Motor Control and Disease

Question 1

What are all movements produced by the skeletal muscles initiated by

Answer 1

Lower motor neurons

Question 2

What are central pattern generators

Answer 2

Part of the spinal cord which can generate complex behaviors without brain input

Question 3

What does stimulation of the motor cortex do

Answer 3

Elicits muscle movement

Question 4

What are neurons found in the brain which control motor function called

Answer 4

Upper motor neurons

Question 5

How is the motor cortex mapped in the lower body

Answer 5

Lower body - medially

Question 6

How is the motor cortex mapped in the upper body

Answer 6

Laterally

Question 7

What do axial muscles control

Answer 7

Trunk movement

Question 8

What do proximal muscles control

Answer 8

Shoulder, elbow, pelvis, knee movement

Question 9

What do distal muscles control

Answer 9

Hands, feet, digits

Question 10

Where does each muscle fiber receive input from

Answer 10

A single lower alpha motor neuron

Each lower motor neuron innervates the fiber of one muscle but can innervate more than one fiber

Question 11

What is a motor unit

Answer 11

Motor neuron and all the fibres it innervates

Question 12

What is a motor neuron pool

Answer 12

All the motor neurons that innervate a single muscle

Question 13

How are motor pools organised

Answer 13

Organised spatially in the spinal cord

All motor neurons innervating a particular muscle are grouped into rod-shaped clusters within the spinal cord extending over vertebral segments

Somatotopic - organization reflects the organization of the body

Question 14

How do Upper motor neurons project to lower motor neurons

Answer 14

Via descending tracts

Question 15

Where do axons of the corticospinal tract derive from

Answer 15

layer 5 of the motor cortex

Question 16

Where do pyramidal cells of the motor cortex project axons to

Answer 16

The corticospinal tract

Question 17

How many layers in the cortex

Answer 17

90% is 6 layered
Main input is through stellate cells in layer 4
Main output from layers 3,5 and 6

Question 18

where do brainstem upper motor neurons project

Answer 18

To medial motor pools primarily concerned with postural movement

Question 19

How do axons in the brainstem project

Answer 19

Ipsilaterally in the vestibulospinal and reticulospinal tract

Question 20

How do axons in the brainstem project

Answer 20

Medially and medially synapse onto lower motor control circuits that control axial muscles –> ventromedial pathway

Question 21

What is the vestibulospinal tract used for

Answer 21

Head balance and turning

Project mainly ipsilaterally and medially

Question 22

What is the tectospinal tract used for

Answer 22

Orienting response

Project mainly ipsilaterally and medially

Question 23

What is the reticulospinal tract used for

Answer 23

Control antigravity reflexes

Project mainly ipsilaterally and medially

Question 24

What do UMN of the motor cortex do

Answer 24

Initiate complex voluntary movement

Project mainly contralaterally via the corticospinal tract primarily to muscles involved in precise limb movements, particularly those of the hands in humans – one of the lateral pathways of the spinal cord
(Also, project via the corticobulbar tract to the hypoglossal nucleus in the brainstem, which controls movements of the tongue - important for speech in humans)

Question 25

What do the UMN of the brainstem do

Answer 25

More concerned with the maintenance of posture and balance Located in several nuclei including Reticular formation Vestibular nucleus (vestibular co-ordination) Superior colliculus (visual co-ordination) Project mainly ipsilaterally to lower motor neurons controlling axial muscles concerned with maintaining posture – the ventromedial pathways of the spinal cord

Question 26

Where do UMN always synapse to

Answer 26

LMN

Question 27

Where do LMN always synapse to

Answer 27

Directly onto muscle fibres

Question 28

What does the anticipatory mechanism do

Answer 28

pre-adjusts body posture to compensate for the forces that will be generated when an object is lifted

Question 29

Why do feedforward mechanisms work

Answer 29

UMN of the cortex are influenced by 2 spinal cord circuits: Anticipation of movement activates an indirect projection to the axial muscles via reticular formation Activation of voluntary movement direct to spinal cord via corticospinal tract Anticipation activates first --> movement initiation

Question 30

What is ALS

Answer 30

Degenerative disease of motor neurons characterised by muscle atrophy and sclerosis of the lateral spinal cord Quick degeneration and early death

Question 31

What is LMN disease characterised by

Answer 31

Muscle paresis (weakness) or paralysis Loss of muscle tone due to loss of stretch reflexes Ultimately, leads to severe muscle atrophy Patients usually die from lung dysfunction (due to atrophy of intercostal muscles)

Question 32

What is UMN disease characterised by

Answer 32

Muscle weakness Spasticity due to increased muscle tone (due to failure of modulation of stretch reflex) Hyperactive reflexes Loss of fine voluntary movement Patients usually die from loss of input to the bulbar muscles (tongue and pharynx) via the corticobulbar

Question 33

What are the causes of neuron degeneration

Answer 33

Exitotoxicity is one possibility, where overstimulation, typically by glutamate, leads to neuronal cell death Sometimes a blocker of glutamate can decrease effects of ALS and motor neuron disease

