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Neuroscience (Yeo) > Motor Control 1 - Spinal Reflexes > Flashcards

Motor Control 1 - Spinal Reflexes Flashcards

1
Q

What stain has been used?

A
  • Myelin

(shows thickness of the white matter tracts)

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2
Q

Which part is the grey matter and which part the white matter?

A
  • White Matter Outside
  • Grey Matter is Butterfly
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3
Q

What does a thick/large dorsal column indicate?

Why would this be so?

A
  • Lots of Fibres
  • Upper Part of the Cord
  • Most Fibres have either not been given off (motor) or have come in (sensory)
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4
Q

What indications are there that this is a cervical transverse section?

A
  • Large White Matter Area
  • Large Gret Matter Enlargement in Ventral Horn (upper limb - brachial plexus)
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5
Q

Where are motor & sensory neurones found in the spinal cord?

A
  • Motor Neurones –> VENTRAL HORN
  • Sensory Neurones –> DORSAL HORN
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6
Q

Where are the nuclei found in the spinal cord?

A

Middle

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7
Q

How is the spinal cord divided up? (what is it called)

A
  • Rexed Lamination (grey matter division)
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8
Q

How many laminas are there in the Rexed Laminations?

Where is Lamina 10 found?

A
  • 10
  • Around central canal
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9
Q

What lamina of rexed are the motor neurones in?

A
  • Motor Neurones in Ventral Horn –> NOT LAYERED
  • Therefore not appropriate system for motor function
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10
Q

How are the Motor Neurones in the Ventral Horn organised? (generally)

A
  • Laterally & Medially –> for AXIAL & DISTAL MUSCLES
  • Close & Far to Central Canal –> for FLEXOR & EXTENSOR
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11
Q

Regarding motor neurones, how are they organised in terms of lateral & medial placement?

A
  • Close to Midline –> control muscles in TRUNK & NECK (axial muscles) –> e.g. posture & balance muscles
  • Lateral (further out) –> control LIMBS & EXTREMITIES –> e.g. fingers & wrists & toes etc.
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12
Q

Describe the radial aspect of organisation for motor neurones.

A
  • Neurones CLOSEST to CENTRAL CANAL –> control FLEXORS
  • Neurones FURTHER from CENTRAL CANAL –> control EXTENSORS
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13
Q

What are extensors very important for?

A
  • Postural Control
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14
Q

What makes up a motor unit?

A
  • Single motor neurone + muscle fibres it contracts

(It is the basic unit of motor organisation)

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15
Q

For a small motor unit, (around) how many muscle fibres would it contract?

Would it have high or low input resistance?

A
  • Around 10-20 muscle fibres
  • Small Motor Neurone –> thus HIGH INPUT RESISTANCE

(e.g. extra-ocular muscles)

Produces weak force

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16
Q

For a large motor unit, (around) how many muscle fibres would it contract?

Would it have high or low input resistance?

A
  • Contact around 1000 muscle fibres
  • Large Motor Neurone –> thus LOW INPUT RESISTANCE

(quadraceps)

Produces a large force

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17
Q

What type of motor neurone innervates muscles & terminates on a number of muscle fibres?

A
  • Alpha Neurone
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18
Q

How can each motor unit create a force over a range?

A
  • It can vary its FIRING RATE (APs)
  • Note that the number of fibres it contracts are still fixed
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19
Q

What 2 factors influence the level of force?

A
  • Size of Motor Unit (number of muscle fibres)
  • *Firing Rate**
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20
Q

What are the 3 components of Ohm’s Law?

What is the equation?

A
  • V = IR
  • Current
  • Voltage
  • Resistance
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21
Q

How does surface area of a neurone impact resistance?

A
  • SA –> determines the amount of membrane –> thus if it is a larger unit –> more SA & memrane –> so more channels (absolute number)
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22
Q

What affects the current a neurone can pass?

A
  • Resistance
  • Thus the amount of current that can pass –> which is related to the number of channels/ions that can flow through

(Small neurone has limited amount of memrane thus few channels compared to large unit)

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23
Q

What happens if you apply the same current to a small & large motor unit?

