Cortical Motor Function, Basal Ganglia and Cerebellum

Question 1

Describe the hierarchical segregation of the motor cprtex

Answer 1

higher = more complex tasks

level 4 = association cortex
level 3 = motor cortex
level 2 = brain stem and cerebellum (side loop structure (SLS))
level 1 = basal ganglia (e.g caudate nucleus) and spinal cord

Question 2

What are the main ares of the motor cortex?

Answer 2

1. primary motor cortex or M1 ( broadmann’s are 4)
2. premotor cortex - area 6
3. supplementary motor cortex - area 6

Question 3

Where is the primary motor cortex located?

Answer 3

frontal lobe

precentral gyrus, anterior to central sulcus

Question 4

What is the function of the primary motor cortex?

Answer 4

control fine, discrete, precise voluntary movement

provides the descending signals to execute movement

Question 5

What are the biggest cells of the cerebral cells?

Answer 5

Betz cells in layer V of cerebral cortex

Question 6

What are the divisions of the corticospinal tract?

Answer 6

*provides innervation to arms, legs and axial structures (trunk and abdomen)

1. lateral corticospinal tract - distal muscles of limbs
   - right hemisphere of cortex -> internal capsule -> emerge as cerebral penucles in midbrain -> medulla oblongata and decussion(crossing over to other side) at pyramids -> anterior horn of spinal cord and synapse with lower motor neurone -> innervation of distal muscles
2. anterior corticospinal tract - proximal limbs and trunk muscle
   * similar pathway but crosses at spinal level

Question 7

**What are the two main sensory pathways?

Answer 7

dorsal column - touch

spinothalamic - temp. and pain

Question 8

What are the corticobulbar pathways?

Answer 8

Hypoglossal neurone

Head region of motor cortex ->genu of internal capsule (cortico tubular tract) -> synapses near inferior cerebellar penucle (switches side) [hyoglossal nuclei] -> inferior olivary nucleus -> Tongue muscles

Upper motor neurones synapse in brain stem after crossing over into the lower motor neurone

Upper MN NT= glutamate
Lower = ACh

Question 9

Desecriibe the somatorophic organisation of the primary motor cortex

Answer 9

Known as Penfield’s motor homunulus

Face and hands have a large area of brain to control them because they have more fine control

Question 10

Describe the location and function of the promotors cortex

Answer 10

Location - frontal lobe, anterior to M1, lateral to suplementary MC

Function - involved in planning movement (involves regulating external cued movement)

Question 11

Describe the location and function of the supplementary motor cortex

Answer 11

Location - frontal lobe, anterior to M1, medial to premolar cortex

Function - planning complex movements, programming sequencing of movement (internally driven movements such as speech and becomes active before move to is executed)

Question 12

What is the association cortex?

Answer 12

Brai areas to strictly motor areas as their activity doesn’t correlate with motor output

Posterior parietal cortex - ensures movements are targeted accurately to objects I external space

Prefrontal cortex - involved in selection of appropriate movements from a particular course of action

Question 13

What are :
Lower motor neurones?

Upper motor neurones?

Pyramidal neurones?

Extrapyramidal neurones?

Answer 13

L = spinal cord, brain stem - sit in spinal cord and project out

U = corticospinal, corticotubular - sit in cortex and projections to spinal cord

P = lateral criticospinal tract

E = basal ganglia, cerebellum - modify output

Question 14

What are the effects of an upper motor neuron lesion/

Answer 14

Loss of function (negative signs)

• paresis (garden weakness of movement)
• paralysis [plegia] (complete loss of muscle activity

Increased abnormal motor function (positive signs) due to loss of inhibitory descending output

• spasticity ( increased muscle tone)
• hyper -reflexia) ( exaggerated reflexes
• clonus (abnormal oscillatory muscle contraction)
• Babinski’s sign (extensor plantar response)

Question 15

What is apraxia?

Answer 15

Disorder of skilled movement - patient not paretic but has lots information on how to perform skilled task

due to lesion of inferior partial lobe or frontal lobe (premolar/supplementary MC)

• most commonly caused by stroke / dementia

Question 16

What are the effects of a lower motor neuron lesion?

Answer 16

Weakness
Hypotonia
Hyporeeflexia
Muscle atrophy
Fsciculations (damaged motor units produce spontaneous action potentials, resulting in. A visible twitch)
Fibrillations ( spontaneous twitching of individual muscle fibres, recorded during needle electromyography examination)

Question 17

What are the effects of motor neurone disease?

