Midterm 2 Study Flashcards
1
Q
Where is Glabrous Skin Located?
A
- Non Hairy Skin
- I.e. Lips, palms of hands, etc.
2
Q
How many Types of Receptors are in Glabrous Skin?
A
- 4
3
Q
How are Receptors Classified?
A
- Receptive Field Size
- Responses to sustained stimulation/indentation of skin (adaption rates)
- Spike train regularity
4
Q
What is the 5th Receptor?
A
- Hair Receptor
5
Q
What is the structure of a Hair Receptor?
A
- Loses Myelin
- Wraps around the hair follicle as free nerve ending
6
Q
What does a hair receptor do?
A
- Responds to bending of hair
7
Q
What are the four Receptors found in Glabrous Skin?
A
- Merkel Disk/Cell
- Meissner’s Corpuscle
- Ruffini Ending
- Pacinian Corpuscle
8
Q
Where are Merkel Disk/Cells located?
A
- Very Close to the skin surface
- In epidermis on the peak/dome of connective tissue
9
Q
What causes Merkel Cells to be deformed?
A
- Indentation of skin
10
Q
What happens when a Merkel Cell experiences indentation of the skin?
A
- The cell is pinched and if enough leakiness it generates AP
11
Q
How is a Merkel Cell classified?
A
Slowly Adapting Type 1 Receptor
12
Q
What happens to a Merkel Cell if an indentation is held?
A
- It continues to fire AP
- It has an irregular discharge, sputters a bit
13
Q
What does a Merkel Cell code for?
A
- Velocity and Magnitude of Indentation
- Velocity during indentation
- Discharge rate that’s proportional to the magnitude of indentation
14
Q
What is the threshold for a Merkel Cell? What is it highly sensitive to?
A
Threshold
- Moderately Low (30um)
Sensitive
- To Edges and Curvature
15
Q
Where are Meissner’s Corpuscle Receptors located?
A
- Right under ridges (in the valleys) in the epidermis
- Very Close to skin Surface
16
Q
What type of receptor is a Meissner’s Corpuscle?
A
- Fast Adapting Type 1
17
Q
What is the Structure of a Meissner’s Corpuscle?
A
- Connective Tissue Ending
- Located in valleys of the epidermis
- Close to skin surface
- Grouping of Connective Tissue that Spirals around
18
Q
What causes a Meissner’s Corpuscle Receptor to Fire?
A
- Pushing/Distorting the connective tissue
19
Q
What do the Meissner’s Corpuscle Receptors Code for?
A
- Velocity of skin indentation
- Motion across Skin
- Love Texture
20
Q
Give an example of when a Meissner’s Corpuscle Receptor would give high bursts of AP
A
- Running nails over receptive field
21
Q
What is the Threshold of a Meissner’s Corpuscle Cell?
A
- Low Threshold (6um)
22
Q
What Receptor Cell makes of the highest percentage in the hand? What are they sensitive to?
A
Location
- 40% of receptors in the hand are Meissner’s Corpuscle
Sensitive
- to Low Frequency Vibrations (40-50Hz, i.e. phone)
23
Q
Where are the Ruffini Endings located?
A
- in the deep dermis layer
- Buried in Collagen of connective tissue
24
Q
Describe the Structure of a Ruffini Ending Receptor
A
- Deep in Dermis
- Buried in Collagen
- Axon shrapnels and weaves amongst collagen
- Lies parallel to surface
25
What causes distortion of the Ruffini Endings?
- Stretching and Pulling on capsule
26
What type of discharge does a Ruffini Ending have?
- Regular discharge when stimulated
- 1/3 have background discharge
27
What type of Receptor is a Ruffini Ending?
- Slowly Adapting Type II
28
What is the Threshold of a Ruffini Ending?
- High Threshold to indentation (300um)
29
What causes Ruffini Endings to Fire?
- Hard and Deep indentation
- Sensitive to lateral skin stretch
- Skin stretch must line up with receptors
30
What is an example of when a Ruffini Ending would be firing?
- Walking (sheer skin pattern through feet)
31
What do Ruffini Endings Code For?
- a bit for velocity
- Fire like a clock during indentation
32
Do non-human primates contain Ruffini Ending Receptors?
- NO
33
What type of receptor is a Pacinian Corpuscle?
- Rapidly Adapting Type II
34
Where are Pacinian Corpuscle Receptors located?
- Very Deep in Collagen of Dermis
35
Describe the Structure of a Pacinian Corpuscle
- Very Deep in Collagen of Dermis
- Connected to a single axon
- Myelinated nerve ending that comes in, and loses its myelin right where it enters multilayered connective tissue (like an onion)
36
What is the Threshold of a Pacinian corpuscle Receptor?
- Very low threshold (0.08um)
37
What is the most common Receptor in the body
- Pacinian Corpuscle
38
What do the Pacinian Corpuscle Receptor Cells Code for?
