L6 - Central Control of Movement

Question 1

What are the 2 descending motor tracts?

Answer 1

Lateral cortico spinal tract - for precise movements

Medial cortico spinal tract - for postural muscles

Question 2

Describe the medial cortico spinal tract

Answer 2

axons from many parts of the CEREBRAL CORTEX go through MIDBRAIN and MEDULLA, where sometimes the nerve fibres cross cover, split and go down both sides of the spinal cord.

Important for postural muscles - eg standing

Question 3

Describe the lateral cortico spinal tract

Answer 3

From PMC down to spinal cord, and cranial nerves (for facial movements)

Extra neurons join at red nucelus in midbrain, important for hand movements

passes through pyramids of medulla, crosses over to contralateral side of spinal cord.

Gives ability to do things on diff sides of body and controls extremeties and limbs

Question 4

What does the Posterior Parietal Cortex (PPC) do?

Answer 4

• one of the first areas active when planning a movement
• receives info about the location of items (Eg. where our limbs are located) in space (controls aim)
• passes this to the prefrontal cortex
• when stimulated, people reported thinking about doing something

Question 5

What does the Prefrontal Cortex (PFC) do?

Answer 5

• Stores sensory information and considers possible outcomes once movement begins
• creates ACTION PLAN
• important for inhibiting movements
• damage here results in illogical, disorganised movements - eg. putting toothpaste cap on toothbrush
• passes onto supp. motor cortex and premotor cortex for fine tuning the action plan that has been generated

Question 6

What does the Premotor Cortex do?

Answer 6

• learning and completing complex movements
• MODIFIES AND IMPROVES
• receives non-arbitrary and arbitrary information

arbitrary - when i clap my hands you jump

non arbitrary - where arm is located (PPC), and the planned action (PFC)

Question 7

What does the Supplementary Motor Cortex (SMC) do?

Answer 7

• Sequences of movements. eg. serving in tennis
• inhibiting habitual movements, like not going to a lecture that’s usually scheduled
• TMS interference lead to forgetting the sequence

Question 8

What is the process of planning movement?

Answer 8

1. Start thinking about it in the posterior parietal cortex, where it receives info from visual and auditory cortices, vestibular system, somatosensory system etc.
2. passes onto the PFC to plan
3. supp and premotor cortex to fine tune
4. to the primary motor cortex to execute!!!!!

Question 9

When is the decision to move made?

Answer 9

• decided 200msec before movement

motor cortex showed readiness potential 500msec before movement, before they even decided

• another study found that they reported the decision at the same time they actually moved, however PFC and PPC active 7-10 seconds prior.

we become aware of the decision late in the process.

Question 10

What is the timeline for voluntary movements?

Answer 10

7-10 secs - PPC active

2-3 secs - SMC Active

0. 5 secs - Evoked potential in PMC
1. 2 secs - Decision is conscious

0 secs - movement

although not that applicable in the real world b/c they’re sitting expecting and waiting to move

Question 11

What is the basal ganglia and what is it important for?

Answer 11

• large group of structures in forebrain that forms loops w/ motor regions.

inputs - PMC + Somatosensory cortex
outputs - PMC, SMC Premotor C and brainstem

important for inhibition of movement and self initiated movement (take plans, amplify or inhibit)

Question 12

How does inhibiting a movement occur?

Answer 12

PFC and basal ganglia are activated while preparing to inhibit a movement

this is poor before age of 5 due to underdeveloped PFC

Question 13

Basal ganglia in autism?

Answer 13

Basal ganglia is structurally altered in autism, affecting gross motor skills (clumsy, uncoordinated, awkward movements).

Can see this early in childhood.

Gait analysis and head lag - they don’t hold their head up.. early signs of basal ganglia abnormalities.

Question 14

What is the cerebellum important for?

Answer 14

• originally thought for balance and coordination
• also found to be important for rapid, repeititve movements where aim is important
• continuous movements are unaffected by cerebellar damage

has multiple zones, lateral zone damage = movement no longer flows. decomposition of movement

Question 15

What is the lateral zone?

Answer 15

A zone in the cerebellum.
it takes info from the PMC, works out how much each muscle needs to move to create desired motion and passes info back to PMC

damage = decomposition of movement

Question 16

What have studies found about motor imagery?

Answer 16

• imagining a movement activates SMC, PPC basal ganglia and cerebellum, just like in the early stages of motor control
• imaginging a demanding task increases repiration and cardiovascular and muscles increase acitivty
• if imagine performing a task to exhaustion, then muscles involve fatigue more quickly