1
The following description is based on lecture notes from Laszlo Zaborszky, from Rutgers University.
1
receptor
Merkel ’s
ending
Free nerve
gland
Sebaceous
corpuscle
Meissne r’s
Hair receptor
corpuscle
Ruffini’s
Septa
Papillary Ridges
corpuscle
Pacinian
Dermis
Epidermis
Glabrous skin
Hairy skin
disks.
4
From Wikibooks
type 4 joint receptors are nociceptors.
direction and speed of movements). The free receptors or
ent characteristics of joint function (position, movements,
and have been divided into four groups. They signal differ-
The joint receptors are low-threshold mechanoreceptors
Joint receptors
tivity can be maintained at any given muscle length.
late the sensitivity of the muscle spindle so that this sensi-
Gamma motor neurons can regu-
called gamma neurons.
fibers are
intrafusal
plying the contractile portions of
are called alpha motor neurons, while the smaller ones sup-
large motor neurons that supply extrafusal muscle fibers
Muscle spindles also receive a motor innervation. The
stretched and each sensory ending fires impulses.
cle is stretched, the central part of the intrafusal fiber is
3
one or more sensory endings applied to it. When the mus-
Anatomy of the Somatosensory System
ever the muscle is stretched, the intrafusal fibers are also
few myofilaments and is non-contractile, but it does have
stretched. The central region of each intrafusal fiber has
intrafusal fibers are attached to extrafusal fibers, so when-
in contrast to the ordinary extrafusal fibers. The ends of the
publishing, see css4.pub.
HTML and CSS for paper-based
third of the fibers. These fibers are called intrafusal fibers,
For more examples of how to use
small muscle fibers with a capsule surrounding the middle
ments. Arrows indicate excitatory connections; filled circles inhibitory connections.
dles. They are quite simple in principle, consisting of a few
body are long, thin, stretch receptors called muscle spin-
Scattered throughout virtually every striated muscle in the
Feedback loops for proprioceptive signals for the perception and control of limb move-
Muscle Spindles
Figure 3:
neurons
with referred pain.
can be chronic and is often associated
poorly localized,
pain, arising from viscera, musculature and joints, is also
The third or deep
poorly localized and poorly tolerated.
tive component is called second pain or burning pain; it is
ized and easily tolerated. The much slower, highly affec-
called first pain or cutaneous pricking pain. It is well local-
is
2
resolution,
which often has high spatial
From Wikibooks
ted signal,
nociceptors are either high-threshold mechanoreceptors
used for transmitting these signals. The rapidly transmit-
skin
Functionally,
nerve fibers
types of
Nociceptors have free nerve endings.
corresponding to different
Nociceptors
nents,
stretching of skin.
Pain signals can be separated into individual compo-
or
and Merkel’s
non-noxious thermoreceptors at high temperatures).
movement
ing (in contrast with the saturating responses displayed by
respond to the lataral
corpuscles
corpuscles
Ruffini
change their response rates as a linear function of warm-
corpuscles,
Ruffini
so respond to temperatures in the range of 40–60°C, and
Meissner
while the slowly adapting
that depends on the degree of tissue deformation. They al-
skin:
punctures of the epithelium, with a response magnitude
vibration,
less)
gives a feeling of
to noxious chemicals. These receptors respond to minute
Activation of the rapidly adapting Pacinian corpuscles
receptors in the glabrous (hair-
only to intense mechanical stimuli, but also to heat and
Polymodal receptors respond not
up to several seconds in duration.
the Pacinian corpuscles and the
tial indentation of skin, but also to sustained indentation
receptors.
hairs. Encapsulated receptors are
axons, slowly adapting fibers respond not only to the ini-
the hair receptors at the roots of
or polymodal
free receptors are
man digits is reduced to 10/mm². Unlike rapidly adapting
Inter-
outside margins.
Muscle
passage of time so that by the age of 50, the density in hu-
Examples for
the table and Figure 3, intrude into the
This innervations density shrinks progressively with the
be free receptors or encapsulated.
bottom of the page. Wide content, like
er glabrous surfaces, and at very low density in hairy skin.
man skin: Mechanoreceptors can
Also, figures are floated to the top/
on whether the page is left or right).
Receptors in the hu-
mouth (50/mm² of skin surface), at lower density in oth-
Figure 1:
margin (on the left or right, depending
are present at high density in the digits and around the
Velocity (primary muscle-spindel afferents)
sidenotes are shown in the outside
Merkel’s receptors
In response to
Notice how figure captions and
receptors mediating form perception,
lifting.
Table 1
for form and texture perception. As would be expected for
tance during the early stages of
burst of action potentials when objects move a small dis-
The slowly adapting Merkel’s receptors are responsible
These afferents respond with a brief
in fingers.
tivity.
of the role played by somatosensory neurons in motor ac-
stretch”. Used for joint position
objects are lifted.
a rapid response to a tactile stimulus is a clear indication
Ruffini’s corpuscle: “A skin
Length error (primary muscle-spindel afferents)
adapting afferents leads to adjustment of grip force when
Sensory information from Meissner corpuscles and rapidly
tion” e.g. tapping with a pencil.
reflexively until the gripped object no longer moves. Such
Length (secondary muscle-spindel afferents)
Pacinian corpuscle: “A diffuse vibra-
rapidly adapting afferent activity, muscle force increases
Gamma bias
Cutaneous receptors
Spindles
about muscle length, muscle tension, and joint angles.
field
fibres.
The receptors in muscles and joints provide information
Force (Golgi tendon organ)
large receptive
central portions of the intrafusal
and pain (nociceptors).
Deep receptor /
feedback
around the non-contractile
edge or “an X” in brail.
face texture (mechano receptors),
velocity
Length &
us about temperature (thermoreceptors), pressure and sur-
coil
tial details, e.g. a round surface
afferent
Force feedback
ceptors in the skin, the so called cutaneous receptors, tell
Merkel’s receptor: Used for spa-
Used for recognizing texture.
a secondary (group II)
and sensors in our muscles, tendons, and joints. The re-
length
tect an insect or a very fine vibration.
a primary (group Ia) afferent and
Muscle
Our somatosensory system consists of sensors in the skin
Muscle force
cle fibres. The sensory endings of
Hair receptor, Meissner’s corpuscle: De-
1
IKIBOOKS
sisting of several intrafusal mus-
field
organs
small receptive
Tendon
with its own motor supply con-
W
forces
Surface receptor /
The spindle is a stretch receptor
ROM
F
External
Slowly adapting
and expanded schematic (right).
Load
cord (middle)
Rapidly adapting
Anatomy of the Somatosensory System
removed.
nections in spinal
signal
article, but some content has been
con-
control
content has been changed in this
in a muscle (left), neuronal
Length
position
signal
called Sensory Systems. None of the
Driving
spindle showing typical
contains a chapter from a Wikibook
Mammalian muscle
signal
showcase page-based formatting. It
control
2:
This is a sample document to
Force
Figure