Practical 4 - Motor control Flashcards
The motor areas of cerebral cortex include:
- primary motor cortex,
- premotor cortex and
- supplementary motor area
main route the brain adresses the spinal cord?
corticospinal tract
describe how corticospinal axons pass through the brain to enter the spinal cord
- Corticospinal axons from the motor cortex run in the internal capsule of the forebrain
- which becomes the cerebral peduncles in the midbrain,
- pass through the pons,
- emerge as the medullary pyramids in the ventral medulla,
- continue as a crossed lateral corticospinal tract (and uncrossed ventral corticospinal tract) in the spinal cord
Damage to the corticospinal tract can result in …
Damage to the corticospinal tract can result in paralysis or paresis.
Motor structures are prominent on the _______ surface of the brainstem
Motor structures are prominent on the ventral surface of the brainstem
which motor strcutures are prominent on the ventral surface of the brainstem
notably;
- the cerebral peduncles,
- medullary pyramids,
- inferior olivary nuclei
what is the cerebllum involved in
motor co-ordination and
motor learning
The cerebellum connects with other structures via ….
The cerebellum connects with other structures via the cerebellar peduncles.
Damage to the cerebellum can result in…
Damage to the cerebellum can result in ataxia.
For muscles innervating the musculature of the head and neck the equivalent system to the corticospinal tract is the ….
For muscles innervating the musculature of the head and neck the equivalent system is the corticobulbar tract
where do the motor areas lie?
The motor areas of the cerebral cortex lie in the frontal lobes (anterior to the central sulcus, which is not always easy to identify)
the axons of what form the corticospinal tract?
the pyramidal neurons in layer V of the motor cortex
the pyramidal neurons in layer V of the motor cortex form the corticospinal tract - describe the path they take
these axons run in the internal capsule of the forebrain,
which becomes the cerebral peduncles in the midbrain,
which pass through the pons,
then emerge caudally as the medullary pyramids in the ventral medulla
describe how the certicobulbar fibres pass through the brain?
Corticobulbar fibres travel with and then leave this pathway (corticospinal pathway) to innervate motorneurons of the motor cranial nerves: V, VII, IX, X, XI, XII (not those controlling eye movements)
as the corticospinal fibres pass from medulla to spinal cord - most of them….
The large majority of corticospinal fibres cross the midline as they pass from medulla to spinal cord
how do corticospinal fibres enter the spinal cord
Corticospinal fibres continue as a crossed lateral corticospinal tract and an uncrossed ventral corticospinal tract into the spinal cord.
is the decending corticospinal tract massive
yes.
more than a million fibres enter the spinal cord on either side
the corticospinal and corticobulbar tracts are the major descending motor pathway in humans.
are there others?
other descending motor pathways are also important,
including cortical projections to the brainstem,
and brainstem projections to the spinal cord.
There are several different areas of frontal lobe cortex which are considered to represent motor function.
give 3
Main one - primary motor cortex (M1) (immediately anterior to central sulcus)
anterior ot M1 - premotor cortex
and supplememntary motor cortex
damage to primary motor cortex leads to
paralysis
damage to ‘Premotor cortex’ and the ‘Supplementary motor areas leads to?
more complex deficits, in which movements are poorly prepared or planned.
Microscopically, two features distinguish the histological structure of the primary motor cortex from other areas:
what are they?
- Deeper cortex (layer V) has population of giant pyramidal neurones - largest cells in brain - and have fastest conducting axons
- thickest area of cortex - yet few small rounded cells (granule cells) - therefore - sometimes called agranular cortex
Most corticospinal fibres arise from…
Most corticospinal fibres arise from the axons of cells in the primary, premotor and supplementary motor cortex
All descending cortical axons pass through what?
All descending cortical axons pass through the internal capsule - a bundle of large, fast-conducting fibres that descend between the nuclei of the basal ganglia and the thalamus.
This huge tract of white matter is a major landmark in the brain
Diagram of the descending corticospinal and corticobulbar system.
