motor systems Flashcards
describe the 3 major types of movement
- SIMPLE PATTERN REFLEXES
- automated, unlearned and stereotyped (predictable)
- involve spinal cord circuits ONLY i.e. no cortical input
- driven by sensory stimulus - COMPLEX POSTURAL ADJUSTMENTS
- flexible and goal-orientated reflexes, not stereotyped
- mostly goal-orientated, therefore require cortical input
- involve spinal cord & supraspinal centers (cerebellum / brainstem [extrapyramidal system]) - VOLUNTARY MOVEMENT
- involve spinal cord, brainstem, & motor cortex
- more CNS areas involved
difference between upper and lower motorneurons
describe the effect resulting from lesions of these motorneurons
UPPER MOTORNEURONS (UMN):
- first order neurons
- cell bodies ABOVE supraspinal connections
- cortical motorneurons of motor tract = pyramidal tract
- motoneurons of brainstem nuclei = red nucleus, tectum, reticular formation, and vestibular nuclei)
- —–> lesion in UMNs results in muscle spasticity. reflexes and muscle tone still exist, muscle tone can even be increased
LOWER MOTORNEURONS (LMN):
- second order neurons
- motorneuons from cranial nerves in brain stem
- alpha + gamma motorneurons from spinal anterior horn
- —–> lesion in LMNs results in flaccid paralysis as the connected skeletal muscle receives no input from cortex
where do alpha motorneurons of the spinal cord receive input?
- pyramidal (motorneurons of cortex) + extrapyramidal (motorneurons of brainstem) tracts
- proprioceptive muscle sensory
- spinal interneurons (part of spinal circuitry)
alpha motorneurons convey this info to skeletal muscle to initiate movement
describe the organisation of motorneurons in the spinal cord
include examples
cerviacal and lumbar levels of spinal cord have the lateral horn
this lateral horn contains motor neurons
medial + ventral areas innervate proximal limbs
lateral + dorsal areas innervate distal limbs
examples:
1) motor neurons for foot contained in dorsal portion of lateral horn (distal = dorsal + lateral)
2) flexors located medially
3) extensors located ventrally and laterally
briefly describe the difference between medially / laterally located motor systems
medial:
- mostly extrapyramidal tracts
- phylogenetically older than the lateral descending motor system
- controls coordinated whole-body postural and orienting movements
lateral:
- lateral corticospinal tract
- phylogenetically younger than other tracts, therefore highly developed
- movement of limbs with emphasis on fine motor control of distal limbs
describe the organisation of the motor cortex
what is the direction of information flow?
primary motor cortex: located on pre-central gyrus
premotor cortex: rostral to pre-central sulcus, LATERAL region of hemispheres
supplementary cortex: rostral to pre-central sulcus, MEDIAL region of hemispheres.
frontal eye field: rostral to premotor cortex
broca’s area (motor speech): rostral to pre-central sulcus, located on opecular and traingular parts of inferior frontal gyrus
INFO FLOW: prefrontal cortex (strategy) ---> premotor cortex (tactics) ---> supplementary cortex (tactics) ---> primary motor cortex (execution)
describe the functional organisation of the prefrontal cortex
LATERAL PFC: rational thinking, planning, problem solving
MEDIA PFCL: sustain attention, detect errors in own social conduct
ORBITAL PFC: control emotional behaviour, predicts behavioural response when planning actions
all areas are interconnected and work together
describe the anatomy and function of supplementary motor cortex
ANATOMY:
- located anterior to pre-central sulcus but located on medial aspects of hemisphere
- middle association complex
- contributes to pyramidal pathway
FUNCTION:
- learning sequence movements
- bilateral coordination (particularly of upper limbs)
- stores skilled memory (know-how)
- mental rehearsment of movements
- initiates movement via internal cues (self-generated
- works closely with basal ganglia
describe the anatomy and function of premotor cortex
ANATOMY:
- located anterior to pre-central sulcus but only on lateral aspects of hemisphere
- middle association complex
- contributes to pyramidal pathway
FUNCTION:
- integrates sensory info into motor plans
- anticipates voluntary movement to coordinate on-going movements
- reacts to externally delivered cues
- works more closely with the cerebellum
what is the result of lesions of the supplementary and premotor cortices?
lesions of the supplementary and premotor cortices causes APRAXIA
inability to execute a practiced motor function
inability to imitate movement
muscle still functions normally
pyramidal pathway
- prefrontal cortex
- secondary motor cortices: supplementary motor cortex + premotor cortex —> giant pyramidal cells in cortical layer V of pre-central gyrus
- primary motor cortex
- travels through corona radiata to enter pyramidal pathway (conscious movement)
5.
