Motor Cortical Control

Question 1

what kind of organisation exists in the motor system?

Answer 1

functional segregation
Motor system organized in a number of different areas that control different aspects of movement
hierarchical organisation depending on complexity of tasks (higher order control programme and decide movement and lower excecute tasks)

Question 2

where does information from the primary motor cortex pass to?

Answer 2

basal ganglia, cerebellum, thalamus, spinal cord and brainstem

• brainstem → muscles of head, neck, facespinal cord → rest of muscles

Question 3

what muscles do motor information in the brainstem get passed to? what about the spinal cord?

Answer 3

brainstem → muscles of head, neck, face

spinal cord → rest of muscles

Question 4

what do the basal ganglia and cerebellum do?

Answer 4

adjust the commands received from other parts of the motor control system

Question 5

what are the pyramidal tracts?

Answer 5

corticospinal and corticobulbar
Voluntary precise movement

Question 6

extrapyramidal tracts?

Answer 6

vestibulospinal, tectospinal, reticulospinal, rubrospinal
Involuntary movement

Question 7

Are extrapyramidal tracts ascending or descending

Answer 7

Descending

Question 8

what makes something pyramidal/extrapyramidal?

Answer 8

either pass through pyramids of medulla or don’t

Question 9

functional differences - what do pyramidal do?

Answer 9

voluntary movements of body and face (motor cortex → cranial nerve nuclei or spinal cord)

Question 10

functional differences - what do extrapyramidal do?

Answer 10

involuntary movements for posture, balance and locomotion
Brainstem nuclei to spinal cord

Question 11

Corticospinal tract

Answer 11

Passes down lateral corticospinal tract or anterior corticospinal tract
Decussation occurs where most go to lateral
Lateral control limb muscles anterior control trunk

Question 12

corticobulbar function?

Answer 12

movements of face and neck → cranial nerve nuclei

Question 13

vestibulospinal function?

Answer 13

stabilise head during body movement , coordinate head movement with eye movement, postural adjustments

Question 14

reticulospinal function?

Answer 14

Muscle tone changes with voluntary movement
postural stability
Primitive descending tact
From medulla and pons

Question 15

tectospinal function?

Answer 15

orientation of head and neck during eye movements
From superior colliculus of midbrain

Question 16

Rubrospinal

Answer 16

Innervate lower motor neurons of flexors of the Upper limb
From red nucleus of the midbrain
Mainly taken over by corticospinal tract

Question 17

negative signs of upper motor neuron lesion?

Answer 17

loss of voluntary motor function
paresis (graded weakness of movements)
paralysis-complete loss of movement

Question 18

Positive signs of upper motor lesions

Answer 18

• spasticityincreased muscle tone
• hyperreflexiaexaggerated reflexes
• clonusabnormal oscillatory muscle contraction
• babinski’s signabnormal upward curling of big toe (normal in infants but not adults) on stimulation

increased abnormal motor function due to loss of inhibitory descending inputs

Question 19

Apraxia

Answer 19

Loss of skilled movement (loss of info is not paretic)
Have lost info about how to perform skilled movement

Question 20

Common cause of apraxia

Answer 20

Stroke and dementia
Lesions of inferior parietal lobe ,frontal lobe (premotor cortex,supplementary motor area)

Question 21

signs of lower motor tract lesion

Answer 21

hypotonia, hyporeflexia, muscle atrophy,weakness

• fasciculationsdamaged motor units → spontaneous action potentials → visible twitch
• fibrillationstwitching of individual muscle fibres recorded during needle electromyography

Question 22

what are dysarthria and dysphagia?

Answer 22

Difficulty speaking or swallowing

Question 23

what is motor neuron disease?

Answer 23

progressive neurodegenerative disorder of motor system → spectrum
Also known as amyotrophic lateral sclerosis
UMN-spasticity,brisk limb and jaw reflex,babinski sign,loss of dexterity,dysarthria,dysphagia
LMN-weakness,muscle wasting,tongue fasicukation,nasal speech,dysphagia

Question 24

basal ganglia main structural elements?

Answer 24

caudate nucleus
lentiform nucleus
substantia nigra (midbrain)
nucleus accumbens
subthalmic nuclei

Question 25

basal ganglia main function?

Answer 25

decision to move performing associated movements e.g. changing facial expression in reaction, swinging arms while walking suppressing unwanted movements performing movements in order

Question 26

what is the striatum?

Answer 26

Caudate nucleus and putamen

Question 27

what is parkinson’s disease?

Answer 27

degeneration of dopaminergic neurons from substantia nigra to striatum Symptoms include bradykinesia, expressionless face → hypomimic, akinesia (difficulty in initiation of movements), rigidity, tremor at rest

Question 28

Huntingtons disease

Answer 28

degeneration of GABAergic neurons in striatum caudate and then putamen Symptoms involve jerky involuntary movement,difficulty swallowing,gait disorder and cognitive decline/dementia Choreic movement

Question 29

What is ballism

Answer 29

Contralateral flinging of extremities Caused by stroke affecting the subthalamic nucleus Symptoms occur contralaterally

Question 30

What separates the cerebrum and cerebellum

Answer 30

Tentorium cerebelli

Question 31

broad function of cerebellum?

