Week 7 Flashcards
Nigel and Sasha visit the clinic to have their tactile acuity tested. Sasha’s tactile acuity thresholds are much lower than Nigel’s. What factors determine whether Sasha’s tactile acuity is better than Nigel’s?
- Greater receptive field size
- Greater density of receptors
- Greater representation in the somatosensory cortex
What cutaneous mechanoreceptor is most likely important for tactile acuity performance?
merkel
What is proprioception?
perception of body movement/orientation in space
Sherrington included which other sense in proprioception?
vestibular
Describe the basic difference between kinsthesia and proprioception?
kinesthesia (movement sense)
- involves consciousness
- sense of movements
- behavioural
proprioception (position sense)
- is more reflexive (not necessarily involved in conscious control/perception
- sense where our body is in space (position)
- can be subconscious/reflexive
What are the 4 major contributors to kinesthesis?
- sense of position and movement of the limbs
- sense of tension or force
- sense of effort or heaviness
- sensations of body image and posture
What is proprioceptive afference? What are the two types?
afferent signals generated by mechanoreceptors in response to stimulation that is produced as a consequence of the positions and movements of body parts and tension in muscles and joints
- ex-afference and re-afference
What is ex-afference?
- external afference
- generated from an external source; often unexpected
- generated by proprioceptors in response to external stimulation
What is re-afference?
- generated from your own movements
- same sense as “re-do”
- generated by proprioceptors in response to internally generated stimuli
What is the proprioception matching task?
simultaneous
- both limbs compared to each other
- target limb vs reference limb
successive
- single limb compared to itsekd
- before vs. after
What is the proprioception discrimination task?
flexion vs. extension
was it moved? how far?
What are the sources of proprioception and what do they code for?
muscle spindles
- length/velocity of muscle
GTO
- tension/force of muscle
joint
- pressure
- ligament forces
- joint position
cutaneous
- length/velocity of skin stretch
- movement onset/offset
What sources code when the middle finger is extended, unanesthetized?
cutaneous, joint, & muscle receptors
What sources code when the middle finger is extended, anesthetized?
only muscle receptors
What sources code when the middle finger is extended, joint anesthetized?
cutaneous & muscle receptors
What sources code when the middle finger is flexed, unanesthetized?
cutaneous & joint receptors
What sources code when the middle finger is flexed, joint anesthetized?
only cutaneous receptors
Which receptor types contribute to proprioception?
muscle receptors, joint receptors, and cutaneous receptors (all mechanreceptors)
Tendon vibration activated type __ muscle spindles?
1A
Tendon vibration =
kinesthetic illusion
What is sensory dominance?
conflict arises and brain chooses one sensation over other sensory information
What is the pinocchio effect?
- participant grabs their nose → cutaneous sensation
- bicep brachii tendon is vibrated → sensation of arm extension
- need to make sense of conflicting sensory information → nose is felt to grow bigger
What are two other examples of sensory dominance?
- bilaterally vibrate the achilles in standing participant braced against a wall → feel triceps surae lengthening → perception of falling forward
- bilaterally vibrate the achilles tenson in standing participant braced against a wall → have them look at a point source of light → perceive light to move upward
In order for kinesthetic illusion to be effective….
the person must not see the limb
How is proprioception impacted after total joint replacement?
little, if any, evidence of decreased joint position sense
Do joint receptors play any role in proprioception?
- if we use that hand posture to isolate muscle/tendon receptors from the distal middle finger joint:
- lignocaine: joint receptor sensitivity ↓, proprioceptive score ↓
- dextran: joint receptor sensitivity ↑, proprioceptive score ↑
- evidence: joint receptors may have a role in proprioception?
What two cutaneous receptors are involved in proprioception?
SAII (ruffini), and FAI (meissner)
How are SAII afferents involved in proprioception?
- detect skin stretch
- SAII’s found to code for finger position
→ discharge rates correspond to finger movements
→ finger flexion: SAII discharge rates increase
→ finger extension: SAII discharge rates decrease
How are FAI afferents involved in proprioception?
- detect initial, rapid change in skin stretch locally
- FAI’s code for which joint is moving
What evidence is there that cutaneous inputs help us determine finger position?
- remove afferent feedback from fingers with anesthetic → stretch skin on back of hand → produced illusion of finger flexion
- kinesiology tape applied to back of hand → reach for cup: shape of grasp changed
How is kinesthetic information obtained?
it’s complex
- signals are ambiguous from one proprioceptor alone (all proprioceptors have limitations
- combination of multiple inputs necessary for accuracy
We can have sensory dominance through…
muscles spindles and vision
How is efference involved in proprioception?
- the motor command plays an essential role generating kinesthesis
- motor command likely cannot generate kinesthetic perceptions in the absence of proprioception (or can it?)
What sensory conflict arises during the pinocchio illusion?
Ia = muscle lengthening vs cutaneous = touching nose
What are the three areas of the motor cortex?
premotor cortex, supplementary motor area, and primary motor cortex (M1)
What is premotor cortex involved in?
- selection of appropriate motor plans for voluntary movements
- preparing complex tasks
The premotor cortex projects/relays information to…
M1
Stimulation of the premotor cortex at high level of current produces…
complex movements
What do the motor-set neurons do?
signal preparation for movement
What is an example of specific neurons for specific actions in the premotor cortex?
left arm extension → neurons for left arm extension discharge during preparation phase (i.e. prior to actual movement)
What are the two types of neurons to know in the premotor cortex?
motor-set and mirror
What do mirror neurons do?
- active in response to sensory aspects associated with motor actions
- not only prepare for particular action, but also respond to sight and sound of action performed by another individual
What does the supplementary motor area do?
- programming complex sequences of movements and coordinating bilateral movements
- based on remembered/previous sequences of movements
What does the supplementary motor area respond to?
- sequences of movements
- mental rehearsal of sequences of movements
Does the motor homunculus represent activity of individual muscles?
No
What does the primary motor cortex do?
elicits movements of individual body parts involving multiple muscles
What is the motor homunculus?
cortical representation of specific body regions
→ increased representation for regions with high degrees of fine motor control/wide range of movements
The primary motor cortex begins discharging/firing how long prior to movement?
5-100 ms
How does the primary motor cortex relay commands?
to the alpha motor neurons via corticospinal motor neurons → corticospinal pathway
What are the three main things the primary motor cortex encodes for?
- force of movement
- direction of movement
- speed of movement
What does good spatial resolution mean?
high accuracy in determining where something happens
What does good temporal resolution mean?
high accuracy in determining when something happens
What is electroencephalography?
- electrodes placed over various positions on the scalp
- record electrical activity underneath each electrode
What are the pros and cons of electroencephalography?
pros: excellent temporal resolution
cons: poor spatial resolution
What is the premise behind functional magnetic resonance imaging?
neuronal activity involves metabolic demand (↑neuronal activity = ↑ metabolism ↑ oxygen demand)
What does an fMRI do?
measures blood flow within cortex
- comparison of deoxygenated blood versus oxygenated blood → can tell what regions are active
What are the pros and cons of fMRI?
pro: excellent spatial resolution
con: poor temporal resolution
What type of technique is transcranial magnetic stimulation? How does it work?
- stimulation technique → allows us to selectively determine what region of the motor cortex to investigate
- magnetic field causes depolarization of motor cortical neurons → activation of muscles innervated by those cortical neurons
EEG and fMRI are what type of technique?
recording techniques - seeing where is active