a) corticobulbar tract goes to cranial nerve nuclei in brainstem via genu of internal capsule. innervates muscles of head and face via cranial nerves
b) corticospinal tract goes through post. limb of internal capsule to alpha-motorneurons in spinal cord. innervates skeletal muscle of body via spinal nerves
what type of fibres exist in the pyramidal tract?
projection fibres, both afferent and efferent
describe the result of various lesion in the pyramidal tract:
1) in the primary motor cortex
2) in the SMC and PMC
3) in the primary sensory cortex
1) lesion in primary motor cortex
- –> leads to paresis (muscle weakness)
- –> upper motor neurons damaged
- –> muscle does not become completely flaccid as lower motor neurons are intact
2) lesion in secondary motor cortices
- –> leads to apraxia (not paresis)
- –> lack of skilled movement
3) lesion in primary sensory cortex
- –> interneurons and neruons of post. horn of spinal cord modulate incoming sensory information to correct ongoing movement
- –> leads to degeneration of motor actions
- –> cannot use sensory feedback to correct movement
describe the 3 sub-structure of the brainstem and what pathways they contain
1) TECTUM (roof):
- most posterior part
- composed of superior + inferior colliculi
- no pathways pass through i.e. only terminating / originating pathways
2) TEGMENTUM (floor):
- anterior to cerebral aqueduct
- contains all brainstem nuclei apart from pontine
- contains ALL ascending pathways that pass through brainstem (sensory pathways)
- contains some descending (extrapyramidal)
3) BASE (basement):
- anterior to tegmentum
- composed of crus cerebri of midbrain + base of pons + pyramids of medulla
- contains pontine nuclei
- contains ONLY descending pathways (pyramidal and corticopontine)
- no ascending pathways
extrapyramidal pathway: reticulospinal tract
EXTENSOR BIASED
1) projection fibres originate in medial column of caudal pontine + rostral medullary reticular formation
2) descends ipsilaterally and bilaterally through ventral funiculus at all levels of spinal cord
3) acts on anti-gravity muscles (extensors) to adjust posture and gait during movement. controls bilateral and coordinated gross movement (e.g. walking)
extrapyramidal pathway: vestibulospinal tract
!!!!!
EXTENSOR BIASED
1) originates in lateral and medial vestibular nuclei of medulla
extrapyramidal pathway: tectospinal tract
!!!!!!!
EXTENSOR BIASED
1) originates in ventral portion of superior colliculi of midbrain
2) most fibres decussate at midbrain. small portion remain ipsilateral
3) contralateral fibres terminate at motor neurons in cervical spinal cord to act on neck and shoulder muscles —> controls reflexes to relevant sensory stimuli. ipsilateral fibres inhibit muscles on the other side **
- WHERE IN SPINAL CORD?
- WHY INHIBIT OTHER SIDE?
extrapyramidal pathway: rubrospinal tract
FLEXOR-BIASED
1) originates in red nucleus of tegmentum in midbrain
2) decussates close to its origin
3) descends contralaterally –> accompanies lateral corticospinal tract
4) travels through lateral funiculus –> ends at cervical level
5) innervates flexor muscles of upper limbs (grabbing behaviour)
* note: the pyramidal pathway has input into the rubrospinal tract in order to modulate its activity. no pyramidal input = constant flexion via rubrospinal tract
list the lateral motor pathways
1) lateral corticospinal tract
2) rubrospinal tract
travel through lateral funiculus
synapse with neurons in lateral motor pool
act unilaterally
fine voluntary movement of limb muscles + flexor-biased movement of upper limbs
list the medial motor pathways
1) anterior corticospinal tract
2) reticulospinal tract
3) tectospinal tract
4) vestibulospinal tract
travel through medial funiculus
synapse with neurons in medial motor pool
act bilaterally
postural and reflex movements of axial and proximal
limb muscles
list the 4 basal ganglia nuclei
1) dorsal striatum (STR)
- —> caudate nucleus + putamen
2) pallidus
- —> globus pallidus internus (GPi) + globus pallidus externus (GPe)
3) subthalamic nucleus (STN)
4) substania nigra
- —> pars compacta (SNc) + pars reticulata (SNr)
lenticular nucleus
