Neuro 8: motor pathways Flashcards
Define functional segregation
Motor system organised in a number of different areas that control different aspects of movement
State the 2 hierarchies
high order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity)
lower level areas of hierarchy perform lower level tasks (execution of movement)
Differntiate pyramidal and extrapyramidal system
Pyramidal= motor cortex receiving info from other cortical areas and sends commands to thalamus and brainstem then spinal cord (i.e. the mechanical pathway)
Extramedullary= cerebellum and basal ganglia adjust commands received from other parts of motor control system (fine tune)
Where is the primary motor cortex (M1)
Precentral gyrus (in front of the central sulcus)
Function of primary motor cortex
control fine, discrete, precise voluntary movement
Provide descending signals to execute movement
6 layers of cortex….. in layer 5 the pyramidal Betz cells which are the largest cells in the CNS. Send their axons down the corticospinal tract
Outline somatotopic organisation of primary motor cortex
Penfied’s motor homunclulus….
Hands and tongue overrepresented (learn where things are)
Differentiate anterior and lateral corticospinal tract
Common at the beginning: originating from the primary motor cortex, passing down the internal capsule, through the cerebral peduncle, through the pons.
The lateral corticospinal tract then decussates at the pyramidal decussation of the medulla and travels on the contralateral side down the spinal cord.
The anterior corticospinal tract does not decussate at the pyramidal decussation, instead passing through the pyramids on the ipsilateral side, all the way down the spinal cord in anterior corticospinal tract until reaching the level at which it needs to exit, at which point it decussates.
Lateral CS tract carries 90% of motor fibres, anterior just 10%
Lateral CS carries motor fibres to ekeltal muscle in the distant part of the limbs, whereas anterior CS carries mtor fibres to skeletal muscles in proximal part of limbs and the trunk.
What are corticobulbar pathways
Pathways leading from the primary motor cortex to supply cranial nerve nuclei in the brainstem. It contains the UPPER MOTOR NEURONS of the cranial nerves. They terminate on motor neurons within brainstem motor nuclei. This is in contrast to the corticospinal tract in which the cerebral cortex connects to spinal motor neurons, and thereby controls movement of the torso, upper and lower limbs.
Where is the premotor cortex
frontal lobe anterior to M1, laterally
Function of premotor cortex
planning of movements
regulates externally cued movements
seeing an apple and reaching out for it requires moving a body part relative to another body part (intra-personal space) and movement of the body in the environment (extra-personal space)
Location of supplementary motor area
frontal lobe anterior to M1, medially
Function of supplementary motor area
planning complex movements; programming sequencing of movements
Regulates internally driven movements (e.g. speech)
SMA becomes active when thinking about a movement before executing that movement
What is association cortex
Brain areas not strictly motor areas as their activity does not correlate with motor output/act, but kind of relates to movement
Give 2 examples of association cortex
Posterior parietal cortex: ensures movements are targeted accurately to objects in external space
Prefrontal cortex: involved in selection of appropriate movements for a particular course of action
Define lower motor neuron
Alpha motor neurons branching out from CNS:
- Spinal cord ending up at neuromuscular junction
- Brainstem… neurons leaving from nuclei of non-oculomotor cranial nerves which have a motor function e.g. hypoglossal
Define upper motor neuron
Fibres leading from the primary motor cortex to the spinal cord (to synapse onto lower motor neurons innervating skeletal muscles) or brainstem (to synapse onto cranial nerve nuclei)
What does pyramidal tract refer to
The term pyramidal tracts refers to upper motor neurons that originate in the cerebral cortex and terminate in the spinal cord (corticospinal) or brainstem (corticobulbar)
Which 2 areas are involved in extrapyramidal system
Basal ganglia, cerebellum
2 examples of negative sings in Upper motor neuron lesion
Negative sign means loss of normal function
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of muscle activity
What are positive signs in Upper motor neuron lesion
Increased abnormal motor function (positive signs) due to loss of inhibitory descending inputs
Spasticity: increased muscle tone
Hyper-reflexia: exaggerated reflexes
Clonus: abnormal oscillatory muscle contraction
Babinski’s sign
What is apraxia
A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements
Lesions to which areas cause apraxia, and what are the most common causes of these lesions
Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area).
