Motor systems II

Question 1

Which of Brodmann’s areas is associated with the primary motor cortex? Where in the brain is it found?

Answer 1

4

Found immediately anterior to the central sulcus

Question 2

What is the result of lesions to the motor cortex?

Answer 2

Paralysis/paresis of specific muscle groups

the larger the lesion, the more muscle groups involved

Question 3

If someone has a stroke involving occlusion of the MCA, what part of the brain is most likely to be affected and what consequences will this have?

Answer 3

Affect almost all of one side of the frontal lobe
result in severe motor disability in all parts of the contralateral body
(**apart from the LOWER limb - this part is supplied by the ACA)

Question 4

What is worse, an infarction in the proximal segment of the MCA (M1) or in the distal segment (M3)? Why?

Answer 4

M1 - this will affect the blood supply to the basal ganglia via the lenticulostriate arteries and also affect blood supply to the motor cortex

If it was M3, it would only affect the motor cortex
(see diagram in lecture for further explanation if necessary)

Question 5

What do the Brodmann areas 6 and 8 represent?

Answer 5

6 = pre motor cortex
8 = supplementary motor cortex

Question 6

What would damage to Brodmann areas 6 + 8 result in?

Answer 6

motor apraxia
- normal reflexes and no muscle weakness, but more difficulty in performing complex motor tasks

(however, if there is only damage to ONE side then the contralateral side may be able to compensate)

Question 7

What Brodmann areas correspond to the posterior parietal cortex?

Answer 7

Areas 7 + 19

Question 8

What would damage to areas 7 + 19 result in?

Answer 8

Sensory apraxia

= Difficulty performing complex motor tasks when triggered by sensory input (i.e. being asked to do something)

Question 9

Where are the frontal eye fields and Broca’s area found?

Answer 9

Adjacent to the premotor area

Question 10

What would damage to Broca’s area result in?

Answer 10

Motor aphasia

= difficulty generating speech output, and linking words into complex sentences

Question 11

What would damage to frontal eye fields result in?

Answer 11

Oculomotor apraxia

= difficulty moving eyes horizontally and moving them quickly

Question 12

If a patient has to turn their head to compensate for lack of eye movement, what might this indicate?

Answer 12

Bilateral lesions to the frontal eye fields

Question 13

What Brodmann areas correspond to the somatosensory cortex?

Answer 13

1, 2 + 3

Question 14

What Brodmann areas correspond to the dorsolateral prefrontal cortex?

Answer 14

9 + 10

Question 15

What is the dorsolateral PFC responsible for?

Answer 15

planning movement, problem solving, judgement = executive functions

Question 16

What are signs of damage to the dorsolateral PFC?

Answer 16

apathy
personality changes
lack of ability to plan/sequence actions
poor working memory for verbal/spatial information

(*can easily be damaged with impact to frontal bone)

Question 17

What Brodmann areas correspond to the orbitofrontal cortex?

Answer 17

11

Question 18

What is the orbitofrontal cortex responsible for?

Answer 18

control/inhibition of motor responses associated with the limbic system (hunger, thirst, sexual drive etc.)

Question 19

What can happen if the orbitofrontal cortex is damaged?

Answer 19

result in the disinhibition of the drives it is responsible for leading to pseudopsychopathic behaviour

Question 20

What is the VA/VL nuclei also called?

Answer 20

Motor thalamus

Question 21

What is the role of the motor thalamus?

Answer 21

Conveys motor commands from the basal ganglia + cerebellum to the corticospinal tract and LMNs

Question 22

Why is the corticobulbospinal tract vulnerable to damage via stroke?

Answer 22

It passes through the internal capsule on its way to the brainstem

Question 23

Where does the corticobulbar component of the CBST terminate in? What is the result of this?

Answer 23

terminates in various cranial nerve nuclei:
V + VII = cortical control of the muscles of the head
III, IV + VI = control of eye movements
also terminates in the pontine nuclei, reticular formation and red nucleus

Question 24

Where does the CST decussate?

