil
bigger
they contract to make
things bigger
Figure 5-9, p. 159
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Lens Accommodates to Focus Near Images
accomodation: makes itselve more round so that
it can focus better.
Lens: focus light to build a clear image.
. When looking to smth near, you need to
accomodate light to focus it and buld a clear
image.
. Lens accomodate to do this. They become more
rounded when we go through look for smth far
away to look for somethig close.
Figure 5-15a, p. 163
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Emmetropia, Myopia, and Hyperopia
good sight
not focus well
things far away.
not focus well
things close.
Not
examinable
Figure
5-15b
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who to convert light to an image: by the retina.
light come in the eye from the pupil and hit the
retin. The retina proccees that info in opposite
direction.
Fotoreceptors: detect light. They detect the light
and change into electrical signal that go to dipolar
cells. They send oit to the gangliar cell and they
sent it to the
The Retinal Layers
Figure 5-16, p. 164
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The Retinal Layers NOTES
1. Light flows through the eye to the
retina
2. Light energy is absorbed by
photoreceptor cells (rods and
cones)
3. Photoreceptors pass the signal to
bipolar cells
4. Bipolar cells pass the signal to
ganglion cells, which travel via the
optic nerve to the occipital cortex.
Figure 5-16, p. 164
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repond to light energy.
Types:
. Cones:
. Rod: rhodopsin (protein). the light is
absorved by it.
Photoreceptors
Not
examinable
Figure 5-19a and b, p. 166
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CLICKER QUESTION
Retinal is a form of:
A.
B.
C.
D.
E.
Protein
Lipid (fat)
Vitamin B
Vitamin A
Vitamin C
it is key for the
redophsin. Deficient of
it is one of the mayor
couses of blindness.
Photoreceptors
proteins
• Contain light-absorbing pigments that undergo chemical
alterations when activated by light
• Rods
– Provides vision only in shades of grey
– Rhodopsin: Absorbs all visible wavelengths
• Cones
– Respond selectively to various wavelengths of light: red,
green, blue
– Make colour vision possible
both repond to llight
all calours.
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Sensitivity of the Three Types of Cones to
Different Wavelengths
Cones that repond to:
Blue range:
Green rage
Red range
Figure 5-21, p. 169
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Colour Blindness Chart
Colour blindness:
inability to
correctly
distinguish colors
some people do not have one cone and can not
differentiate that colour.
Most common: can distinguish red and green.
Figure 5-22, p. 170
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CLICKER QUESTION
Which of the following is correct?
see the iamge.
A. Rods are more abundant than cones
B. Cones are more abundant than rods
C. There are about equal amounts of rods and cones in the
retina
The Retinal Layers
Figure 5-16, p. 164
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Photoreceptor Acuity
do not need much lught to be activated.
Rods better in a dark room.
• Rods: High sensitivity, less acuity
– Multiple rod cells converge on one bipolar cell, so less
stimulation is needed to generate a signal, but the
origin of the signal is less clear.
we need less stimulation to get a signal. We do not need much light to activate the bipolar zone. Rodes are more
sensitive
PROBLEM: brain can tell where the light come from. The image we get from rodes is less clear.
I can really say how is in a dark room.
• Cones: Low sensitivity, high acuity
– Only one cone cell communicates with each bipolar
cell, so greater stimulation (more light) is needed to
generate a signal, but the origin of the signal is clear.
1 cone goes to 1 polar cell. We need enough light to sufficiently go to each cone. Requierd a lot of
light. Brain get exacly where the lighht came from and we can see with more detailed.
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Dark
no incoming light, photoreceptors
cells are depolarized. Ca channels
are opened and
Dark
Photoreceptor cells (rods)
Retinal remains in cis form
Rods
OPEN
Na+ channels
Depolarization of
photoreceptor
Bipolar cells
Ganglion
cells
Opens Ca+ channels
_
HYPERpolarization of
bipolar cell
NO action potential in
ganglion cell
No transmission via
optic nerve to visual
cortex
Perceived as darkness
↑ neurotransmitter
release
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Phototransduction: Light
Light
fotoreceptor becom hyperpolarized when
hitten by light.
Photoreceptor cells (rods)
Retinal → all-trans form
Rods
Signal transduction cascade that
closes Na+ channels
Depolarization of
bipolar cell
Action potential in
ganglion cell
no action potential
Hyperpolarization of
photoreceptor
Transmission via optic
nerve to visual cortex
to get an action potential
Bipolar cells
Ganglion
cells
Closes Ca+ channels
Illuminated
photoreceptors
perceived as vision
↓ neurotransmitter
release
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Phototransduction: Light
Key Points:
know this well. 2 slides
above not really.
1. Light causes conformational change in retinal in
photoreceptor cells
2. The conformational change causes Na+ channels to
close and photoreceptor cells HYPERPOLARIZE.
In darkness, Na+ channels are open and
photoreceptor cells are DEPOLARIZED
3. When light is detected, photoreceptor cells
communicate with bipolar cells, which then
communicate with ganglion cells that form the optic
nerve
Crossing of Visual Fields in Cortex
Information from the
left visual field is
received on the right
visual cortex
Information from the
right visual field is
received on the left
visual cortex
Overlapping areas
give binocular vision
which is important
for depth perception
Figure 5-24, p. 171
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CLICKER QUESTION
Damage to the left visual cortex would cause:
A.
B.
C.
D.
Loss of vision from the left eye
Loss of vision from the right eye
Loss of vision from the left visual field
Loss of vision from the right visual field
Table 5-4, p. 171
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Table 5-4 (cont’d), p. 171
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Key Points
• The body detects visceral and sensory (external) sensations
through various sensory receptors (mechano-, chemo-,
thermo-, photo-, osmo)
• Sensory receptors translate stimuli into electrical impulses
that travel to the brain
• Somato-sensation = touch, pressure, temperature, pain and
position of joints/muscles
• Vision is the detection of light waves through photoreceptors
in the retina
• Light hyperpolarizes photoreceptor cells, which ultimately
sends a signal via bipolar and ganglion cells trough the optic
nerve to the occipital cortex
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Review Homework
1. List the different types of sensation you can perceive in your
hand and the type of receptor that senses each.
2. Trace the path of sensory information from:
a. Touching something with your right foot to perception in
the brain
b. Touching a hot stove (a painful stimulus) with your left
hand. )Note: there are two pathways to trace here: 1. the
spinal reflex, 2. the ascending pathway to the brain
3. Describe two key paths by which opioids modulate pain
transmission.
4. Trace the pathway of light from a light source through the
eye, transduction from light to electrical signal, and
transmission to the occipital cortex.
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Review Homework
5. Label the key anatomy of the eye in the diagram below.
d.
e.
a.
b.
c.
d.
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