Common cause: stroke and dementia
Presentation of lower motor lesions
Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations
Fibrillations
Differentiate fasciculations with fibrillation
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
(in fasciculation you get denervation of a muscle, so another motor unit reinnervates this area, but generates random APs)
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination
What is motor neuron disease
Progressive neurodegenerative disorder of the motor system. Affects BOTH upper and lower motor neurons (so if you have a mix of signs, could be this!)
SPECTRUM of disorder
Amyotrophic Lateral Sclerosis
NO SENSORY INVOLVEMENT
Which neurons does motor neuron disease affect
Upper and lower
Sigsn in MND
Upper motor:
Increased muscle tone (spasticity of limbs and tongue)
Brisk limbs and jaw reflexes
Babinski’s sign
Loss of dexterity
Dysarthria (unclear articulation of speech that is otherwise linguistically normal)
Dysphagia
Lower signs: Weakness Muscle wasting Tongue fasciculations and wasting Nasal speech Dysphagia
Key areas of basal ganglia
EXTRAPYRAMIDAL
Caudate nucleus
Lentiform (putamen + external globus pallidus)
Subthalamic nucleus, Substantia nigra (in the brainstem)
(Ventral pallidum, claustrum, nucleus accumbens, nucleus basalis of Meynert (this is acetylcholinergic, projects to the whole of the cortex, implicated in alzheimers and parkinsons)
use the real diagrams to help
Structure of basal galngia anteriorly
On lateral wall of lateral ventricle, the caudate nucleus anteriorly. Lateral to this, the internal capsule (not much anteriorly). Lateral to this, the putamen. Ventral to the caudate is the nucleus accumbens.
Futher back, the internal capsule becomes bigger and the caudate is reduced in size. Putamen same size.
Further back, thalamus is now lateral and we are at the third ventricle. The caudate is much smaller and more dorsal (higher, because it is teardrop shaped). The putamen and global pallidus form a triangular shape laterally.
Even furhter back, thalamus is still lateral to 3rd ventricle, putamen and global pallidus making triangle still. Remember lentiform= external global pallidus and putamen
What is the corpus striatum
lentiform + caudate…..
But ventral striatum= nucleus accumbens
Dorsal= caudate and putamen
Which membrane lies between the lateral ventricles
septum pellucidum
Functions of basal ganglia
Elaborating associated movements (arm swinging and chaning facial expression to match emotion)
Moderating and coordinating movement (suppressing unwanted movements)
Performing movements in order
So execution of movement
Which connection in the BG circuitry does PD affect?
connection between substantia nigra and striatum
Which connection in the BG circuitry does Huntingtons affect?
connection between striatum and globus palidus (connections within the BG)
Which area is damaged in ballism (ballistic movements)
Subthalamic nucleus
Which vertebral column sign is associated with parkinson’s
Kyphosis
State the neuopathology of parkinson’s
neurodegeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
What gives the black colour to the substantia nigra
Release of neuromelanin (a byproduct of dopamine production in the dopaminergic neurons)…
Locus classicus of parkisnons disease is when there is a loss of this byproduct in the substantia nigra, so this area is less black in parkinsons patients
Look at the nigro-striatal pathway
…
Motor signs of parkinson’s
Reynolds Building And The Hospital
Bradykinesia: slowness of (small) movements (doing up buttons, handling a knife)
Rigidity: muscle tone increase, causing resistance to externally imposed joint movements
Tremor at rest: 4-7 Hz, starts in one hand (“pill-rolling tremor”)
Hypomimic face:
expressionless, mask-like (absence of movements that normally animate the face)
Akinesia:
difficulty in the initiation of movements because cannot initiate movements internally
What happens in huntington’s
There is a loss of the caudate nucleus…..
genetic neurodegenerative autosome dominant
State the genetic basis of huntingtons
Number of repeats of CAG in the huntingtin gene on chromosome 4 (more than 35 –> huntingtons)
What kind of neurons are degenerated in Huntington’s
GABAergic neurons in the striatum, caudate and then putamen
so you lose inhibitions
Motor signs of huntington’s
SCULD
Speech impairment
Choreic movements (Chorea) rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
Unsteady gait
Later stages, cognitive decline and dementia
Difficulty swallowing
Name the layers of the cerebellum
Molculeclar layer (few cells), piriform (purkinje cells=main processing cell), granular cell layer.