putamen + pallidum
cortico-basal ganglia-cortical loop: direct
=> cerebral cortex EXCITES striatum (SNc also excites striatum via D1 receptors)
=> striatum STRONGLY INHIBITS GPi + SNr
=> GPi + SNr DISINHIBIT thalamus (VA, VL)
=> thalamus STRONGLY EXCITES cortex —> thalamocortical tract
disinhibition of thalamocortical tract = increase in thalamocortical tone = promotion of voluntary movement
all intrinsic connections of basal ganglia are GABAergic = inhibitory
cortico-basal ganglia-cortical loop: indirect
=> cerebral cortex EXCITES striatum (SNc can inhibit striatum via D2 receptors)
=> striatum STRONGLY INHIBITS GPe
=> GPe DISINHIBITS subthalamic nucleus
=> subthalamic nucleus STRONGLY EXCITES GPi + SNr (only glutamatergic connection = excitatory)
=> GPi + SNr STRONGLY INHIBITS thalamus (VA, VL)
=> thalamus WEAKLY EXCITES cortex —> thalamocortical tract
inhibition of thalamocortical tract = decrease in thalamocortical tone = suppression of involuntary movement
how do the basal ganglia connect to the spinal cord
basal ganglia feed into reticulospinal tract to make an indirect connection with the spinal cord
describe relationship between Parkinson’s disease and dopaminergic input
no/less dopaminergic input leads to reduced activity of direct pathway and increased activity of indirect pathway
reduced initiation of movement = slowness of movement (hypokinesia) or lack of movement (akinesia)
results in Parkinson’s disease
describe the dopamine input to the striatum (dorsal vs ventral)
VTA (ventral tegmental area) has dopamine input into the ventral striatum (nucleus accumbens)
- –> reward feeling
- –> e.g. food, drinks, drugs, sex
SNc has dopamine input into the dorsal striatum
- –> initiate movements that are predicted to having rewarding effects
- –> reinforcement learning
how is the basal ganglia involved in reward based learning?
cerebral cortex sends a copy of motor command to basal ganglia for selection of actions (motor patterns)
basal ganglia initiate specific motor patterns from a large number of possible motor patterns that are most consistent with motor command
within the basal ganglia, SNc is believed to guide the selection of relevant motor patterns (activation of direct pathway) by predicting reward values of the motor patterns
hence basal ganglia are involved in reward-based (REINFORCEMENT) learning of motor activities
cortico-basal ganglia-cortical loop: hyperdirect
=> primary motor cortex EXCITES subthalamic nucleus
=> subthalamic nucleus STRONGLY EXCITES GPi + SNr
=> GPi + SNr STRONGLY INHIBITS thalamus (VA, VL)
=> thalamus WEAKLY EXCITES primary motor cortex
does not require input from striatum
fast inhibition of all motor programs
allows for precise selection of motor program by direct pathway
list two examples of hyperkinetic disorders
defects in indirect pathway = involuntary movement
1) HEMIBALLISM
- –> underactivity in striatum = overactivity of thalamocortical tract
- –> uncontrollable, rapid ballistic movements of the contralateral limbs (motions produced via proximal limb joins movement [shoulder+elbow])
2) CHOREA HUNTINGTON
- –> underactivity in putamen = overactivity of thalamocortical tract
- –> involuntary rapid and random limb and trunk movement
list an example of a hypokinetic disorder (treatments?)
PARKINSON’S DISEASE
- –> degeneration of SNc = reduction of dopamine input
- –> overactivity of indirect pathway
- –> thalamus receives strong inhibitory tone = strong reduction in excitatory inpuit from thalamus to cortex
TREATMENTS
1) subthalamic nucleus lesion
2) GPi lesion
these normalise the excessive output from the GPi –> normal activity of indirect pathway
what type of fibres are present in the cerebellum?
ONLY projection fibres
therefore NO DECUSSATIONS
list the lobes and fissures of the cerebellum
LOBES:
1) anterior
2) posterior
3) flocculonodular
* intermediate hemisphere lateral to vermis
FISSURES:
1) primary ==> deepest ==> separates anterior and posterior lobes
2) horizontal ==> divides into equal inferior and superior halves
3) posterolateral ==> separates posterior and flocculonodular lobes
where d the superior and inferior medullary vela merge?