- Acceleration: change in indentation rates
- High-Frequency Vibrations (300-400Hz)
- Microacceleraions with ground
39
What is an example of when a Pacinian corpuscle receptor would be helpful?
- Walking in heels versus sneakers will have different frequency characteristics
40
How does Pacinian Corpuscle Receptors Vibration Sensitivity work?
- Concentrically arranged fluid-filled lamellae around sensory nerve terminal
- Fluid between layers of connective tissue filters out low frequencies
- High Frequencies reach the axon
- Transducers of acceleration
41
What are Pacinian Corpuscle Receptors built for?
- being an accelerometer in joints, skin, and mesentery of gut
42
What are Pacinian corpuscles very sensitive to?
- alternating inputs, such as mechanical vibrations
43
What does each cycle of vibrations do to a Pacinian Corpuscle do?
- Generates an AP
44
What do the 4 Receptors have in common?
- All tied to a single axon
- all are smaller than 1a and 1b, closer to spindle secondary size
- All Roughly the same in nature
- all classic mechanoreceptors that rely on deformation
45
What is Mechanotransduction?
- The process whereby mechanical energy gets converted to voltage change in sensory afferent neurons
46
What is common about how the 4 receptors work?
- all classic mechanoreceptors, rely on deformation
- ending has many channels, deformation causes membrane shift
- membrane shift causes AP generation
- All work with voltage changes
47
What is the one type of receptor cell that gets deformed?
- Slowly adapting type I (Merkel Cell)
48
What is a Cutaneous Receptive Field?
- The region of skin that is capable of driving a response in a particular neuron
49
What is unique about type II receptor's cutaneous receptive fields?
- Large, obscure borders
50
Do the different Cutaneous Receptive Fields Overlap?
- Yes
51
Describe a Cutaneous Receptive Field
- Area of stimulation for a particular neuron (receptor cell)
- Central sensitivity, like a bullseye target
- Relative densities vary across different skin regions
52
What Receptors have higher Cutaneous Receptive Field Densities in the tips of fingers?
- Slow-Adapting Type I (Merkel)
- Fast-Adapting Type I (Meissner's Corpuscle)
53
Which Receptors have more equally Distributed Cutaneous Receptive Field Densities?
- Slow-Adapting type II (Ruffini Endings)
- Fast-Adapting Type II (Pacinian corpuscle)
54
What do the cutaneous receptive fields of Type I FA & Type I SA receptors have in common?
- small receptive fields, with sharp borders
- almost half in the hands are on the finger tips
- Edge Sensitive
55
What is the difference between the cutaneous receptive fields of Type 1 FA & Type 1 SA receptors?
- Type 1 FA has a more equally distributed gradient
- Type 1 SA has gradient towards hand
56
Describe the Cutaneous Receptive Field for Type II FA (Pacinian Corpuscles)
- Huge receptive Field
- Very Low threshold
57
Describe the cutaneous receptive field for Type II SA (Ruffini Endings)
- Large receptive field
- tied to skin stretch
- sensitive to lateral skin strain
58
How are fingertips able to pick up small objects like pins?
- High Density of Type I receptors (especially Meissner's
- Incredible resolution of tactile information
59
How do the size and shape of objects get coded for when holding them?
- SA1s (Merkel)
60
What happens to FA receptors during sustained contact?
- They go quiet
61
How do Merkel (SA1s) code for the curvature of an object?
- Using the Receptors as a population
- Varying the size and shape of an object over the receptive field changes the coding
- smaller probe are has higher discharge rate with fewer receptors
- Larger probe has lower discharge rate but more receptors are active
62
Why do we not need a large number of FA2 and SA2 receptors?
- Very Large Receptive Fields
63
What is the functional role of the Merkel Cells (SA1)?
- Senses edges, curvature and texture
- Contact information as you tap i.e. phone
64
What is the functional role of Meissner's corpuscle?
- Motion Detection and grip control
- Knowing how slippery something is on contact
- i.e. holding glass of beer
65
What is the functional role of Ruffini Endings?
- Skin stretch, skin strain pattern
- can help gauge how far apart your fingers are
- Proprioception of the hand
66
What is the functional role of the Pacinian corpuscle receptors?
- feeling through objects, perception of finer texture
- information about contact i.e. walking cane
67
How do you test the control of grip force?
- Record glabrous skin receptors during pinch grasp using microneurography
- task: grab and hold the object
- Vary: weight, interface, or if the object in air or on ground
- Monitor: acceleration, grasp force, sheer on object
- Results: see what happens when 'load' is increased by monitoring the activity of skin receptors as load pulls them down
68
How do we code for accidental slips (of object)?