A
  • Small Motor Unit –> Small Neurone –> thus Small SA –> thus Less Channels –> Higher Resistance
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24
Q

What happens in terms of resistance and current as you increase surface area (i.e. neurone size)?

A
  • More SA –> More Membrane –> More Channels –> Less Resistance
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25
Q

What has high or low resistance between small & large motor units?

A
  • Small Motor Units –> HIGH RESISTANCE (easier to activate)
  • Large Motor Units –> LOW RESISTANCE
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26
Q

Does high resistance increase or decrease the ease of reaching threshold?

A
  • High Resistance –> EASIER to ACTIVATE NEURONE
  • Because HIGHER RESISTANCE –> in V=IR --> means HIGHER VOLTAGE for a CERTAIN CURRENT –> thus enough VOLTAGE to REACH THRESHOLD
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27
Q

What 2 factors increase voltage?

A
  • Current Size
  • Resistance

V=IR

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28
Q

How does neurone resistance help in synaptic drive?

A
  • Approx Equivalent Current Source (not voltage)
  • Therefore depolarisation on the post-synaptic side –> relates to input resistance & current –> which determines voltage
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29
Q

What 2 reasonable assumptions are made for this model?

A
  • Same Density of Channels across All the Neurones
  • Same Types of Channels
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30
Q

What occurs in low levels of acitvation to a motoneurone pool?

A
  • Activation of small high resistance motor neurones (small motor units)
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31
Q

What is this method of recruitment called?

A
  • Motor units –> recruited according to ‘size principle’ to generate increasing amounts of tension
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32
Q

What occurs in high levels of activation to a motoneurone pool?

A
  • Activation of larger & lower resistance motor neurones (large motor units) - aswell as small
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33
Q

What is basal contraction? What does it cause?

A
  • Most muscles have low amounts of activity
  • This gives their muscle tone
  • Smallest motor units/neurones –> require very little synaptic drive from background activity from interneurones –> thus small sensory drive can keep them activated all the time
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34
Q

What occurs in complete muscle denervation?

A

Lose Muscle Tone

Flaccidity

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35
Q

What determines the muscles involved in muscle tone?

A
  • Size Principal
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36
Q

From where do signals come from for voluntary mvoements?

A
  • Motor Cortex (minority)
  • Interneurones (majority)
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37
Q

What 2 inputs do spinal interneurones get?

A
  • Information from motor cortex
  • Somatosensory information from segmental level (consider muscle reflexes in motor control)
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38
Q

What 2 peices of somatosensory information come into interneurones?

A
  • Muscle Spindles
  • Golgi Tendon Organ
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39
Q

What do muscle spindles measure?

A
  • Distance

(length over which muscles have changes - stabalise length)

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40
Q

What do golgi tendon organs measure?

A
  • Tension

(resultant force generated from the muscle - i.e. force generated tension)

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41
Q

Why are the 2 somatosensory inputs to the spinal cords important?

A
  • Essential for control & movement
  • Increases movement accuracy (allows for fine control)
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42
Q

What are the 2 afferent neurone fibres to muscle spindles called?

A
  • 1a Afferents
  • Type II (A-beta) afferents/fibres
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43
Q

What exactly are the 1a afferents responsible for measuring?

A
  • Dynamic Changes (in distance)
  • Dynamic aspects of stretch –> such as acceleration & velocity of stretch

(picks up the early part as soon as muscle starts moving to see how rapid the stretch it)

Fire during the cahnge

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44
Q

What exactly are the Type II (A-beta) afferents responsible for measuring?

A
  • Static Distance Changes
  • Static Length of Muscle
  • Signals over a Period of Time

(sends constant information - thus if you push down and hold on a tendon –> thus they measure the change when its done)

45
Q

How are muscle spindles arranged?

A
  • Parralel with Extrafusal Fibres

(thus measure length rather than tension - would be series)

(There are a lot more extrafusal fibres compared to spindles)

46
Q

What are the muscle spindles anchored to either side?

