Motor Control

Question 1

hierarchical organisation

Answer 1

• high order areas of hierarchy are involved in more complex tasks (programming and deciding on movements, coordinating muscle activity)
• lower level areas of hierarchy perform lower level tasks (execution of movement)

Question 2

functional segregation

Answer 2

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

Question 3

motor system hierarchy

Answer 3

motor cortex receives info from other cortical areas and sends commands to brainstem and thalamus

cerebellum and basal ganglia adjust the commands received from other parts of the motor control system

brainstem passes commands from cortex to spinal cord

Question 4

major descending tracts

Answer 4

pyramidal tracts (pass through pyramids of the medulla) - voluntary movements of body and face
extrapyramidal tracts (do not pass through pyramids of medulla)- involuntary movements for balance, posture and locomotion

Question 5

pyramidal tracts

Answer 5

UMN in motor cortex directly innervate LMN in anterior horn of spinal cord:

• corticospinal
• corticobulbar

Question 6

extrapyramidal tracts

Answer 6

UMN in brainstem do not directly innervate LMN, interneurones innervate muscle groups:

• vestibulospinal
• tectospinal
• reticulospinal
• rubrospinal

Question 7

corticospinal tract

Answer 7

UMN cell bodies in primary motor cortex
axon fibres go through internal capsule to form medullary pyramid on ventral surface of brainstem
at the level of the medulla:
- 90% of fibres decussate to form lateral corticospinal tract
- these fibres synapse with LMN in the anterior horn of the spinal cord to innervate limb muscles
- 10% of fibres do not cross and from the anterior corticospinal tract
- these fibres cross over and then synapse with LMN in the anterior horn of the spinal cord to innervate the trunk muscles

Question 8

corticobulbar tract

Answer 8

UMN cell bodies in primary motor cortex
axon fibres go alongside corticospinal tract to brainstem

These axons will depart the tract and synapse directly with the contralateral lower motor neurons for Cranial Nerves V, VII, XI, and XII at their corresponding levels of the Pons and medulla

Some of the upper motor neurons branch into two fibers which synapse with both the ipsilateral and contralateral motor nuclei

These include cranial nerves V, which controls the muscles for chewing, XI, which controls the muscles of the neck, and the part of VII that innervates the muscles in the upper half of the face

This means the muscles innervated by these nerves receive motor signals from the motor cortex from both hemispheres of the brain

The upper motor neurons of cranial nerve VII that control the lower half of the face, and cranial nerve XII, which control tongue movement, crossover in the brainstem without branching and only synapse with the contralateral nuclei

So the muscles innervated by these cranial nerves only receive motor information from the contralateral cerebral cortex

Question 9

vestibulospinal tract

Answer 9

From the vestibular nuclei
Stabilise head during body movements, or as head moves
Coordinate head movements with eye movements to keep vision fixed
Mediate postural adjustments

Question 10

reticulospinal tract

Answer 10

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

Question 11

tectospinal tract

Answer 11

From superior colliculus of midbrain(visual system)

Orientation of the head and neck during eye movements

Question 12

rubrospinal tract

Answer 12

From red nucleus of midbrain
In humans mainly taken over by corticospinal tract , active in primitive species.
Innervate lower motor neurons of flexors of the upper limb

Question 13

upper motor neuron lesion

Answer 13

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

Positive signs:
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

Question 14

apraxia

Answer 14

consequence of UMN lesion

• a disorder of skilled movement
• patients not paralyzed but have lost information about how to perform skilled movements
• lesion of inferior parietal lobe/ frontal lobe (premotor cortex, supplementary motor area)
• any disease of these areas can cause apraxia, most commonly stroke and dementia

Question 15

lower motor neuron lesion

Answer 15

Weakness
Hypotonia (reduced muscle tone)
hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch at the NMJ
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination Smaller AP fasciculations not visible to naked eye

signs found in cranial nerve nuclei if LMN of CORTICOBULBAR
signs found in spinal cord if LMN of CORTICOSPINAL

Question 16

motor neuron disease (MND)

Answer 16

(also known as amyotrophic lateral sclerosis (ALS))

progressive neurodegenerative spectrum of disorders of the motor system that can affect both UMN and LMN

Question 17

MND UMN signs

Answer 17

Spasticity (increased tone of limbs and tongue)
Brisk limbs and jaw reflexes 
Babinski’s sign
Loss of dexterity
Dysarthria (difficulty speaking)
Dysphagia (difficulty swallowing)

Question 18

MND LMN signs

Answer 18

Weakness
Muscle wasting
Tongue fasciculations and wasting
Nasal speech
Dysphagia

Question 19

basal ganglia structure

Answer 19

Caudate nucleus
Lentiform nucleus (putamen + external globus pallidus) – together caudate and putamen are known as the striatum
Thalamus
Nucleus accumbens
Subthalamic nuclei
Amygdala
Anterior commisure
Substantia nigra (midbrain)
Ventral pallidum, claustrum, nucleus basalis (of Meynert)

Question 20

basal ganglia function

Answer 20

Decision to move
Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)
Moderating and coordinating movement (suppressing unwanted movements)
Performing movements in order

Question 21

basal ganglia circuitry problems

Answer 21

Parkinson’s -Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum

Huntington’s disease- Degeneration of GABAergic neurons in the striatum, caudate and then putamen

Ballism-Usually from stroke affecting the subthalamic nucleus.

