Motor systems II Flashcards
Which of Brodmann’s areas is associated with the primary motor cortex? Where in the brain is it found?
4
Found immediately anterior to the central sulcus
What is the result of lesions to the motor cortex?
Paralysis/paresis of specific muscle groups
the larger the lesion, the more muscle groups involved
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?
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)
What is worse, an infarction in the proximal segment of the MCA (M1) or in the distal segment (M3)? Why?
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)
What do the Brodmann areas 6 and 8 represent?
6 = pre motor cortex 8 = supplementary motor cortex
What would damage to Brodmann areas 6 + 8 result in?
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)
What Brodmann areas correspond to the posterior parietal cortex?
Areas 7 + 19
What would damage to areas 7 + 19 result in?
Sensory apraxia
= Difficulty performing complex motor tasks when triggered by sensory input (i.e. being asked to do something)
Where are the frontal eye fields and Broca’s area found?
Adjacent to the premotor area
What would damage to Broca’s area result in?
Motor aphasia
= difficulty generating speech output, and linking words into complex sentences
What would damage to frontal eye fields result in?
Oculomotor apraxia
= difficulty moving eyes horizontally and moving them quickly
If a patient has to turn their head to compensate for lack of eye movement, what might this indicate?
Bilateral lesions to the frontal eye fields
What Brodmann areas correspond to the somatosensory cortex?
1, 2 + 3
What Brodmann areas correspond to the dorsolateral prefrontal cortex?
9 + 10
What is the dorsolateral PFC responsible for?
planning movement, problem solving, judgement = executive functions
What are signs of damage to the dorsolateral PFC?
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)
What Brodmann areas correspond to the orbitofrontal cortex?
11
What is the orbitofrontal cortex responsible for?
control/inhibition of motor responses associated with the limbic system (hunger, thirst, sexual drive etc.)
What can happen if the orbitofrontal cortex is damaged?
result in the disinhibition of the drives it is responsible for leading to pseudopsychopathic behaviour
What is the VA/VL nuclei also called?
Motor thalamus
What is the role of the motor thalamus?
Conveys motor commands from the basal ganglia + cerebellum to the corticospinal tract and LMNs
Why is the corticobulbospinal tract vulnerable to damage via stroke?
It passes through the internal capsule on its way to the brainstem
Where does the corticobulbar component of the CBST terminate in? What is the result of this?
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
Where does the CST decussate?
Lower medulla (medullary pyramids) - forms large lateral and small medial CSTS
Then the motor decussation occurs in the upper spinal cord (C1-C5)
What part of the spinal cord does the lateral and anterior CST run in?
lateral = dorsolateral cord anterior = medial ventral cord
Where is the only place in the body that the CST has monosynaptic connections with?
Thumb and digits
has spinal interneurones to initiate motor actions in other muscles
What does damage to the CST result in?
Loss of control of hands and fingers
Posture/locomotion/gait not usually affected
Which side is affected depends on location of the lesion
What other motor systems (not CST) mediate locomotion and gait?
Extrapyramidal systems
Main components of this: lateral vestibulospinal and the reticulopsinal tracts
Where does the lateral vestibulospinal tract originate and what is its role?
Originates in the vestibular nuclei in the upper medulla and lower pons
Controls posture and balance
Where does the reticulospinal tract originate and what is its role?
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
Where does the rubrospinal tract originate and what is its role?
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)
What is the tectospinal tract, where does it originate and what is its role?
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)
What is the medial vestibulospinal tract, where does it originate and what is its role?
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
Where do the UMNs act directly on the LMNS?
Thumbs + fingers
Lips + tongue
Define spasticity. Is this the result of a UMN or LMN lesion?
Abnormally increase muscle tone and increased tendon reflexes
this is characteristic of a UMN lesion
Define clonus.
series of jerky contractions of a particular muscle following sudden stretching of the muscle
Define hyperreflexia.
Where an abnormally brisk tendon reflex is seen on one or more muscles
What is decorticate posturing?
Arms are adducted and flexed (wrists + fingers flexed on chest)
Legs may be internally rotated and stiffly extended with plantarflexion
What is decerebrate posturing?
Arms are adducted and extended (wrists pronated and fingers flexed)
Legs may be internally rotated and stiffly extended with plantarflexion
Which is more serious, decorticate or decerebrate posturing?
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)
What are the acute effects of lesions of the motor mortex?
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
What are the chronic effects of lesions of the motor cortex?
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
What are the acute effects of spinal shock?
Paralysis/paresis
Reduced reflex response below level of the injury
What are the chronic effects of spinal shock?
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
