8.1 Motor Cortex, Cerebellum and Basal Ganglia Flashcards
List 4 important extra-pyramidal structures and state the overall function of these
1) Thalamus
2) Basal Ganglia
3) Cerebellum
4) Brain stem
Function to ‘fine tune’ the signals
What are the 4 things our brain must do to allow movement?
1) Initial desire to move
2) Initiation
3) planning
4) programming
What 2 systems are involved in planning of movement and state what each does
1) Limbic system: this is the where our desire to move originates
2) Prefrontal/premotor and supplementary motor cortex: this is where our attention, understanding and planning of movement occurs
What structure is responsible for Execution of movement?
Where do these signals travel to?
Primary motor cortex: sends direct signals to spinal cord
What 4 important structures comprise the limbic system?
Explain the role of each
1) Amygdala: emotion
2) Hippocampus: short term memory
3) Thalamus: rely net output of circuit to cortex
4) Hypothalamus: homestatis
How does the Limbic system communicate with the pre-frontal cortex?
Via Cingulate gyrus
From the motor cortex, where do signals pass through to generate a response
motor cortex ➞ thalamus ➞ pyramidal system ➞ lateral corticospinal tract
The basal ganglia and the cerebellum are both considered _________ structures
subcortical
What is the specific role of the basal ganglia and the cerebellum
Basal ganglia: fine tune (make the decision regarding correct vs incorrect response)
Cerebellum: coordinate movement (corrects and checks the movement choosen by the basal ganglia)
What tract is the ‘chief organiser and executor of motor function’
Is this Pyramidal or Extrapyramidal?
Corticospinal tracts: travel through the pyramids of medulla oblongata and is therfore a pyramidal tract
What 4 tracts comprise the Extrapyramidal tract
Rubrospinal
Vestibulospinal
Reticulospinal
Tectospinal
(remember the basal ganglia and cerebellum are considered ‘extrapyramidal structures’ NOT tracts)
Are Extrapyramidal or Pyramidal responsible for movements beyond voluntary control
Extrapyramidal
List 4 signs seen in an UMN lesion and explain the reason for each
1) Weakness/ spastic paralysis: AP cant propagate from UMN to LMN
2) Increased tone: spasticity caused by overexaggerated stretch reflex
3) Increased tendon reflexes (Hyperreflexia): caused by lack of descending inhibitory pathways
4) Extensor plantars (Babinski sign): because normally extension is inhibited but when UMN is damaged, inhibition is blocked resulting in extension of great toe
List 5 signs seen in an LMN lesion and explain the reason for each
1) Weakness: due to loss/decreased innervation to effector muscles
2) Decreased tone: since tone is partially dependent on the monosynaptic reflex arc that links muscle spindles to LMN
3) Loss of tendon reflexes: due to loss/decreased innervation to effector muscles
4) Wasting and atrophy of muscles: due to damage to alpha motor neurones = lack of trophic factors needed by the muscles fibres
5) Fasciculations: spontaneous AP ➞ firing of the motor unit ➞ twitch
Define hyperkinesia and hypokinesia
Hyperkinesia: abnormal, involuntary movements
Hypokinesia: reduced movements
What will and will NOT be affected in an extrapyramidal lesions
WILL: Impair the regulation of voluntary movement
WILL NOT: affect the strength of movement (no atrophy)
What is a key clinical feature of extrapyramidal lesion and define this
Tremor: a rhythmic oscillatory movement that can occur at rest or on movement
Can be normal BUT abnormal may be benign essential tremor, intention tremor, resting tremor
Define Chorea and define Hemiballismus
Chorea: rapid irregular, unpredictable, involuntary muscle jerks (nearly always abnormal)
Hemiballismus: unilateral, usually violent, chorea
*** Signs of an extrapyramidal lesions
Define Dystonia
Excessive or inappropriate muscle contractions/spasm
*** Sign of an extrapyramidal lesions
Define Bradykinesia and what a progression of this is known as?
Bradykinesia is slowness of movement which can progress to akinesia which is absence of movement
*** Sign of an extrapyramidal lesions
Define Tics and state 2 instances when they may occur
Fleeting purposeless actions
Can be normal… or may occur in times of stress or in childhood
*** Sign of an extrapyramidal lesions
Define Athetosis
Involuntary slow writhing movements hands or face
*** Signs of a extrapyramidal lesions
What is Tardive dyskinesia and what is it assciated with?
An iatrogenic cause of parkinsonism-like effects which has features including oral grimaces, sucking, chewing
Associated with medication
*** Sign of an extrapyramidal lesions
Label the image of the basal ganglia
What is indicated on the image and what is important about this structure?
