27 - Lesions III Flashcards
Basal ganglia function
Inhibition and facilitation
Describe inhibition of the basal ganglia
Inhibiting involuntary movement at rest
Stopping volitional movements upon completion
Describe facilitation of the basal ganglia
Releasing or disinhibiting voluntary movements
Accelerating voluntary movements
Chorea
dance-like, involuntary, rapid movements. Can be associated with Huntington disease, rheumatic fever, systemic lupus erythematosus, and other conditions
Athetosis
slow, twisting, writhing movements, with larger amplitude than chorea, commonly involving the hands
Hemiballism
jerking and twitching movements of one side of the body (involuntary violent flinging or jerking of a limb or limbs in an uncoordinated manner caused by a lesion of the contralateral subthalamus)
Dystonia
impaired or disordered tonicity, especially muscle tone (involuntary muscle spasms)
What area of the brain is Parkinson’s disease associated with?
Basal ganglia
What causes Parkinson’s disease?
Death of dopaminergic cells in the pars compacta of the substantia nigra
How do you treat Parkinson’s disease?
L-dopa metabolized to dopamine by dopaminergic cells
What are the key symptoms of Parkinson’s disease?
- Rigidity
- Slowness of movement (bradykinesia)
- Slumped posture
- Resting tremor
What is the cause of the rigidity, slowness of movement and slumped posture?
It is a basal ganglia problem
Excessive inhibition with a lack of facilitation
What is the cause of the resting tremor?
It is a basal ganglia problem
Lack of suppression of involuntary movement
What is the striatum in relation to the basal ganglia?
The striatum is the “input gate” to the basal ganglia
How is the striatum affected by Parkinson’s disease? How is it affected by Huntington’s disease?
Parkinson’s disease results in loss of dopaminergic innervation to the striatum (and other basal ganglia) and a cascade of subsequent consequences.
Atrophy of the striatum is also involved in Huntington’s disease, choreas, choreoathetosis, and dyskinesias.
What is Tourette’s syndrome?
An inherited neuropsychiatric disorder with onset in childhood, characterized by multiple physical (motor) tics and at least one vocal (phonic) tic. These tics characteristically wax and wane, can be suppressed temporarily, and are preceded by a premonitory urge.
What two signs must be present to define Tourette’s?
Motor and vocal tics
What one sign, in particular, makes Tourette’s unique among all extrapyramidal syndromes?
Vocal tics
What is the cerebellum responsible for?
Precision
Movements are precise, on time and on target
In more detail, what is the function of the cerebellum?
- Integration of equilibrium and locomotion
- Integration of head and eye movements
- Coordinating voluntary movements
What does coordination of voluntary movements entail?
- Comparing cortical input with motor output
- Providing feedback for ongoing movements
- Making adjustments to ongoing movements
- Ensuring accurate targeting
Ataxia
impaired ability to coordinate muscular movement usually associated with staggering gait and postural imbalance
Nystagmus
Involuntary eye movements
Dysmetria
Refers to a lack of coordination of movement typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye. It is a type of ataxia. It is sometimes described as an inability to judge distance or scale
Dysdiadochokinesia
Inability to quickly substitute antagonistic motor impulses to produce antagonistic muscular movements
Inability to perform rapid alternating movements (e.g., pronation/supination of hands)
Indicates cerebellar dysfunction
What is the midline cerebellum responsible for (vermal area)?
spinocerebellum- muscle tone and adjusting movements of axial trunk and proximal limbs
Think spine like a spine right down the middle
What is the lateral cerebellum (hemispheric area) responsible for?
cerebrocerebellum- precise control of executed movements (timing, duration, force, velocity and trajectory of movements, of extremities, especially hands and fingers
Think cerebro like the two sides of the brain - on the lateral sides
Where would you see movement problems that result from a lesion in the vermal area of the cerebellum
Midline cerebellum lesion
Symptoms will be present in the axial trunk and proximal portions of the limbs
Where would you see movement problems that result from a lesion in the hemispheric area of the cerebellum
Lateral cerebellum lesion
Symptoms will be present in the distal extremities, especially the hands and fingers
There will be a loss of precise control of detailed finger movements like typing or playing the piano
Describe why cerebellar arterial syndromes typically manifest a mix of cerebellar and brainstem signs and symptoms
???