When the object moves relative to you
- detected by accelerometer
- Both FA2 and SA1 receptors respond to microslips between object and skin
69
How do FA2 (Pacinian) respond to microslips between an object and the skin?
- Upon contact FA2 discharges
Slip do to inefficient grip strength
- FA2 senses the acceleration of object
- FA2 Fires
- Response is increase in grip force relative to load
- response is unconscious
70
How does SA1 (Merkel) code for microslips between an object and skin?
- Brief acceleration during microslip
- Instant SA1 burst
- Continue to fire while increasing grip to force ratio
71
How many unconscious automatic channels correct microslips?
- 2 FA2 and SA1
72
How do FA1s respond to different surfaces?
Slipperiness
- Not-slippery: few spikes
- Slippery: high activity
Velocity of Grab
- Code as a population for slow
Surface type
- change in interface between skin and object (sandpaper vs suede vs silk)
73
How do FA1 (Meissner's) react to slippery surfaces?
- Higher activity and discharge
- ridges in fingertips move up and down on contact, slippery objects have more movement
74
What do FA1's tell you about an object when grabbing it?
- When you make contact
- How fast you make contact
- How slippery the thing is you are grabbing
75
When can FA1's be critical?
- During walking to help adjust for slippery surfaces
76
What is a limb matching task?
- Closed eyes and matching position and speed of on limb to other limbs
77
What are the sources of Proprioception and Kinesthesis?
- Muscle Spindle
- Skin
- Joints
- GTO
78
How does a muscle spindle contribute to proprioception and kinesthesis?
- Velocity and length of the muscle
- reflexively onto motor neurons and up to the brain
- Primary and secondary: two pipelines dedicated to change in muscle length
79
How does the skin help with proprioception and kinesthesis?
- length and velocity of skin stretch
- onset of movement
- acceleration
- changes its length around a joint, skin strain (ruffini)
80
How do Joint help with proprioception and kinesthesis?
- Pressure
- contraction
- sensitivity
- reflexes: tuning the gamma system in the spindle
- can modulate joint receptors
81
How do Golgi Tendon Organs help with proprioception and Kinesthesis?
- Tension and Force Sensing
82
Is Kinesthesis Conscious? how?
Yes
- Involves an interpretation/judgment of where you are in space
83
What are the four main contributors to Kinesthesis? What do they contribute?
- Sense of Position and Movement of Limbs: position relative to you and world around you, how fast they are moving
- Sense of Tension and Force: GTO to some extent
- Sense of Effort and Heaviness: Force output stays the same/ fatigue requires more effort
- Sensations of Body Image and Posture: clinical conditions to pain, distortion
84
Is proprioception conscious? why?
More Reflexive
- Happens before you know to prevent you from falling over
85
What is some early evidence of a somatosensory role in proprioception and kinesthesis?
- Dorsal Rhizotomy in animals
- Human Deafferented Subjects
- Clinical Conditions
- Vitamin B6 Toxicity in Cat
86
How does Dorsal Rhizotomy in animals support the somatosensory role in proprioception and kinesthesis?
- fine motor control disappeared: movement deteriorates
- reflex orientates within spinal cord
- tactile information not getting to brain
87
What is a dorsal rhizotomy
surgical removal of dorsal root afferent input
88
How do humans who have been deafferented support somatosensory role in proprioception and kinestheis?
- Familiar tasks remain intact
- New tasks are difficult
89
How does Guillain-Barre Syndrome support the somatosensory role in proprioception and kinesthesis?
- Woman lost vocal proprioception and sounded deaf
90
What is Gullain-Barre Syndrome?
- loss of sensation (motor, sensory, or both)
- or increase in pain due to demyelination
- can recover
91
What does a Vitamin B6 toxicity in cats do?
- Leads to large fibre neuropathy (loss of proprioceptive inputs)
92
How does vitamin B6 toxicity in cats support a somatosensory role in proprioception and kinesthesis?
- 1as, secondaries, 1bs, afferents from joints and skin demyelinate
- loss of sensory information
93
What happens when the code for somatosensory is interrupted?
- a dramatic reduction in control and perception of movement
- code is critical for performing normal movements
94
How are cortical projections for 1a afferents important for kinesthesis?
3rd neuron projection
- medial lemniscus pathway carries information all the way to the cortex
- use information for proprioception and kinesthesis
- muscle spindles very useful for providing code on length and velocity
95
What is strong evidence that muscle spindles play a conscious role in position/movement sense?
- Illusion of muscle lengthening when vibrating
- Joint and skin receptors arent activated while this is happening
- has to be on the muscle itself, if it isn't the illusion disappears
96
What are some examples using vibrations to create an illusion of movement? what do they show?
- Pinocchio effect
- Falling Forward/Backwards
Shows evidence of selectively attending to muscle spindle feedback to determine where you are in space
97
How do you produce the Pinocchio Effect?
