The Neural Control of Movement

Question 1

what is the hierarchical organisation of movement

Answer 1

1. Lower motoneurons (LMN)
2. Upper motoneurons (UMN)
3. Cerebellum
4. Basal ganglia

Question 2

what are LMNs

Answer 2

• these are alpha motoneurons that constitute the final common pathway of all motor commands
• they are part of a motor unit

Question 3

what do the LMNs innervate

Answer 3

Directly innervate skeletal muscles to produce muscle contractions

Question 4

where are the cell bodies of the LMNs

Answer 4

Cell bodies in the ventral horn of the spinal cord and exit via ventral roots

Question 5

what are the 4 anatomical points where the LMN injury can occur

Answer 5

1. Ventral horn
2. Ventral root
3. The NMJ
4. Skeletal muscle itself

Question 6

what does Lower motor neurone injury arise from

Answer 6

• arises from damage to alpha motoneurons
• for example diseases that selectively affect alpha motor neurones such as polio or localised lesions near the spinal cord

Question 7

what are the characteristics set of symptoms symptoms of LMN injury

Answer 7

1. Muscle atrophy
2. Hypotonia (reduced muscle tone) – because alpha motor neurons are the only way to stimulate extrafusal muscle fibres, the loss of these neurons causes a decrease in muscle tone
3. Hyporeflexia (reduced or absent myotactic /stretch reflexes) this is because the alpha motor neuornes that cause muscle contraction are damaged
4. Flaccid paralysis / muscle weakness
5. Fasciculations- damaged alpha motor neurons produce spontaneous action potentials  visible twitches of affected muscle(s).
6. Fibrillations

Question 8

what are Upper motor neurones

Answer 8

All motor system neurons higher in the hierarchy are referred to as UMNs

Question 9

what do UMN do

Answer 9

these carry voluntary motor commands to LMNs

• they directly or indirectly synapse onto the LMNs
• there are 3 functionally distinct motor tracts

Question 10

where are the cell bodies of the UMNs

Answer 10

Cell bodies in the cerebral cortex and brainstem

Question 11

what are the upper motor neurone tracts

Answer 11

Corticospinal (lateral & anterior/ventral)

Reticulospinal & Vestibulospinal

Rubrospinal

Question 12

what does the corticospinal tract do

Answer 12

precise motor movements

Question 13

what do the reticulospinal and vestibulospinal tract do

Answer 13

Gross movements

Facilitates flexor movement

Question 14

what does the rubrospinal tract do

Answer 14

posture and balance

Question 15

what are the 3 main synaptic inputs into the LMNs

Answer 15

1. UMN of descending tracts (corticospinal, reticulospinal, vestibulospinal, rubrospinal)
2. interneurons locally
3. Local sensory nerve fibres (part of reflex arcs)

Question 16

where does the corticobulbopsinal tract run

Answer 16

From the motor cortex

To the brainstem

Courses through the internal capsule (a bundle of axons from the motor cortex)

Question 17

what are the 2 components of the corticokbulbospinal tract

Answer 17

• corticobulbal fibres

- corticospinal tract

Question 18

where do the corticobulbal fibres decussate

Answer 18

• they decussate at the midbrain
• synapse onto LMNs destined for the face
• will synapse onto motor fibres of the CNV

Question 19

where do the corticospinal tract decussate

Answer 19

motor fibres destined for the arms & legs continue down and decussate at the lower medulla

Question 20

what do the corticospinal tract form

Answer 20

• lateral corticospinal tract and small anterior corticospinal tract

Question 21

what does the lateral corticospinal tract innervate

Answer 21

innervate LMNs going to muscles of the limbs (hands & thumbs)

Question 22

what does the anterior corticospinal tract innervate

Answer 22

 innervate LMNs going to shoulder and neck muscles (axial muscles)

Question 23

what makes up the extrapyramidal system and where does it originate from

Answer 23

• they originate from the brainstem as the uMN cell body is in the brainstem

Reticulospinal – originates from the reticular formation of pons

Vestibulospinal – originates from the vestibular nuclei in the upper medulla/lower pons

Rubrospinal – originates from the red nucleus in the midbrain

Question 24

what is tension in the muscles due to

Answer 24

Tension in muscles due to small amounts of contraction (this produces slight resistance to passive movement)

Question 25

how is Tone maintained

Answer 25

Tone is maintained reflexively by stretch & gamma motoneurons, and is adjusted to the needs of posture and movement - it is also regulated by descending motor pathways

