Date:
Monday, 24 September 2018
Experiment:
Kinesthesia, Proprioception & Estimation of Muscle Tension
Conducted by:
Group Number A3
Luke Sanderson, Phoebe Burns, Rachel Pongi, Tanya Kaur
Aims:
• Determine how vibration impacts kinaesthetic proprioceptive sensation.
• Explain the physiological principles of how vibration impacts proprioceptive sensation.
• Explain the physiological principles of sense of effort and estimation of tension.
Introduction:
Proprioception is the sense of one’s orientation of their body parts in space. Proprioceptors provide information about mechanical forces within the body. They receive stimuli and provide proprioception to muscle spindles, tendons and fibrous membranes. (Purves, 2012). Information from proprioceptors and the vestibular system is integrated in the brain. This helps determine the overall position, movement and acceleration of the body. There are two classes of proprioceptors; Golgi tendon organs and muscle spindles. (Purves, 2012).
Muscle spindles are found in parallel with extrafusal muscle fibres, and primarily detect changes in muscle length. The central nervous system receives length information via afferent nerve fibres. This enables the brain to determine position of body parts from this information. Responses of muscle spindles to changes in length play a vital role in muscle contraction regulation. The muscle spindle consists of sensory and motor components. The sensory component consists of primary type Ia and secondary type II fibres. These spiral around muscle fibres within the spindle. The motor component is conveyed by up to a dozen gamma motor neurons. Muscle spindles transmit proprioceptive information to the spinocerebellum via the dorsal spinocerebellar and cuneocerebellar tracts from the lower and upper limbs respectively. Activation of motor neurons occurs via the stretch reflex to resist muscle stretch. (Purves, 2012).
The stretch reflex refers to muscle contraction in response to stretching in a muscle. The sensory signal for the stretch reflex originates in muscle spindles, and is embedded in most muscles. The stretch reflex is monosynaptic. It consists of only a single sensory and motor neuron. It involves transmission of information from a sensory neuron to a corresponding motor neuron across a single synapse within then spinal cord. Brief stimulation of muscle spindles results in contraction of the agonist muscle. For example, stimulation of the Achille’s tendon causes an action potential being sent to motor neurons. This then leads to contraction in the calf muscles. (Purves, 2012).
Gamma motor neurons have a pivotal role in controlling the excitability of muscle spindles. They essentially alter the sensitivity of detecting changes in muscle length. These are a type of lower motor neurons, representing 30% of Group A nerve fibres heading towards the muscle. They solely innervate intrafusal muscle fibres within the muscle spindle. There are three types of intrafusal muscle fibres. These include dynamic, static nuclear and nuclear chain fibres. Intrafusal muscle fibres are skeletal muscle fibres, serving as proprioceptors. They detect the amount and rate of change in muscle length. They constitute of a muscle spindle and are innervated by one motor and one sensory axon. Nuclear bag fibres line in the centre of a muscle spindle, with many nuclei concentrated in bags leading to excitation of primary and secondary nerve fibres. Dynamic nuclear fibres are sensitive to changes in stretch of fibres. Static nuclear bag fibres are sensitive to stationary, steady state stretch of muscles. (Purves, 2012).
Golgi tendon organs are in series with extrafusal muscle fibres. They sense changes in muscle tension, and provide the sensory component of the Golgi tendon reflex. They are encapsulated afferent nerve endings, with the body comprising of strands of collagen, connected at one end of the muscle fibres, merging into the tendon proper at the other end. Upon compression of the sensory terminal, the terminals of the Ib afferent axon are deformed, stretch sensitive cation channels are opened, depolarising the Ib axon, and nerve impulses propagate to the spinal cord. (Purves, 2012).
