Week 8 Flashcards
What is the basal ganglia?
- sub-cortical “structure” (group of various distinct cell clusters i.e. ganglia/nuclei)
- part of the extrapyramidal system
What is the function of the basal ganglia?
modulate voluntary movement through facilitation or inhibition of signals descending from the motor cortex
The basal ganglia receives input from…
cortex (primary motor and frontal)
Does the basal ganglia have direct output to the spinal cord?
No
Where does the basal ganglia send output?
pre-motor area, supplementary motor area, primary motor cortex, frontal cortex (all via thalamus)
What are the 4 main nuclei in the basal ganglia?
- striatum
- globus pallidus (internal and external segments)
- subthalamic nucleus
- substantia nigra
The basal ganglia relays to…
the thalamus
Each nucleus in the basal ganglia is somatotopically organized. What does this mean?
neurons grouped by specificity of movement (e.g. direction, amplitude and velocity)
Which nuclei in the BG is the first to receive input from the motor cortex?
striatum
Which nuclei in the BG is the last stop before going to the thalamus?
globus pallidus internal
Is the pathway from MI to the striatum direct or indirect?
direct
The subthalamic nucleus receives input from the…
motor cortex
What neurotransmitters are involved in the basal ganglia?
GABA, glutamate, dopamine
What is GABA? Where does it come from in the BG? What is it’s action?
- gamma-aminonutyric acid
- GABAergic neurons
- action: inhibitory
Where does glutamate come from in the BG? What is it’s action?
- glutamatergic neurons
- action: excitatory
Where does dopamine come from in the BG? What is its action?
- dopaminergic neurons
- action: depends on the receptor it binds with (D1 or D2)
What are D1 receptors?
- excitatory
- involved in the direct pathway
What are D2 receptors?
- inhibitory
- involved in the indirect pathway
What is the direct functional pathway in the BG?
neural pathway involving the Basal Ganglia vital to the initiation and facilitation of voluntary movement
What is the indirect functional pathway in the BG?
works in conjunction with the direct pathway, functions to inhibit unwanted movement
Which nuclei within the basal ganglia can act as an excitatory nucleus?
substantia nigra
What is parkinson’s disease?
- progressive neurodegenerative disorder
- 1/100 individuals > 60 years of age
- incidence 1.5x higher in males than females
- life expectancy: 10-20 years after diagnosis
- no cure → treatments target symptom management
What are the 4 main motor symptoms of parkinson’s disease?
- resting tremor
- ridgdity (e.g. at joints)
- bradykinesia - slowness of movements
- “parkinsonian gait”
cannot initiate movement properly
What are lewy bodies? How are they involved in the pathophysiology of Parkinson’s?
- abnormal aggregates of protein that displace other cell components and disrupt cell function
- present within neurons in the substantia nigra
- leads to death of the neurons
What are the steps in the pathophysiology for Parkinson’s that we should know for this class?
death of dopaminergic neurons in the Sub. Nigra → reduced dopamine release in the BG → direct pathway cannot aid in initiation/facilitation of movement → movement symptoms of Parkinson’s disease
What nucleus within the basal ganglia contains dopaminergic neurons? Where does this nucleus project to within the basal ganglia?
Substantia Nigra projects to: 1. Striatum: dopamine transmission
2. subthalamic nucleus: inhibitory neurotransmitters sent back in negative feedback loop
What is the cerebellum?
- translates to “little brain”
- 10% of total brain volume but over 50% of total brain volume
- is our computer:
→ receives afferent (sensory) and efferent (motor) information
→ compares intention vs what happened
What are the three main functions of the cerebellum?
- maintenance of balance and posture
- coordination of voluntary movements
- motor learning
What is the cerebellum’s function of maintenance of balance and posture?
- important for making postural adjustments
- integrates sensory information relevant to balance & modulates information sent to motor neurons to control postural muscles
What is the cerebellum’s function of coordination of voluntary movements?
coordinates timing and force of different muscle groups to plan and produce smooth movements
What is the cerebellum’s function of motor learning?
- adapt and fine-tune motor commands to make accurate movement
- trial-and-error process
What is the cerebellum anatomy?
- similar to the cerebrum, the cerebellum has two symmetrical hemispheres
- 4 symmetrical sections
When considering function, the cerebellum can be divided into 4 symmetrical sections. What are they?
- hemisphere
- vermis
-intermediate zone - flocculonodular lobe
What are the 3 pathways of the cerebellum?
spinocerebellar, cerebrocerebellar, vestibulocerebellar
What is the spiniocerebellar pathway?
- location: vermis & intermediate zones
- integrates sensory & motor information
- motor coordination
What is the cerebrocerebellar pathway?
- location: lateral hemisphere
- involves cortical input
- planning and timing of movements
What is the vestibulocerebellar pathway?
- location: flocculonodular lobe
- involves vestibular nuclei input
- posture and vestibular reflexes
What is the cerebellum important for?
- planning smooth, coordinated movements (spinocerebellar and cerebrocerebellar pathways)
- balance control (vestibulocerebellar pathway)
How do we know what the cerebellum is important for?
through those with damage or loss of cerebellar tissue
What are the 4 main symptoms of cerebellum dysfunction?
- ataxia, dystermia, hypotonia, large amounts of sway
What is ataxia?
“A” not, without
“Taxis” order
- lack of coordination
- decomposition of movement
- jerky movement
What is dysmetria?
“dys” bad, difficult
“metry” to measure
- inability to make accurate voluntary movements
- overshoot/undershoot of movement
What does hypotonia mean?
“hypo” under, less
“tonia” tension, stretching
- decrease in muscle tone/resistance
What is efference?
motor command sent from motor cortex to body
What is an efference copy?
copy of motor command uses to update other brain regions on the action about to be performed
What is corollary discharge?
- signal created within the cerebellum → represents the re-afference we expect to get from a self-generated movement
- used to inhibit expected feedback from self-generated movement that may interfere with execution of a motor task (frees up cortical resources)
- if there is any unexpected afferent information we get from a voluntary movement → does not get inhibited and gets sent to cortex to update on unexpected information
Comparison occurs within the ____________
cerebellum
What is the first step in the cerebellum feedforward motor learning model?
- movement goal is sent to motor cortex
→ select appropriate motor plan based on previous experience (force, speed, direction of movement, correct MU recruitment, etc)
What is the second step in the cerebellum feedforward motor learning model?
- Efference (motor command) sent to effector muscles in the body
→ execute appropriate motor plan based on previous experience (force, speed, direction of movement, correct MU recruitment etc.)
- efference copy (copy of motor command0 sent to cerebellum to update on what is about to happen
- Efference (motor command) sent to effector muscles in the body
What is the third step in the cerebellum feedforward motor learning model?
- corollary discharge is produced by the cerebrum
→ created from efference copy
→ represents the expected sensory feedback we should get from executed movement
→ used to inhibit any response to self-generated movement that may interfere with execution of the motor task
- reafference is produced from the body
→ the actual sensory feedback we get from the executed movement
- corollary discharge is produced by the cerebrum
What is the fourth step in the cerebellum feedforward motor learning model?
- comparison of corollary discharge and reafference occurs in the cerebellum
→ expected vs. actual sensory information
→ expected and actual information match = successful movement execution
→ if they don’t match = unsuccessful execution & need to update cortex
What is the fifth step in the cerebellum feedforward motor learning model?
- cerebellum updates motor cortex about reafference information that didn’t match
→ adjust motor plan until desired movement is achieved
