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Neuro 8: motor pathways Flashcards

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1
Q

Define functional segregation

A

Motor system organised in a number of different areas that control different aspects of movement

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2
Q

State the 2 hierarchies

A

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)

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3
Q

Differntiate pyramidal and extrapyramidal system

A

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)

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4
Q

Where is the primary motor cortex (M1)

A

Precentral gyrus (in front of the central sulcus)

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5
Q

Function of primary motor cortex

A

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

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6
Q

Outline somatotopic organisation of primary motor cortex

A

Penfied’s motor homunclulus….

Hands and tongue overrepresented (learn where things are)

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7
Q

Differentiate anterior and lateral corticospinal tract

A

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.

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8
Q

What are corticobulbar pathways

A

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.

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9
Q

Where is the premotor cortex

A

frontal lobe anterior to M1, laterally

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10
Q

Function of premotor cortex

A

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)

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11
Q

Location of supplementary motor area

A

frontal lobe anterior to M1, medially

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12
Q

Function of supplementary motor area

A

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

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13
Q

What is association cortex

A

Brain areas not strictly motor areas as their activity does not correlate with motor output/act, but kind of relates to movement

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14
Q

Give 2 examples of association cortex

A

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

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15
Q

Define lower motor neuron

A

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
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16
Q

Define upper motor neuron

A

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)

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17
Q

What does pyramidal tract refer to

A

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)

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18
Q

Which 2 areas are involved in extrapyramidal system

A

Basal ganglia, cerebellum

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19
Q

2 examples of negative sings in Upper motor neuron lesion

A

Negative sign means loss of normal function

Paresis: graded weakness of movements

Paralysis (plegia): complete loss of muscle activity

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20
Q

What are positive signs in Upper motor neuron lesion

A

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

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21
Q

What is apraxia

A

A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements

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22
Q

Lesions to which areas cause apraxia, and what are the most common causes of these lesions

A

Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area).

Common cause: stroke and dementia

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23
Q

Presentation of lower motor lesions

A

Weakness

Hypotonia (reduced muscle tone)

Hyporeflexia (reduced reflexes)

Muscle atrophy

Fasciculations

Fibrillations

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24
Q

Differentiate fasciculations with fibrillation

A

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

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25
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
26
Which neurons does motor neuron disease affect
Upper and lower
27
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 ```
28
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
29
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
30
What is the corpus striatum
lentiform + caudate..... But ventral striatum= nucleus accumbens Dorsal= caudate and putamen
31
Which membrane lies between the lateral ventricles
septum pellucidum
32
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
33
Which connection in the BG circuitry does PD affect?
connection between substantia nigra and striatum
34
Which connection in the BG circuitry does Huntingtons affect?
connection between striatum and globus palidus (connections within the BG)
35
Which area is damaged in ballism (ballistic movements)
Subthalamic nucleus
36
Which vertebral column sign is associated with parkinson's
Kyphosis
37
State the neuopathology of parkinson's
neurodegeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
38
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
39
Look at the nigro-striatal pathway
...
40
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
41
What happens in huntington's
There is a loss of the caudate nucleus..... genetic neurodegenerative autosome dominant
42
State the genetic basis of huntingtons
Number of repeats of CAG in the huntingtin gene on chromosome 4 (more than 35 --> huntingtons)
43
What kind of neurons are degenerated in Huntington's
GABAergic neurons in the striatum, caudate and then putamen so you lose inhibitions
44
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
45
Name the layers of the cerebellum
Molculeclar layer (few cells), piriform (purkinje cells=main processing cell), granular cell layer. Umderying is the white matter
46
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
47
Outline output from cerebellum
All output from Purkinje cells via deep nuclei
48
State 3 divisios of the cerebellum
Vestibulocerebellum, Spinocerebellum | and Cerebrocerebellum
49
Role of Vestibulocerebellum
Regulation of gait, posture and equilibrium Coordination of head movements with eye movements (superior colliculi)
50
Role of spinocerebellm
Coordination of speech Adjustment of muscle tone Coordination of limb movements
51
Role of Cerebrocerebellum
Coordination of skilled movements Cognitive function, attention, processing of language Emotional control
52
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)
53
Signs of spinocerebellar syndrome
Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)
54
Signs of Cerebrocerebellar or Lateral Cerebellar Syndrome
Damage affects mainly arms/skilled coordinated movements (tremor) and speech
55
What is spinocerebellar damage associated with
Chronic alcoholism
56
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)
57
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
58
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
59
What is the nucleus accumbens made up of
Fused anterior part of the caudate with the putamen
60
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
61
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
62
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
63
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
64
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.
65
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

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