motor cortical control

Question 1

what does hierarchical organisation mean in terms of motor control in the brain?

Answer 1

higher order areas of hierarchy are involved in more complex tasks (programme and decide movements, coorinate muscle activity)

lower areas of hierarchy perform lower level tasks (execution of movement)

Question 2

what is functional segregation with respect to motor control

Answer 2

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

eg. primary motor cortex, non primary motor cortex, basal ganglia and cerebellum, thalamus, brainstem, spinal cord. all these interact with each other to bring about involuntary and voluntary movement

Question 3

what are the major classes of descending tracts?

Answer 3

pyramidal tracts

extrapyramidal tracts

Question 4

what are pyramidal tracts and give examples?

Answer 4

pass through the pyramids of the medulla

output neurones in motor cortex -> spinal cord or cranial nerve nuclei in the brainstem

voluntary movements of the body and face

eg. corticospinal and corticobulbar

Question 5

what are extrapyramidal tracts and give examples?

Answer 5

do not pass through the pyramids of the medulla

upper motor neurones in the cortex, lower motor neurones in brainstem nuclei -> spinal cord

involuntary movements for balance, posture and locomotion

eg. vestibulospinal, tectospinal, reticulospinal, rubrospinal

Question 6

what is the primary motor cortex

Answer 6

located in the precentral gyrus, anterior to the central sulcus

controls fine, discrete, precise voluntary movements.
provides descending signals to execute movements

final common pathway from the brain down to the lower motor neurones

Question 7

what is the premotor area?

Answer 7

located anterior to the primary motor cortex (and laterally)

involved in planning movements

regulates externally cued movements (seeing an apple and reaching out for it)

Question 8

what is the supplementary motor area?

Answer 8

located anterior and medially to the primary motor cortex

involved in planning complex movements, internally cues (eg. speech)

becomes active prior to voluntary movement

Question 9

what is the corticospinal tract?

Answer 9

descending pyramidal tract

upper motor neurones in the cortex pass through the cerebral peduncle in the midbrain. they then enter the pyramids of the medulla. here they become the corticospinal tract

85-90% decussate in the medulla - forms the lateral corticospinal tract which supplies the limb muscles

10-15% do not decussate - forms the anterior corticospinal tract, which supplies the trunk muscles.

(when nerves of the tract leave the spinal cord they form lower motor neurones)

Question 10

what is the corticobulbar tract?

Answer 10

descending pyramidal tract

upper motor neurones are in the primary motor cortex. these synapse with brainstem cranial nerve nuclei

principal motor pathway for the voluntary movements of the face and neck

Question 11

what is the vestibulospinal tract?

Answer 11

descending extrapyramidal tract

stabilises head during body movements
or as head moves coordinates head movements with eye movements
mediates postural adjustments

Question 12

what is the reticulospinal tract?

Answer 12

descending extrapyramidal tract

most primitive descending tract - from medulla and pons

responsible for changes in muscle tone associated with voluntary movement and postural stability.

Question 13

what is the tectospinal tract?

Answer 13

descending extrapyramidal tract

from superior colliculus of midbrain

orientation of the head and neck during eye movements

Question 14

what is the rubrospinal tract?

Answer 14

descending extrapyramidal tract

from red nucleus of midbrai

in humans mainly taken over by the corticospinal tract

innervate lower motor neurones of flexors of the upper limb

Question 15

what are the signs of an upper motor lesion?

Answer 15

negative signs:
loss of voluntary motor function
paresis - graded weakness of movements
paralysis - 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
clonus - abnormal ascillatory muscle contraction
babinskis sign

Question 16

what is apraxia?

Answer 16

a disorder of skilled movements. patients are not paretic but have lost information about how to perform skilled movements

due to a lesion of the inferior parietal lobe or the frontal lobe (premotor cortex, supplementary motor cortex

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

Question 17

lesions where in the brain are likely to cause apraxia?

Answer 17

inferior parietal and frontal lobe

damage to premotor cortex and supplementary motor area

Question 18

where does the corticospinal tract decussate?

Answer 18

85% in the medulla - forms lateral corticospinal tract, supplies muscles of the limbs

15% dont decussate - form the anterior corticospinal tract, supplies muscles of the trunk

Question 19

what are signs of a lower motor lesion?

