3. Motor systems Flashcards
Which regions of the cortex are involved in motor control?
All of the frontal lobe
The more anatomically anterior the cortical region, the more abstract or complex it’s role in movement
What is the primary motor cortex and where is it located?
Aka. area 4 Primary region of the motor system which works in association with other motor areas
The primary motor cortex is the lowest level of motor hierarchy Located immediately anterior to the central sulcus GO TO LAST FLASHCARDS
What is neuronal plasticity? Why is this advantages?
Reorganisation of neural pathways in the brain
Also known as remapping of the motor map In instances of neuronal lesions, neuronal plasticity limits the level of damage that occurs
How can a stroke impact motor movement?
If a stroke results in the occlusion of the middle cerebral artery then this can affect almost all of one side of the frontal lobe - produces severe motor disability in all parts of the contralateral body (apart from the lower limb)
This occlusion will also affect the blood supply to the basal ganglia via lenticulostriate arteries
What is apraxia?
Motor disorder - an inability to perform complex motor tasks due to neuronal damage e.g. tying your shoelaces, writing, playing the piano - can still move but complex tasks cannot be performed
These patients will have normal reflexes and no muscle weakness but will have difficultly performing motor tasks
How can apraxia occur?
Due to damage i.e. lesions to the premotor cortex (anterior to the motor cortex) or damage to the supplementary motor cortex
Will apraxia occur if there is damage to only one side of the premotor/supplementary motor cortex?
There may be only a very minimal level of apraxia in this instance
Only minimal symptoms will occur as the contralateral area may be able to take over some functions of the damaged tissue
What is the relevance of the frontal eye fields (FEF) and Broca’s area and where are these located?
FEF and Broca’s area - are both specialised cortical areas dedicated to motor control of specific systems
FEF - motor control of the extraocular eye muscles
Broca’s - motor control of the muscles regulating speech These are both located adjacent to the premotor cortex
What is the specific function of the FEF and Broca’s area?
Broca’s - enables people to put words together into a sentence i.e. the programming of the sequence of words
FEF - the programming of specific eye movements - of looking from one thing to another
How would damage to Broca’s area present in a patient?
This is known as motor aphasia: These patients will have difficulty putting words together in a sentence - so will use very simple or one-word sentences
Patients will have no problem understanding but will have a problem in replying to someone complexly
How would damage to the FEFs present in a patient?
This is known as oculomotor apraxia (OMA)
Patients will have a difficulty in moving their eyes horizontally and in moving them quickly to follow a moving object
Patients will have to turn their head in order to compensate for a lack of eye movement initiation to follow an oject
What is the role of the parietal lobe in motor control?
This is where the somatosensory cortex lies
From here, 40% of the corticobulbospinal tracts arise
These axons transmit commands to the spinal cord for sensory input and modulation of reflexes
Which regions in the frontal lobe are associated with motor control?
Prefrontal cortex - areas 9 and 10 Orbitofrontal cortex - area 11
Where is the prefrontal cortex and what is it’s role in movement?
This is located in the frontal lobe - areas 9 and 10
Has the most complex relationship with movement - involved in the planning of movement - where you are generating different potential movements depending on what happens next
Also involved in executive functions
What are the executive functions of the brain?
These are problem solving, judgment
What is the orbitofrontal cortex and what is it’s role in motor control?
Located in the frontal lobe - area 11
Concerned with the control/inhibition of the limbic system i.e. emotion/emotive behaviour e.g. hunger, thirst, sexual drives
How would damage to the orbitofrontal cortex present in a patient?
These patients would have a ‘pseudopsychopathic’ behaviour i.e. impulsive, jocular attitude, sexual disinhibition, complete lack of concern for others
How does the basal ganglia have an effect on the motor cortex?
Has an effect via the motor thalamus
SO basal ganglia –> motor thalamus –> motor cortex NB. the cerebellum also projects to the motor thalamus to to the motor cortex
How will damage to the motor thalamus present?
Damage to the motor thalamus can result in severe paralysis
What is the corticobulbospinal tract composed of?
Composed of two motor tracts - the corticobulbar tract and the corticospinal tract
Through which structure does the corticobulbospinal tract pass?
Passes through the internal capsule - this is a fibre bundle passing between the caudate and the putamen nuclei
Through which part of the brainstem does the corticobulbospinal tract pass?
These two motor tracts pass through the midbrain and then through the medulla
SO motor cortex –> internal capsule –> midbrain –> medulla –> spinal cord
Give the path and function of the corticobulbar tract
Motor functions of the non-oculomotor cranial nerves (muscles of the head, face and neck)
Motor cortex to the medullary pyramids
Terminates on the cells of the relevant cranial nerve nuclei
Terminates on cells of the pontine nuclei, reticular formation and the red nucleus
What is the red nucleus?
Aka. nucleus ruber
This is a large, round nucleus in the midbrain next to the subtantia nigra Involved in motor coordination
Give the path of the corticospinal tract
This follows the corticibulbar tract and then splits at the medulla - continues onto the lower medulla
Here, it decussates to form the large lateral corticospinal tract and the small medial corticospinal tract
Where is the motor deficit if there is a lesion above/below the spinal cord? Why is this?
Lesion above spinal cord - motor deficit on the OPPOSITE side Lesion of spinal cord - motor deficit on the SAME side
This is because decussation of motor tracts occurs in the upper portion/just above the spinal cord
What is located at the region of the primary motor cortex?
The motor homonculus is located along this region
What is the layout of the motor homonculus?
The feet and legs are in the central region where a sagittal section would be
Then to the hip, trunk, shoulder, elbow
Then to the hands and fingers
Finally the face
What is the result of lesions in the primary motor cortex?
This results in paralysis or paresis of specific muscle groups depending on the region of the homonoculus
Define spasticity
Abnormally increased muscle tone
Often have incresed tendon reflexes
What is the cause of spasticity?
Upper motor neurone lesion
Define clonus
Series of jery contractions of a particular muscle
What is the cause of clonus?
Sudden stretching of the muscle
What is meant by hyperreflexia?
Where abnormally brisk tendon reflexes are seen in one or more muscles
Overactive/overresspinsive reflexes
Due to damage to the spinal cord at the level of T5 or above
What do spasticity, clonus and hyperreflexia signifty damage to?
Corticospinal tract
What is decorticate posturing and what does this signify damage to?
Lying supine and arms are adducted and flexed
Wrists are also flexed and legs are internally rotated/extended
Planter flexion of the feet
Damage to the corticospinal tract in the medulla
What is decerebrate posturing and what does this indicated damage to?
Arms adducted and extended and wrists pronated and fingers flexed
Planter flextion of the feet
Indicated severe injury to the brain at the level of the brainstem, including damage to corticospinal and rubrospinal tracts
Out of decerebrate and decrotical posturing, which is the more serious?
Decerebrate
How will someone with an acute lesion in the motor cortex present and why?
Initial paralysis - followed by a variable degree of recovery (motor weakness and fatigue will not recovery)
This is due to plasticity in the cortex
What is meant by ‘hemiplegic dystonia’?
Persistant spasticity and a profound motor weakness - persistant flexion of the arms and persistant extension of the legs
What is the ‘clasp knife reflex’?
Hyperactivity of the flexor muscles
What does the clasp knife reflex indicated damage to?
Chronic cerebral motor lesion
What is spinal shock?
Clincal condition occuring after acute damage to the spinal cord - to any of the descending tracts
Chronic signs of spinal shock
Clonus
Hyepractive and exaggerated reflexes
Babinski