Dashed lines = fibres controlling the limbs via the spinal cord (corticospinal),
solid lines = the projections to the brainstem motor nuclei (corticobulbar).
Dashed lines indicate fibres controlling the limbs via the spinal cord (corticospinal), solid lines are the projections to the brainstem motor nuclei (corticobulbar).
Motor structures are prominent on the _____ surface of the brainstem
Motor structures are prominent on the ventral surface of the brainstem
what forms the cerebral peduncles
In the midbrain, the rostral part of the brainstem, fibres from the internal capsule form the cerebral peduncles
why are cortical fibres difficult to distinguish in the pons
some pass through (the corticospinal and corticobulbar fibres), others terminate in the pons (corticopontine)
Coronal section through the hemispheres showing the internal capsule running between the thalamus and the basal ganglia
Coronal section through the hemispheres showing the internal capsule running between the thalamus and the basal ganglia
Surface of the ventral brainstem
Surface of the ventral brainstem
what marks the boundary between the medulla and the spinal. cord
motor decussation (crossing of motor fibres as they decend ot the spinal cord)
describe how corticospinal fibres pass from the pons to the spinal cord
In the medulla, corticospinal fibres emerge from the pons as the prominent medullary pyramids, and decussate (cross the midline) as the fibres descend into the spinal cord
before the corticospinal fibres enter the spinal cord - what happens to the corticobulbar fibres?
leave the tract to enter the brainstem, destined for motor nuclei in the medulla (= “bulb”, hence the term corticobulbar) and pons
what do the corticobulbar fibres innervate?
they innervate the motor nuclei of the cranial nerves to control facial (VII), jaw (V), tongue (XII) laryngeal and pharyngeal (IX & X) muscles
are corticobulbar fibres bilaterally or unilaterally distributed to the brainstem motor nuclei?
bilaterally
are oculomotor nuclei (III, IV & VI) directly innervated by the corticbulbar tract>?
Note that the oculomotor nuclei (III, IV & VI) are not directly innervated by the corticospinal tract: the eyes need to move consensually (together) and are controlled by brainstem structures
ventral medulla - what lies lateral to the pyramids?
inferior olives
what are the medullary inferior olives asociated with
climbing fibre input to the cerebellum
Section through the upper midbrain
The cerebral peduncles (CP, or basis pedunculi, “stalk”) on the ventral aspect of the midbrain are massive bundles of fibres descending from the cerebral cortex to the brainstem and spinal cord. Just deep to the peduncles are the dopaminergic neurones of the substantia nigra (SN) (Practical 4) and the red nuclei (RN).
SC, superior colliculi. A, aqueduct
Section through pons
Fibres in the cerebral peduncles descend into the pons (“bridge”). Most fibres in the cerebral peduncles terminate in the pons onto neurons that project as mossy fibres into the cerebellum so the cerebral peduncles are larger than the pyramids of the medulla. Arrows indicate the location of corticospinal fibres in the pons, but these are not readily visible on real specimens
why are the cerebral peduncles are larger than the pyramids of the medulla
Most fibres in the cerebral peduncles terminate in the pons onto neurons that project as mossy fibres into the cerebellum (see below), so the cerebral peduncles are larger than the pyramids of the medulla
what happens to the majority of corticospinal fibres travelling in the lateral and ventral corticospinal tracts
terminate on spinal interneurons in the spinal grey matter, where they can influence both motor and sensory information processing.
in most mammals this is the main patheway by which movement is controlled - but primates have another pathway
in addition to spina linterneurones - what other pahway do primates prosses?
why is it useful?
a parallel direct projection of some corticospinal fibres, especially the large ones, to alpha- motoneurons (cortico-motoneuronal connections).
This connection is unique to some primates and is especially common for distal muscle control (i.e. intrinsic hand and footmuscles).
This type of connection is particularly well developed in the great apes and especially in humans, and underlies our manual dexterity.
Section through the mid- medulla
Section through the mid- medulla
Revise the dorsal column nuclei (DCN), spinal trigeminal nuclei (V) and medial lemniscus (ML) from Practical 2.