A
  • Extrafusal Fibres
47
Q

What must change to cause activation of muscle spindles?

A
  • Change in Muscle Length
48
Q

Which parts of a movement do the 1a afferents & Type II afferents measure?

A
  • 1a afferents –> DYNAMIC/RAPID RECEPTOR
  • Type II afferents –> STATIC RECEPTOR

Thus the INITAL (dynamic) PART is measured by 1a Afferents –> however the ONGOING (static) PART is measured by Type II Afferents

(signals fades after the dynamic change is made for 1a afferents)

49
Q

Describe 1a afferents.

A
  • Largest Diameter Axons in PNS
  • Myelinated
  • Very Fast (50-70ms)
50
Q

Where is the only monosynaptci reflex?

A
  • Bicep Reflex
51
Q

What is a homonymous muscle?

A
  • Where the MOTOR OUTPUT is to the SAME MUSCLE as where the SENSORY SIGNAL came from
52
Q

What are synergistic muscles?

A
  • Muscles that have the same action function
  • Motor neurones can have collaterals to these other muscles (not common though)
53
Q

Describe Type II (A-beta) fibres.

A
  • large diameters (not as large as 1a afferents)
54
Q

Where else does the 1a afferents branch to?

A
  • 1a Inhibitory Interneurones (GABAergic)
  • Projects to antagonist muscle neurone in the joint
  • Inhibits the antagonist muscle (slight relaxation)
  • Therefore there is no co-contraction around the joint
  • Thus lowering the force on the joint
    *
55
Q

What is inhibition of the antagonist muscle when contracting called?

A
  • Reciprical Inhibition
56
Q

What 2 things does recipricol inhibition help with?

A
  1. Reduces Stress on Joint
  2. Reduces Energy Consumption
57
Q

What mediates jerk reflexes (e.g. knee jerk reflex)?

A
  • Muscle Spindles (not golgi tendon organs)
58
Q

What are the stretch reflexes & muscle spindles important for?

A
  • Holding Muscle in a Certain Position
  • Jerk Reflexes
59
Q

What keeps the limb at a maintained position?

A
  • Type II Fibres –> STATIC INFORMATION –> thus ONGOING INFORMATION to KEEP it there

(1a afferents detect dynamic aspects when the load is first dropped onto outstretched arm)

60
Q

How are the spinal reflexes important in the spinal cord?

A
  • Keep you still against gravity
  • Reflexes working all the time
  • Keep things where you want them to be (bring them back to where you want in miniature amounts)
  • Muscle spindles –> key part of motor control
    *
61
Q

Why do the spinal reflexes (muscle spindles) interact with voluntary movement systems?

A
  • Correct movements
  • Allow for central command
62
Q

Describe the muscle spindle activation pathways in passive stretch.

A
63
Q

How does the muscle spindle still stay ‘alert’ during contraction? Is it not laxed?

A
  • Muscle Fibres (extra-fusal fibres) + Spindles –> CO-CONTRACT

Ensures that they are still able to detect stretch (length change)

NB: Spindle is contractile itself

64
Q

Wha are the 2 parts of the muscle spindles?

A
  • Equator Region –> Middle Sensing Part
  • Polar Region –> Polar Contractile Part (contractile elements here)

These are effectively modified muscle fibres which shorten with the extra-fusal cells

65
Q

How is the signal sent out for contraction to extra-fusal and muscle spindles?

A
  • Extra-fusal Muscles –> get a direct monosynaptic signal from 1a afferents
  • Spindles –> go via interneurone
66
Q

Do the extrafusal & muscle spindles contract to the same length?

A
  • No
  • Muscle Spindles --> get own motor instruction from GAMMA MOTOR NEURONES (very small motor neurones from ventral horne)

These ensure they are approcimately the same length

67
Q

Why do we have precision control in terms of muscle spindles?

A
  • Split Alpha-Gamma Co-Activation System
68
Q

What is active contraction?

A
69
Q

How does Alpha-Gamma Co-Activation work?

