supraspinal/motor control Flashcards
what is supraspinal control
the way the brain influences spinal cord activity
what are groups of descending pathways
they are motor pathways;
ventromedial pathways: particularly associated with neck and axial muscles thus posture and balance;
ventrolateral pathways: mostly influence motorneurones for distal muscles
corticospinal and rubrospinal tracts control fine movements of limbs and fingers
describe the corticospinal tract
2 components:
lateral/ crossed CST: terminates on distal muscle motorneurones, the lateral CST decussates in the medulla
anterior/ direct CST: terminates on axial and proximal muscle motor neurones
describe the anatomy/ location of motor regions in the brain
primary motor cortex/M1 is in precentral gyrus (just in front of/ anterior to central sulcus), also identified as brodmann area 4,
premotor cortex is anterior to M1, also identified as brodmann area 6, made up of 2 parts; lateral part is premotor area (PM), the medial region is called the supplementary motor area
primary motor cortex and premotor cortex are major contributors to CST
what are inputs from brain to the motor cortex
thalamic input to primary motor cortex is via the ventral lateral nucleus
thalamic input to premotor cortex and supplementary motor area is via ventral anterior nucleus
how does the motor cortical regions project to different areas of the body
primary motor cortex: the most medial (central part) represents toes and lower limbs/ legs, as it goes more laterally it represents the trunk and then upper limbs, then hands and fingers and then the face. Very large amount of space devoted to hands, fingers and face
how do primary motor cortical neurones relate to their post synaptic neurones
motor cortex mapping is not a simple 1:1 projects; there are high levels of convergence from M1 pyramidal neurones upon spinal motor neurones (10s or 100s of pyramidal neurones influence a single spinal motorneurones, due to this convergence this means that mapping for M1 is not clear cut and that there is overlap
there is also divergence of M1 pyramidal neurones upon spinal motorneurones (the axons diverge and form multiple synapses at spinal motorneurones, often using interneurones between extensor and flexor motorneurones
what do neurones of primary motor cortex effect
primary motor cortex neurones code for muscle force, some fibres code for dynamic aspects(changes in level of force) (10%), some code for dynamic and static aspects (65%) and some code for just static aspects of the force (25%)
what are inputs/outputs of the premotor cortex and what are its functions
the premotor cortex influences both the motor cortex and corticospinal tract
the premotor area and supplementary motor area project to primary motor cortex
premotor area has strong inputs from the cerebellum via the thalamus
supplementary motor area has strong inputs from basal ganglia via the thalamus
premotor area is involved with planning movements based on external, especially visual cues
supplementary motor area is involved with planning movements based on internally generated strategies (e.g. learned sequences of movements)
what areas of brain are involved with the different parts of the timeline for movements
functional imaging shows primary motor cortex is active during simple flexion and sequenced movement tasks, supplementary motor area is active during movement tasks and during mental rehearsal of those tasks, SMA is involved with motor planning
what are inputs to the cerebellum
cerebellum receives lots sensory inputs, such as light touch, pain, temperature, proprioceptive info from muscle spindle and golgi tendon organs, coming from ascending spino-cerebellar pathways
cerbellum also receives vestibular inputs from semi-circular canal system, information containing head movement and acceleration
cerebellum receives copies of descending efferent inputs mainly corticospinal information
what does cerebellum do
cerebellum monitors progress of movements, since it receives input as to efferent outputs in the CST as well as what is happening to it may receive any discrepancies between the two, allowing for learning and modulation and improvement of movement
what are cerebellar outputs
no direct output from cerebellum to spinal cord,
cerebellar hemispheres influences the CST via the cerebellar nuclei which projects to ventrolateral and ventroanterior thalamus, providing input to primary motor cortex and premotor cortex (premotor area).