Note the location of the medullary pyramids (P) and the inferior olivary nuclei (O).
The lower medulla
The lower medulla
Note the location of the motor decussation (D); about 85% of the corticospinal fibres cross the midline at this level and continue contralaterally as the lateral corticospinal tract. Almost all of the remaining fibres (15%) descend ipsilaterally, mainly in the medial part of the ventral funiculus of the spinal cord (an equivalent location to the medullary pyramid) as the ventral corticospinal tract; most of these cross the midline before terminating in the spinal cord.
Section through the spinal cord
Section through the spinal cord
Note the locations of the lateral corticospinal tract (LCS), containing crossed fibres that originated from the contralateral motor cortex, and the ventral corticospinal tract (VCS), containing uncrossed fibres from the ipsilateral motor cortex.
Brain stem and spinal cord after a stroke
Other descending motor pathways:
describe the vestibulospinal tracts
The vestibulospinal tracts descend in the ventral columns of the spinal cord.
They arise in the vestibular nuclei in the dorsal medulla.
The vestibulospinal tract exerts its actions mainly on extensor (antigravity) limb muscles and proximal muscles (neck & trunk) and is involved in maintaining posture and equilibrium.
other descending motor pathways
describe the reticulospinal fibres
Reticulospinal fibres originate from many cell groups in the reticular formation of the pons and medulla. The reticular formation is a poorly understood but extensive region of grey matter extending through the core of the brainstem from spinal cord to medulla.
Several groups of neurons in the reticular formation give rise to descending fibres, which are fast conducting and project throughout the length of the spinal cord.
These pathways are important for posture and for coordinated body movement (e.g. locomotion, reaching).
describe the Rubrospinal tract
Fibres from the Red Nucleus of the midbrain (Rubrospinal tract) are numerous in most mammals (including cats and dogs). The red nucleus in humans is large but has few (if any) fibres that descend to the spinal cord. In humans, the red nucleus gets inputs from the cerebellar nuclei and the motor areas of the cerebral cortex and its output is mainly to the inferior olivary nucleus, the origin of cerebellar climbing fibres (see below).
It is thought to function in motor skills learning.
whats the main purposes of the cerebellum
involved in motor co-ordination
oncerned with feedforward motor control, in predicting commands for future movements.
The cerebellum is therefore particularly important in learning motor skills, and automating movement.
is the cerebellar cortex folded?
yep
Cerebellar cortex is much _____ than the cerebral cortex, ……
Cerebellar cortex is much thinner than the cerebral cortex, so the folds are smaller and more tightly packed
could you point out the vermis of the cerebellum?
middle worm section running vertically down the midline
side lobes of the cerebellum are called…
Large lateral masses, the cerebellar hemispheres, on each side.
On the ventral aspect of the brain, the cerebellar hemisphere is connected to the pons by the…..
On the ventral aspect of the brain, the hemisphere is connected to the pons by the
large middle cerebellar peduncle, containing fibres originating from the pons projecting into the cerebellum.
describe the cerebello pontine angle?
ventral aspect of the cerebellum
a very small, semi-detached part of cerebellar cortex called the flocculus (concerned with vestibular function). The facial and vestibulocochlear nerves enter the brain at this location
what is the tonsil of the cerebellum
On each side, small parts of the cerebellar cortex ‘overhang’ the dorso-lateral aspect of the medulla
why is the cerebellar tonsil clinically important
- close proximity to medulla nad foramen magnum
- in patients with raised intra- cranial pressure there is risk of the tonsils collapsing into the foramen magnum if CSF is withdrawn by lumbar puncture, resulting in pressure on the brainstem and sudden death due to pressure on the “vital centres” for respiratory and autonomic control in the medulla (“coning”)
*
when might lumbar puncture be contra-indicated (cranial pressure wise)
Lumbar puncture is, therefore, usually contra-indicated in a patient with symptoms and signs suggestive of raised intra-cranial pressure (e.g. papilloedema, swelling of the optic nerve head).