- Grab nose / close eyes
- vibrate bicep: makes it feel like elbow extend
- nose must grow to maintain contact
98
How do you produce the falling forward illusion?
- bilaterally vibrate tricpes surae tendons in standing position
- illusion of tricep extend and lengthen
99
How do you activate the falling backwards illusion?
- light source
- vibrate Achille's tendon
- light source moves vertically upward
100
What did the Assigned Readin #3 Discuss?
For fast movements, muscle spindles in the agonist may go quiet / become unloaded
- extrafusal muscle shortening faster than .2 resting length/s may result in muscle spindle unloaded, even with gamma drive
- If the agonist muscle spindle is unable to code for position/movement, then antagonist muscle does
101
What happens to your finger proprioception when you isolate the finger and selectively remove sensation?
- Limited loss in proprioception
- Muscle spindle afferent feedback intact in forearm muscles
102
What happens when you pull on the muscle tendons during a carpel tunnel surgery?
- People perceive finger movement depending on direction pulled
- activates spindles and interpret discharge as movement
103
What is evidence that muscle spindles are involved in proprioception?
- Vibration Illusions
- Removal of all Senses other than Spindles, still have proprioception
104
What happens to proprioception after a total joint replacement? What does it say about joint receptors?
- No evidence of a significant decrease in joint position sense
- Joint receptors are not essential for proprioception in this case
105
What experiment showed people that skin was involved in proprioception?
Isolate muscle tendons and mechanically move the finger. Remove joint receptors, and test proprioception with only skin receptors active. Decreased, but still active.
106
What is an experiment that shows that joint receptors are used in proprioception?
Inject dextran to joint, joint swells and activates joint receptors. This resulted in higher detection in proprioception, specifically for the hand.
107
What do we know about joint and skin receptors in the hand regarding proprioception?
Joint
- Definitely play a role in the hand
Skin
- Skin strain around a joint is involved (Ruffini Endings)
108
When can SA2's be recorded on the back of the hand?
During Flexion and Extension Movement
- Codes for lateral skin stretch
109
What happens when you push on a Ruffini Ending? What about when you stretch the skin?
Push
- Regular discharge
Stretch
- Increase firing rate (codes for finger position)
110
What does the map of SA2s on the front and back of the wrist do?
- Measures skin strain when you flex or extend
- I.e. throwing a baseball pitch
111
What is the Problem for SA2?
- Doesn't distinguish which finger is firing when moving two individually, just says it was moving
112
Does each finger have a subpopulation of FA1's? what happens when that a finger moves?
Yes
- The population associated with that subpopulation fires
113
What is similar about SA2's and FA1s? What is different?
Same
- similar code
Different
- FA1's tells which finger is firing
114
What is evidence that you pay more attention to skin strain pattern on back of the hand over what the spindles tell you?
Using ring block to selectively remove joint, skin, spindle receptor feedback. Move finger and they can tell it moves but cant feel it. Stretch skin and make you think finger was flexed when extended - vice versa.
115
What does Functional Knee Bracing do to proprioception?
Facilitates Skin Strain around knee joint
- increases proprioceptive awareness and accuracy
*useful if there is a deficit
116
What do pressure undergarments do for proprioception?
Creates skin strain pattern
- helps tell more accurately how you're moving
- i.e. how hips are rotating
- modifies cutaneous feedback
117
What are the problems with codes from muscle spindles? how can it be identified?
Problems
- Ambiguous Nature to code
- Code is changed by the gamma system
- Has Gamma bias
Identification
- Gamma system sends efference copy to cortex/cerebellum
- Subtract gamma bias from afferent feedback
- now you have the code
118
How does your brain compare and analyze movement?
Copy of motor command goes to sensory centers
- for comparison and error detection
119
What happens when you send a central command to extrafusal fibres?
Get a bunch of Afferent Feedback to the sensory cortex associated with that movement
- GTO feedback on twitch force
- Spindles on muscle length and velocity
- Skin/joint receptors
120
What is a corollary discharge?
- When you make a contraction and send a copy of the motor command to the sensory centres
121
How do we correct errors in movement?
Compare corollary discharge with afferent feedback at the sensory cortex and make a correction
122
What are the different classifications of Joint Receptors? what are they based on?
4 subtypes
- based on type of axon connected to
123
What are the four subtypes of joint receptors/
- I
- II
- III
- IV
124
What Joint Receptors are mechanoreceptors? what are their characteristics?
Subtypes I, II, III
- larger
- Myelinated Axons
125
What Joint Receptor is a Nocireceptor? What does is code for?
IV
- Pain
126
Where are the Joint Receptors located? where are they not located?
Located
- Joint Capsule
- Joint Ligaments
- Loose Articular Tissue
Not Located
- Cartilaginous surfaces
- Synovial Membranes
127
Where are Type IV joint receptors located?