Answer 19

weakness
hypotonia
hyporeflexia
muscle atrophy
fasciculations (damaged motor units produce spontaneous action potentials, resulting in a twitch)
fibrillations (spontaneous twitching of individual muscle fibres, recorded during needle electromyography examination, not visible to the naked eye, unlike above)

Question 20

what is motor neurone disease?

Answer 20

progressive neurodegenerative disorder of the motor system

spectrum of disordrs
aka amyotrophic lateral sclerosis (ALS)

affects upper motor neurones, lower motor neurones of the brainstem (eg. voluntary tongue movement), intercostal muscles, upper and lower limb muscles

currently no cure, results in death through lack of respiratory muscle function

Question 21

what are some symptoms of motor neurone disease?

Answer 21

upper motor neurone:
spasticity, brisk limbs and jaw reflexes, babinskis sign, loss of dexterity, dysarthria, dysphagia

lower motor neurone signs:
weakness, muscle wasting, tongue fasciculations and wasting, nasal speech, dysphagia

Question 22

what is the structure of the basal ganglia?

Answer 22

Caudate nucleus
Lentiform nucleus (putamen +
external globus pallidus)
Putamen + caudate = striatum
 Nucleus accumbens
Subthalamic nucleus
 Substantia nigra  (mid brain, important in parkisons))
Ventral pallidum, claustram,
nucleus basalis (Of Meynert)

look at a diagram

Question 23

what is the function of the basal ganglia?

Answer 23

decision to move (intention, eg in parkinsons)

elaborating associated movements (facial expressions to emotions, arms to walking)

moderating and coordinating movement (suppresses unwanted movements)

performing movements in order

Question 24

what is the basal ganglia circuitry?

Answer 24

many input and output pathways between everything

look up the diagram

Question 25

what is Parkinsons disease?

Answer 25

degeneration of dopaminergic neurones that originate in the substantia nigra (midbrain) and project to the striatum

Question 26

what are the symptoms of parkinsons?

Answer 26

bradykinesia - slowness of small movements
hypomimic face - expressionless, mask like
akinesia - difficulty in the initiation of movements, cant initiate them internally
rigidity - muscle tone increase, resistance to externally imposed joint movements
tremor at rest - slow, starts in one hand, with time spreads to other parts of the body

visibly less substantia nigra

Question 27

what is huntingtons disease?

Answer 27

degeneration of GABAergic (inhibitory) neurones in the striatum, caudate and then putamen

genetic neurodegenerative disorder

chromasome 4, autosomal dominant

CAG repeat

visible destruction pf brain matter

Question 28

what are some symptoms of huntingtons disease?

Answer 28

choreic movements
rapid, involuntary, jerky movements of the hands and face first. then legs and rest of body
speech impairment
difficulty swallowing
unsteady gait
later: cognitive decline and dementia

Question 29

what is ballism?

Answer 29

usually from stroke affecting subthalamic nucleus

sudden uncontrolled flinging of the extrematies

symptoms occur contralaterally
generally one sided

Question 30

what is the cerebellum

Answer 30

located in the posterior cranial fossa

covered by the tentorium cerebelli

coordinator and predictor of movement
takes signals on the way down to muscles, and compares with what is returning from sensory receptors. makes movements fluid

pons connects the two cerebellar lobes round the front

Question 31

what does the vestibulocerebellum do? what does damage to it do?

Answer 31

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

Question 32

what does the spinocerebellum do? what does damage to it do?

Answer 32

coordinates speech
adjusts muscle tone
coordinates limb movements

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

Question 33

what does the cerebrocerebellum do? what does damage to it do?

Answer 33

coordination of skilled movements, cognitive function, attention, processing of language, emotional control

damage effects mainly arms and skilled coordinated movements and speech

Question 34

what are the areas of the cerebellum?

Answer 34

vestibulocerebellum

spinocerebellum

cerebrocerebellum

Question 35

what are the main signs of cerebellar dysfunction?

Answer 35

APPARENT ONLY ON MOVEMENT

ataxia- impairment of movement coordination and accuracy, staggering gait

dysmetria - inappropriate force for target directed movement

intention tremor

dysdiadochokinesia - inability to perform rapidly alternating movements

scanning speech - staccato, due to impaired coordination of speech muscles