Question 34

What do the basal ganglia and cerebellum do

Answer 34

Influence movement indirectly by regulating the function of UMN

Question 35

Where is the basal ganglia and what is inside of it

Answer 35

Forebrain Caudate Putamen Globus Pallidus Subthalamic nucleus

Question 36

What are the key components of the initiation of movement

Answer 36

``` Motor cortex (telencephalon) Basal ganglia (forebrain) Ventral lateral nucleus of thalamus (diencephalon) Substantia nigra (midbrain) ```

Question 37

What is the motor loop

Answer 37

The motor cortex connecting to the basal ganglia which feedsback to the premotor area via the ventrolateral complex of the thalamus to control the initiation of movement 2 pathways indirect and direct

Question 38

What is the direct pathway of the basal ganglia

Answer 38

Globus pallidus inhibits the VLo --> input from many cortical regions converge on the striatum --> when activated by the input the striatum inhibits the inhibitory activity of the GPi releasing VLo which activates area 6 and initiates movement

Question 39

Why is the direct pathway set up like this

Answer 39

Integration of cortical inputs to trigger a response | Rapidity of response – “engine is running”; inhibition of inhibition releases the “brake”

Question 40

What is the indirect pathway of the basal ganglia

Answer 40

Involves substantia nigra which acts via the striatum to maintain the balance between inhibition and activation of the VLo Excitatory input from the SN stimulates VLo activation by activating inhibition of the GPi through direct pathway In the indirect, inhibition of GPi by GPe is inhibited by the striatum and so VLo is inhibited However inhibitory input from the SN decreases striatum inhibition of the GPe which inhibits the GPi allowing activation of VLo So the SN is balancing/tuning the activation of the VLo

Question 41

What is VLo

Answer 41

Ventral lateral thalamus is activated to initiate movement

Question 42

What is parkinsons disease (Symptoms and how it is passed on)

Answer 42

``` 2nd most common ND disorder Sporadic (85-90%) Familial cases (10-15%) Symptoms: Hypokinesia - paucity/insufficiency of movement Bradykinesia - very slow movements Akinesia - no movements Increased muscle tone - rigidity Resting Tremor - @4-5Hz- ‘pill rolling’ Shuffling gait and flexed posture, impaired balance Mask-like expression Non-motor symptoms (i.e. mood disorders, loss of sense of smell) ```

Question 43

What causes PD

Answer 43

Dopamine loss due to reduction of dopaminergic neurons in Substantia Nigra Degeneration is marked by presence of Lewy bodies (protein aggregates)

Question 44

How does L-DOPA effect PD

Answer 44

Works by boosting capacity of surviving DA-ergic neurons in substantia nigra (SN) to make dopamine (DA) However, does not stop the degeneration of SN neurons Eventually there are insufficient SN neurons left to make DA Also has side effects: increase in motor response fluctuations and drug related dyskinesias. Only around 5 years

Question 45

What does Reduced dopaminergic input from substantia nigra to striatum lead to

Answer 45

Increased activity of the indirect pathway Decreased activity of the direct pathway Less inhibition of the GPi and so inhibitory activity is increased so less activation of VLo so less motor cortex activation

Question 46

What is hypokinesis

Answer 46

Reduced movement

Question 47

What is Huntingtons disease (Symptoms and how it is passed on)

Answer 47

Rare, hereditary, progressive and fatal Early: hyperkinesia or dyskinesia, ‘chorea’ (involuntary jerking or twitching movements) Late: akinesia and dystonia (muscle spasms), dementia, personality disorder (psychosis)

Question 48

What are the causes of HD

Answer 48

Autosomal dominant genetic disease resulting in neuronal degeneration: initially in the indirect pathway components of the striatum, subsequently in the direct pathway components & in the GPe

Question 49

What does the Substantia nigra regulate

Answer 49

caudate, putamen and globus pallidus

Question 50

What causes the first symptoms of HD

Answer 50

Degeneration of the striatum which leads to hyperkinesia and then to akinesis

Question 51

What causes PD

Answer 51

PD is due to degeneration of the substantia nigra and leads to hypokinesis

Question 52

What causes Huntingtons

Answer 52

Mutation in HTT (Huntingtin protein)

Question 53

What is the role of the cerebellum in motor learning

Answer 53

Modulates upper motor neurons – no direct connections to spinal cord Required for the learned execution of planned, voluntary, multijoint movements

Question 54

What is motor learning

Answer 54

Predictions based on past experience of movements. | Importantly, cerebellum also compares what is intended with what actually happens – motor learning

Question 55

What is dyssynergia

Answer 55

decomposition of movement due to breakdown of normal coordinated execution of a voluntary movement.

Question 56

How doe the cerebellum form a loop with the motor cortex

Answer 56

The cerebellum receives massive input from many areas of the cortex, corticopontocerebellar projection, and sensory information from the spinal cord and vestibular system In turn, it projects back to the motor cortex via the thalamus (VLc), but it has no direct output to spinal cord.

Question 57

What is the function of the cerebellum motor cortex loop

Answer 57

to detect and correct differences between the intended movement and the actual movement - the so-called motor error.

Question 58

What can lesions in the cerebellum cause

Answer 58

Cerebella ataxia Poorly integrated movement (dyssynergia)