Supra-spinal Control 1 - Cortical Motor Control Flashcards
1
Q
Name the 4 main descending motor pathways.
A
- Corticospinal Tracts
- Rubrospinal Tract
- Reticulospinal Tract
- Vestibulospinal Tract
2
Q
Where in the spinal cord is the reticular formation’s reticulospinal tract found?
A
- Medial Pathway
- Lateral Pathway
3
Q
What is the reticulospinal tract (reticular formation) important for?
A
- Important in modulating locomotion patterns
4
Q
What occurs in corticospinal tract damage?
A
- Loss of voluntary movement control
- Restored due to take-over by other systems
5
Q
What pathway usually takes over if there is damage in the corticospinal tract?
A
- Rubrospinal Tract
6
Q
From where does the vestibulospinal tract get its information from?
A
- Vestibular System
- Head
- Semi-Circular Canals
It measures translational movements in these systems
7
Q
What is the function of the vestibulospinal function?
A
- Detects Translational Movement
- Sends information down to the spinal cord
- Maintains balance as a function of head movements deviations
Important in posture & head movements
8
Q
Name the 2 lateral pathways.
A
- Corticospinal Tract
- Rubrospinal Tract
9
Q
What are the functions of the lateral pathways?
A
- Fine & fractionated movements of the limbs & fingers
10
Q
Name the 4 ventromedial pathways.
A
- Vestibulospinal Tract
- Tectospinal Tract
- Pontine Tract
- Medullary Reticulospinal Tracts
11
Q
What are the functions of the vestibulospinal & tectospinal tracts?
A
- Control Posture of the Head & Neck
12
Q
What are the functions of the pontine & medullary reticulospinal tracts?
A
- Control posture of the trunk & antigravity muscles of the limbs
13
Q
Which area if Primary Motor Cortex (M1)?
A
Area 4
14
Q
Which broddman area is premotor cortex?
A
Area 6
15
Q
What 2 regions does the premotor cortex contain?
A
- Premotor Area (PM)
- Supplementary Motor Area (SMA)
16
Q
Where is the Supplementary Motor Area (SMA)?
A
- Medial to the Premotor Area
17
Q
Where are the motor areas located?
A
18
Q
How did broddman divide up parts of the brains?
A
- Based on shape and neuronal patterns from histological sections
They were functionally accurate areas
19
Q
Why are electrodes used on the brain surface?
A
- Stimulate Parts of the Cortex
- Check for residual function (e.g. after removing tumour)
- Used commonly after/before procedures
20
Q
Which area has the lowest threshold for stimulation? (i.e. easiest to get movement if you stimulate)
A
- Primary Motor Cortex (M1)
21
Q
What are 2 other places that if stimulated can cause movement (but need more than M1)?
A
- Premotor Cortex
- Somatosensory Cortex (S1)
However these need much more stimulation –> they can do this due to rich connections & some descending projections
22
Q
Where is the SMA found?
A
- Dorsal Side
- Medial Face of the Cortex
- It is medial to the premotor area (which runs up to the midline before SMA starts)
23
Q
What are the parietal regions involved in?
A
- Movement Control
- Set up visual space in which out moves are made
- Give us a sense of allocentric & egocentric space
24
Q
What is allocentric space?
A
Pointing to places relative to you as a whole
25
What is **egocentric** **space**?
* This is the concept of own space
* Where movements have to be created around yourself and relative to yourself (own personal space)
(e.g. touching your nose)
26
From where in the **thalamus** does **_most_** of the input to the **primary** **motor cortex (M1)** come from?
* **Ventral Lateral Nucleus** (thalamus)
27
From where do most of the **input** in the **thalamus** come from going to the **Premotor Cortex (PM + SMA)**?
* **Ventral** **_Anterior_** **Nucleus** (thalamus)
28
Where does the **_lateral_** **geniculate** **body** of the **thalamus** project out to?
* Visual Cortex
29
Where does the **_medial_** **geniculate** **body** of the **thalamus** project out to?
* Auditory Cortex
30
How can we distinguish between the cortices?
* **Thalamic** **projections** to the **cerebral** **cortex** allows us to distinguish
31
What is the **problem** **distinguishing** between the **Ventral** **_Anterior_** & **Ventral** **_Lateral_** nuclei of the thalamus?
* **Difficult** to find the **division** at the **thalamus**
* Thus **cannot** **trace** it back very easily
32
Describe the pathways of the corticospinal system.
33
How is the **primary** **motor** **cortex** arranged**?**
* **Somatotopic Arrangement**
i. e. a motor map which means certain parts are for certain movements (found using electrodes & fMRI)
34
What passes through the **Posterior** **Limb** of the **Internal** **Capsule**?