Answer 31

Coordinates and predictions of movement

Question 32

Three main parts of cerebellum

Answer 32

vestibulocerebellum (central strip), spinocerebellum (medial vertical stripe), cerebrocerebellum (lateral stripe) - vestibulocerebellum regulate gait, posture and equilibrium, coordinate head and eye movements. Damage (tumour) causes gait ataxia and tendency to fall even when sitting with eyes open - spinocerebellum coordinate speech, coordinate limb movements, adjust muscle tone. Damage (degeneration and atrophy associated with chronic alcoholism) affect leg causing abnormal gait and stance (wide) - cerebrocerebellum coordinate skilled movements, cognitive function & attention, process language, emotional control. Damage affects mainly arms/skilled coordinated movements and speech

Question 33

main signs of cerebellar dysfunction?

Answer 33

- ataxia gait disturbance - dysmetria inappropriate force and distance for target oriented movement - intention tremor oscillatory limb trajectory in target directed movement - dysdiadochokinesia inability to perform rapidly alternating movements - scanning speech staccato bc impairment of speech muscle coordination --- - lower motor neurons of brainstem and spinal cord

Question 34

Alpha motor neurons

Answer 34

Lower motor neurons of brainstem and spinal cord Innervate extrafusal muscle fibres if skeletal muscle Extrafusal muscle fibres generate force for muscle contraction

Question 35

Activation of alpha motor neurons

Answer 35

Causes muscle contraction

Question 36

what is a motor unit?

Answer 36

single motor neuron along with all the muscle fibres it innervates On average each motor neuron innervates 600 muscle fibres

Question 37

different types of motor unit?

Answer 37

slow (type I)- small dendritic trees cell bodies and axons fast & fatigue resistant (type IIA)-large dendritic trees cell bodie and axons fast & fatiguable (type IIB)-large dendritic trees cell bodies and axons

Question 38

difference in force produced by IIA and IIB?

Answer 38

IIA is weaker, IIB (fatiguable) is stronger

Question 39

Order of motor unit recruitment

Answer 39

Small first to allow slow twitch units (fine movement allowed)

Question 40

Rate coding

Answer 40

Way for brain to regulate force a muscle produces The higher the firing rate the more force produced

Question 41

Summation

Answer 41

unit fires at too fast a frequency to allow muscle relaxation between contractions → recruitment of other motor units -

Question 42

what are neurotrophic factors?

Answer 42

growth factors that prevent neuron death and promote growth after injury

Question 43

what does cross innervation of muscle fibres do?

Answer 43

some properties are switched e.g. muscle fibres can become faster or slower dependent on nerve

Question 44

What change does aging cause

Answer 44

preferential loss of type II fibres → slower contraction times

Question 45

- what determines the magnitude and timing of reflex functions?

Answer 45

Intensity and onset stimulus

Question 46

reflexes can’t be controlled but can be influenced e.g. by Jendrassik manoeuvre → what is that?

Answer 46

pulling against locked fingers to increase magnitude of knee jerk reflex Can also bite down teeth or clench fist

Question 47

supraspinal control of reflex arcs under normal conditions?

Answer 47

Inhibitory

Question 48

what reveals the excitatory control?

Answer 48

Decerebration

Question 49

how can brain damage affect reflexes?

Answer 49

rigidity and spasticity from brain damage can result in over-active stretch reflexes

Question 50

hyperreflexia is associated with what kind of lesion?

Answer 50

upper motor neuron lesion → loss of descending inhibition

Question 51

defining features of clonus?

Answer 51

involuntary and rhythmic muscle contractions

Question 52

hyporeflexia is associated with what kind of disorder?

Answer 52

Lower motor neurone disease

Question 53

Descending supraspimal control of reflex

Answer 53

1. Activating alpha motor neurons 2.activating inhibitory interneurons 3.activating propriospinal neurons 4.activating gamma motor neurons 5.actuvating terminal of afferent fibres

Question 54

Primary motor cortex

Answer 54

Located in pre central gyrus anterior to central sulcus Controls fine discrete precise voluntary movement Provide descending signal to execute movement

Question 55

Premotor area

Answer 55

Located anterior to primary motor cortex Involved in planning movement Regulates externally cued movement Eg seeing an apple and reaching out for it

Question 56

Supplementary motor area

Answer 56

Located anterior and medial to primary motor cortex Plans complex movement eg internally cued speech Becomes active prior to voluntary movement

Question 57

Where are alpha motor neurones found

Answer 57

Anterior horn of grey matter of spinal cord and in brainstem

Question 58

Why does doing the jendrassik movement cause a large reflex

Answer 58

Removes descending inhibition from brain