CNS Unit 11 Cerebellum and Basal Ganglia Flashcards
Where does the Cerebellum receive sensory Information from?
Where does it send information back to?
From the brain and spinal cord about body position and movement (Rate, Timing and Force)
- Exerts it influence by sending information back to motor systems of the cortex and brainstem to correct the movement
What is the Main Role of the Cerebellum?
To detect any movement that deviates from the intended cortical commands
“Error detector-movement corrector”
What are the 3 Major Functions of the Cerebellum?
Synergy of Movement
- Properly grouping movements for the performance of selective response and also has a role in motor learning
Maintenance of Upright Posture
- With respects to one’s position in space
Maintenance of Tone
- Maintaining tension/firmness (ie tone) during a muscle contraction
What are the Functional Regions of the Cerebellum, what are their functions and what motor pathway influences them?
-
Lateral Hemisphere
-Function: Motor Planning for extremities
-Motor Pathways influenced: Lateral corticospinal tract -
Intermediate Hemisphere:
-Function: Distal Limb Coordination
-Motor Pathway Influenced: Lateral corticospinal tract -
Vermis and Flocculondular Lobe:
-Function: Proximal limb and Truck Coordination ; Balance and Vestibulo-ocular reflexes
-Motor Pathway Influenced: Anterior Corticospoinal tract, reticulospinal tract, vestibulospinal tract and tectospinal tract
(This is for prox. limb and trunk coordination)
Medial Longitudinal Fasciculus
(This is for balance and vestibulo-ocular reflexes)
What are the Deep Cerebellar Nuclei, and what is their function?
“Dont Eat Greasy Food”
- Dentate: Input from lateral regions. (This is the largest, its active just before voluntary movements, and works on our extremities)
- Emboliform: Input from intermediate regions
- Globase: Input from intermediate regions
- Fastigial: Input from medial regions (Often works together with the Vestibular Neclei, they tend to influence the vermis and flocculonodular lobes, they exert influence over the trunk)
- Vestibular Nuclei (Brainstem): Function in some ways like deep cerebellar nuclei, input from inferior vermis and flocculi
The Emboliform and Globase together make the Interposed Nuclei (These movements are active during and in relation to the movement, they work mainly on our limbs)
In the Cerebellum, what are two kinds of Synaptic Inputs?
- Mossy Fibers, these climb up and as they enter the molecular layer they bifurcate and turn into parallel fibers, become inverwoven with in Purkinje cells and thats how they synapse, these Purkinje cells send information down and out to our Deep Cerebellar Nuclei and Vestibular Nuclei
- Climbing Fibers, similar to mossy fibers
- Mossy Fibers receives input from Pontine nuclei and other sources
- Climing Fibers receives input from inferior olivary nucleus
What are the Principles of Cerebellar lesions?
- Ataxia is Ipsilateral to the side of the lesion
- Midline lesions cause unsteady gait (Truncal Ataxia) and eye movement abnormailites
- Lesions to lateral vermis cause limb ataxia (Appendicular Ataxia)
What are the Cerebellar Output Pathways?
Pathways from the cerebellum to the lateral motor systems and periphery are double crossed. (This is why deficits and coordination occur ipsilateral to the lesion)
- Lesions of the vermis dont cause unilateral deficits because medial motor systems influence the proximal trunk musculature bilaterally
What are the Cerebellar Input Pathways?
2 Major Input Pathways
- Pontocerebellar Fibers: Mostly from primary sensory and motor cortex and part of visual cortex (via corticopontine fibers). {Senses relayed from the pons to the cerebellum}
- Spinocerebellar Pathways (This has 4 tracts)
-Dorsal Spinocerebellar Tract (LE) and Cuneocerebellar Tract (UE): Unconscious proprioception of limb movements
-Ventral Spinocerebellar Tract (LE) and Rostral Spinocerebellar Tract (UE): Reflect the amount of activity of the inter-neurons in descending pathways
What are the 3 branches of Arteries that supply the Cerebellum?
- SCA
- AICA
- PICA
What are the S/S of a Cerebellar Artery Infarct?