A
  1. Motor Instructions (either from direct or indirect source) –> sends a VERSION of the MOTOR COMMAND –> to the GAMMA NEURONE (aswell as to extrafusal neurones)
  2. Thus they CO-CONTRACT via 2 SERPARATE SYSTEMS
70
Q

What is beta innervation?

A
  • Motor Neurone –> diverges to control both the spindles & extrafusal fibres (thus limited function - not much precision control)

(it has properties of both alpha & gamma neurones)

71
Q

Do humans have beta innervation?

A
  • Yes
  • e.g. hips & shoulders
  • Where fine control is not needed & beta-innervation is sufficient
72
Q

How does the split alpha-gamma system work to increase precision?

A
  • Differential Activation of Gamma & Alpha Neurones (allows for high precision movements)
  • Increase Precision –> by pre-stretching the spindles (via gamma) more than usual –> to get them into a sensitive part of their range

(This however limits travel -> thus cannot get as much force & travel - but helps with things such as threading a needle)

(balance between range & accurate)

73
Q

How are pathologies involved in split system?

A
  • They can differentially effect the alpha-gamma systems
74
Q

How are the gamma neurones activated?

A
  • They are co-activated (not at the exact same time)
  • The contraction caused by alpha neurone –> causes stretch of spindle –> causing reflex to the gamma neurone –> causing it correct its length in line with alpha neurone contraction

(1a responds to motor instruction & gamma responds to contraction)

75
Q

Why cant the muscle spindle (gamma) contract at the exact same time as the alpha (extrafusal fibres) contract?

A
  • Would cause a reflex response –> due to spindle stretch at the wrong length
  • Would propogate itself –> causing positive feedback
76
Q

How does spindle sensitivity work?

A
77
Q

What does EMG stand for?

A
  • Electrical Muscle Signal
78
Q

Do the 1a afferents activate during voluntary movement?

A
  • Yes
  • They correct the movement & keep it controlled
79
Q

When do you see the primary afferent signal for the gamma (spindle) come in?

A
  • After the EMG (motor signal)
  • Thus it corrects it shortly after

(cannot be the same time)

80
Q

What technique do you use to record individual axons?

A
  • Microneurography
81
Q

How does recipricol inhibitory control work?

A
  • 1a afferent neurone –> gives a collateral which sends an inhibitory neurone to antagonist muscle
82
Q

Why is it important there isn’t complete relaxation of the antagonist muscle?

A
  • All Weight on a flexed knee –> cannot hand loose
  • Needs partial co-contraction to support it before you hit the deck
  • Thus so you can remain standing with a bent knee (hamstring needs to be tense)
    *
83
Q

What occurs when there is co-contraction of muscles across a knee joint?

A
  • Knee Joint is Stiff
  • Both Muscle Contract (shorten)
  • Thus highly resistant to movement on the joint
84
Q

What measures muscle tensions at a joint?

A
  • Golgi Tendon Organ
85
Q

In what arrangement is the golgi tendon organ found?

A
  • Series with Extrafusal Fibres
86
Q

What happens when there is pull on the golgi tendon organ?

A
  • Pull on Spring Balance
  • Muscle pulls on the tendon
  • Neural Spring Balance –> causing 1b afferents sending information back
87
Q

How are the sensory endings of the 1b afferents arranged?

A
  • Weave in-between the collagen fibres
  • Therefore, when tension applied they squeeze –> causing signals sent about tension
88
Q

What are the golgi tendon organs located?

A
  • One End –> EXTRAFUSAL MUSCLE FIBRE
  • Other End –> TENDON
89
Q

How is tension distributed across golgi tendon organs?

A
  • Load Muscle Passively onto Tendon
  • Many Golgi Tendon Organs are in parrallel with each other
  • Therefore, actual force of load is divided among the number of supporting golgi tendon organs

(Therefore they are very sensitive as only a fraction of the weight is being measured by each tendon organ)

90
Q

How do they respond to a range of tensions?

