Motor Control 1 - Spinal Reflexes Flashcards
1
Q
What stain has been used?
A
- Myelin
(shows thickness of the white matter tracts)
2
Q
Which part is the grey matter and which part the white matter?
A
- White Matter Outside
- Grey Matter is Butterfly
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)
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)
5
Q
Where are motor & sensory neurones found in the spinal cord?
A
- Motor Neurones –> VENTRAL HORN
- Sensory Neurones –> DORSAL HORN
6
Q
Where are the nuclei found in the spinal cord?
A
Middle
7
Q
How is the spinal cord divided up? (what is it called)
A
- Rexed Lamination (grey matter division)
8
Q
How many laminas are there in the Rexed Laminations?
Where is Lamina 10 found?
A
- 10
- Around central canal
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
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
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.
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
13
Q
What are extensors very important for?
A
- Postural Control
14
Q
What makes up a motor unit?
A
- Single motor neurone + muscle fibres it contracts
(It is the basic unit of motor organisation)
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
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
17
Q
What type of motor neurone innervates muscles & terminates on a number of muscle fibres?
A
- Alpha Neurone
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
19
Q
What 2 factors influence the level of force?
A
- Size of Motor Unit (number of muscle fibres)
- *Firing Rate**
20
Q
What are the 3 components of Ohm’s Law?
What is the equation?
A
- V = IR
- Current
- Voltage
- Resistance
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)
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)
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
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
25
What has **high** or **low** **resistance** between **small** & **large** **motor** **units**?
* **Small** Motor Units --\> **_HIGH_** **RESISTANCE** (easier to activate)
* **Large** Motor Units --\> **_LOW_** **RESISTANCE**
26
Does **_high_** **resistance** **increase** or **decrease** the ease of reaching threshold?
* 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**
27
What 2 factors increase voltage?
* Current Size
* Resistance
V=IR
28
How does neurone resistance help in synaptic drive?
* Approx Equivalent Current Source (not voltage)
* Therefore **depolarisation** on the **post**-**synaptic** **side** --\> relates to **_input resistance_** & **_current_** --\> which determines **voltage**
29
What 2 reasonable assumptions are made for this model?
* Same Density of Channels across All the Neurones
* Same Types of Channels
30
What occurs in low levels of acitvation to a motoneurone pool?
* Activation of **small high resistance motor neurones** (small motor units)
31
What is this method of recruitment called?
* **Motor** **units** --\> **recruited** according to **'size principle'** to generate **increasing** **amounts** of **tension**
32
What occurs in high levels of activation to a motoneurone pool?
* Activation of **larger & lower resistance motor neurones** (large motor units) - aswell as small
33
What is basal contraction? What does it cause?
* 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**
34
What occurs in complete muscle denervation?
Lose Muscle Tone
Flaccidity
35
What determines the muscles involved in muscle tone?
* Size Principal
36
From where do signals come from for voluntary mvoements?
* Motor Cortex (minority)
* Interneurones (majority)
37
What 2 inputs do spinal interneurones get?
* Information from **motor** **cortex**
* **Somatosensory** **information** from **segmental** **level** (consider muscle reflexes in motor control)
38
What 2 peices of somatosensory information come into interneurones?
* Muscle Spindles
* Golgi Tendon Organ
39
What do **muscle** **spindles** measure?
* Distance
(length over which muscles have changes - stabalise length)
40
What do **golgi** **tendon** **organs** measure?
* **Tension**
(resultant force generated from the muscle - i.e. force generated tension)
41
Why are the 2 somatosensory inputs to the spinal cords important?
* Essential for **control** & **movement**
* **_Increases movement accuracy_** (allows for fine control)
42
What are the **2 afferent neurone fibres** to **muscle** **spindles** called?
* **1a** Afferents
* **Type II (A-beta)** afferents/fibres
43
What exactly are the 1a afferents responsible for measuring?
* **_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
44
What exactly are the Type II (A-beta) afferents responsible for measuring?
* **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
How are muscle spindles arranged?
* Parralel with Extrafusal Fibres
(thus measure length rather than tension - would be series)
(There are a lot more extrafusal fibres compared to spindles)
46
What are the muscle spindles anchored to either side?
* Extrafusal Fibres
47
What must change to cause activation of muscle spindles?
* Change in Muscle Length
48
Which parts of a movement do the **1a** afferents & **Type II** afferents measure?
* 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
Describe 1a afferents.
* Largest Diameter Axons in PNS
* Myelinated
* Very Fast (50-70ms)
50
Where is the only monosynaptci reflex?
* Bicep Reflex
51
What is a homonymous muscle?
* Where the **MOTOR** **OUTPUT** is to the **_SAME_** **MUSCLE** as where the **SENSORY** **SIGNAL** came from
52
What are synergistic muscles?
* Muscles that have the **_same_** **action** **function**
* Motor neurones can have **collaterals** to these **other** **muscles** (not common though)
53
Describe Type II (A-beta) fibres.
* large diameters (not as large as 1a afferents)
54
Where else does the **1a afferents** branch to?
* **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
What is inhibition of the antagonist muscle when contracting called?
* Reciprical Inhibition
56
What 2 things does recipricol inhibition help with?
1. Reduces Stress on Joint
2. Reduces Energy Consumption
57
What mediates jerk reflexes (e.g. knee jerk reflex)?
* **Muscle Spindles** (not golgi tendon organs)
58
What are the **stretch** **reflexes** & **muscle** **spindles** important for?
* Holding Muscle in a Certain Position
* Jerk Reflexes
59
What keeps the limb at a maintained position?
* **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
How are the **spinal** **reflexes** important in the **spinal** **cord**?
