final Flashcards

1
Q

SAI

A

=Merkel cell

  • just under epidermis
  • moderately low threshold
  • irregular discharge
  • sensitive to edges and curvature
  • continue to fire when pressure is held (slowly adapting behavior)
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2
Q

SAII

A

=Ruffini ending

  • in dermis
  • high threshold to indentation
  • regular discharge
  • sensitive to lateral skin stretch (and direction)
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3
Q

FAI

A

Meissners corpusles

  • just under epidermis in peaks
  • low threshold, sensitive to low-frequency vibration
  • don’t continue to fire w/stimulation (fast-adapting behavior)
  • sensitive to velocity and motion across skin (not how hard the indent is)
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4
Q

FAII

A

=pacinian corpuscle

  • deep in dermis
  • very low threshold, sensitive to high frequency vibration
  • don’t continue to fire w/stimulation
  • sensitive to acceleration of indent
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5
Q

receptor fields

A

=region of skin that will elicit a response in a particular neuron
type I: small receptor fields, merkels have specific borders and more obscure for ruffini
type II: large receptor fields, distinct borders for messner’s and more obscure for pacinian

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6
Q

which receptors are more concentrated in the fingertips?

A

SAI and FAI merkel and meissner

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7
Q

how do SAI’s code for shape and size?

curvature?

A
  • for smaller probe, there’s a higher discharge in fewer receptors
  • for larger probe, there’s a lower discharge in more receptors (less velocity specific)
  • curvature is determined based on how many and which are firing (ie as a population code)
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8
Q

what are some functional roles for each receptor?

A
  • SAI-edges, curvature, texture
  • SAII-skin stretch
  • FAI-motion detection, grip control
  • FAII-feeling through objects, fine textures
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9
Q

which receptors respond to accidental slips while holding an object?

A

SA1 and FA2

FA1 controls grip-ie there’s more activity for slippery objects

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10
Q

what is the role of skin receptors in the feet in standing?

A
  • sensitive to contact pressures and potential changes in pressure distribution
  • evidence: stim of plantar skin increases sway, cooling/ischemic block of leg increases sway
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11
Q

where was multi-unit activity predominately evoked in the foot?

A

-medial or lateral aspect

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12
Q

which receptor types were present in the foot sole?
which had the lowest thresholds?
receptor fields?

A
  • all four
  • SAI and SAII had similar sized receptor fields, type Is had 4–6 hotspots
  • FAII had lowest thresholds and obscure fields, SAII had highest (single hotspot)
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13
Q

were the SAII receptors sensitive to direction?

was there background activity?

A

no background activity

all sixteen demonstrated preferential skin strain axis

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14
Q

does movement at a joint evoke a particular response from cutaneous afferents in the skin overlying it?

A

-yes, bending the toes elicited a response in FAIs, SAIs, and SAIIs

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15
Q

name differences in receptors specific to the foot

A
  1. large percentage of rapidly adapting receptors
  2. higher activation thresholds than hand (skin thickness?) + much larger receptor fields
  3. absence of background activity (is sometimes present in SIIs)
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16
Q

kinesthesis

A

-orientation in space and perception of body movement involving consciousness

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17
Q

proprioception

A

reflexive perception of body movement and orientation in space involving

  1. sense of position and movement of the limbs
  2. sense of tension or force
  3. sense of effort or heaviness
  4. sense of body image and posture
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18
Q

evidence of somatosensory role in proprioception and kinesthesis

A
  • removal of afferent inputs causes reduced control of movement-eg GL and IW
  • muscle spindles: vibration leads to perception of lengthening and a dissociation b/t velocity and length (position)–>ie muscle spindles play a conscious role
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19
Q

examples of muscle vibration illusions

A

a. vibrate both achilles w/subject against wall and they think they’re falling forward
b. vibrate biceps with finger on nose and nose seems to grow out to keep in contact with “extending” arm

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20
Q

joint receptors in proprioception/kinesthesis

A
  • there is little if any evidence of decreased joint position sense after replacement
  • receptors get better with increased sensitivity (swelling) and worse with anesthetic
  • better for faster movements, ie may play some role
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21
Q

cutaneous receptors

A

SAII found to code for finger position (and velocity weakly)

a. stretching the skin can cause illusions of finger moving (numb skin) (stretch=contraction, release=extension)
b. functional knee braces, which heighten skin stretch, can increase proprioceptive awareness around the joint
- also the purpose behind compression garments

22
Q

what is sense of effort?

A

a signal of central origin associated with level of perceived force

23
Q

what were subjects asked to do to test sense of effort?

A

match effort and position of one hand with the other

  • hand passively moved to different targets and either just matched or matched with 20% MVC
  • people were generally good at matching effort without vision
  • then they paralyzed the hand with a cuff and people thought they were making flexion/extension efforts despite no EMG activity + thought position of hand was extended when making extension efforts and vice versa
  • this was magnitude sensitive-if they were making a greater effort, there was a greater perceived error in position (shown in a couple subjects)
24
Q

reflex

A

automatic, stereotyped motor response to sensory stimulus

  • from stimulation of peripheral receptors
  • involves sensory neuron, interneuron, motor neuron
25
Q

stretch reflex

A

monosynaptic
-contraction evoked by mm stretch through 1a afferent of spindle which projects to all MN’s of the same muscle
=autogenic excitation
-1a also projects to many MN’s of other muscles (synergists) and the 1a inhibitory interneuron of the antagonist
=reciprocal inhibition

26
Q

how do you reduce reciprocal inhibition and why would you want to?