Small nerve endings
- within bone, surface tissue of bone
- Not in Joint Capsule
128
Where are Type III Joint Receptors Located?
Part of External Ligament (tibial collateral)
- lots of them
129
Where Are Type I Joint receptors located?
- Superficial layers of capsule
- Denser in proximal joints
- Denser in Cervical Spine (vs Lumbar)
130
Describe Type I Joint Receptor Threshold/firing
- Low THreshold
- Slow Adapting
- Fires as soon as stretch starts
- continues firing throughout stretch
131
Describe the Type I Joint Receptor structure
- Globular or Ovoid Corpuscles
- As it gets in tissue, loses myelin and branches that imbed
132
Where are Type II Joint Receptors Located?
- Deep layers in capsule and articular fat pads
- More in distal articulations
133
Describe Type II Joint Receptor Threshold/Firing
- Low Threshold
- Rapid adapting
- Fires only during transitions (transient)
134
What is the structure of Type II Joint Receptors?
- Elongated
- Cylindrical Corpuscle
- Modified Pacinian Corpuscles
- Axon is in middle of numerous layers
135
What are Type III Joint Receptors known as?
- Golgi Receptors
136
Where are Type III Joint Receptors Located?
- Intrinsic and Extrinsic Joint Ligaments
- Embed in ligaments
137
Describe the Type III Joint Receptor threshold/firing
- High Threshold
- Slow Adapting
- Takes a lot of tension to fire, will continue to fire if tension maintained
138
What is the structure of Type III Joint Receptors?
- Fusiform Corpuscles (identical to GTO)
- Embedded in ligaments
139
What is the Neural Code?
- Respond to extreme limits and joint pressure (swelling or compression)
140
How do Joint Receptors code for joint position?
- Fire in limited way
- Respond mainly to extremes
- Respond to joint pressure
- code ambiguously for joint movements
- Respond to both flexion and extension (not specific to what is occurring)
141
What is an example of the ambiguity of Joint Receptor Coding?
Metatarsal Phalangeal Joint
- Increase discharge when held in flexion (velocity and static code of position of joint)
- Extension fired the same way
142
How does the firing rate of Joint Receptors at different joint angles contribute to their ambiguity?
- Don't Fire at midrange
- Has inverted U-shape as extension is continued
- Same firing rate at two different points
- Does not help physiologically define range/angle
143
What implies that Joint Receptors have a strong connection to higher-order sensory neurons?
- Joint afferents reach the supraspinal centre
- Stimulation of Joint afferents evoke distinct sensation of rotation, deep pressure and well defined somatosensory evoked potentials
144
What Joint Receptors have strong projections on Alpha MN?
- High Threshold (mainly nocirecptors)
145
what Joint Receptors have a weak and infrequent effect on Alpha MN?
- Low threshold (mechanosensive)
146
What is an indication of protective muscle reflexes in knee ligaments?
- Require heavy stretching for measurable EMG activity
147
Which is more influenced by low threshold joint afferents? Alpha MN or Gamma MN?
- Gamma MN
148
What causes strong excitatory and inhibitory effects on static and dynamic Gamma MN?
- Low threshold Joint Mechanoreceptors
149
How can Joint Receptors indirectly influence muscular control and proprioception?
JR excites or inhibits static and dynamic gamma MN
- Gamma modulates spindle behavior
- muscle spindle plays a key role in reflexive control of muscles and movement, position sense
150
Why does a damaged Joint Receptor decrease proprioception?
JR feedback to gamma MN which codes for velocity and static
- Damaged JR results in loss of regulation of muscle spindle (it doesn't know what to code for)
151
What is an example of the simple monosynaptic reflex?
- Drinking from a mug
- add to the load
- stretches biceps and activates spindles
- feedback from spindle to MNP of biceps
- Causes contraction to correct for increased load
152
What is a massive convergence?
- A large amount of spindles in muscle
- All go back and connect up with every single MN in muscle
153
What is a massive divergence?
- Every Spindle connects to every neuron in the MNP
154
How fast is the simple monosynaptic reflex?
- Quick, rapid corrects in 22ms
155
Describe the Simple monosynaptic reflex in the anterior arm
- Very strong connections to MNs in biceps
- Weaker connection to MNs in other muscles that flex (brachialis, brachioradialis) `
156
What is the Hoffman (H) Reflex?
- EMG response
- An artificial copy of the monosynaptic reflex
- Requires artificial stimulus
157
What nerve can the Hoffman Reflex stimulate?
- any nerve
158
What is the Hoffman Reflex used for?
- To test the level of excitability of a MNP
159
How can the Hoffman Reflex vary in certain populations?
- Hypo or Hyper
160
What is the Pulse rate for the Hoffman Reflex?
- 1ms pulse/ 5s
161
What was the Hoffman Reflex intended for?
