Transcript Articular Receptors

Lecture 5:
Receptors
Perception:
 Exteroception (vision, hearing, smell, touch)
 Interoception (internal objects, organs)
 Proprioception (position of body parts)
Proprioceptor Neuron
Spinal cord
Ganglion
Neuron
body
T-shaped
axon
Sensory
ending
The body of a sensory
neuron is located in a
ganglion near the spinal
cord. One branch of its Tshaped axon goes to the
peripheral sensory ending,
and another branch goes
through the dorsal roots
into the spinal cord.
Proprioceptor Neuron
 Body, long T-shaped axon, and sensory
ending
 Body is in spinal ganglia
 Sensory endings generate APs in response
to a specific stimulus (deformation, light,
etc.)
 Antidromic conduction
 No dendrites, no synapses on the body
Muscle Spindle
Extrafusal fiber
BFdyn
Ia
BFst
II
CF
Extrafusal fiber
A muscle spindle is oriented parallel to extrafusal muscle fibers. It is covered
with a capsule and contains two types of intrafusal muscle fibers: bag fibers
(BF) and chain fibers (CF). Two types of sensory endings can be found in
muscle spindles: primary (Ia) and secondary (II). Primary endings are
typically seen in virtually all intrafusal fibers. Secondary endings are seen in
CF and in static BF, but not in dynamic BF.
Spindle Response to Stretch
(Primary Ending)
Length
Action potentials
Time
Typical responses of a primary spindle ending to an
externally imposed muscle stretch at different velocities.
The response increases with muscle length and with the
velocity of the stretch.
Spindle Response to Stretch
(Secondary Ending)
Length
Action potentials
Time
A typical response of a secondary spindle ending to an
externally imposed muscle stretch and shortening. The
response increases with muscle length and does not depend
on velocity.
Gamma Motoneurons
gdyn -motoneuron
gst -motoneurons
There are two types of small
motoneurons (g-motoneurons)
innervating intrafusal fibers of
muscle spindles.
 Dynamic g-motoneurons
innervate dynamic bag
fibers and change the
sensitivity of primary
endings.
BFdyn
BFst
CF
 Static g-motoneurons
innervate static bag and
chain fibers. They change
the sensitivity of primary
and secondary endings.
Gamma Motoneurons: Effects
on Spindle Reaction to Stretch
Length
g-dynamic stimulation
Time
The effects of an activity of dynamic g-motoneurons on a response
of a primary spindle ending to muscle stretch and shortening. In
the lower graph, a g-dynamic stimulation was applied during the
same changes in muscle length.
Muscle Spindle
Two types of endings:
 Primary (Ia afferents): sensitive to length and
velocity of muscle fibers
 Secondary (II afferents): sensitive only to length of
muscle fibers
Gamma-motoneurons:
 A system to modify sensitivity of the spindle endings
 Gamma-MNs innervate intrafusal muscle fibers
Golgi Tendon Organs
Ganglion
Ib afferent
Golgi tendon organ
Muscle fibers
Tendon
Golgi tendon organs are located in series with extrafusal muscle
fibers at their junction with the tendon. They are innervated with
fast-conducting Ib axons of sensory neurons in spinal ganglia.
Golgi Tendon Organs:
Response to Muscle Force
Muscle force
Action
potentials
Time
A response of a Golgi
tendon organ to
muscle force. Note
that it is similar to the
response of secondary
spindle endings to
muscle length.
Articular Receptors
Frequency of firing
Angle
Anatomical
limits
Most articular receptors fire
in rather narrow ranges of
joint angle, mostly close to the
anatomical limits. An increase
in muscle force leads to an
increase in joint capsule
tension, and articular
receptors increase their
response (bold lines).
GTO and Articular Receptors
GTO: a passive sensory ending sensitive only to
tendon force
Articular receptors:
 Sensitive to joint angle close to the anatomical
limits of joint rotation
 Sensitive to joint capsule tension
Cutaneous and Subcutaneous
Receptors
Skin surface
Meissner corpuscles
Merkel disks
Ruffini endings
Pacinian corpuscles
Major types of cutaneous and subcutaneous mechanoreceptors
in the glabrous skin of the hand.
Cutaneous and Subcutaneous
Receptors
Name
What They Measure
Features
Merkel disks
Vertical pressure
Several are innervated
by one axon
Meissner
corpuscles
Quickly changing
pressure
Each is innervated by
≥ 2 axons
Ruffini
endings
Deformation of
large skin areas
Slowly adapting
Pacinian
corpuscles
Rapidly changing
Huge (1–5 mm)
mechanical deformation
(such as vibration)
Central Axons
of Proprioceptive Neurons
To the brain
Spindle
MN
Ia
Ia, II
Articular
receptor
Golgi organ
Ib
INs
Skin receptors
Afferent nerves from
peripheral receptors go into
the spinal cord through the
dorsal roots. There they make
synapses on interneurons and
motoneurons (only primary
spindle endings) and send
signals to the brain. Note that
the same interneurons may
receive signals from afferents
of different modalities.