A

training causes more efficient movements (immobilization leads to more co-activation)

27
Q

1b GTO inhibition reflex

A
  • disynaptic, sometimes trisynaptic
  • mm inhibits itself through the 1b interneuron
  • called autogenic inhibition: the 1b afferent excites the 1b inhibitory interneuron, which inhibits the muscle
  • 1b receives input from joint receptors, cutaneous receptors, and descending input, which can be excitatory or inhibitory
  • ie lots of convergence in this pathway
28
Q

flexor and crossed-extension reflex

A
  1. coordinated flexion (withdrawl) in one limb to withdraw from pain (which is actually faster than the pain fibers ie the feeling) and inhibition of extensors
  2. activation of extensors in opposite limb to support body weight
29
Q

recurrent inhibition

A

a collateral from a motor neuron activates a Renshaw cell which causes inhibition to the MN pool by a rapid negative feedback loop as the muscle contracts

  • ie in order to create lots of force, inhibit renshaw
  • the Renshaw cell projects to 1a inhibitory interneurons, gamma MNs, and other renshaw cells
  • it receives input from descending pathways and cutaneous and type II afferents
30
Q

what would facillatory input on a reshaw cell do?

A

increase recurrent inhibition and increase inhibitory interneuron inhibition in the antagonist which facilitates the antagonist

31
Q

pre-synaptic inhibition

A
  • cuts of influence of pre-synaptic neuron while still allowing post-snaptic neuron to be influenced by other inputs
  • axo-axonal synapse to selectively inhibit the pre-synaptic neuron
32
Q

what is sensory feedback likely important for in walking?

A
  • initialting walking-rapid influx of info may kickstart the central pattern (MLR region in cats stimulation starts walking, increased causes gallop)
  • controlling phase transitions
  • regulating level of muscle activity
  • correcting for disturbances
33
Q

phase transitions and sensory feedback

A
  1. feedback helps CPG know when to go to next phase
    hip extension=trigger for hip flexion, but only at a certain level of weight bearing on that leg)
    -if the leg is more weight bearing, it will go further into extension
    -eg preventing leg extension in babies stops motion in that leg (think skatebording)
34
Q

can afferent info shut the CPG off?

A
  • possibly:
  • stimulation of 1a/1b afferents in decerabrate cat inhibits flexion during stimulation
  • see persistant activation of MG (extension) during stimulation
35
Q

muscle activity level and sensory feedback

A
  • mm activity corrected immediately based on load
  • cat stepping on forceplate that moved down: EMG decreases when plate is moving and increases when it stops
  • ie, CPG interacts with feedback so that it doesn’t have to decide how long and how much to turn on each muscle
36
Q

what is tonic input influence on reflexes and why is it important?

A

descending input can change background activity

  • can cause an input to cause an AP when it previously would not have by bringing activity level closer to threshold
  • reflexes need to be tuned up or down for tasks
  • eg less more recurrent inhibition for contraction
37
Q

walking control

A

CPG in spinal chord
-segmental feedback regulates motor program
initiation by tonic brainstem signals
supraspinal control influence balance, stability, task selection, navigation, and obstacle avoidance

38
Q

how is angular acceleration detected?

A

-endolymph in semicircular canals has natural inertia and pushes against the ampulla when the head rotates–>bend cilia

39
Q

what other information is necessary to use vestibular information for position sense?

A

integration of proprioception and info from skin and vision

40
Q

which vestibular structure is better at coding for side-to side-motion

A
the utricle (which doesn't like up and down as much)
saccule likes up and down and not side to side motion
41
Q

vestibular-ocular reflex

A

VOR-projections from semicircular canals and the otoliths to the occular muscles
-allows rotation of head while fixated on certain point

42
Q

vestibulo-colic reflex

A

VCR-projections from vestibular apparatus to neck muscles

-bring head to neutral after unexpected tilt

43
Q

vestibulo-spinal reflex

A

VSR-projections from lateral vestibular nucleus to extensors of limbs

44
Q

postural control

A

controlling one’s body position in space for orientation and equalibrium

45
Q

postural orientation

A
  • relative position of body segments relative to each other and the environment
  • important for maintaining alignment b/t segments and to the environment
  • establishes vertical alignment to counteract gravity
46
Q

what does stability depend on?

A
  1. area of base of support
  2. distance from COG to edge of base of support
  3. height of COM over base of support
47
Q

goals of postural control system

A
  1. maintain anti-gravity posture (during quasi-static standing)
  2. reactive postural control compensations to perturbation-uses feedback
  3. anticipatory postural control-APA during voluntary movements is faster than voluntary but not reflex
48
Q

spinothalamic pathway

A
  • pain, temp, light touch, pressure
  • 1st order enters dorsal root and synapses in dorsal horn
  • 2nd order decussates (through ventral white comissure), then ascends in ventrolateral white matter of spinal chord to thalamus
  • *means pain immediately jumps to the other side
  • 3rd order thalamus to somatosensory cortex
49
Q

Medial lemniscus pathway

A
  • 1st order in dorsal root and ascends in dorsal column to synapse in lower medulla nucleii
  • 2nd order decussates then ascends in medial lemniscus to thalamus
  • 3rd order thalamus to somatosensory cortex
50
Q

golgi tendon organs

A
  • caspule is continuous with muscle tendon
  • 0.1-1mm in diameter
  • 10-20mm fibers from different motor units (fibers in series, those that don’t pass through are in parallel)
  • innervated by the 1b afferent, whose endings lie among collagen fibers and fire when pinched
  • codes for muscle force (discharge rate increases approximately linearly),f more sensitive for active movements
  • no background discharge (fires during movement)
  • better as ensemble at higher levels of force (muscle fibers in parallel also effect it)