Answer 24

Lower medulla (medullary pyramids) - forms large lateral and small medial CSTS

Then the motor decussation occurs in the upper spinal cord (C1-C5)

Question 25

What part of the spinal cord does the lateral and anterior CST run in?

Answer 25

``` lateral = dorsolateral cord anterior = medial ventral cord ```

Question 26

Where is the only place in the body that the CST has monosynaptic connections with?

Answer 26

Thumb and digits | has spinal interneurones to initiate motor actions in other muscles

Question 27

What does damage to the CST result in?

Answer 27

Loss of control of hands and fingers Posture/locomotion/gait not usually affected Which side is affected depends on location of the lesion

Question 28

What other motor systems (not CST) mediate locomotion and gait?

Answer 28

Extrapyramidal systems | Main components of this: lateral vestibulospinal and the reticulopsinal tracts

Question 29

Where does the lateral vestibulospinal tract originate and what is its role?

Answer 29

Originates in the vestibular nuclei in the upper medulla and lower pons Controls posture and balance

Question 30

Where does the reticulospinal tract originate and what is its role?

Answer 30

Originates in the reticular formation of the pons + medulla Responsible for autonomic control (drives sympathetic preganglionic neurones) Also provides the drive for respiration (phrenic nerve) Plays a role in "general arousal" of the spinal cord

Question 31

Where does the rubrospinal tract originate and what is its role?

Answer 31

Originates in the red nucleus in the brainstem Large muscle movement in upper limb - mainly flexion It carries cerebellar commands to the spinal cord (as the red nucleus receives its main input from the cerebellum)

Question 32

What is the tectospinal tract, where does it originate and what is its role?

Answer 32

This is a minor extrapyramidal pathway It originates in the superior colliculus and is also known as the optic tectum as it receives afferents from the retina It is responsible for coordinating voluntary head and eye movements (reflex movements in head in response to visual + auditory stimuli)

Question 33

What is the medial vestibulospinal tract, where does it originate and what is its role?

Answer 33

Another minor extrapyramidal pathway and a continuation of MLF it mediates reflex coordination of the head and neck muscles with the extraocular eye muscles to maintain objects in view

Question 34

Where do the UMNs act directly on the LMNS?

Answer 34

Thumbs + fingers | Lips + tongue

Question 35

Define spasticity. Is this the result of a UMN or LMN lesion?

Answer 35

Abnormally increase muscle tone and increased tendon reflexes this is characteristic of a UMN lesion

Question 36

Define clonus.

Answer 36

series of jerky contractions of a particular muscle following sudden stretching of the muscle

Question 37

Define hyperreflexia.

Answer 37

Where an abnormally brisk tendon reflex is seen on one or more muscles

Question 38

What is decorticate posturing?

Answer 38

Arms are adducted and flexed (wrists + fingers flexed on chest) Legs may be internally rotated and stiffly extended with plantarflexion

Question 39

What is decerebrate posturing?

Answer 39

Arms are adducted and extended (wrists pronated and fingers flexed) Legs may be internally rotated and stiffly extended with plantarflexion

Question 40

Which is more serious, decorticate or decerebrate posturing?

Answer 40

Decerebrate - due to severe injury to the brainstem (below the level of the red nucleus), including damage to the CST and rubrospinal tract - due to excessive activity in the EPS (esp. vestibulospinal tract)

Question 41

What are the acute effects of lesions of the motor mortex?

Answer 41

Initial paralysis Weakness Clumsiness + fatigue of movements recovery will occur due to plasticity of the cortex (homonculus may change) Larger lesions = slower recovery and permanent loss of certain movements

Question 42

What are the chronic effects of lesions of the motor cortex?

Answer 42

SMALL lesion = good recovery, but motor weakness and fatigue are always present Hemiplegia dystonia = persistent flexion of arms and extension of legs due to persistent spasticity following a lesion

Question 43

What are the acute effects of spinal shock?

Answer 43

Paralysis/paresis | Reduced reflex response below level of the injury

Question 44

What are the chronic effects of spinal shock?

Answer 44

Shock wears off Weak monosynpatic reflexes reappear Crossed extensor reflexes may also recover These reflexes may become exaggerated and hyperactive May have clonus and Babinski sign