Exam 2 week 8 ppt 4 & 5 GTOs & Joint Receptors Proprioception Flashcards
what does GTO stand for?
Golgi Tendon Organ
What is a GTO?
A slowly adapting, encapsulated receptor located in junction of striated muscle and tendon
- –Axons of GTO intertwined with collagen bundles of tendon
- –Axon contains modality-gated Na+ pores that are activated when the tension is developed in the tendon during muscle contraction
Describe how the GTO functions? (5 steps)
- –Tension in tendon from muscle force stimulates Ib (Aa) primary afferent.
- –Excites inhibitory interneurons
- –Inhibitory interneurons reduce the activity of motor neurons to the same muscle
- –This reduces the force development of the muscle
- –Often thought of as a protective reflex at high muscle forces
What do GTOs respond to?
–Dynamic and static responses to increase tension in tendon
- §Moderate response to tension produced by stretch (a)
- §Higher response to active tension (b) due to muscle contraction
does the GTO funciton just at high levels of tension or at all levels of tension?
GTO is often thought of as a protective reflex at high muscle forces, but this is inccorect.
It actually fires at all levels of tension so involved in regulation of muscle tone not just protection of the tendon
when are GTOs relatively ppor sensors of ROM?
When no load is applied
when are GTOs very snesitive to ROM?
–With application of low level of force (B) GTOs are very sensitive to change of joint angle
what might GTOs be able to do in addition to measuring tendon tension?
in addition to measuring tendon tension GTOs may act as proprioreceptors and be able to assess joint angle as well when slight tension placed on tendon during ROM
what is a muscle receptor?
a sensory organ that responds to muscle stretch or tension, including muscle spindles and tendon organs
http://medical-dictionary.thefreedictionary.com/muscle+receptor
Describe evidence of use of muscle and tendon receptors as proprioceptors: (2 things)
- §Vibration applied to muscle or tendon produces the sensation of limb movement but not when applied to joints - importance of muscle receptors
- §When unmoving limb muscles vibrated and subjects were asked to fix their gaze on the unseen limb, the eyes moved to mimic the movement of the limb
What is the logic behind the idea that a balance of muscle spindle and GTO activity may help regulate muscle tone? (3)
- –Excitation of lower motor neurons by muscle spindle reflex
- –Inhibition of lower motor neurons by Golgi tendon organ reflex
- –Balance between the two may help regulate muscle tone
There is some evidence that a Balance of Muscle Spindle & GTO Activity May Help Regulate Muscle Tone. Remember there is Excitation of lower motor neurons by muscle spindle reflexes and Inhibition of lower motor neurons by Golgi tendon organ reflexes so it is logical that a Balance between the two may help regulate muscle tone
The three types of mechanoreceptors distributed in the joint capsule and ligaments
- –Pacinian-like
- –Ruffini-like
- –Golgi tendon organ–like
How many types of mechanoreceptors are at the joints?
4
(but only three of them are in the capsule and ligaments)
what are alternate names for the four mechanoreceptors in the joint?
Type I (Pacinian endings)
Type II (Ruffini endings)
Type III (Gogli ending)
Type IV (Unencapsulated endings)
Pacinian endings: (5)
alternate name
threshold
adaption rate
response properties
signals
- Also called type I joint receptors
- –Low threshold to stimulation
- –Fast adaptation rate
- –Dynamic response properties
- –Signals angular acceleration of joint
Ruffini endings (5)
alternate name
threshold
adaption rate
response properties
signals
- Also called Type II joint receptors
- –Low threshold to stimulation
- –Slow adaptation rate
- –Static & dynamic response properties
- –Can signal position, displacement and angular velocity of joint
Golgi Ending: (5)
alternate name
threshold
adaption rate
two thing they assess
- Also called type III joint receptors
- –High threshold to stimulation
- –Slow adaptation rate
- –Assesses tension in the ligaments
- –Probably would be able to assess extremes of ROM
Unencapsulated endings (6):
alternate name
threshold
adaption rate
locaton
function (2)
- Also called Type IV joint receptors
- tend to be hight threshold
- slowly adapting
- –located on Joint capsule & surface of articular cartilage
- –Joint nociception with no proprioception role
- –very powerful inhibition of postural muscles - extensors of LE – joint “giving way” with pain
Explain the study that shows the role of proprioeption in the skin:
everything
- –Anesthesia applied to nerves from skin & joint receptors of hand
- Dramatic decrease in sensitivity to movement and position
- Small decrease sensitivity in movement & position sense with anesthesia applied to joint receptor afferents (gray) compared to control (black)
- –Anesthesia applied to nerves from skin & joint receptors of knee
- §Little change in sensitivity to movement and position
- –Importance of skin & joint receptors in hand due to small muscle volume
- –Proximal joints (knee) have > proprioceptive contributions from muscle receptors so do not need skin & joint receptors as much
This can be seen from a study where Anesthesia was applied to nerves from skin & joint receptors of hand. There were Dramatic decreases in sensitivity to movement and position when this was done with the greatest decline in sensitivity with when Anesthesia was applied to nerves from the skin. Anesthesia applied to nerves from skin & joint receptors of hand you can see that there was only a small decrease sensitivity in movement & position sense with anesthesia applied to joint receptor afferents (gray) compared to control (black). Again notice the very large difference when Anesthesia applied to nerves from skin (gray) compared to control (black)
However in the same study when Anesthesia was applied to nerves from skin & joint receptors of knee, there was very Little change in sensitivity to movement and position
These results suggest that skin & joint receptors in hand are important proprioceptors of the hand, probably due the high density of Ruffini endings in the skin of the hands and to the relatively small muscles that are very distant from the hand joints. Even though these muscles have very high muscle spindle densities, since they are multijoint muscle stretch of these muscles would not unambiguously mean movement of the joints of the hand.
Proximal joints (knee) have much greater proprioceptive contributions from muscle receptors so do not need skin & joint receptors as much. The knee is controlled by both mutli-joint muscles and single joint muscles.
