Lecture 10- Basal ganglia, cerebellum and movement disorders

Question 1

basic function of the basal ganglia is to

Answer 1

analyse motor plans produced by the primary motor cortex

Question 2

key components of the basal ganglia

Answer 2

• Key components
  
  • Thalamus
  • Internal capsule
  • Lentiform nucleus
    
    • Putamen- superficial
      
      • Putamen and caudate nucleus (C shaped) closely related
      • Connected to each other- same ancestral nucleus  together referred to as the striatum
      • The striatum receives input from the cortex
    • Globus pallidus- further subdivided
      
      • External
      • Internal
      • Sends output back to the cortex via the thalamus
  • Substantia nigra (part of the midbrain)
    
    • Dopaminergic neurones which sends axons up to striatum (putamen)via the Nigro striatal pathways

Question 3

which structures are reffered to together as the striatum

Answer 3

putamen and caudate nucleus

Question 4

Substantia nigra

Answer 4

(part of the midbrain)

Dopaminergic neurones which sends axons up to striatum (putamen)via the Nigro striatal pathways

Question 5

location of the cerebellum

Answer 5

• Sits dorsal to the pons
• Forms the roof of the fourth ventricle
• Separated from the occipital love by the tentorium cerebeli

Question 6

basic anatomy of the cerebellum

Answer 6

• Sits in the posterior cranial fossa
• 3 major components
  
  • 2 laterally placed cerebellar hemispheres
  • 1 midline cerebellar vermis
• Connected to the brainstem by Cerebellar peduncles

Question 7

cerebellar peduncles

Answer 7

3 pathways

• Superior medulla peduncle- connecting cerebellum to midbrain
• Middle -connecting cerebellum to pons
  
  • Largest
  • Huge amount of input get to the cerebellar from the motor cortex via the corticoponto cerebellar pathway –> passes through middle peduncle
• Inferior- connecting cerebellum tomedulla

Question 8

superior surface of the cerebellum

Answer 8

• Top of cerebellum flatter and bottom more irregular
• Vermis= midline structure
• 2 lateral hemispheres
• Topography
  
  • Vermis- trunk musculature
  • Hemisphere- distal muscles

Question 9

inferior surface of the cerebellum

Answer 9

• Triangle shape next to the vermis= cerebellar tonsil
  
  • If ICP increases- tonsils (herniation) can be forced down through foramen magnum causing compression of the medulla
• Can see forth ventricle
• Can see cerebellar peduncles

Question 10

normal function of the basal ganglia and cerebellum can be thought of as

Answer 10

• Looping circuits going from the cortex to the basal ganglia and back to the cortex and the cortex to the cerebellum and back up to the cortex
• Loops – analysis of motor programs produced by the primary motor cortex

Question 11

Basal ganglia function

Answer 11

Takes an idea or motor plan decided by the prefrontal cortex and determines the most appropriate set of movements for a task

• Direct pathway
  
  • Facilitates appropriate movements
• Indirect pathway
  
  • Inhibits inappropriate movements

Dopamine from SNcircuit can be thought as a ‘kick starter’ and finer tuner

Question 12

Cerebellum function

Answer 12

Looks at the position of limbs currently and determines an appropriate sequence to conduct the motor plan

Question 13

basal ganglia pathway

Answer 13

Question 14

When thinking about normal functions of the basal ganglia, start at the putament and ignore dopamine…. outline the direct pathway

Answer 14

Facilitation of appropriate movements- net excitatory to motor cortex

1. Putamen communicates with the internal segment of the globus pallidus- inhibitory (GABA)
2. Globus pallidus normally inhibits the thalamus (GABA)
3. Thalamus excites the cortex (glutamate)
4. Therefore we have inhibition of a normally inhibitory pathways (-ve + -ve = +Ve)
5. Therefore we decrease amount of inhibition on thalamus, therefore we get a net increase in activity of the motor cortex

Question 15

When thinking about normal functions of the basal ganglia, start at the putament and ignore dopamine…. outline the indirect pathway

Answer 15

inhibits inappropriate movements- net inhibitory to motor cortex

1. Putamen sends inhibitory neurones down to the external segment of the globus pallidus (GPe) (GABA)
2. GPe is normally inhibitory on the subthalamic nucleus (STN) (GABA)
3. Therefore if the putamen is inhibiting the GPe, then there is inhibition of inhibitory effect of GPe on the subthalamic nucleus (STN)
4. Therefore STN can provide more excitatory stimulation the internal segment of the globus pallidus
5. when stimulated GPi will give more inhibitory stimulation of the thalamus
6. Therefore inhibition of the thalamus even more
7. Therefore inhibitory on the motor cortex

Question 16

parkinsons caused by

Answer 16

degeneration of dopaminergic neruones present in the susbtantia nigra

Question 17

When thinking about Parkinsons disease in relation to the basal ganglia circuit start at the…..