What is SCA syndrome?
Superior cerebellar artery syndrome
Describe SCA syndrome
SCA syndrome is due to thrombosis of the superior cerebellar artery that supplies the spinothalamic tract and the superior cerebellar peduncle - It’s a STROKE/INFARCT
There is incoordination in performing skilled movements, with loss of pain and temperature senses on the side of the face and body opposite to that of the lesion.
What are the specific symptoms of SCA syndrome?
- Ipsilateral dysmetria and limb ataxia
- Contralateral pain and temperature loss
- Contralateral superior oblique paralysis (SO4)
- Ipsilateral Horner’s syndrome
Horner’s syndrome
- Drooping of upper eyelid (partial ptosis)
- Constricted pupil
- Flushed, dry face
Describe the main functions of the limbic system
Hippocampus - “memory”
Amygdala - “fear”
Describe the hippocampus function
- Short term memory
- Consolidation into long term memory
Describe the amygdala function
- Basic drives (fear, rage, sexual arousal)
- Organizing behavior appropriate to drives
What part of the brain is responsible for “working memory”? Give an example
Frontal cortex
Declarative memory examples
Episodic (experience) = Putting the milk on the shelf instead of the refrigerator and not remembering you did it
Semantic (factual) = Adding up a set of numbers with no intent to memorize
What part of the brain is responsible for short-term memory? Give an example
Hippocampus
Declarative memory examples
Episodic (experience) = Meeting someone for the first time and learning their name, which you intend to remember
Semantic (factual) = studying neuroanatomy and trying to remember the function of the hippocampus
What part of the brain is responsible for long-term memory? Give an example
Association area of the cortex
Declarative memory examples
Episodic (experience) = Remembering walking down the aisle on your wedding day
Semantic (factual) = Remembering you childhood phone number
What are symptoms of Alzheimer’s disease?
Alzheimer’s disease is a degenerative disorder of the brain - most common form of dementia in elderly
Individuals with this disease are unable to form new memories
With progression of the disease, confusion and deficits in executive function occur
What causes Alzheimer’s disease?
This disease is caused by pathologic alterations including neurofibrillary tangles, neuritic plaques and neuronal degeneration
Where do these pathologic alterations occur?
First they appear in the entorhinal cortex (memory and navigation) of the medial temporal lobe
From there, degeneration spreads to the hippocampus
As the disease progresses, it progresses to deeper layers of the entorhinal cortex
What is the effect of this degeneration?
The neuronal degeneration hinders the normal flow of information through the hippocampal formation
What will occur as the disease progresses? Why?
Confusion deficits in executive function will occur following further spread of neurofibrillary tangles to the temporal pole and prefrontal cortex
Subicular pathology (degeneration in the subiculum of the hippocampus (lowest region)) occurs roughly at the same time that neurofibrillary tangles invade the temporal neocortex
Describe the symptoms of temporal lobe epilepsy
In temporal lobe epilepsy, patients sometimes display bizarre behaviors or have psychological disturbances, even between seizures
How are these symptoms associated with lesions?
These symptoms can be present in patients with very clear temporal lobe lesions (i.e. tumors) or even in patients without lesions
This leads to the hypothesis that the temporal lobe, specifically the medial portion of the temporal lobe, may be structurally or physiologically abnormal even if no lesion is detected there
What can very fine resolution MRI imaging of the temporal lobe reveal?
Using coronal imaging, often times temporal sclerosis is found in patients with temporal lobe epilepsy
This shows up as subtle scarring and lose of volume of the parahippocampal gyri
There is a loss of volume and loss of neurons in this region and the surrounding structures
What is a syndrome that is caused by thiamine deficiency from the diet?
Korsakoff’s syndrome or amnestic cofabulatory syndrome
In what cases do we typically see Korsakoff’s syndrome?
