Motor Control

Question 1

What are broad principles of motor control

Answer 1

Hierarchical organisation
Functional segregation

Question 2

What is meant by hierarchical organisation

Answer 2

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)

Question 3

What is meant by functional segregation?

Answer 3

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

Question 4

What are 2 major descending tracts?

Answer 4

Pyramidal tracts
Extrapyramidal tracts

Question 5

What are 2 pathways of the pyramidal tracts

Answer 5

Corticospinal
Corticobulbar

(pass through pyramids in medulla)

Question 5

What are pathways of the extrapyramidal tracts

Answer 5

Vestibulospinal
Tectospinal
Reticulospinal
Rubrospinal

(do not pass through pyramids in medulla)

Question 6

What are the functions of the pyramidal tract?

Answer 6

Motor cortex to spinal cord or cranial nerve nuclei in brainstem
Voluntary movements of body and face

Question 7

What are the functions of the extrapyramidal tracts?

Answer 7

Brainstem nuclei to spinal cord
Involuntary (automatic) movements for balance, posture and locamotion

Question 8

Where is the primary motor cortex located?

What does the it do?

Answer 8

Located in precentral gyrus, anterior to the central sulcus

Controls fine, discrete, precise voluntary movements.
Provides descending signals to execute movements.

Question 9

Where is the premotor area?

What does it do?

Answer 9

Located anterior to primary motor cortex

involved in planning movements

Regulates externally cued movements
e.g. seeing an apple and reaching out for it

Question 10

Where is the supplementary area?

What does it do?

Answer 10

Located anterior and medial to primary motor cortex

Involved in planning complex movements (e.g. internally cued, speech)

Becomes active prior to voluntary movement

Question 11

Describe the path of the corticospinal tract?

What are two tracts it split into and where ?

Where doe they then innvervate?

Answer 11

Question 12

What does homunculus show?

What does the somatotopic representation show?

Answer 12

How much brain is needed for parts to work?

Where innervates where

Question 13

What does the corticobulbar tract do

Answer 13

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

Question 14

What do moto neurons from the following nuclei do?

Oculomotor and trochlear ?

Trigeminal?

Abducens?

Facial?

Hypoglossal?

Answer 14

Eye movements

Muscles of the jaw

Muscles of the face

The tongue

Question 15

What do the vestibulospinal tract do?

Answer 15

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

Question 16

What does the reticulospinal tract do?

Answer 16

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

Question 17

What does the tectoospinal tract do?

Answer 17

From superior colliculus of midbrain
Orientation of the head and neck during eye movements

Question 18

What does the rubrospinal tract do?

Answer 18

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

Question 19

What are negative signs of upper motor neurone lesions?

Answer 19

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

Question 20

What are positive signs of upper motor neurone lesions?

Answer 20

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 21

What is apraxia

What causes it

Answer 21

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)

Any disease of these areas can cause apraxia, although stroke and dementia are the most common causes

Question 22

What happens with a low motor neuron lesion

Answer 22

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

Question 23

What is motor neurone disease?

Answer 23

Progressive neurodegenerative disorder of the motor system

Also known as Amyotrophic Lateral Sclerosis (ALS)

Question 24

What are upper motor neurone signs of MND?

Answer 24

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 25

What are lower motor neurone signs of MND?

Answer 25

Weakness Muscle wasting Tongue fasciculations and wasting Nasal speech Dysphagia

Question 26

Describe the structure of basal ganglia

Answer 26

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

Question 27

Describe the function of basal ganglia

Answer 27

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 28

What is Parkinson's disease? Name some signs of Parkinsons disease

Answer 28

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

Question 29

What is Huntington's disease What are the signs

Answer 29

Degeneration of GABAergic neurons in the striatum, caudate and then putamen 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 Genetic neurodegenerative disorder Chromosome 4, autosomal dominant CAG repeat

Question 30

What is ballism

Answer 30

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

Question 31

Where is the cerebellum What is its function

Answer 31

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

Question 32

What is the function of the vestibulocerebellum What does damage cause to it

Answer 32

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)

Question 33

What is the spinocerebellum What does damage cause

Answer 33

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 34

What does cerebrocerebellum do What does damage to it do

Answer 34

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

Question 35

What is ataxia

Answer 35

General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait

Question 36

What is dysmetria

Answer 36

Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)

Question 37

What is an intention tremmor

Answer 37

Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)

Question 38

What is dysdiadochoikensia

Answer 38

Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)

Question 39

What is scanning speech

Answer 39

Staccato, due to impaired coordination of speech muscles

Question 40

What are the main signs of cerebellar dysfunction and when are they apparent

Answer 40

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 41

What are alpha neurones

Answer 41

They are lower motor neurons of the brainstem and the spinal cord Innervate the extrafusal muscle fibres of the skeletal muscles Activation causes muscle contraction

Question 42

What is the motor neuron pool

Answer 42

Motor neuron pool contains all alpha motor neurons innervating a single muscle

Question 43

What is a motor unit

Answer 43

a single motor neuron together with all the muscle fibres that it innervates. It is the smallest functional unit with which to produce force Stimulation of one motor unit causes contraction of all the muscle fibres in that unit.

Question 44

What are the types of motor units?

Answer 44

Slow (S, type I) smallest diameter cell bodies small dendritic trees thinnest axons slowest conduction velocity e.g.posture Fast, fatigue resistant (FR, type IIA) larger diameter cell bodies larger dendritic trees thicker axons faster conduction velocity e.g.sprinting Fast, fatiguable (FF, type IIB) larger diameter cell bodies larger dendritic trees thicker axons faster conduction velocity Different portions based on genetics and environment

Question 45

How are the 3 different motor unit types classified?

Answer 45

amount of tension generated speed of contraction fatiguability

Question 46

What are the 2 mechanisms by which the brain regulates the force that a single muscle can produce

Answer 46

Recruitment Motor units are not randomly recruited. There is an order to this. Governed by the “size principle”. Smaller units are recruited first (these are generally the slow twitch units). As more force is required, more units are recruited. This allows fine control (e.g. when writing), under which low force levels are required. Rate coding 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.

Question 47

What are neurotrophic factors

Answer 47

Are a type of growth factor Prevent neuronal death Promote growth of neurons after injury

Question 48

What is hypo-reflexia

Answer 48

Below normal or absent reflexes Associated with lower motor neuron diseases

Question 49

Explain the plasticity of motor units

Answer 49

Fibre types can change properties under many different conditions. 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 (evidence from slower contraction times).

Question 50

What is the function of a reflex

Answer 50

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. “…….the magnitude and timing of which 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.

Question 51

What is the Jendrassik manoeuvre

Answer 51

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

Question 52

Descending (supraspinal) control of reflexes

Answer 52

Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex. Inhibitory control dominates in normal conditions (N). Decerebration reveals the excitatory control from supraspinal areas (D). Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex.

Question 53

What is hyper-reflexia

Answer 53

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

Question 54

What is clonus

Answer 54

Involuntary and rhythmic muscle contractions Loss of descending inhibition