The vestibular system is the sensory system contributing to the perception of head position, self-motion and spatial orientation relative to gravity. The vestibular system is comprised of semi-circular canals and otoliths. The three semi-circular canals are interconnected tubes in the innermost part of the ear, including the horizontal, superior and posterior semi-circular canals. These indicate rotational movements, such as turning of the head. The two otolith organs include the utricle and saccule. These indicate displacements and linear movements such as gravity. (Tortora & Derrickson, 2013).
Methods:
PART 1A
Our blindfolded subject was seated on the bench, elbow resting. We used a physiotherapy vibrator at 100Hz. This was placed on the tendon of the biceps brachii on one arm. We tracked the movement of both the non-vibrated and vibrated arm. Observations on the subject’s ability to accurately match the two arms were made.
PART 1B
The subject remained blindfolded, stood in a relaxed position with heels together and skin over both Achilles tendons accessible. We assigned a team member to stand behind the subject to catch them should they became unstable. We then placed the physiotherapy vibrator to stimulate both Achilles tendons simultaneously. Observations of any postural changes and sensations reported by the subject were noted.
PART 1C
The “finger to nose test” was then carried out. Again, the subject remained blindfolded, with heels together and arms stretched out sideways. We assigned a team member to hold the arm proximal to the elbow joint. The subject, by bending the arm only at the elbow joints, slowly moved their hand towards their face, placing their index finger as near as possible to their nose. We then repeated the above protocol, however this time placed the physiotherapy vibrator firmly against the triceps muscle. We noted any differences in arm movement and asked the subject to report any sensations.
PART 2
The subject remained blindfolded, seated and forearms in supination position, flat on the bench. Elbows were placed in line of the point from which the degree lines radiate from the protractor. Next, the subject completely relaxed their arm, whilst a team member lightly took hold of the subject’s left wrist. Then, the left arm was moved to a new angle. After 10 seconds the subject indicated the angle of the left arm, by moving the right arm to match the same angle. Measurements were made at 10 different angles (5-90 degrees). We also recorded right and left arm angles, as well as the difference between these angles. We then repeated the experiment as above. However, this time a 100Hz physiotherapy vibrator was turned on and placed over the tendon and muscle belly of the left biceps with the forearm relaxed in hand. We re-commenced the experiment when the tonic vibration flexion reflex was felt..
PART 3
Initially, we discussed possible mechanisms underlying sensation of heaviness of a lifted object. The effect on sensation upon lifting a heavy suitcase for an extended period was discussed.
We then conducted the matching experiment, commencing with the control. We were given a dual pulley and bucket set up, which was used for comparison of weights by the forearms. The subject’s hand remained in supination position, and the straps were placed around the wrists. We ensured the buckets were sat on the floor, and not visible to subject. We set up a reference weight of 2kg in the bucket, and attached the bucket to the non-dominant arm. The weight was noted and remained the same for the remainder of the experiment.
Next, a random “test” weight was placed in the opposite bucket. We asked the subject to judge whether the test bucket feels heavier, the same or lighter than the reference bucket. Then, both buckets were lowered onto the floor, whilst the subject rested.
We then altered the weights in the test bucket. If the subject judged the test weight as heavier, weights were removed from the test buckets. If the subject judged the test weight as lighter, weights were added to the test bucket. We kept the amount of weight added or removed random, however kept increments or decrements within about 400g (i.e. 20% of the reference weight).
The above weight matching task was continued until the subject reported the weight of the reference and test buckets to be the same. We recorded the test weights and discrepancies between test and reference weights on a table. This task was repeated 15 times, with the 2kg reference weight unchanged. Differences in weight were recorded.
Finally, the fatigue matching experiment was conducted. This was essentially the same as the weight matching experiment, repeated 15 times, however the reference bucket was held continuously for the entire 15 minutes. During each minute, the subject repeated the weight matching task until the subject judged test and reference weights to be equal. Similarly to the previous experiment, the weights in the test bucket was recorded upon being judged by the subject as equal to the reference bucket.
We carried the fatigue matching experiment out on one team member. We considered repeating the experiment on a second subject, however time did not permit for this.