The cerebellum and adjacent brainstem: sagittal section
does teh cerebellar cortex have any direct output to the brain?
where is its output?
no
All of the cortical output is directed to a group of nuclei buried below the cortical folds, the deep cerebellar nuclei.
is cerebellar cortical output inhibitory?
yep
describe the ceerebellar deep nuclei?
There are three true deep nuclei on each side: the dentate nucleus, the nucleus interpositus (globose and emboliform), and the fastigial nucleus
T or F
An exception is that some areas of cerebellar cortex (the flocculus, and the buried flocculonodular lobe) send outputs to the vestibular nuclei in the medulla (the evolutionary origin of the deep cerebellar nuclei is from the vestibular nuclei).
T§
where do the cerebellar nuclei transmit the output to?
nuclei transmit the entire output of the cerebellum, and have projections to brainstem descending motor pathways, and mostly to the motor areas of cerebral cortex (via the thalamus).
why is the dentate nucleus special?
how does it look?
The dentate nucleus is by far the largest and most important nucleus in humans, and the only one that you are likely to see.
In cross-section the dentate nucleus appears as a convoluted line of grey matter within the white matter.
what do the cerebellar peduncles do>
connect the cerebellum with the brainstem on each side
what are the 3 cerebellar peduncles?
the small inferior cerebellar peduncle (from the medulla); the large middle cerebellar peduncle (from the pons) and the superior cerebellar peduncle (deep nuclear output).
which cerebellar peduncle is the largest?
what does this show us?
The middle cerebellar peduncle is by far the largest, reflecting the enormous traffic between cerebral cortex and cerebellum via the pons.
describe the superior cerebellar peduncle
The superior cerebellar peduncle is the major output pathway from the deep nuclei (mainly the dentate nucleus in humans) and is obvious dorsally in the pons, and where it crosses the midline (decussates) in the low mid brain. It then sends fibres through (and some fibres to) the red nucleus (RN)
The cerebellar output projects to the where?
The cerebellar output projects to the motor parts of the thalamus (ventrolateral nucleus, projecting to primary motor cortex; ventroanterior nucleus, to the premotor and supplementary motor areas).
A thin plate of tissue bridges the gap between the superior peduncles on either side, so forming the ….
A thin plate of tissue bridges the gap between the superior peduncles on either side, so forming the roof of the rostral part of the fourth ventricle.
Superior cerebellar peduncle in cross-section
Inputs to the cerebellum are via ….
Inputs to the cerebellum are via the pons and inferior olive.
Inputs to the cerebellum are via the pons and inferior olive.
elaborate…..
Fibres from cerebral cortex pass through the internal capsule and cerebral peduncles to terminate ipsilaterally on neurons in the pons; these neurons send their axons across the midline through the middle cerebellar peduncle, to the contralateral cerebellum, as mossy fibres, the major type of cerebellar input.
input output for cerebellum
go ove the cerebullum - its confusing
noice
T or F
Unlike other areas of brain the cerebellar cortex has a small number of characteristic cell types and is precisely geometrically arranged
t
The cerebellar cortex has ____ clearly defined layers that you can see by eye
The cerebellar cortex has three clearly-defined layers that you can see by eye
describe the outer layer of the cerebellar cortex
An outer molecular layer with a low cell density. It consists mainly of the thin axons of granule cells (parallel fibres) which run parallel to the folia and cell dendrites
describe the intermediate cerebellar cortex layer
An intermediate Purkinje cell layer. This layer is a single cell thick and the Purkinje cells are large enough to be visible under a low power microscope
describe the inner cerebellar cortex layer
An inner granular layer, containing vast numbers of small granule cells.
whats beneath the 3 clearly defined layers of the cerebellar cortex
Beneath these layers is the cerebellar white matter containing fibres running to and from the cerebellar cortex.
Purkinje cells are the ____ cells of the cerebellar cortex.
Purkinje cells are the output cells of the cerebellar cortex.
characteristics of purkinje cells
- extensive dendrites that form a planar sheet
- lie in a plane at right angles to the long axis of the folia
- each Purkinje cell to receive synaptic contacts from an enormous number of parallel fibres (some estimate as many as 250,000)
- only cells, which send axons out of the cortex, they inhibit cells in the deep cerebellar nuclei (GABA is their neurotransmitter)
Circuit diagram of cerebellar cortex
Major clinical disorders of motor function will follow damage to the,…..
