Basal ganglia & Cerebellum

Question 1

What is the motor cortex made up of and where is it found?

Answer 1

Primary motor cortex (M1) - found on posterior part of frontal lobe.

Secondary motor cotex - found infront of primary motor cortex There are 4 cortical areas:
- Supplementary motor area (SMA)
- Cingulate gyrus
- Ventral premotor cortex
- Dorsal premotor cortex

NOTE: view image on notes!

Question 2

What is the function of the motor cortex (part of the cerebral cortex)?

Answer 2

1. Planning movement
2. Initiating movement

Question 3

Which side of the body does the primary cortex control?

Answer 3

Muscles on the opposite side of the body.

Question 4

What does the secondary cortex control?

Answer 4

Muscles on both sides of the body.

Question 5

What is the motor cortex homunculus?

Answer 5

Topographic representation of the body parts & its correspondents along the precentral gyrus of the frontal lobe.

NOTE: view diagram on notes- in purple!

Different to sensory homunculus!
- topographic representation of the body parts along the postcentral gyrus of the parietal lobe.

Question 6

What 4 structures make up the basal ganglia? Where are they found?

Answer 6

Basal ganglia = group of structures found deep w/in the cerebral hemisphere.
- one basal ganglia in each hemisphere

1. Striatum
   - Caudate nucleus
   - Putamen
2. Globus pallidus
3. Subthalamic nucleus - this structure modulates planned motor behaviour through its dopamine receptors.
4. Substantia nigra

NOTE: view diagram on notes

Question 7

What is the function of the basal ganglia?

Answer 7

• Receives excitatory input from motor cortex.
• Projects outputs to thalamus, spinal cord & back to cerebral cortex.
  -Allows planned movement to occur - it usually inhibits movement but it can reverse this. i.e. programming or tactics.
• Involved in motor memory.

Question 8

How do the basal ganglia allow movement to occur (3 pathways)?

Answer 8

1. Hyperdirect pathway
2. Direct pathway
3. Indirect pathway

Question 9

Describe the Hyperdirect pathway

Answer 9

The motor cortex initiates planned pathways

The Thalamus inhibits the motor cortex - we need to turn this inhibition off to make a movement.

1. The motor cortex sends a signal, glutamate, to Subthalamic nucleus (STN). Bypasses striatum.
2. STN sends glutamate to Globus pallidus
3. Globus pallidus releases GABA to inhibit the Thalamus
4. Inhibiting the thalamus stops inhibition of the motor cortex, so movement can occur.

NOTE: view diagram on notes!

Question 10

Describe the Direct pathway

Answer 10

1. Motor cortex sends glutamate signal to the Stratium (caudate nucleus & putamen).
2. The stratium releases GABA to inhibit Globus pallidus & Substantia nigra
3. The neurones from the Globus pallidus & Substantia nigra inhibit Thalamus
4. Allows the motor cortext to initiate planned behaviour

Note: view diagram on notes!

Question 11

Describe the indirect pathway

Answer 11

1. Motor cortex sends glutamate signal to Striatum.
2. Striatum has neurones that connect to the external globus pallidus.
3. The neurones from the external globus pallidus send inhibitory signals to the subthalamic nucleus, rather than directly to the thalamus (hence “indirect”).
4. Subthalamic nucleus sends neurones to globus pallidus & substantia nigra.
5. Globus pallidus & substantia nigra release GABA to inhibit thalamus.

NOTE: view diagram on notes

Question 12

Where is the cerebellum located?

Answer 12

Located at the back of the head.

Below the temporal & occipital lobes and above the brain stem.

NOTE: view diagram on notes!

Question 13

What is the function of the cerebellum?

Answer 13

• Identifies any errors in movement & corrects them
• Compares the intended output w/ sensory signals of what is actually happening.
• Involved in motor learning= foresee errors = faster & smoother movement.
• Balance control

Question 14

Name the 3 functional subdivisions of the cerebellum and their function.

Answer 14

1. Cerebrocerebellum - recieves input from cerebral cortex. - Planning movements & motor learning.
2. Spinocerebellum - recieves somatosensory input from the sensory cortex about limb position, touch& pressure.
   - Involved in error correction
3. Vestibulocerebellum- involved in balance & eye movements.
   - Recieves inputs from the vestinular system.

NOTE: view diagram on notes

Question 15

How is the cerebellum connected to the brainstem?

Answer 15

Connected by 3 pairs of peduncles:
- Superior peduncles - connects to midbrain.
- Middle peduncles - connects to pons.
- Inferior peduncles - connects to medulla oblongata.

The 3 cerebellar peduncles are how the cerebellum communicates w/ rest of the nervous system, by connecting the cerebellum to the brainstem.

Question 16

How does the cerebellum correct movement errors?

Answer 16

1. Cerebellum is informed of movement by motor cortex before it occurs.
2. Cerebellum processes sensory info from the muscle spindles & golgi tendon organs to generate an error signal
3. This is fed back to motor cortex & movement is adjusted.

Question 17

Summarise the function of the motor cortex, basal ganglia & cerebellum

Answer 17

Motor cortex (plans the movement) → basal ganglia (allows the movement to happen) → cerebellum (corrects movement & then allows the actual movement to occur).