Answer 17

Progressive neurodegeneative disorder of the motor system (affects both upper and lower MC)

Also known as amyotrophic lateral sclerosis (ALS)

Upper motor neuron signs:
Increased muscle tone (spasticity f limbs and tongue)
Brisk limbs and jaw reflexes
Babinski’s sign
Loss of dexterity
Dysarthria (motor speech disorder)
Dysphasia (problems with swallowing n eating)

Lower mot neuron signs:
Weakness
Muscle weakening
Tongue fasciculations and wasting
Nasal speech
Dysphasia

Question 18

What are the ey ares of the basal ganglia?

Answer 18

*Extrapyramidal

Includes:
Caudate nucleus
Lentiform nucleus (putamen + external globus pallidus)
Subthalamic nucleus
Substantial nigra 
Ventral pallidum
Claustrum
Nucleus accumbens
Nucleus basalis
Meynert

**striatum = lentiform + caudate

Question 19

What is the function of the basal ganglia?

Answer 19

Elaborates associated movements e.g swinging arms when waking

Moderates and coordinates movement (whilst suppressing unwanted movements, changing facial expressions to match emotions)

Performs movements in order

Question 20

Describe the circuitry of the basal ganglia

Answer 20

Primary motor cortex -> BG -> Thalamus -> motor cortex -> muscles

Cortex -> striatum

Striatum -> globus pallidus subthalamic nucleus -> globus pallidus -> thalamus
[ballism]

Striatum -> globus pallidus -> T
[affected by HD]

Striatum substantia nigra (r)
[affected by PD]

*see diagram

Question 21

What are the pathophysioogical feactures of Parkinson’s disease?

Answer 21

Neuronal degeneration of substantia nigra pars compacta (SNc) -> 80% loss of DA cells

Degeneration of DA neurones causes loss of nigra-striatal neurones and disrupts fine balance of excitation and inhibition leading to reduction of excitation in motor cortex

Question 22

What are the main signs of Parkinson’s?

Answer 22

Bradykinesia (slow movement)
Hypomimic face (expressionless)
Akinesia (difficulty in initiation of movements )
Tremor at rest
Gait and posture - walking slow, small shuffling steps, reduced arm swing and head bent forward and downward

Question 23

Describe the pathophysiology of Huntington’s disease

Answer 23

Abnormality in Chr4

Autosomal dominant

CAG repeats (>35)

Degeneration of GABA neurones in striatum(caudate then putamen)

Disrupts fine balance
Motor cortex gets excessive excitatory input so tends to send continuous involuntary commands to the muscles

Question 24

What are the main signs of Huntington’s?

Answer 24

Choreic movements (rapid jerky involuntary movements of the body, hands and face affected first -> legs and rest of the body)

Speech affected

Difficulty swallowing

Unsteady gait

Later stages - cognitive decline and dementia

Question 25

Describe the structure of the cerebellum

Answer 25

Horizontally divide into 3 lobes:
Anterior
Posterior
Flocculonodular

Sagitally divided into 3 zones:
Vermis
Intermediate hemisphere
Lateral hemisphere

Question 26

Describe the layers of the cerebellum

Answer 26

3 layers

Molecular - very few neurones, some glial cells

Piriform - purkinje cells found here

Granular - very small neurones found, closely packed

Question 27

Describe the input and output of the cerebellum?

Answer 27

Inferior olive projects to purkinje cells via climbing fibres

All other input to granule cells via mossy fibres and then onwards via parallel fibres

All output from purkinje cells via deep nuclei

Question 28

What are the functions of each of the divisions of the cerebellum?

Answer 28

Vestibulocerbellum

• regulation of gait, posture and equilibrium
• coordination of head movements with eye movements

Spinocerbellum

• coordinates speech
• adjustment of muscle tone
• coordination of limb movements

Cerebrocerebellum

• coordination of skilled movements
• cognitive function, attention, processing of language
• emotional control

Question 29

What does dysfunction in each division of the cerebellum cause?

Answer 29

Vestibulocerbellar syndrome - damage (tumour) causes syndrome similar to vestibular disease leading to gait at axis and tendency to fall (even when sitting and eyes open)

Spinocerebellar - damage ( degeneration/ atrophy with chronic alcoholism) affects annoy legs,causes abnormal gait and stance (wide-based)

Cererocellebelalr/ lateral cerebellar - damage affects mainly arms/ skilleeed coordinated movements (tremor) and sech

Question 30

What are the main signs of cerebellar dysfunction?

Answer 30

Deficits apparent only upon movement

Ataxia

• general imparments in movement coordination and accuracy
• disturbances of posture or gait
• wide- base
• staggering gait

Dysmetria
- inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)

Intention tremor
- increasing oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)

Dydiadochokinesia
- inability to perform rapidly alternating movements
(rapidly pronating and supinating hands an forearms)

Scanning speech
- staccato due to impaired coordination of speech muscles