Motor 2

Question 1

How is direction of movement encoded by our neurons?

Answer 1

Lots of neurons fire for a movement and they have preferred directions for which they will fire stronger.

So the overall movement direction is population vector based on the integrated activity of lots of neurons.

Question 2

Explain the concept of predictive posture?

Answer 2

You spinal tracts are involved in feedback and feed forward systems to correct and predict postural instability:

• Vestibulospinal acts as feedback, detecting instability and correcting for it
• Reticulospinal carries info from the reticular formation to stablize for a movement before you make it (Feed Forward)

Question 3

What are the symptoms of UMN damage?

Answer 3

• Spinal Shock (Spinal hypotonia due to loss of cortical input)
• Babinski sign (Plantar extension instead of flexion)
• Spasticity (increased muscle tone, hyperreflexia & clonus due to loss of UMN suppression of LMNs)
• Loss of fine finger movements

Question 4

List the basal ganglia?

Answer 4

Input = Caudate nucleus and putamen

Output = Globus Pallidus & Substantia Nigra

(Anatomically the globus pallidus and putamen together form the lentiform nucleus)

Question 5

Whats the function of the basal ganglia?

Answer 5

They’re involved in intitiating movements.
This occurs as part of a positive feedback loop.
Basically they focus widespread cortical activity from the somatosensory, premotor and motor parts of the cerebrum to the supplementary motor area.
Its believed the GO signal for a movement is when the Basal Ganglia boost the Supplementary Motor Area (SMA) beyond a certain threshold

Question 6

Explain the process by which the Basal ganglia boosts SMA activity:

Answer 6

This is known as the direct pathway

• Medium spiny neurons in putamen excited by signals from cerebrum motor cortices
• Putamen inhibits GPinterna & the Substantia nigra
• GPinterna & SN then STOP inhibiting the Thalamus’ VLo Neurons
• Thalamus’ VLo neurons are free to excite the SMA

This is the process for body movements, the process for eye movements is basically the same except the caudate nucleus rather than the putamen is used

Question 7

If the SMA is boosted to enact an action by the basal ganglia Direct Pathway. What does the indirect pathway do?

Answer 7

IT suppresses competeting or innapropriate actions

• Striated nuclei (Caudate/putamen) inhibit the GPexterna
• GPexterna ceases inhibiting the STN, SN & GPinterna
• STN excites GPinterna & SN (STN also recieves excitatory fibres direct from the motor cortex)
• GPinterna & SN inhibit the VLo
• Thus the VLo cant boost the SMA
• innapropriate actions are inhibited

Question 8

Name two disorders of the basal ganglia?

Answer 8

Parkinson’s

Huntington’s

Question 9

What is the function of the cerebellum in movement?

Answer 9

Fine Tuning complex movements
There’s a cortico-pontine-cerebellar projection through which the cerebellum passes instructions on direction, timing and force of movements. Making use of motor learning stored in the cerebellum.

Question 10

So what would happen with a cerebellar lesion

Answer 10

Uncoordinated inaccurate movements (ataxia)

This can also be caused by alcohol depressing the cerebellum