- Artificially set up APs that go to spinal cord and come back as part of reflex
- Electrically activate 1a afferents and alpha motor neurons
162
Why do both 1a afferents and alpha motor neurons activate during the Hoffman Reflex?
- They are the largest diameter axons (most sensitive)
- cross-sectional size of axon is critical
162
Why do both 1a afferents and alpha motor neurons activate during the Hoffman Reflex?
- They are the largest diameter axons (most sensitive)
- cross-sectional size of axon is critical
163
What is the largest axon in the peripheral nerve?
- 1a Afferents
164
Why did Hoffman test the strength of the monosynaptic reflex?
- to see if it was stronger or weaker in certain populations
- To test the excitability of different MNP
165
What happened when Hoffman turned up the current?
- Excite progressively smaller diameter axons
- At high level, it directly stimulated largest diameter motor neurons axons
166
What is the highest threshold MN?
- Big axons that connect to biggest cell bodies
167
What two reasons are there for a change in the Hoffman Reflex if the current is kept the same?
- Strength of coupling between 1a afferent and MN
- MNP changed its state
168
What is Orthodromic?
- The correct direction of potential travel for afferent and efferent
169
What is the Orthodromic current for 1a afferents?
- AP goes along axon into the spinal cord
170
What happens if during an Orthodromic 1a Afferent there is sufficient EPSPs onto the MNP?
- Lowest threshold MN will fire
- AP goes to nerve
171
How long does it take for an H-reflex to occur?
- 30-33ms after stimulus
172
What is the Orthodromic direction for an Alpha motor neuron?
- Ap goes down the muscle
173
What is an Antidromic Current? How can this happen?
- Backwards Propagation of the potential
- Stimulate the nerve in the middle
- No refractory period
174
What is an Antidromic path for a 1a Afferent?
- AP goes back down to muscle spindle
- dissipates
175
What is the path of an antidromic current in alpha motor neurons?
- AP goes back up towards the cell bodies
176
What is the relationship between the H-reflex and the M-wave?
- Increasing Current Increases H-reflex
- Increasing H-reflex activates M-wave
- As M-wave increases, H-reflex decreases
- At M-max, H-reflex disappears
177
Why does the H-reflex get smaller as the M-wave increases?
- Due to Anti and Orthodromic Activation in the nerves
- Antidromic AP of Motor Neuron causes depolarization and hyperpolarization of cell body
- Brief Period MN cannot be activated
178
What does a plot of M-wave and H-reflex amplitudes measure?
- Peak-to-peak amplitude of the response
- M-wave starts to recruit more and more MN until max
- H-reflex grows until antidromic consequence causes it to disappear
179
How to tell if you are always hitting the nerve with the same stimulus?
- M-wave is present and stable
- Close to Solid H-reflex
180
How would you know if you are not hitting the nerve with the same stimulus?
- H-reflex start to grow and change
181
What happens if the H-reflex changes while the M-wave is constant?
- Change in MNP excitability or
- Strength of synapse changed
182
Whats the Difference between activating a T-reflex and H-reflex?
H-reflex
- Electrically stimulated
T-reflex
- Activate spindle by tapping the tendon
183
Which is totally dependent on a transducer? H-reflex or T-reflex?
T-reflex
- requires spindle to generate AP, H-reflex does not
184
What is the size of the T-reflex dependent on?
The size of the tap
- Larger tap equals bigger volley of APs from spindle
185
How does a small contraction influence a T-reflex? why?
Larger one
- lowest threshold MUs are above the threshold, rest are right near
186
Describe a reflex
- Automatic motor response to sensory stimulus
- Evoked from stimulation of peripheral receptors
-widespread effect on MNP
- Adaptable depending on context/task/state
187
What does a reflex involve?
- Sensory Neuron
- Interneuron
- Motorneuron
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What is the exception to the Reflex circuitry?
Monosynaptic Stretch Reflex
- 1a afferent directly to MN
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Where can there be an influence on a Reflex?
- First Synapse between afferent and interneuron
- other connections at interneuron
- where the interneuron connects to MN
- IPSP or EPSP Interneuron
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What is Autogenic Excitation?
- When the 1a afferents project to all the MN of the same muscle
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what is a Reciprocal Inhibition of a Reflex? Example?
Homonymous Stretch Reflex that also connects to 1a inhibitory interneuron
- disynaptic reflex (1 IPSP and 1 EPSP)
- Creates balance across the joint
Example
- Bicep fires
- Tricep Inhibited
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What is an Autogenic Inhibition? What is an example?
AI
- When a reflex inhibits its own muscle
Example
- 1b (GTO) inhibition
- active muscle activates GTO
- 1b afferent enters spinal cord has disynaptic to MN
- MN goes back to the original muscle
- GTO senses tension and force
- GTO uses 1b inhibitory interneuron to inhibit
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Why is the 1b Inhibitiroy Interneuron misnamed?