A
  • Contract Some Muscle Fibres –> then only the golgi tendon organs associated with those muscle fibres are activated –> but they would be very sensitive
  • Large relative force applied –> depending on level of force –> will affect number of golgi tendon organs involved –> thus able to report a range of tensions in individual fibres –> depending on number of individual fibres involved (all together) –> giving good indications of overall loadings (not just protective feature) –> they manage forces
91
Q

When do you need the golgi tendon organ and cannot use a spindle receptors?

A
  • Co-contraction
  • There is no length change during co-contraction –> thus spindles not involved
  • Golgi tendon organ –> can measure tension instead
92
Q

Describe the golgi tendon organ pathway.

A
  • 1b afferents pick up tension signal
  • These are dynamic & fast-conducting fibres
  • They synapse onto 1b inhibitory interneurones
93
Q

What occurs when there is high tension?

A
  • Activation of 1b inhibitory interneurones –> slow firing
  • Causes homonymous muscle (self-muscle) to relax
  • This causes the opposite of the stretch reflex (‘inverse myotatic reflex’)
  • This is due to tension change

(Someone holding a knife if you pull someone’s arm away but they cannot resist after a certain point thus suddenly release to stop damage to muscle - protective reflex)

94
Q

What are the 2 functions of the golgi tendon organ?

(generally)

A
  • Protective Mechanism (high loads)
    Sensitivity Receptor
95
Q

Why is convergence important onto 1b interneurones?

A
  • Important for descending control convergence
  • Receive command instructions from a variety of place
96
Q

Name 3 places the 1b interneurone will get inputs from?

A
  1. Golgi Tendon Apparatus
  2. Input from Joints
  3. Input from Cutaneous Receptors
97
Q

Why do you get inputs from joints & cutaneous receptors to the 1b inhibitory interneurones?

A
  • These are high threshold nociceptive inputs (including pain & temperature receptors in the joint)
  • e.g. badly inflamed joint (arthiritis) –> causes excitatory firing to 1b inhibitory interneurone –> causing inhibition of motor neurones –> thus difficult to activate –> therefore cannot contract very much
  • Protective Reflex (stop certain movements –> allow for body repair
98
Q

What are the 2 types of nociceptors?

A
  • C-fibres (slow)
  • A-deltas (fast)
99
Q

Which nociceptor is involved in flexion-withdrawal reflex?

A
  • A-delta nociceptors
  • Fast conducting
100
Q

Briefly describe the flexion-withdrawal reflex.

A
  1. Relaxation of extensor + contraction of flexor
  2. Allows for flexion withdrawal –> to lift foot away from sharp object –> with no counter balance from the limb

Nociceptive Signals can illicit reflex –> causes effect via cross-extension reflex

101
Q

What is walking patterns essentially made up by?

A
  • Extension-Withdrawal Patterns –> REPEATED
102
Q

What is a renshaw cell?

A
  • Further Inhibitory Interneurone found in the spinal cord
103
Q

What is the function of a renshaw cell?

A
  • Gives motor units in the agonist muscle –> a break (time off)
  • This occurs when fibres have been very active (allows other fibres to take over)
104
Q

How is a renshaw cell innervated?

A
  • Alpha Motor Neurone –> sends a collateral to the renshaw cell –> driving inhibition back to the same motor neurone
  • Therefore there is co-activation of the inhibitory neurone onto itself
105
Q

Describe how the renshaw cell works.

A
  • Threshold Strategy
  • Motor neurones fire for a long time –> at some point they weaken –> allowing the inhibitory command to be strong enough to inhibit it –> allowing muscle fibre to rest
  • Allows for switching between fibres in motor pool (distribution of work load)
106
Q

What does the renshaw cell do in relation to antagonist muscle?

A
  • Recipricol Control
  • Controls 1a inhibitory interneurones –> to disinhibit the inhibitory neurones on the antagonist
107
Q

What other fibres makes contact with renshaw cells?

A
  • Descending Pathways
108
Q

What drives the oculo-motor reflex?

A
  • Vestibular Input from Semi-Circular Canals

Neuroscience (Yeo) (8 decks)

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