* 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
Why do the spinal reflexes (muscle spindles) interact with voluntary movement systems?
* Correct movements
* Allow for central command
62
Describe the muscle spindle activation pathways in passive stretch.
63
How does the muscle spindle still stay 'alert' during contraction? Is it not laxed?
* **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
Wha are the 2 parts of the muscle spindles?
* **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
How is the signal sent out for contraction to extra-fusal and muscle spindles?
* Extra-fusal Muscles --\> get a direct monosynaptic signal from 1a afferents
* Spindles --\> go via **interneurone**
66
Do the **extrafusal** & **muscle spindles** contract to the same length?
* 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
Why do we have precision control in terms of muscle spindles?
* Split Alpha-Gamma Co-Activation System
68
What is active contraction?
69
How does **Alpha-Gamma Co-Activation** work?
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
What is **beta innervation**?
* 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
Do humans have beta innervation?
* Yes
* e.g. hips & shoulders
* Where **fine** **control** is **_not_** needed & **beta-innervation is sufficient**
72
How does the split alpha-gamma system work to increase precision?
* **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
How are pathologies involved in split system?
* They can **_differentially_** **effect** the **alpha-gamma systems**
74
How are the gamma neurones activated?
* 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
Why cant the muscle spindle (gamma) contract at the exact same time as the alpha (extrafusal fibres) contract?
* Would cause a **reflex response** --\> due to **spindle** **stretch** at the **_wrong_** **length**
* Would **propogate** **itself** --\> causing **positive** **feedback**
76
How does spindle sensitivity work?
77
What does **EMG** stand for?
* Electrical Muscle Signal
78
Do the **1a afferents** activate during **voluntary** **movement**?
* Yes
* They **correct** the **movement** & **keep** **it controlled**
79
When do you see the p**rimary afferent signal** for the **gamma** (spindle) come in?
* **After** the **EMG** (motor signal)
* Thus it corrects it **shortly** **after**
(cannot be the same time)
80
What technique do you use to record individual axons?
* Microneurography
81
How does recipricol inhibitory control work?
* **1a afferent neurone** --\> gives a **collateral** which sends an **inhibitory neurone** to **antagonist** muscle
82
Why is it important there isn't complete relaxation of the antagonist muscle?
* 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
What occurs when there is **co-contraction** of **muscles** across a **knee** **joint**?
* **Knee** **Joint** is **Stiff**
* **Both** **Muscle** **Contract** (shorten)
* Thus **highly** **resistant** to **movement** on the **joint**
84
What measures **muscle** **tensions** at a **joint**?
* Golgi Tendon Organ
85
In what arrangement is the **golgi tendon organ** found?
* **Series** with **Extrafusal** **Fibres**
86
What happens when there is pull on the golgi tendon organ?
* Pull on Spring Balance
* Muscle pulls on the tendon
* Neural Spring Balance --\> causing **1b afferents** sending information back
87
How are the sensory endings of the 1b afferents arranged?
* **Weave** **in-between** the **collagen** **fibres**
* Therefore, when tension **applied** they **squeeze** --\> causing **signals** **sent** about **tension**
88
What are the golgi tendon organs located?
* One End --\> EXTRAFUSAL MUSCLE FIBRE
* Other End --\> TENDON
89
How is tension distributed across golgi tendon organs?
* 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
How do they respond to a range of tensions?
* 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
When do you need the golgi tendon organ and cannot use a spindle receptors?
* **Co-contraction**
* There is **no length change** during co-contraction --\> thus spindles **not** **involved**
* Golgi tendon organ --\> can **measure** **tension** instead
92
Describe the **golgi** **tendon** **organ** pathway.
* **1b afferents** pick up tension signal
* These are **dynamic** & **fast-conducting** fibres
* They synapse onto **1b inhibitory interneurones**
93
What occurs when there is **high** **tension**?
* **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
What are the **2 functions** of the **golgi** **tendon** **organ**?
(generally)
* Protective Mechanism (high loads)
Sensitivity Receptor
95
Why is **convergence** important onto **1b interneurones**?
* Important for **descending control convergence**
* Receive **command** **instructions** from a variety of place
96
Name **3 places** the **1b interneurone** will get inputs from?
1. **Golgi Tendon Apparatus**
2. Input from **Joints**
3. Input from **Cutaneous** **Receptors**
97
Why do you get inputs from **_joints_** & **_cutaneous_** **receptors** to the **1b inhibitory** **interneurones**?
* 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
What are the **2 types** of **nociceptors**?
* C-fibres (slow)
* A-deltas (fast)
99
Which nociceptor is involved in **flexion**-**withdrawal** **reflex**?
* A-delta nociceptors
* Fast conducting
100
Briefly describe the **flexion**-**withdrawal** **reflex**.
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
What is walking patterns essentially made up by?
* Extension-Withdrawal Patterns --\> REPEATED
102
What is a **renshaw** **cell**?
* **Further** **Inhibitory** **Interneurone** found in the **spinal** **cord**
103
What is the **function** of a **renshaw** **cell**?
* 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
How is a **renshaw** **cell** **innervated**?
* **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
Describe how the **renshaw** **cell** works.
* 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
What does the renshaw cell do in relation to antagonist muscle?
* **Recipricol Control**
* Controls **1a inhibitory interneurones** --\> to **disinhibit** the **inhibitory** **neurones** on the **antagonist**
107
What **other** **fibres** makes contact with **renshaw** **cells?**
* Descending Pathways
108
What drives the **oculo**-**motor** **reflex**?
* **Vestibular** **Input** from **Semi**-**Circular** **Canals**
