4.2 Basal ganglia and cerebellum Flashcards
The pyramidal system (main output to voluntary muscles) occurs via the ______________, and the output is modulated by the extrapyramidal system (basal ganglia & cerebellum):
• Impinge on the motor cortex to refine the outputs of the cortex on the way down to the motor neurones in the spinal cord
• Basal ganglia has an _____________ via the thalamus, while cerebellum has a _____________- via the thalamus → balance allows for smooth coordinated movement
• Disturbances in either system will present as movement disorders
corticospinal tract;
inhibitory effect;
positive effect
What does the basal ganglia consist of?
grey matter areas within the subcortical part of the brain:
1. Caudate nucleus and putamen
2. Internal and external globus pallidus (GPi and GPe)
3. Subthalamic nucleus (STN) 4
. Pars reticulate & pars compacta of substantia nigra (SNr and SNc)
*Lentiform nucleus is made of the putamen and globus pallidus, while the striatum is made of the caudate nucleus and lentiform nucleus.
From the cerebral cortex, the ____________________ (5) all project to the caudate nucleus and putamen:
• Putamen then projects via the direct pathway (to ___________) or the indirect pathway (to the _____________i)
o Refer to “Drugs Affecting the CNS – Parkinson’s disease” for more details
• _____________ are the only output of the basal ganglia, and project to the thalamus
• Thalamus then projects back to the ________________ → involved in movement preparation and planning
supplementary motor area (SMA), premotor area (PMA), primary motor cortex (M1), somatosensory cortex, and parietal cortex;
GPi and SNr;
GPe → STN → GP;
GPi and SNr;
cortex (SMA and PMA)
The globus pallidus (GPi) inhibits the __________ and the ____________ inhibits the GPi (via GABA), which thus releases the thalamus from inhibition:
• Thalamus releases selected movement via _________________
• Correct balance is mediated by the SNc (provides excitatory inputs to the _______________ (via dopamine)) → nigro-striatal pathway (positive excitatory)
• GPi and SNr are the messengers of all information from the basal ganglia (inhibits the thalamus)
thalamus;
putamen;
projections to cortex (positive innervation);
caudate nucleus and putamen
[Parkinson’s disease]
The substantia nigra is pigmented by _____________ (by-product of normal metabolism in dopaminergic neurones) → gets darker with age due to build-up:
• Parkinson’s disease occurs due to __________________ (nigro-striatal pathway) → indicated by pallor of substantia nigra
• Positron Emission Tomography (PET) 18F-DOPA (visualising dopaminergic innervation in the caudate nucleus and putamen): symmetrical in normal subjects; __________________ in Parkinson’s patients
o Unilateral in onset, then progresses to bilateral loss
neuromelanin ;
neuronal degeneration of the substantia nigra;
asymmetry and loss of dopamine signal in the basal ganglia;
Patients with Parkinson’s disease present with the following signs and symptoms due to _______________ (impaired nigro-striatal excitatory pathway → no release)
- bradykinesia: Slowness of movements (slow walking, small steps, shuffling feet, reduced arm swing, ______ turning)
- difficulty in small movements e.g. buttoning of shirt
- face _________: Absence of movements which normally animate the face → expressionless and mask-like face
- _______: Difficulty initiating movements → require external sensory triggers to initiate movement (e.g. visual trigger; internal initiation impossible)
- Tremor at rest: Cease with ________, usually starts in one hand (asymmetry) and tends to spread with time to other parts of the body
- Rigidity (not spasticity): Type of resistance to passive movements → passively moving the patient’s limb feels like _______________
- ___________ posture: Head and body bent forward and downwards
increased inhibition from GPi
en-bloc;
voluntary activity;
hypomimic;
akinesia
bending a lead pipe (lead pipe rigidity);
Stooped
Huntington’s disease is caused by an autosomal dominant mutation in the _________________(CAG repeat disease):
• Due to degeneration of spiny GABAergic neurones in the striatum (____________ first then ______________ later) → may produce profound atrophy of both
• Present with _______________ → rapid jerky involuntary movements of the body (usually affecting hands and face at first) → no inhibition of thalamus
o Patients can mask the spontaneous movements (early stages) by incorporating them into socially acceptable movements o Gradually increase over time until the patients become totally incapacitated ]
• Eventually experiences cognitive decline and dementia, with death occurring 10 – 15 years after the onset of symptoms
huntingtin gene on chromosome 4 ;
caudate nucleus ;
putamen;
choreic movements (chorea)
The cerebellum makes up the roof of 4th ventricle and lies immediately posterior to the pons:
• Cerebellum and brainstem occupy the posterior cranial fossa with the occipital lobe superior to it (separated by the _____________)
• Can be divided horizontally into 3 lobes (_______, ________, _______) or sagittally into 3 lobes (________ in midline, ___________, and _______ cerebellum
tentorium cerebelli;
anterior, posterior, flocculonodular;
vermis; intermediate; lateral
what does the deep nuclei (in white matter of cerebellum) contain?