Answer 17

SNc

–> substantia nigra

Question 18

Normal dopamine action on the basal ganglia pathway

Question 19

overall affect of loss of dopamine in parkinsons disease

Answer 19

We get decreased cortex activity

Question 20

summary of parkinsons and its relation to decreased dopaminergic neurones in the SN

Question 21

a decrease in cortical actvity seen in parkinsons disease manifests in what sort of symptoms

Question 22

Huntingonts chorea primarily causes by

Answer 22

• Primary problem= degeneration of inhibitory influences running from the putamen to the globus pallidus externus (indirect pathway)
  
  • If we lose inhibition of the GPe then the GPe activity will increase
  • Therefore increased inhibitory influence of Subthalamic nucleus by the GPe
  • Therefore activity of the STN decreases, meaning less stimulation of the GPi
  • Meaning less inhibition of the thalamus
  • Thalamus activity increase
  • Cortical activity increase

Question 23

symptoms and signs of Huntingtons chorea

Answer 23

Movement increases (hyperkinesia)

• Choreiform movements- involuntary
• Dystonia
• Incoordination
• Psychiatric features

Question 24

Hemiballismus

Answer 24

• Another hyperkinetic disorder
• Involuntary, explosive unilateral movements ‘ hemi’- half , ‘ballistic’

Question 25

primarly problem in hemiballismus

Answer 25

damage to the subthalamic nucleus in the basal ganglia

Question 26

Blood supply to cerebellum is from the

Answer 26

vertebra basilar system * occlusion of the three cerebellar arteries produce similar syndrome (don’t forget the brainstem) Therefore should also examine cranial nerves in order to establish if brainstem involvement

Question 27

cerebellar lesions can present with

Question 28

where will signs occur if there is a lesion in one of the cerebellar hemispheres

Answer 28

* cerebellar signs on ipsilateral side * distal part of the uppper and lower limbs

Question 29

where will cerebellar signs occur if there is a lesion in the vermis of the cerebellum

Answer 29

in the trunk - trunal ataxia

Question 30

classic cerebellar lesion symptoms and signs

Answer 30

DANISH pneumonic

Question 31

Primary motor cortex (MI) communicates with lower motor neurones via

Answer 31

* the corticospinal tracts (UMNs) * LMN (final common path) creates behaviour

Question 32

more detail on the function of the basal ganglia (read)

Answer 32

* Basal ganglia edits information coming from the primary motor cortex- decides whether movements are appropriate or not to achieve a goal * Crude motor plan produced by the primary motor cortex needs to be analysed by the basal ganglia * Components of the plan that lead to flexion of the joints need to be facilitated * Basal ganglia stimulate primary motor cortex via the direct pathway * Components of the plan that lead to inappropriate extension need to be inhibited * Basal ganglia inhibits primary motor cortex via the indirect pathway * This creates a cortical loop --\> refines movement plan

Question 33

basal ganglia function example

Answer 33

We want to pick up a cup need to coordinate muscle appropriate * For each joint involved in picking up a cup there is a set of agonists and antagonistic muscles at play * E.g. holding cup flexion of the fingers and wrist * E.g. bring the cup to the mouth involves flexing the elbow and shoulder * Therefore FLEX, FLEX, FLEX at the wrist, elbow and shoulder- we do not want any extension

Question 34

more detail on the function of the cerebellum (read)

Answer 34

* Cerebellum receives info from the motor cortex concerning the motor plan- looks at the sequence of movements and decides if they are most appropriate to achieve goal * E.g. order of flexion at joints for picking up tea * Need to flex the fingers first, then the elbow, then the shoulder * However also needs to coordinate sequence based on the current position of the limbs * E.g. reaching for a drink on top of a cupboard or from the floor – would required flexion at joints in a different order

Question 35

how does the cerebellum decide which order joints need to flex/extend?