Question 22

parkinsons

Answer 22

Bradykinesia - slowness of (small) movements (doing up buttons, handling a knife) Hard for dexterous movements
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

Question 23

huntingtons

Answer 23

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
Gabaergic neurons-loss of inhibitory functions
Genetic neurodegenerative disorder , Chromosome 4, autosomal dominant , CAG repeat

Question 24

ballism

Answer 24

Sudden uncontrolled flinging of the extremities
Symptoms occur contralaterally.
Rotatory movement of limbs-opposite side of body usually from stroke that affects subthalamic nucleus

Question 25

cerebellum

Answer 25

Located in posterior cranial fossa covered by a layer of dura. Separated from cerebrum above by tentorium cerebelli Coordinator and predictor of movement Takes signals down, compare what CNS receiving and outputting-Coordinate movements and make them fluid. Pons connect 2 cerebellum lobes Cerebral peduncles in the anterior inferior view-large motor tracts down to the pyramids where many fibers cross over

Question 26

vestibulocerebellum

Answer 26

Regulation of gait, posture and equilibrium Relate to ataxis – poor coordination with walking and falling 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)

Question 27

spinocerebellum

Answer 27

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)

Question 28

cerebrocerebellum

Answer 28

Coordination of skilled movements Cognitive function, attention, processing of language Lateral side- coordinate skilled movemnts Emotional control Damage affects mainly arms/skilled coordinated movements (tremor) and speech

Question 29

main signs of cerebellar dysfunction

Answer 29

apparent only on movement: - 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

Question 30

alpha motor neurons

Answer 30

Lower motor neurons of the brainstem and spinal cord Innervate extrafusal muscle fibres of skeletal muscles- the contractile elements Intrafusal-contain the sensory elements for stretch- status of muscle for reflex Anterior horn cells active grey matter, which when activated cause contraction Motor neuron poll contains all the alpha motor neuron innervating a single muscle

Question 31

motor unit

Answer 31

a single motor neuron together with all the muscle fibres that it innervates. It is the smallest functional unit with which to produce force. 2 neurons in the horn, in birth the motor neurons may overlap with muscle. In development a single neuron will win out for muscle fibre innervation. The lower the number-the higher the resolution and precise control and smaller increases in grain.

Question 32

motor unit classification

Answer 32

classified by: - Amount of tension generated - Speed of contraction - Fatiguability

Question 33

motor unit types

Answer 33

``` Slow (S, type I)- •smallest diameter cell bodies •small dendritic trees •thinnest axons •slowest conduction velocity ``` ``` Fast, fatigue resistant (FR, type IIA)- •larger diameter cell bodies •larger dendritic trees •thicker axons •faster conduction velocity ``` ``` Fast, fatigable (FF, type IIB)- •larger diameter cell bodies •larger dendritic trees •thicker axons •faster conduction velocity ```

Question 34

regulation of muscle force

Answer 34

done in four ways: - recruitment - rate coding - neurotrophic factors - cross innervation

Question 35

recruitment

Answer 35

- Recruited in order, governed by size principle. - Smaller units first-usually type I, as more forced need more units and different type of units - Allows for fine control when low levels of forced needed. - Typical ramp up and ramp down contraction

Question 36

rate coding

Answer 36

- Motor unit fire at a range of frequencies, Type 1 at a lower frequency - As Hz’s increase, forced produced increase - Summation occurs when units fire at frequency to allow muscle relax between arriving action potentials- hence slower muscle in constant usage.

Question 37

neurotrophic factors

Answer 37

- growth factor to prevent neuronal death and promote neuronal growth post injury - Motor neurones provide more than action potential

Question 38

cross innervation

Answer 38

- If a fast twitch muscle and a slow muscle are cross innervated, the soleus (calf muscle) becomes fast and the FDL becomes slow. - this shows that the motor neuron has some effect on the properties of the muscle fibres it innervates.

Question 39

plasticity

Answer 39

- Type IIB to Type IIA - Training - Type I to type II - Severe deconditioning or spinal cord injury, Microgravity during spaceflight results in shift from slow to fast muscle fibre types and atrophy - Loss of Type I and II fibres – preferential loss of type II with ageing. Larger proportion of type I fibres in aged muscle- evident by slower contraction times

Question 40

reflex

Answer 40

- 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. - Integrated in the CNS then back to muscle - An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli - the magnitude and timing of reflex are determined respectively by the intensity and onset of the stimulus - Reflexes differ from voluntary movements in that once they are released, they can’t be stopped. Monosynaptic reflex. Sensory -> Afferent -> Dorsal root ganglia -> Lower motor neurone -> Muscle(to antagonist)

Question 41

Jendrassik maneuver

Answer 41

alter reflex amplitude by removing inhibition by upper CNS and neurons exert on the reflexes. Removes descending inhibition eg when the patellar tendon is tapped. •Higher centres of the CNS exert inhibitory and excitatory regulation on the stretch reflex •Inhibitory control dominate in normal •Decerebration reveals excitatory control from supraspinal areas •Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex. •Separates cerebral cortex from lower- greater reflex response and goes into a phasic & tonic.

Question 42

hyper-reflexia

Answer 42

Overactive reflexes Loss of descending inhibition Associated with upper motor neuron lesion-loss of voluntary pathway

Question 43

clonus

Answer 43

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

Question 44

Babinski sign

Answer 44

When sole stimulated with blunt instrument the big toe- outside of sole and balls of feet stroked outside to inside Curls downwards – normal-Especially big toe Curls upwards – abnormal in adults. This is a positive Babinski sign. Associated with upper motor neuron lesions Note: Toe curls upwards in infants – this is normal.