4.1 Proprioception

Question 1

What is proprioception?

Answer 1

• Awareness of body in space
• Sense of movement
• Sensations related to muscle force and heaviness

Question 2

Outline the overall scheme of proprioception

Answer 2

Proprioception recieves input from:
1. “Efferent copy” of motor movements
2. Sensory signals (muscle spindles, golgi tendons, joint receptors, vision etc.)
3. Vestibular sense from cerebellum

Question 3

Where are muscle spindles located? What do they detect?

Answer 3

• Located in belly of skeletal muscles
• Detect muscle stretch and length

Question 4

Where are golgi tendon organs located?

Answer 4

Tendons within joint capsules.

Question 5

What do golgi tendons measure?

Answer 5

The amount of tension applied to a tendon

Question 6

Through which axons do golgi tendons/muscle spindles relay afferent information?

Answer 6

Muscle spindle: 1a afferent (a = better = in muscle)

Golgi tendon: 1b afferents (b = worse = in tendon)

Question 7

A subject is blindfolded, told to keep their hand still, and their bicep is vibrated. Why does their elbow flex?

Answer 7

• Muscle spindles interpret vibration as increase in muscle length
• Activate extrafusal fibres, causing contraction and therefore flexion

Question 8

Recall the four types of skin mechanoreceptors. Which are slow/fast and which are deep/superficial?

Answer 8

Superficial = M-starting (meissner’s and merkel). Therefore deep are Ruffini and pacinian.

Fast = M(i)P = Meissner’s and pacinian

Slow = M(r)R = Merkel’s and Ruffini’s

Question 9

What do pacinian corpuscles detect?

Answer 9

Vibration (pacini = opera = vibrations of stage)

Question 10

What do meissner’s corpuscle detect?

Answer 10

Low-frequency vibration (mice playing bass guitar)

Question 11

True or false: nearly all deep skin mechanoreceptors respond to movement of the joint

Answer 11

True (that’s the power of leverage, baby)

Question 12

What do Ruffini’s receptors detect?

Answer 12

• Skin stretch (and joint movement, since deep)

(Rough = Ruffini = skin stretch)

Question 13

True or false: most joint receptors have some tonic level of input, regardless of joint position

Answer 13

• False
• They are mostly silent until the extremes of joint angle, when there is a rapid increase in discharge

Question 14

How can you eliminate the effect of skin mechanoreceptors on proprioception for testing purposes?

Answer 14

Local anaesthetic

Question 15

How can you eliminate the effect of muscle spindles/golgi tendons on proprioception for testing purposes

Answer 15

By putting the body in certain postures (such as flexing the middle finger)

Question 16

What are the relative contributions of peripheral sensors to proprioception (compared to each other)?

Answer 16

• Muscle receptors are greatest
• Skin and joint are less important

Question 17

How does proprioceptive information from peripheral receptors reach the brain? (full pathway). Think about it: which pathway does proprioception?

Answer 17

• Joint, skin, and muscle receptors
• Travels via (bipolar) sensory neurons through the DCML pathway to the dorsal column nuclei in brainstem, where it synapses
• Decussates, and heads to thalamus
• From thalamus, heads to: 1° somatosensory cortex, 2° somatosensory cortex (just inferiolateral; small), and posterior parietal lobe.

Question 18

What is the function of the secondary somatosensory cortex?

Answer 18

Store, process, and retain somatosensory information.

Question 19

Explain the Pinnochio Illusion

Answer 19

• Person is blindfolded, and their finger is placed on their nose.
• Biceps tendon vibrated.
• Brain thinks bicep is stretching out, but also thinks that hand is touching nose.
• Nose “extends”

Question 20

Explain the rubber hand illusion

Answer 20

• Set up fake hand, and keep real hand out of sight
• Stroke fingers at same position/timing, and they’ll become convinced it’s theirs
• Then, hurt the hand, and see what happens

Question 21

What do Merkel receptors detect?

Answer 21

Sustained pressure. (Getting merked)