Lecture 10- Basal ganglia, cerebellum and movement disorders Flashcards Preview

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Flashcards in Lecture 10- Basal ganglia, cerebellum and movement disorders Deck (45)
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1
Q

basic function of the basal ganglia is to

A

analyse motor plans produced by the primary motor cortex

2
Q

key components of the basal ganglia

A
  • 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
3
Q

which structures are reffered to together as the striatum

A

putamen and caudate nucleus

4
Q

Substantia nigra

A

(part of the midbrain)

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

5
Q

location of the cerebellum

A
  • Sits dorsal to the pons
  • Forms the roof of the fourth ventricle
  • Separated from the occipital love by the tentorium cerebeli
6
Q

basic anatomy of the cerebellum

A
  • 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
7
Q

cerebellar peduncles

A

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
8
Q

superior surface of the cerebellum

A
  • Top of cerebellum flatter and bottom more irregular
  • Vermis= midline structure
  • 2 lateral hemispheres
  • Topography
    • Vermis- trunk musculature
    • Hemisphere- distal muscles
9
Q

inferior surface of the cerebellum

A
  • 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
10
Q

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

A
  • 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
11
Q

Basal ganglia function

A

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

12
Q

Cerebellum function

A

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

13
Q

basal ganglia pathway

A
14
Q

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

A

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
15
Q

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

A

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
16
Q

parkinsons caused by

A

degeneration of dopaminergic neruones present in the susbtantia nigra

17
Q

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

A

SNc

–> substantia nigra

18
Q

Normal dopamine action on the basal ganglia pathway

A
19
Q

overall affect of loss of dopamine in parkinsons disease

A

We get decreased cortex activity

20
Q

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

A
21
Q

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

A
22
Q

Huntingonts chorea primarily causes by

A
  • 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
23
Q

symptoms and signs of Huntingtons chorea

A

Movement increases (hyperkinesia)

  • Choreiform movements- involuntary
  • Dystonia
  • Incoordination
  • Psychiatric features
24
Q

Hemiballismus

A
  • Another hyperkinetic disorder
  • Involuntary, explosive unilateral movements ‘ hemi’- half , ‘ballistic’
25
Q

primarly problem in hemiballismus

A

damage to the subthalamic nucleus in the basal ganglia

26
Q

Blood supply to cerebellum is from the

A

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

27
Q

cerebellar lesions can present with

A
28
Q

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

A
  • cerebellar signs on ipsilateral side
  • distal part of the uppper and lower limbs
29
Q

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

A

in the trunk

  • trunal ataxia
30
Q

classic cerebellar lesion symptoms and signs

A

DANISH pneumonic

31
Q

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

A
  • the corticospinal tracts (UMNs)
  • LMN (final common path) creates behaviour
32
Q

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

A
  • 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
33
Q

basal ganglia function example

A

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
34
Q

more detail on the function of the cerebellum (read)

A
  • 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
35
Q

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

A
  • 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)
36
Q

summarise basal ganglia lesion

A
  • Signs and symptoms on the contralateral side of the body
  • Because the corticospinal tract decussates
37
Q

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

A
  • 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)
38
Q

why do bsal ganglia lesions tend to be bilateral

A
  • However basal ganglia lesions tend to be bilateral due to them usually being damaged by neurodegenerative disorders therefore losses may seem bilateral
39
Q

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

A

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
40
Q

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

A
  • 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)
41
Q

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

A

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

42
Q

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

A
43
Q

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

A
  • Pink= putamen
  • blue= external globus pallidus
  • orange= internal GP
44
Q

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

A
45
Q

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)

A

From the ears of mini mouse midbrain