- Vertigo
- Nausea and Vomiting
- Horizontal Nystagmus
- Limb Ataxia
- Unsteady Gait
- Headache
What would happen if there was an AICA infarct?
There would be unilateral hearing loss
AICA supplies internal auditory artery
SCA infarcts mostly involve what? What would this cause?
- Involves mostly the cerebellum and spare the lateral brainstem
- Ipsilateral ataxia with little/no brainstem signs
What would happen if the Cerebellum Swells?
“The Cerebellum would push laterally and down”
- This would compress the 4th Ventricle, which can lead to hydrocephalus and increased intracrainal pressure
- The brainstem can potentially herniate through the foramen magnum
What would be the S/S of Cerebellar Hemorrhage?
- Headache
- Nausea/ Vomiting
- Ataxia
- Nystagus
Sometimes initially presents only with GI symptoms of n/v (fatal gastroenteritis)
What would happen if there was a Large Cerebellar Hemorrhage?
- The 4th ventricle can become involved and can cause hydrocephalus, it can cause CN 7 palsy and impaired consciousness
- This may eventually cause brainstem compression and death
What are the Clinical Findings and Localization of Cerebellar Lesions?
- Ataxia (lack of order)
- Dysrhythmia (abnormal timing)
- Dysdiadochokinesia (abnormal rapid alternating movement, RAM)
- Dysmetria (abnormal trajectories)
What is the difference between Truncal Ataxia and Appendicular Ataxia?
- Truncal Ataxia: this is the result from lesions of vermis or the most medial part of the cerebellum, medial motor systems get affected which control our trunk in an upright position, particularlly while walking. These patients have a wide based unsteady gait
- Appendicular Ataxia: this is the result from lesions of the intermediate and the lateral cerebellum. This affects the lateral motor systems (Lateral corticospinal tract and rubrospinal tract), these deal with our extremities. These patient sometimes have an intention tremor
Lesions often involve both vermis and hemispheres, so truncal and appendicular ataxia can coexist in the same patient
What do lesions of the Cerebellar Hemisphere or Cerebellar Peduncles cause?
Ipsilateral Ataxia of the extremities
What can False Localization of Ataxia be caused by?
Lesions outside of the cerebellum that involve cerebellum input or output pathways
What are S/S of Cerebellar Disorders?
- Nausea/Vomiting
- Vertigo
- Slurred speech
- unsteadiness
- uncoordinated limb movement
- headaches on side of lesion
Use the Image
Going from lateral to medial, what are the structures of the Basal Ganglia? What are some non-BG structures that we may also see?
Non-BG structures:
- Insular Cortex: Most lateral structure
- Extreme Capsule
- Claustrum
- External Capsule
BG structures:
- Putamen (most lateral of BG)
- Globus Pallidus
- Internal Capsule
- Caudate Nucleus
- Thalamus
With the Basal Ganglia, describe the Direct Pathway.
- The cortex releases Glutamate, this is going to be very excitatory. (The striatum is going to be excited)
- Because the striatum is excited, its going to release GABA (which is inhibited)
- When GABA is inhibited, the GPi and SNr are inhibited. This will then not release anymore GABA to the Thalamus.
- This means that the Thalamus is not going to be inhibited
- Thalamus not inhibited (Disinhibited) = Movement
In other words, The Direct Pathway results in Movement
With the Basal Ganglia, describe the Indirect Pathway.
- The Cortex is going to release Glutamate, however the substantia nigra par compacta releases dopamine which is inhibitory
- Because of the the Striatum sends out an inhibitory GABA to the Globus Pallidus Externus segment, this then does not inhibit the Subthalamic nucleus
- This then causes the Subthalamic Nucleus to release Glutamate, which is going to excite the Globus Pallidus internal segment and Substantia nigra par reticularis
- GPi and SNr then release GABA which is inhibitory to the Thalamus
- When the Thalamus is inhibited, we dont move
In other word the Indirect pathway results in No or reduction movement
What are Gross Pathological Changes with Huntington’s Disease?
- On the right the Caudate Nucleus has degenerated to much, which leads to enlarged lateral ventricals
- The Sulci are also much deeper on the right, due to degeneration of the gray matter