* **Motor** Projections
* **Sensory** Projections
* **Visual** Pathways
* **Auditory** Pathwys
35
What is the vascular supply to the motor cortex?
Where does it arise from?
* **Lenticula-Striate Arteries**
* These **penetrate** the **brain** (modest perfusion)
* Arises from the **middle cerebral artery**
36
What can cause a **stroke** in the **posterior** **limb** of the **internal** **capsule**?
* Middle Cerebral Stroke
(commonly gets damaged in cortical strokes)
37
What is te difference between a **cortical** and **capsular** **stroke**?
* **Cortical Stroke (rarer)** --\> unlikely to **lose** the **whole** **territory** --\> may just **lose** a **branch** (e.g. loss of nerves of the hand/arm in one region)
* **Capsular Stroke (common)** --\> complete **hemiplegia**
38
What is a **hemiplegia**?
* **Paralyses** of the **one** **whole** **side** of the **body**
One side of face | Contralateral side of the body
39
What usually causes a **complete** **hemiplegia**?
* **Stroke** affecting the **Internal** **Capsule** (capsular stroke)
40
Describe the **corticospinal** **fibre** **pathway**.
* **Converges** --\> runs through **posterior limb**
* Gives off fibres to **cranial nerve nuclei** on **ipsilateral** **side** (e.g. voluntary eye movements)
* Descends to **lower** **medulla** --\> **pyramidal** **decussation**
* Takes up either a **_lateral_** or **_dorsal_** (small) position
* Supplies **muscles** on **contralateral** **side**
41
How is the motor cortex mapped?
* Not a **simple 1:1 projection (it is many-to-1)**
* **Pyramidal** **cells** in **M1** --\> **converge** onto **motoneurone**/**interneurone** --\> which then goes to **muscle**
42
How are the different parts of the body mapped in the cortex
* There are distinctions
* However there is some overlap (spread)
* However, once they converge --\> it is mostly that one part
43
Describe the conversion of neurones in the motor cortex.
* Many cortical neurones --\> **converge** --\> then **project down**
* **_Not_** a strict map
* **Map** of **best** **fit** (not precise)
* This is called **principal** **convergence**
44
How are **M1 pyramidal neurones** from the cortex **distributed**?
* Project to several **_motoneurones_** & **_interneurone_** **pools**
A single corticospinal axos projects widely in the interneurone & motoneurone region of the spinal cord
* There is **divergence** of **M1 pyramidal neurone inputs** upon **spinal** **motoneurones**
45
How does a **single motor corticospinal neurone** distribute itself?
* Corticospinal neurones **diverges** to lots of differnet **_motor_** & **_interneurone_** **pools** (not just individual motor neurones)
* Controls a **range** of **different** **motor** **neurones**
46
What 2 important points must be remembered in relation to motor neurones & pyramidal neurones?
1. **No privileged communication line** (i.e. no single corticospinal neurone synapses a single motoneurone)
2. **_Many_** **corticospinal** **neurones** can communicate with **one** **motor**/**interneurone** **pool** (different corticospinal neurones can communicate various things)
47
What happens in terms of **M1 distribution** after **cutting** a **nerve** (e.g. facial nerve)?
* **Cut** --\> thus **no** **longer** has any **motor** **neurone**
* Thus **cannot** **carry out function** --\> die back & dissapear (movement no longer possible)
* **Motor Cortex (M1)** --\> **Somatotomic** **Map** is **remapped**
* **Adjacent** **regions** now **take** **over** (infiltrate)
*
48
What **2 reasons** can explain the **redistribution** of **parts** of the **motor** **cortex**?
1. Adjacent Regions were **already present in the lost area** (no sharp borders)
2. Adjacent regions have **grown into the area**
(Probably a mixture of both - it is just a mixture and somthing dominates/wins out)
There is a lot of plasticity --\> which is optimistic for stroke recovery
49
What **3 ways** can **primary** **motor** **cortex** neurones code for in terms of **muscle** **force**?
1. Code for **dynamic** aspects of force
2. Code for **dynamic** & **static** aspects of force
3. Code for **static** aspects of force
50
What causes an increase in force for a motor unit?
* Increased Firing Frequency
51
What does **static** **aspect** coding mean?
* **Code** for the **Force** (when taking place)
* Not active when force is low
52
What does **dynapic phase** **aspect** coding of movement mean?
* **The differential**
* The **changing** from a **rest** **position**
* **Responsive to change**
53
What does **mixture of dynamic & static** **aspect** coding of movement mean?