Substantia nigra is where our dopanergic neruons are located (dopamine = NT impt in the motor pathway)
What comprises the basal ganglia (broadly speaking)?
Consist of multiple deep, sub-cortical nuclei
What 5 specific structures comprise the basal ganglia?
- Caudate
- Putamen
- Globus pallidus
- Substantia nigra (midbrain)
- Subthalamic nuclei (ventral thalamus)
What are the 4 functions of the basal ganglia?
1) Smooth motor movements
2) Amplitude and velocity
3) Posture control
4) Resting muscle tone
How does the Basal ganglia influence activity movement
Influences activity movement by regulating activity of UMNs (NOTE: these do not project directly onto LMNs)
List 3 problems that may occur due to defects of the basal ganglia
1) Cause inability to control movement
2) Problems when switching between commands
3) Problems initiating and terminating movements
What is the name of the input region on the basal ganglia where projections from the cerebral cortex enter?
corpus striatum (= caudate + putamen)
What 2 circuits are formed by projections from the CC to the basal ganglia and where do these feedback to?
Direct and indirect circuits which feedback to the cerebral cortex via the thalamus
What does GPi and GPe stand for?
Globus Pallidus Internal and Globus Pallidus External
Briefly describe the direct circuit
Excitatory…. release neurons from inhibition
Briefly describe the Indirect circuit
Inhibitory: supress neurons further – a brake on the system
Compare the Striatum vs Cortex in terms of their main NT’s
Striatum is a complete GABA structure (extremely inhibitory)
Cortex is very glutamatergic (very excitatory)
What important NT acts as a filter and decides whether the system progresses or not?
Where does this act?
DOPAMINE! acts on the Striatum
Describe the response of the GPi to dopamine and where it will be released
If we want a movement to progress, we require dopamine to ‘inhibit the inhibitor’ (GPi), making it active.
It does this by simultaneously activating and inhibiting the direct and indirect ganglion.
Dopamine will exist only in the synapse that corresponds to the area of the striatum with the movment we want and when released the GPi is activated leading to subsequent activation of the thalamus and striatum
Compare the direct and Indirect pathways in terms of GABA released
In the direct pathway LESS GABA is released by the GPi (allowing movement)
In the indirect pathway MORE GABA is released from the GPi (not allowing movement)
What is the role of the cerebellum?
Like the basal ganglia it influences movements by interaction with UMNs rather than projecting directly to LMNs. It functions to correct and check (fine tune) the movement chosen by the basal ganglia
It is involved in feedback loops with the motor cortex and brain stem nuclei
What is the anatomical location of the cerebellum?
In the Hindbrain, it is infratentorial (below the tentorium cerebelli) in the posterior fossa
How does the cerebellum connect to the brainstem?
Connects to the brainstem (pons and medulla) via 3 peduncles (superior, inferior and middle)
How are the 2 hemispheres of the cerebellum joined?
What is the function of this structure and what is its clinical relevance?
Joined in the middle by the vermis
The vermis determines balance and hence degeneration of the vermis is seen in chronic alcoholics
Describe the outer and inner cerebellum, incl what the 2 predominant cell types found here?
Outer cerebellar cortex and subcortical cerebellar nuclei
The predominant cell types are purkinje and granule cells
What is the specific name given to the white matter of the cerebellum?
arbor vitae
List 4 specific functions of the cerebellum
1) Coordinates smooth skeletal muscle movements
2) Balance
3) Learning and memory
4) Processes sensory information to monitor the course of movement/ feedback
List some structures where the cerebellum recieves input from
Cerebral cortex, brainstem, ascending pathways, joint position sense, muscle length/tension etc…
What 3 structures do outputs from the cerebellum travel to?
To brain stem nuclei, thalamus and cerebral cortex
List 4 important signs seen is a patient with cerebellar dysfunction and explain each
1) Dysdiadochokinesis: inability to perform and sustain a series of repeated movements
2) Ataxia: gross incoordination of movements (gait /rebound
3) Slurred speech: speech may be imprecise slow and distorted
4) Pass pointing (dysmetria): the patient overshoots when touching the examiners finger
Why does Pass pointing (dysmetria) occur in cerebellar lesions?
In cerebellar lesions (ie. stroke) when patient tries to touch nose then your finger, they will overshoot when they try to touch your finger.
When they try and fix the overshoot they will overcorrect etc… (pendulum movement)
This overcorrection is caused by the basal ganglia. As the cerebllum is not fuctioning correctly the basal ganglia takes over. However, because it cannot do real time-feedback and cannot process responses in the same way the cerebellum can it leads to dysmetria