- Because it can be both faciliatory and inhibitory
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What does the 1b inhibitory interneuron connect to other than the 1b pathways? What is this an example of?
- Joint Afferents
- Cutaneous Afferents
- Descending Inputs
Example of Convergence
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Why is it good to have an interneuron?
So you can make a contraction without it being prevented
- Interneuron can prevent large IPSP from stoping EPSPs from GTO
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What does 1b feedback have a facilitatory effect on?
-Antagonist MNs
197
How does the 1b inhibitory interneuron excite an antagonist MN?
Facilitates by Inhibiting inhibition (passive)
- Release IPSP onto interneuron
- Interneuron goes to mnp of antagonist
- IPSP inhibits the inhibition on the antagonist MN
198
What is the Flexor (withdrawal) Reflex?
Protective reflex that coordinates activation of limb flexor muscles
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How does the Flexor Reflex work? (two ways)
The interneuron connects to another interneuron that connects to MNP
- IPSP onto MNP = prevents muscle extending further into stimulus
Connects via 2 interneurons with EPSP on MNP of muscle to flex away from stimulus
- goes to everything that can flex away (major divergence)
200
What is the Crossed-Extension Reflex?
In opposite limb
- Activation of extensors
- Inhibition of Flexors
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How can reflex responses be modulated?
- Through interactions at different components of the reflex arc
202
Where do mechanisms to modulate reflex responses occur?
- Peripheral inputs (reflex connecting to reflex)
- Descending inputs (brainstem, cortex, etc)
203
What mechanisms can be used to modulate reflex responses?
Excitability of MN
- make really negative (prevent reflex)
Change sensitivity of interneurons
- severe negative, no 1b inhibition
Change MNP excitability
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Wha tis a Renshaw Cell?
- Interneuron located really close to the alpha MNP
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How is a Renshaw cell activated?
- Collateral from alpha MN (EPSP)
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What do R-cells Project to?
- Motor Neurons
- 1a Inhibitory interneurons
- Gamma motorneurons (weakly)
- other R-cells (weakly)
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What do R-cells receive input from?
- Descending pathways
- Cutaneous afferents
- Type II afferents
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Is a Renshaw Cell inhibitory or excitatory?
- Inhibitory
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What does the R-cell do?
- Biases own MN not to fire
- Remove inhibition to the antagonist
210
What is Axo-axonal synapse? How does work? What does it do?
When presynaptic neuron connects to post synaptic neuron
- Selective inhibition of only the presynaptic neuron
Used
- Chlorine Conductance
- Decrease the size of propagated AP
- Decrease Ca release, decrease NT release, Decrease EPSP
Do
- Enables a change in the input-output relationship
- Helps to control monosynaptic reflex
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What is the Latency Response length of pre-programmed reactions compared to monosynaptic response and voluntary reaction times?
- Shorter than Voluntary reaction times
- Longer than a monosynaptic response
212
Example of how Pre-programmed reactions work?
Stretch Wrist
- stretch all forearm flexors
- M1 is monosynaptic reflex
- M2-3 is a big burst in EMG between M1 and voluntary response
- M2-3 can be preprogrammed
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What does the pre-programmed reactions involve? what does it travel via?
Involves
- Parallel spinal and supraspinal pathways
Travels
- via dorsal column medial lemniscus pathway
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Is the M2-3 Response Transcortical?
- Yes
215
Where does evidence come from for the Pre-programmed reactions? What is that evidence?
Klippel-Feil Patients
- Bifid movements (one side of cortex drives both sides upper body)
Evidence
- Stretch right hand, M2-3 response right and left wrist
- Stretch one side causes preprogrammed response out of bilateral muscle
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Are rhythmic movements still possible following a complete transection of the spinal cord? How
Yes
- circuitry resides in the spinal cord
- rhythmic movement generated distal to lesion
217
what is central rhythm generation an inherent characteristic of?
- spinal cord
218
What is the Central Pattern Generator (CPG)?
EMG and Kinematic Pattern that looks normal due to rhythmic patterns generated by the spinal cord
- No Brain Involement
219
What is an oscillator involved in Central Pattern Generator?
Group of interneurons
- When they start going, create rhymical oscillating pattern within spinal cord
220
What is the Half Centre Model?
Interneuron excites flexor and inhibits extensor
- collateral comes back at itself with IPSP and briefly inhibit other side before terminated
- Same input can excite the other side, and oscillate back and forth
221
How does Central Pattern Generator work for Walking?
- Supraspinal input hits spinal cord
- CPG starts, dont have to physically think about moving
- Creates scaffolding for locomotion
222
What happens after an injury or disease that inhibits descending inputs? Example?