* **65% of neurones are like this**
* Mixture of **dynamic** & **static** types
* This is how most **motor** & **somatosensory** system coding is managed
54
How are the 3 different types of neurones distributed? (percentages)
* **Dynamic Aspect** --\> 10%
* **Mixture (dynamic + static)** --\> 65%
* **Static** **Aspect** --\> 25%
55
When is M1 active?
* **Before** Movement (thinking about movement you are about to execute)
* **During** Movement
56
When is M1 active?
* **Before** Movement (thinking about movement you are about to execute)
* **During** Movement
57
What else does the **Primary Motor Cortex (M1)** code for?
* **Directionality**
**Coarse** **coding** for **direction** --\> by **individual** **neurones**
58
What does primary motor cortex code for?
* **Direction of Movement**
* Coding is coarse --\> the neurone will fire in a **range** of **movement** **directions**
59
What is the mechanism called for accurately coding for directionality?
* Population Coding
60
How does the **motor** **cortex** code for **accurate** **directions**?
* **Vector sum** of **all motor cortex neuronal activity** --\> gives a close approximation of the **direction of movement**
61
How does **population** **coding** work for **M1**?
* **Firing rate** of **lots** of **different** **neurones** are **recorded**
* Take the **vector sum** of the **_magnitudes_** & **_directions_** of each neurone
* Look at **entire population (population coding)** --\> look at their **vector** **sums** --\> and see the **overall** **direction**
* This is **very** **similar** to **direction** the **arm** **took**
62
What is population coding an example of?
* Higher Level Aspects of coding
* Population coding
63
What occurs if you use trains of microstimulation on the Premotor cortex & M1?
* Complex Movements
(e. g. causes hand movement to the mouth from any point)
This is an example of egocentric movements (defined point on the body where you move to regardless of starting posiiton - M1 is a lot more complex than initially thought)
64
What are the 2 parts of the premotor cortex?
Where are they found?
* **Premotor Area (PM)** --\> Lateral
* *Supplementary Motor Area (SMA)** --\> Medial
65
Where do the **premotor area (PM)** and **supplementary motor area (SMA)** project to?
* Primary Motor Cortex (M1)
66
What does the **Premotor Area (PM)** have strong inputs from?
* **Cerebellum** (via the thalamus)
67
What does the **Supplementary Motor Area (SMA)** have strong inputs from?
* **Basal Ganglia** (via the thalamus)
68
What is the function of the **Premotor Area (PM)**?
* **Planning Movements** (before movement)
* Based on **External (especially) visual cues**
(e.g. picking up something infront of you)
69
What is the function of the **Supplementary Motor Area (SMA)**?
* **Planning Movements**
* Based on **internally** **generated** **strategies** (e.g. learning sequences of movements)
(e.g. drawing a question mark in mid-air - as you already know the shape & movement so you are bringing it from memory store)
70
Where are PM & SMA relative to M1 in hierarchy?
* PM & SMA --\> are higher in **hierarchy** of **coding**
## Footnote
**(but M1 is not lower than we thought - it is slightly more complex)**
71
What is responsible for planning movements for external & internal cues?
* **Premotor Area (PM)** --\> External Cues
* **Supplementary Motor Area (SMA)** --\> Internal Cues
72
What occurs if there is a lesion in the **Premotor Area (PM)**?
* Severe impairement on **visual conditional motor task**
(e. g. pulling handle if light is blue and twisting if light is red)
73
What occurs if there is a lesion in the **Supplementary Motor Area (SMA)**?
* Severe impairement on **motor sequence learning task**
(e. g. learning to open a lid by pushing, twisting & then lifting)
74
When is M1 active?
* During **all** **tasks** (whether internal or external/visual cue)
75
Which neurones are **active** during **preparation** to **move** in a **visually** **cued** **task**?
* **Set-related neurones** in the **dorsal** **Premotor** **Area**
Active during instruction-movement interval
76
When is **supplementary** **motor** **area** active?
* During **sequenced movement tasks** (e.g. learning to play sequence on piano)
* During **mental rehearsal of tasks** (e.g. mentally playing it in your head)
Involved in **movement** **planning**
77
What is active during **visually** **cued** **behaviour** **movements**?
* Premotor Areas
* M1 (for everything!)
78
What is active during movement (e.g. wriggling finger)?
* **M1** (hand area)
* **Somatosensory Cortex** (propioceptive information coming back + information from skin)
79
When is the SMA active?
* **Planning movements** based on **internally** **generated** **strategies** (e.g. learned patterns)