Results:
Part 1: Qualitative observations of vibration-induced illusions of movement:
• The blindfolded subject was seated on the bench with elbows rested. A 100Hz physiotherapy vibrator was placed over the biceps brachii on the left arm. We passively moved the vibrated arm at the elbow joint. The non-vibrated, right arm, actively tracked the vibrated arm, matching its movement. We noted the subject’s inability to accurately match the arms in the presence of vibration. They perceived the vibrated arm to be more elongated than it truly was.
• The subject stood upright, heels together and eyes closed. We assigned a team member to stand behind the subject, to catch them if they become unstable. We placed the physiotherapy vibrator to simultaneously stimulate both Achilles tendons. We observed the subject’s became somewhat unbalanced in the presence of the vibrator, and appeared to stumble backwards.
• The subject stood upright, with heels together, eyes closed and arms stretched out wards. Another team member kept the arm proximal to the elbow joint. The subject’s hand was slowly moved towards their face, and the index finger was placed as close to their nose as possible. Later, the physiotherapy vibrator was placed firmly against the triceps muscle, and the experiment was repeated. In the presence of the vibrator, the subject had some difficulty placed their index finger as close to their nose as possible.
Subject Number Trial Control Vibration
Right arm angle Left arm angle Discrepancy (left-right) Right arm angle Left arm angle Discrepancy
(left-right)
Subject 1
1 40 40 0 30 40 -10
2 65 60 5 40 60 -20
3 20 20 0 20 20 -10
4 55 55 0 45 55 -10
5 70 70 0 65 70 -5
6 5 10 -5 10 10 0
7 30 35 5 30 35 -5
8 80 80 0 70 80 -10
9 90 90 0 80 90 -10
10 5 5 0 0 5 -5
Subject 2
1 35 40 -5 30 40 -10
2 60 60 0 65 60 -5
3 20 20 0 25 20 -5
4 55 55 0 55 55 0
5 75 70 5 65 70 -5
6 10 10 0 10 10 0
7 40 35 -5 35 35 0
8 90 80 10 70 80 -10
9 95 90 5 85 90 -5
10 5 5 0 5 5 0
Table 1. Discrepancies between measured and matched angles, in the presence and absence of vibration.
Figure 1. Results of position sense experiment for subject 1. Angles measured between the forearm at the elbow joint and table.
During the control experiment, subject 1 displayed accurate joint matching, with low discrepancy, in the absence of vibration. In the presence of vibration, the angle between the table and forearm in the non-vibrated arm was perceived as lower, than it truly was. The length of the biceps brachii was shorter in the vibrated muscle than the non-vibrated muscle.
Figure 2. Results of position sense experiment for subject 2. Angles measured between the forearm at the elbow joint and table.
During the control experiment, subject 2 displayed accurate joint matching, with low discrepancy, in the absence of vibration. In the presence of vibration, the angle between the table and forearm in the non-vibrated arm was perceived as lower, than it truly was. The length of the biceps brachii was shorter in the vibrated muscle than the non-vibrated muscle.
Trial Reference weight used = 2kg
Control Fatigue
Test weight (kg) Discrepancy (test-references) Test weight (kg) Discrepancy (test-references)
1 2.70 0.70 2.20 0.20
2 2.20 0.20 1.70 -0.30
3 2.10 0.10 1.80 -0.20
4 2.00 0.00 1.80 -0.20
5 2.10 0.10 2.30 0.30
6 2.05 0.05 2.20 0.20
7 2.00 0.00 2.25 0.25
8 1.90 -0.10 2.40 0.40
9 2.10 0.10 2.40 0.40
10 2.20 0.20 2.50 0.50
11 2.00 0.00 2.60 0.60
12 1.95 -0.05 2.65 0.65
13 2.05 0.05 3.30 1.30
14 1.90 -0.10 2.80 0.20
15 2.20 0.20 2.75 0.75
Table 2. Discrepancies between test and reference weights, in the presence and absence of fatigue conditions.