the superior and inferior medullary vela merge at the fastiguim
fastiguim = “highest point”
==> highest point in the roof of the 4th ventricle
cerebellar tonsils
part of posterior lobe
possess no distinct function
herniation of tonsils through foramen magnum occurs under increased cranial pressure
compression of medulla ==> lose control of respiratory and cardiac control centres ==> death
blood supply to cerebellum
** horizontal fissure divides cerebellum into equal inferior and superior halves
superior cerebellar artery
==> supplies superior half of cerebellum = posterior lobe
==> branches of basilar artery
posteior inferior cerebellar artery
==> supplies inferior half of cerebellum = anterior portion of posterior lobe lobe
==> branches of vertebral artery
anterior inferior cerebellar artery
==> supplies inferior half of cerebellum = anterior lobe
==> branches of basilar artery
describe the fibres in each of the cerebellar peduncles
peduncle = axonal bundles
all axons that enter or exit the cerebellum have to pass through the cerebellar peduncles
SUPERIOR CEREBELLAR PEDUNCLE:
- fibres travelling to/from the midbrain (mainly efferent);
- —–> dentatothalmic tract (to motor cortex via thalamus)
- —–> dentatorubral tract (to red nucleus via parvocellular tract)
MIDDLE CEREBELLAR PEDUNCLE:
- only afferent fibres from pons
- pontocerebellar tract is largest input
- —–> pontine nuclei receive input from ipsilateral cerebral cortex and project to contralateral cerebellum
INFERIOR CEREBELLAR PEDUNCLE:
- efferent fibres to medulla;
- —–> cerebroreticular tract (to reticulospinal tract)
- —–> cerebroolivary (to inferior olivary nucleus)
- —–> cerebrovestibular (to vestibulospinal tract)
- afferent fibres from medulla;
- —–> posterior spinocerebellar tract (proprioception)
- —–> olivocerebellar tract (climbing fibres from inferior olivary nucleus)
- —–> vestibulocerebellar tract (from vestibular nuclei)
list the nuclei found in the white matter of the cerebellum
- dentate nuclei (located laterally)
- fastigial nuclei (located medially)
- interposed nuclei (emboliform nuclei + globose nuclei, 2 globose nuclei each side)
major function of the cerebellum?
cerebellum compares motor actions & sensory feedbacks (is a comparator)
detects disparity (error) between motor actions & sensory feedbacks (is an error detector)
involved in the process of error correction
==> therefore, cerebellum is responsible for coordination of all body movements
lesion of the cerebellum leads to ataxia i.e. lack of coordinated movement
describe the afferent and efferent connections within the cerebellum
=> all afferent fibres entering the cerebellum terminate in the cerebellar cortex
=> collateral copies of the afferent fibres are ALWAYS given to the cerebellar nuclei
=> all efferent fibres that EXIT THE CEREBELLAR CORTEX are INHIBITORY axons of the cortical purkinje neurones that mostly synapse with neurons of the cerebellar nuclei
=> efferent fibres that EXIT THE CEREBELLUM are mostly EXCITATORY and originate from the cerebellar nuclei
vestiubulocerebellar loop
unconscious functional loop (no involvement of cerebral cortex)
1) integration of sensory and motor information occurs at flocculonodular lobe
2) flocculonodular lobe and fastigial nuclei to vestibular nuclei of medulla via cerebellovestibular tract
3) vestibular nuclei travels ipsilaterally to spinal cord via vestibulospinal tract, then to skeletal muscle
4) feedback to flocculonodular lobe via vestibulocerebellar tract. afferent copy sent to fastigial nuclei
FUNCTIONS:
vestibulospinal reflex:
keeps the body in the centre of gravity (body equilibrium) by maintaining muscle tone and activating antigravity muscles (= function of lateral vestibulospinal tracts)
vestibulocervical reflex:
stabilizes position of the head (= function of medial vestibulospinal tracts)
vestibulo-ocular reflex:
stabilises gaze during head movement (= function of medial vestibular nucleus)
spinocerebellar loop
1) cerebellar cortex to fastigial and interposed nuclei via purkinje cells
2) cerebellar nuclei to brainstem and on to extrapyramidal pathways (excluding tectospinal)
3) travels to spinal cord via these tracts and to skeletal muscle
4) feedback to cerebellar cortex via spinocerebellar tract
FUNCTION:
modulates muscle tone, posture and body balance
cerebrocerebellar loop
1) lateral hemispheres of cerebellum to dentate nuclei via purkinje cells
2) dentate nuclei to VA nuclei in ipsilateral thalamus via dentatothalamic tract
3) thalamus to ipsilateral primary motor cortex via thalamocortical tract
4) motor cortex to ipsilateral pontine nuclei via corticopontine tract
5) pontine nuclei back to lateral hemispheres via pontocerebellar tract. afferent copy sent to dentate nuclei
FUNCTION:
coordinates fast and alternating movement (e.g. speech) by planning motor actions