Major clinical disorders of motor function will follow damage to the corticospinal pathway
In mild stroke occurring above the motor decussation, the major effect is ….
In mild stroke occurring above the motor decussation, the major effect is a contralateral weakness (hemiparesis). More severe strokes will give contralateral paralysis (hemiplegia).
Upper motor neuron lesions involve the motor cortex or its output fibres. Such lesions are usually above the ….
and produce…,
Upper motor neuron lesions involve the motor cortex or its output fibres. Such lesions are usually above the pyramidal decussation and produce contralateral signs
Strokes, cerebral palsy and multiple sclerosis are common causes of upper neuron signs.
Lower motor neuron lesions occur in the….
Lower motor neuron lesions occur in the spinal cord or peripherally, e.g. in Poliomyelitis.
T or F
The clinical signs of upper and lower motor neuron lesions differ.
T
The clinical signs of upper and lower motor neuron lesions differ.
Upper neuron lesions involve …..
Upper neuron lesions involve an immediate flaccid paralysis, which gradually becomes spastic with hyperreflexia, clonus and a positive Babinski sign: voluntary movement is impaired, but reflex muscle contraction remains.
Lower motor neuron lesions involve ….
Lower motor neuron lesions involve muscular weakness, flaccid paralysis, muscle wasting and areflexia.
following a stroke can ipsilateral descending fibres
reorganise to allow recovery of function in adults
no
Although a substantial number of corticospinal fibres in humans descend ipsilaterally in the ventral spinal cord, there is little evidence that these can contribute to ipsilateral limb function, particularly of the hands: they either cross the midline before terminating, or they control axial (limb girdle and trunk) muscles. Thus, following a stroke, ipsilateral descending fibres cannot reorganise to allow recovery of function in adults or in children over a few months old (although they can do so following damage prenatally or in early neonatal life – an example of developmental windows for plasticity).
what are Arteriovenous Malformations (AVM)
congenital vascular anomalies consisting of direct arterial to venous connections (‘fistulas’) without an intervening capillary bed and can occur in the brain and spinal cord.
Arteriovenous Malformations (AVM) have a propensity to ….
treatment?
The abnormal vessels have a propensity to bleeding.
Treatment to prevent future haemorrhage can involve surgical resection, focused radiotherapy, or endovascular embolization.
what are Cavernomas
cavernomas are composed of thin dilated vascular channels that do not have a feeding artery and therefore do not appear on angiograms (in contrast to AVMs, above). They can occur in the brain or spinal cord and are familial in a proportion of cases. The risk of bleeding is usually lower than AVMs but if multiple haemorrhages occur then surgical resection is considered.
difference between cavernomas and AVMs
Unlike arteriovenous malformations, there is little blood flow in cavernomas
facial problems following a unilateral stroke
Corticobulbar fibres to some motor nuclei provide bilateral innervation, (e.g. nerves V and XII). Because of this, complete jaw and tongue paralysis does not follow a unilateral stroke, although movements will be weaker on the affected side (opposite to the side of the brain affected by stroke). Damage to the corticospinal innervation of the hypoglossal nucleus frequently means that the tongue becomes lopsided.
On the other hand, the motor nuclei of the branches of the facial nerve to the lower facial muscles are unilaterally innervated, and these may be completely paralysed after a stroke. Thus stroke frequently produces a contralateral lower facial paralysis (loss of ability to smile or make expressions with the mouth), while the upper face retains some function through intact ipsilateral projections from motor cortex
T or F
stroke frequently produces a contralateral lower facial paralysis (loss of ability to smile or make expressions with the mouth)
T
while the upper face retains some function through intact ipsilateral projections from motor cortex.
cerebellar issues -
caused by degenerative diseases or by traume.
bad clumsy movement - uncoordinated.
poor scaling of movement
fat
mamba
