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Neurology > Motor Cortical Control > Flashcards

Motor Cortical Control Flashcards

1
Q

Broad principles of motor control

A

Hierarchical organisation

Functional segregation

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2
Q

Motor system hierarchy

A 
Primary motor cortex
Basal ganglia and cerebellum
Thalamus
Brainstem
Spinal cord
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3
Q

Major descending tracts

A

Pyramidal tracts - pass through thepyramidsof the medulla - Motor cortex to spinal cord or cranial nerve nuclei in brainstem - Voluntary movements of body and face

Extrapyramidal tracts - Do not pass through thepyramidsof the medulla - Brainstem nuclei to spinal cord - involuntary (automatic) movements for balance, posture and locomotion

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4
Q

Pyramidal tracts

A

Corticospinal

Corticobulbar

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5
Q

Extrapyramidal tracts

A

Vestibulospinal
Tectospinal
Reticulospinal
Rubrospinal

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6
Q

Primary motor cortex location

A

Located in precentral gyrus, anterior to the central sulcus

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7
Q

Premotor area location

A

Located anterior to primary motor cortex

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8
Q

Supplementary motor area location

A

Located anterior and medial to primary motor cortex

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9
Q

Corticospinal tract

A

From upper motor neurons down cerebral peduncle to midbrain and pyramids in medulla
Decussate
85-90% crossed fibres - Limb muscles - Lateral corticospinal tract
10-15% uncrossed fibres - Trunk muscles - Anterior corticospinal tract

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10
Q

Homunculus and somatotopy

A

Motor homunculus

Somatotopic representation

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11
Q

Corticobulbar tract

A

Basal ganglia

Principal motor pathway for voluntary movements of the face (and neck)

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12
Q

Vestibulospinal

A

Stabilise head during body movements, or as head moves
Coordinate head movements with eye movements
Mediate postural adjustments

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13
Q

Reticulospinal

A

Most primitive descending tract - from medulla and pons
Changes in muscles tone associated with voluntary movement
Postural stability

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14
Q

Tectospinal

A

From superior colliculus of midbrain

Orientation of the head and neck during eye movements

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15
Q

Rubrospinal

A

From red nucleus of midbrain
In humans mainly taken over by corticospinal tract
Innervate lower motor neurons of flexors of the upper limb

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16
Q

Upper motor neuron lesion

A

Loss of voluntary motor function
Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity

Increased abnormal motor function 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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17
Q

Apraxia

A

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

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

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18
Q

Lower motor neuron lesion

A

Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination

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19
Q

Motor neuron disease (MND)

A

Progressive neurodegenerative disorder of the motor system

Also known as Amyotrophic Lateral Sclerosis (ALS)

20
Q

Caudate nucleus

A

Decision to move

21
Q

Lentiform nucleus (putamen + external globus pallidus) – together caudate and putamen are known as the striatum
Nucleus accumbens
Subthalamic nuclei

A

Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)

22
Q 
Substantia nigra (midbrain)
Ventral pallidum, claustrum, nucleus basalis (of Meynert)
A

Moderating and coordinating movement (suppressing unwanted movements)

Performing movements in order

23
Q

Parkinson’s disease

A

Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum

24
Q

Parkinson’s disease symptoms

A

Bradykinesia - slowness of (small) movements (doing up buttons, handling a knife)
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
Rigidity - muscle tone increase, causing resistance to externally imposed joint movements
Tremor at rest - 4-7 Hz, starts in one hand (“pill-rolling tremor”); with time spreads to other parts of the body

25
Q

Huntington’s disease

A

Degeneration of GABAergic neurons in the striatum, caudate and then putamen

26
Q

Huntington’s disease symptoms

A

Choreic movements (chorea - dance)
rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages, cognitive decline and dementia

27
Q

Ballism

A

Usually from stroke affecting the subthalamic nucleus.
Sudden uncontrolled flinging of the extremities
Symptoms occur contralaterally.

28
Q

Cerebellum

A

Located in posterior cranial fossa
Separated from cerebrum above by tentorium cerebelli
Coordinator and predictor of movement

29
Q

Vestibulocerebellum

A

Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements

Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)

30
Q

Spinocerebellum

A

Coordination of speech
Adjustment of muscle tone
Coordination of limb movements

Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)

31
Q

Cerebrocerebellum

A

Coordination of skilled movements
Cognitive function, attention,
processing of language
Emotional control

Damage affects mainly arms/skilled coordinated movements (tremor) and speech

32
Q

Main signs of cerebellar dysfunction

A

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

33
Q

Alpha motor neuron

A

The lower motor neurons of the brainstem and the spinal cord
Innervate the extrafusal muscle fibres of the skeletal muscles
Motor neuron pool contains all alpha motor neurons innervating a single muscle

34
Q

Motor unit

A

a single motor neuron together with all the muscle fibres that it innervates. It is the smallest functional unit with which to produce force.

35
Q

Types of motor unit

A

Slow (S, type I) - slowest conduction velocity
Fast, fatigue resistant (FR, type IIA) - faster conduction velocity
Fast, fatiguable (FF, type IIB) - faster conduction velocity

36
Q

Regulation of muscle force

A

Governed by the “size principle”. Smaller units are recruited first. As more force is required, more units are recruited. This allows fine control (e.g. when writing), under which low force levels are required.

A motor unit can fire at a range of frequencies. Slow units fire at a lower frequency.
As the firing rate increases, the force produced by the unit increases.
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.

37
Q

Neurotrophic factors

A

Prevent neuronal death
Promote growth of neurons after injury

Motor unit and fibre characteristics are dependent on the nerve which innervates them.

The motor neuron has some effect on the properties of the muscle fibres it innervates.

38
Q

Plasticity of motor units/muscle fibres

A

Type IIB to IIA most common following training

Type I to II possible in cases of severe deconditioning or spinal cord injury. Microgravity during spaceflight results in shift from slow to fast muscle fibre types

Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle.

39
Q

Reflex

A

An automatic response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness.

An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli.

40
Q

Jendrassik manoeuvre

A

Try clenching the teeth, making a fist, or pulling against locked fingers when having patellar tendon tapped. The reflex becomes larger

41
Q

Descending (supraspinal) control of reflexes

A

Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex.

Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex.

42
Q

Descending (supraspinal) control of reflexes process

A
  1. Activating alpha motor neurons
  2. Activating inhibitory interneurons
  3. Activating propriospinal neurons
  4. Activating gamma motor neurons
  5. Activating terminals of afferent fibres
43
Q

Hyper-reflexia

A

Overactive reflexes
Loss of descending inhibition
Associated with upper motor neuron lesions

44
Q

Clonus

A

Involuntary and rhythmic muscle contractions
Loss of descending inhibition
Associated with upper motor neuron lesions

45
Q

Babinski sign

A

When sole stimulated with blunt instrument the big toe:
Curls downwards - normal
Curls upwards – abnormal in adults. This is a positive Babinski sign.
Associated with upper motor neuron lesions
Toe curls upwards in infants – this is normal.

46
Q

Hypo-reflexia

A

Below normal or absent reflexes

Associated with lower motor neuron diseases

Neurology (9 decks)

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