4.1 Proprioception Flashcards
What is proprioception?
- Awareness of body in space
- Sense of movement
- Sensations related to muscle force and heaviness
Outline the overall scheme of proprioception
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
Where are muscle spindles located? What do they detect?
- Located in belly of skeletal muscles
- Detect muscle stretch and length
Where are golgi tendon organs located?
Tendons within joint capsules.
What do golgi tendons measure?
The amount of tension applied to a tendon
Through which axons do golgi tendons/muscle spindles relay afferent information?
Muscle spindle: 1a afferent (a = better = in muscle)
Golgi tendon: 1b afferents (b = worse = in tendon)
A subject is blindfolded, told to keep their hand still, and their bicep is vibrated. Why does their elbow flex?
- Muscle spindles interpret vibration as increase in muscle length
- Activate extrafusal fibres, causing contraction and therefore flexion
Recall the four types of skin mechanoreceptors. Which are slow/fast and which are deep/superficial?
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
What do pacinian corpuscles detect?
Vibration (pacini = opera = vibrations of stage)
What do meissner’s corpuscle detect?
Low-frequency vibration (mice playing bass guitar)
True or false: nearly all deep skin mechanoreceptors respond to movement of the joint
True (that’s the power of leverage, baby)
What do Ruffini’s receptors detect?
- Skin stretch (and joint movement, since deep)
(Rough = Ruffini = skin stretch)
True or false: most joint receptors have some tonic level of input, regardless of joint position
- False
- They are mostly silent until the extremes of joint angle, when there is a rapid increase in discharge
How can you eliminate the effect of skin mechanoreceptors on proprioception for testing purposes?
Local anaesthetic
How can you eliminate the effect of muscle spindles/golgi tendons on proprioception for testing purposes
By putting the body in certain postures (such as flexing the middle finger)
What are the relative contributions of peripheral sensors to proprioception (compared to each other)?
- Muscle receptors are greatest
- Skin and joint are less important
How does proprioceptive information from peripheral receptors reach the brain? (full pathway). Think about it: which pathway does proprioception?
- 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.
What is the function of the secondary somatosensory cortex?
Store, process, and retain somatosensory information.
Explain the Pinnochio Illusion
- 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”
Explain the rubber hand illusion
- 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
What do Merkel receptors detect?
Sustained pressure. (Getting merked)