Deep white matter contains distinct nuclei (neuronal cell bodies):
• Dentate nucleus is the largest, and is the main output nucleus
• Other nuclei include the interposed nucleus and fastigial nucleus
What is the structural functions of the cerebellar peduncles?
fibre tracts with both functional and structural roles → holds cerebellum to the back of the brainstem at the level of the pons
what does the superior cerebellar peduncle contain?
Main output pathway (in terms of modulating motor function)
what does the middle cerebellar peduncle contain?
Largest; bridging fibres joining the 2 halves of the cerebellum
what does the inferior cerebellar peduncle contain?
Consists of ascending fibres from the spinal cord
The vestibulocerebellum includes the ____________ lobe (oldest part of the cerebellum):
• Receives input from the vestibular system (__________________) to the flocculonodular cortex (reciprocal connections through the _____________)
• Involved in the regulation of _______________and coordination of head movements with eye movements (e.g. watching
tennis)
flocculonodular ;
vestibular nuclei of CN VIII and the vestibular nerve;
inferior cerebellar peduncle;
gait, posture, and equilibrium
The spinocerebellum consists of the vermis (projects to the ____________) and the intermediate cerebellum (projects to the ______________):
• Input from spinal cord (dorsal & ventral spinocerebellar tracts):
o Vermis: from _________________
o Intermediate cerebellum: from the __________
o Cerebellar cortex is organised somatotopically
- Output occurs via the __________ (via fastigial and interposed nuclei) → _________ (midbrain) → ____________ (pons) → ________________ tracts → spinal cord motor neurones
- Modulates voluntary movement based on proprioception input through cerebellum → coordination of speech and limb movements and adjustment of muscle tone
fastigial nucleus;
interposed nucleus;
axial parts of the body, trigeminal, visual, auditory inputs ;
limbs;
superior cerebellar peduncle;
red nucleus;
reticular formation nuclei;
reticulospinal and rubrospinal
The cerebrocerebellum includes the _________(projects to the ______________):
• Receives input from the _______________ nuclei (via middle cerebellar peduncle) and the _______________i (via inferior cerebellar peduncle)
• Some connectivity exists within the cerebellum
• Outputs from the dentate nucleus (via the superior cerebellar peduncle) → __________ → cortical projections to main
motor cortical areas → project back down to the _________________
• Involved in coordination of ______________
dentate nuclei;
lateral lobes;
reticular formation and pontine;
inferior olivary nucle;
thalamus;
reticular formation, pontine nuclei and inferior olivary nuclei;
skilled movements (e.g. playing the piano) and tactics of immediate movements
what is the definition of ataxia (sign of cerebellar disorder)?
Instability when standing or walking, wide-based stance, staggering and wide-based walking (looks drunk):
• Muscles involved differ d
what is the negative romberg sign (sign of cerebellar disorder)?
Loss of balance even when patient opens his eyes while standing
What is hypotonia (sign of cerebellar disorder)?
Reduced muscle tone (floppy limbs)
What is dysmetria (sign of cerebellar disorder)?
Inability to judge distance and when to stop (cannot control range of movement)
What is dysarthria (sign of cerebellar disorder)?
Slurred speech (cannot articulate words correctly) and inappropriate phrasing
What is dysdiadochokinesia (sign of cerebellar disorder)?
Inability to coordinate movements (cannot perform rapidly-alternating movements) → heel-to-shin/finger-to-toe test
what is intention tremor (sign of cerebellar disorder)?
when limb approaches target
What is nystagmus (sign of cerebellar disorder)?
Involuntary rapid eyeball oscillation (horizontal/vertical/rotary) with the fast component towards the side of lesion
what is postural tremor (sign of cerebellar disorder)?
when fixed posture/weight bearing is attempted
what is scanning speech (sign of cerebellar disorder)?
Slow enunciation with tendency to hesitate at beginning of a word/syllable
what are the more prominent signs of vestibulocerebellum disorder?
Loss of balance while standing upright, eye movement abnormalities (e.g. nystagmus), hypotonia
what are the more prominent signs of spinocerebellum disorder?
Truncal ataxia (wide-based gait with small shuffling movements), dysdiadochokinesia, dysmetria, speech disorders (e.g. dysarthria or staccato speech), action/intention tremors
what are the more prominent signs of cerebrocerebellum disorder?
Impairments in highly skilled sequences of learned movements (e.g. playing musical instrument)
