The Control of Movement - Supraspinal Control (Prof. Yeo)

Question 1

What are the 3 descending motor pathways classified by Kuypers in 1981 ?
What do they control ?

Answer 1

Group A (ventromedial) pathways: particularly associated w/ neck and axial muscles, so especially concerned w/ posture and balance
Group B (lateral) pathways: mostly influence the MNs for distal muscles
Corticospinal Tract (CST) = 2 components:
- lateral CST terminates on distal muscle MNs
- ventral CST terminates on axial and proximal muscle MNs.

Question 2

What are the main ascending sensory pathways of the spinal chord ?

Answer 2

The dorsal columns, the spinothalamic tracts and the spinocerebellar tracts.

Question 3

What kind of info is carried by the dorsal columns ?

Answer 3

Proprioception, light touch information to the dorsal column nuclei of the medulla, then crossing to contralateral thalamus and on to contralateral somatosensory cortex.

Question 4

What kind of info is carried by the spinothalamic tracts ?

Answer 4

Higher threshold touch, nociceptive and temperature information crosses in the spinal cord and projects to contralateral thalamus and on to contralateral somatosensory cortex.

Question 5

What kind of info is carried by the spinocerebellar tracts ?

Answer 5

Proprioception, light and higher threshold touch, nociception and temperature through spinocerebellar tracts to the ipsilateral cerebellum.

Question 6

What are the three major brain regions controlling mvnt ?

Answer 6

The motor cortex, the cerebellum and the basal ganglia.

Question 7

What are the three major different regions of the motor cortex ?

Answer 7

The primary motor cortex (M1), the Pre-Motor Cortex (PM) and the Supplementary Motor Area (SMA).

Question 8

Where is M1 and how are the muscle groups controlled mapped in it ?

Answer 8

M1 is in the precentral gyrus. Layer V pyramidal cells project long axons down the corticospinal tract to contact spinal motoneurons (MNs) directly (about 5%) and the rest to spinal interneurons. Different muscle groups are controlled by different parts of M1 - face and upper body by lower (ventrolateral) parts of M1, lower limbs by upper (dorsomedial) parts.

Question 9

From which regions does M1 receive inputs ?

Answer 9

Via the thalamus receives inputs from the dorsal column systems, spinal cord and cerebellum. Receives cortico- cortical connections from somatosensory cortex, PM cortex and SMA.

Question 10

How many M1 pyramidal neurons control distal muscles ?

Proximal muscles ?

Answer 10

Small clusters for distal muscles (e.g.fingers); broader, less dense clusters for proximal muscles.

Question 11

How is muscle force and direction of movement coded for by M1 pyramidal cells ?

Answer 11

Firing frequency codes muscle force. Population firing (vector sum of directional tuning properties of all cells firing) codes overall direction of movement.

Question 12

Where do PM and SMA project and from where do they receive inputs ?

Answer 12

PM and SMA project to M1. Both receive various thalamic inputs. Via thalamus, PM has strong inputs from the cerebellum. SMA has strong reciprocal connections with the basal ganglia.

Question 13

What are the PM and SMA important for ?

How are they distinct in their fcts ?

Answer 13

Both PM and SMA are important for the planning of movements.
PM is involved with planning movements based on external (especially visual) cues.
SMA is involved with planning movements based on internally generated strategies (e.g. learned sequences of movements).

Question 14

In the M1 mapping a 1:1 projection ?

Answer 14

Definitely not. There is convergence from M1 pyramidal cells upon spinal motoneurons, which makes compensation possible (e.g. in the case of a stroke).

Question 15

What is the major input to M1 ?

Answer 15

The Ventral Lateral Nucleus (VLN).

Question 16

What is the major input to PM and SMA ?

Answer 16

The Ventral Anterior Nucleus (VAN).

Question 17

Where is the cerebellum situated ?

How is it structured ?

Answer 17

It lies above the 4th ventricle.
The outer, grey matter or cortex is convoluted into many folia. The anterior lobe is most rostral, followed by posterior lobe and flocculo-nodular lobe more caudally.

Question 18

What 3 main sagittal divisions are recognized in the cerebellum ?

Answer 18

Three major sagittal divisions are recognized. The central longitudinal strip of cortex is the vermis. On each side, the vermis is divided from the lateral cerebellar hemispheres by the narrow pars intermedia.

Question 19

What nuclei make up the cerebellum and how are they connected ?

Answer 19

The cerebellar cortex overlies a collection of nuclei - the cerebellar deep nuclei. These receive inputs from the cortex and project out to the thalamus, red nucleus and brainstem. From medial to lateral they are the fastigial, interpositus (in man, this is subdivided into the globose and emboliform nuclei) and dentate nuclei. They receive inputs from vermis, pars intermedia and hemispheres, respectively.

Question 20

What are mossy fibres (MFs) ?