lateral cerebellum inputs into contralateral cerebral cortex particularly primary motor cortex and premotor cortex
medial parts of cerebellum project to the red nucleus to influence to rubrospinal system as well as projecting to the vestibular system influencing balance
the cerebellar hemispheres inputs to cerebral cortex decussate at superior cerebellar peduncles, cerebellar inputs to body also decussate downstream, so the right side of the cerebellum inputs to left cerebral cortex which inputs right side of the body
which different cerebellar regions effect control of movement differently
the flocculo-nodular lobe controls balance and eye movements
the vermis and pars intermedia adjust ongoing movement of the whole body and posture
the cerebellar hemispheres help coordinate the planning of limb movements, they project in particular to the premotor area
what is effect of cerebellar lesions
major effect is ataxia; loss of co-ordination characterised by deficiencies in movement distance (dysmetria), velocity and rhythm of muscle contractions. Loss of co-ordination between different or agonist/antagonist muscle groups (asynergia) and postural abnormalities
ataxia of trunk and legs leads to ataxia of gait
ataxia of arms leads to loss of smooth movements resulting in intention tremor
hypotonus: loss of muscle tone
dysdiadochokinesia: force and rhythm deficits
cooling cerebellar nuclei disturbs agonist-antagonist interactions causing intention tremor
what is the mechanism of cerebellar control of movement
cerebellum receives copies of movement plans from other structures such as the motor cortex and from descending pathways such as CST, called efference copy (when it receives it from descending pathways), and internal feedback from proprioceptors.
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 by using discrepencies between efference copy and reafference
cerebellum is involved in motor learning involving modifications of parallel fibre to purkinje cell synapses under the influence of climbing fibre instructions
what are the basal ganglia
basal ganglia: collection of nuclei in the diencephalon and in the midbrain, function as a group
consist of caudate nucleus, the putamen (caudate nucleus+ putamen; the striatum), very similar in structure and physiology
globus pallidus has a external/lateral and internal/medial section
globus pallidus + putamen = lentiform nucleus
subthalamic nucleus is also important
substantia nigra: contains pars compacta and pars reticularis
describe the basal ganglia connections
striatum receives input from cerebral cortex such as premotor cortex and primary cortex as well as others and is the input for the basal ganglia
the GPI (internal globus pallidus) and pars reticularis are the output of the basal ganglia they send information to the thalamus which relays to cerebral cortex especially supplementary motor area and primary motor cortex
cortex provides excitatory input to striatum via glutamate
describe the direct pathway
direct pathway: striatum may then send information via GABA to the GPi and pars reticularis which then relays with GABA to thalamus and supplementary motor area, direct pathway provides inhibitory input to GPi and pars reticularis
since GPi/ pars reticularis input to thalamus is inhibitory, inhibitory input to it via direct pathway causes less inhibition of thalamus, which excites supplementary motor area
describe indirect pathway
indirect pathway: striatum otherwise may send to GPe via GABA which relays to subthalamic nucleus via GABA which relays to GPi and pars reticularis via glutamate, from then on it follows direct pathway, indirect pathway provides excitatory input to GPi and pars reticularis
input from subthalamic nucleus to GPi and pars reticularis is excitatory and so more inhibition to thalamus
what is role of dopamine in basal ganglia connections
dopamine may activate direct pathway from pars compacta but exciting D1 receptors in striatum, this is regulated by GABA to pars compacta from striatum
overall direct pathway is excitatory on movement, dopamine activates direct pathway and so increases movement
dopamine inhibits indirect pathway via inhibitory D2 receptors on cells that project to GPe
describe basal ganglia function
cortical excitation to striatum flows through both direct and indirect pathways, when excited thalamus activates SMA, helps make decisions about which movement to make as well as to make movement
how does basal ganglia malfunction relate to disease
hypokinetic basal ganglia disorders like parkinsons disease prevent movement initiation, due to loss of dopamine from pars compacta
hyperkinetic disorders such as ballism (damage to subthalamic nucleus) and huntingtons disease (degeneration of striatal cholinergic and GABA-ergic neurones) indicate that basal ganglia may normally filter out unwanted movement, indicates indirect pathway regulates/controls movement