Question 26

how do you maintain posture

Answer 26

- To maintain posture, muscle tone is constantly finely adjusted (happens unconsciously) - Input from higher levels of the nervous system

Question 27

define spasticity

Answer 27

Increased muscle tone due to loss of inhibition of gamma () motoneurons

Question 28

define rigidity

Answer 28

Increased muscle tone due to loss of inhibition of α motoneurons

Question 29

why does spasticity occur

Answer 29

- The strength of the stretch reflex is controlled by the gamma motoneurons. - Normally, gamma motoneurons receive both excitatory & inhibitory input in balance. However when there is increased excitation or decreased inhibition of gamma motoneurons this increases the tension of intrafusal muscle fibres which cause the 1a muscle spindle afferent to become more sensitive to muscle stretch. This results in spasticity.

Question 30

what can upper motor neurone be due to

Answer 30

due to stroke, tumors, blunt trauma

Question 31

what are the characteristic symptoms of upper motor neurone injury

Answer 31

``` Spasticity Hyperreflexia Cog wheel rigidity Clonus/ clonic reflexes Babinski sign ```

Question 32

what are the regions of the cortex involved in the motor control

Answer 32

``` A – Prefrontal cortex B – Frontal eye fields C – Premotor cortex & Supplementary cortex D – Primary motor cortex (Broca’s) ```

Question 33

what makes up the motor cortex

Answer 33

1. posterior parietal cortex 2, association motor cortex 3. primary motor cortex

Question 34

what does the posterior parietal cortex do

Answer 34

Areas 5&7 | Decide to move (READY)

Question 35

what does the association motor cortex do

Answer 35

Premotor & supplementary cortex Area 6 (& 8) Planning to perform complex tasks or movements (SET)

Question 36

what does the primary motor cortex do

Answer 36

Area 4 | Activation of descending motor pathways to bring about movement (GO!)

Question 37

what does damage to the association cortex result in

Answer 37

apraxia

Question 38

What is apraxia

Answer 38

Apraxia is the impairment in motor planning and strategies, and the inability to perform complex learned motor tasks

Question 39

How do you test for Apraxia

Answer 39

get patient to arrange a set of blocks to match an example block-structure in front of them. They can move the blocks individually, but cannot come up with a motor plan to arrange them properly.

Question 40

what is a neuromuscular disorder

Answer 40

A condition affecting one or more of the following: - Muscles - Nerves - NMJ - Motor or sensory nerve cell body

Question 41

what is myasthenia gravis

Answer 41

- this is a chronic and autoimmune condition and a disorder of the NMJ

Question 42

what are the symptoms of NMJ

Answer 42

Weakness in skeletal muscles Fatiguability Worsens after periods of activity and improves after periods of rest.   Muscles that control eye and eyelid movement, facial expression, chewing, talkingand swallowing are most commonly affected, although muscles that control breathing, neck and limb movements may also be affected.

Question 43

what causes myasthenia gravis

Answer 43

In myasthenia gravis, antibodies (immune proteins) block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction, which prevents the muscle from contracting.

Question 44

what is Gower's Sign

Answer 44

indicates weakness of proximal muscles in the lower limbs. Patient has to use their arms and hands to ‘walk’ up their own body from a squatting position due to lack of hip and thigh muscle strength.

Question 45

what are primary motor muscle disorders

Answer 45

- Gower's Sign - inflammatory myopathies (polymyositis) - congenital myopathies, - Duchenne muscular dystrophy

Question 46

what are the 3 lobes of the cerebellum

Answer 46

anterior, posterior and flocculonodular

Question 47

what are the 3 clinically important function zones of the cerebellum

Answer 47

Vestibulocerebellum Spinocerebellum Cerebrocerebellum

Question 48

what does the vestibulocerebellum do

Answer 48

``` Balance & posture Eye movements (VOR) ```

Question 49

what does the spinocerebellum do

Answer 49

Locomotion | Voluntary movements of arms & legs

Question 50

what does the cerebrocerebellum do

Answer 50

skilled motor tasks e.g. speech, hand-eye co-ordination, and cognitive eye movements

Question 51

what is the role of the basal ganglia

Answer 51

Initiation and sequencing/maintenance of voluntary movements Enables motor program switch Regulates intensity of slow and stereotyped movements Inhibits unnecessary movements - basically it controls the selection, start and stop posts of motor programs

Question 52

what is the basal ganglia made out of

Answer 52

1. Caudate (head and tail) 2. Putamen 3. Globus pallidus (internal and external) 4. Substantia nigra (pars compacta and pars reticulata) 5. Subthalamic nucleus