Answer 20

MFs are fibers that arise from the spinal cord (conveying prorioceptive feedback), pontine nuclei (largest source of cerebellar afferents - conveying cerebral cortical information and copies of motor instructions before they pass down the spinal cord) and reticular nuclei (that receive ascending and descending information).
They synapse on granule cells (most numerous cell in entire brain) which send up parallel fibres to the Purkinje cell - the output cell of the cerebellar cortex. Each Purkinje cell receives up to 250,000 parallel fibre inputs.

Question 21

What are climbing fibres (CFs) ?

Answer 21

These a fibers that arise exclusively from the inferior olive (IO). IO receives variety of inputs - from spinal cord, dorsal column nuclei, cerebral cortex, red nucleus. Each olivary cell axon branches to give approx 10-15 CFs. These terminate with great precision on a Purkinje cell within the cortex and, via a collateral to the cerebellar nuclei, to give very detailed maps. Each Purkinje cell receives only one olivary climbing fibre input (though with multiple synapses from the same fibre).

Question 22

Are outputs of the cerebellum directly or indirectly involved in mvnt ?

Answer 22

Indirectly !

The cerebellum outputs are to other motor regions, not directly to the spinal chord.

Question 23

What kind of info does the cerebellum receive ?

Answer 23

The cerebellum receives copies of movement plans from other structures (e.g. motor cortex) - internal feedback or efference copy. It receives external feedback or reafference about sensory consequences of movement. It uses these types of information to adjust motor outputs for the fine control of movements and to maintain calibration of reflexes.

Question 24

What does the fluculo-nudular lobe control (most caudal region) ?

Answer 24

Balance and eye mvnts.

Question 25

What do the vermis and pars intermedia control ?

Answer 25

The vermis and pars intermedia adjust the ongoing mvnt of the body.

Question 26

What do the cerebellar hemispheres control ?

Answer 26

They coordinate the planing of limb mvnts - they project in particular to PM cortex.

Question 27

How could the cerebellum be involved in motor learning ?

Answer 27

One important idea would involve modifications of parallel fibre to Purkinje cell synapses under the influence of climbing fibre instructions.

Question 28

What is hypotonus ?

Answer 28

The loss of muscle tone - reduced spindle discharge ?

Question 29

What is ataxia ?

Answer 29

Ataxia is loss of coordination.
It can lead to deficiencies in movement distance (dysmetria), velocity and rhythm of muscle contractions, loss of co-ordination between different muscle groups (asynergia) and postural abnormalities. Ataxia of trunk and legs leads to ataxia of gait. Ataxia of arms leads to decomposition of smooth movements with intention tremor.

Question 30

What id dysdiadochokinesia ?

Answer 30

Force and rhythm deficits.

Question 31

What is the Basal Ganglia (BG) ?

Answer 31

A collection of five nuclei: caudate, putamen (caudate and putamen are very similar in structure and function and are known collectively as the striatum), globus pallidus (internal - GPi - and external - GPe - segments), subthalamic nucleus (STN) and substantia nigra (pars reticulata - SNr - and pars compacta - SNc).

Question 32

Where does the BG nuclei receive inputs from ?

Answer 32

The BG nuclei receive inputs from the cerebral cortex and their outputs are back, through the thalamus, to prefrontal, SMA, PM and M1 cortex. Basal ganglia diseases (Parkinsons Disease, Huntington’s Chorea) produce severe and characteristic impairments of movement.

Question 33

What are the 2 main pathways interconnecting the BG ?

Answer 33

The direct and indirect pathway.
The direct pathway leads from cortex > striatum > GPi + SNr > Thalamus > SMA. The two inhibitory links lead to this pathway overall increasing motor output
The indirect pathway leads from cortex > striatum > GPe > STN > GPi + SNr > Thalamus > SMA. The three inhibitory links lead to this pathway overall inhibiting motor output

Question 34

What is the SNc role on mvnt control and how is this disrupted in Parkinsons disease ?

Answer 34

SNc modulates activity in both the direct and indirect pathways with dopamine inputs to the striatum. SNc dopamine inputs excite the direct pathway and inhibit the indirect pathway - both lead to increases in movement. In Parkinson’s disease, dopamine production in the SNc fails and the excitatory imbalance leads firstly to tremor and then to rigidity and lack of movement.

Question 35

What happens in Huntington’s chorea ?

Answer 35

Striatal cholinergic and GABA neurons degenerate in Huntington’s chorea, leading to increased and uncontrolled movements.

Question 36

Where else does the striatum receive inputs from ?

What are these separate regions of cells called ?

Answer 36

The striatum receives inputs from limbic cortex (which is involved in regulation of emotional behaviour) in separate islands of cells called strisomes. There may be important modulation of activity in the “motor loop” by activity in the “limbic loop” - an interface between motor planning and motor control.

Question 37

What are the lateral motor pathways and what do they control ?

Answer 37

The lateral pathways are the corticospinal and rubrospinal tracts, which control control fine, fractionated movements of the limbs and fingers

Question 38

What are the ventromedial motor pathways and what do they control ?

Answer 38

The vestibulospinal and tectospinal tracts control
posture of the head and neck.
The pontine (which is actually medial!) and medullary reticulospinal tracts control posture of the trunk and antigravity muscles of the limbs.