The Control of Movement - Supraspinal Control (Prof. Yeo) Flashcards
What are the 3 descending motor pathways classified by Kuypers in 1981 ?
What do they control ?
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.
What are the main ascending sensory pathways of the spinal chord ?
The dorsal columns, the spinothalamic tracts and the spinocerebellar tracts.
What kind of info is carried by the dorsal columns ?
Proprioception, light touch information to the dorsal column nuclei of the medulla, then crossing to contralateral thalamus and on to contralateral somatosensory cortex.
What kind of info is carried by the spinothalamic tracts ?
Higher threshold touch, nociceptive and temperature information crosses in the spinal cord and projects to contralateral thalamus and on to contralateral somatosensory cortex.
What kind of info is carried by the spinocerebellar tracts ?
Proprioception, light and higher threshold touch, nociception and temperature through spinocerebellar tracts to the ipsilateral cerebellum.
What are the three major brain regions controlling mvnt ?
The motor cortex, the cerebellum and the basal ganglia.
What are the three major different regions of the motor cortex ?
The primary motor cortex (M1), the Pre-Motor Cortex (PM) and the Supplementary Motor Area (SMA).
Where is M1 and how are the muscle groups controlled mapped in it ?
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.
From which regions does M1 receive inputs ?
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.
How many M1 pyramidal neurons control distal muscles ?
Proximal muscles ?
Small clusters for distal muscles (e.g.fingers); broader, less dense clusters for proximal muscles.
How is muscle force and direction of movement coded for by M1 pyramidal cells ?
Firing frequency codes muscle force. Population firing (vector sum of directional tuning properties of all cells firing) codes overall direction of movement.
Where do PM and SMA project and from where do they receive inputs ?
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.
What are the PM and SMA important for ?
How are they distinct in their fcts ?
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).
In the M1 mapping a 1:1 projection ?
Definitely not. There is convergence from M1 pyramidal cells upon spinal motoneurons, which makes compensation possible (e.g. in the case of a stroke).
What is the major input to M1 ?
The Ventral Lateral Nucleus (VLN).
What is the major input to PM and SMA ?
The Ventral Anterior Nucleus (VAN).
Where is the cerebellum situated ?
How is it structured ?
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.
What 3 main sagittal divisions are recognized in the cerebellum ?
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.
What nuclei make up the cerebellum and how are they connected ?
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.
What are mossy fibres (MFs) ?
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.
What are climbing fibres (CFs) ?
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).
Are outputs of the cerebellum directly or indirectly involved in mvnt ?
Indirectly !
The cerebellum outputs are to other motor regions, not directly to the spinal chord.
What kind of info does the cerebellum receive ?
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.
What does the fluculo-nudular lobe control (most caudal region) ?
Balance and eye mvnts.