Umderying is the white matter
Outline input circuitry to the cerebullum
Fibres from inferior olive branch projects via ‘climbing fibres’ (which go from brainstem to cerebeullum via inferior cerebellar peduncle!) and synapsing to the on dendritic trees of purkinje cells
All other input to granule cells via mossy fibres (from cortex and other areas, go to cerebellum via middle cerebellar peduncle!) and then onwards from granular cell via parallel fibres
Outline output from cerebellum
All output from Purkinje cells via deep nuclei
State 3 divisios of the cerebellum
Vestibulocerebellum, Spinocerebellum
and Cerebrocerebellum
Role of Vestibulocerebellum
Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements (superior colliculi)
Role of spinocerebellm
Coordination of speech
Adjustment of muscle tone
Coordination of limb movements
Role of Cerebrocerebellum
Coordination of skilled movements
Cognitive function, attention,
processing of language
Emotional control
Signs of vestibulocerebellar syndrome
Damage (tumor) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)
Signs of spinocerebellar syndrome
Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)
Signs of Cerebrocerebellar or Lateral Cerebellar Syndrome
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
What is spinocerebellar damage associated with
Chronic alcoholism
Signs of cerebellar dysfunctin
Ataxia
General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Dysmetria
Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor
Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dysdiadochokinesia
Inability to perform rapidly alternating movements, (rapidly pronating and supinating hands and forearms)
Scanning speech
Staccato, due to impaired coordination of speech muscles
AS (speech scanning, Alternating movement (=dysdiadachokinesia))
IF (Intention tremor, force i,e, dysmetria)
A (Ataxia)
What are externally cued movements
movements that are carried out as a result of a sensory cue or stimulus, or reflex-reactions to external conditions or changes
Pre-frontal cortex regulates this
Differentiate spasticity vs rigidity
Both types of too much tone…
Spasticity is velocity dependent and may be different in one direction to another
Rigidity is not vecotiy dependent and same in all directions
What is the nucleus accumbens made up of
Fused anterior part of the caudate with the putamen
State the connections in the layers of the primary motor cortex
DORSAL –> VENTRAL
layer 1-3 =cortico-cortical connection
Layer 4= input from thalamus
layer 5-6= connections with subcortical, brainstem and spinal cord
t/f all motor fibres cross in the brainstem
F…. fibres innvervating trunk and proximal parts of limbs come from PMC, internal capsule, cerebral peduncle, braintem, spinal cord as the ANTERIOR corticospinal tract, and then synapse and cross over
T/f… motor fibres in the lateral corticospinal tracts in the spinal cord are upper motor neurons
T… at the pyramidal decussation there is no synapse, so the neurons just cross over and are the same neurons as those which originated from the primary motor cortex
T/F some motor fibres synapse in the brainstem
T….in corticobulbar pathways, there upper moto rneuron synapses onto the cranial nerve nucleus (cranial nerve is lower motor neuron) for example hypoglossal nucleus
State the function of the inferior and superior olivary nuclei
The inferior olivary nucleus is the part of the olivary body that assists in cerebellar motor learning and functioning. The cerebellum is located in the lower, back part of the brain.
The superior olivary nucleus is the part of the olivary body that belongs to the auditory system and assists with sound perception.
Summarise the organisation of alpha motor neurons within the spinal cord
In the ventral horn (gray matter)
Rexed laminae
Extensor a-motor neurons most ventral in the spinal cord ventral horn
Flexor a-motor neurons bit more posterior but still in ventral horn of course
