This document provides an extensive exploration of the senses and the somatic nervous system, detailing how the body perceives and processes various stimuli from the environment. It begins with an overview of sensory systems, focusing on how sensory information is received through afferent pathways...
Module
3:
The
Senses
and
Somatic
Nervous
System
The
Senses:
Introduction
and
Vision:
→
Types
of
sensations
include…
pain,
touch,
vibrations,
pressure,
and
temperature
-
All
come
from
various
receptors
located
throughout
the
body
-
Proprioception
:
a
critical
sensory
ability
that
enables
individuals
to
understand
their
body’s
position
in
space.
It
involved
sensory
feedback
from
stretch
receptors
in
muscles
and
joint
connective
tissue.
-
Vision
also
plays
a
role
in
spatial
awareness,
but
spatial
orientation
is
not
solely
dependent
on
visual
inputs.
-
Visceral
stimuli
like
blood
oxygen
levels,
pH,
and
osmolarity
are
sensory
inputs
the
body
detects
and
responds
to,
integrating
these
signals
like
other
sensory
information.
Circuitry
Involved
in
Sensory
Pathways:
→
Afferent
Pathways
and
Sensory
Neurons:
-
Afferent
pathways
are
the
routes
by
which
sensory
information
reaches
the
CNS.
These
pathways
are
with
afferent
sensory
neurons.
-
Sensory
neurons
reside
in
structures
called
ganglia
,
located
outside
the
CNS
within
the
peripheral
nervous
system.
An
example
is
the
dorsal
root
ganglion.
-
The
dorsal
root
ganglion
is
positioned
on
the
dorsal
side
of
the
spinal
cord.
-
Pseudounipolar:
a
single
axon
that
extends
in
two
directions
-
When
a
strong
enough
stimulus
is
detected
(e.g.,
pain),
it
generates
action
potentials
in
the
neuron,
which
travels
along
the
axon,
bypassing
the
cell
body
and
continuing
towards
the
CNS,
entering
through
the
spinal
cord.
-
Once
in
the
CNS,
the
sensory
information
carried
by
the
action
potentials
is
synapsed
with
other
neurons,
which
integrate
the
information.
-
This
integrated
information
can
lead
to
various
responses
initiated
by
the
CNS,
communicated
back
to
different
body
parts
via
efferent
pathways.
Somatosensation:
→
includes
various
sensory
experiences
(particularly
related
to
touch
and
pressure)
and
sensory
detection
in
somatosensation,
which
is
facilitated
by
afferent
neurons
equipped
with
mechanoreceptors
in
their
endings.
-
The
morphology
of
the
nerve
endings
influences
what
specific
stimuli
they
can
detect.
-
Free
nerve
endings
:
-
Primarily
sensitive
to
touch
-
Consists
of
the
bare
ends
of
axons,
often
located
near
the
skin’s
surface
-
Encapsulated
nerve
endings
:
-
feature
a
protective
capsule
with
layers
of
cells
and
fluid
around
the
nerve
ending
-
Allows
receptors
to
detect
specific
stimuli,
such
as
vibrations
of
certain
frequencies -
Stretch
receptors
:
-
In
muscles,
tendons,
and
joints
-
Crucial
for
proprioception
-
Respond
to
stretching
or
deformation
of
their
membrane
-
Thermoreceptors
:
1.
Cold
thermoreceptors
-
It
can
bind
to
menthol,
which
mimics
the
sensation
of
cold
2.
Heat-sensitive
thermoreceptors
-
It
can
bind
capsaicin,
which
produces
a
sensation
similar
to
heat.
-
The
depth
at
which
nerve
endings
are
in
the
skin/muscle
also
determines
the
type
of
stimulant
they
can
respond
to,
affecting
sensitivity
to
different
tactile
sensations.
Visual
System:
→
used
to
determine
the
shape
and
color
of
objects
and
their
movement.
Light
particles
have
wavelengths
and
energies
associated
with
different
colors
-
Eye
:
Functions
like
a
camera
to
focus
light
on
the
retina
using
a
lens
and
a
pupil
whose
size
can
be
adjusted
to
change
the
amount
of
entering
light
-
Vision
:
the
process
by
which
light
reflected
from
external
objects
is
translated
into
a
mental
image.
1.
Light
enters
the
eye
and
is
focused
by
a
lens
onto
the
retina
2.
Retinal
photoreceptors
transduce
light
energy
into
electrical
signals
3.
Processing
of
the
electrical
signals
through
neural
pathways
Cornea
:
most
of
the
focus
occurs
here
due
to
air/cornea
density
differences
Lens
:
adjusts
for
change
in
distance
-
Changes
in
the
shape
of
the
lens
focus
the
light
onto
the
retina
Pupil
:
adjusts
the
amount
of
light
entering
Retina:
contains
the
photoreceptors,
rods,
and
cones
-
Rods:
low
light
vision
-
Cones:
color
vision
Ciliary
Muscles
surround
the
eye's
lens
and
are
crucial
for
focusing.
They
are
connected
to
the
lens
via
zonular
fibers.
Lens
Adjustment:
-
Muscle
contraction:
When
ciliary
muscles
contract,
they
shorten,
decreasing
the
diameter
of
the
ring
they
form
and
reducing
tension
on
the
zonular
fibers.
This
allows
the
lens
to
adopt
a
more
spherical
shape
for
focusing
on
nearby
objects.
-
Muscle
relaxation
:
Conversely,
when
these
muscles
relax,
they
elongate,
increasing
the
ring's
diameter
and
the
tension
on
the
zonular
fibers
,
flattening
the
lens
to
focus
on
distant
objects.
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