No Supraspinal Input
- Intact CPG, still have rudimentary walking
Example
- Kids born with corticospinal tract demyelination
- pick up, the legs oscillate
223
What is sensory feedback for regarding locomotion?
- Initiating walking
- controlling phase transitions
- Regulating the level of muscle activity
- correcting for unexpected disturbances
224
How does sensory feedback help regulate level of muscle activity during locomotion?
- CPG tells you the pattern
- Afferent feedback is highly involved in tuning MNP
225
How does sensory feedback help correct for unexpected disturbances in locomotion?
Stumbling-corrective response
- afferent feedback layers on CPG so when you trip you keep walking
226
How does sensory feedback help control phase transitions when walking?
Stretch of hip flexors - muscle spindles
- determine how far hip is going to extension
Unloading of extensor muscle -GTO
- Monitor force required to put out to stay upright
Use load to determine when its safe to transition
227
Explain the Stumbling-corrective Response
Encounter obstacle during swing phase
- automatic flexion response to step over
- All in spinal cord
If during stance phase
- extension of limb
228
What is a Phase-dependent Reflex reversal?
Response to the obstacle depends on the phase
- stim of top foot during swing, flexion of limb
- Stim top foot during stance, extension of limb
Same stimulus leads to different responses, depending on phase of locomotion
- Afferent driven
229
Where are Golgi Tendon Organs located?
- Tendon Junctions
- In Series
230
What is the Structure of GTO?
- capsule (1mm by 0.1mm)
- 10-20 muscle fibers
231
What afferent fiber innervates the Golgi Tendon Organ?
- 1b Afferent
232
Describe the Extrafusal Muscle Fibers of GTO
- each belongs to different motor unit
- not all muscle fibers associated with GTO
233
What do GTOs do?
- Muscle Receptors that provide feedback to the CNS about muscle force and tension
234
Describe the sensory innervation of GTOs
- Single 1b afferent (2% of GTOs have 2 ib afferents)
- Nerve endings interdigitate among collagen fibers
235
Are GTOs designed to monitor force production on active or passive force generation?
- Active Muscle
236
What will each GTO's discharge rate scale with increasing force in muscle?
- Linearly
237
What was the setup for Assigned Reading #3?
- 4m/4f university students (blindfolded ex. 1)
- Vibrations of 95Hz amplitude 2mm (measured by accelerometer)
- Angle of arm recorded by potentiometers
238
What was the setup of experiment 1 of Reading #3?
- Right limb moved to fixed targets (20,40,60%)
- Moves at 60degrees / second
- Match with left limb
- Conditions (no vibrations, antagonist vibration, agonist vibration)
239
What was the results of Experiment 1 of Reading #3?
- Antagonist muscle vibrations caused an overshoot in perceived movement magnitude
- Overshoot was same for all three target distances
240
What was the setup for Experiment 2 of Reading #3?
- Right arm flexed to line up middle finger to visual target
- Match with other arm
- Three conditions (no vibrate, vibrate antagonist, vibrate agonist)
241
What were the results of experiment 2 of Reading #3?
- Antagonist vibration resulted in overshoot
242
What was the purpose of the experiment in Reading #4?
- Why illusions of movement when non movement happens and no sensory Feedback
243
Describe how the experiment was performed in Assigned Reading #4
First
- Participants accuracy of effort level tested
Second
- Participants matching of wrist position was tested
Third
- BP cuff used to block motor and sensory function of arm
- Participants asked to make effortful extension or flexion
- Participants perceived position of wrist was recorded
244
What did participants in Reading #4 perceive with effortful movement of an isolated and paralyzed wrist? why?
Perception
- perceived extension or flexion in direction of effort
Reason
- No afferetn feedback
- Paying attention to the command of effort and interpreting it as sensation of movement
245
What were the results of the experiment done in Reading #4? what is this evidence of?
Results
- Error matching limb position
- Error dependent on effort direction
- Error dependent on the magnitude of effort
Evidence
- Kinesthesis is not just sensory, motor plays a role
246
What was the purpose of the experiment in Assigned Reading #5?
- Use height or possible postural perturbation to increase threat
- compare H/T reflexes to see if level of threat changes spinal reflexes
247
How did they control the H-reflex generated in Reading #5?
- Tap Achille's with load cell to ensure force is the same
248
What does measuring the T-reflex and H-reflex together in Reading #5 say?
- inform about the excitability of MNP
- Inform about strength or monosynaptic connection
- T-reflex will inform spindle activity
249
What might have caused the different peak to peak amplitude of the T-reflex during high and low levels for Reading #5? What does an unchanged H-reflex tell you about this?
Potential Causes
- Change in MNP excitability
- Strength of synapse increased
- Spindle changed sensitivity (gamma system)
H-reflex
- No change in MNP excitability
- No change in strength of synapse
- Spindle had to change sensitivity