Figure 3. Results of perception of force with and without fatigue conditions. Discrepancy in weight matching between forearms in fatigued and control arms, with the weights not visible to the subject.
The reference weight was held continuously for the length of the 15 trials, whilst we performed fatigue weight matching trials. During the control trials, we lowered the reference weight to the floor. Differences in the reference and test weights, when perceived by the subject as the same, were recorded as discrepancies. Throughout this experiment, we maintained the reference weight at 2.0kg.
Discussion
Vibration is responsible for illusion in movement. In the presence of vibration, the brain is led to believe that elongation of a muscle in the vibrated limb is greater than it truly is. Upon matching, the non-vibrated limb tends to be stretched out further than the vibrated limb, making a lower angle and thus negative discrepancies in our results. (Purves, 2012).
In Parts 1A and 2 of our experiments, we observed that the ability of our subjects to correctly track the opposite arm was diminished in the presence of vibration. In Figures 1 and 2 and Table 1 we can see greater discrepancy between the matched and reference angles, in the presence of vibration. This can be explained by the biceps brachii being perceived by the brain to be more elongated in the presence of vibration. When the muscle belly of the biceps brachii is vibrated, the nerve endings of type Ia afferent fibres that innervate the muscle spindle are activated. During elongation, the type Ia afferent fibres are typically activated. Proprioception is signalled by muscle spindles via the dorsal column medial lemniscus pathway. The information transmitted via this pathway is transmitted to the primary somatosensory cortex, which is where this illusion is deemed. (Purves, 2012).
In Part 1B, we observed that the subject became somewhat unbalanced upon vibration of the Achilles tendon. This can be explained by muscle spindles stretching, upon vibration of muscles attached to the heel. The brain believes that the soleus muscle is elongated, which typically only occurs when one walks forward. To help maintain postural frame, contraction of the gastrocnemius occurs. This causes the body to move backwards, explaining the loss of balance observed. (Purves, 2012). In Part 1C of our experiment, we observed that the subject’s ability to move their hand toward their face and place their index finger as close to their nose as possible was diminished in the presence of vibration. This can be explained by the fact that the triceps brachii is an extensor muscle, and in the presence of vibration, the triceps brachii are perceived to have been elongated, affecting proprioception. (Purves, 2012).
The Golgi tendon organs are a class of proprioceptors. They provide information about heaviness of load and changes in muscle tension via Ib afferent fibres. A single Ib sensory nerve fibre innervates each Golgi tendon organ, branching and terminating as spiral endings around the collagen strands. Stimulation of Golgi tendon organs leads to autogenic inhibition, an associated muscle reflex, by interrupting contraction. Continual fatigue causes these organs to be desensitized, impeding weight matching across arms. This is demonstrated in Table 2 and Figure 3, where there are large discrepancies between the test and reference weights. This demonstrates the subject perceives the test weight to be lighter than it truly is, with increasing fatigue, across 15 minutes. (Purves, 2012).
Fatigue causes less force to be exerted than necessary. It is still unknown whether this perception is from centrally generated sensations from peripheral sensations originating from innervation of efferent pathways (“sense of force”) or corollary discharges (“sense of effort). Corollary discharge is a copy of motor command sent to muscles leading to movement. This copy is transmitted to sensory centres in the brain, informing the brain of imminent movement. Movement is not produced itself, but directed to other regions of the brain informing them in anticipation of movement. The sensitivity of signals relayed to afferent sensory nerves is often adjusted by efferent signals. (Poulet, 2007).
Conclusion:
In conclusion, this experiment enabled us to see how illusions in movement are created, upon vibration of several limbs. We were also able to see the effect of vibration on the ability to match joint angles between the left and right arms. Finally, this experiment also demonstrated the effect of fatigue on the body’s ability to sense force.