Answer 35

* Receives this info from the primary sensory cortex and the **spinocerebellar** tract (information from proprioceptors in the muscles up the spinal cord into the cerebellum) * Cerebellum than communicates back to the primary motor cortex (via the thalamus)

Question 36

summarise basal ganglia lesion

Answer 36

* Signs and symptoms on the contralateral side of the body * Because the corticospinal tract decussates

Question 37

outline the mechanism that means basal ganglia lesion signs and symptoms occurs on the contralateral side?

Answer 37

* Corticospinal pathway (red) * Cell body of UMN starts in the primary motor cortex * Axon passes down through the corona radiata into the internal capsule and into the brainstem via the cerebral peduncles of the midbrain * The UMN will decussate in the medulla * Passes down the spinal cord and synapses with the LMN lateral to muscle being innervates * LMN synapses with muscles fibres * Corticostriatal pathway (pink) * Originates within the motor cortex and projects down to the striatum (putamen and the caudate nucleus) – how the motor cortex sends the plan down to the basal ganglia * Basal ganglia analyses motor plan proposed by motor cortex and sends results of analysis (via the thalamus) back up to the cortex via the pallidothalamocortical pathway (green) * Pallidothalamocortical pathway (green) * Analysis information by the basal ganglia from the globus pallidus via the thalamus to motor cortex * Nigrostriatal pathway (black)- dopaminergic pathway * Dopamine provided by the substantia nigra (within the midbrain) to the striatum (inhibits or excites certain movement plans)

Question 38

why do bsal ganglia lesions tend to be bilateral

Answer 38

* However basal ganglia lesions tend to be bilateral due to them usually being damaged by neurodegenerative disorders therefore losses may seem bilateral

Question 39

why do signs and symptoms of cerebellum lesions occur on the ipsilateral side?

Answer 39

due to double decussation showed by these pathways: * **Normal corticospinal pathway (red)** * **Corticopontine pathway (pink)** * Motor cortex communicates motor plan to cerebellum via the corticopontine pathway which synapses with neurones in the pons * Neurones of the pontine nuclei decussate to the contralateral cerebellar hemisphere * **Cerebellothalamocortical pathway (green)** * Neurones within the cerebellar hemispheres communicate with the contralateral thalamus * Neurones of the contralateral thalamus project back to the motor cortex sending its analysis of the appropriate sequence of movements for a behaviour e.g. picking up a cup * **Spinocerebellar pathways (blue)- sensory pathway** * Collects info from muscle spindle (proprioceptors) and sends info to cerebellum on the ipsilateral side

Question 40

Anatomy of the basal ganglia using 3D constructed MR data: ventricles

Answer 40

* Lateral ventricles- C shaped * Third ventricle flattened between the thalamus (the hole represents the interthalamic adhesion between the 2 halves of the thalamus) * Fourth ventricles (found inbetween cerebellar hemispheres)

Question 41

Anatomy of the basal ganglia using 3D constructed MR data: ventricles + the thalamus

Answer 41

Can see the thalamus is arranged in a series of different nuclei e.g. input from the somatosensory / input from the cerebellum Left thalami added Sit beneath the lateral ventricles

Question 42

Anatomy of the basal ganglia using 3D constructed MR data: ventricles + the thalamus (light blue)+ caudate nucleus (dark green)

Answer 42

Question 43

Anatomy of the basal ganglia using 3D constructed MR data: ventricles + the thalamus (light blue)+ caudate nucleus (dark green) + lentiform nucleus (pink and blue)

Answer 43

* Pink= putamen * blue= external globus pallidus * orange= internal GP

Question 44

Anatomy of the basal ganglia using 3D constructed MR data: ventricles + the thalamus (light blue)+ caudate nucleus (dark green) + internal capsule (black part)

Answer 44

Question 45

Anatomy of the basal ganglia using 3D constructed MR data: ventricles + the thalamus (light blue)+ caudate nucleus (dark green) + internal capsule (black part) + substantia nigra (brown/green)

Answer 45

From the ears of mini mouse midbrain