It is a disorder most often resulting from a thiamine (B1) nutritional deficiency in chronic alcoholism
Describe the symptoms and patient presentation of thiamine deficiency (Korsakoff’s syndrome)
Affected individuals have loss of recent memory and in order to compensate (cover) for this memory loss, they make up fictitious information or events to “fill in the gaps”
What morphological changes occur with individuals with thiamine deficiency?
Changes occur in the…
- Hippocampal formation
- Columns of the fornix
- Mamillary bodies of the hypothalamus
- Medial dorsal nucleus of the thalamus
Which area exhibits the MOST drastic modification and is considered unique to thiamine deficiency?
Drastic modification in the medial dorsal nucleus of the thalamus
More about the cerebellum…
Just an FYI
This is from lectures slides, not the handout
What are three goals of the cerebellum?
1 - Integration of equilibrium and locomotion
2 - Integration of head and eye movements
3 - Coordinating voluntary movements
How does the cerebellum integrate head and eye movements?
Via the MLF
Note that when there is a deficit in the ability to coordinate head and eye movements, there is likely an implication with the medial longitudinal fasciculus (MLF)
What four ways does the cerebellum coordinate voluntary movemetns?
1 - Comparing cortical input with motor output
2 - Providing feedback for ongoing movements
3 - Making adjustmetns to ongoing movements
4 - Ensuring accurate targeting
How does the cerebelllum accomplish the task of comparing cortical input with motor output?
Corticopontocerebellar pathway
Brings a copy of the motor plan down to the cerebellum
How does the cerebellum accomplish the task of providing feedback for ongoign movements?
Cerebellum cortex and dentorubrothalamic tract
How does the cerebellum accomplish the task of making adjustments to ongoing movements?
Vestibulospinal tract
Reticulospinal tract
Rubrospinal tract
Describe the role of the cerebellum ensuring accurate targeting
PRECISION – this is the importance of the cerebellum
How can you determine whether a tremor is caused by a lesion in the basal ganglia or the cerebellum?
If you have a tremor while resting, think BASAL GANGLIA***
If you have a tremor while doing something active like reaching, think CEREBELLUM***
For the vermis region, paravermal region and lateral region, what body regions do they contribute to?
In the vermis region –> control of AXIAL muscles
In the paravermal region –> control of INTERMEDIATE muscles or PROXIMAL muscles
In the lateral region –> control of EXTREMITY muscles
How can the results of tandem walking tell you which side of the cerebellum the lesion is on?
Tandem walking – get patient to walk heel-to-toe –> if the lesion is in the midline of the cerebellum, the patient has an equal chance of falling to the right or left – will fall to both sides
If you have a RIGHT hemispheric lesion, patient will fall to the right
If you have a LEFT hemispheric lesion, patient will fall to the left
What are some other cerebellar tests?
Finger to nose test and finger-nose-finger test –> cerebellar test
What is interesting about cerebellar arteries?
The arteries are circumferential from the ventral side
They have to make a path around to the back of the brainstem to the cerebellar region
They “drop off” some branches on the way
AICA path and branches
When dealing with the cerebellum we have the AICA – anterior inferior surface of cerebellum
In order to get there, you need to go around something (part of the PONS)
The external anatomy is then very important to us
Why not drop off a few arteries and supply that region? It does that – supplies the lateral aspect of the pons at the ponto-medullary junction
PICA path and branches
If you were to look at the PICA
In order to make the way there, need to run around the medulla of the brain stem
Might as well drop off some branches so it does
Have this image in mind
SCA path and branches
Now look at SCA
Gets to the superior part of cerebellum
Has to cross over the lateral surface of the midbrain, so it decides to drop some branches there
In lecture we called these the quadrigeminal arteries and supply the quadrigeminal area (some variation is present)
Which CNs “cross over”?
There are only two CNs that cross over
CN III has a partial
Trochlear (CN IV) has a full decussation
Trochlear emerges from the DORSAL aspect of the brainstem –> Will see CONTRALATERAL symptoms
Think of Spocter’s “naughty significant other” example… Strange but it works.
How does the alzheimer’s brain change?
Age-matched normal brain-note some
widening of sulci (gyri shrinkage)
Alzheimer’s- note widening of ventricles
And shrinkage of hippocampal structures
