Brain Control of Movement Flashcards
1
Q
- What are descending spinal tracts & how many do we have?
A
- A tract is a whole bunch of axons which travel together. In the spinal cord, these tracts travel down in two pathways.
- The Lateral Pathway (2) = Corticospinal tract + Rubrospinal tract
- The Ventromedial pathway(4) = Tectospinal tract + Vestibulospinal Tract & Pontine reticulospinal tract + Medullary reticulospinal tract
2
Q
- What is the function of the Lateral Pathway in the spinal cord?
A
- Lateral pathway= responsible for conscious movement
- Lesions here = no arm/hand movement, paralysed on opposite side, lose fine motor skills (can’t write).
- The lateral pathway consists of 2 tracts which travel down the spinal cord
Corticospinal/ Pyramidal Tract: Right motor cortex -> midbrain -> medulla (decussation at pyramid) -> spinal cord as tract -> control opposite side
Rubrospinal Tract
Midbrain Red nucleus -> comes down as rubrospinal tract
3
Q
- What is the function of the Ventromedial pathway?
A
- The ventromedial pathway & lateral pathway is an important descending series of tracts coming from the brain to the spinal cord, which are responsible for motor functions.
- The ventromedial pathway is mainly responsible for posture and movement (the lateral pathway= conscious movement).
- It starts at the motor cortex -> brain stem -> then travels down as 4 tracts
4
Q
- Where does decussation take place in the spinal cords descending tract?
A
- Decussation is where tracts (bunch of axons) cross in the brain in order to provide motor functions to the opposite side of the body.
- In the lateral path decussation occurs at two spots:
- Corticospinal Tract: crosses @ Medulla in the medullary pyramid
- Rubrospina tract: crosses @ Medulla
- In the Ventromedial pathways: no crossing of axons occur in this pathway. Straight from cortex -> brainstem -> spinal cord
5
Q
- What regions of the cortex are considered to provide motor functions?
A
There are 2 main motor areas located in front of the central sulcus:
- Area 4 or M1= main motor cortex. It’s in front of the central sulcus.
- Area 6 is higher motor region. Its divided into a lateral (premotor area/PMA) and medial (supplementary motor area/ SMA).
(A somatotopic map of the precentral gyrus provides us with a ‘cortical homunculus’ which maps out innervation of muscle groups.)
Other areas of the cortex which are important for planning of movement includes:
-
Posterior Parietal contributions:
- Area 5: gets information from somatosensory regions 3, 1, 2
- Area 7: gets info from professional areas of the cortex (middle temporal area MT)
- Anterior Frontal lobe: abstract thoughts and planning of action and what happens after the action
6
Q
- What is the basal ganglia?
A
- Bunch of structures (5) responsible for choosing and initiating conscious movement -> projecting into the ventral lateral nucleus (Vlo) -> to provide info to Area 6 (an area of the cortex responsible for motor control):
- Striatum:
- Caudate Nucleus
- Putamen (excitatory)
- Globus pallidus
- Subthalamic nucleus
- Substantia Nigra
- Striatum:
7
Q
- How is the basal ganglia involved in movement?
A
- The basal ganglia provides excitation to the cortex
- The putamen gets excited first which
- Stops Globus pallidus
- Stops Vlo(nuclear group of ventral thalamus) from being inhibited (Vlo becomes active)
- Leads to the supplementary motor area being stimulated (Motor cortex= area 4/6-> comes down as lateral/ ventromedial pathways)
8
Q
- Which part of the motor cortex is responsible for starting movement
A
- Area 4 AKA M1/ primary motor cortex
9
Q
- What can happen if there is a defect in motor loop at the basal ganglia?
A
The basal ganglia is important for initiation of motor movement (-> ventral lateral nucleus -> Area 6 motor cortex-> descending pathway). Damage to this can lead to:
- Parkinsons: The striatum does not receive any dopamine (failed to be provided substantia nigra)
- No DA-> Thalamus stops looping motor info
- Defect: slow movement, Akinesia (hard to start), rigid, tremor at rest
- Tx: increase DA (Levadopa)
- Huntingtons: Less neurons in parts of basal ganglia (caudate nucleus, putamen and globus pallidus) + thalamus fails to provide info
- Less action of globus pallidus (means Vlo does not get told to stop) means thalamus doesn’t get told to slow down. = constant excitatory info being sent to cortex (frontal region)
- Symptoms: hyperkinesia, dyskinesia (can’t move), dementia, poor cognition, disordered personality
- Hemiballismus: when body moves dramatically on one side
10
Q
- What will damage to the cerebellum lead to?
A
- poor coordination (ataxia)
- joints cant move smoothly in simultaneous manner (dysnergia)
- bad at aiming (dysmetria)
11
Q
- Can you live without the cerebellum?
A
- Yes you can
- But mental impairment, bad movement, epilepsy and ICP can take place
- Brain plasticity (brain adaptation) can allow for mild symptoms
12
Q
- What are the 3 main parts of the cerebellum:
A
- Deep cerebellar nuclei: sends cortex info to the -> brain step
- Vermis: sends info to ventromedial pathway for posture + movement
- Hemispheres of Cerebellum: initiate movement of LIMBS (lateral pathway- conscious movement)
13
Q
- Where do motor loops occur @ cerebellum?
A
- Ventral lateral thalamus (Vlc) -> On lateral sides of cerebellum -> motor cortex -> corticopontocerebellar projection -> planned movements
14
Q
- Which pathway and specific tract is responsible for planned movement at the cerebellum?
A
- The lateral sides of the cerebellum will send info down the lateral pathway via the corticopontocerebella tract for planned movements
15
Q
Fill in the table on an action and their associations:
Walking
About to throw
Planning throw
Throw!
A
Walking
Ventromedial pathway (movement + posture)
About to throw (Strategy)
Neocortex (it’s apart of the cortex) -> ventromedial pathway
Planning throw
Parietal/ prefrontal cortex Area 6 (high motor area where prefrontal + parietal cortex join)
Throw!
- Initiation: basal ganglia activated
- Release antigravity muscles: SMA -> M1 activated -> corticopontocerebellar tract of lateral pathway tells CEREBRUM to activate muscles + cortex talks to reticular formation ( nuclei’s across brainstem )
- Contract= lateral pathway talks to motor neurons and tell them to
- Strategy= neocortex + basal ganglia of forebrain
- Tactics= Motor cortex + Cerebellum
- Execution (lowest level)= brain stem + spinal cord
- Sensory info = posterior parietal and prefrontal cortex
